Background: Although studies proved that psychological stress (PS) is perpetuating factor in temporomandibular disorders (TMD), it is clinically unethical to prove the role of PS as initiative factor in TMD. A Previous study showed the ability of PS to induce TMD in rat model. However, the distinctive effect of PS on TMJ versus other joints will augment the specificity of PS to induce TMD.

Aim: Compare the effect of PS on the TMJ versus knee joint in rats.

Study Design: A 32 male albino rats was randomly divided into 3 groups, control group (CG), foot shock group (SG) and psychological stress group (PSG). SG was merely used to induce stress for PSG and did not participate in analysis, through the communication box chambers. After 4 weeks, PSG and CG were anesthetized, right joints of TMJ, and knee were prepared for histological study.

Results: Histological examination of the right knee joints of PSG showed intimal thickening, surface irregularity, thinning of cartilage, degenerated chondrocytes. On other hand, TMJ showed matrix discontinuity, degenerated bone trabeculae, areas of superficial ossification, and reduced cellularity of fibrous layer of mandibular cartilage. Also, there was a highly significant destructive morphometric changes between the PSG and CGs in the TMJ and knee joints in all three examined parameters (mean cartilage thickness, mean area percentage of co1lagen fibers and mean color density of IL-1β immune- expression).

Conclusion: PS produces histological effects on TMJ and knee joints, however its impact on TMJ is significantly higher.