Correlation between eminence steepness and condyle disc movements in temporomandibular joints with internal derangements on magnetic resonance imaging

A steep articular eminence is reported to be a predisposing factor for the development of disc displacement. The purpose of this study was to evaluate the biomechanics of the temporomandibular joint (TMJ) in internal derangem ents and, additionally, to investigate whether a relationship exists betwee n the steepness of the articular eminence and disc displacement, with (DDR) and without reduction (DDWR). The material consisted of the sagittal TMJ magnetic resonance images (MRIs) of 39 joints (26 DDR and 13 DDWR). Sagittal and coronal TMJ MRIs were obta ined at maximum inter-cuspation and in the maximum mouth-opening position. The steepness of the articular eminence, disc, and condyle rotation, and co ndyle translation were investigated. A Student's t-test was performed and c orrelation coefficients calculated. The results revealed an increase in disc rotation in the DDR group and in c ondyle translation in the DDWR group (P< 0.01). Concyle rotation and the st eepness of the articular eminence were similar in both groups. Disc rotatio n was positively correlated with condyle rotation and negatively correlated with condyle translation in the DDR group (P < 0.05, r = 0.44). Condyle tr anslation was positively correlated with steepness of the articular eminenc e in the DDWR group (P < 0.01, r = 0.74). There was no correlation between movements of the disc-condyle assembly and the steepness of the articular e minence in the DDR group. Nevertheless, a relationship between condyle tran slation and the steepness of the articular eminence was found in the DDWR s ubjects.