Functional appliance therapy accelerates and enhances condylar growth.

The present study was designed to quantitatively assess the temporal pattern of expression of Sox 9, the regulator of chondrocyte differentiation and type II collagen, the major component of the cartilage matrix during forward mandibular positioning, and compare it with the expression during natural growth. Female Sprague-Dawley rats, 5 weeks old, were used. Results showed that the expression of Sox 9 and type II collagen are accelerated and enhanced when the mandible is positioned forward. Furthermore, we monitored the amount of new bone formation during mandibular advancement and after the removal of bite-jumping appliances. A substantial increase was observed in the amount of newly formed bone when the mandible was positioned forward. No significant difference in new bone formation could be found after the appliance was removed when compared with natural growth. Thus, functional appliance therapy accelerates and enhances condylar growth by accelerating the differentiation of mesenchymal cells into chondrocytes, leading to an earlier formation and increase in amount of cartilage matrix. This enhancement of growth did not result in a subsequent pattern of subnormal growth for most of the growth period; this indicates that functional appliance therapy can truly enhance condylar growth.