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Skeletal Differences in Patients With Temporomandibular Joint Disc Displacement According to Sagittal Jaw Relationship
J Oral Maxillofac Surg 70:e349-e360, 2012
Skeletal Differences in Patients With Temporomandibular Joint Disc Displacement According to Sagittal Jaw Relationship Il-Hyung Yang, DDS, MSD, PhD,* Beom-Seok Moon, DDS, MSD,† Seung-Pyo Lee, DDS, MSD, PhD,‡ and Sug-Joon Ahn, DDS, MSD, PhD§ Purpose: The present study was designed to analyze the skeletal differences in patients with temporo-
mandibular joint (TMJ) disc displacement (DD), according to the sagittal jaw relationship. Materials and Methods: We implemented a cross-sectional study design and enrolled a sample of Korean women older than age 17 years. The subjects were classified into 3 groups according to the magnetic resonance images of the bilateral TMJs: bilateral normal disc position (BN), bilateral disc displacement with reduction, and bilateral disc displacement without reduction. Each group was subdivided into 2 groups using the mandibular body length to anterior cranial base ratio as a sagittal jaw parameter: normal-size mandible (NM) and oversized mandible (OM). Seventeen variables from the lateral cephalograms were analyzed using 2-way analysis of variance to analyze the differences in skeletal characteristics with respect to the mandible size and TMJ DD status. Results: The subjects with TMJ DD generally had a short ramus height and clockwise rotation of the ramus and mandible compared with those with BN in both OM and NM groups. However, significant differences were present in the skeletal characteristics of the TMJ DD patients between the NM and OM groups. Significant backward positioning and rotation of the ramus and mandible were found between BN and bilateral disc displacement with reduction or bilateral disc displacement without reduction in the OM group, while those of the ramus and mandible were found between BN and bilateral disc displacement with reduction or bilateral disc displacement without reduction in the NM group. Conclusions: The results of our study suggest that the skeletal characteristics associated with TMJ DD are differently represented according to the sagittal jaw relationship. © 2012 American Association of Oral and Maxillofacial Surgeons J Oral Maxillofac Surg 70:e349-e360, 2012
*Assistant Professor, Seoul National University Dental Hospital, Jongro-Gu, Seoul, Korea. †Graduate Student, Seoul National University School of Dentistry, Jongro-Gu, Seoul, Korea. ‡Associate Professor, Dental Research Institute and Department of Oral Anatomy, Seoul National University School of Dentistry, Jongro-Gu, Seoul, Korea. §Associate Professor, Dental Research Institute and Department of Orthodontics, Seoul National University School of Dentistry, Jongro-Gu, Seoul, Korea. This research was supported by the Basic Science Research Program through the National Research Foundation of Korea,
funded by the Ministry of Education, Science, and Technology (grant 2009-0070913). Address correspondence and reprint requests to Dr Ahn: Department of Orthodontics, Dental Research Institute, Seoul National University School of Dentistry, 28-22 Yungeon-Dong, Jongro-Gu Seoul 110-768 Korea; e-mail: [email protected] © 2012 American Association of Oral and Maxillofacial Surgeons
0278-2391/12/7005-0$36.00/0 doi:10.1016/j.joms.2011.08.027
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e350 Disc displacement (DD) is defined as a localized mechanical fault interfering with smooth joint movement.1 Temporomandibular joint (TMJ) DD is the most common TMJ arthropathy, characterized by several stages of dysfunction that involve the condyle– disc relation.1 TMJ DD generally progresses from reduction to nonreduction and can lead to TMJ clicking, crepitus, pain, and limitation in jaw movement.2 A wide variety of methods and devices are used to diagnose TMJ DD. Among them, magnetic resonance imaging (MRI) is known to be a sensitive method of identifying TMJ DD and is the only method that directly depicts the disc in either a normal or an abnormal position.3 It also offers many advantages, including noninvasiveness, minimal pain, minimal risk, and freedom from exposure to ionizing radiation.4 The prevalence of DD is approximately 30% in the asymptomatic adult population and 84% in symptomatic patients when using MRI to determine the disc position.5,6 Recently, concern has been increasing regarding the relationships between TMJ DD and facial morphology. Several cephalometric variables have been identified as being associated with TMJ DD. Generally, patients with TMJ DD have a backward rotation of the mandibular plane, decreased SNB, and increased ANB compared with those with a normal disc position. This is associated with skeletal Class II patterns with a retrognathic mandible.7-10 Thus, there might be a low incidence of TMJ DD in patients showing a skeletal Class III pattern, and the dentoskeletal characteristics of skeletal Class III patients with TMJ DD might be different from those of skeletal Class I patients with TMJ DD or normal TMJs. However, there have been few studies about the relationships between TMJ DD and skeletal morphology in patients with the skeletal Class III pattern, because most studies have focused on research about TMJ DD patients with a skeletal Class II pattern or an anterior open bite. As a result, the skeletal characteristics of TMJ DD patients according to the sagittal jaw relationships are still unclear. The aim of the present study was to investigate the skeletal differences in patients with TMJ DD according to the sagittal jaw relationship. The null hypothesis of our study was that the skeletal characteristics in the patients with TMJ DD would not be influenced by the sagittal jaw relationships.
Materials and Methods To address the research purpose, we designed and implemented a cross-sectional study and enrolled a sample derived from the population of patients who presented to the Department of Orthodontics, Seoul National University Dental Hospital for an orthodontic
TMJ DISC DISPLACEMENT AND SAGITTAL JAW RELATIONSHIP
evaluation between 2002 and 2010. To be included in the study sample, the patients had to be women older than 17 years to avoid gender-related size differences and growth-related size differences. The patients had to agree to bilateral high-resolution MRI in the sagittal (opened and closed) and coronal (closed) planes to evaluate the TMJs. Patients were excluded as study subjects if they had any systemic disease, a history of orthodontic treatment, a history of trauma involving the TMJs, or juvenile rheumatoid arthritis. The institutional review board of the University Hospital reviewed and approved the research protocol. Routine lateral cephalograms were taken of all the subjects using Asahi CX-90SP II (Asahi Roentgen, Kyoto, Japan). Most subjects had clinical signs and symptoms of TMJ dysfunction, such as pain, joint sounds, and muscle tenderness. Some patients who did not show any detectable TMJ signs and symptoms had skeletal malocclusions such as an anterior open bite, a retrognathic mandible, and facial asymmetry, reported to be associated with TMJ DD.7,8,11 Radiologists with TMJ MRI experience interpreted the images without clinical information of the patients. The TMJ disc status was divided into 3 categories as follows: 1. Normal disc position (Figs 1A,B): in the closed mouth position, the intermediate zone of the disc was interposed between the condyle and the posterior slope of the articular eminence, with the anterior and posterior bands equally spaced on either side of the condylar load point. 2. Disc displacement with reduction (Figs 1C,D): the disc was anteriorly displaced relative to the posterior slope of the articular eminence and the head of the condyle. However, the disc displacement was reduced on mouth opening. 3. Disc displacement without reduction (Figs 1E,F): The disc was anteriorly displaced relative to the posterior slope of the articular eminence and the head, without reductrion of disc on mouth opening. The position and shape of the disc were evaluated carefully according to the classification criteria for the disc position. Ambiguous cases were excluded from the present study. A total of 301 patients were originally selected and analyzed. Among them, the subjects with bilateral normal disc status (BN), bilateral disc displacement with reduction (DDR), and bilateral disc displacement without reduction (DDNR) only were included in the present study. This was because the possible skeletal characteristics associated with unilateral DD would
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FIGURE 1. Normal TMJ disc position to condyle in A, closed-mouth and (Figure 1 continued on next page.) Yang et al. TMJ disc displacement and sagittal jaw relationship. J Oral Maxillofac Surg 2012.
have been obscured by the averaging of the right and left landmarks used in determining their locations.11 A single investigator traced all cephalograms. The tracings were recorded using a digitizer with a desktop computer. Fifteen landmarks were digitized on each radiograph, from which the cephalometric variables were calculated. To analyze the cephalometric characteristics of the subjects with TMJ DD according to their sagittal jaw relationship, the subjects should be classified using a sagittal jaw parameter. However, we could not use the traditional sagittal parameters, such as ANB, SNB, and facial convexity, because those parameters are significantly influenced by the backward rotation of mandible and decrease in ramus height, the main skeletal characteristics of patients with TMJ DD.8-10 Instead, the subjects were classified
according to the mandibular body length to the anterior cranial base ratio (MNACBR), because MNACBR is one of the important markers of the skeletal Class III patterns12 and would not be influenced by the skeletal changes associated with TMJ DD. The subjects who had a MNACBR within ⫾1 standard deviation of normal Korean women (1.08 ⫾ 0.04) were included in the normal-size mandible (NM) group. The subjects in the oversized mandible (OM) group had a MNACBR of more than 1.12. Unless an alteration in the skeletal jaw relationship occurs with TMJ DD, the NM and OM groups could be equivalent to the Class I and Class III skeletal pattern, respectively. To select the study variables for analysis, Pearson correlation coefficients were calculated between the MNACBR and the other cephalometric variables. The
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FIGURE 1 (cont’d). B, open-mouth sagittal images. Intermediate zone of disc (arrow) interposed between condyle (C) in both positions. (Figure 1 continued on next page.) Yang et al. TMJ disc displacement and sagittal jaw relationship. J Oral Maxillofac Surg 2012.
variables with a coefficient larger than 0.5 or smaller than ⫺0.5, simultaneously with a significance level lower than 0.05, were excluded owing to their correlations with the MNACBR. Finally, 17 cephalometric variables were chosen. For convenience of analysis, these variables were subdivided into 4 categories: maxillomandibular morphology, vertical skeletal morphology, size and form of the mandible, and dental morphology. The positions of all the landmarks are shown in Figure 2, and their measurements are shown in Figures 3 and 4. To test the magnitude of the measurement error involved in our study, the lateral cephalograms of 20 randomly selected patients were measured again. The reliability of the tracing, landmark identification, and
analytical measurements had intraclass correlation coefficients greater than 0.98. Descriptive statistics for each variable in the NM and OM groups were calculated. The differences in the cephalometric variables with respect to the sagittal jaw relationship and TMJ DD status were tested with 2-way factorial analysis of variance. Scheffe’s multiple comparisons were performed at a significance level of 0.05 to analyze the between-group comparisons.
Results A total of 136 Korean women were selected for this study (Table 1). Of the 110 patients with bilateral TMJ
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FIGURE 1 (cont’d). DDR to condyle in C, closed-mouth and (Figure 1 continued on next page.) Yang et al. TMJ disc displacement and sagittal jaw relationship. J Oral Maxillofac Surg 2012.
DD, 26 (23.6%) did not show any detectable TMJ signs and symptoms. Of the 57 patients with bilateral normal TMJs, 24 (42.1%) showed TMJ signs and symptoms on at least 1 side of both TMJs. The differences in cephalometric characteristics with respect to TMJ DD status (BN, DDR, and DDNR) and sagittal jaw relationship (NM and OM group) are listed in Table 2. The results showed that both TMJ DD status and sagittal jaw relationship have significant effects on the cephalometric variables (Table 3). However, TMJ DD status can influence some cephalometric variables differently, depending on the sagittal jaw relationship (Table 3). The variables associated with the mandible were statistically significant, and the variables associated with the maxilla (SNA and nasion (N) perpendicular
to point A) were not statistically significant in the maxillomandibular morphology (Tables 2 and 3). Generally, the subjects with TMJ DD had anteroposterior skeletal discrepancies between the maxilla and mandible by a backward rotation and position of the mandible. However, the jaw bone discrepancies associated with TMJ DD status were different between the NM and OM groups. Significant differences in SNB, ANB, and facial convexity were found between BN or DDR and DDNR in the NM group, and those differences were found between BN and DDR or DDNR in the OM group (Table 3). The vertical skeletal morphology was significantly influenced by TMJ DD status but not by the sagittal jaw relationship (Tables 2 and 3). The FMA, maxillomandibular plane angle, and the facial height ratio
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FIGURE 1 (cont’d). D, open-mouth sagittal images. Disc (arrow) anteriorly displaced relative to posterior slope of articular eminence (E) and head of condyle (C). However, disc reduced on mouth opening. (Figure 1 continued on next page.) Yang et al. TMJ disc displacement and sagittal jaw relationship. J Oral Maxillofac Surg 2012.
(total posterior facial height to total anterior facial height ratio) were statistically significant between patients with BN or DDR and patients with DDNR, with no significant difference in those variables between BN and DDR (Table 3). Consequently, the patients with DDNR had a steeper mandibular plane and more backward rotation of the mandibles than those with BN or DDR. The difference in vertical skeletal morphology resulted from the decreased total posterior facial height, because the total anterior facial height
and lower anterior facial height were similar among those with BN, DDR, and DDNR (Table 3). Both TMJ DD status and the sagittal jaw relationship influenced the variables representing the size and form of the mandible differently (Table 3). As expected, the subjects in the OM group had a greater MNACBR than those in the NM group. The ramus inclination, effective mandibular length, and gonial angle showed significant differences between BN or DDR and DDNR in the NM group but between BN and
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FIGURE 1 (cont’d). DDNR to condyle in E, closed-mouth and (Figure 1 continued on next page.) Yang et al. TMJ disc displacement and sagittal jaw relationship. J Oral Maxillofac Surg 2012.
DDR or DDNR in the OM group (Table 3). The gonial angle did not show any significant difference among the different TMJ DD groups in the NM group but did show a significant difference between BN and DDR or DDNR in the OM group. The ramus height showed statistically significant differences between BN and DDR and between DDR and DDNR in both NM and OM groups. An overbite was not significantly influenced by the TMJ DD status or sagittal jaw relationship. Overjet was significantly different among BN, DDR,
and DDNR in both NM and OM groups; however, the difference between BN and DDR was more significant in the OM group than in the NM group (Table 3).
Discussion TMJ DD has been reported to be associated with an altered facial morphology, such as a backward rotation and position of the ramus and mandible—a skeletal Class II relationship with a retrognathic mandi-
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FIGURE 1 (cont’d). F, open-mouth sagittal images. Disc (arrow) anteriorly displaced relative to posterior slope of articular eminence (E) and head of condyle (C), without reduction of disc on mouth opening. Yang et al. TMJ disc displacement and sagittal jaw relationship. J Oral Maxillofac Surg 2012.
ble.7-10 Thus, the skeletal characteristics of TMJ DD patients might be different according to their sagittal jaw relationship. However, few studies have investigated the skeletal differences in TMJ DD patients according to the sagittal jaw relationships, even though there has been abundant research about TMJ DD and patients with a Class II skeletal pattern. The purpose of the present study was to analyze the differences in skeletal characteristics of patients with TMJ DD status, according to their sagittal jaw relationships. We found that the skeletal characteristics associated with TMJ DD are differently represented according to the sagittal jaw relationship, and the null hypothesis of the present study was rejected.
The present study showed an association between TMJ DD and altered skeletal morphology, although a cause– effect relationship is unclear. TMJ DD might cause skeletal changes or DD might occur because of the biomechanics associated with an altered skeletal morphology. It is also possible that both DD and altered skeletal morphology are the results of another influencing factor not yet identified. Nevertheless, these results suggest that TMJ DD can be a contributing factor to the alteration of skeletal morphology, such as a decrease in ramus height, a decrease in the effective size of the mandible, and a backward rotation of the ramus (Table 2). The differences in skeletal morphology associated with TMJ DD might result from osseous changes in the condylar head.
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FIGURE 2. Landmarks used in study: 1, nasion; 2, sella; 3, orbitale; 4, porion; 5, anterior nasal spine; 6, posterior nasal spine; 7, articulare; 8, point A; 9, incisal end of maxillary incisor; 10, incisal end of mandibular incisor; 11, point B; 12, pogonion; 13, menton; 14, gonion; and 15, articulation of maxillary and mandibular molars. Yang et al. TMJ disc displacement and sagittal jaw relationship. J Oral Maxillofac Surg 2012.
Previous studies have reported bony changes on the articular surface of the mandibular condyle in patients with TMJ DD, such as a decreased condylar height with a distally inclined condylar head.13,14 The changes in condylar shape in patients with TMJ DD might significantly influence the skeletal morphology (in particular, the size and form of the mandible), such as a decrease in the ramus height and effective mandibular length and backward rotation of the ramus (Table 2). This could, in turn, influence the maxillomandibular morphology, manifesting a decreased SNB, increased ANB, and increased facial convexity. The present study showed that the skeletal characteristics associated with TMJ DD patients were different between the NM and OM groups (Tables 2 and 3). The subjects in the OM group manifested a backward position of the mandible (decreased SNB and ANB and increased facial convexity), a backward rotation of the ramus (increased ramus inclination), and a decreased effective mandibular length between BN and DDR or DDNR, while these differences were shown between BN or DDR and DDNR in the subjects in NM group. These results are not in full accordance with the results of the previous study.7 The previous study
e357 showed that significant skeletal differences were found between BN or DDR and DDNR and between BN and DDR, although the sample size of the previous study was smaller than that of the present study. The main reason for the different results might be that the samples of the previous study were not classified according to the sagittal jaw relationships, which could be referred to as a more detailed experimental design of the present study. The reasons for the different cephalometric characteristics between the NM and OM groups are unclear. However, the skeletal differences between OM and NM did not result from ethnic or racial differences in the subjects. This is because we consecutively recruited subjects who visited only 1 dental hospital in 1 region and because Koreans are reported to be the most ethnically homogeneous population in the world.15 It seems that the subjects with a skeletal Class III pattern would have less resisting ability against the functional stress produced by TMJ DD than those with a skeletal Class I pattern. Thus, an early stage of TMJ DD would easily influence the skeletal morphology in the subjects with a Class III pattern, but the subjects with a Class I pattern would not show significant skeletal alterations until the TMJ DD had progressed to DDNR, a more severe condition. Additional studies are needed to investigate the differences in skeletal morphology among the different
FIGURE 3. Angular measurements used in study: 1, gonial angle (Ar-Go-Me); 2, maxillomandibular plane angle; 3, FH to mandibular plane angle; 4, SNA angle; 5, SNB angle; 6, ANB angle; 7, ramus inclination (N–S to Ar-Go); and 8, facial convexity. Yang et al. TMJ disc displacement and sagittal jaw relationship. J Oral Maxillofac Surg 2012.
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FIGURE 4. Linear measurements used in study: 1, N perpendicular to point A; 2, ramus height (Ar-Go); 3, effective mandibular length (Ar-Pog); 4, total anterior facial height (N-Me); 5, total posterior facial height (S-Go). Yang et al. TMJ disc displacement and sagittal jaw relationship. J Oral Maxillofac Surg 2012.
TMJ DD categories according to the sagittal jaw relationship. The cephalometric differences between the NM and OM groups in the subjects with TMJ DD have important clinical significance. This is because TMJ DD patients with an oversized mandible can manifest skeletal Class I or II ranges of SNB, ANB, and facial convexity by a backward rotation and positioning of the mandible (Table 2). Therefore, the ranges of these variables in the OM group with TMJ DD might overlap with those of the variables in the NM group with BN or TMJ DD, although all subjects in the OM group had oversized mandibles with a MNACBR greater than
1.12. Thus, the patients with an oversized mandible and TMJ DD can be classified as having a skeletal Class I or II pattern, despite their larger mandible. These results suggest that orthodontists should be careful not to overlook these skeletal characteristics of TMJ DD patients with an oversized mandible at the initial examination. In the present study, the gonial angle was significantly decreased in the OM group in the presence of TMJ DD, with no significant difference in the gonial angle in the NM group among the different TMJ DD categories (Tables 2 and 3). The decreased gonial angle is associated with bone remodeling in the gonial region, which might result from a localized alteration in the functional environment created by TMJ DD. This is partly supported by a previous study that showed excessive bone growth in the gonial area as compensation for a decreased ramus height experimentally induced by TMJ DD.16 The change in gonial angle would be one of the key factors indicating potential TMJ DD in subjects with an oversized mandible, because no significant change was found in the gonial angle in TMJ DD patients with other malocclusions.7,8 In contrast to other variables, the ramus height can discriminate the differences among BN, DDR, and DDNR in both NM and OM groups (Table 3). This might be because the ramus height is directly influenced by bony changes in the mandibular condyle associated with TMJ DD, in which the condyle clearly changes from BN to DDNR by way of DDR.13 The results from the present study were derived from cross-sectional data, and they do not show true longitudinal changes. Longitudinal studies might aid in the identification of the causative and associated factors. However, it is very difficult to collect sufficient longitudinal samples with matched MRI data, because MRI is too expensive to be regularly performed. Thus, our results provide valuable information on the differences in the skeletal characteristics of TMJ DD patients according to the sagit-
Table 1. NUMBER AND AGE OF SUBJECTS STRATIFIED BY CLASSIFICATION USED
Group NM Subjects (n) Age (yr) OM Subjects (n) Age (yr)
BN (n ⫽ 57)
DDR (n ⫽ 49)
DDNR (n ⫽ 61)
Total
19 21.2 ⫾ 2.3
29 24.5 ⫾ 5.5
22 25.4 ⫾ 5.1
70 23.9 ⫾ 4.9
33 23.1 ⫾ 5.1
16 24.3 ⫾ 4.5
17 23.0 ⫾ 3.7
66 23.4 ⫾ 4.6
Abbreviations: BN, bilateral normal disc position; DDR, bilateral disc placement with reduction; DDNR, bilateral disc displacement without reduction; NM, normal size mandible (mandibular body to anterior cranial base ratio of 1.08 ⫾ 0.04); OM, oversized mandible (mandibular body to anterior cranial base ratio of ⬎1.12). Yang et al. TMJ disc displacement and sagittal jaw relationship. J Oral Maxillofac Surg 2012.
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Table 2. COMPARISON OF CEPHALOMETRIC VARIABLES
NM Group Variable Maxillomandibular morphology SNA angle (°) SNB angle (°) N perpendicular to point A (mm) Facial convexity (°) ANB angle (°) Vertical skeletal morphology FH to mandibular plane angle (°) Maxillomandibular plane angle (°) Total anterior facial height (mm) Total posterior facial height (mm) Total anterior facial height/total posterior facial height (%) Size and form of mandible Ramus height (mm) Ramus inclination (°) Effective mandibular length (mm) Mandibular body length/anterior cranial base ratio (%) Gonial angle(°) Dental morphology Overbite (mm) Overjet (mm)
OM Group
BN
DDR
DDNR
BN
DDR
DDNR
81.3 ⫾ 2.8 78.1 ⫾ 3.5 1.8 ⫾ 2.9 6.5 ⫾ 7.5 3.2 ⫾ 3.5
82.0 ⫾ 2.3 77.3 ⫾ 2.7 1.5 ⫾ 3.1 9.9 ⫾ 5.1 4.7 ⫾ 2.2
81.7 ⫾ 3.5 73.9 ⫾ 3.5 1.0 ⫾ 4.0 16.3 ⫾ 5.8 7.7 ⫾ 2.2
82.3 ⫾ 2.9 82.4 ⫾ 4.1 2.5 ⫾ 2.7 ⫺0.5 ⫾ 7.8 ⫺0.1 ⫾ 3.5
82.1 ⫾ 3.9 76.7 ⫾ 3.8 3.4 ⫾ 2.6 10.8 ⫾ 6.1 5.4 ⫾ 2.4
82.4 ⫾ 3.9 75.7 ⫾ 4.2 1.6 ⫾ 3.4 13.0 ⫾ 5.7 6.7 ⫾ 2.6
28.4 ⫾ 6.0 28.2 ⫾ 6.8 132.4 ⫾ 4.9 84.3 ⫾ 5.9 63.8 ⫾ 5.2
30.4 ⫾ 7.6 30.7 ⫾ 7.8 131.7 ⫾ 6.9 83.0 ⫾ 6.1 63.2 ⫾ 5.3
37.7 ⫾ 7.1 37.0 ⫾ 6.6 133.0 ⫾ 5.0 77.4 ⫾ 5.2 58.8 ⫾ 4.3
29.2 ⫾ 5.4 28.9 ⫾ 5.7 133.5 ⫾ 5.5 83.7 ⫾ 5.5 63.2 ⫾ 5.3
30.0 ⫾ 3.9 29.8 ⫾ 5.9 133.2 ⫾ 5.3 82.3 ⫾ 6.7 61.7 ⫾ 3.8
34.1 ⫾ 6.1 33.8 ⫾ 6.6 133.3 ⫾ 7.5 80.6 ⫾ 8.2 60.5 ⫾ 5.4
51.2 ⫾ 5.0 97.2 ⫾ 6.1 112.4 ⫾ 6.7 109.0 ⫾ 2.2 121.5 ⫾ 8.1
48.8 ⫾ 5.5 96.1 ⫾ 4.9 111.3 ⫾ 6.0 108.1 ⫾ 2.0 123.7 ⫾ 7.1
45.3 ⫾ 3.9 103.4 ⫾ 5.9 106.3 ⫾ 6.8 107.2 ⫾ 2.4 123.4 ⫾ 6.6
51.6 ⫾ 3.9 92.4 ⫾ 5.7 119.0 ⫾ 5.1 119.3 ⫾ 5.3 126.7 ⫾ 6.6
48.6 ⫾ 5.7 102.9 ⫾ 5.8 110.8 ⫾ 6.8 117.6 ⫾ 3.8 118.2 ⫾ 5.7
46.0 ⫾ 5.4 104.5 ⫾ 7.0 106.4 ⫾ 5.7 116.0 ⫾ 3.3 118.6 ⫾ 6.5
⫺0.1 ⫾ 2.6 3.0 ⫾ 2.4
⫺0.4 ⫾ 3.2 4.9 ⫾ 2.1
0.2 ⫾ 3.0 6.7 ⫾ 2.5
⫺0.8 ⫾ 2.7 0.0 ⫾ 3.0
0.4 ⫾ 2.9 5.2 ⫾ 2.0
0.1 ⫾ 2.8 6.5 ⫾ 2.2
Abbreviations: BN, bilateral normal disc position; DDR, bilateral disc placement with reduction; DDNR, bilateral disc displacement without reduction; NM, normal size mandible (mandibular body to anterior cranial base ratio of 1.08 ⫾ 0.04); OM, oversized mandible (mandibular body to anterior cranial base ratio of ⬎1.12). Data presented as mean ⫾ standard deviation. Yang et al. TMJ disc displacement and sagittal jaw relationship. J Oral Maxillofac Surg 2012.
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Table 3. RESULTS OF BETWEEN-GROUP COMPARISONS WITH RESPECT TO TMJ STATUS
Significance* Variable Maxillomandibular morphology SNA angle (°) SNB angle (°) N perpendicular to point A (mm) Facial convexity (°) ANB angle (°) Vertical skeletal morphology FH to mandibular plane angle (°) Maxillomandibular plane angle (°) Total anterior facial height (mm) Total posterior facial height (mm) Total anterior facial height/total posterior facial height (%) Size and form of mandible Ramus height (mm) Ramus inclination (°) Effective mandibular length (mm) Mandibular body length/anterior cranial base ratio (%) Gonial angle (°) Dental morphology Overbite (mm) Overjet (mm)
TMJ Status
Sagittal Jaw Relationship
NS NS NM (BN ⫽ DDR ⬎ DDNR)†; OM (BN ⬎ DDR ⫽ DDNR)† NS NS NM (BN ⫽ DDR ⬍ DDNR)‡; OM (BN ⬍ DDR ⫽ DDNR)‡ NM (BN ⫽ DDR ⬍ DDNR)†; OM (BN ⬍ DDR ⫽ DDNR)† (BN ⫽ DDR ⬍ (BN ⫽ DDR ⬍ NS (BN ⫽ DDR ⬍ (BN ⫽ DDR ⬍
DDNR)§ DDNR)§ DDNR)† DDNR)†
NS NS NS NS NS
(BN ⬎ DDR ⬎ DDNR)§ NS NM (BN ⫽ DDR ⬍ DDNR)§; OM (BN ⬍ DDR ⫽ DDNR)§ NM (BN ⫽ DDR ⬎ DDNR)†; OM (BN ⬎ DDR ⫽ DDNR)† (BN ⬎ DDR ⫽ DDNR)‡ (NM ⬍ OM)‡ NM (BN ⫽ DDR ⫽ DDNR)§; OM (BN ⬎ DDR ⫽ DDNR)§ NS NS NM (BN ⬍ DDR ⬍ DDNR)†; OM (BN ⬍⬍ DDR ⬍ DDNR)†
Abbreviations: NS, not significant; other abbreviations as in Table 1. *Scheffe’s multiple comparisons performed at significance level of 0.05 to analyze between-group comparisons. †P ⬍ .05. ‡P ⬍ .01. §P ⬍ .001. Yang et al. TMJ disc displacement and sagittal jaw relationship. J Oral Maxillofac Surg 2012.
tal jaw relationship. Future studies are needed to clarify the effects of TMJ DD status on the dentofacial changes using an animal study or longitudinal data.
References 1. Dolwick MF, Riggs RR: Diagnosis and treatment of internal derangements of the temporomandibular joint. Dent Clin North Am 27:561, 1983 2. Rasmussen OC: Description of population and progress of symptoms in a longitudinal study of temporomandibular arthropathy. Scand J Dent Res 89:196, 1981 3. Westesson PL: Reliability and validity of imaging diagnosis of temporomandibular joint disorder. Adv Dent Res 7:137, 1993 4. Cirbus MT, Smilack MS, Beltran J, et al: Magnetic resonance imaging in confirming internal derangement of the temporomandibular joint. J Prosthet Dent 57:488, 1987 5. Katzberg RW, Westesson PL, Tallents RH, et al: Anatomic disorders of the temporomandibular joint disc in asymptomatic subjects. J Oral Maxillofac Surg 54:147, 53, 1996 6. Tasaki MM, Westesson PL, Isberg AM, et al: Classification and prevalence of temporomandibular joint disk displacement in patients and symptom-free volunteers. Am J Orthod Dentofacial Orthop 109:249, 1996 7. Ahn SJ, Baek SH, Kim TW, et al: Discrimination of internal derangement of temporomandibular joint by lateral cephalometric analysis. Am J Orthod Dentofacial Orthop 130:331, 2006
8. Ahn SJ, Kim TW, Nahm DS: Cephalometric keys to internal derangement of temporomandibular joint in women with class II malocclusions. Am J Orthod Dentofacial Orthop 126:486, 94, 2004 9. Brand JW, Nielson KJ, Tallents RH, et al: Lateral cephalometric analysis of skeletal patterns in patients with and without internal derangement of the temporomandibular joint. Am J Orthod Dentofacial Orthop 107:121, 1995 10. Nebbe B, Major PW, Prasad N: Female adolescent facial pattern associated with TMJ disk displacement and reduction in disk length: Part I. Am J Orthod Dentofacial Orthop 116:168, 1999 11. Ahn SJ, Lee SP, Nahm DS: Relationship between temporomandibular joint internal derangement and facial asymmetry in women. Am J Orthod Dentofacial Orthop 128:583, 2005 12. Tollaro I, Baccetti T, Bassarelli V, et al: Class III malocclusion in the deciduous dentition: A morphological and correlation study. Eur J Orthod 16:401, 1994 13. Ahn SJ, Kim TW, Lee DY, et al: Evaluation of internal derangement of the temporomandibular joint by panoramic radiographs compared with magnetic resonance imaging. Am J Orthod Dentofacial Orthop 129:479, 2006 14. Kurita H, Ohtsuka A, Kobayashi H, et al: Relationship between increased horizontal condylar angle and resorption of the posterosuperior region of the lateral pole of the mandibular condyle in temporomandibular joint internal derangement. Dentomaxillofac Radiol 32:26, 2003 15. Annett A: Social fractionalization, political instability, and the size of government. IMF Staff Pap 48:561, 2001 16. Legrell PE, Isberg A: Mandibular length and midline asymmetry after experimentally induced temporomandibular joint disk displacement in rabbits. Am J Orthod Dentofacial Orthop 115: 247, 1999
Skeletal Differences in Patients With Temporomandibular Joint Disc Displacement According to Sagittal Jaw Relationship Il-Hyung Yang, DDS, MSD, PhD,* Beom-Seok Moon, DDS, MSD,† Seung-Pyo Lee, DDS, MSD, PhD,‡ and Sug-Joon Ahn, DDS, MSD, PhD§ Purpose: The present study was designed to analyze the skeletal differences in patients with temporo-
mandibular joint (TMJ) disc displacement (DD), according to the sagittal jaw relationship. Materials and Methods: We implemented a cross-sectional study design and enrolled a sample of Korean women older than age 17 years. The subjects were classified into 3 groups according to the magnetic resonance images of the bilateral TMJs: bilateral normal disc position (BN), bilateral disc displacement with reduction, and bilateral disc displacement without reduction. Each group was subdivided into 2 groups using the mandibular body length to anterior cranial base ratio as a sagittal jaw parameter: normal-size mandible (NM) and oversized mandible (OM). Seventeen variables from the lateral cephalograms were analyzed using 2-way analysis of variance to analyze the differences in skeletal characteristics with respect to the mandible size and TMJ DD status. Results: The subjects with TMJ DD generally had a short ramus height and clockwise rotation of the ramus and mandible compared with those with BN in both OM and NM groups. However, significant differences were present in the skeletal characteristics of the TMJ DD patients between the NM and OM groups. Significant backward positioning and rotation of the ramus and mandible were found between BN and bilateral disc displacement with reduction or bilateral disc displacement without reduction in the OM group, while those of the ramus and mandible were found between BN and bilateral disc displacement with reduction or bilateral disc displacement without reduction in the NM group. Conclusions: The results of our study suggest that the skeletal characteristics associated with TMJ DD are differently represented according to the sagittal jaw relationship. © 2012 American Association of Oral and Maxillofacial Surgeons J Oral Maxillofac Surg 70:e349-e360, 2012
*Assistant Professor, Seoul National University Dental Hospital, Jongro-Gu, Seoul, Korea. †Graduate Student, Seoul National University School of Dentistry, Jongro-Gu, Seoul, Korea. ‡Associate Professor, Dental Research Institute and Department of Oral Anatomy, Seoul National University School of Dentistry, Jongro-Gu, Seoul, Korea. §Associate Professor, Dental Research Institute and Department of Orthodontics, Seoul National University School of Dentistry, Jongro-Gu, Seoul, Korea. This research was supported by the Basic Science Research Program through the National Research Foundation of Korea,
funded by the Ministry of Education, Science, and Technology (grant 2009-0070913). Address correspondence and reprint requests to Dr Ahn: Department of Orthodontics, Dental Research Institute, Seoul National University School of Dentistry, 28-22 Yungeon-Dong, Jongro-Gu Seoul 110-768 Korea; e-mail: [email protected] © 2012 American Association of Oral and Maxillofacial Surgeons
0278-2391/12/7005-0$36.00/0 doi:10.1016/j.joms.2011.08.027
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e350 Disc displacement (DD) is defined as a localized mechanical fault interfering with smooth joint movement.1 Temporomandibular joint (TMJ) DD is the most common TMJ arthropathy, characterized by several stages of dysfunction that involve the condyle– disc relation.1 TMJ DD generally progresses from reduction to nonreduction and can lead to TMJ clicking, crepitus, pain, and limitation in jaw movement.2 A wide variety of methods and devices are used to diagnose TMJ DD. Among them, magnetic resonance imaging (MRI) is known to be a sensitive method of identifying TMJ DD and is the only method that directly depicts the disc in either a normal or an abnormal position.3 It also offers many advantages, including noninvasiveness, minimal pain, minimal risk, and freedom from exposure to ionizing radiation.4 The prevalence of DD is approximately 30% in the asymptomatic adult population and 84% in symptomatic patients when using MRI to determine the disc position.5,6 Recently, concern has been increasing regarding the relationships between TMJ DD and facial morphology. Several cephalometric variables have been identified as being associated with TMJ DD. Generally, patients with TMJ DD have a backward rotation of the mandibular plane, decreased SNB, and increased ANB compared with those with a normal disc position. This is associated with skeletal Class II patterns with a retrognathic mandible.7-10 Thus, there might be a low incidence of TMJ DD in patients showing a skeletal Class III pattern, and the dentoskeletal characteristics of skeletal Class III patients with TMJ DD might be different from those of skeletal Class I patients with TMJ DD or normal TMJs. However, there have been few studies about the relationships between TMJ DD and skeletal morphology in patients with the skeletal Class III pattern, because most studies have focused on research about TMJ DD patients with a skeletal Class II pattern or an anterior open bite. As a result, the skeletal characteristics of TMJ DD patients according to the sagittal jaw relationships are still unclear. The aim of the present study was to investigate the skeletal differences in patients with TMJ DD according to the sagittal jaw relationship. The null hypothesis of our study was that the skeletal characteristics in the patients with TMJ DD would not be influenced by the sagittal jaw relationships.
Materials and Methods To address the research purpose, we designed and implemented a cross-sectional study and enrolled a sample derived from the population of patients who presented to the Department of Orthodontics, Seoul National University Dental Hospital for an orthodontic
TMJ DISC DISPLACEMENT AND SAGITTAL JAW RELATIONSHIP
evaluation between 2002 and 2010. To be included in the study sample, the patients had to be women older than 17 years to avoid gender-related size differences and growth-related size differences. The patients had to agree to bilateral high-resolution MRI in the sagittal (opened and closed) and coronal (closed) planes to evaluate the TMJs. Patients were excluded as study subjects if they had any systemic disease, a history of orthodontic treatment, a history of trauma involving the TMJs, or juvenile rheumatoid arthritis. The institutional review board of the University Hospital reviewed and approved the research protocol. Routine lateral cephalograms were taken of all the subjects using Asahi CX-90SP II (Asahi Roentgen, Kyoto, Japan). Most subjects had clinical signs and symptoms of TMJ dysfunction, such as pain, joint sounds, and muscle tenderness. Some patients who did not show any detectable TMJ signs and symptoms had skeletal malocclusions such as an anterior open bite, a retrognathic mandible, and facial asymmetry, reported to be associated with TMJ DD.7,8,11 Radiologists with TMJ MRI experience interpreted the images without clinical information of the patients. The TMJ disc status was divided into 3 categories as follows: 1. Normal disc position (Figs 1A,B): in the closed mouth position, the intermediate zone of the disc was interposed between the condyle and the posterior slope of the articular eminence, with the anterior and posterior bands equally spaced on either side of the condylar load point. 2. Disc displacement with reduction (Figs 1C,D): the disc was anteriorly displaced relative to the posterior slope of the articular eminence and the head of the condyle. However, the disc displacement was reduced on mouth opening. 3. Disc displacement without reduction (Figs 1E,F): The disc was anteriorly displaced relative to the posterior slope of the articular eminence and the head, without reductrion of disc on mouth opening. The position and shape of the disc were evaluated carefully according to the classification criteria for the disc position. Ambiguous cases were excluded from the present study. A total of 301 patients were originally selected and analyzed. Among them, the subjects with bilateral normal disc status (BN), bilateral disc displacement with reduction (DDR), and bilateral disc displacement without reduction (DDNR) only were included in the present study. This was because the possible skeletal characteristics associated with unilateral DD would
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FIGURE 1. Normal TMJ disc position to condyle in A, closed-mouth and (Figure 1 continued on next page.) Yang et al. TMJ disc displacement and sagittal jaw relationship. J Oral Maxillofac Surg 2012.
have been obscured by the averaging of the right and left landmarks used in determining their locations.11 A single investigator traced all cephalograms. The tracings were recorded using a digitizer with a desktop computer. Fifteen landmarks were digitized on each radiograph, from which the cephalometric variables were calculated. To analyze the cephalometric characteristics of the subjects with TMJ DD according to their sagittal jaw relationship, the subjects should be classified using a sagittal jaw parameter. However, we could not use the traditional sagittal parameters, such as ANB, SNB, and facial convexity, because those parameters are significantly influenced by the backward rotation of mandible and decrease in ramus height, the main skeletal characteristics of patients with TMJ DD.8-10 Instead, the subjects were classified
according to the mandibular body length to the anterior cranial base ratio (MNACBR), because MNACBR is one of the important markers of the skeletal Class III patterns12 and would not be influenced by the skeletal changes associated with TMJ DD. The subjects who had a MNACBR within ⫾1 standard deviation of normal Korean women (1.08 ⫾ 0.04) were included in the normal-size mandible (NM) group. The subjects in the oversized mandible (OM) group had a MNACBR of more than 1.12. Unless an alteration in the skeletal jaw relationship occurs with TMJ DD, the NM and OM groups could be equivalent to the Class I and Class III skeletal pattern, respectively. To select the study variables for analysis, Pearson correlation coefficients were calculated between the MNACBR and the other cephalometric variables. The
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FIGURE 1 (cont’d). B, open-mouth sagittal images. Intermediate zone of disc (arrow) interposed between condyle (C) in both positions. (Figure 1 continued on next page.) Yang et al. TMJ disc displacement and sagittal jaw relationship. J Oral Maxillofac Surg 2012.
variables with a coefficient larger than 0.5 or smaller than ⫺0.5, simultaneously with a significance level lower than 0.05, were excluded owing to their correlations with the MNACBR. Finally, 17 cephalometric variables were chosen. For convenience of analysis, these variables were subdivided into 4 categories: maxillomandibular morphology, vertical skeletal morphology, size and form of the mandible, and dental morphology. The positions of all the landmarks are shown in Figure 2, and their measurements are shown in Figures 3 and 4. To test the magnitude of the measurement error involved in our study, the lateral cephalograms of 20 randomly selected patients were measured again. The reliability of the tracing, landmark identification, and
analytical measurements had intraclass correlation coefficients greater than 0.98. Descriptive statistics for each variable in the NM and OM groups were calculated. The differences in the cephalometric variables with respect to the sagittal jaw relationship and TMJ DD status were tested with 2-way factorial analysis of variance. Scheffe’s multiple comparisons were performed at a significance level of 0.05 to analyze the between-group comparisons.
Results A total of 136 Korean women were selected for this study (Table 1). Of the 110 patients with bilateral TMJ
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FIGURE 1 (cont’d). DDR to condyle in C, closed-mouth and (Figure 1 continued on next page.) Yang et al. TMJ disc displacement and sagittal jaw relationship. J Oral Maxillofac Surg 2012.
DD, 26 (23.6%) did not show any detectable TMJ signs and symptoms. Of the 57 patients with bilateral normal TMJs, 24 (42.1%) showed TMJ signs and symptoms on at least 1 side of both TMJs. The differences in cephalometric characteristics with respect to TMJ DD status (BN, DDR, and DDNR) and sagittal jaw relationship (NM and OM group) are listed in Table 2. The results showed that both TMJ DD status and sagittal jaw relationship have significant effects on the cephalometric variables (Table 3). However, TMJ DD status can influence some cephalometric variables differently, depending on the sagittal jaw relationship (Table 3). The variables associated with the mandible were statistically significant, and the variables associated with the maxilla (SNA and nasion (N) perpendicular
to point A) were not statistically significant in the maxillomandibular morphology (Tables 2 and 3). Generally, the subjects with TMJ DD had anteroposterior skeletal discrepancies between the maxilla and mandible by a backward rotation and position of the mandible. However, the jaw bone discrepancies associated with TMJ DD status were different between the NM and OM groups. Significant differences in SNB, ANB, and facial convexity were found between BN or DDR and DDNR in the NM group, and those differences were found between BN and DDR or DDNR in the OM group (Table 3). The vertical skeletal morphology was significantly influenced by TMJ DD status but not by the sagittal jaw relationship (Tables 2 and 3). The FMA, maxillomandibular plane angle, and the facial height ratio
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FIGURE 1 (cont’d). D, open-mouth sagittal images. Disc (arrow) anteriorly displaced relative to posterior slope of articular eminence (E) and head of condyle (C). However, disc reduced on mouth opening. (Figure 1 continued on next page.) Yang et al. TMJ disc displacement and sagittal jaw relationship. J Oral Maxillofac Surg 2012.
(total posterior facial height to total anterior facial height ratio) were statistically significant between patients with BN or DDR and patients with DDNR, with no significant difference in those variables between BN and DDR (Table 3). Consequently, the patients with DDNR had a steeper mandibular plane and more backward rotation of the mandibles than those with BN or DDR. The difference in vertical skeletal morphology resulted from the decreased total posterior facial height, because the total anterior facial height
and lower anterior facial height were similar among those with BN, DDR, and DDNR (Table 3). Both TMJ DD status and the sagittal jaw relationship influenced the variables representing the size and form of the mandible differently (Table 3). As expected, the subjects in the OM group had a greater MNACBR than those in the NM group. The ramus inclination, effective mandibular length, and gonial angle showed significant differences between BN or DDR and DDNR in the NM group but between BN and
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FIGURE 1 (cont’d). DDNR to condyle in E, closed-mouth and (Figure 1 continued on next page.) Yang et al. TMJ disc displacement and sagittal jaw relationship. J Oral Maxillofac Surg 2012.
DDR or DDNR in the OM group (Table 3). The gonial angle did not show any significant difference among the different TMJ DD groups in the NM group but did show a significant difference between BN and DDR or DDNR in the OM group. The ramus height showed statistically significant differences between BN and DDR and between DDR and DDNR in both NM and OM groups. An overbite was not significantly influenced by the TMJ DD status or sagittal jaw relationship. Overjet was significantly different among BN, DDR,
and DDNR in both NM and OM groups; however, the difference between BN and DDR was more significant in the OM group than in the NM group (Table 3).
Discussion TMJ DD has been reported to be associated with an altered facial morphology, such as a backward rotation and position of the ramus and mandible—a skeletal Class II relationship with a retrognathic mandi-
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FIGURE 1 (cont’d). F, open-mouth sagittal images. Disc (arrow) anteriorly displaced relative to posterior slope of articular eminence (E) and head of condyle (C), without reduction of disc on mouth opening. Yang et al. TMJ disc displacement and sagittal jaw relationship. J Oral Maxillofac Surg 2012.
ble.7-10 Thus, the skeletal characteristics of TMJ DD patients might be different according to their sagittal jaw relationship. However, few studies have investigated the skeletal differences in TMJ DD patients according to the sagittal jaw relationships, even though there has been abundant research about TMJ DD and patients with a Class II skeletal pattern. The purpose of the present study was to analyze the differences in skeletal characteristics of patients with TMJ DD status, according to their sagittal jaw relationships. We found that the skeletal characteristics associated with TMJ DD are differently represented according to the sagittal jaw relationship, and the null hypothesis of the present study was rejected.
The present study showed an association between TMJ DD and altered skeletal morphology, although a cause– effect relationship is unclear. TMJ DD might cause skeletal changes or DD might occur because of the biomechanics associated with an altered skeletal morphology. It is also possible that both DD and altered skeletal morphology are the results of another influencing factor not yet identified. Nevertheless, these results suggest that TMJ DD can be a contributing factor to the alteration of skeletal morphology, such as a decrease in ramus height, a decrease in the effective size of the mandible, and a backward rotation of the ramus (Table 2). The differences in skeletal morphology associated with TMJ DD might result from osseous changes in the condylar head.
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FIGURE 2. Landmarks used in study: 1, nasion; 2, sella; 3, orbitale; 4, porion; 5, anterior nasal spine; 6, posterior nasal spine; 7, articulare; 8, point A; 9, incisal end of maxillary incisor; 10, incisal end of mandibular incisor; 11, point B; 12, pogonion; 13, menton; 14, gonion; and 15, articulation of maxillary and mandibular molars. Yang et al. TMJ disc displacement and sagittal jaw relationship. J Oral Maxillofac Surg 2012.
Previous studies have reported bony changes on the articular surface of the mandibular condyle in patients with TMJ DD, such as a decreased condylar height with a distally inclined condylar head.13,14 The changes in condylar shape in patients with TMJ DD might significantly influence the skeletal morphology (in particular, the size and form of the mandible), such as a decrease in the ramus height and effective mandibular length and backward rotation of the ramus (Table 2). This could, in turn, influence the maxillomandibular morphology, manifesting a decreased SNB, increased ANB, and increased facial convexity. The present study showed that the skeletal characteristics associated with TMJ DD patients were different between the NM and OM groups (Tables 2 and 3). The subjects in the OM group manifested a backward position of the mandible (decreased SNB and ANB and increased facial convexity), a backward rotation of the ramus (increased ramus inclination), and a decreased effective mandibular length between BN and DDR or DDNR, while these differences were shown between BN or DDR and DDNR in the subjects in NM group. These results are not in full accordance with the results of the previous study.7 The previous study
e357 showed that significant skeletal differences were found between BN or DDR and DDNR and between BN and DDR, although the sample size of the previous study was smaller than that of the present study. The main reason for the different results might be that the samples of the previous study were not classified according to the sagittal jaw relationships, which could be referred to as a more detailed experimental design of the present study. The reasons for the different cephalometric characteristics between the NM and OM groups are unclear. However, the skeletal differences between OM and NM did not result from ethnic or racial differences in the subjects. This is because we consecutively recruited subjects who visited only 1 dental hospital in 1 region and because Koreans are reported to be the most ethnically homogeneous population in the world.15 It seems that the subjects with a skeletal Class III pattern would have less resisting ability against the functional stress produced by TMJ DD than those with a skeletal Class I pattern. Thus, an early stage of TMJ DD would easily influence the skeletal morphology in the subjects with a Class III pattern, but the subjects with a Class I pattern would not show significant skeletal alterations until the TMJ DD had progressed to DDNR, a more severe condition. Additional studies are needed to investigate the differences in skeletal morphology among the different
FIGURE 3. Angular measurements used in study: 1, gonial angle (Ar-Go-Me); 2, maxillomandibular plane angle; 3, FH to mandibular plane angle; 4, SNA angle; 5, SNB angle; 6, ANB angle; 7, ramus inclination (N–S to Ar-Go); and 8, facial convexity. Yang et al. TMJ disc displacement and sagittal jaw relationship. J Oral Maxillofac Surg 2012.
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FIGURE 4. Linear measurements used in study: 1, N perpendicular to point A; 2, ramus height (Ar-Go); 3, effective mandibular length (Ar-Pog); 4, total anterior facial height (N-Me); 5, total posterior facial height (S-Go). Yang et al. TMJ disc displacement and sagittal jaw relationship. J Oral Maxillofac Surg 2012.
TMJ DD categories according to the sagittal jaw relationship. The cephalometric differences between the NM and OM groups in the subjects with TMJ DD have important clinical significance. This is because TMJ DD patients with an oversized mandible can manifest skeletal Class I or II ranges of SNB, ANB, and facial convexity by a backward rotation and positioning of the mandible (Table 2). Therefore, the ranges of these variables in the OM group with TMJ DD might overlap with those of the variables in the NM group with BN or TMJ DD, although all subjects in the OM group had oversized mandibles with a MNACBR greater than
1.12. Thus, the patients with an oversized mandible and TMJ DD can be classified as having a skeletal Class I or II pattern, despite their larger mandible. These results suggest that orthodontists should be careful not to overlook these skeletal characteristics of TMJ DD patients with an oversized mandible at the initial examination. In the present study, the gonial angle was significantly decreased in the OM group in the presence of TMJ DD, with no significant difference in the gonial angle in the NM group among the different TMJ DD categories (Tables 2 and 3). The decreased gonial angle is associated with bone remodeling in the gonial region, which might result from a localized alteration in the functional environment created by TMJ DD. This is partly supported by a previous study that showed excessive bone growth in the gonial area as compensation for a decreased ramus height experimentally induced by TMJ DD.16 The change in gonial angle would be one of the key factors indicating potential TMJ DD in subjects with an oversized mandible, because no significant change was found in the gonial angle in TMJ DD patients with other malocclusions.7,8 In contrast to other variables, the ramus height can discriminate the differences among BN, DDR, and DDNR in both NM and OM groups (Table 3). This might be because the ramus height is directly influenced by bony changes in the mandibular condyle associated with TMJ DD, in which the condyle clearly changes from BN to DDNR by way of DDR.13 The results from the present study were derived from cross-sectional data, and they do not show true longitudinal changes. Longitudinal studies might aid in the identification of the causative and associated factors. However, it is very difficult to collect sufficient longitudinal samples with matched MRI data, because MRI is too expensive to be regularly performed. Thus, our results provide valuable information on the differences in the skeletal characteristics of TMJ DD patients according to the sagit-
Table 1. NUMBER AND AGE OF SUBJECTS STRATIFIED BY CLASSIFICATION USED
Group NM Subjects (n) Age (yr) OM Subjects (n) Age (yr)
BN (n ⫽ 57)
DDR (n ⫽ 49)
DDNR (n ⫽ 61)
Total
19 21.2 ⫾ 2.3
29 24.5 ⫾ 5.5
22 25.4 ⫾ 5.1
70 23.9 ⫾ 4.9
33 23.1 ⫾ 5.1
16 24.3 ⫾ 4.5
17 23.0 ⫾ 3.7
66 23.4 ⫾ 4.6
Abbreviations: BN, bilateral normal disc position; DDR, bilateral disc placement with reduction; DDNR, bilateral disc displacement without reduction; NM, normal size mandible (mandibular body to anterior cranial base ratio of 1.08 ⫾ 0.04); OM, oversized mandible (mandibular body to anterior cranial base ratio of ⬎1.12). Yang et al. TMJ disc displacement and sagittal jaw relationship. J Oral Maxillofac Surg 2012.
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Table 2. COMPARISON OF CEPHALOMETRIC VARIABLES
NM Group Variable Maxillomandibular morphology SNA angle (°) SNB angle (°) N perpendicular to point A (mm) Facial convexity (°) ANB angle (°) Vertical skeletal morphology FH to mandibular plane angle (°) Maxillomandibular plane angle (°) Total anterior facial height (mm) Total posterior facial height (mm) Total anterior facial height/total posterior facial height (%) Size and form of mandible Ramus height (mm) Ramus inclination (°) Effective mandibular length (mm) Mandibular body length/anterior cranial base ratio (%) Gonial angle(°) Dental morphology Overbite (mm) Overjet (mm)
OM Group
BN
DDR
DDNR
BN
DDR
DDNR
81.3 ⫾ 2.8 78.1 ⫾ 3.5 1.8 ⫾ 2.9 6.5 ⫾ 7.5 3.2 ⫾ 3.5
82.0 ⫾ 2.3 77.3 ⫾ 2.7 1.5 ⫾ 3.1 9.9 ⫾ 5.1 4.7 ⫾ 2.2
81.7 ⫾ 3.5 73.9 ⫾ 3.5 1.0 ⫾ 4.0 16.3 ⫾ 5.8 7.7 ⫾ 2.2
82.3 ⫾ 2.9 82.4 ⫾ 4.1 2.5 ⫾ 2.7 ⫺0.5 ⫾ 7.8 ⫺0.1 ⫾ 3.5
82.1 ⫾ 3.9 76.7 ⫾ 3.8 3.4 ⫾ 2.6 10.8 ⫾ 6.1 5.4 ⫾ 2.4
82.4 ⫾ 3.9 75.7 ⫾ 4.2 1.6 ⫾ 3.4 13.0 ⫾ 5.7 6.7 ⫾ 2.6
28.4 ⫾ 6.0 28.2 ⫾ 6.8 132.4 ⫾ 4.9 84.3 ⫾ 5.9 63.8 ⫾ 5.2
30.4 ⫾ 7.6 30.7 ⫾ 7.8 131.7 ⫾ 6.9 83.0 ⫾ 6.1 63.2 ⫾ 5.3
37.7 ⫾ 7.1 37.0 ⫾ 6.6 133.0 ⫾ 5.0 77.4 ⫾ 5.2 58.8 ⫾ 4.3
29.2 ⫾ 5.4 28.9 ⫾ 5.7 133.5 ⫾ 5.5 83.7 ⫾ 5.5 63.2 ⫾ 5.3
30.0 ⫾ 3.9 29.8 ⫾ 5.9 133.2 ⫾ 5.3 82.3 ⫾ 6.7 61.7 ⫾ 3.8
34.1 ⫾ 6.1 33.8 ⫾ 6.6 133.3 ⫾ 7.5 80.6 ⫾ 8.2 60.5 ⫾ 5.4
51.2 ⫾ 5.0 97.2 ⫾ 6.1 112.4 ⫾ 6.7 109.0 ⫾ 2.2 121.5 ⫾ 8.1
48.8 ⫾ 5.5 96.1 ⫾ 4.9 111.3 ⫾ 6.0 108.1 ⫾ 2.0 123.7 ⫾ 7.1
45.3 ⫾ 3.9 103.4 ⫾ 5.9 106.3 ⫾ 6.8 107.2 ⫾ 2.4 123.4 ⫾ 6.6
51.6 ⫾ 3.9 92.4 ⫾ 5.7 119.0 ⫾ 5.1 119.3 ⫾ 5.3 126.7 ⫾ 6.6
48.6 ⫾ 5.7 102.9 ⫾ 5.8 110.8 ⫾ 6.8 117.6 ⫾ 3.8 118.2 ⫾ 5.7
46.0 ⫾ 5.4 104.5 ⫾ 7.0 106.4 ⫾ 5.7 116.0 ⫾ 3.3 118.6 ⫾ 6.5
⫺0.1 ⫾ 2.6 3.0 ⫾ 2.4
⫺0.4 ⫾ 3.2 4.9 ⫾ 2.1
0.2 ⫾ 3.0 6.7 ⫾ 2.5
⫺0.8 ⫾ 2.7 0.0 ⫾ 3.0
0.4 ⫾ 2.9 5.2 ⫾ 2.0
0.1 ⫾ 2.8 6.5 ⫾ 2.2
Abbreviations: BN, bilateral normal disc position; DDR, bilateral disc placement with reduction; DDNR, bilateral disc displacement without reduction; NM, normal size mandible (mandibular body to anterior cranial base ratio of 1.08 ⫾ 0.04); OM, oversized mandible (mandibular body to anterior cranial base ratio of ⬎1.12). Data presented as mean ⫾ standard deviation. Yang et al. TMJ disc displacement and sagittal jaw relationship. J Oral Maxillofac Surg 2012.
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Table 3. RESULTS OF BETWEEN-GROUP COMPARISONS WITH RESPECT TO TMJ STATUS
Significance* Variable Maxillomandibular morphology SNA angle (°) SNB angle (°) N perpendicular to point A (mm) Facial convexity (°) ANB angle (°) Vertical skeletal morphology FH to mandibular plane angle (°) Maxillomandibular plane angle (°) Total anterior facial height (mm) Total posterior facial height (mm) Total anterior facial height/total posterior facial height (%) Size and form of mandible Ramus height (mm) Ramus inclination (°) Effective mandibular length (mm) Mandibular body length/anterior cranial base ratio (%) Gonial angle (°) Dental morphology Overbite (mm) Overjet (mm)
TMJ Status
Sagittal Jaw Relationship
NS NS NM (BN ⫽ DDR ⬎ DDNR)†; OM (BN ⬎ DDR ⫽ DDNR)† NS NS NM (BN ⫽ DDR ⬍ DDNR)‡; OM (BN ⬍ DDR ⫽ DDNR)‡ NM (BN ⫽ DDR ⬍ DDNR)†; OM (BN ⬍ DDR ⫽ DDNR)† (BN ⫽ DDR ⬍ (BN ⫽ DDR ⬍ NS (BN ⫽ DDR ⬍ (BN ⫽ DDR ⬍
DDNR)§ DDNR)§ DDNR)† DDNR)†
NS NS NS NS NS
(BN ⬎ DDR ⬎ DDNR)§ NS NM (BN ⫽ DDR ⬍ DDNR)§; OM (BN ⬍ DDR ⫽ DDNR)§ NM (BN ⫽ DDR ⬎ DDNR)†; OM (BN ⬎ DDR ⫽ DDNR)† (BN ⬎ DDR ⫽ DDNR)‡ (NM ⬍ OM)‡ NM (BN ⫽ DDR ⫽ DDNR)§; OM (BN ⬎ DDR ⫽ DDNR)§ NS NS NM (BN ⬍ DDR ⬍ DDNR)†; OM (BN ⬍⬍ DDR ⬍ DDNR)†
Abbreviations: NS, not significant; other abbreviations as in Table 1. *Scheffe’s multiple comparisons performed at significance level of 0.05 to analyze between-group comparisons. †P ⬍ .05. ‡P ⬍ .01. §P ⬍ .001. Yang et al. TMJ disc displacement and sagittal jaw relationship. J Oral Maxillofac Surg 2012.
tal jaw relationship. Future studies are needed to clarify the effects of TMJ DD status on the dentofacial changes using an animal study or longitudinal data.
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