Collagen Crimping in TMJ Disc in Response to Tensile Forces

Objectives: To detect the changes in collagen crimping in the pig temporomandibular joint articular disc after applying sustained tensile loads. Methods: The articular discs obtained from the pigs TMJs were cut into the form of 12 anterior-posterior, 4-5mm wide strips for the experiments. Six randomly selected strips were subjected to tensile loads and six served as controls. The specimens to be loaded were fixed at one end by a needle holder and a weight was attached to the opposite end by a clamp to produce a static force of 170N for eight hours. Specimens were maintained under physiological conditions. At the end of the experimental period, the strips were removed and fixed in 10% neutral buffered formalin for 24 hours, processed into paraffin blocks in the sagittal plane, sectioned at 7microns and stained by the haematoxylin and eosin method. Sections were observed in bright field and polarised light on a Zeiss Axiophot microscope. Images were recorded digitally using Axioplan software. Results: In the control specimens, the collagen bundles were found to form a complex three- dimensional weave, with general anterior-posterior orientation. In polarised light a regular crimped appearance was seen. In the specimens subjected to load, the discs appeared to be extended and flattened, and showed areas of translucency. Histological sections revealed that in many areas the crimped appearances had been eliminated in some bundle groups. These exhibited a uniform polarisation pattern with increased birefringence and loss of crimping. The collagen adjacent to the fracture zone invariably showed loss of crimping. Conclusions: The findings suggest that crimping may account for the stress-strain characteristics of the articular disc.