Abstract:

The presence of intracapsular conditions have been associated to the morphology of the upper joint compartment. Several authors have suggested that a steep articular eminence is a predisposing factor for TMJ disc displacement, but recent studies have failed to confirm this relationship. To be able to quantitatively compare the shapes of biological bodies, a method is needed for cataloguing the forms under consideration. This can be done using different techniques. The choice of the type of method to be used for analytical purposes depends upon the nature of the biological object under study.

Several morphometric methods have been proposed for the analysis of biologic objects homologous variables: Metric distances, area, angles and ratios can be calculated for the left and right sides separately, and the difference between homologous measurements will supply information about the dominant side.

Characteristic like mandibular asymmetry and condylar asymmetry have been evaluated, but articular eminence shape symmetry and its relationship with temporomandibular disorders have not been investigated.

The purposes of this study were to determine symmetry based on the articular eminence shape of the TMJ using four different morphometric methods and to evaluate the relationship between articular eminence symmetry with temporomandibular disorders clinical characteristics and jaw function among subjects with or without disc displacement with reduction.

A total of thirty four (34) subjects participated in this study. Inclusion criteria were: generally healthy intact dentitions without large restorations or large interdental spaces.

Exclusion criteria were: arthritides, orofacial pain, gross asymmetries in clinically observable craniomandibular anatomy, and pregnancy as determined by medical histories and examination. Confirmation of clinical status was determined by a calibrated examiner using the Research Diagnostic Criteria for temporomandibular disorders. Subjects who met inclusion and exclusion criteria were categorized according to position of the TMJ discs as determined by a calibrated radiologist using magnetic resonance images.

Each subject was seen for three appointments. Prior the first appointment, subjects had an MRI which was examined by a medical radiologist for diagnosis of healthy joint or TMJ disc displacement. At the first visit a screening exam was performed in which the RDC/TMD was applied to identify the status of the TMJ. Using this information, in combination with MRI results, subjects were placed into one of the following two categories: Controls (no TMJ disc displacement and no myofascial pain), and TMJ disc displacement with no myofascial pain.

Also during the first appointment the following records were made: impressions of maxillary and mandibular teeth for plaster models to fabricate the jaw tracking appliance. Second and third appointments involved jaw tracking and were scheduled at least one day apart.

Linear regression, asymmetry index in percentage, Asymmetry Based Gradient for the Variable I (ABGi) in mm, and Euclidean distance analysis were calculated for all subjects to determine symmetry and based on results the Euclidian distance method was selected as the tool to be use to evaluate articular eminence shape symmetry/ asymmetry and its relation with the presence of clinical characteristics of TMD. Using the Euclidian distance method, five subjects of our study population showed differences in left-right eminence shapes.

Means and standard deviations for age between symmetric and asymmetric subjects were calculated. No significant effect was shown in age among these two groups ( p -value <0.05). Among the symmetry individuals, 48% had normal positioned disc, and 52 % had disc displacement. In the asymmetric group, 80% presented with disc displacement, while 20% had normal disc position. No statistical significance was found among the groups ( P = 0.355, Fisher's exact test). Evaluation of the presence of disc displacement among symmetric and asymmetric subjects showed that disc displacement occurred more frequently in asymmetric individuals, but a greater sample size is needed in order to confirm this relationship.

Vertical and horizontal range of motion were evaluated and no significance difference was found in any movement between symmetric and asymmetric subjects ( p -value <0.05). No difference among symmetric and asymmetric individuals related with the presence of click sounds during vertical and horizontal movements was found in our study. Most of the symmetric and asymmetric individuals presented with 3 click sounds during these movements. In terms of crepitus sounds, no crepitus was detected on the asymmetric group during opening and closing.

The Jaw Functional Limitation Scale was used to evaluate jaw function. No significant difference was found among symmetric and asymmetric individuals related with common behaviors performance as talking, chewing, yawning, etc