Effects Of Total Edentulousness On Temporomandibular Joints In Rabbits: A Histological And Scanning Electron Microscopic Study

Objective: To explore the histological effects of total edentulousness on the temporomandibular joints (TMJ) in rabbits. Methods: Twenty- two adult New Zealand white rabbits (Oryctolagus cuniculus) were divided into 11 groups with 2 animals in each. Two groups were the control and the other nine groups were served as experimental animals. In the experimental groups, the total teeth of the rabbits were extracted under the condition of general anesthesia. After surgical extracting, each experimental group was sacrificed respectively at 1 week (2 groups), 2 weeks (1 group), 4 weeks (1 group), 8 weeks (1 group), 16 weeks (2 groups) and 26 weeks (2 groups). Then the bilateral temporomandibular joints of each experimental animal were removed entirely and prepared according to the certain procedure. Among the 1w, 16w and 26w experimental animals, each one group were picked out to be examined by scanning electron microscopy (SEM). The other TMJ samples were sectioned and stained with hematoxylin/eosin (HE) and toluidine blue, then observed by light microscope. Results: The results of the SEM observation were: in the experimental groups, the surface of the discs and condyles was degenerated obviously; in the 16-week group, the changes occurred most apparently; the main changes showed that the gelatin-like material twisted or even disappeared on the surface of the discs and condyles, the collagen fibers were exposed and ranked disorderedly, some small holes and fissures could be seen on the surfaceof the discs and condyles which became tough; however, in the 26-week group, the traumatic changes were less obvious than the other two groups. In addition, the findings of the light microscopy examination were: the fibrous layer loosened and hyalinized, the spaces between fibrous enlarged, and the surface of this layer became rough and broken; the reserve cell layer and the chondroblastic layer as well as the hypertrophic layer became thinner or discontinued partly; focal hemorrhage occurred in marrow cavity; micro-fracture in the subchondral bone and clustering of chondrocytes in the discs were also found occasionally; meanwhile, for the discs, the spaces between fibrous increased, the surface of the discs cracked; the condyles adhered to the discs somewhere additionally. Conclusion: The present study suggests that total edentulousness may lead to temporomandibular joint degenerative changes. Therefore, there might be a relationship between total edentulousness and temporomandibular joint disorder.