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 is frequently associated with a clicking sound, and DD without reduction is often associated with limitation of jaw opening.2 Autopsy studies in both young and mature adults show DD in 10–32% of individuals in the general population.34 Several studies have suggested that DD occurs in asymptomatic subjects with a prevalence ranging from 10–33%.5–11

The interesting finding of a high prevalence of DD in asymptomatic volunteers (AVs) is not unique to the TMJ. Magnetic resonance imaging (MRI) studies of asymptomatic subjects in the knee, cervical spine, and lumbar spine indicate a similar disease prevalence in asymptomatic subjects.12–17 MRI studies have also shown DD to be common in knees of asymptomatic athletes.18 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 within the TMJ in symptomatic patients.19 Paesani et al20 studied 115 patients having signs and symptoms of TMD. Seventy-eight percent had unilateral or bilateral DD. Twenty-two percent had bilaterally normal TMJs. Paesani et al20 also concluded that the structural difference between painful and nonpainful DD, as seen in imaging studies, is not yet clear. Although there was radiologic evidence of DD in a significant proportion (78%) of the patients in their series, this does not necessarily indicate that DD is the source of the pain in every patient.

DD has been suggested to affect skeletal morphology. Nebbe et al21 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 al22 also demonstrated that associations exist between DD and craniofacial morphology in a sample of adolescent female subjects. Using posteroanterior films, a recent study investigated the amount of craniofacial asymmetry in female orthodontic patients with uni- or bilateral TMJ DD compared with female controls without DD. The authors concluded that a female patient with uni- or bilateral DD may present with or develop a vertical mandibular asymmetry.23 Schellhas et al24 and Dibbets et al25 suggested that there are morphologic changes in children with DD and symptoms, respectively.

Brand et al19 and Bosio et al26 also suggested that there are skeletal changes associated with DD. Patients referred for orthognathic surgery have also showed a high prevalence of DD,2728 and animal studies have suggested that there are arthrotic changes associated with surgically created DD.29–32 This study will evaluate AVs and symptomatic bilateral DD with reduction (BDDR) 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 through 5 summarize the angular and linear cephalometric measurements used in this study. These measurements were categorized as cranial base measurements, profile analysis, denture base, dental pattern, and vertical relationship measurements.

View Figure

• Download as Powerpoint
• Download Figure

TABLE 1.  Cranial Base Measurements Used in This Study^a

View Fullscreen

RESULTS

Tables 1 through 5 summarize the findings of the measurements. Table 1 demonstrates that there are cranial base differences between the two groups. The anterior (S-Na) and posterior (S-Ba) cranial base lengths were smaller for the BDDR group. The denture base measurements showed smaller values of the SNA and SNB angles (Table 3).

TABLE 3.  Denture Base Measurements Used in This Study^a

View Fullscreen

The dental characteristics demonstrated that the interincisal angle was larger, the upper incisor was more retroclined, and the lower incisor was more retruded (L1 perpendicular to A-Pog) in the BDDR sample (Table 4). No significant differences were found in the profile analysis (Table 2) or in the vertical pattern (Table 5). The significant measurements are shown in Figures 2 and 3.

TABLE 4.  Denture Pattern Used in This Study^a

View Fullscreen

TABLE 2.  Profile Analysis Used in This Study^a

View Fullscreen

TABLE 5.  Vertical Relationships Used in This Study^a

View Fullscreen

View Figure

• Download as Powerpoint
• Download Figure

View Figure

• Download as Powerpoint
• Download Figure

DISCUSSION

DD is quite prevalent in the asymptomatic population. Using TMJ arthrography, Westesson et al5 found that 15% of their AVs had unilateral DD. Tallents et al,6 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 al7 found that the prevalence of DD in asymptomatic children and young adults was 34%, whereas the prevalence of DD was 86% in symptomatic TMD patients. Their results showed that 13.8% had bilateral symptomatic but normal joints, 28% had unilateral DD, and 58% had bilateral DD. They suggested that DD is relatively common in AVs. Similar results (32%) in AVs were found by Kircos et al.11 The interesting finding of a high prevalence of DD in AVs is not unique to the TMJ. MRI studies of the knee, cervical spine, and lumbar spine in asymptomatic subjects indicate a similar disease prevalence in those body parts as well.12–17 Brunner et al18 showed that half of the asymptomatic athletes included in the study had significant baseline knee MRI scan abnormalities. Oberg et al3 macroscopically examined the shape, size, and appearance of the joint surfaces in the right TMJs of 155 cadavers of different ages. They found, among other things, that below the age of 20 years, all TMJs appeared normal, but 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. DD has been suggested to cause facial asymmetry.22–2427

In this study we evaluated the effect of BDDR on the skeletal and dental pattern of the affected individuals. Both anterior (S-Na) and posterior (S-Ba) cranial base measurements were smaller in the BDDR group. This finding agrees with that of Nebbe et al.22 They also found a more acute cranial base angle, which was not significantly different in our group, but did not clarify whether their subjects had DD with or without reduction. Both SNA and SNB angles were smaller in our symptomatic group. This can be attributed to the smaller linear measurement of the anterior cranial base, which positions point Nasion more posteriorly. Bosio et al26 also found a smaller mean SNB angle in patients with bilateral DD than in AVs. The SNB angle determines the mandibular position in relation to the anterior cranial base. The mean SNB angle is smaller in subjects with DD; thus, one could speculate that the mandible is retropositioned as a result of anterior displacement of the articular disk. Bosio et al26 did not find any significant differences among the three groups in the facial plane angle, which also shows the position of the mandible. Our profile analysis (Table 2) also showed no difference in the facial plane angle. This suggests that the smaller SNB angle can be attributed to the shorter anterior cranial base rather than to a retropositioned mandible.

There were significant differences in the denture pattern. The interincisal angle was larger. The inclination of the lower incisor was within the normal range, but the upper incisor was retroclined. This suggests that the larger value of the interincisal angle in the symptomatic group can be attributed to the altered upper-incisor inclination. The clinical significance of this finding is unknown.

Our study agrees with previous studies, which have suggested that DD can affect skeletal morphology and symmetry. Link and Nickerson27 and Schellhas et al24 have suggested that there is a cause-and-effect relationship between DD and facial growth. Nebbe et al22 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. There was an increased mandibular and palatal plane relative to Sella-Nasion, posterior rotation of the mandible, a decrease in Ricketts' facial axis, reduced posterior facial height and ramal height, as well as a slight increase in middle anterior facial height and a decreased posterior cranial base height.22

Schellhas et al24 in their study of children 14 years of age or younger concluded that TMJ derangements are common in children and 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. 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), ultimately causing mandibular deficiency or asymmetry.24 Dibbets et al25 performed morphometric analyses on children with TMJ symptoms and considered the different symptoms of TMJ dysfunction as indicators of specific growth patterns. They showed that children with symptoms of dysfunction formed a morphologically clearly recognizable group. These children had a profile close to that for Class II and had a shorter corpus and a ramus with decreased posterior facial height. Dibbets et al25 concluded that TMJ dysfunction might be associated with the growth of the mandible. Brand et al19 indicated that patients with DD had significantly shorter maxillary and mandibular lengths, compared with those of asymptomatic normal individuals with normal TMJs. Their 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. Bosio et al26 suggested that symptomatic TMD patients with bilateral DD had a retropositioned mandible indicated by a smaller mean SNB angle compared with AVs and symptomatic patients with no DD. Using posteroanterior films, another study investigated the amount of craniofacial asymmetry in female orthodontic patients with uni- or bilateral TMJ DD compared with normal controls without DD.23 Females 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 uni- or bilateral DD might present with or develop a vertical mandibular deficiency.23

Increased prevalence of DD has been found in patients with mandibular retrognathia presenting for orthognathic surgery. Link and Nickerson27studied 39 patients referred for orthognathic surgery, 38 of whom 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; ie, loss of condylar height or growth (or both) secondary to the DD caused or worsened the horizontal or vertical ramus mandibular deficiency.27 Schellhas et al,28 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 that it leads to alterations in the facial structure in a high percentage of patients.

CONCLUSIONS

The results of this study show that alterations in skeletal morphology may be associated with DD. The severity of these alterations does not seem to be as extensive as the ones demonstrated by Nebbe et al21 and Schellhas et al24 who evaluated patients with severe degenerative joint disease. Longitudinal studies will shed some light on that aspect. The mechanisms by which DD is produced, or the mechanisms that cause that skeletal alteration, are yet to be clarified. This study and the studies mentioned suggest that DD 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.