Comparative evaluation of unilateral anterior crossbite and monoiodoacetate injection models for temporomandibular joint osteoarthritis in rats

To systematically compare unilateral anterior crossbite (UAC) and monosodium iodoacetate (MIA) models for temporomandibular joint osteoarthritis (TMJOA) research. This study used healthy adult male SPF-grade Sprague–Dawley (SD) rats, aged 6–8 weeks and weighing 180–200 g, with a total of 24 rats. After a 7-day acclimatization period, the rats were randomly and equally allocated into three groups: a normal control group (NC), an occlusion intervention group (UAC), and a drug injection group (MIA). Condylar height at the anterior, central, and posterior regions was quantitatively measured via a computer-aided image analysis system to elucidate the observed morphological alterations. Pathological assessments of the TMJ were conducted using Safranin O-Fast Green staining, hematoxylin and eosin (HE) staining, and immunohistochemistry (IHC). Both occlusion intervention and drug injection models exhibited cartilage degeneration with subchondral bone alterations evident on histological examination, a substantial reduction in chondrocyte count, and altered cellular morphology characterized by shrinkage. Furthermore, significant increases were observed in the Mankin score, OARSI score, and the number of positive inflammatory markers in both experimental groups compared to the control group. Notably, the drug injection group exhibited a more pronounced increase in these parameters compared to the occlusion intervention group. Under the tested conditions and observation period, the intra-articular MIA model produced more rapid and severe condylar degeneration than the UAC model, whereas the UAC model induced milder, progressively developing changes. Both models showed model-, dose-, and time-dependent characteristics, and neither fully recapitulates the complex pathogenesis of human TMJOA. Model selection should therefore be guided by the specific research question and the disease stage of interest, rather than by a general ranking of superiority.