The effect of bite-opening appliances on mandibular rotational growth and remodeling in the rhesus monkey (Macaca mulatta).

Previous experimental studies that have used a bite-block cemented to the maxillary dental arch have shown that the direction of growth of the maxillary complex is redirected in a superior and anterior direction for approximately 12 weeks but reassumes a normal inferior and anterior direction after that time. The purposes of this study were (1) to examine the effect of increased vertical dimension and altered mandibular posture on growth of the mandible and (2) to determine whether or not an alteration in chronic mandibular position alters mandibular intramatrix rotation. Eleven Macaca mulatta monkeys wore 15 mm vertical bite-opening appliances for 24 or 48 weeks. Nine untreated animals were used as controls. All animals received tantalum bone implants to facilitate cephalometric analysis. Serial lateral radiographs of the mandible were traced and superimposed on bone implants for each animal to determine overall changes in mandibular shape (gonial angle) and the location of bone remodeling. During normal growth, the gonial angle closed an average of 0.1 degrees over a 48-week period. In the experimental animals, the gonial angle opened 6.4 degrees (p less than 0.005) as a result of remodeling during the period that mandibular posture was altered. Once normal mandibular posture was restored, this process was reversed; the gonial angle once again became more acute over time, and remodeling along the body and ramus of the mandible was similar to that observed in control animals. These results suggest that mandibular growth and remodeling can be influenced by altered mandibular vertical posture.