Sectional And Imaging Anatomy Of The Temporomandibular Joint At Different Functional Positions

Objectives: ①To investigate the morphological variations of the human temporomandibular joint (TMJ) dics and its adiacent structures. ②To provide sectional anatomical data with comparative study section and MRI of the TMJ at the desired position of the mandibule, such as closed mouth of dental occlusion, wide-opened mouth, protrusive and lateral displacement, were cut in coronal, sagittal and transverse sections. ③To reconstruct the three-dimensional digitized visible model of the TMJ in the different functional positions to provide assist for surgical planning and demo, even operation of virtual arthroscopy of the TMJ. Methods: ①The 31 temporomandibular articular discs of adult cadaver at closed mouth position were measured with a venier caliper and all date were analysed. The shape and relations of articular discs and adjacent structures were observed. ②The models of the TMJ in closed mouth,wide opened mouth, protrusive and lateral displacement were established in 11 fresh head specimens between 20 and 40 years. Four cases of closed mouth, and the other 3 different functional positions each one were chosed to cut into 1.0mm of thickness on the transverse, oblique coronal and oblique sagittal by plastination technique. Serial thin sections of 14 sides of TMJ were obtained . The 4 cases at different functional positions of the TMJ with colorful filling material after decalcification were cut into 0.9mm on transverse, oblique coronal and oblique sagittal by frozen cryomicrotome. Serial thin sections of 8 sides of TMJ were obtained. ③MRI scanning of the TMJs on the transverse, oblique coronal and oblique sagittal were performed in 4 cadaver heads at different functional positions and 2 young volunteers without temporomandibular disorder and bruxisrm. ④The articular discs, condyler process and articular fossa were reconstructed and measured on SGI work-station. Results: ①The middle part of temporomandibular articular discs showed thinner than the circumjacent part of oneselves. The posterior band was the thickest, and the intermediate band was the thinnest. The average thickness of the articular discs was 1.52±0.58mm. The superior and inferior pterygoid muscles were intercrossed near the capsule of the TMJ, and few pterygoid muscl inserted to the disc. ②With comparative observation of MRI and section of the TMJ at different functional positions, we found both the superior and inferior pterygoid muscles contracted in the wide opened mouth, the protrusion displacement and the non-working side of the lateral displacement of mandibular, which made the adaptability between the disc and the bone surface of the joint was not good, and the disc was compressed. While in the working side of the lateral displacement of mandibular and closed mouth, both the superior and inferior pterygoid muscles loosened, And the aricular disc was not compressed. The condylar process not only glided forward and downward but also turned at the same time in the wide-open and the non-working side of the lateral displacement of mandibular, The condylar process only glided at the protrusion displacement. ③3D reconstructed structures of TMJ demonstrated the shape variety of the disc and the anatomical relation among the disc, condylar process and mandibular fossa, The the intermediate band of aricular disc of the TMJ was compressed in the protrusion displacement, the non-working side of the lateral displacement of mandibular and wide opened mouth. In 3D measurement of TMJ, the shape change of the articular disc was the most in the wide opened mouth and was no change in the worked side of the lateral displacement of mandibular. Conclusions: ①The intramuscular fibres of superior pterygoid muscles which inserted the TMJ disc didn't really cause the replacement of the TMJ dics. ②The morphological variations of the human TMJ dics was mainly at lateral parts of intermediate and posterior of bands . The TMJ disc of the didn't shift as only the condylar process was gliding along articular tuberculum or the condylar process was turning in articular fossa. But when the two movements took place at the same time, the articular discs shifted. ③It was very important to combine 3D reconstruction and sectional specimen for explaining movement of TMJ, displaying the shape variety of articular regional structures and measuring the joint, providing assist for surgical planning and demo, even operation of virtual arthroscopy of the TMJ.