Abstract
The human mandible experiences mechanical stress from several directions as a result of activities such as speaking, chewing, and other everyday actions. The TMJ disc facilitates mandibular motion and absorbs all of the stresses associated with daily activities. Thus, the TMJ disc is likely to be susceptible to rupture. Hence, it is crucial to investigate its susceptibility to failure and rupture. The aim of this study was to determine the impact of fracture orientation, sample thickness, and crack-to-width ratio on the amount of energy needed to cause the growth of flaws on the disc. Fracture toughness was investigated by conducting cyclic tensile testing on 40 ovine TMJ discs in two different notch orientations: anteroposterior and mediolateral. The J-integral was chosen as a measure of the critical fracture energy of the TMJ disc. The Shapiro-Wilk test showed that fracture toughness data did not follow a normal distribution (P-value < 0.05). Due to unequal variances, the Kruskal-Wallis test was used to examine the data. The study revealed that the fracture toughness in the anteroposterior direction was much higher than that of the mediolateral, indicating a superior ability to resist tearing and fracture in the anteroposterior direction. Furthermore, the study's findings revealed that both the direction of the crack and its initial crack-to-width ratio influenced the TMJ disc's fracture toughness. The study also evaluated TMJ disc failure patterns to better understand its pathophysiology. The results showed that the crack growth profile in two orientations has a completely different structure. The 2D finite element analysis results also indicated a significant relationship between the fracture toughness and the percentage of cracks, demonstrating that increasing the crack-to-width ratio leads to a rise in fracture toughness. These findings help understand TMJ injuries to the disk and develop better treatments.