Combined effects of unilateral nasal obstruction and occlusal bite-raising on mandibular condylar development in growing rats.

BACKGROUND: Unilateral nasal obstruction (UNO) alters mandibular condylar growth, while bite-raising increases mechanical loading on the temporomandibular joint (TMJ). Hypoxia induced by UNO may exacerbate TMJ osteoarthritis (TMJOA)-like changes associated with occlusal disturbances during growth, and understanding their combined effects is clinically relevant. This study aimed to investigate whether UNO and bite-raising synergistically contribute to TMJ osteoarthritis (TMJOA)-like changes in growing rats.

METHODS: Twenty-four 4-week-old male Wistar rats were randomly divided into four groups: control, bite-raising (iOVD; 2-mm composite resin on the upper molars), UNO (complete left nostril sutured), and combined group (iOVD + UNO). Micro-CT was used to assess mandibular morphology and trabecular structure. Histological and immunohistochemical analyses were performed to evaluate cartilage degeneration, bone remodeling, and extracellular matrix changes. Gene expression levels of HIF-1α, IL-1β, IL-6, NF-κB, TGF-β1, and Postn were analyzed by qPCR.

RESULTS: At 9 weeks, SpO2 was significantly reduced in the UNO and iOVD + UNO groups. Micro-CT revealed increased trabecular separation and decreased bone volume fraction in the iOVD + UNO group, with suppressed bone formation and enhanced resorption confirmed by TRAP/ALP staining. Histology showed cartilage degeneration and reduced proteoglycans in all experimental groups, most pronounced in the iOVD + UNO group. Immunohistochemistry demonstrated increased expression of HIF-1α, MMP-13, and Postn, and decreased type II collagen in the iOVD + UNO group. qPCR analysis revealed elevated mRNA expression of HIF-1α, IL-1β, NF-κB, and Postn in the iOVD + UNO group.

CONCLUSION: These findings suggest that the combination of nasal obstruction and bite-raising exacerbates the disruption of cartilage homeostasis and subchondral bone remodeling in the mandibular condyle, contributing to TMJOA-like structural and biological changes in growing rats.