Experimentally created unilateral anterior crossbite induces a degenerative ossification phenotype in mandibular condyle of growing Sprague-Dawley rats.

The effect of unilateral anterior crossbite on the remodelling of mandibular condyle needs to be investigated. This study aimed to investigate the effects of experimentally created unilateral anterior crossbite on the remodelling of mandibular condyle and explore the changes in the expression of relevant transcription factors and growth factors. The experimental unilateral anterior crossbite was created in 6-week-old female growing rats by bonding metal tubes to the left pairs of incisors. Remodelings of mandibular condylar cartilage was assessed histologically at 2, 4 and 8 weeks. Protein and mRNA levels of Sox9, runt-related transcription factor 2 (Runx2), Osterix (Osx), transforming growth factor beta 1 (TGFβ1), transforming growth factor beta receptor 2 (TGFβr2) and type X collagen (ColX) were investigated by immunohistochemistry and real-time PCR, while alkaline phosphatise (ALP) by histochemistry and real-time PCR. Decreased ratio of hypertrophic cartilage layer was noticed in the 4w experimental group versus controls. At all the time points, the expression of Sox9 and ALP increased but that of TGFβ1 and TGFβr2 decreased in experimental groups (P < 0·05). The expression of Runx2, Osx and Col X increased at 2w, but decrease at 4w (P < 0·05). The results that obvious cartilage degradation and altered expression of related transcription factors and growth factors were detected in the mandibular condyles of the experimental group suggested that the present unilateral anterior crossbite plays an adverse role in the TMJ, and thus leading to the degenerative endochondral ossification.