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The Use of Optical Coherence Tomography in Dental Diagnostics: A State-of-the-Art Review.

1. Introduction

Medical imaging is the basis of effective medical diagnosis and is now the mainstream of a dynamically developing branch of science, which is biomedical engineering. Its development started after an accidental discovery of Wilhelm Conrad Roentgen, a professor of physics, who in 1895 observed little fluorescence during his research on electrical discharges and cathode rays. X-radiation turned out to be a fundamental discovery which is still used in medicine today.

Another milestone was the development of the first computed tomography (CT) device by Godfrey Newbold Houns-field in 1967. The concept of tomography refers to a method that provides images showing sections of the tested structure. The first CT scanner initiated rapid development of medical imaging techniques. A common feature of different types of CT devices is noninvasive imaging of tissue structures and internal organs, as well as their functional parameters. The desire to minimize invasiveness of methods such as biopsy or exploratory surgery, which are painful and may cause deterioration in the patient's condition, was an impetus for the improvement of computed tomography equipment. As a result, completely new technologies were developed, such as magnetic resonance imaging (MRI), ultrasonography (USG), positron emission tomography (PET), single photon emission computed tomography (SPECT), and the latest and more widely used optical coherence tomography (OCT).

The method of optical coherence tomography using interferometry with partially coherent light was first presented in 1991 at the Institute of Technology of the University of Massachusetts [1]. The first in vivo measurements of the section of the human retina were made two years later in Vienna [2]. The first commercial optical tomography device was produced in 1996 by Zeiss-Humphrey [3].

The article depicts the types of optical tomographs and the schematic construction based on the academic knowledge and enunciates the up-to-date knowledge concluded in the articles accessible in the US National Library of Medicine National Institutes of Health (PubMed), Dentistry & Oral Sciences Source EBSCO, and the http://octnews.org website.

2. Types of Optical Coherence Tomography

Optical coherence tomography (OCT) uses a beam of partially coherent light to create tomographic images. Currently, there are two basic types of optical coherence tomography: time domain optical coherence tomography (TdOCT) and Fourier domain optical coherence tomography (FdOCT). The former technique was developed in 1991 by the abovementioned group of researchers from the Massachusetts Institute of Technology in the United States [1] for use in ophthalmic diagnosis. It can produce tomographic images of relatively low quality, resulting from long time of measurement, but it does not allow for three-dimensional imaging of objects [4]. Modern optical tomography with detection in the frequency domain (Fourier domain optical coherence tomography) reduces the capture time by more than a hundred times and creates three-dimensional images of the test object.

Optical coherence tomography enables the study of objects that are partially transparent for light from the near infrared range. In the OCT scanner based on this method, the information about the location of scattering (reflecting) layers along the sample beam is contained in the modulation frequency of the light intensity measured as a function of frequency. The electric signal resulting from detection of spectra of interfering beams is called the signal of spectral bands. Nowadays, two methods of practical realization of this type of detection are used. The first is spectral optical coherence tomography (SOCT). The other method is swept source OCT or optical Fourier domain imaging (OFDI) [4]. The common elements, used in both methods (SOCT and OFDI), are fixed reference mirrors (as opposed to time domain OCT).

This improves mechanical stability of the system. An interference image is obtained by the numerical Fourier transform of registered spectral bands. However, the method of detection of an interference signal is different. In SOCT, the light source generates a broadband light beam. A spectrometer is used to detect signals for individual optical frequencies. In OFDI, an ordinary photodetector is used instead of a spectrometer, because the applied fast tunable laser generates light of a narrow spectral line individually for each wavelength.

The recently introduced SS-OCT uses a short cavity swept laser with a tunable wavelength of operation instead of the diode laser used in spectral-domain OCT [5] The SS-OCT has improved image penetration using a wavelength of 1050 nm and has an axial resolution of 5.3 [micro]m and an axial scan rate of 100, 000 scans per second. Prototype models could reach faster scan speed of more than 400, 000 scans per second [6, 7]. The 12 x 9 mm scan enables simultaneous imaging of the macula, the peripapillary area, and the optic nerve head and the choroidal thickness. The 12 x 9 mm scan comprises 256 B scans each comprising 512 A scans with a total acquisition time of 1.3 s [8] SS-OCT also provides the capability of a wide field up to 12 x 12 mm images [9]. SS-OCT enables clear simultaneous visualization of the vitreous and the posterior precortical vitreous pockets and the choroid and the sclera [10].

3. Operating Principle of Optical Coherence Tomography

OCT is a modular device. It consists of coupled hardware components. It contains the software and five basic modules: a partially coherent light source, an imaging apparatus, a measurement head, a module of data processing, and image generation as well as a computer control system. The light source used in the device determines its axial resolution and penetration depth of the light beam. The OCT imaging apparatus module is the central element of the system. This may be any measuring device capable of measuring the reflected or backscattered light with high sensitivity and resolution. Instruments that enable lossless signal transmission are also indispensable.

Other elements of the described OCT system are the measuring head and the system for bringing the probe beam to the test structure. They take different forms, depending on the field of medicine for which they are intended. Their shape also depends on the structure of the imaging apparatus block. The purpose of this module is to acquire measurement data from the imaging apparatus. Another necessary step is analysis of the obtained values, their processing, and presentation. This is achieved through a variety of techniques in the field of image processing, such as noise reduction algorithms, motion and visualization correction algorithms, segmentation, and image resolution enhancement.

The computer control system controls the entire OCT scanner. It enables to control scanning the reference arm of the interferometer and synchronize the operation of all components. Moreover, it allows for communication between the apparatus and the image processing block as well as the display of measurement results in real time as it is shown in Figure 1 [11].

OCT imaging is possible by measuring the intensity and time delay of the "echo" of the reflected or backscattered light. The method of OCT imaging is analogous to ultrasoonography. However, they differ in terms of data measurement techniques. This is due to the fact that the speed of light is almost one million times greater than the speed of sound and, as a result, the distance measured by OCT is characterized by a much higher time resolution than USG. OCT resolution is 10 fm, and in ultrasonography, it is 150 [micro]m. OCT, on the other hand, has a more limited tissue penetration ability. A light wave in OCT reaches a depth of 2 mm, whereas a sound wave in USG a depth of 10 cm. In the case of USG, electronic detectors can be used for detection of the returning acoustic wave reflected from an object. The use of such devices for detecting light waves is impossible, because the rate of signal changes is too high. The basis of optical tomography is the phenomenon of interference of two partially coherent light beams coming from a single source--the reference beam and the probe beam. Biological objects, such as tissues and organs, are for light waves, the centres with nonuniform distribution of a refractive index. The analysis of interference signal enables to locate the points at which the refractive index changes. These points are situated along the direction of propagation of the probe beam. The graph of reflected wave power density as a function of the position of the reflective point, which is the source of the wave, is called an A-scan. B scans give sagittal scans of the object and C scans--lateral scanning images at a constant depth. Combination of measurement results lying in one plane (numerous parallel directions of the probe beam) creates a two-dimensional image of the section of the test object [12].

The localization of the boundaries of layers with different refractive indices, that is, determination of the waveform of refractive index changes as a function of light beam penetration depth is realized by interferometric distance measurement systems. They use the property of light waves, which is the ability to overlap. This property is dependent on coherence of light. There are two types of light coherence: spatial--defining the phase correlation between wave sequences generated by different points of the light source and time--defining the phase correlation of wave sequences emitted by a single point of the light source at different points in time [13]. The time consistency of light is examined using the Michelson interferometer [14]. The schematic diagram of the operation of the Michelson interferometer is shown in Figure 2.

The light wave incident on the semi-transparent mirror BS (beam splitter) splits into two beams. The light source (LS) changing its direction into perpendicular after passing through BS is reflected by the movable mirror M1, again passes through BS, without changing its direction, and reaches the screen D (detector). The second beam formed by the passage of the primary beam through BS without changing its direction is reflected by the fixed mirror M2, then passes through BS changing the direction into perpendicular, and falls on screen D. The beam incident on the screen forms an interference image.

4. The Short History of OCT in Dentistry

Attempts to use optical coherence tomography in dentistry were first made in 1998 by researchers from the Laboratory of Medical Technology of Livermore, California, in collaboration with researchers from the University of Connecticut. In their work, they presented a prototype of dental optical coherence tomography and its in vivo application [15].

The device designed by them scanned hard tissues to a depth of 3 mm and soft tissues to a depth of 1.5 mm, which even now, 14 years after the creation of this sample design, is comparable to the possibilities of the latest generation apparatus. Two years later, the same group of researchers presented the first intraoral scans not only of the hard tissues but also soft tissues of the oral cavity, using another specifically designed CT prototype. In the published work, they demonstrated the possibility of imaging the gum margin, periodontal pockets, and attachments, both epithelial and connective, using an infrared beam of light [16]. The usefulness of optical coherence tomography in the recognition of lesions in the structure of both soft and hard tissues of the oral cavity was also presented in the same year 1998 by experimental and clinical studies conducted by Feldchtein et al. [17], which was actually the first mention of the possibility of OCT examination of hard tissue. In 2000, the same scientific center compared two OCT prototypes having different wavelengths of light: 850 and 1310 nm. Analysis of the quality of scans from individual devices and the evaluation of the possibility of reflecting the anatomical details of the oral cavity showed greater effectiveness of the apparatus using longer wavelengths of light [18]. Five years later, as an experiment, twenty-one dentists were asked to analyze fissure sealants, composite fillings, or tissue enamel based on OCT scans. Despite the lack of knowledge of the techniques of OCT scan interpretation, the dentists who took part in the study obtained clinically acceptable results, which proved the potential clinical application of OCT [19]. The possibility of assessing caries developing under fissure sealants, which is difficult to diagnose, was subject to similar verification. After 90-minute training, doctors assessed the correctness of the enamel structure under 5 different types of sealing materials. When analysing OCT scans, the doctors detected caries more frequently compared with clinical or radiological assessment [20].

In the following years, a leading center dealing with optical tomography became the University of California in San Francisco. A series of articles was published, broadening the knowledge on the aspects of OCT application in conservative dentistry. The described issues were related to imaging of caries incipiens, their remineralization, and monitoring of the progressing or stopped demineralization of the enamel surface or tooth structure underneath fillings [21-29]. The issue of enamel remineralization is still continued [12]. In 2010, an innovative work was presented on attempts of enamel remineralization with chitosan. The penetration depth of chitosan into the enamel structure was evaluated by optical tomography. An attempt of complete enamel remineralization using this method did not prove to be successful, but the exploratory efficiency of the used diagnostic method was once again confirmed [30]. In the same year, the enamel structure of primary teeth was analysed. Since caries is a disease that affects both primary and permanent teeth, the authors verified the effectiveness of the new method of caries diagnosis in the primary dentition. They proved a high potential of optical tomography in paediatric dentistry, as a technique for effective, painless, and noninvasive detection of early tooth decay [31]. The next studies described the effectiveness of optical coherence tomography in monitoring the range and efficiency of infrared and fractional CO2 lasers in caries removal [32-37]. The effectiveness of a diode laser and Nd-YAG laser in the development of root canals during endodontic treatment was also verified [38]. An attempt was also made to use OCT in endodontic in vitro studies [39]. The results of studies evaluating the errors in prosthetic treatment were also published: defects in the structure of the materials used in prosthetic restoration and microleakage at the contact surface of the reconstruction and the tooth as well as the appropriateness of using OCT to control the internal structure of the prosthetic restoration without the need for its removal [34, 40].

Attempts were also made to visualize and measure the length of periodontal ligaments before and during orthodontic tooth movement. Incisors of rats were moved by applying successively varying sizes of forces and then the teeth were removed. The condition of the ligaments was imaged using optical coherence tomography and X-rays. OCT scans showed differences in periodontal ligament arrangement depending on the size of the applied force and their significant twist when using the greatest forces [41]. In subsequent studies, scans of the periodontium were performed and the lengths of both stretched and relaxed ligaments were measured. These structures were imaged using standard radio visual graphic intraoral images. However, they did not prove useful in the evaluation of periodontal elements obstructed in the image by tooth tissues. OCT enabled three-dimensional measurement and multilateral imaging of ligaments. The results obtained when using a CT scanner were different from those obtained by means of standard two-dimensional imaging. Periodontal fibres measured in X-ray images appeared to be much thinner than in reality [42].

Another application of OCT was an attempt to evaluate the salivary pellicle. In order to compare the results and to improve the resolution and specificity of images, an optical coherence microscope (OCM) was used. Salivary pellicle islands were visible in the samples incubated in saliva, which grow into complexes completely covering the enamel surface [43]. The aim of the next study was to evaluate the retention of the biofilm around orthodontic hooks depending on the ligaturing method using OCT and microbiological samples. Both microbiological and optical (OCT) analysis showed a significant difference in biofilm formation depending on the ligaturing method. The hooks ligaturated with elastic elements showed a greater amount of cariogenic Streptococcus mutans, whereas metal ligatures showed much less biofilm retention. The study found that optical coherence tomography may also be treated as a full-fledged quantitative indicator of bacterial plaque, which can be quickly and reliably visualized around orthodontic hooks [44]. Similar problems were presented in an ex vivo models. They proved the possibility of calculating the biofilm mass by measuring the distribution of light intensity scattering to a depth of the biofilm. An indirect possibility of characterizing the examined ecosystem on the surface of various types of composite materials was also demonstrated [45]. The study on biofilm imaging, describing the impact of dental calculus, enamel decalcification, and plaque, was an attempt to use optical coherence tomography not only in dentistry but also clinical periodontics. These studies confirmed the possibility of detecting enamel decalcification despite the presence of dental calculus or plaque and their diversification in the scans [46].

Another direction of research using the OCT technique has become the assessment of restorations with composite fillings in conservative dentistry. The study demonstrated, based on analysis of OCT scans, the leakage of composite restorations of enamel defects. The fissures were on average 50 [micro]m. The results were confirmed by X-ray images and optical microscopy. The study resulted in the development of their own spectral CT scanner, which was based on the Michelson interferometer. The created device, as well as the modern optical tomography instrument, divides monochromatic light into two beams, allowing for the reflection of the beams from semi-transparent mirrors and their subsequent interference. Using such a device, the researchers revealed the errors of composite reconstruction in the form of visible pits and fissures at the border between the filling and the cavity wall [47]. Enamel cracks at the border between the enamel and the composite filling reinforced with glass fibre were evaluated in a similar manner [48].The subject of evaluation was also the tightness of three selected composite fillings, cracks of composite reconstruction reinforced with glass fibre, which were imaged using optical coherence tomography (OCT), scanning electron microscopy (SEM), and optical microscopy (OM) [49]. The results enabled to describe the internal cracks of composites, which were not accessible during SEM or OM imaging. It was also observed that the assessment by means of optical coherent tomography required no special sample preparation, making it less expensive compared with the assessment in the scanning electron microscope [50]. In a further step, the efficiency of optical coherence tomography and confocal microscope in the evaluation of composite materials was compared [51].

There are also publications extending the above issue and evaluating marginal adaptation, porosity, and internal integrity of composite fillings. The potential of OCT and high resolution scans, allowing for critical assessment of the structure of fillings, previously inaccessible using common diagnostic methods, has thus been proven [52]. Similar studies evaluating polymerization shrinkage showed significant differences in its size depending on the tested materials [53]. Composite fillings restoring bovine enamel defects and their marginal adaptation with the use of self-etching techniques were also studied. The findings confirmed the thesis that optical coherence tomography is an effective tool in the accurate assessment of tightness of composite fillings [54]. The study of Senawongse et al. [55] made it possible to visualize the adhesive connection between the bonding system and the dentin, analyse carious lesions within the crown and root of the tooth, and assess secondary caries [56, 57]. From a clinical point of view, the studies identifying the relationship between the quality of OCT scans and the level of tooth hydration are very important [58, 59]. It directly affects the strength of the enamel prisms to injuries and the colour of the tissue, which is to be reproduced during conservative or prosthetic restorations. The use of OCT for educational purposes was also presented. The mistakes in the fillings made by dental students were discussed based on performed scans [60].

A further development of work on using an optical scanner and analysis of images was the research which used the potential of OCT to evaluate light scatter and the magnitude of the local refractive index depending on the state of the enamel and dentin. Optical properties of the prisms of the human enamel and dentin tubules were imaged [61].

OCT was also used to evaluate enamel cracks. The results were verified using a stereomicroscope and histological samples of individual enamel layers. Enamel cracks were identified by CT as intensified signals appearing in exactly the same places where damage to the histological samples and stereomicroscopic images was visible. The results showed that OCT very accurately identified cracks and their size, so measurements of the scanned teeth yielded results that were equally reliable to those obtained from stereomicroscopy and histological examination of subsequent enamel layers [62].

In order to improve the quality of OCT scans and facilitate their interpretation, gold nanoparticles were applied. They are normally used as contrast in SEM imaging to visualize the hybrid layer and dentin tubules [63]. This was a significant advancement in dentin imaging because until then only a qualitative and quantitative evaluation of tooth decay had been possible, without distinguishing histological structures [64].

Attempts were also made to use optical coherence tomography in maxillofacial surgery for separating normal and dysplastic fragments of oral epithelium and distinguishing between solid and bullous lesions [65, 66].

The latest studies continue to focus primarily on early diagnosis of caries, assessment of the quality and thickness of dentin, and assessment of dental fillings [67-74]. The precise topics and conclusions of the articles from the last 5 years, according to field of dentistry are summarized in Tables 1, 2, 3, 4, 5, 6, 7, and 8. In the first table, there is set of publications [61, 75-94] that are exposing the facilities of OCT and the possibility of diagnostics in dentistry.

Table 2 collects publications [12, 19, 28, 58, 60, 62, 63, 67, 69-74, 95-148] which show the advancement in cariology and restorative dentistry that has taken place by using the OCT. Publications [39, 56, 149-158] presented in Table 3 are hastening the experiments and the results that were taken in endodontics. The publication [159] contained in Table 4 is the only recent publication connected directly with the pedodontics. Table 5 present the articles in the field of prosthetics [160-165]. Table 6 collects the articles [45, 65, 66, 166-180] about OCT in periodontology and diagnostics of oral tissues and implantology. The articles about diagnostics in orthodontics are presented in Table 7 [181-188]. Table 8 is collecting the other review articles that can be useful in extending the knowledge about OCT in dentistry.

5. Discussion

The common objectives of the discussed studies were increased diagnostic capabilities in the oral cavity, more accurate understanding of physiological and pathophysiological processes related to soft and hard tissues of the oral cavity, and monitoring the effects of treatment.

OCT capabilities commonly applied in many fields of medicine (such as ophthalmology) are not yet fully used in dentistry, mainly due to the low availability of customized intraoral equipment and insufficient range of OCT rays, which penetrate into the tissue to a depth of only a few millimeters depending on the apparatus type. Lesions within the tooth tissue usually reach deeper and are often measured in centimeters, which makes it necessary to perform hundreds or even thousands of scans to illustrate the entire lesion. Latest studies [56, 168, 169] are using the intraoral probes, which show that this obstacle is being slowly eliminated in the intraoral diagnostics.

To maximize the efficiency of the dental diagnostic OCT, the wavelengths of light responsible for generating the image should be subjected to testing. In the near infrared light range, the central wavelength determines the maximum depth of penetration into the tissue due to scattering and absorption properties [71]. A wavelength below 1000 nm provides the greatest imaging efficiency because light scattering properties are similar to the size of tissue particles. Hydrated tissues dissipate much more energy than hard tissues containing a small percentage of water. For this reason, universal dental OCT should offer the possibility of controlling the wavelength depending on the type of the tested tissues. A different wavelength must be used for imaging the periodontal and tooth tissue per se.

However, the technical limitation of the dental OCT is not the only problem. A very important issue is the golden standard that lacks the methodology in many publications. Only few experiments design the study in a manner that compares the obtained results to other more or less conventional methods. There are studies that practice the golden standard by comparing it, for example, to the transverse microradiography [52], microscope [58], standard histopathology [61], confocal laser scanning microscope and light microscopy [70], micro-OCT [74], cone beam computed tomography [82], synchrotron radiation microtomography [103], laser [108], SEM [114], and microfocus X-ray computed tomography [116]. It is important to focus on this topic during analyzing and citing the published results.

Another problem arising in dental diagnosis is the quality of individual teeth. The enamel can vary in its structure in a single subject. Likewise, dental fillings or prosthetic materials having a different composition reflect or absorb light at varying degrees, which has a decisive effect on the image quality and the possibility of its correct interpretation. Materials whose reflectance index is similar to that of the background will give a similar image. In addition to image quality, the possibility of performing objective measurements of the obtained scans is very important. To date, publications have been mainly focused on the possibility of obtaining images of individual structures and their acquisition rate, which is especially important in in vivo studies. The authors of the present paper attempted to develop an algorithm for rapid and accurate measurements of tooth tissues. This algorithm works fully automatically, without any operator intervention, enables to quantify the changes in the structure of enamel, allows for quantitative assessment of the effectiveness of cleaning the tooth surface and the effectiveness of the use of selected methods of enamel development. The analysis time of a sequence of 2D images does not exceed 5 seconds when using the Core i5 CPU M460 @ 2.5 GHz 4 GB RAM. The results of the mean thickness of the tooth enamel and minimum and maximum values as well as standard deviation are analysed automatically and saved to text files [sup.*].txt and Excel [sup.*].xls. Automatic analysis of tooth enamel thickness provides a number of further possibilities. These include area analysis of enamel thickness (for each individual tooth area separately) and enamel texture analysis. Imaging and quantitative measurement of the enamel structure before installation of braces and after their removal enables to expose the tooth tissue damage extent depending on the used brackets and method of attachment. This makes it possible to deduce which brackets and what technique of their installation is the safest for tooth enamel. This solution has been published in work [72]. There are also a few other possibilities for using the quantitative analysis of the intraoral structures and tissue conditions such as dental enamel and dental caries [86], dental abfraction and attrition [98], enamel erosion [101], enamel demineralization [109], thickness of dentin layer [121], and soft tissues [173].

6. Conclusions

OCT is a very important tool for the study of various tissues in vivo and in vitro. Despite problems with equipment, the possibility of early diagnosis of caries in conservative dentistry in adults and children has already been proven. It is a unique improvement in relation to X-ray diagnostics exposing patients to X-ray radiation, which is often unable to visualize the early stages of caries.

OCT allows for soft-tissue imaging, which is important in the treatment of periodontal diseases, inaccessible to direct clinical assessment, and offers great perspectives for early diagnosis of lesions in the oral mucosa. Early differentiation of the observed lesion is of great importance in the treatment of a patient due to the frequent occurrence of tumours in the oral cavity. The use of long light waves will also enable the early diagnosis of tumours of the jaw bones.

OCT provides tissue sections in a noncontact and noninvasive manner and allows for real time tissue imaging in situ, without the need for biopsy, histological procedures, or the use of X-rays, so after solving the problems related to the availability and quality of equipment, it will be the method of choice in modern dental diagnostics.

https://doi.org/ 10.1155/2017/7560645

Conflicts of Interest

The authors declare that there is no conflict of interest regarding the publication of this paper.

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[151] J. Ding, A. Ebihara, S. Watanabe et al., "Application of optical coherence tomography to identify pulp exposure during access cavity preparation using an Er:YAG laser," Photomedicine and Laser Surgery, vol. 32, pp. 356-359, 2014.

[152] R. Chavda, F. Mannocci, M. Andiappan, and S. Patel, "Comparing the in vivo diagnostic accuracy of digital periapical radiography with cone-beam computed tomography for the detection of vertical root fracture," Journal of Endodontia, vol. 40, pp. 1524-1529, 2014.

[153] Y. Iino, A. Ebihara, T. Yoshioka et al., "Detection of a second mesiobuccal canal in maxillary molars by swept-source optical coherence tomography," Journal of Endodontia, vol. 40, pp. 1865-1868, 2014.

[154] P. Majkut, A. Sadr, Y. Shimada, Y. Sumi, and J. Tagami, "Validation of optical coherence tomography against micro-computed tomography for evaluation of remaining coronal dentin thickness," Journal of Endodontia, vol. 41, pp. 1349-1352, 2015.

[155] T. Minamino, A. Mine, M. Matsumoto et al., "Nondestructive observation of teeth post core-space using optical coherence tomography: comparison with microcomputed tomography and live images," Journal of Biomedical Optics, vol. 20, article 107001, 2015.

[156] N. Scotti, C. Alovisi, A. Comba et al., "Evaluation of composite adaptation to pulpal chamber floor using optical coherence tomography," Journal of Endodontia, vol. 42, pp. 160-163, 2016.

[157] R. C. Lee, C. L. Darling, M. Staninec, A. Ragadio, and D. Fried, "Activity assessment of root caries lesions with thermal and near-IR imaging methods," Journal of Biophotonics, vol. 10, pp. 433-445, 2017.

[158] J. M. Park, C. H. Hammerle, and G. I. Benic, "Digital technique for in vivo assessment of internal and marginal fit of fixed dental prostheses," The Journal of Prosthetic Dentistry, no. 17, pp. 30008-30002, 2017.

[159] P. Lenton, J. Rudney, A. Fok, and R. S. Jones, "Clinical cross-polarization optical coherence tomography assessment of subsurface enamel below dental resin composite restorations," Journal of Medical Imaging (Bellingham), vol. 1, no. 1, artcle 016001, 2014.

[160] C. L. Lin, W. C. Kuo, J. J. Yu, and S. F. Huang, "Examination of ceramic restorative material interfacial debonding using acoustic emission and optical coherence tomography," Dental Materials, vol. 29, pp. 382-388, 2013.

[161] C. L. Lin, W. C. Kuo, Y. H. Chang, J. J. Yu, and Y. C. Lin, "Examination of ceramic/enamel interfacial debonding using acoustic emission and optical coherence tomography," Dental Materials, vol. 30, pp. 910-916, 2014.

[162] C. A. Madaras, C. Sinescu, M. L. Negrutiu et al., "Material defects in ceramic crowns identification by optical coherence tomography and microCT," Key Engineering Materials, vol. 614, pp. 124-133, 2014.

[163] L. O. Fernandes, N. D. Graca, L. S. Melo, C. H. Silva, and A. S. Gomes, "Optical coherence tomography investigations of ceramic lumineers," Proceedings of SPIE, Lasers in Dentistry, article 96920P, 2016.

[164] A. Gabor, A. Jivanescu, C. Zaharia, S. Hategan, and F. I. Topala, "OCT evaluation of single ceramic crowns: comparison between conventional and chair-side CAD/CAM technologies," Proceedings of SPIE 9670, Sixth International Conference Lasers in Medicine, article 96700Z, 2016.

[165] A. G. Turk, M. Sabuncu, S. Unal, B. Onal, and M. Ulusoy, "Comparison of the marginal adaptation of direct and indirect composite inlay restorations with optical coherence tomography," Journal of Applied Oral Science, vol. 24, pp. 383-390, 2016.

[166] N. Gladkova, E. Kiseleva, N. Robakidze et al., "Evaluation of oral mucosa collagen condition with cross-polarization optical coherence tomography," Journal of Biophotonics, vol. 6, pp. 321-329, 2013.

[167] J. R. Weber, F. Baribeau, P. Grenier et al., "Towards a bimodal proximity sensor for in situ neurovascular bundle detection during dental implant surgery," Biomedical Optics Express, vol. 5, pp. 16-30, 2013.

[168] K. Kikuchi, N. Akiba, A. Sadr, Y. Sumi, J. Tagami, and S. Minakuchi, "Evaluation of the marginal fit at implant-abutment interface by optical coherence tomography," Journal of Biomedical Optics, vol. 19, article 055002, 2014.

[169] C. C. Mota, L. O. Fernandes, R. Cimoes, and A. S. Gomes, "Non-invasive periodontal probing through Fourier-domain optical coherence tomography," Journal of Periodontology, vol. 86, pp. 1087-1094, 2015.

[170] J. Boadi, J. Fernandes, S. Mittar et al., "Imaging of 3D tissue-engineered models of oral cancer using 890 and 1300 nm optical coherence tomography," Sovremennye Tehnologii v Medicine, vol. 7, pp. 60-67, 2015.

[171] M. Sanda, M. Shiota, C. Imakita, A. Sakuyama, S. Kasugai, and Y. Sumi, "The effectiveness of optical coherence tomography for evaluating peri-implant tissue: a pilot study," Imaging Science in Dentistry, vol. 46, pp. 173-178, 2016.

[172] V. Damodaran, N. J. Vasa, R. Sarathi, and S. R. Rao, "Non-invasive detection of periodontal loss of attachment using optical coherence tomography," Proceedings of SPIE, International Conference of Optics and Photonics, article 96540Q, 2015.

[173] L. O. Fernandes, N. D. Graca, L. S. Melo, C. H. Silva, and A. S. Gomes, "Monitoring the gingival regeneration after aesthetic surgery with optical coherence tomography," Proceedings of SPIE, Lasers in Dentistry, article 96920Q, 2016.

[174] D. Augustine, R. S. Rao, and S. Patil, "Optical coherence tomography in oral cancer detection," International Journal of Contemporary Dental and Medical Reviews, article 010316, 2016.

[175] M. L. Negrutiu, C. Sinescu, C. M. Bortun et al., "Assessment of dental plaque by optoelectronic methods," Proceedings of SPIE 9670, Sixth International Conference Lasers in Medicine, article 96700W, 2016.

[176] L. O. Fernandes, C. C. Mota, L. S. de Melo, S. M. U. da Costa, D. da Silva Feitosa, and A. S. Gomes, "In vivo assessment of periodontal structures and measurement of gingival sulcus with optical coherence tomography: a pilot study," Journal of Biophotonics, 2016.

[177] H. S. Salehi, A. Kosa, M. Mahdian, S. Moslehpour, H. Alnajjar, and A. Tadinada, "Characterization of human oral tissues based on quantitative analysis of optical coherence tomography images," Proceedings of SPIE, Lasers in Dentistry, article 1004406, 2017.

[178] K. Englund, J. Nikrad, and R. Jones, "Assessing the dynamic biofilm removal of sulfonated phenolics using CP-OCT," Proceedings o fSPIE, Lasers in Dentistry, article 1004409, 2017.

[179] S. Bordin, C. M. Pino, J. Mavadia-Shukla, and X. Li, "Optical coherence technology detects early signs of peri-implant mucositis in the minipig model," International Journal of Dentistry and Oral Science, vol. 3, pp. 375-379l, 2017.

[180] S. H. Kim, S. R. Kang, H. J. Park, J. M. Kim, W. Yi, and T. I. Kim, "Improved accuracy in periodontal pocket depth measurement using optical coherence tomography," Journal of Periodontal & Implant Science, vol. 47, pp. 13-19, 2017.

[181] R. Koprowski, M. Machoy, K. Wozniak, and Z. Wrobel, "Automatic method of analysis of OCT images in the assessment of the tooth enamel surface after orthodontic treatment with fixed braces," Biomedical Engineering Online, vol. 13, p. 48, 2014.

[182] J. Seeliger, M. Machoy, R. Koprowski, K. Safranow, T. Gedrange, and K. Wozniak, "Enamel thickness before and after orthodontic treatment analysed in optical coherence tomography," BioMed Research International, vol. 8390575, 2017.

[183] M. M. Pithon, .M. D. Santos, C. A. Souza et al., "Effectiveness of fluoride sealant in the prevention of carious lesions around orthodontic brackets: an OCT evaluation," Dental press journal of orthodontics, vol. 20, pp. 37-42, 2015.

[184] J. C. Leao Filho, A. K. Braz, R. E. de Araujo, O. M. Tanaka, and M. M. Pithon, "Enamel quality after debonding: evaluation by optical coherence tomography," Brazilian Dental Journal, vol. 26, pp. 384-389, 2015.

[185] M. M. Pithon, M. J. Dos Santos, C. S. Andrade et al., "Effectiveness of varnish with CPP-ACP in prevention of caries lesions around orthodontic brackets: an OCT evaluation," European Journal of Orthodontics, vol. 37, pp. 177-182, 2015.

[186] A. Nee, K. Chan, H. Kang, M. Staninec, C. L. Darling, and D. Fried, "Longitudinal monitoring of demineralization peripheral to orthodontic brackets using cross polarization optical coherence tomography," Journal of Dentistry, vol. 42, pp. 547-555, 2014.

[187] D. M. Isfeld, C. Aparicio, and R. S. Jones, "Assessing near infrared optical properties of ceramic orthodontic brackets using cross-polarization optical coherence tomography," Journal of Biomedical Materials Research. Part B, Applied Biomaterials, vol. 102, pp. 516-523, 2014.

[188] J. C. Leao Filho, A. K. Braz, T. R. de Souza, R. E. de Araujo, M. M. Pithon, and O. M. Tanaka, "Optical coherence tomography for debonding evaluation: an in-vitro qualitative study," American Journal of Orthodontics and Dentofacial Orthopedics, vol. 143, pp. 61-68, 2013.

[189] D. M. Clarkson, "Optical technology: an update on optical coherence tomography in dentistry," Dental Update, vol. 41, pp. 174-176, 2014, 179 - 80.

[190] G. Gupta, S. Dhaded, and B. N. Shalini, "Optical coherence tomography: a new era in dentistry," Bangladesh Journal of Medical Science, vol. 13, pp. 388-390, 2014.

[191] S. Canjau, C. Todea, M. L. Negrutiu, C. Sinescu, and F. I. Topala, "Optical coherence tomography for non-invasive ex vivo investigations in dental medicine - a joint group experience," Sovremennye Tehnologii v Medicine, vol. 7, pp. 97-114, 2015.

[192] G. I. Benic, M. Elmasry, and C. H. Hammerle, "Novel digital imaging techniques to assess the outcome in oral rehabilitation with dental implants: a narrative review," Clinical oral implants research, vol. 26, pp. 86-96, 2015.

[193] M. Singh, S. Singh, A. Nagpal, and S. Laller, "Optical coherence tomography- a imaging modality in dentistry beyond X-rays," Int. J. Oral Maxillofac. Res., vol. 1, pp. 22-25, 2015.

[194] Y. S. Hsieh, Y. C. Ho, S. Y. Lee et al., "Dental optical coherence tomography," Sensors (Basel), vol. 13, pp. 8928-8949, 2013.

[195] Y. Shimada, A. Sadr, Y. Sumi, and J. Tagami, "Application of optical coherence tomography (OCT) for diagnosis of caries, cracks, and defects of restorations," Current Oral Health Reports, vol. 2, pp. 73-80, 2015.

[196] G. Benic, M. Elmasry, and C. H. Hammerle, "Novel digital imaging techniques to assess the outcome in oral rehabilitation with dental implants: a narrative review," Clinical oral implants research, vol. 11, pp. 86-96, 2015.

[197] B. W. Colston Jr., M. J. Everett, U. S. Sathyam, L. B. DaSilva, and L. L. Otis, "Imaging of the oral cavity using optical coherence tomography," Monographs in Oral Science, vol. 17, pp. 32-55, 2000.

[198] P. Se-Wook, L. Young-Joon, L. Won-Jin, and L. Jun-Jae, "Study on application to the field of dentistry using optical coherence tomography (OCT)," The Journal of Korean Academy of Prosthodontics, vol. 55, pp. 100-110, 2017.

Monika Machoy, (1) Julia Seeliger, (2) Liliana Szyszka-Sommerfeld, (1) Robert Koprowski, (3) Tomasz Gedrange, (2) and Krzysztof Wozniak (1)

(1) Division of Orthodontics, Pomeranian Medical University in Szczecin, Ul Powstahcow Wlkp 72, 70-111 Szczecin, Poland

(2) Division of Orthodontics, Technical University Dresden, Fetscherstrasse 74, 01307 Dresden, Germany

(3) Department of Biomedical Computer Systems, Faculty of Computer Science and Materials Science, Institute of Computer Science,

University of Silesia, Ul. Bgdzihska 39, 41-200 Sosnowiec, Poland

Correspondence should be addressed to Monika Machoy; m.machoy@gmail.com

Received 17 February 2017; Revised 2 May 2017; Accepted 31 May 2017; Published 16 July 2017

Academic Editor: Joao Manuel R.S. Tavares

Caption: FIGURE 1: Modular diagram showing the operating principle of OCT.

Caption: FIGURE 2: Schematic diagram of the operation of the Michelson interferometer.
TABLE 1: The OCT facilities and diagnostics in the last 5 years of
publications.

Number   Reference        Author                 Title
          number

(1)        [75]         Shi et al.        Monte Carlo modeling
                                         of human tooth optical
                                          coherence tomography

                                                imaging
(2)        [76]        Fried et al.        Near-IR imaging of
                                            cracks in teeth

(3)        [77]         Tom et al.         Near-IR imaging of
                                         demineralization under
                                                sealants

(4)        [78]         Lee et al.           Dental optical
                                         coherence tomography:
                                             new potential
                                         diagnostic system for
                                         cracked-tooth syndrome

(5)        [79]        Simon et al.      Near-infrared imaging
                                          of secondary caries
                                             lesions around
                                         composite restorations
                                          at wavelengths from
                                              1300-1700 nm

(6)        [80]         Chan et al.      Clinical monitoring of
                                         smooth surface enamel
                                          lesions using CP-OCT
                                           during nonsurgical
                                              intervention

(7)        [81]       Al-Azri et al.       Optical coherence
                                         tomography use in the
                                          diagnosis of enamel
                                                defects

(8)        [82]        Tezuka et al.     Assessment of cervical
                                            demineralization
                                               induced by
                                          Streptococcus mutans
                                           using swept-source
                                           optical coherence
                                               tomography
(9)        [83]         Kang et al.        Enhancement of OCT
                                           images with vinyl
                                           polysiloxane (VPS)

(10)       [84]      Damodaran et al.      Optical coherence
                                            tomography-based
                                           imaging of dental
                                          demineralisation and
                                         cavity restoration in
                                           840 nm and 1310 nm
                                           wavelength regions
(11)       [85]         Duma et al.        Handheld scanning
                                           probes for optical
                                         coherence tomography:
                                             developments,
                                           applications, and
                                              perspectives

(12)       [86]       Mahdian et al.             Tissue
                                         characterization using
                                           optical coherence
                                          tomography and cone
                                             beam computed
                                             tomography: a
                                           comparative pilot
                                                 study
(13)       [87]        Bakhsh et al.        Ultrastructural
                                              features of
                                         dentinoenamel junction
                                          revealed by focused
                                            gallium ion beam
                                                milling
(14)       [88]        Oguro et al.        The role of enamel
                                             thickness and
                                          refractive index on
                                          human tooth colours
(15)       [89]       Algarni et al.        Enamel thickness
                                            determination by
                                           optical coherence
                                          tomography: in vitro
                                               validation

(16)       [90]      Wijesinghe et al.   Bio-photonic detection
                                            and quantitative
                                         evaluation method for
                                           the progression of
                                          dental caries using
                                           optical frequency
                                         domain imaging method

(17)       [91]       Watanabe et al.          Resolution
                                           characteristics of
                                           optical coherence
                                         tomography for dental
                                                  use

(18)       [92]         Kim et al.       Automatic detection of
                                            tooth cracks in
                                           optical coherence
                                           tomography images

(19)       [93]       Segarra et al.       Three-dimensional
                                           analysis of enamel
                                          crack behavior using
                                           optical coherence
                                               tomography

(20)       [94]        Simon et al.        Near-IR and CP-OCT
                                          imaging of suspected
                                            occlusal caries
                                                lesions
(21)       [61]        Hariri et al.     Effects of structural
                                         orientation of enamel
                                          and dentine on light
                                         attenuation and local
                                          refractive index: an
                                           optical coherence
                                           tomography study.

Number                      Significance

(1)           This modeling will become a powerful and
          accurate tool for a preliminary numerical study
          of the OCT technique on diseases of dental hard
                               tissue
                          in human teeth.
(2)      Cracks were clearly visible using near-IR imaging
          at 1300 nm in both in vitro and in vivo images.
          Cracks and fractures also interfered with light
              propagation in the tooth aiding in crack
             identification and assessment of depth and
                             severity.
(3)          The wavelength region between 1500-1700 nm
           yielded the highest contrast of lesions under
           sealants for near-IR reflectance measurements.

(4)          Crack lines shown in the SS-OCT images had
           distinct characteristics, and structural crack
          lines and craze lines could be distinguished in
           SS-OCT images. Thus, the detection ability of
             SS-OCT renders it an acceptable diagnostic
                 device for cracked-tooth syndrome.
(5)        Intensity changes in NIR images at wavelengths
            ranging from 1300 to 1700 nm correlate with
           increased mineral loss measured using TMR. NIR
          reflectance and transillumination at wavelengths
             coincident with increased water absorption
         yielded significantly higher (P < 0.001) contrast
          between sound enamel and adjacent demineralized
           enamel. In addition, NIR reflectance exhibited
          significantly higher (P < 0.01) contrast between
          sound enamel and adjacent composite restorations
                     than visible reflectance.
(6)       Even though it appears that most of the lesions
           manifested little change with fluoride varnish
          application in the 30 weeks of the study, CP-OCT
             was able to measure the depth and internal
             structure of all the lesions including the
           thickness of the important transparent surface
            zone located at the surface of the lesions,
            indicating that CP-OCT is ideally suited for
                monitoring lesion severity in vivo.
(7)        OCT imaging enabled the identification of the
           type of enamel defect and the determination of
          the extent of the enamel defects in MIH with the
           advantage of being a radiation free diagnostic
                             technique.
(8)        The gaps along the dentinoenamel junction were
            additionally observed in SS-OCT. SS-OCT was
                 capable of monitoring the cervical
          demineralization induced by a cariogenic biofilm
          and is considered to be a promising modality for
            the diagnosis of cervical demineralization.

(9)        Vinyl polysiloxane (VPS) impression materials
         which are routinely used in dentistry can be used
          to enhance the detection of dentinal lesions on
                      tooth occlusal surfaces.
(10)     Were comparable with that of the widely used 1310
           nm OCT system. In the case of restoration with
              filler material, the 1310 nm OCT imaging
           displayed better imaging capacity due to lower
                  scattering than 840 nm imaging.

(11)      Two probes are constructed almost entirely from
           off-the-shelf components, while a third, final
         variant is constructed with dedicated components,
          in an ergonomic design. The handheld probes have
             unidimensional (1D) galvanometer scanners;
            therefore, they achieve transversal sections
           through the biological sample investigated--in
             contrast to handheld probes equipped with
         bidimensional (2D) scanners that can also achieve
          volumetric (3D) reconstructions of the samples.
          These latter handheld probes are therefore also
           discussed, as well as the possibility to equip
         them with galvanometer 2D scanners or with Risley
           prisms. For galvanometer scanners, the optimal
             scanning functions studied in a series of
          previous works are pointed out; these functions
          offer a higher temporal efficiency-duty cycle of
           the scanning process, as well as artifact-free
                            OCT images.
(12)        Within the limitations of this ex vivo pilot
          study, OCT can reliably differentiate between a
                  range of hard and soft tissues.

(13)        The great potential of cryo-FIB in handling
           different biological tissues having different
           physical properties, with great precision and
                  accuracy and minimum artefacts.

(14)       Enamel affected tooth colour, in which n was a
           statistically significant predictor for tooth
                           colour change.

(15)      Human enamel samples were prepared and evaluated
           with [mu]-CT and PS-OCT and then sectioned and
               observed via digital transversal light
              microscopy. For all methods, a standard
          transversal section (B-scan) in each sample was
          selected, and the enamel thickness was measured
           at three predetermined positions using ImageJ
              analysis software. The results revealed
           significant high agreement between all tested
          methods, indicating the potential of PS-OCT as a
            clinical tool to effectively measure enamel
                             thickness.
(16)       The physicians were able to diagnose the tooth
           volumetric and thickness changes at an initial
            stage by considering the obtained results as
           promising threshold parameters, which will be
         useful to barricade the progression of caries. To
         enhance the accuracy of the threshold parameters,
              quantitative (thickness and volumetric)
         information of multiple in vivo specimens will be
           evaluated, averaged, and normalized along with
                 clinical trials in future studies.
(17)      This study successfully clarified the resolution
             characteristics of two types of OCTs. The
             obtained data may be useful for diagnostic
         purposes, and the glass chart device used in this
           study may be useful for OCT quality assurance
                            programmes.
(18)      The authors were able to distinguish structural
           cracks, craze lines, and split lines in tooth
          cracks using SS-OCT images and to automatically
          detect the position of various cracks in the OCT
           images. Therefore, the detection capability of
          SS-OCT images provides a useful diagnostic tool
                    for cracked tooth syndrome.
(19)       Crack pattern, tooth type, and the location of
             the crack on the tooth exhibited a strong
           correlation. We show that the use of 3D SS-OCT
           permits for the nondestructive 3D imaging and
          analysis of enamel crack behavior in whole human
         teeth in vitro. 3D SS-OCT possesses potential for
            use in clinical studies for the analysis of
                       enamel crack behavior.
(20)      Near-IR imaging methods have great potential for
             improving the early diagnosis of occlusal
                              lesions.

(21)       Unlike enamel, refractive index and OCT signal
          patterns in dentine vary according to structural
           orientation, with dentine tubules playing the
           role. Attenuation of OCT signal intensity was
         small in enamel. The findings may contribute to a
         better understanding of the interactions of light
             with the dental tissue. Precise records of
         refractive indices and OCT signal patterns may be
           important for clinical diagnosis of caries and
           measurement of structural depth for operative
             purposes using this technology. Effects of
            dentine structural orientation on refractive
          index and scattering pattern must be considered
                 when observing human teeth by OCT
                      cross-sectional imaging.

TABLE 2: OCT in cariology and restorative dentistry in the last 5
years of publications.

Number   Reference        Author                    Title
          number

(1)        [95]       Shimada et al.     Noninvasive cross-sectional
                                         imaging of proximal caries
                                         using swept-source optical
                                            coherence tomography
                                              (SS-OCT) in vivo
(2)        [96]       Van Hilsen and      Comparing potential early
                           Jones          caries assessment methods
                                              for teledentistry

(3)        [97]        Nazari et al.      3D assessment of void and
                                          gap formation in flowable
                                           resin composites using
                                              optical coherence
                                                 tomography

(4)        [98]       Mandurah et al.    Monitoring remineralization
                                            of enamel subsurface
                                             lesions by optical
                                            coherence tomography
(5)        [99]      de Oliveira Mota         Optical coherence
                          et al.         tomography as an auxiliary
                                          tool for the screening of
                                          radiation-related caries

(6)        [100]       Bista et al.       Nondestructive assessment
                                             of current one-step
                                         self-etch dental adhesives
                                           using optical coherence
                                                 tomography
(7)        [101]        Park et al.       Assessment of interfacial
                                            defects at composite
                                            restorations by swept
                                          source optical coherence
                                                 tomography
(8)        [102]        Marcauteanu      Quantitative evaluation of
                          et al.            dental abfraction and
                                          attrition using a swept-
                                          source optical coherence
                                              tomography system

(9)        [103]       Liu and Jones     Evaluating a novel fissure
                                          caries model using swept
                                          source optical coherence
                                                 tomography

(10)       [104]     Chan K. H. et al.    Use of 2D images of depth
                                         and integrated reflectivity
                                          to represent the severity
                                           of demineralization in
                                         cross-polarization optical
                                            coherence tomography
(11)       [105]        Chew et al.       Measuring initial enamel
                                          erosion with quantitative
                                         light-induced fluorescence
                                            and optical coherence
                                           tomography: an in vitro
                                              validation study
(12)       [106]      Nakajima et al.       Detection of occlusal
                                           caries in primary teeth
                                         using swept source optical
                                            coherence tomography

(13)       [107]       Rominu et al.      Zirconia enriched dental
                                          adhesive: a solution for
                                          OCT contrast enhancement.
                                           Demonstrative study by
                                            synchrotron radiation
                                               microtomography
(14)       [108]      Mandurah et al.        Characterization of
                                            transparent dentin in
                                            attrited teeth using
                                              optical coherence
                                                 tomography

(15)       [109]         Ku et al.       Detection of early changes
                                           in caries lesion using
                                                QLF-D and OCT

(16)       [110]     Turkistani et al.     Sealing performance of
                                          resin cements before and
                                           after thermal cycling:
                                            evaluation by optical
                                            coherence tomography
(17)       [111]        Lee et al.       Automated assessment of the
                                             remineralization of
                                          artificial enamel lesions
                                         with polarization-sensitive
                                              optical coherence
                                                 tomography
(18)       [112]        Chan et al.        A method for monitoring
                                         enamel erosion using laser
                                           irradiated surfaces and
                                              optical coherence
                                                 tomography

(19)       [113]        Cara et al.           Evaluation of two
                                            quantitative analysis
                                             methods of optical
                                          coherence tomography for
                                             detection of enamel
                                            demineralization and
                                               comparison with
                                                microhardness
(20)       [114]       Oancea et al.          Assessment of the
                                           sealant/tooth interface
                                           using optical coherence
                                                 tomography
(21)       [115]     Damodaran et al.         Development of an

                                           electro-optically tuned
                                              optical coherence
                                            tomography system for
                                           imaging dental lesions

(22)       [116]        Wada et al.      Clinical assessment of non
                                           carious cervical lesion
                                         using swept-source optical
                                            coherence tomography

(23)       [117]      Anadioti et al.    Internal fit of pressed and
                                               computer-aided
                                            design/computer-aided
                                            manufacturing ceramic
                                          crowns made from digital
                                              and conventional
                                                 impressions
(24)       [118]     Bortolotto et al.       Failure analysis of
                                         adhesive restorations with
                                         SEM and OCT: from marginal
                                          gaps to restoration loss

(25)       [119]      Alsayed et al.          Optical coherence
                                          tomography for evaluation
                                          of enamel and protective
                                                  coatings

(26)       [120]     Espigares et al.       Assessment of natural
                                         enamel lesions with optical
                                           coherence tomography in
                                         comparison with microfocus
                                          X-ray computed tomography

(27)       [121]        Sun et al.            Sensing of tooth
                                            microleakage based on
                                          dental optical coherence
                                                 tomography

(28)       [122]        Park et al.       Assessment of defects at
                                             tooth/self-adhering
                                             flowable composite
                                               interface using
                                            swept-source optical
                                            coherence tomography
                                                  (SS-OCT)
(29)       [123]       Milly et al.       Surface pre-conditioning
                                            with bioactive glass
                                          air-abrasion can enhance
                                          enamel white spot lesion
                                              remineralization

(30)       [124]        Min et al.        Evaluation of penetration
                                         effect of resin infiltrant
                                           using optical coherence
                                                 tomography

(31)       [125]      Sinescu et al.      Noninvasive quantitative
                                          evaluation of the dentin
                                             layer during dental
                                          procedures using optical
                                            coherence tomography
(32)       [126]       Majkut et al.        Validation of optical
                                            coherence tomography
                                           against micro-computed
                                          tomography for evaluation
                                         of remaining coronal dentin
                                                  thickness

(33)       [127]     Turkistani et al.          Microgaps and
                                          demineralization progress
                                              around composite
                                                restorations

(34)       [128]        Mota et al.           Optical coherence
                                          tomography applied to the
                                            evaluation of wear of
                                             composite resin for
                                               posterior teeth
(35)       [129]      Barbosa et al.      Analysis of photodynamic
                                           cream effect in dental
                                            caries using optical
                                            coherence tomography
(36)       [130]      Makishi et al.        Assessment of current
                                            adhesives in class I
                                           cavity: nondestructive
                                            imaging using optical
                                          coherence tomography and
                                         microtensile bond strength

(37)       [74]       Ibusuki et al.      Observation of white spot
                                         lesions using swept source
                                              optical coherence
                                           tomography (SS-OCT): in
                                           vitro and in vivo study
(38)       [131]     Yoshimine et al.     Interfacial adaptation of
                                           composite restorations
                                           before and after light
                                         curing: effects of adhesive
                                            and filling technique
(39)       [132]      Sampaio et al.        Effect of restorative
                                         system and thermal cycling
                                          on the tooth restoration
                                          interface--OCT evaluation

(40)       [130]      Makishi et al.        Assessment of current
                                            adhesives in class I
                                           cavity: nondestructive
                                            imaging using optical
                                          coherence tomography and
                                         microtensile bond strength

(41)       [133]       Borges et al.        Marginal and internal
                                            analysis of preheated
                                           dental fissure-sealing
                                           materials using optical
                                            coherence tomography
(42)       [134]       Dsouza et al.        Assessment of curing
                                         behavior of light-activated
                                           dental composites using
                                         intensity correlation based
                                         multiple reference optical
                                            coherence tomography

(43)       [135]        Han et al.       Non-destructive evaluation
                                          of an internal adaptation
                                             of resin composite
                                              restoration with
                                            swept-source optical
                                          coherence tomography and
                                                  micro-CT

(44)       [137]        Tom et al.       Near-IR image-guided laser
                                                 ablation of
                                          demineralization on tooth
                                              occlusal surfaces

(45)       [138]      Cassimiro-Silva       Mitigation of enamel
                          et al.          erosion using commercial
                                         toothpastes evaluated with
                                              optical coherence
                                                 tomography

(46)       [139]     Dao Luong et al.     Fractography of interface
                                           after microtensile bond
                                             strength test using
                                            swept-source optical
                                            coherence tomography

(47)       [140]        Ito et al.         Assessment of occlusal
                                          fissure depth and sealant
                                          penetration using optical
                                            coherence tomography

(48)       [141]        Han et al.         Internal adaptation of
                                           resin composites at two
                                          configurations: influence
                                         of polymerization shrinkage
                                                 and stress

(49)       [142]       Horie et al.       Monitoring of cariogenic
                                           demineralization at the
                                         enamel-composite interface
                                         using swept-source optical
                                            coherence tomography

(50)       [143]        Zhou et al.        Assessment of bacterial
                                           demineralization around
                                           composite restorations
                                         using swept-source optical
                                            coherence tomography
                                                  (SS-OCT)

(51)       [144]     de Moraes et al.      Progression of erosive
                                         lesions after Nd:YAG laser
                                         and fluoride using optical
                                            coherence tomography
(52)       [145]        Ueno et al.      Optical analysis of enamel
                                            and dentin caries in
                                         relation to mineral density
                                         using swept-source optical
                                            coherence tomography

(53)       [146]       Sugita et al.     A pilot study to assess the
                                         morphology and progression
                                           of non-carious cervical
                                                   lesions

(54)       [147]     Schneider et al.    Imaging resin infiltration
                                         into non-cavitated carious
                                             lesions by optical
                                            coherence tomography
(55)       [20]       Holtzman et al.        Ability of optical
                                           coherence tomography to
                                            detect caries beneath
                                            commonly used dental
                                                  sealants
(56)       [12]         Kang et al.       Nondestructive monitoring
                                           of the repair of enamel
                                          artificial lesions by an
                                           acidic remineralization
                                                 model using
                                           polarization-sensitive
                                              optical coherence
                                                 tomography
(57)       [28]         Kang et al.       Nondestructive assessment
                                               of early tooth
                                           demineralization using
                                         cross-polarization optical
                                            coherence tomography
(58)       [58]        Nazari et al.       Effect of hydration on
                                         assessment of early enamel
                                          lesion using swept-source
                                              optical coherence
                                                 tomography

(59)       [60]       Shimada et al.     3D evaluation of composite
                                            resin restoration at
                                          practical training using
                                            swept-source optical
                                            coherence tomography
                                                  (SS-OCT)

(60)       [62]       Nakajima et al.    Noninvasive cross-sectional
                                         imaging of incomplete crown
                                          fractures (cracks) using
                                            swept-source optical
                                            coherence tomography
(61)       [63]         Braz et al.      In situ gold nanoparticles
                                          formation: contrast agent
                                             for dental optical
                                            coherence tomography

(62)       [67]       Holtzman et al.        Assessment of early
                                          occlusal caries pre- and
                                         post-sealant application--an
                                              imaging approach

(63)       [69]        Sugita et al.     A pilot study to assess the
                                         morphology and progression
                                           of non-carious cervical
                                                   lesions

(64)       [70]         Zhou et al.        Assessment of bacterial
                                           demineralization around
                                           composite restorations
                                         using swept-source optical
                                            coherence tomography
                                                  (SS-OCT)
(65)       [71]         Maia et al.      Evaluation of dental enamel
                                           caries assessment using
                                         quantitative light induced
                                          fluorescence and optical
                                            coherence tomography

(66)       [72]        Horie et al.       Monitoring of cariogenic
                                           demineralization at the
                                         enamel-composite interface
                                         using swept-source optical
                                            coherence tomography

(67)       [73]      Damodaran et al.         Optical coherence
                                         tomography based imaging of
                                         dental demineralization and
                                          cavity restoration in 840
                                          nm and 1310 nm wavelength
                                                   regions

Number                       Significance

(1)            SS-OCT appears to be a more reliable and
          accurate method than bitewing radiographs for the
          detection and estimation of the depth of proximal
                 lesions in the clinical environment.

(2)        Although MID and CP-OCT were useful in detecting
           the presence of demineralization, examiners were
           not able to utilize these devices to adequately
            assess the depth of the demineralization. This
             study found that MID and CPOCT did not have
           markedly superior diagnostic values from simple
               CAM assessment for use in teledentistry.
(3)                The flowable composite with SDR
            (stress-decreasing resin) technology performed
               better than the conventional composite;
            however, bulk filling a 4 mm-deep cavity will
           compromise the sealing of the bonding interface
            regardless of the type of composite. OCT is a
            unique method of characterizing materials and
           their behaviors nondestructively and precisely.
(4)        OCT signal attenuation demonstrated a capability
           for monitoring changes of enamel lesions during
                          remineralization.

(5)           The OCT technique was able to characterize
            radiation-related caries, from a morphological
               point of view. Also demonstrated was its
              potential benefit for use in the clinical
           monitoring of radiation-related carious process.
(6)       OCT is a unique tool to nondestructively evaluate
             the sealing performance of the restoratives
            through the cavity, provided that cavity walls
           have a certain minimum inclination with respect
                             to the beam.
(7)       OCT imaging has the potential to nondestructively
            assess the interfacial adaptation of composite
            restorations and to detect internal defects in
                   the layered composite material.

(8)        A valuable tool in the evaluation of the dynamic
              evolution of ex vivo artificially induced
            abfractions and attritions is able to measure
            minute changes in the tooth morphology, having
          the potential to be employed as an effective tool
           for monitoring the temporal evolution of dental
           wear. OCT can offer the possibility of providing
                 in vivo volumetric measurements and
          identification of fractural lines in dentine. The
           2D and 3D pictures prove the OCT ability in the
           evaluation of dental abfractions and attritions.
          The system could measure a minimal volume of 2352
           [micro]m to 32,352 [micro][m.sup.3], where each
                          volume is acquired
                     as 25, 000 A scans in 2.5 s.
(9)       Despite correctly evaluating the depth, this work
             showed that the lesion width calculated from
            SS-OCT reflectivity images did not accurately
            predict the demineralized width. The relative
           reflectivity could not accurately determine the
            mineral density of the demineralized lesions.
         SS-OCT detected subsurface fissure demineralization
             and could be used to determine if the decay
            process was advancing toward the enamel-dentin
                              junction.
(10)       Calculated lesion depths from OCT were compared
            with lesion depths measured from histological
               sections examined using polarized light
          microscopy. The 2D images of the lesion depth and
             integrated reflectivity are well suited for
               visualization of early demineralization.
(11)       OCT and QLF were able to detect demineralization
            after 10 min of erosive challenge and could be
                  used to monitor the progression of
            demineralization of initial enamel erosion in
                                vitro.

(12)      The results obtained from SS-OCT and conventional
            visual inspections were compared with those of
               CLSM. SS-OCT detects both cavitated and
                noncavitated lesions. The magnitude of
           sensitivity for SS-OCT was higher than those for
               visual inspection (sensitivity of visual
             inspection and SS-OCT, 0.70 versus 0.93 for
            enamel demineralization, 0.49 versus 0.89 for
          enamel cavitated caries, and 0.36 versus 0.75 for
          dentin caries). Occlusal caries of a few clinical
           cases were observed using SS-OCT in vivo. SS-OCT
             has a great detecting potential for occlusal
                       caries in primary teeth.
(13)        The present study proved the capability of the
             OCT method in visualizing the morphology and
              integrity of zirconia-doped tooth adhesive
            fillings to be used for a further in vivo tool
                             development.

(14)       Physiological changes in transparent dentin that
              involve deposition of mineral casts in the
          dentinal tubules lead to lower attenuation of OCT
              signal. OCT has a potential role to detect
            transparent dentin on the surface of attrited
          teeth and can be used in the future as a clinical
                            adjunct tool.
(15)       The QLF-D and SS-OCT could detect subtle changes
           in mineral loss and lesion depth with respect to
            demineralized time. Furthermore, these devices
            were useful for monitoring changes in mineral
                       amount and lesion depth.
(16)        OCT could be used for monitoring of composite
          inlays with several interfacial resin layers. The
             application of a direct bonding agent in the
             resin-coating technique improved interfacial
             sealing and durability of all resin cements.
(17)       PS-OCT can automatically measure the changes in
           artificial enamel lesion structure and severity
             upon exposure to remineralization solutions.

(18)       Irradiation of the enamel surface with a pulsed
           carbon dioxide laser at subablative intensities
           results in significant inhibition of erosion and
              demineralization under the acid challenge
              employed in this study. In addition, these
          results suggest that it may be feasible to modify
           regions of the enamel surface using the laser to
           serve as reference marks to monitor the rate of
                           erosion in vivo.
(19)      Both methods for signal analysis from OCT allowed
               detection of demineralization with good
              performance. The AUC-OCT approach enables
                 obtaining a linear relation with the
              microhardness results, for a quantitative
              assessment of mineral loss in human teeth.

(20)          Optical inspection and X-ray investigation
              revealed no defects, while SS-OCT assesses
              exactly the position, the nature, and the
              dimensions of each type of these defects.
(21)        The tuning range for LiNb[O.sub.3] and KTP was
                               found to
            be in the order of few micrometers whereas KTN
          (potassium tantalate niobate) using the quadratic
          electro-optic effect is expected to show scanning
            range of tens of micrometers. KTN based hybrid
              scanning for dental caries imaging is also
                               planned.
(22)       SS-OCT results confirm that dentin mineral loss
             and occlusal attrition were associated with
               larger NCCLs and can be considered as an
           etiological fact or information and progress of
                            these lesions.
(23)        The combination of the digital impression and
              pressed crown produced the least accurate
                            internal fit.

(24)        When marginal imperfections, or noncontinuous
          margins, were detected by SEM, also imperfections
             beneath the surface could be observed at the
          tooth-restoration interface with OCT. Restoration
            loss occurred above the bor derline of 50% of
             marginal gaps on enamel and dentin. Marginal
              discrepancies of adhesive restorations can
               propagate inside the cavity and lead to
                          restoration loss.
(25)          The coatings showed different thicknesses
              (60-250 micrometers) and various levels of
           structural and interfacial integrity. OCT could
              detect a demineralization inhibition zone
               adjacent to the edge of the fluoride-and
                calcium-releasing material. Localized
              demineralization was occasionally observed
                under thinner coatings. Protection of
              susceptible enamel surfaces by thin resin-
             basedbioactive coatings provides protection
              from demineralization. OCT can be used to
            nondestructively monitor the integrity of such
           coatings, as well as enamel changes beneath and
                          adjacent to them.
(26)      The images obtained clinically in real time using
            the dental SS-OCT system are suitable for the
             assessment of natural subsurface lesions and
           their surface layer, providing comparable images
            to a laboratory high resolution [mu]CT without
                          the use of X-ray.
(27)       The results of this study show that microleakage
          can be detected with oral probing using SS-OCT in
           vivo. The calculated microleakage length was 401
           [micro]m and the width is 148 [micro]m, which is
                              consistent
                 with the related histological biopsy
            measurements. The diagnosis of microleakage in
          teeth could be useful for prevention of secondary
           caries in the clinical treatment plans developed
                    in the field of oral medicine.
(28)        Given the high proportion of adhesive defects
             with the experimental self-adhering flowable
           composite, its use as the definitive restorative
           material in class-V cavities must be critically
             scrutinized and clinical indications must be
            investigated further with in vitro and in vivo
                               trials.
(29)           Bioactive glass air-abrasion was used to
                precondition enamel white spot lesion.
            Preconditioning increased the average surface
          roughness of the lesion. An ultrathin, clinically
           insignificant layer was removed from the lesion
             surface. Preconditioning enhanced subsequent
               remineralization using bioactive glass.
(30)      The OCT was the promising quantitative evaluation
           method for RI penetrated into EC. The OCT would
              be used as a nondestructive and real-time
          evaluation method for resin infiltrant penetrated
              into caries lesion on clinical procedure.
(31)         The study demonstrates the usefulness of OCT
          imaging in guiding such evaluations during dental
                             procedures.

(32)        We used optical coherence tomography (OCT) and
           microcomputed tomographic (micro-CT) imaging to
           scan teeth after deep dentin caries removal. The
           remaining dentin thickness (RDT) at pulpal horns
           was measured and compared. A strong correlation
           was found in measurements between OCT and micro-
           CT imaging. It was possible to clearly visualize
           pulp horns with RDT up to 1.5 mm in thickness. A
              refractive index value of 1.54 is valid to
                convert optical readings of RDT by OC.
(33)       Microgaps forming at the margins of restorations
           depend on adhesives and significantly contribute
            to the progress of demineralization around the
           margins, while fluoride release may decrease the
                         rate of progression.
(34)          90% of the restorations of both groups had
           fractures and/or points of stress concentration,
           considered niches for early dissemination of new
                           fracture lines.

(35)          The OCT technique demonstrated that cream
               associated with laser showed the lowest
               quantitative enamel mineral loses after
                        cariogenic challenge.
(36)           Sealing performance was measured in five
              adhesives by optical coherence tomography.
             Sealing and bond strength performance within
          individual specimens were correlated. Interfacial
           defects increased after thermal aging. Increased
           interfacial defects tended to decrease the bond
           strength. Two-and three-dimensional images were
               useful in assessing bonding performance.
(37)          SS-OCT appears to be an effective tool for
            observation of the internal structure of WSLs,
            enabling quantitative assessment of WSL depth.
             Such data can be considered in the clinical
                   management of white spot lesion.
(38)        SS-OCT is a unique method to observe the pre-
           existing interfacial defects and gaps developed
          during polymerization, which were found to depend
          on both placement technique and applied adhesive.

(39)        The self-etching adhesive system (CSE) showed
            better dentin marginal integrity after thermal
           cycling, compared with the etch-and-rinse (SB2),
           regardless of the type of resin composite used.
              Enamel was not affected even after thermal
                               cycling.
(40)           Sealing performance was measured in five
              adhesives by optical coherence tomography.
             Sealing and bond strength performance within
          individual specimens were correlated. Interfacial
           defects increased after thermal aging. Increased
           interfacial defects tended to decrease the bond
           strength. Two-and three-dimensional images were
               useful in assessing bonding performance.
(41)        Preheated flowable composite provided the best
              marginal sealing of fissures and internal
                     homogeneity of the material.

(42)       These results show that MR-OCT has the potential
          to measure the curing time and monitor the curing
           process as a function of depth. Moreover, MR-OCT
              as a product has potential to be compact,
            low-cost, and to fit into a smartphone. Using
            such a device for monitoring the curing of the
                resin will be suitable for dentists in
               stationary and mobile clinical settings.
(43)       Micro-CT and SS-OCT may be useful nondestructive
           methods for evaluating internal adaptation. The
           microleakage measured by micro-CT was lower than
            that of SS-OCT; however, the two measurements
            were relatively high-correlated. When adhesion
           depends mostly on the dentin surface, a two-step
            self-etch adhesive system should be considered
                       for long-term longevity.
(44)           Sequential near-IR reflectance images at
                 1500-1700 nm can be used to guide a
                9.3 [micro]m C[O.sub.2] laser for the
             selective ablation of early demineralization
                     on tooth occlusal surfaces.
(45)         A significant increase in the mean roughness
            values was observed on eroded surface and also
              on treated surface as revealed by scanning
             electron microscopy. The use of Sn[F.sub.2]/
             NaF toothpaste was the most effective method
              for reducing mineral loss. As quantitative
           methods, OCT and contact profilometry showed no
             statistical differences. OCT, which was used
             for this purpose for the first time, has the
             advantage of being noninvasive and therefore
             has the potential for clinical application.
(46)       Testing MTBS samples at higher crosshead speeds
             induced more cracks in dentin. Lining with a
           flowable composite improved the bonding quality
             and increased the bond strength. SS-OCT can
            visualize interfacial cracks after restoration
                              debonding.
(47)        The diagnostic power of SS-OCT was higher than
             that of visual inspection for fissure depth.
            Additionally, clear cross-sectional images of
           sealant penetration into fissures were observed
             with SS-OCT. SS-OCT can be used to evaluate
            fissure depth and monitor sealant penetration.
(48)      Internal adaptation in a high C-factor cavity was
            inferior to that in a low C-factor cavity for
            both conventional and bulk-filled composites.
            Internal adaptation, polymerization shrinkage,
              and stress were different among composite
              materials. Polymerization stress under the
           compliance-allowed condition showed significant
            correlations with internal adaptations in high
                      and low C-factor cavities.
(49)        The carious demineralization around composite
            restorations was observed as a bright zone in
                SS-OCT during the process of bacterial
               demineralization. SS-OCT appears to be a
            promising modality for the detection of caries
                 adjacent to an existing restoration.
(50)               SS-OCT nondestructively detected
            demineralization around composite restorations
              and interfacial gaps created by S. mutans
                   biofilm in this in vitro model.

(51)      The OCT technique is promising for diagnosing and
              monitoring erosive lesion damage; however,
           further in vitro and in vivo research is needed
                         to improve its use.
(52)        Both enamel and dentin demineralization showed
           significantly higher IS200 and [mu][mu] than the
                                sound
            tooth substrate from the sagittal scan. Enamel
             demineralization showed significantly higher
           IS200 than sound enamel, even with low levels of
            demineralization. In demineralized dentin, the
                               [mu][mu]
            from the horizontal scan consistently trended
                downward compared to the sound dentin.
(53)        The dimensional analysis demonstrated notable
                progression with large variations. The
                wedge-shaped lesions appeared to show
              greater [D.sub.max] values compared to the
                        saucer-shaped lesions.
(54)      Resin infiltration can be increased by optimizing
          the etching process. Optical coherence tomography
          provides information about the process and degree
                        of resin infiltration.
(55)       Dentists were able to detect tooth decay beneath
           four commonly used dental sealants based on OCT
           images. Clinical investigations are now underway
           to determine the usefulness of this approach in
                                vivo.
(56)       This study demonstrated that PS-OCT can be used
            to nondestructively measure changes in lesion
          structure and severity upon exposure to an acidic
               remineralization model. This study also
            demonstrated that automated algorithms can be
           used to assess the lesion severity even with the
            presence of a weakly reflective surface zone.

(57)           Cross-polarization OCT is ideally suited
              for the nondestructive assessment of early
                          demineralization.

(58)      In summary, the strong relationship found between
           DH and lesion extent indicates the potential of
          this method for assessment of early enamel lesion
           using SS-OCT. However, further studies on DH for
             evaluation of a wider range of demineralized
           lesions as well as remineralization, accompanied
              by a clinically relevant drying method are
           necessary to optimize the suggested methodology.
(59)       SS-OCT could detect the internal gaps and voids
             within the restorations in tomography images
           synthesized based on the backscatter signal from
           within the restoration. It is suggested that the
           SS-OCT is promising diagnostic modality, as well
           as educational imaging device for the detection
              of internal gaps in adhesive restorations.
(60)        SS-OCT can clearly discriminate cracks, which
          appear as highlighted lines due to the scattering
            of light. The results obtained from the three
            scanning directions were correlated well with
                 those of the histological sections.
(61)      The results show that the OCT technique, using in
              situ formed gold nanoparticles as contrast
              enhancers, can be used to visualize dentin
            structures in a noninvasive and nondestructive
                                 way.
(62)       This study found that OCT-based imaging combined
            with a simple diagnostic algorithm accurately
           assessed the severity of natural early caries on
           occlusal surfaces in extracted teeth both in the
             absence and presence of dental sealant. The
           findings of this study support the clinical use
             of OCT imaging for assessment and monitoring
           progression of early noncavitated caries lesions
          on occlusal surfaces including areas under dental
                              sealants.
(63)        The dimensional analysis demonstrated notable
            progression with large variations. The wedge-
           shaped lesions appeared to show greater maximal
            values compared to the saucer-shaped lesions.
             With respect to the depth, the wedge-shaped
           lesions may progress at a greater rate compared
                    to the saucer-shaped lesions.
(64)               SS-OCT nondestructively detected
            demineralization around composite restorations
              and interfacial gaps created by S. mutans
                   biofilm in this in vitro model.

(65)          Comparison of the percentage of alteration
               between optical properties of sound and
           artificial enamel caries regions showed that OCT
          processed images through the attenuation of light
           enhanced the tooth optical alterations more than
           fluorescence detected by QLF system. QLF versus
              OCT imaging of enamel caries: a photonics
                             assessment.
(66)        The carious demineralization around composite
            restorations was observed as a bright zone in
                SS-OCT during the process of bacterial
               demineralization. SS-OCT appears to be a
            promising modality for the detection of caries
                 adjacent to an existing restoration.
(67)       Results were comparable with that of the widely
               used 1310 nm OCT system. In the case of
            restoration with filler material, the 1310 nm
            OCT imaging displayed better imaging capacity
             due to lower scattering than 840 nm imaging.

TABLE 3: OCT in endodontics in the last 5 years of publications.

Number   Reference        Author                    Title
          number

(1)        [148]       de Oliviera        Detection of apical root
                          et al.        cracks using spectral domain
                                              and swept-source
                                        optical coherence tomography
(2)        [149]       Brady et al.       A comparison of cone beam
                                           computed tomography and
                                         periapical radiography for
                                          the detection of vertical
                                              root fractures in
                                          nonendodontically treated
                                                    teeth

(3)        [150]     Minamino et al.     Nondestructive observation
                                          of teeth post core space
                                           using optical coherence
                                          tomography: a pilot study

(4)        [151]       Ding et al.         Application of optical
                                           coherence tomography to
                                           identify pulp exposure
                                            during access cavity
                                         preparation using an Er:YAG
                                                    laser
(5)        [152]     Chavda R. et al.   Comparing in vivo diagnostic
                                             accuracy of digital
                                         periapical radiography with
                                             cone-beam computed
                                        tomography for the detection
                                          of vertical root fracture
(6)        [153]       Iino et al.          Detection of a second
                                            mesiobuccal canal in
                                             maxillary molars by
                                            swept-source optical
                                            coherence tomography
(7)        [154]      Majkut et al.         Validation of optical
                                        coherence tomography against
                                          micro-computed tomography
                                         for evaluation of remaining
                                          coronal dentin thickness

(8)        [155]     Minamino et al.     Nondestructive observation
                                          of teeth post core-space
                                           using optical coherence
                                         tomography: comparison with
                                        microcomputed tomography and
                                                 live images

(9)        [156]      Scotti et al.        Evaluation of composite
                                        adaptation to pulpal chamber
                                             floor using optical
                                            coherence tomography

(10)       [157]        Lee et al.       Activity assessment of root
                                         caries lesions with thermal
                                         and near-IR imaging methods

(11)       [39]       Shemesh et al.     Diagnosis of vertical root
                                           fractures with optical
                                            coherence tomography
(12)       [56]       Natsume et al.        Estimation of lesion
                                         progress in artificial root
                                           caries by swept source
                                        optical coherence tomography
                                         in comparison to transverse
                                              microradiography

Number                      Significance

(1)         The detection ability verified for both OCT
            systems renders them promising tools for the
                  diagnosis of apical microcracks.

(2)         Under the conditions of this ex vivo study,
          periapical radiographs and CBCT were unreliable
          for the detection of simulated incomplete VRFs.
          The widths of the fractures appeared to have an
          impact on the diagnostic accuracy of CBCT as the
          detection of VRFs of [greater than or equal to]
          50 [micro]m was significantly higher than those
            of < 50 [micro]m. The detection of complete
             fractures was significantly higher for all
             systems than that of incomplete fractures.
(3)          In the cementum absent group, the internal
         structure of the root could be visualized clearly
           compared with the cementum present group. The
          root internal structure could be observed by OCT
           and the image became clearer when cementum was
                              removed.
(4)      Swept-source OCT is a useful tool for identifying
          pulp exposure during access opening with the Er:
                             YAG laser.

(5)          Both DR and CBCT imaging have significant
              limitations when detecting vertical root
                             fractures.

(6)          SS-OCT imaging is noninvasive, involves no
            ionizing radiation, and is accurate for the
                      detection of MB2 canals.

(7)      Further analysis indicated linear regression with
             a slope of 1.54 and no intercept, closely
         matching the bulk refractive index of dentin. OCT
            enables visualization of anatomic structures
           during deep caries excavation. Exposure of the
          vital dental pulp because of the removal of very
         thin remaining coronal dentin can be avoided with
                 this novel noninvasive technique.
(8)          The resulting OCT images were superior for
         identifying gap formation at the interface, while
            [mu]CT[mu]CT images were better to grasp the
           tooth form. Continuous tomographic images from
                               real-
              time OCT observation allowed successful
          construction of a video of the resin core build-
                           up procedure.
(9)      Composite adaptation to the pulp chamber floor is
           fundamental for endodontic treatment outcome.
              Optical coherence tomography is the most
           noninvasive method to assess interfaces. Less
            interfacial gaps were observed when flowable
             resins were used. Any differences between
           conventional flow and bulk fill composite were
                               shown.
(10)     The PS-OCT algorithm for the automated assessment
           of remineralization successfully detected the
          highly mineralized surface layer on both natural
          and simulated lesions. Thermal imaging provided
         the most accurate diagnosis of root caries lesion
          activity. These results demonstrate that thermal
          imaging and PS-OCT may be ideally suited for the
         nondestructive root caries lesion activity during
                      a clinical examination.
(11)      OCT is a promising nondestructive imaging method
                     for the diagnosis of VRFs.

(12)        The OCT showed a potential for quantitative
          estimation of lesion depth and mineral loss with
                 cavitated dentin lesions in vitro.

TABLE 4: OCT in pedodontics in the last 5 years of publications.

Number   Reference   Author                  Title
          number

(1)        [159]     Lenton   Clinical cross-polarization optical
                     et al.    coherence tomography assessment of
                                 subsurface enamel below dental
                                  resin composite restorations

Number                  Significance

(1)      CP-OCT imaging may be used to confirm the
         subsurface marginal integrity below resin
          composite restorations but with careful
            consideration of limitations of the
         imaging modality. CP-OCT imaging may be a
             useful adjunct to clinical visual
         investigation to confirm that a composite
            margin has a sound and well-adapted
                         interface.

TABLE 5: OCT in prosthetics in the last 5 years of publications.

Number   Reference    Author                    Title
          number

(1)        [158]       Park         Digital technique for in vivo
                      et al.     assessment of internal and marginal
                                   fit of fixed dental prostheses

(2)        [160]        Lin      Examination of ceramic restorative
                      et al.       material interfacial debonding
                                 using acoustic emission and optical
                                        coherence tomography
(3)        [161]        Lin         Examination of ceramic/enamel
                      et al.         interfacial debonding using
                                    acoustic emission and optical
                                        coherence tomography

(4)        [162]      Madaras    Material defects in ceramic crowns
                      et al.     identification by optical coherence
                                       tomography and microCT

(5)        [163]     Fernandes      Optical coherence tomography
                      et al.     investigations of ceramic lumineers
(6)        [164]       Gabor      OCT evaluation of single ceramic
                      et al.         crowns: comparison between
                                 conventional and chair-side CAD/CAM
                                            technologies
(7)        [165]       Turk          Comparison of the marginal
                      et al.      adaptation of direct and indirect
                                  composite inlay restorations with
                                    optical coherence tomography

Number                           Significance

(1)         Digital approaches to assess the misfit of fixed dental
           prostheses have been limited to in vitro evaluation. The
          present article describes a fully digital technique for the
          in vivo assessment of the fit of fixed dental prostheses by
             means of a chairside optical scanner and software for
          three-dimensional (3D) analysis. The 3D digital capture is
          performed in 3 steps: an extraoral scan of the restoration,
           an intraoral scan of the abutment tooth, and an intraoral
            registration scan of the restoration positioned on the
                                abutment tooth.
(2)        Sustainable cyclic load stresses in ceramic-dentin-bonded
           specimens were substantially lower than the measured SBS.
           Predicted S-N curve showed that the maximum endured load
                was 4.18 MPa passing [10.sup.6] fatigue cyclic.
(3)          The acoustic emission technique combined with OCT MPa
           images as a preclinical assessment tool to determine the
              integrity of cemented load bearing restored ceramic
                 material. Sustainable cyclic load stresses in
           ceramic-enamel-bonded specimens were substantially lower
            than the measured SBS. Predicted S-N curve showed that
              \the maximum endured load was 10.98 (about 34.48 N)
                      passing [10.sup.6] fatigue cyclic.

(4)       OCT technology can be considered an early diagnosis method
           of faults contained in the table structure of the ceramic
              crowns before inserting them in the oral cavity, by
                 reducing the risks of a prosthetic treatment.
(5)        The OCT is an effective and promising method to clinical
                evaluation of the cementing line in lumineers.
(6)       The marginal accuracy of all ceramic crowns fabricated with
           digital impression and the CAD/ CAM technique is superior
                   to the conventional impression technique.

(7)         Within the limitations of this in vitro study, marginal
          discrepancies of inlay restorations were quantitatively and
           noninvasively evaluated by the OCT system. The following
           conclusions may be drawn: direct inlays presented smaller
          marginal gap values than indirect inlays. The marginal gap
               values were increased for all restorations after
                                 cementation.

TABLE 6: OCT in periodontology and diagnostics of oral tissues and
implantology in the last 5 years of publications.

Number   Reference        Author                  Title
          number

(1)        [166]     Gladkova et al.    Evaluation of oral mucosa
                                         collagen condition with
                                           cross-polarization
                                            optical coherence
                                               tomography

(2)        [167]       Weber et al.         Towards a bimodal
                                         proximity sensor for in
                                        situ neurovascular bundle
                                         detection during dental
                                             implant surgery

(3)        [168]      Kikuchi et al.        Evaluation of the
                                             marginal fit at
                                            implant-abutment
                                          interface by optical
                                          coherence tomography
(4)        [169]       Mota et al.      Non-invasive periodontal
                                             probing through
                                         Fourier-domain optical
                                          coherence tomography

(5)        [170]       Boadi et al.           Imaging of 3D
                                        tissue-engineered models
                                        of oral cancer using 890
                                           and 1300 nm optical
                                          coherence tomography

(6)        [171]       Sanda et al.       The effectiveness of
                                            optical coherence
                                        tomography for evaluating
                                         peri-implant tissue: a
                                               pilot study

(7)        [172]     Damodaran et al.   Non-invasive detection of
                                           periodontal loss of
                                        attachment using optical
                                          coherence tomography

(8)        [173]     Fernandes et al.    Monitoring the gingival
                                           regeneration after
                                         aesthetic surgery with
                                            optical coherence
                                               tomography
(9)        [174]     Augustine et al.       Optical coherence
                                        tomography in oral cancer
                                                detection

(10)       [175]     Negrutiu et al.      Assessment of dental
                                        plaque by optoelectronic
                                                 methods

(11)       [176]     Fernandes et al.     In vivo assessment of
                                         periodontal structures
                                           and measurement of
                                          gingival sulcus with
                                            optical coherence
                                        tomography: a pilot study

(12)       [177]      Salehi et al.     Characterization of human
                                          oral tissues based on
                                        quantitative analysis of
                                            optical coherence
                                            tomography images

(13)       [178]      Englund et al.      Assessing the dynamic
                                           biofilm removal of
                                          sulfonated phenolics
                                              using CP-OCT
(14)       [179]      Bordin et al.         Optical coherence
                                        technology detects early
                                          signs of peri-implant
                                        mucositis in the minipig
                                                  model
(15)       [180]        Kim et al.        Improved accuracy in
                                        periodontal pocket depth
                                        measurement using optical
                                          coherence tomography

(16)       [45]        Chen et al.         Quantifying dental
                                          biofilm growth using
                                           cross-polarization
                                            optical coherence
                                               tomography

(17)       [65]       Adegun et al.     Quantitative analysis of
                                            optical coherence
                                             tomography and
                                        histopathology images of
                                          normal and dysplastic
                                          oral mucosal tissues
(18)       [66]       Adegun et al.       Quantitative optical
                                         coherence tomography of
                                        fluid-filled oral mucosal
                                                 lesions

Number                    Significance

(1)       The OCT signal SD in cross-polarized images
              reflects two boundary conditions of
           collagen disorganization, namely, loss of
            fibre properties at active inflammation
            which attenuates the signal and fibrosis
             that occurs due to synthesis of a new
           remodeled collagen which amplifies the OCT
                            signal.
(2)        The proximity to the neurovascular bundle
          can be tracked in real time in the range of
           a few millimeters with NIR signals, after
             which higher resolution imaging OCT to
           provide finer ranging in the submillimeter
                           distances.
(3)          OCT appeared as an effective tool for
           evaluating the misfit of implant-abutment
               under thin layers of soft tissue.

(4)           Regarding the ability of the two OCT
                systems to visualize periodontal
          structures, the system operating at 1325 nm
             shows a better performance, owing to a
             longer central wavelength that allows
          deeper tissue penetration. The results with
           the system at 930 nm can also be used, but
           some features could not be observed due to
           its lower penetration depth in the tissue.
(5)           890 nm OCT retains some of its known
             advantages of higher contrast between
             anatomical tissue layers when used to
            observe dysplastic and malignant 3D oral
           mucosa constructs. However, 1300 nm OCT is
           confirmed to possess a greater ability to
             image the full thickness of the model
            epithelia, and in particular, it is more
           suited to imaging through the keratinized
                             layer.
(6)        Cement remnants at the submucosal area can
            be detected in some cases, which can be
               helpful in preventing peri-implant
             diseases. Still, though there are some
           restrictions to its application, OCT could
           have potential as an effective diagnostic
               instrument in the field of implant
                       dentistry as well.
(7)         The conventional time domain OCT system
           acquisition speed is limited by the speed
          of the mechanical scanning system. In order
                to overcome this issue, a novel
             electro-optic-based scanning system is
                   proposed and demonstrated.
(8)            OCT is an efficient method in the
              evaluation of regeneration gingival.

(9)        OCT can pinpoint epithelial changes; this
            imaging tool has sought potential broad
           applications in other mucosal lesions such
            as vesiculobullous and vascular lesions.
            The possibility of this application for
               bone-related disease imaging is an
             interesting research prospect. Future
             research should focus on the suitable
           wavelength of the light source of OCT for
          better observation of oral diseases. Faster
                              and
(10)          The biofilm network was dramatically
            destroyed after the professional dental
           cleaning. OCT noninvasive methods can act
                 as a valuable tool for the 3D
              characterization of dental biofilms.
(11)      OCT has the potential to be a reliable tool
           for in vivo periodontal tissues evaluation
               and for reproducible sulcus depth
             measurements in healthy sites. Further
             technological advances are required to
             reduce the procedure time and promote
             evaluation of posterior oral regions.
(12)            These OCT features can reliably
           differentiate between a range of hard and
              soft tissues and could be extremely
           valuable in assisting dentists for in vivo
              evaluation of oral tissues and early
             detection of pathologic changes in the
                            tissues.
(13)       This novel CP-OCT flow cell assay has the
            potential to examine rapid interactions
           between antibiofilm agents and tooth like
                           surfaces.
(14)      Development of clinical applications of OCT
            imaging for early diagnosis of mucositis
           could lead to therapeutic interventions to
              reduce one of the causes of implant
                            failure.
(15)         OCT was able to visualize periodontal
              pockets and show attachment loss. By
             calculating the calibration factor to
            determine the accurate axial resolution,
              quantitative standards for measuring
          periodontal pocket depth can be established
           regardless of the position of periodontal
                    pocket in the OCT image.
(16)       CP-OCT has the ability to nondestructively
            monitor biofilm growth and elucidate the
           growth characteristics of these microcosms
           on different dental material compositions.
          CP-OCT was able to quantify the mass of the
                biofilm by measuring the overall
           depth-resolved scattering of the biofilm.
(17)       Quantitative differentiation of normal and
             dysplastic lesions using OCT offers a
               noninvasive objective approach for
           localizing the most representative site to
           biopsy, particularly in oral lesions with
                   similar clinical features.
(18)           The differentiation of normal and
            fluid-filled areas using individual SID
             values yielded both a sensitivity and
             specificity of approximately 80%. OCT
            complemented by SID analysis provides a
           potential in vivo clinical tool that would
         enable noninvasive objective visualization of
                        the oral mucosa.

TABLE 7: OCT in orthodontics in the last 5 years of publications.

Number   Reference     Author                    Title
          number

(1)        [181]     Koprowski    Automatic method of analysis of OCT
                       et al.       images in the assessment of the
                                       tooth enamel surface after
                                    orthodontic treatment with fixed
                                                 braces

(2)        [182]      Seeliger     Enamel thickness before and after
                                   orthodontic treatment analysed in
                                      optical coherence tomography

(3)        [183]       Pithon      Effectiveness of fluoride sealant
                       et al.         in the prevention of carious
                                       lesions around orthodontic
                                      brackets: an OCT evaluation

(4)        [184]     Leao Filho     Enamel quality after debonding:
                       et al.       evaluation by optical coherence
                                               tomography

(5)        [185]       Pithon      Effectiveness of varnish with CPP-
                       et al.     ACP in prevention of caries lesions
                                  around orthodontic brackets: an OCT
                                               evaluation

(6)        [186]     Nee et al.        Longitudinal monitoring of
                                     demineralization peripheral to
                                    orthodontic brackets using cross
                                     polarization optical coherence
                                               tomography
(7)        [187]       Isfeld       Assessing near infrared optical
                       et al.      properties of ceramic orthodontic
                                   brackets using cross-polarization
                                      optical coherence tomography

(8)        [188]     Leao Filho     Optical coherence tomography for
                       et al.      debonding evaluation: an in-vitro
                                           qualitative study

Number                    Significance

(1)      This paper presents an automatic quantitative
           method for the assessment of tooth enamel
           thickness captured on the OCT scans. This
              method has proven to be an effective
         diagnostic tool that allows evaluation of the
           surface and cross section of tooth enamel
             after orthodontic treatment with fixed
            thin-arched braces and proper selection
                of the methodology and course of
                           treatment.
(2)          The range of variations in the enamel
              thickness after treatment with fixed
             thin-arched braces is not subjected to
          modification of a factor such as the type of
            adhesive system. The OCT is an effective
          diagnostic tool to evaluate the thickness of
             the enamel tissue before and after the
                completed orthodontic treatment.
(3)         Pro Seal sealant alone or combined with
           brushing and/or brushing and the use of a
         mouthwash with fluoride was more effective in
          protecting enamel, in comparison to brushing
                             alone.
(4)           The results demonstrated that enamel
          fractures were observed only in the samples
         bonded with ceramic brackets, and the type of
           pliers did not influence the incidence and
          extent of enamel damage. Moreover, the type
           of debonding technique (with side-cutting
           pliers or anterior bracket removal pliers)
         and the type of bracket did not influence the
         amount of adhesive remaining after debonding.
          The burs at low speed removed the remaining
            adhesive more effectively during cleanup
                          procedures.
(5)      The major limitation of this study is that it
            is a study in which demineralization was
           obtained with the use of chemical products
            and did not occur due to the presence of
         Streptococcus mutans and its acid byproducts.
           Application of CPP-ACP-containing varnish
             irrespective of being associated with
         brushing and mouthwash, or not, reduced depth
              of caries lesions around orthodontic
                           brackets.
(6)         CP-OCT was able to measure a significant
          increase in demineralization (P < 0.0001) at
            the base of orthodontic brackets over a
                      period of 12 months.

(7)         Noninvasive, near infrared (NIR) cross-
           polarization optical coherence tomography
          (CP-OCT) has potential to effectively image
             through portions of ceramic brackets;
            however, further investigation into the
          optical effects of resin integration in the
           base portion of the brackets is warranted.
(8)         The analysis of the two-dimensional and
          three-dimensional images allows observation
          and evaluation of adhesive remnants, enamel
           damage, and superficial aspects of enamel
           from different methods of adhesive remnant
          removal. The 2D optical coherence tomography
          analysis allows in-depth observation of the
           adhesive remnant layer. Optical coherence
             tomography can be a powerful tool for
           academic and clinical applications for the
              evaluation of debonding procedures.

TABLE 8: OCT in dentistry review articles in the last 5 years.

Number   Reference       Author                    Title
          number

(1)        [189]        Clarkson       Optical technology: an update
                         et al.            on optical coherence
                                          tomography in dentistry

(2)        [190]      Gupta et al.     Optical coherence tomography:
                                          a new era in dentistry

(3)        [191]     Canjau et al.     Optical coherence tomography
                                         for non-invasive ex vivo
                                         investigations in dental
                                          medicine--a joint group
                                                experience
(4)        [192]      Benic et al.         Novel digital imaging
                                         techniques to assess the
                                      outcome in oral rehabilitation
                                          with dental implants: a
                                             narrative review

(5)        [193]        Singh M.             Optical coherence
                         et al.            tomography--a imaging
                                           modality in dentistry
                                               beyond X-rays

(6)        [194]      Hsieh et al.       Dental optical coherence
                                                tomography

(7)        [195]     Shimada et al.       Application of optical
                                      coherence tomography (OCT) for
                                       diagnosis of caries, cracks,
                                        and defects of restorations

(8)        [196]      Benic et al.         Novel digital imaging
                                         techniques to assess the
                                      outcome in oral rehabilitation
                                          with dental implants: a
                                             narrative review
(9)        [197]     Colston et al.     Imaging of the oral cavity
                                          using optical coherence
                                                tomography

(10)       [198]     Se-Wook et al.     Study on application to the
                                         field of dentistry using
                                       optical coherence tomography
                                                   (OCT)

Number                     Significance

(1)      The technique of optical coherence tomography is
              considered to be significant since the
          technology involved allows imaging using light
            to around 2-3 mm in the teeth and can, for
           example, allow the extent and progression of
                 carious lesions to be determined.

(2)        It can be used for noninvasive investigations
         for both in vivo and in vitro structural imaging
                      within the oral cavity.
(3)      Complementary studies are possible embracing OCT
          with more traditional methods, such as confocal
              microscopy and micro-CT. Combination of
           principles is expected to evolve due to their
              limitations when considered separately.
(4)      New optical imaging techniques may be considered
          possible approaches for monitoring peri-implant
            soft tissue health. MRI and ultrasonography
          appear promising non-ionizing radiation-imaging
         modalities for the assessment of soft tissue and
          bone defect morphologies. Optical scanners and
         OCT may represent efficient clinical methods for
           accurate assessment of the misfit between the
                 reconstructions and the implants.
(5)      OCT offers noninvasive, noncontact, in vivo, and
            real-time subsurface images with high-depth
         resolution. OCT represents a valuable method for
            investigation and assessment of the health
          status of soft oral tissues and of hard dental
           structures. OCT can be used for evaluation of
           dental treatments reducing their failure rate
           and saving time and resources, by eliminating
         incorrect restorations before their insertion in
                         the oral cavity.
(6)        Dental OCT demonstrates broad applications in
         soft and hard tissue imaging and early detection
         of caries, periodontal disease, and oral cancer.
           OCT can be used for gingiva, periodontal, and
               mucosa imaging. OCT may also apply in
           bone-related disease imaging. OCT and PS-OCT
          represent powerful ability for early diagnosis
                of caries. Mineral changes at early
          demineralization stages can be distinguished by
             PS-OCT. Subgingival calculus can also be
          detected by OCT. OCT provides images of dental
           tissue in situ and real-time and allows early
            detection of many oral diseases, including
           caries, periodontal disease, and oral cancer.
(7)        Describes the use of OCT for detecting dental
          caries, tooth fractures, and interfacial aps in
           intraoral restorations. OCT can be a reliable
          and accurate method and a safer alternative to
                        X-ray radiography.
(8)      Optical scanners and OCT may represent efficient
          clinical methods for accurate assessment of the
            misfit between the reconstructions and the
                             implants.

(9)      The intensity of backscattered light is measured
             as a function of depth in the tissue. Low
          coherence interferometry is used to selectively
           remove the component of backscattered signal
          that has undergone multiple scattering events,
           resulting in very high resolution images (<15
           microns). Lateral scanning of the probe beam
           across the biological tissue is then used to
             generate a 2D intensity plot, similar to
          ultrasound images. This imaging method provides
           information that is currently unobtainable by
           any other means, making possible such diverse
             applications as diagnosis of periodontal
           disease, caries detection, and evaluation of
                      restoration integrity.
(10)         This review discusses not only the basic
          principles of operation, types, advantages, and
             disadvantages of OCT but also the future
             applications of OCT technology and their
            potential in the field of dental diagnosis.
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Author:Machoy, Monika; Seeliger, Julia; Szyszka-Sommerfeld, Liliana; Koprowski, Robert; Gedrange, Tomasz; W
Publication:Journal of Healthcare Engineering
Date:Jan 1, 2017
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