Thickness measurements and micro-CT imaging of human temporo-mandibular discs

The temporo-mandibular joint (TMJ) links the mandibular condyle to the skull, with an interposed fibrocartilaginous articular disc. The TMJ disc has a nonuniform thickness that matches the topographic relation between the temporal bone and the mandibular condyle. The disc is a stress-distributing and load-absorbing structure that is capable of deforming and adapting its shape to that of the articular bone surfaces. The aim of this study was to analyze the morphology of human discs through thickness measurements. Forty-four temporomandibular joint discs were dissected bilaterally from 22 formalin-fixed human postmortem subjects. The thickness of each disc was manually measured at nine points distributed in a grid formed by three zones in the anteroposterior direction (anterior band, intermediate band and posterior band) and the three zones in the mediolateral direction (medial zone, middle zone and lateral zone) of the disc. Microtomographic imaging analysis was performed on four samples. The thickness of the postero-middle and the postero-medial points was significantly higher than all the other measured points. A significant difference was found between the thickness of the intermediate and the posterior bands and between the anterior and the posterior bands. A significant difference was also found between the thickness of the middle and the lateral zones (p < 0.01) and between the lateral and the medial zones (p < 0.01). Disc perforations were observed in 8 of the discs and were mostly (87.5%) located in the lateral area. Micro-CT imaging offered a new possibility to map thickness variations of the disc and showed very similar results to those taken with the calipers. The presented data contribute to increasing the knowledge of this specific joint and of the complex 3D relations between all its parts. They also open the door to pioneering studies that could lead to clinically applicable techniques in the future and enhance the diagnosis of disc perforations associated with osteoarthritis.