Classification of the temporomandibular joint disc displacement without reduction using MRI in the mouth-opening position.

OBJECTIVES: This study aimed to analyze the positional characteristics of the temporomandibular joint (TMJ) disc in patients with anterior disc displacement without reduction (ADDWoR) using magnetic resonance imaging (MRI). MATERIALS AND METHODS: 2,827 MRI images from 2,168 ADDWoR patients were collected and categorized into two groups: without limited opening (WoLO) group and with limited opening (WLO) group. The position of TMJ disc and their distribution characteristics in these two groups were analyzed from the oblique sagittal planes of MRI. RESULTS: The disc positions were classified into 11 types based on oblique sagittal MRI images during maximum mouth opening. Anterior displacement was the most common in both groups, with 39.65% in WoLO and 41.96% in WLO. Anteroinferior displacement and anteroinferior displacement in the lateral part were also prevalent, particularly in the WLO group. While the MRI imaging features of superior displacement did not appear in the WLO group, due to mouth opening limitation. The effect of masticatory muscles and condylar excursion during mouth opening play a crucial role in the displacement of TMJ disc. CONCLUSIONS: ADDWoR patients of WoLO group primarily manifest disc anterior displacement, anteroinferior in the lateral part, and anteroinferior displacement. ADDWoR patients of WLO group are more likely to exhibit disc anterior displacement and anteroinferior displacement, without the manifestation of superior displacement. CLINICAL RELEVANCE: The position of the anterior displaced disc can guide treatment strategies, conservative treatment alleviating restricted mouth opening for anteroinferior displacement patients, or controlling excessive mouth opening to relieve ligamentous laxity for anterosuperior displacement patients.