Temporomandibular disc direction and shape: a cross-sectional study in adolescents

OBJECTIVES: The aim of this retrospective cross-sectional study was to analyze the temporomandibular joint (TMJ) disc direction and shape among adolescents with temporomandibular disorders (TMD), and  to evaluate its relationship with bilaterality and with the capacity of reduction in mouth opening, through an evaluation of Magnetic Resonance Imaging (MRI), with the ultimate purpose of preventing the problem and identifying it early in case the pathology is already present  in growing patients.

MATERIALS AND METHODS: Bilateral TMJ MRI of 60 adolescents aged between 11 and 18 were evaluated. The sample was divided in two groups, that were retrospectively selected from the institutional database based on MRI and clinical data availability.
The patients in the control group did not present signs and symptoms of TMD and the resonance images had been previously requested for ENT reasons, unrelated to this study. The patients in the study group were diagnosed with intra-articular TMD and MRI of the TMJ was prescribed by the treating physicians of the patients, to complete the diagnosis and not as part of this study.
Patients with systemic disease, craniofacial syndromes or malformations, head and neck neoplasms, neurological disorders, previous maxillofacial surgeries; and the patients who were under pharmacological treatment were excluded from the sample.
In each TMJ, the position and shape of the disc in the closed mouth and the reduction capacity in the open mouth were evaluated. The Chi2 test was used to perform the statistical comparison. The level of significance was established at p <0.05.

RESULTS: From a population of 102 patients, 60 adolescents between 11 and 18 years old who met the inclusion criteria were included.
The study group consisted of 45 patients with TMD (29 females and 16 males) with a mean age of 15.73±2.13 years old and the control group comprised of 15 no- TMD patients (9 females and 6 males) with a mean age of 13.47±1.76 years old. In the study group, 73.3% were from the 15-18 age group, while in the control group, 66.7% were from the 11-14 age group.
In the study group the bilateral disc displacement was the most frequent bilateral disc position with anterior direction on both sides (p = 0.003). When the displacement was unilateral the disc direction was anterior, there were no cases of unilateral rotational displacement (p = 0.005).
In DDwR the most common form was lengthened (0.035) while in DDwoR was folded (p = 0.040). In the unilateral displacement, on the side with the normal disc position, the shape of the disc was not biconcave, but it was lengthened (p = 0.001).

CONCLUSIONS: Bilateral displacement was frequent among adolescents with TMD presenting the same reduction capacity and the same direction of displacement in both TMJ.
The anterior displacement was the most common direction associated with the folded disc shape in DDwoR. In patients with unilateral displacement, TMJ with normal disc position presented an alteration of the shape of the disc.

CLINICAL SIGNIFICANCE: The results of this study suggest that in adolescent with intra-articular TMD both TMJs are affected together with different degrees
of severity. TMD tends to increase with age and may be accompanied by pain, so it must be detected early.

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