Neovascularization and mandibular condylar bone remodeling in adult rats under mechanical strain

The present study was designed to explore the relationship between neovascularization, hypertrophic cartilage and the microstructural properties of cancellous bone in adult rat's condyle in response to mechanical strain produced by mandibular advancement. Seventy-eight 120-day-old female Sprague-Dawley rats were randomly allotted to six groups, nine animals in each experimental group according to different time points. Mandibular advancement appliances were used to produce mechanical strain onto to the mandibular condyles of rats. Immunostaining of VEGF and type X collagen were carried out. Tartrate-Resistant Acid Phosphatase ( TRAP) reaction was used to assess the activity of chondroclasts. Direct three-dimensional morphometric analysis was carried out with microcomputed tomography (Micro-CT) scanning to evaluate the properties of microstructure of cancellous bone in the mandibular condyles. Results showed that mechanical strain produced by mandibular advancement induced neovascularization in the posterior condyle marked by the increased expression of VEGF. Neovascularization coupled the remodeling of calcified cartilage as marked by the expression of type X collagen and new bone formation. The new bone formed in the adult condyle was characterized by thinner trabecular thickness, more trabecular number and increased trabecular space. In conclusion, mechanical strain produced by mandibular advancement induces neovascularization and osteogenesis leading to adaptive growth of condyle in adult rats.