Development of animal model for anterior open bite and mechanism of temporomandibular joint morphological change: an implication for MAC surgery

Although mandibular autorotation concept (MAC) surgery is a novel technique for addressing long-term stability issues in patients with mandibular retrusion and open bite accompanied by temporomandibular joint osteoarthritis (TMJOA), studies on MAC surgery in animal models and its mechanisms are scarce. This study aimed to develop an animal model for anterior open bite and investigate the underlying histological and molecular mechanisms of TMJ changes, with the expectation of contributing to the MAC surgery concept. Thirty-six, 5-weeks-old female Wistar rats were randomly divided into three groups: (1) Bite-raise group (2-mm resin added to the upper molars at 5 weeks of age) (2), Recovery group (resin added at 5 weeks of age and removed at 13 weeks of age), and (3) Control group (normal rats). Micro-CT imaging was used to assess 3D morphology and bone structure. Histological and immunohistochemical analyses were performed to evaluate the cartilage changes, bone cell differentiation, and extracellular matrix degradation. Gene expression of inflammatory factors (IL-1β, IL-6, TNF-α), TGF-β1, and Postn were measured by qPCR. At 13 weeks of age, both Bite-raise and Recovery groups exhibited TMJOA-like changes, including decreased cartilage thickness and increased inflammatory gene expression. At 21 weeks of age, the Recovery group showed improved bone volume, reduced osteoclast activity, and lower MMP-13 and Postn levels than the Bite-raise group. These results suggest the successful development of an animal model for anterior open bite and demonstrate that MAC surgery facilitates the recovery of compromised condyles.