Factors regulating mandibular condylar growth.

Factors regulating condylar growth have not been identified before. This study was designed to identify a series of these factors, such as Sox 9 transcription factor and vascular endothelial growth factor (VEGF), and also to correlate the amount of type X collagen expressed during natural growth to the amount of bone newly formed. We used 115 Sprague-Dawley rats, 35 days old, in this study. The expression of these factors was identified on protein level by using immunostaining. Type X collagen was identified on mRNA and protein levels. Sox 9 was expressed by cells in the proliferative layer and by chondrocytes. Type X was expressed only by hypertrophic chondrocytes, and its expression precedes the onset of endochondral ossification. VEGF is expressed by hypertrophic chondrocytes, and its maximum level of expression precedes the maximum level of bone formation. Condylar growth involves a sequence of transitory stages uniquely defined by molecules that are intrinsically synthesized by cells in the condyles.