Comparison of Skeletal and Dental Morphology in Asymptomatic Volunteers and Symptomatic Patients with Unilateral Disk Displacement with Reduction

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 with reduction (DDR) is frequently associated with a clicking sound, and DD without reduction (DDN) is often associated with the limitation of jaw opening.2 Previous studies have suggested that DDN is a more advanced stage of pathology in the TMJ and may progress to osteoarthritis.3–6 

Autopsy studies in both young and mature adults show DD in 10–32% of the general population.7,8 Several studies have suggested that DD occurs in asymptomatic subjects with a prevalence ranging from 10% to 33%.9–15 The reported high prevalence of DD in asymptomatic volunteers (AV) is not unique to the TMJ. 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 in symptomatic patients can be related to DD within the TMJ. Paesani et al23 studied 115 patients with signs and symptoms of TMD and found that 78% had unilateral or bilateral DD (UDD or BDD) but 22% had bilaterally normal TMJs.

DD has been suggested to affect skeletal morphology. Nebbe et al24 suggested that adolescent female patients presenting for orthodontic treatment with BDD show numerous angular and linear cephalometric differences compared with aged-matched female controls. Nebbe et al25 and Trpkova et al26 also demonstrated that associations exist between subjects with DD and craniofacial morphology in an adolescent sample of female orthodontic patients. Schellhas et al27 and Dibbets et al28 suggested that there are morphologic changes in children with DD and symptoms, respectively. Recently, Henrikson et al29 demonstrated that subjects with Class II malocclusions have an increase in TMD symptoms compared with subjects with a normal occlusion. In fact, 87% of the Class II sample had a horizontal overlap of more than four mm, suggesting a sagittal growth discrepancy.

Brand et al,30 Bosio et al,31 and Gidarakou et al32 also suggested that there are skeletal changes associated with DD. Patients referred for orthognathic surgery have also shown a high prevalence of DD,5,33 and animal studies have suggested that there are morphologic changes associated with surgically created DD.34–38 UDD may be associated with skeletal asymmetry as shown by clinical39 and animal studies.38,40 

MRI was used in this study to validate the presence or absence of DD. Roberts et al41 demonstrated that the ability to predict the presence or absence of DD in patients has a sensitivity and specificity of 59% and 38% for symptomatic normals, 60% and 66% for DDR, and 58% and 76% for DDN, respectively. This would suggest that the ability to predict DD is low and the number of false-positive andfalse-negative examinations is high. This study will evaluate AV and symptomatic subjects with UDD with reduction (UDDR) presenting with localized jaw joint pain for skeletal and dental morphologic changes.

The parent database included 46 Caucasian female AV and 202 Caucasian consecutive symptomatic female temporomandibular disorder patients who answered a solicitation posted at the University of Rochester and Eastman Department of Dentistry. The symptomatic TMD patients included 42 symptomatic but normal patients, 18 patients with UDDR, 12 with UDDN, 59 with BDDN, 32 with BDDR, and 29 with BDDN with degenerative joint disease.

This study included 46 Caucasian normal female AV and 18 Caucasian symptomatic age-matched women with UDDR included in this study.

The mean age of the AV subjects was 28.3 ± 6.7 years, whereas the mean age of the symptomatic subjects was 29.2 ± 10.7 years. All study participants were examined in the Division of Orthodontics and were not seeking orthodontic care. They read and signed an informed consent before the study initiation that was approved by the Research Subjects Review Board of the University of Rochester School of Medicine and Dentistry.

The AV were examined by one investigator (RHT) and were accepted in the study after completion of the following:

• A TMJ subjective questionnaire documenting the absence of jaw pain, joint noise, locking, and positive history of TMD

• A clinical TMJ and dental examination for signs and symptoms commonly associated with TMD or internal derangement. All symptomatic subjects had localized jaw joint pain and pain on movement or when eating. Vertical opening and right and left mandibular movements were measured and recorded. The masseter, anterior, middle and posterior temporalis, and temporalis tendon area were digitally palpated. All AV demonstrated a maximal opening of at least 40 mm. The asymptomatic and symptomatic subjects were not blinded to the examiner. There were no volunteers with complete or removable dentures or fixed partial dentures. Nineteen percent of the asymptomatic subjects and 25% of the symptomatic patients had one or two missing posterior teeth. The prevalence of previous orthodontic treatment was 37% in the volunteers and 25% in the symptomatic TMD subjects.

• All study participants had bilateral high-resolution MRI scans in the sagittal (closed and open) and coronal (closed) planes to evaluate the TMJs as described by Katzberg et al42 and Westesson et al.43 Each study participant was classified as AV or symptomatic BDDR.

• All study participants had lateral cephalograms with the teeth in centric occlusion position and with Frankfort horizontal parallel to the floor. All cephalograms were taken at the Orthodontic Clinic on the same radiographic machine set for standardized exposure.

There are no statistically significant differences among skeletal, denture base, and dental characteristics of symptomatic UDDR patients compared with a sample of individuals with bilateral normal asymptomatic TMJs.

Figure 1 shows the cephalometric landmarks 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. The examiner was blinded as to whether the films were from an AV or symptomatic TMD subject.

The analysis of variance was used to reveal any statistically significant differences between the control group and the experimental group. All subjects were matched for age. The P value was calculated for each of the variables with a level of significance for each test established at .05. There was no power analysis performed because this would require preliminary data.

Errors in landmark localization during tracing were evaluated by retracing 20 cephalograms in the experimental and control groups. The reliability of tracing, landmark identification, and analytical measurements had an intraclass correlation coefficient greater than 0.92.

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 (Ba-S) cranial base lengths were reduced for the UDDR group. The cranial base flexure was more obtuse in the symptomatic group. SNA and SNB were smaller in the UDDR group (Table 3). These two denture base measurements demonstrate that both the maxillary and the mandibular denture bases were retruded in the symptomatic group. The measurements of the vertical relationships showed a shorter ramal height in the UDDR subjects (Table 5). No significant differences were found in the profile analysis and the denture base measurements and the denture pattern. The significant measurements are shown in Figures 2 through 4.

There is quite a high prevalence of DD in the asymptomatic population. Westesson et al9 found 15% of their AV to have UDD using TMJ arthrography. Tallents et al10 in a study of evaluation of TMJ sounds in AV found that 24% had one or two joints with DD as diagnosed by MRI. Kircos et al15 found a 32% prevalence of DD in AV. 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 UDD, and 58% had BDD. They suggested that DD is relatively common in AV (34;pc).

A high prevalence of DD in AV 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 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 with respect to the shape, size, and appearance of the joint surfaces. They found that with increasing age, the number of joints with local changes in 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 altered skeletal morphology.5,25–27,31,32 In this study, we evaluated the effect of UDDR on the skeletal and dental pattern of the affected individuals. There were significant cranial base differences between the two groups. Both anterior (S-Na) and posterior (Ba-S) cranial base measurements were smaller in the UDDR patients. The cranial base flexure was more obtuse, as shown by the increased value of the Ba-S-Na angle. This agrees with Nebbe et al,25 who found decreased Ba-Na length. In our study of UDDN and BDDR, both S-Na and Ba-Na measurements were smaller.32 Thus, there are skeletal alterations in the cranial base of symptomatic patients with DD, with or without reduction.

We found retrusion of the upper and lower denture bases (smaller SNA and SNB angles, respectively). This finding agrees with our previous studies on BDDR32 and bilateral degenerative joint disease32 (BDJD) patients, where both the previously mentioned angles were smaller compared with asymptomatic normal individuals. However, in the BDJD patients there was a significantly larger ANB angle because of a more retropositioned point B (I. K. Gidarakou et al, in preparation). Bosio et al31 also found a smaller mean SNB angle in patients with BDD compared with AV. On the contrary, in our study of UDDN, we found no significant differences for the SNA and SNB angles (I. K. Gidarakou et al, in preparation).

There were also significant differences in the vertical relationships. The posterior ramal height (Ar-Go) was shorter in the symptomatic group. We did not distinguish the left from the right side, but we may attribute the shortness of the posterior ramal height to the DD. This agrees with our previous studies on BDDN, BDJD, and UDDN patients (I. K. Gidarakou et al, in preparation). The previously mentioned groups with BDD or UDD (BDDN, BDJD, and UDDN) showed reduced ramal heights. These patients (UDDN, BDDN, and BDJD) showed more significant differences in addition to the reduced ramal height (I. K. Gidarakou et al, in preparation). For example, the mandibular plane was steeper in all three groups of symptomatic patients. We can then speculate that the patients with UDDR exhibit the least vertical changes as compared with the patients with UDDN, BDDN, and BDJD because the alterations in their TMJs are not that severe. Dibbets et al28 and Nebbe et al25 have also reported shorter ramal heights in children and adolescents presenting with degenerative joint disease and DD, respectively. Animal models with DD also showed reduced ramal height. Shortening and flattening of the condylar head with loss of posterior height have been demonstrated in the growing rabbit after unilateral surgically created DD.38,40 Legrell et al40 found that rabbits with surgically created UDD exhibited a deviant growth pattern and mandibular asymmetry. They concluded that UDD can cause mandibular asymmetry in growing rabbits, including shortening of the ramus and excessive vertical growth along the lower mandibular border and the gonial angle region. This agrees with the clinical study by Trpkova et al,26 who 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. Women with BDD 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 UDD or BDD may present with or develop a vertical mandibular asymmetry. Tallents et al39 studied 12 consecutive patients presenting with facial asymmetry thought to represent unilateral condylar hyperplasia. However, half these patients were found to have UDD occurring on the short side. Therefore, the clinician should be aware of the possibility of the presence of DD in asymmetric patients.

Our study agrees with previous studies that have suggested that DD can affect skeletal morphology and symmetry. Link and Nickerson5 and Schellhas et al27 have suggested that there is a cause and effect relationship between DD and facial growth. Nebbe et al25 have suggested that adolescent female patients presenting for orthodontic treatment with BDD show numerous angular and linear cephalometric differences compared with aged-matched female controls. There was an increased mandibular and palatal plane relative to sella-nasion, posterior rotation of the mandible, a decrease in Rickett's 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.25 Schellhas et al27 in their study of children 14 years or younger 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 mandibular deficiency or asymmetry occurring ultimately.27 Dibbets et al28 showed that children with symptoms of dysfunction form a morphologically clearly recognizable group. Their profile was more Class II, and they had a shorter corpus and ramus and exhibited decreased posterior facial height. They concluded that TMJ dysfunction might be associated with the growth of the mandible.28 Brand et al30 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 UDD and BDD and could not account for any asymmetries because the right and left landmarks in the cephalometric radiograph were averaged.

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 whom were found to have DD before surgery. All their open-bite patients and 88% of the patients with Class II malocclusion had BDD. 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 or growth secondary to the DD caused or worsened the horizontal or vertical ramus mandibular deficiency.5 Schellhas et al,33 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.

The results of this study show that alterations in skeletal morphology may be associated with UDDR. This finding agrees with previous studies. The mechanisms by which DD is produced, or the mechanisms that cause that skeletal alteration, are yet to be clarified. We found altered skeletal morphology in our symptomatic sample with UDDR. Other studies have also demonstrated that DD may cause facial asymmetry. This study and the studies mentioned suggest that UDDR may affect the skeletal morphology, symmetry, and growth pattern of the affected individual. The clinician should be aware of these possibilities, especially while treating children and orthognathic surgery candidates.