Abstract
This retrospective study was designed to analyze the relationships between temporomandibular joint (TMJ) disk displacement and skeletal deformities in orthodontic patients. Subjects consisted of 460 adult patients. Before treatment, lateral cephalograms and TMJ magnetic resonance imaging (MRI) were recorded. Subjects were divided into six groups based on TMJ MRI according to increasing severity of TMJ disk displacement, in the following order: bilateral normal TMJs, unilateral disk displacement with reduction (DDR) and contralateral normal, bilateral DDR, unilateral disk displacement without reduction (DDNR) and contralateral normal, unilateral DDR and contralateral DDNR, and bilateral DDNR. Subjects were subdivided sagittally into skeletal Class I, II, and III deformities based on the ANB (point A, nasion, point B) angle and subdivided vertically into hypodivergent, normodivergent, and hyperdivergent deformities based on the facial height ratio. Linear trends between severity of TMJ disk displacement and sagittal or vertical deformities were analyzed by Cochran–Mantel–Haenszel test. The severity of TMJ disk displacement increased as the sagittal skeletal classification changed from skeletal Class III to skeletal Class II and the vertical skeletal classification changed from hypodivergent to hyperdivergent. There were no significant differences in the linear trend of TMJ disk displacement severity between the sexes according to the skeletal deformities. This study suggests that subjects with skeletal Class II and/or hyperdivergent deformities have a high possibility of severe TMJ disk displacement, regardless of sex.
Disk displacement is defined as an altered position of the disk from its normal location on the top of the mandibular condyle in the temporomandibular joint (TMJ). It may lead to TMJ clicking, pain, and jaw movement limitations. TMJ disk displacement is the principal clinical sign of internal derangement of the TMJ, which progresses from reduction to nonreduction.
There are currently several methods and devices used to diagnose TMJ disk displacement. Magnetic resonance imaging (MRI) has been used to evaluate the TMJ disk with direct visualization of the articular disk position. In addition, MRI has many advantages, such as non-invasiveness, no soft tissue distortion, no exposure to ionizing radiation, and multiplanar imaging.
Previous studies have reported relationships between TMJ disk displacement and facial morphology using MRI. In general, a decreased posterior facial height and backward position and rotation of the mandible are principal characteristics associated with TMJ disk displacement. This means that patients with TMJ disk displacement may have a lower possibility of having skeletal Class III and hypodivergent deformities. However, there have been few studies addressing the association of TMJ disk displacement with sagittal or vertical skeletal deformities, specifically skeletal Class III or hypodivergent deformities. In addition, most studies have only included female participants and it is still unclear if TMJ disk displacement is associated with dentofacial morphology in males.
The purpose of the present study was to analyze the relationships between TMJ disk displacement and sagittal or vertical skeletal deformities in adult male and female patients with various malocclusions using TMJ MRI. The null hypothesis of our study is that there are no linear correlations between TMJ disk displacement and sagittal or vertical skeletal deformities.
Materials and methods
Subjects seeking orthodontic or surgical orthodontic treatments who visited a department of orthodontics from 2002 to 2012 were recruited. A total of 460 adult patients (117 males and 343 females) were selected and analyzed in this study ( Table 1 ). The age range of male patients was 18.1–37.8 years (mean age 22.7 ± 5.8 years), while that of female patients was 17.0–47.3 years (mean age 24.1 ± 4.9 years). There was no significant difference in age distribution among the six study groups (defined below) or between the sexes. To be included in the study sample, men had to be over the age of 18 years and women over the age of 17 years, in order to avoid growth-related size differences; growth in Korean males and females is almost complete after the age of 17 and 16 years, respectively. Exclusion criteria were (1) any systemic disease, (2) history of orthodontic treatment, (3) history of facial cosmetic surgery or orthognathic surgery, (4) history of trauma involving the TMJs, (5) juvenile rheumatoid arthritis, and (6) history of TMJ treatment. Routine lateral cephalograms were taken for all the subjects using an Asahi CX-90SP II instrument (Asahi Roentgen, Kyoto, Japan).
| Group 1 a (mean ± SD) | Group 2 b (mean ± SD) | Group 3 c (mean ± SD) | Group 4 d (mean ± SD) | Group 5 e (mean ± SD) | Group 6 f (mean ± SD) | |
|---|---|---|---|---|---|---|
| Male | 22.3 ± 3.2 | 22.5 ± 3.9 | 25.7 ± 9.9 | 22.2 ± 3.5 | 21.8 ± 3.0 | 21.8 ± 2.5 |
| Female | 23.4 ± 6.1 | 25.1 ± 7.1 | 24.9 ± 5.8 | 25.3 ± 6.4 | 22.4 ± 4.4 | 24.1 ± 5.2 |
| Total | 23.0 ± 5.3 | 24.4 ± 6.5 | 25.1 ± 6.7 | 24.3 ± 5.8 | 22.3 ± 4.2 | 23.7 ± 4.9 |
b Unilateral disk displacement with reduction and normal contralateral TMJ.
c Bilateral disk displacement with reduction.
d Unilateral disk displacement without reduction and normal contralateral TMJ.
e Unilateral disk displacement with reduction and disk displacement without reduction in the contralateral TMJ.
Patients with a history of TMJ symptoms, such as TMJ sounds, TMJ pain on palpation, limitation of mandibular movement, and locking, and patients in whom specific skeletal characteristics associated with TMJ disk displacement were present, such as an anterior open bite, a retrognathic mandible, severe facial asymmetry, and decreased posterior facial height, were examined using MRI. The MRIs were obtained using a Signa Horizon instrument (GE, Waukesha, WI, USA) operating at 1.5 T, with a unilateral 3 inch surface receiver coil (GE). Initially, the axial scout images were obtained at the level of the TMJs in order to identify the long axes of the condyles. Non-orthogonal sagittal sections were obtained perpendicular to the condyles and non-orthogonal coronal oblique sections were also obtained. Closed mouth images were obtained at maximum dental intercuspation, and open mouth images were taken at maximum unassisted vertical mandibular opening, using a Burnett bidirectional TMJ device (Medrad, Pittsburgh, PA, USA). T1-weighted 600/12 (repetition time (TR) ms/echo time (TE) ms) and proton-density 4000/14 (TR ms/TE ms) pulse sequences were performed in the sagittal plane using a 3-mm slice thickness, a 10-cm field of view, a number of excitations of 2, and an image matrix of 254 × 192 pixels. A T1-weighted 500/12 (TR ms/TE ms) pulse sequence was performed in the coronal plane under the same conditions.
Two radiologists with TMJ MRI experience interpreted the images without clinical information on the patient. TMJ disk position was divided into three categories according to the following criteria. (1) Normal disk position: in the closed mouth position, the intermediate zone of the disk is interposed between the condyle and the posterior slope of the articular eminence, with anterior and posterior bands equally spaced on either side of the condylar load point. (2) Disk displacement with reduction (DDR): the disk is anteriorly displaced relative to the posterior slope of the articular eminence and the head of the condyle; however, the disk is reduced on mouth opening. (3) Disk displacement without reduction (DDNR): the disk is anteriorly displaced relative to the posterior slope of the articular eminence and the head of the condyle, but without reduction of the disk on mouth opening.
TMJ disk status was carefully evaluated according to the classification criteria for disk position. Ambiguous cases such as partial disk displacement or partial disk reduction were excluded in this study.
Subjects were divided into six groups based on the results of TMJ MRI according to increased TMJ disk displacement severity, in the following order: bilateral normal TMJs (BN, group 1), unilateral DDR and normal contralateral TMJ (group 2), bilateral DDR (group 3), unilateral DDNR and normal contralateral TMJ (group 4), unilateral DDR and DDNR in the contralateral TMJ (group 5), and bilateral DDNR (group 6).
All cephalograms were traced by a single investigator and recorded using a digitizer with a desktop computer. The positions of all landmarks and the measurements used in this study are shown in Figs. 1 and 2 . In order to analyze relationships between the severity of TMJ disk displacement and sagittal or vertical skeletal deformities, we selected the ANB (point A, nasion, point B) angle and facial height ratio (FHR) as references of sagittal and vertical skeletal classifications, respectively. Subjects with an ANB angle or FHR within ±1 standard deviation (SD) of normal Korean adults, were designated as skeletal Class I (ANB angle 1.4–4.4° in males and 0.8–4.4° in females) or normodivergent pattern (FHR 66.0–72.0 in males and 63.0–68.0 in females), respectively. Subjects with an ANB angle of greater than 1 SD were designated as having a skeletal Class II deformity (ANB angle of >4.4° in both males and females) and those with an ANB angle of less than 1 SD were designated as having a skeletal Class III deformity (ANB angle <1.4° in males and <0.8° in females). Those with a FHR greater than 1 SD from average FHR measurements were assigned a hypodivergent deformity (FHR >72.0 in males and >68.0 in females) and those with a FHR less than 1 SD from the average were assigned a hyperdivergent deformity (FHR <66.0 in males and <63.0 in females).
Before data were analyzed, duplicate determinations were performed on 30 cephalometric radiographs, from which measurement errors were calculated with an intraclass correlation coefficient. The tracing reliability, landmark identification, and analytical measurements had intraclass correlation coefficients of >0.98.
Two-way analysis of variance (ANOVA) with Scheffe’s multiple comparisons was used to determine any significant differences in age according to sex and TMJ disk displacement status. The linear trend in TMJ disk displacement severity according to sagittal or vertical skeletal deformities in both sexes was confirmed by a general correlation coefficient method through the Cochran–Mantel–Haenszel test. In order to evaluate relationships between TMJ disk displacement and specific skeletal deformities, homogeneity or differences in severity of TMJ disk displacement in patients with specific skeletal deformities were analyzed by χ 2 test. Values were considered statistically significant when P < 0.05.
Results
Table 2 shows the distribution of patients with various TMJ disk displacements. Seventy-five (64.1%) of 117 male patients and 274 (79.9%) of 343 female patients had TMJ disk displacement. Twenty-five (33.3%) of 75 male patients who had TMJ disk displacement did not show any detectable TMJ signs or symptoms, while 28 (35.8%) of the symptomatic male patients had bilateral normal TMJs. Among female patients, 108 (39.4%) out of 274 female patients who had TMJ disk displacement did not show any detectable TMJ signs or symptoms, while 26.0% of symptomatic patients had bilateral normal TMJs (data not shown).
| Group 1 a | Group 2 b | Group 3 c | Group 4 d | Group 5 e | Group 6 f | Total | |
|---|---|---|---|---|---|---|---|
| Male | 42 (35.9) | 19 (16.2) | 17 (14.5) | 9 (7.7) | 11 (9.4) | 19 (16.2) | 117 (100) |
| Female | 69 (20.1) | 52 (15.2) | 73 (21.3) | 18 (5.2) | 48 (14.0) | 83 (24.2) | 343 (100) |
| Total | 111 (24.1) | 71 (15.4) | 90 (19.6) | 27 (5.9) | 59 (12.8) | 102 (22.2) | 460 (100) |
b Unilateral disk displacement with reduction and normal contralateral TMJ.
c Bilateral disk displacement with reduction.
d Unilateral disk displacement without reduction and normal contralateral TMJ.
e Unilateral disk displacement with reduction and disk displacement without reduction in the contralateral TMJ.
Fig. 3 and Table 3 show the relationships between the severity of TMJ disk displacement and sagittal skeletal deformities in male and female patients. Since the linear trend in the severity of TMJ disk displacement was not significantly different between the sexes, the results of both sexes were combined. Results indicated that TMJ disk displacement severity from BN to bilateral DDNR (from groups 1 to 6) increased as the sagittal skeletal classification changed from skeletal Class III to Class II ( P < 0.0001). In contrast, TMJ disk displacement severity from groups 1 to 6 decreased as the sagittal skeletal classification changed from skeletal Class II to Class III ( P < 0.0001). As a result, bilateral DDNR was most prevalent in patients with skeletal Class II, whereas BN was most prevalent in patients with skeletal Class III. In addition, 88.1% of patients with skeletal Class II had TMJ disk displacement on at least one side of the TMJ. This indicates that the severity of TMJ disk displacement is associated with sagittal skeletal deformities.
| Group 1 a | Group 2 b | Group 3 c | Group 4 d | Group 5 e | Group 6 f | Total | |
|---|---|---|---|---|---|---|---|
| Male | |||||||
| Skeletal Class III | 28 (23.9) | 15 (12.8) | 4 (3.4) | 2 (1.7) | 2 (1.7) | 0 (0.0) | 51 (43.6) |
| Skeletal Class I | 9 (7.7) | 3 (2.6) | 5 (4.3) | 3 (2.6) | 3 (2.6) | 2 (1.7) | 25 (21.4) |
| Skeletal Class II | 5 (4.3) | 1 (0.9) | 8 (6.8) | 4 (3.4) | 6 (5.1) | 17 (14.5) | 41 (35.0) |
| Total | 42 (35.9) | 19 (16.2) | 17 (14.5) | 9 (7.7) | 11 (9.4) | 19 (16.2) | 117 (100) |
| Female | |||||||
| Skeletal Class III | 29 (8.5) | 10 (2.9) | 2 (0.6) | 6 (1.7) | 2 (0.6) | 1 (0.3) | 50 (14.6) |
| Skeletal Class I | 16 (4.7) | 23 (6.7) | 25 (7.3) | 7 (2.0) | 14 (4.1) | 6 (1.7) | 91 (26.5) |
| Skeletal Class II | 24 (7.0) | 19 (5.5) | 46 (13.4) | 5 (1.5) | 32 (9.3) | 76 (22.2) | 202 (58.9) |
| Total | 69 (20.1) | 52 (15.2) | 73 (21.3) | 18 (5.2) | 48 (14.0) | 83 (24.2) | 343 (100) |
| Both sexes | |||||||
| Skeletal Class III | 57 (12.4) | 25 (5.4) | 6 (1.3) | 8 (1.7) | 4 (0.9) | 1 (0.2) | 101 (22.0) |
| Skeletal Class I | 25 (5.4) | 26 (5.7) | 30 (6.5) | 10 (2.2) | 17 (3.7) | 8 (1.7) | 116 (25.2) |
| Skeletal Class II | 29 (6.3) | 20 (4.3) | 54 (11.7) | 9 (2.0) | 38 (8.3) | 93 (20.2) | 243 (52.8) |
| Total | 111 (24.1) | 71 (15.4) | 90 (19.6) | 27 (5.9) | 59 (12.8) | 102 (22.2) | 460 (100) |
b Unilateral disk displacement with reduction and normal contralateral TMJ.
c Bilateral disk displacement with reduction.
d Unilateral disk displacement without reduction and normal contralateral TMJ.
e Unilateral disk displacement with reduction and disk displacement without reduction in the contralateral TMJ.
Fig. 4 and Table 4 show the relationships between the severity of TMJ disk displacement and vertical skeletal deformities. Given that there was no significant difference between the sexes in the linear trend of TMJ disk displacement severity according to the FHR, the results of both sexes were combined. Although linear trends in the severity of TMJ disk displacement according to vertical skeletal deformities were less evident than those of sagittal skeletal deformities, trends in the severity of TMJ disk displacement from BN to bilateral DDNR (from groups 1 to 6) increased as vertical skeletal classes changed from hypodivergent to hyperdivergent deformities ( P < 0.01). This indicates that the severity of TMJ disk displacement is associated with different vertical skeletal deformities and that TMJ disk displacement is more prevalent in patients with a hyperdivergent deformity than those with a hypodivergent deformity or the normodivergent. As a result, bilateral DDNR was found to have the highest prevalence in patients with a hyperdivergent deformity, while BN had the highest prevalence in patients with a hypodivergent deformity.
