INTRODUCTION

Temporomandibular joint disorder (TMD) is a collective term embracing a number of clinical problems that involve the masticatory musculature, the temporomandibular joint (TMJ), and associated structures or both.1 Disk displacement (DD) with reduction (DDR) is frequently associated with a clicking sound, and DD without reduction (DDN) is often associated with limitation of jaw opening.2 Previous studies have suggested that DDN may progress to osteoarthritis in the TMJ.3–6

Autopsy studies in both young and mature adults show DD in 10–32% in the general population.78 Several studies have suggested that DD occurs in asymptomatic subjects with a prevalence ranging from 10–33%.9–15

A high prevalence of DD in asymptomatic volunteers (AVs) is not unique to the TMJ because magnetic resonance imaging (MRI) studies of asymptomatic subjects in the knee, cervical spine, and lumbar spine indicate similar disease prevalences in asymptomatic subjects.16–22 These studies demonstrate that DD can be present in patients without clinical signs and symptoms. On the other hand, it has been shown, that not all TMJ pain, clicking, and limited jaw motion can be related to DD in symptomatic patients. Paesani et al23 found that 78% of their symptomatic TMD sample had unilateral or bilateral DD whereas 22% had bilaterally normal TMJs. They also concluded that the structural difference between painful and nonpainful DD as seen on imaging studies is not yet clear.

DD has been suggested to affect skeletal morphology. Nebbe et al24 have suggested that adolescent female patients presenting for orthodontic treatment with bilateral DD show numerous angular and linear cephalometric differences compared with age-matched female controls. Nebbe et al25 also demonstrated that associations exist between subjects with DD and craniofacial morphology in a female adolescent sample. Turpkova et al26 investigated the amount of craniofacial asymmetry in female orthodontic patients with unilateral or bilateral TMJ DD compared with female controls without DD using frontal radiographs. They concluded that a female patient with unilateral or bilateral DD may present with or develop a vertical mandibular asymmetry.26 Schellhas et al27 and Dibbets et al28 suggested that there are morphologic changes in children with DD and symptoms, respectively. Brand et al,29 Bosio et al,30 and Gidarakou et al3132 have also suggested that DD might be associated with skeletal changes. Patients referred for orthognathic surgery are also found to exhibit a high prevalence of DD,533 and animal studies have suggested that there are arthrotic changes associated with surgically created DD.34–38 This study will evaluate AVs and symptomatic bilateral DD without reduction (BDDN) subjects presenting with localized jaw joint pain for skeletal and dental morphologic changes.

MATERIALS AND METHODS

Cephalometric measurements

Figure 1 shows the cephalometric points used. Tables 1– 5 summarize the angular and linear cephalometric measurements used in this study. These were categorized as cranial base measurements, profile analysis, denture base, dental pattern, and vertical relationship measurements.

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TABLE 1.  Cranial Base Measurements

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RESULTS

Tables 1–5 summarize the findings of the measurements. Table 1 demonstrates that the cranial base length (Ba-Na) was smaller in the BDDN group. In the profile analysis (Table 2) the facial plane angle was smaller and the angle of convexity larger in the symptomatic group. The only significant difference found in the denture base measurements was a smaller SNB angle as seen in Table 3. The overjet was increased in the BDDN subjects and that was the only significant difference found in the denture pattern measurements (Table 4).

TABLE 2.  Profile Analysis

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TABLE 3.  Denture Base Measurements

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TABLE 4.  Denture Pattern

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The measurements of the vertical relationships showed numerous differences (Table 5). There was a steeper mandibular plane angle, a more vertical (larger) Y-axis (S-Gn to FH angle), a shorter ramal height (Ar-Go), and an increased divergence of the palatal and mandibular planes (PP to MP angle) in the BDDN subjects. The significant measurements are shown in Figures 2–5.

TABLE 5.  Vertical Relationships

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DISCUSSION

A high prevalence of DD in AVs has been suggested. Westesson et al9 found 15% of their AVs to have unilateral DD using TMJ arthrography. Tallents et al10 in a study of evaluation of TMJ sounds in AVs found that 24% had one or two joints with DD as diagnosed by MRI. Ribeiro et al11 found the prevalence of DD in asymptomatic children and young adults to be 34%, whereas 86% of the symptomatic temporomandibular disorder patients had DD. Their results showed that 13.8% had bilateral symptomatic, but normal joints, 28% had unilateral DD, and 58% had bilateral DD. Kircos et al15 found similar results (32%) in AVs.

A high prevalence of DD in AVs is not unique to the TMJ. MRI studies of asymptomatic subjects in the knee, cervical spine, and lumbar spine indicate similar disease prevalences in asymptomatic subjects in those body parts as well.16–21 Brunner et al22 showed that half of the asymptomatic athletes included in the study had significant baseline knee MRI scan abnormalities. Oberg et al7 macroscopically examined the right TMJs of 155 cadavers of different ages regarding the shape, size, and appearance of the joint surfaces. They found that with increasing age the number of joints with local changes in the shape, remodeling, or arthritic changes of the articular surfaces increased. The arthritic changes were significantly more prevalent in women.

Previous studies have suggested that DDN may progress to osteoarthritis in the TMJ.3–5 Eriksson and Westesson4 suggested that DDR and DDN are two different entities and that DDN seems to be a more advanced condition and may in some cases be a precursor of osteoarthritis. Yamada et al6 have also suggested that there is a correlation between degenerative changes and DDN.

DD has been suggested to affect skeletal morphology.525–27 In this study we evaluated the effect of BDDN on the skeletal and dental pattern of the affected individuals. There was a smaller cranial base length (Ba-Na) in the BDDN group. In our study with BDDR we also found differences in the cranial base, namely shorter anterior (S-Na) and total (Ba-Na) cranial base lengths.31 Nebbe et al25 found a shorter posterior cranial base length and also a more acute cranial base angle, which was not significantly different in our group, but they did not clarify if their subjects had DD with or without reduction.

The mandible of the symptomatic subjects was retruded in relation to the forehead as seen by the smaller facial plane angle and the larger angle of convexity. The mandibular denture base was also retruded as demonstrated by the smaller SNB angle and there was increased overjet in our BDDN sample. These findings agree with previously published studies.

In our study of patients with BDJD, the affected individuals exhibited smaller facial plane angle and SNB angle but also smaller Lande's and SNA angles.32 Bosio et al30 found a smaller mean SNB angle in patients with bilateral DD compared with AVs. Schellhas et al27 in their study of children 14 years of age or younger concluded that TMJ derangements may contribute to the development of retrognathia, with or without asymmetry. Ninety-three percent of the retrognathic subjects were found to have DD, generally bilateral. Dibbets et al28 suggested that TMJ dysfunction might be associated with altered growth of the mandible and may cause retrognathia in children.

There were numerous significant differences in the vertical relationships. The mandibular plane angle was steeper, the Y-axis more vertical, the posterior ramal height (Ar-Go) was shorter, and there was a divergence of the palatal and mandibular plane indicative of posterior mandibular rotation in the symptomatic group. We found similar findings (steeper mandibular plane and shortened ramal height) in our study with BDDR patients and BDJD patients (steeper mandibular plane, decreased ramal height, divergence of mandibular plane to palatal plane).3132 Dibbets et al28 and Nebbe et al25 have also reported steeper mandibular plane and shorter ramal height in children and adolescents presenting with degenerative joint disease and DD, respectively. Nebbe et al25 also found an increased mandibular and palatal plane relative to sella-nasion and posterior rotation of the mandible.

Our study agrees with previous studies, which have suggested that DD can affect skeletal morphology and symmetry. The present study's findings are more severe than the findings of our previous study of BDDR patients31 and less severe than our findings of BDJD patients,32 which can be expected because DD may progress to DJD. Bosio et al30 also suggested that symptomatic TMD patients with BDD have a retropositioned mandible.

Link and Nickerson5 and Schellhas et al27 have suggested that there is a cause and effect relationship between DD and facial growth. Schellhas et al27 concluded that TMJ derangements are both common in children and may contribute to the development of retrognathia, with or without asymmetry. In cases of lower face asymmetry, the chin was uniformly deviated toward the smaller or more degenerated TMJ. They proposed that in the growing facial skeleton, DD either retards or arrests condylar growth, which results in decreased vertical dimension in the proximal mandibular segment(s) with ultimately mandibular deficiency or asymmetry.27 Nebbe et al25 have suggested that adolescent female patients presenting for orthodontic treatment with bilateral DD show numerous angular and linear cephalometric differences compared with age-matched female controls indicative of mandibular posterior rotation and retrognathia. Dibbets et al28 showed that children with symptoms of dysfunction formed a morphologically clearly recognizable group. Their profile was more Class II and had a shorter corpus and ramus with decreased posterior facial height. They concluded that TMJ dysfunction might be associated with the growth of the mandible.28 Brand et al29 indicated that patients with DD had significantly shorter maxillary and mandibular lengths compared with asymptomatic normal individuals with normal TMJs. That investigation did not distinguish between unilateral and bilateral DD and could not account for any asymmetries because the right and left landmarks in the cephalometric radiograph were averaged.

Trpkova et al26 investigated the amount of craniofacial asymmetry in female orthodontic patients with unilateral or bilateral TMJ DD compared with normal controls without DD using posteroanterior films. Female subjects with bilateral DD had significantly greater asymmetry in the vertical position of the antegonion. If the DD was more advanced on one side, then the ipsilateral ramus was shorter resulting in significant asymmetry of the mandible. The authors concluded that a female patient with unilateral or bilateral DD might present with or develop a vertical mandibular deficiency.26

Increased prevalence of DD has been found in patients with mandibular retrognathia presenting for orthognathic surgery. Link and Nickerson5 studied 39 patients referred for orthognathic surgery, 38 of who were found to have DD before surgery. All their open-bite patients and 88% of the patients with Class II malocclusion had bilateral DD. They suggested that DD may be a contributing factor in the development of dentofacial deformities and that new loading of deranged joints after orthognathic surgery may be a cause of a new arthrosis and skeletal relapse suggesting a progression of TMJ pathology. They suggested that DD should be suspected in individuals with sagittal mandibular deficiency, vertical ramus deficiency, or a unilateral sagittal deficiency. The high degree of association of DD with mandibular deficiency suggests that DD may have a role in causing these deformities. That is, loss of condylar height and/or growth secondary to the DD caused or worsened the horizontal or vertical ramus mandibular deficiency.5 Schellhas et al33 in their retrospective study of 100 consecutive orthognathic surgery candidates found that DD was prevalent especially in patients who exhibited change in their facial contour in the year before the evaluation. The degree of joint degeneration directly paralleled the severity of retrognathia. They concluded that TMJ DD is common in cases of mandibular retrusion and leads to the facial morphology in a high percentage of patients.

CONCLUSIONS

The results of this study show that alterations in skeletal morphology may be associated with BDDN. The skeletal differences are more pronounced in patients with BDDN than in patients with BDDR and less severe than in patients with BDJD as reported by Gidarakou et al3132 The present study agrees with previous studies suggesting that DD may affect the skeletal morphology and especially the mandibular position and rotation. The underlying mechanisms causing DD or the mechanisms that cause that skeletal alteration are yet to be identified. Because the present and previous studies suggest that BDDN may affect skeletal morphology and growth pattern, the clinician should be aware of these possibilities especially for the growing patient and the orthognathic surgery candidate.