[The frequency of various types of disk displacement and its relation to occlusion]

The aim of this study is to observe the frequency of the different types of disc displacements (d.d.) of the TMJ (ATM) and to evaluate if these types are related or not with malocclusions. One hundred patients and 13 asymtomatic volunteers underwent full clinic examination. sagittal MRI (mouth open and closed) and coronal MRI (mouth closed). The different types of disc displacements were noted and cumulated in frequency and in relation with several occlusal criteria. Unlike the general opinion stating that the antero-medial d.d. (d.d. a-m) are the most frequent amongst the internal derangements, the result of this study reveals that the antero-lateral d.d. (d.d. a-l) are more frequent amongst the patients (35.1%) and the asymptomatic volunteers in general and particularly in view of a malocclusion (exagerated anterior overlapping and posterior cross bite). The study gives rise to the question of the etiology of a antero-lateral d.d. and sets back the hypothesis of the lateral pterygoid muscle fundamental role in the disc displacements.