Cone beam computed tomography in implant dentistry/Kompjuterizovana tomografija konusnog zraka u oralnojimplantologiji.
In modern dentistry, when planning implant placement, precision is of utmost importance. It is important to take the anatomical relations into account, in order to avoid unforeseen situations, to determine the best position for implants, and to choose the most suitable implant system. This can be achieved using two-dimensional (2D) and three-dimensional (3D) planning, stereolithography and realistic 3D biomodels. Conventional radiographic techniques (occlusal, retroalveolar, orthopantomography and tomography images) have disadvantages (deformation, poor resolution, zooming, etc.) and limitations while interpreting soft and bone tissues. Therefore, they are replaced by more recent, advanced radiographic methods, such as computed tomography, (cone beam computed tomography--CBCT and fan beam computed tomography--FBCT), as well as digital volume tomography (DVT). New techniques are used in combination with appropriate interactive 3D interpretation and digital image analysis software. Identification of pathological processes and analysis of anatomical structures, important for adequate planning in implant dentistry, are based precisely on modern radiographic methods. Sagittal and transverse sections, as well as 3D reconstruction, enable more successful preoperative planning and adequate positioning of the implant. Stereolithography and other biomodels are modern methods of organ-model reproduction, and they are used for 3D display of complex anatomical structures. Production of surgical splints is based on preoperative implant placement in models. Interactive, computer-aided diagnosis has a great advantage compared to conventional planning techniques. Selection of recording technique should take into consideration clinical variables such as: number of places for implants, volume of alveolar bone and the need for bone grafting, quality and availability, costs of recording methods, and low radiation exposure.
Cone Beam Computed Tomography
Cone Beam Computed Tomography is an advanced digital recording technique that allows the operator to generate multiplanar "slices" and to reconstruct a 3D image of the target area using rotating conical X-ray through a series of mathematical algorithms (Figure 1). Mozzo introduced CBCT technology in 1998, and a new form of 3D evolution was established . Several studies showed that CBCT technique makes high quality and precise cross-sectional images with a relatively low exposure to radiation . The use of CBCT in dentistry is growing exponentially, due to increased production of equipment and a growing acceptance of this recording technique. The size of the field of view (FOV) describes the scan volume of CBCT scanning machines and depends on the size of the detector, its shape, beam projection geometry and possibilities of beam focusing, which may differ from manufacturer to manufacturer. Collimation width of ionizing radiation is limited to the recording target area, due to which the exposition is lower, and the FOV is selected specifically for each case.
In general, based on the size of the FOV, CBCT units can be classified into small, medium and large volume units. Small volume CBCT machines are used to scan sextants or quadrants of one jaw only. They usually provide higher image resolution since the X-ray scattering (noise) is reduced, as well as the FOV. Medium volume CBCT machines are used to scan both jaws, while large FOV equipment allows visualization of the entire head . The main limitation of the large FOV CBCT units is the size of the field exposed to radiation.
If the selected voxel size is minimal, devices with large FOV have reduced image resolution compared with intraoral radiographs or with images recorded on small FOV CBCT devices with inherently small size of voxels . Curtailing the volume should be based on the clinician's evaluation of a particular situation. For the purposes of implant placement, small and medium FOV are suitable to visualize the desired area. CBCT equipment with a small volume provides several advantages over the CBCT equipment with a large volume: increased spatial resolution, reduced radiation exposure, smaller interpretation area, cheaper appliances, etc.
--Fast scanning; acquisitions in 10-20 sec, complete 3D image reconstruction in less than a minute
--Small form factor (117 cm (46") x 137 cm (54"), suitable for installation even in the smallest offices
--FOV--16 cm x 13 cm to 16 cm x 21 cm in extended FOV mode
--High resolution; voxel sizes down to 100 microns with a focal spot of 0.5 mm
--Digital flat rate detector is incomparably superior to image intensifier and transmits the lowest doses of radiation, that do not increase over time
--The highest efficiency in its class allows minimal radiation dose
--14 bit sensor provides 16.384 shades of gray in favor of a better contrast
--Image processing protocols with extremely low radiation dose
--X-ray tube with a fixed anode has low maintenance costs and long service life
--Software for detailed and accurate visualization and image processing in 3D format
--Adjustable panoramic tools and cross-sections enable easy planning of implant installation and precise geometric measurements
--Predefined protocols and templates save time and increase productivity
--Export to digital imaging and communications in medicine (DICOM) 3.0 and compatibility with all leading picture archiving and communication system (PACS) and DICOM Worklist systems allow easy integration in large imaging centers
--Networking ensures multiple workstations over a network access images within one doctor's office.
Advantages and limitations of CBCT
Cone Beam Computed Tomography imaging provides direct visualization of the dental status, including 3D images of the maxillofacial skeleton, compared to 2D imaging that provides insight in only 2 dimensions. The ability to visualize a complete geometrical shape of the target region, avoiding superposition and planar observation, allows accurate radiological interpretation without any assumptions . Significance of this recording combined with 3D optical input model has the potential to reduce the percentage of mistakes in implant placing. However, the quality of the interpretation is based on the evaluation skills and thoroughness of the diagnostician, on using native and independent treatment planning softwares, and on determination of the appropriate fOV for each particular case (Figure 2). There are several manufacturers of CBCT machines in dental radiology. This has led to significant variability in radiation dosage, scanning, facilitated utilization, image resolution and software dynamics among the CBCT appliances.
The most significant limitations of CBCT devices are the lack of accurate presentation of the soft tissue internal structure, limited correlation between Hounsfield units for standardized quantification of bone density, and different types of artifacts arising mainly from metal restorations that can interfere with the diagnostic process by masking the underlying structure . In order to improve visualization of the gingival soft tissue contour and thickness, it is necessary to place cotton rolls or separate the lip from the buccal cavity by air.
The highest aspects of available software applications include their ease of navigation, costs, quantity and quality of available diagnostic tools, and implant planning modules. By application of advanced softwares, waste impacts or artifact can be significantly reduced, all in order to enhance the accuracy of diagnosis and reduce the limitations of this type of recording.
Cone Beam Computed Tomography technique in implant dentistry
The use of 3D data in the field of diagnostics and treatment planning has been improved through the availability of CBCT. Its implementation helps the clinicians to estimate the 3D anatomy of the area where the implant is to be placed. After collection and processing the data, the software reconstructs the CBCT information . In order to meet prosthetic requirements it is necessary to choose an ideal location for the implant placement, defining the appropriate quality and volume of the bone where osteotomy can be performed, and a stable position for the implant provided. The 3D visualization and evaluation of the implant area structure is defined by planning phase analysis using the following parameters:
1. Assessment of the available bone (height, width, relative quality of the cortical and spongious parts)
2. Determination of the 3D topography of the alveolar ridge
3. Identification and localization of vital anatomical structures such as inferior alveolar nerve, mental foramen, maxillary sinus, floor of the nasal cavity, etc.
4. Potential tissue for implant placement evaluation
5. Fabrication of CBCT-derived implant surgical guides
6. Communication of the diagnostic treatment planning information to all implant team members
7. Evaluation of prosthetic/restorative possibilities via implant software applications
8. Evaluation of postoperative acceptance of implants.
In addition, a CBCT scan, combined with software modeling, can be used as a platform for treatment planning and it can virtually simulate perfect placement of the implant defining the surgical, prosthetic and orthodontic conditions.
There are about 30 different types of CBCT devices, so it is important to entirely conduct the research on the same device.
Implementation of the CBCT technique in implant dentistry is divided into 4 categories:
1. CBCT and diagnostics
Cone Beam Computed Tomography is an excellent diagnostic modality in oral implantology, which is used to assess the implant site, presence of pathological changes and foreign bodies, morphology and relation with the surrounding anatomical structures.
2. CBCT and implant planning
In dental implant planning, the CBCT technique is most frequently used in the linear measurement of the ridge. CBCT images are reliable and show all the data on the amount of existing bone in the jaw for preoperative planning. The existence of metals, prosthetic restorations, does not affect the measurement accuracy of the CBCT images. Another advantage is the possibility of determining the topography of the ridge and the relation between the surrounding anatomical structures in all three dimensions. CBCT can accurately determine the thickness of the cortical bone (buccal, lingual and palatal), floor of the nasal cavity and maxillary sinus walls.
Evaluation of bone density is of a great importance. It is proved that CBCT can determine distribution of trabecular bones, showing a high correlation with the primary stability of the implant. It identifies the blood vessels on the side walls of the maxillary sinus, which is necessary in cases of sinus augmentation. CBCT technique is of great importance to doctors in the prevention of postoperative complications.
3. CBCT and surgical guidance
In oral surgery, CBCT is divided into passive, semi-active and active.
--Passive CBCT provides information on linear measurements, relative bone quality, 3D ridge topography, and proximity of vital anatomical structures.
--Semi-active CBCT includes the use of imported data that simulate the virtual implant preceding the development of surgical guides being used during the implant placement. Selecting the site of implant placement is in accordance with the restorative needs and depends on the computer program protocol. A template should be made prior to the scanning.
--Active CBCT refers to the use of data for surgical navigation systems performing fully computer-guided implant placement.
4. CBCT and post-implant assessment
The presence of beam hardening and artifacts surrounding the implant in some cases may complicate the CBCT visualization of the bone-implant interface.
The decision whether to use Cone Beam Computed Tomography should be based on clinical history and examination. The benefits must exceed the risk of exposing the patient to ionizing radiation, especially when children are involved, and when a recording with a large field of view volume is necessary.
Based on information obtained by three-dimensional imaging procedures, it is suggested that the Cone Beam Computed Tomography technique should be used as an imaging alternative in cases where bone augmentation is suspected, where conventional radiography may not be able to determine the structure in three dimensions as previously described:
--Computer guided implant planning and placement including navigation systems
--Placement of the implant in a highly esthetic zone
--Pre- and post-surgical evaluation of implant acceptance
--History or trauma to the jaws, foreign bodies, maxillofacial lesions, developmental anomalies, etc.
--Evaluation of post-implant complications.
It is important to bear in mind that the smallest possible field of view should be used, and that the entire image volume should be interpreted.
The use of Cone Beam Computed Tomography requires careful and proper handling and Cone Beam Computed Tomography scans help to improve the surgical accuracy, reduce postoperative morbidity, and are valuable in restorative phase of treatment.
Abbreviations 2D --two-dimensional 3D --three-dimensional CBCT --cone beam computed tomography FBCT --fan beam computed tomography DVT --digital volume tomography FOV --field of view DICOM --digital imaging and communications in medicine
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Rad je primljen 29. XI 2016.
Recenziran 22. XI 2016.
Prihvacen za stampu 5. I 2017.
Zagorka M. MITROVIC and Ana J. TADIC
University of Novi Sad, Faculty of Medicine Department of Dentistry
Corresponding Author: Dr Zagorka Mitrovic, Klinika za stomatologiju Vojvodine, 21000 Novi Sad, Hajduk Veljkova 12, E-mail: firstname.lastname@example.org
Caption: Figure 1. Placement of the implant using a 3D image
Slika 1. Pozicioniranje implantata pomocu trodimenzionalnog snimka
Caption: Figure 2. Surgical planning
Slika 2. Hirursko planiranje
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|Title Annotation:||Professional article/Strucni clanak|
|Author:||Mitrovic, Zagorka M.; Tadic, Ana J.|
|Date:||Mar 1, 2017|
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