Mandibular Asymmetry in Adult Patients with Unilateral Degenerative Joint Disease

Various pathological conditions that affect the temporomandibular joint (TMJ) can manifest themselves as facial asymmetries, including congenital disorders such as hemifacial microsomia,1–3 condylar hyperplasia,4,5 internal derangements (ID),6,7 rheumatoid arthritis,8,9 and osteoarthritis.9–13 Osteoarthritis or degenerative joint disease (DJD) is primarily a noninflammatory disorder of diarthrodial joints characterized by deterioration and abrasion of the articular cartilage and the underlying bone.14,15 

A potential relationship between TMJ-ID and facial growth aberrations resulting in mandibular asymmetry or retrognathia has been previously suggested.10,16,17 Although the etiology of skeletal asymmetry is not well understood, it has been suggested that advanced joint degeneration may lead to shortening of the condyle with subsequent skeletal asymmetry.10,18 Inui et al7 studied facial asymmetry on frontal cephalometric radiographs in adult female patients (mean age = 23.6) with signs or symptoms of TMJD and reported that the degree of the disc displacement was significantly related to the cant of the occlusal and mandibular plane, indicating reduced vertical dimension of the posterior occlusal level and ramal height ipsilateral to the ID. Trpkova et al6 also reported using frontal radiographs that female subjects studied with bilateral TMJ-ID had significantly greater asymmetry in the vertical position of the antigonion. In the last two studies,6,7 the asymmetry was correlated to the position of the disc.

This retrospective study evaluated the effect of unilateral TMJ DJD (UDJD) on the facial symmetry. The results were compared with asymptomatic volunteers (AVs) having bilateral normal joints.

This study included 20 (11 men and nine women) AVs without disc displacement and 20 (five males and 15 females) patients with UDJD (Table 1). The diagnosis for both samples was based on magnetic resonance imaging (MRI) and clinical examination. The AV group was selected from a larger sample that included asymptomatic subjects with and without disc displacement and this has been used in previous studies.16 The mean age was 29.6 years for the AV group and 32.6 years for the UDJD group. All study participants read and signed an informed consent that was approved by the Research Subjects Review Board of the University of Rochester, School of Medicine and Dentistry.

The AVs were examined by one investigator and were accepted in the study after completion of (1) a TMJ subjective questionnaire documenting the absence of jaw pain, noise, locking, or positive history of temporomandibular disorder (TMD) and (2) a clinical and dental examination for signs and symptoms commonly associated with TMD or ID.

The patients with the DJD presented in the clinic with TMD symptoms including pain and limited opening.

All study participants had bilateral high-resolution MRI scans in the sagittal (closed and opened) and coronal (closed) planes to evaluate the TMJs as described by Katzberg et al19 and Westesson et al.20 The two readers used established criteria for DD and were blinded as to group (AV, symptomatic DJD) and clinical information. The patients with unilateral DJD joints had flattening of the condylar head or osteophyte formation. Each study participant was classified as AV or UDJD.

Posteroanterior (frontal) cephalometric radiographs were used to evaluate lower facial asymmetry in all research subjects. These were obtained with the head positioned such that the Frankfurt horizontal plane was oriented parallel to the floor and the mandible was at centric occlusion. The radiographs were traced on acetate paper. Standard cephalometric landmarks were identified, and reference lines were drawn as demonstrated previously by Sassouni,21 Subtelny,22 Grummons and Kappeyne,23 and Laspos et al24,25 taking under consideration the reproducibility of the landmark identification as reported by Major et al26 and the validity of reference lines by Trpkova et al.27 The landmarks and reference lines used are shown in Figure 1.

The following measurements were assessed:

• Vertical asymmetry: the difference of the perpendicular distances of ag and ag′, na and na′, ma and ma′, ju and ju′, mo and mo′, za and za′ from LOL′ named DAGV, DNAV, DMAV, DJUV, DMOV, DZAV, respectively.

• Horizontal asymmetry: the difference of the perpendicular distances of ag and ag′, na and na′, ma and ma′, ju and ju′, mo and mo′, za and za′, from LOM named DAGH, DNAH, DMAH, DJUH, DMOH, DZAH, respectively.

The difference between the right (R) and left (L) side for all the measurements was used. The difference (L − R) was negative when R > L.

Also, the angle formed by the LOM and the line connecting the midpoint of lo and lo′ and the me named degree of mandibular lateral displacement (Me angle) was measured to confirm the mandibular (me) shifting.

Bilateral full profile mandibular laminographs were used to assess mandibular asymmetry in all the individuals. These were obtained at 25 degrees with a Quint Sectograph. The center cut laminograph was selected for measurement. Laminagraphic films were traced, and the lines drawn are shown in Figure 2. Total ramal height (RamH) was defined as the length on the line tangent to the posterior margin of the ramus from the intersection with the perpendicular to the summit of the condyle and the mandibular plane. Condylar height (ConH) was defined as the length from the intersection with the perpendicular originated from the deepest point of the sigmoid notch to the intersection with the perpendicular to the summit of the condyle. The gonial angle (GoAngle) (defined by lines 1 and 2) was also measured. The depth of the antegonial notching (notch) was measured as the distance from the deepest point of the notch perpendicular to the tangent of the lower border of the mandible. The difference between the right (R) and left (L) side for all the measurements (DRamH, DConH, DGoangle, and Dnotch) was used. The difference (L − R) was negative when R > L.

The two-way analysis of variance was used to reveal any significant differences between three groups (the controls, patients with left and patients with right TMJ DJD) and between the men and women. The P value was calculated for each of the variables with a level of significance set P < .05.

All the measurements were performed by one investigator (Dr Kambylafkas). To evaluate intraexaminer reliability, the records of 10 subjects were fully analyzed twice with a one week interval, and the intraexaminer correlation coefficient was calculated to be satisfactory (r > .9) for all the measurements performed in this study.

There were no significant differences between men and women for any of the mean values of the measurements that were used.

No significant differences between the groups were found for the vertical measurements. No significant differences between the controls and the patients with right joint DJD were observed for the horizontal measurements. However, comparison of AVs with patients having left DJD revealed the differences for the following measurements: the antegonion horizontal (dagh), the deviation of the menton (me) and the mandibular dental midline (InsI), and the mandibular asymmetry degree angle (MeDe). The cant of the occlusal plane, as evaluated by the vertical distance of the point mo (first mandibular molar), was not significantly different between the AV and the UDJD groups (Table 2).

No significant difference was found between the groups for the total ramal height asymmetry. However, the difference for the condylar height and the depth of the mandibular notching between the patients with left TMJ DJD and the controls was significant. The condylar height was found decreased on the affected side. The antegonial notching was deeper in the affected side. No significant differences were found between the subjects with the right TMJ affected and the controls (Table 3).

Many studies have previously suggested that a correlation exists between TMJ-ID and mandibular asymmetry.6,7 IDs may present with or without condylar remodeling.28–31 ID has often been associated with condylar resorption and has been known to affect the mandibular growth.32–34 However, patients may have a mandibular deficiency without disc displacement, and patients with normal mandibular growth commonly have disc displacement. Therefore, it is difficult to assign a cause and affect relationship for disc displacement and mandibular growth deficiency.35 

Adult patients with a hypoplastic or deformed condyle with DJD have been reported to demonstrate deviation of the chin toward the affected side.36 It has also been proposed that preexisting asymmetry can either camouflage or exaggerate any reduction or lack of condylar growth in the TMJ.6 In our study, the group with the right side affected did not exhibit significant differences compared with the controls. An individual with right side dominance and right TMJ DJD may actually present “correction” and even “overcorrection” of the natural asymmetry. If the left side (the small side) is affected the asymmetry will be magnified and probably will be clinically detected.

In this study, no significant asymmetry for the total ramal height was found. However, significant asymmetry in condylar height was demonstrated by the laminographs for the patients with the left DJD. Although the condylar height is reduced because of the degenerative lesions, the total ramal height is not affected or is less affected because of the compensatory mechanism taking place at the gonial angle.33,37–40 

This study suggests that symptomatic adults with unilateral DJD may have remarkable mandibular notching on the affected side. The formation and the depth of the antegonial notching have been suggested to be affected by the amount and direction of the mandibular growth.32,41,42 Dibbets et al43 reported the formation of an antigonial notch in children with a flattened condylar head. The increased depth of the antigonial notch on the side with degenerative disease can be either the result of aberrant growth42 or the result of adaptive remodeling on the gonial angle.32 Mandibular asymmetry can be developmental or acquired.44 In our study, only adult individuals of both sexes participated. One problem in this study, which is a common problem in adult studies, is that the time of the onset of the ID and the arthritic lesions is unknown.

In our study, the vertical measurements were not significantly different for the UDJD group compared with the bilateral normal subjects. A possible explanation is that the changes may have taken place in the mandibular fossa and the cranial base. Among the possible compensatory mechanisms taking place in joints with DJD is the thickening of the roof of the glenoid fossa, which is observed to increase progressively from normal joints to joints with disk displacement and degenerative disease.45 Moreover, in growing rabbits surgically induced disc displacement may result in cranial base asymmetries.46 Lower face asymmetry is the result of three-dimensionally differential growth or changes between the left and right side and can be attributed to the mandible or the cranial base.

The purpose of this study was to compare subjects with unilateral degenerative disease with subjects having normal TMJs as diagnosed by MRI. Treatment planning for orthodontic treatment of adults with degenerative disease and compensatory adapting mechanisms is a problem because surgical treatment may be necessary to treat the transverse asymmetry. In many cases, asymmetry is camouflaged by adapting mechanisms. In some cases, asymmetry is evident and must be an alert for the clinician to diagnose the underlying etiology. The unilateral DJD is a possible differential diagnosis associated with mandibular asymmetry, and in this case further investigation for a more accurate diagnosis and successful treatment is recommended.

The results of this study suggest that the UDJD may be associated with lower face asymmetries in certain cases. Factors like the dominant mandibular side and the side affected by the disease as well as compensatory adaptive mechanisms may mask this asymmetry in adults. The clinician must be aware of this and include the DJD as a possible diagnosis when treatment is to be provided to individuals with mandibular asymmetry.