EVALUATION OF SHEAR-STRESS OF THE HUMAN TEMPOROMANDIBULAR-JOINT DISC

The aim of this study was to determine the shear stress of the human p ostmortem temporomandibular joint (TMJ) disc. Correlation of shear str ess with age or with the region of the disc was determined. Nine discs were removed unilaterally from postmortem humans, ages 36 to 76 years . Discs were sectioned into lateral (eight), central (eight), and medi al (eight) specimens. Each specimen was attached by cyanoacrylate adhe sive to a servohydraulic test system apparatus within 48 hours of retr ieval. Shear properties were measured under quasistatic conditions wit h a linear increase of displacement until the specimen failed to maint ain maximum resistance to the applied force. The shear,noduli were ana lyzed by means of the Wilcoxon's signed ranks test. The results showed that values of shear moduli on peripheral portions (lateral and media l) there significantly higher than on central portions (P = 0.0013). T he correlation between the shear moduli of TMJ discs and age showed a regression slope for shear moduli of-0.326 + 0.031 x age (r = 0.769; P < 0.01). Peripheral portions (lateral and medial) have a higher shear moduli and ale stiffer than the central portions of !discs and shear moduli ol stiffness of TMJ discs increase with age.