Temporomandibular joint (TMJ) disorders may show non-specific clinical presentations, and diverse conditions may be responsible for the patient’s symptoms. The conditions affecting the TMJ can be classified into three groups: (1) muscle disorders, (2) disc displacements and (3) joint pain, arthritis, and arthosis. TMJ disc displacement has been defined as an abnormal relationship between the articular disc and the mandibular condyle, articular fossa, and eminence. Signs and symptoms associated with TMJ disorders affect between 4% and 28% of the adult population and tend to occur more often in women.

Classification of the disc location in the closed mouth position (CMP) may be based on a clock-hands analogy. The disk is considered to be in its normal position when the thicker portion of its posterior band lies on the uppermost portion of the condyle, i.e. between 11 and 1 o’clock in relation to the condyle. Discs in a position between 9 and 11 o’clock are considered displaced.

Magnetic resonance imaging (MRI) is currently the best imaging modality for the evaluation of disc position. With this method, it is possible to visualize soft tissue and joint structures, allowing better understanding of sources of pain and eventual discrepancies between other imaging findings and clinical symptoms. MRI has been considered the gold standard for the study and diagnosis of soft tissue components of TMJ.

The position and morphology of the components of the TMJ are of great importance in the diagnosis of TMJ disorders. Several parameters can be used to evaluate the relationship between the mandibular condyle, articular fossa, and disc. These parameters include subjective criteria for articular spaces, the position of the condyle in the articular fossa, the horizontal angle of the condyle, and the slope of the articular eminence.

This study assessed the correlation between biometric parameters of anatomic structures of the TMJ not fully explored previously and articular disc displacement, using MRI, in patients with and without joint pain.

Materials and methods

The study was approved by the Human Research Ethics Committee of the Federal University of Bahia, Brazil (reference No. 0022036800010). Two hundred consecutive exams from patients referred to a private diagnostic imaging clinic for bilateral MRI of the TMJ during the period from May to September 2011 were included in the sample. Exclusion criteria included the presence of TMJ bony pathologies and patients aged less than 18 years. Gender and the presence of joint pain, i.e. as reported by the patient, were registered according to information in the patient records. Oblique parasagittal sections were obtained and corrected by the horizontal angulation of the condyle, in both the open mouth position (OMP) and the CMP. A Signa MR system (General Electric, Milwaukee, WI, USA) was used, operating at 1.5 T with a 6 × 8-cm bilateral surface coil, in the supine position, with the sagittal plane perpendicular to the horizontal plane, and the Frankfort plane parallel to the opening of the scanner. A 256 × 256 matrix was used, 145-mm field of view, and pixel size of 0.60 mm × 0.57 mm. Ten slices, 2-mm thick, were obtained for each TMJ using a T1 sequence. For the acquisition of OMP images, a device (Burnett TMJ device, TMJ-200s/n 0650; Medrad, Pittsburgh, PA, USA) was used to keep the mouth open during the examination.

The examinations were assessed by an oral and maxillofacial radiologist with over 10 years’ experience in MRI for TMJs. Criteria described by Katzberg and Westesson and adapted by Milano et al. were followed. Joints were then grouped, according to their diagnosis, as in a normal position or as disc displacement ( Fig. 1 ). Patients were grouped according to the presence of disc displacement: no disc displacement, unilateral displacement, and bilateral displacement. Furthermore, in the OMP, normal or abnormal disc position was registered.

MRI sagittal images of TMJs displaying the hyposignal areas (arrows) corresponding to the anterior (a) and posterior (p) bands of the articular discs. The disc is in its normal position in A, and disc displacement is observed in B. Note that cortical bone is seen as dark areas (hyposignal) in MRI T1 images.

The images were then submitted to two previously calibrated independent observers who performed linear measurements of the condyles using a computer program (Centricity DICOM Viewer, version 2.2, 2004, GE Medical Systems). Measurements were performed in optimal environmental conditions in three different sessions. The right and left TMJs of each patient were assessed sequentially, in the same sessions. All measurements were then repeated, with at least a 2-week interval between each measurement session. Inter-rater agreement was measured according to Lin’s concordance correlation coefficient.

The most central area of the mandibular condyle was selected to assess the biometric parameters of the structures. The antero-posterior lengths of the condyle at the lateral pole (D1L) and medial pole (D1M) were measured in the axial plane. The transverse length of the condyle (D2) was measured in the coronal plane ( Fig. 2 ).

(A) MRI axial image of the right mandibular condyle, identifying the medial and lateral regions where D1L and D1M were measured. (B) MRI coronal image of the TMJ, showing the extent of D2 in the left mandibular condyle.

Statistical analyses were used to assess potential differences in measurements among TMJ diagnoses and patient groups, i.e. disc displacement ( t -test and ANOVA, respectively), disc position in the OMP ( t -test), and gender ( t -test). Additionally, the χ ² test was used to compare the presence of pain among groups. The significance level was set at 0.05.