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Cone-beam tomography assessment of condylar position discrepancy between centric relation and maximal intercuspation.

Introduction

Discrepancies between the centric relation (CR) and the maximal intercuspation (MI) positions and their therapeutic implications have been extensively debated. (1-3) Opinions diverge greatly with regard to the clinical use of these maxillomandibular positions. Systematic literature reviews include authors in favor of an extensive use of CR in the planning of occlusal rehabilitation therapy and orthodontics, (1,3) alongside others who suggest an individual analysis of each clinical situation when determining which maxillomandibular relationship should be considered correct. (4,5) Despite the different opinions about how and when to use either of these two maxillomandibular positions, one point of relative acceptance among scientists is that most individuals in the population have discrepancies between CR and MI, (4) mainly symptomatic individuals and those with Class II and III malocclusions. (6-11) Among the methodological resources most widely used in studies comparing variations between maxillomandibular relations are articulator casts and conventional radiography. (1,2,10) These studies, in several cases, have established statistically significant differences between the two positions. In other studies, however, the differences found between the two positions showed little statistical significance. (11) The goal of the present study was to take advantage of the precision of cone-beam computed tomography technology to measure the condylar variations found between the CR and MI positions in young, asymptomatic patients with full dentitions, who present different occlusion patterns.

Methodology

Twenty young adult volunteers took part in this study after approval by the Ethics Committee of the Federal University of Uberlandia (n. 127). The criteria for inclusion in the research were as follows:

* age 18 to 25,

* both sexes,

* all healthy teeth,

* no symptoms and

* no previous orthodontic treatment or occlusal adjustments.

The twenty patients were divided equally into four groups of five participants each. One group consisted of individuals with normal occlusion, whereas the other three groups consisted of individuals with Angle Classes I, II, and III malocclusions, respectively. The research procedures were divided into two main sections.

Section 1

Initially, a clinical survey was carried out to identify the occlusal features of each patient. Manipulation of the mandible was performed and an anterior deprogramming device (JIG) (12) was used to record the centric relation position. This device was fabricated using chemically activated acrylic resin (CAAR) (Duralay Reliance; Dental Mfg. Co., Chicago, USA). The first contact between the maxillary and mandibular arches corresponding to the temporomandibular joint in CR was identified for the purpose of maintaining a CR position during the tomographic examination. Next, the palatal acclivity of the JIG was ground carefully until this first occlusal contact was obtained. A standardized channel leading to the CR position was made with CAAR to be used as a stable and safe reference for the patient's occlusion during the CR tomography.

Section 2

This section was conducted by the same radiologist and operator. Each of the 20 patients underwent two cone-beam computed tomographic examinations of the temporomandibular joints (TMJs), the first in MI and the second in CR. Lateral and vertical cone beam scans were obtained with a NewTom 3G gantry tomographer (Quantitative Radiology, Verona, Italy). Ball-point pen marks standardized the patient's head position during the two scans. For the first scan, the patient was instructed to stabilize his/her occlusion in the maximal intercuspal position, whereas, for the second scan, the patient was instructed to open his/her mouth so that the operator could adjust the JIG in the upper central incisors. Primary reconstructions of the images were immediately performed by QRNNT software version 2.00, coupled to the NewTom 3G device.

Image selection and measurements

Following the same methodological sequence as that followed for the CR and MI scanning of the right and left TMJs, the radiologist acquired lateral and frontal cuts to obtain secondary reconstructions. Four lateral cuts and four frontal cuts were placed side by side and received specific file names to be used during the CR/MI comparison performed for each patient. The cuts in each patient file were named as follows:

* Right Lateral MI/Right Lateral CR,

* Left Lateral MI/Left Lateral CR,

* Right Frontal MI/Right Frontal CR, and

* Left Frontal MI/Left Frontal CR.

The measurements were made using Basic 3G software, coupled to the NewTom 3G device. The same trained operator performed all the measurements, starting with the Right Lateral CR cut. Reference line 1 was traced tangentially to the lowest posterior and anterior extremities of the mandibular fossa. Reference line segment 2 was then traced on a segment of line 1 overlapping the condylar process, and its value was recorded. Reference line segment 3 was traced overlapping exactly half of line segment 2, and its value was also recorded. An angle tool was then used to form a 90[degrees] angle, which was then placed at a 45[degrees] angle to reference line 1. The angle's vertex met the end of line segment 3 at a point named the middle point of reference. For future reference, the distance between the middle point of reference and the uppermost point of the condylar process was measured along reference line 4, which coincided with the vertical arrow of the angle tool. The distance between the uppermost point of the condyle and the closest internal point of the mandibular fossa overlapping the vertical arrow of the angle tool was then measured. This measurement was named "superior". Another measurement, named "anterior," was obtained in a similar fashion, except for an anterior variation of 45[degrees] in relation to the vertical arrow, and a final measurement, named "posterior," was obtained in the same way, except for a posterior variation of 45[degrees] in relation to the vertical arrow (Figure 1). After these three measurements of the Right Lateral CR were recorded, the Right Lateral MI cut was performed for comparison. For this purpose, the operator identified the same points and traced the same reference lines accurately to confirm that the same measurements were obtained as those obtained in the previous comparable cut. Next, the same three condyle-to-fossa measurements--superior, anterior, and posterior--were recorded. The entire measuring process was conducted identically on the lateral cuts of the left side.

[FIGURE 1 OMITTED]

Measuring of the frontal cuts started with the Right Frontal CR cut. Initially, the most medial and lateral points of the condylar head were identified. The line measuring tool was used to connect these points to produce an alpha line. A segment line was then traced overlapping the alpha line up to exactly half of its length, and this line was termed the beta line segment. A point at the end of the beta line segment was named the middle point of reference for the frontal cut. Again, the angle tool was used to form a 90[degrees] angle, which was then placed at a 45[degrees] angle to the alpha line. The angle's vertex was adjusted to meet the middle point of reference, and then the "superior," "medial," and "lateral" measurements were obtained in the same manner as the "superior," "anterior," and "posterior" measurements were obtained in the lateral cuts, as described previously. The distance between the middle point of reference and the uppermost point of the condyle head along the vertical arrow of the angle tool positioned at 90[degrees] was measured to serve as future reference for measurement checking, just as reference line segment 3 served as a reference in the lateral cut measuring procedure. This measurement was named the gamma line segment (Figure 2). All measurement values were duly recorded. Assessment of the Right Frontal MI cut was then performed by the same examiner in the same way as previously performed for the CR cut, to allow direct comparison of the corresponding measurements. In order to validate the comparison, the alpha, beta, and gamma line measurements should necessarily present the same values in the two cuts, thus confirming the correct identification of the same middle points of reference in both procedures. Twenty days after the first measurement session and before the statistical analysis was performed, an intra-examiner methodological error test was conducted by selecting and repeating two measurements in five randomly selected patients. This test confirmed the reliability of the results using Student's t-test set at p > 0.05 (measurement 1: p = 0.0374/measurement 2: p = 1.000). Finally, the data were submitted to statistical analysis using Student's t-test (p > 0.05).

[FIGURE 2 OMITTED]

Results

The four lateral cuts provided 12 measurements, and the four frontal cuts also provided 12 measurements, for a total of 24 measurements for each patient. The results show that 95.4% of the 240 pairs of measurements used for direct comparison between MI and CR were different. The means observed for the left and right sides of the TMJ in the entire research sample and also in each individual group (MI or CR) were compared using Student's t-test. There were no statistically significant differences between the two positions (p > 0.05) (Tables 1 through 5).

Discussion

Much of the investigative work aiming at determining the quantitative discrepancies between the CR and MI maxillomandibular positions was based on different conceptions of centric relation, registration techniques and methodologies used to estimate the reproducibility of the condyle/glenoid fossa relationship, either through articulators that do not take into account neither the presence of TMJ soft tissue nor its anatomical variability, or by means of radiographs obtained under varying degrees of magnification and restricted to the two-dimensional plane. The limitations of these methods used to examine TMJ anatomy are subject to much controversy and debate in scientific circles, warranting further clarification. (1,2,4)

The introduction of cone-beam computerized tomography, a reliable and affordable three-dimensional diagnostic tool, created the possibility of faithfully reproducing any anatomical condition of the craniofacial complex. (11) It is well known that spatial variations in the position of the condyle relative to the mandibular fossa in the RC and MI maxillomandibular positions are mostly very small--on the order of millimeters--and occur in approximately 90% of the entire population. (4,5)

Even though we used one of the most advanced imaging methods available for application in Dentistry, the Ethics Committee of the Federal University of Uberlandia determined that our sample be reduced to 20 individuals because of the exposure of human subjects to X radiation.

In the present study, we compared each measurement mean found in the MI and RC positions, considering the whole sample and individual groups. In most cases (95.4%), the mean measurement values were different (Tables 1 through 5). These results agree with those of several authors who recognize the existence of discrepancies between the two positions (MI and RC) (4,6-11) in more than 90% of individuals. (4) However, these differences were not statistically significant, in either the lateral or the frontal cuts. This may have occurred because the differences between MI and CR are generally very small. (4,5) In our study these differences may have been even smaller owing to the relatively higher accuracy of the imaging method we used, as compared to those used in several other studies, namely the methods of conventional radiographic examination and models mounted on articulators. (1,2) Some of these studies found statistically significant differences between the MI and RC positions. (6-11)

Other factors may also have contributed to the divergence observed between our results and those found in the literature. (4,5). Our research sample consisted of young asymptomatic adults having all permanent teeth (except third molars) and no periodontal disease, whereas other research was conducted with older patients displaying symptoms of TMD and missing teeth.

The clinical applicability of these maxillomandibular positions is also subject to widely differing opinions because of the existence of contradictory results in the literature. (3-5)

Many authors support the use of CR in occlusal rehabilitation therapy, (3,11) since they consider it an easily reproducible reference position, and also in orthodontics, (1,3) strongly advocating the need to plan any treatment by mounting study models on an articulator and performing diagnostic teleradiography, both using CR.

Several other authors are opposed to using CR in various oral rehabilitation procedures, on account of the conceptual differences observed throughout history regarding a true CR position, varied reproducibility rates, nearly negligible discrepancies between the RC and MI positions, the lack of scientific evidence supporting the assumption that condylar position and orthodontic treatment may be related to TMDs, and the limitations of articulators to reproduce TMJ anatomy and function. (3-5)

Some authors, however, have reported more balanced views, admitting that both RC and MI may be used in oral rehabilitation according to each patient's specific situation. According to this view, extensive prosthetic restorations, occlusal adjustments, parafunction management, rehabilitation after orthognathic surgery, unsatisfactory MI, TMD management, and orthodontic therapy of greater complexity would be indications for using CR. In contrast, less extensive oral rehabilitations, a stable MI position, the absence of signs and symptoms, and less complex orthodontic therapy would be indications for using MI. (3-5)

Based on the results of the present study, the latter approach seems to be a more logical choice. Despite the limitations previously discussed, the absence of symptoms and the relative similarity of results in our study sample suggest the existence of a relative balance capable of preventing pathologic changes in the condyle/fossa relationship, a balance which could be maintained after low-complexity procedures.

Conclusions

Within the limitations of this study, it can be concluded that there were no significant condyle/ mandibular fossa relationship discrepancies between the centric relation and the maximum intercuspation positions in asymptomatic patients with practically intact dentitions, using cone-beam computed tomography.

This study also found a high rate of variation in condyle position in both CR and MI, even though the measurement differences were statistically insignificant. The fact that our sample consisted of young, asymptomatic individuals with intact dentition suggests the existence of a range of adaptive possibilities for the condyle/articular fossa relationship compatible with a balanced condition and normal function in these patients.

References

(1.) Utt TW, Meyers CE Jr, Wierzba TF, Hondrum SO. A three-dimensional comparison of condylar position changes between centric relation and centric occlusion using the mandibular position indicator. Am J Orthod Dentofacial Orthop. 1995 Mar;107(3):298-308.

(2.) Hidaka O, Adachi S, Takada K. The difference in condylar position between centric relation and centric occlusion in pretreatment japanese orthodontic patients. Angle Orthod. 2002 Aug;72(4):295-301.

(3.) Wood GN. C entric relation and the treatment position in rehabilitating occlusions: a physiologic approach. Part II: the treatment position. J Prosthet Dent. 1988 Jul;60(1):15-8.

(4.) Keshvad A, Winstanley RB. An appraisal of the literature on centric relation. Part III. J Oral Rehabil. 2001 Jan;28(1):55-63.

(5.) Carlsson GL. Insights into occlusal problems through the use of centric relation procedures. Part two. Northwest Dent. 2007 Mar-Apr;86(2):31-4,37, 39.

(6.) Weffort SY, de Fantini SM. Condylar displacement between centric relation and maximum intercuspation in symptomatic and asymptomatic individuals. Angle Orthod. 2010 Sep;80(5):835-42.

(7.) Afzal A, Shameem A. Comparison of condylar positions in centric relation and centric occlusion in pre-treatment malocclusion cases. J Coll Physicians Surg Pak. 2005 Oct;15(10):620-3.

(8.) He SS, Deng X, Wamalwa P, Chen S. Correlation between centric relation, maximum intercuspation discrepancy and temporomandibular joint dysfunction. Acta Odontol Scand. 2010 Nov;68(6):368-76.

(9.) Fantini SM, de Paiva JB, Neto JR, Dominguez GC, Abrao J, Vigorito JW. Increase of condylar displacement between centric retation and maximal habitual intercuspation after occlusal splint therapy. Braz Oral Res. 2005 Jul-Sep;19(3):176-82

(10.) Deng x, Wan Z, He SS, Wamalwa P, Chen S, Zhang ZY. [The centric relation-maximum intercuspation discrepancy in adult angle's class II pretreatment patients]. West China J Stomatol. 2011 Feb;29(1):48-52. Chinese.

(11.) Ikeda K, Kawamura A, Ikeda R. Assessment of optimal condylar position in the coronal and axial planes with limited cone-beam computed tomography. J Prosthodont. 2011 Aug;20(6):432-8.

(12.) Lucia VO. A technique for recording centric relation. J Prosthet Dent. 1964;14(3):492-505.

Joao Cesar Guimaraes Henriques (a)

Alfredo Julio Fernandes Neto (a)

Guilherme de Araujo Almeida (b)

Naila Aparecida de Godoi Machado (a)

Everton Ribeiro Lelis (a)

(a) Department of Occlusion, Fixed Prosthodontics and Dental Materials, School of Dentistry, Federal University of Uberlandia, Uberlandia, MG, Brazil.

(b) Department of Orthodontics, School of Dentistry, Federal University of Uberlandia, Uberlandia, MG, Brazil.

Declaration of Interests: The authors certify that they have no commercial or associative interest that represents a conflict of interest in connection with the manuscript.

Corresponding author:

Guilherme de Araujo Almeida

Email: galmeidaorto@prove.ufu.br

Received for publication on Aug 18, 2011

Accepted for publication on Oct 11, 2011
Table 1--Comparison of mean measurements (mm) obtained
for all groups in the MI and CR positions (n = 20).
Student's t-test (p > 0.05).

Measurement   Position   Mean    Standard    Student's   p-value
                                 Deviation    t-test

Right Lat        MI      1.87      0.512      -0.105      0.917
  POST           CR      1.89      0.684
Right Lat        MI      1.915    0.9354      -0.235      0.815
  ANT            CR      1.980    0.8082
Right Lat        MI      2.315    0.7869      -0.208      0.836
  SUP            CR      2.365    0.7315
Right Fron       MI      2.090    0.9002      -0.225      0.823
  LAT            CR      2.155    0.9254
Right Fron       MI      2.47      0.838      -0.125      0.901
  SUP            CR      2.51      0.930
Right Fron       MI      2.520    0.9860      -0.515      0.609
  MED            CR      2.690    1.0978
Left Lat         MI      1.980    0.6296       0.464      0.645
  POST           CR      1.890    0.5973
Left Lat         MI      2.015    0.9304       0.227      0.822
  ANT            CR      1.950    0.8829
Left Lat         MI      2.565    0.8113       0.039      0.969
  SUP            CR      2.555    0.8056
Left Fron        MI      2.26      0.741       0.127      0.899
  LAT            CR      2.23      0.749
Left Fron        MI      2.82      0.827       0.073      0.942
  SUP            CR      2.80      0.899

Table 2--Comparison of the mean measurements (mm)
obtained for patients with normal occlusion in the MI and CR
positions. Student's t-test (p > 0.05).

Measurement   Position   Mean    Standard    Student's   p-value
                                 Deviation    t-test

Right Lat        MI      1.940    0.5413       1.332      0.219
  POST           CR      1.580    0.2683
Right Lat        MI      1.840    0.9017      -0.499      0.631
  ANT            CR      2.140    0.9965
Right Lat        MI      2.460    0.9607       0.349      0.736
  SUP            CR      2.280    0.6380
Right Fron       MI      2.560    0.7861      -0.313      0.763
  LAT            CR      2.720    0.8319
Right Fron       MI      2.960    0.9263       0.068      0.947
  SUP            CR      2.920    0.9338
Right Fron       MI      2.64      1.036       0.097      0.925
  MED            CR      2.58      0.915
Left Lat         MI      1.82      0.492       1.412      0.196
  POST           CR      1.46      0.288
Left Lat         MI      2.220    0.4025       0.300      0.772
  ANT            CR      2.140    0.4393
Left Lat         MI      2.54      0.979       0.476      0.647
  SUP            CR      2.26      0.879
Left Fron        MI      2.380    0.8468       0.000      1.000
  LAT            CR      2.380    0.8672
Left Fron        MI      2.960    0.8678       0.068      0.948
  SUP            CR      2.920    0.9910
Left Fron        MI      2.820    0.5891       0.213      0.837
  MED            CR      2.720    0.8701

Table 3--Comparison of the mean measurements (mm) obtained
for Angle Class I patients, in the MI and CR positions.
Student's t-test (p > 0.05).

Measurement   Position   Mean    Standard    Student's   p-value
                                 Deviation    t-test

Right Lat        MI      1.820    0.5718       0.524      0.614
  POST           CR      1.640    0.5128
Right Lat        MI      1.680    0.6458      -0.762      0.468
  ANT            CR      2.000    0.6819
Right Lat        MI      2.360    0.7403      -0.269      0.795
  SUP            CR      2.480    0.6686
Right Fron       MI      2.080    0.7981      -0.121      0.907
  LAT            CR      2.140    0.7701
Right Fron       MI      2.660    0.5505       0.367      0.723
  SUP            CR      2.540    0.4827
Right Fron       MI      2.860    0.9397       0.155      0.881
  MED            CR      2.760    1.0922
Left Lat         MI      1.960    0.6269       0.202      0.845
  POST           CR      1.880    0.6261
Left Lat         MI      1.540    0.8473      -0.128      0.902
  ANT            CR      1.600    0.6205
Left Lat         MI      2.84      0.727       0.581      0.577
  SUP            CR      2.60      0.570
Left Fron        MI      2.56      0.456       0.553      0.595
  LAT            CR      2.42      0.335
Left Fron        MI      3.060    0.6427       0.414      0.690
  SUP            CR      2.880    0.7294
Left Fron        MI      2.880    1.2215       0.026      0.980
  MED            CR      2.860    1.1929

Table 4--Comparison of the mean measurements (mm) obtained for
Angle Class II patients, in the MI and CR positions. Student's
t-test (p > 0.05).

Measurement      Position   Mean    Standard    Student's   p-value
                                    Deviation    t-test

Right Lat POST   MI         1.94    0.568        -1.720      0.124
                 CR         2.66    0.744
Right Lat ANT    MI         2.020   1.1389        0.121      0.906
                 CR         1.940   0.9343
Right Lat SUP    MI         2.720   0.7887       -0.799      0.447
                 CR         3.060   0.5320
Right Fron LAT   MI         2.640   0.7956        -0.39      0.970
                 CR         2.660   0.8112
Right Fron SUP   MI         2.66    0.737        -0.663      0.526
                 CR         3.02    0.965
Right Fron MED   MI         2.840   1.0922       -0.917      0.386
                 CR         3.500   1.1811
Left Lat POST    MI         2.140   0.9450       -0.333      0.748
                 CR         2.320   0.7530
Left Lat ANT     MI         1.800   0.9055        0.667      0.524
                 CR         1.480   0.5762
Left Lat SUP     MI         2.680   0.6834       -0.646      0.536
                 CR         3.000   0.8718
Left Fron LAT    MI         2.14    0.508        -1.004      0.345
                 CR         2.44    0.434
Left Fron SUP    MI         2.78    0.572        -0.284      0.784
                 CR         2.92    0.942
Left Fron MED    MI         3.04    0.750        -0.034      0.973
                 CR         3,06    1,060

Table 5--Comparison of the mean measurement (mm) obtained for Angle
Class III patients, in the MI and CR positions. Student's t-test
(p > 0.05).

Measurement       Position   Mean    Standard    Student's   p-value
                                     Deviation    t-test

Right Lat POST       MI      1.760   0.5225        0.288      0.780
                     CR      1.660   0.5727
Right Lat ANT        MI      2.120   1.2194        0.422      0.684
                     CR      1.840   0.8444
Right Lat SUP        MI      1.720   0.4147        0.332      0.748
                     CR      1.640   0.3435
Right Front LAT      MI      1.080   0.1789       -0.206      0.842
                     CR      1.100   0.1225
Right Front SUP      MI      1.60    0.543         0.165      0.873
                     CR      1.54    0.602
Right Front MED      MI      1.740   0.6465       -0.378      0.715
                     CR      1.920   0.8468
Left Lat POST        MI      2.000   0.5385        0.323      0.755
                     CR      1.900   0.4359
Left Lat ANT         MI      2.500   1.3134       -0.095      0.927
                     CR      2.580   1.3498
Left Lat SUP         MI      2.200   0.9460       -0.273      0.792
                     CR      2.360   0.9044
Left Front LAT       MI      1.940   1.0714        0.420      0.686
                     CR      1.660   1.0383
Left Front SUP       MI      2.460   1.2239        0.000      1.000
                     CR      2.460   1.1194
Left Front MED       MI      2.600   1.2042       -0.173      0.867
                     CR      2.720   0.9706
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Title Annotation:Occlusion
Author:Henriques, Joao Cesar Guimaraes; Neto, Alfredo Julio Fernandes; Almeida, Guilherme de Araujo; Machad
Publication:Brazilian Oral Research
Date:Jan 1, 2012
Words:3934
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