Dentoalveolar changes related to mandibular forward growth in untreated Class II persons.

The purpose of this study was to investigate dentoalveolar changes related to mandibular forward growth in persons with Class II malocclusions. The longitudinal cephalometric films of 40 subjects with untreated Class II malocclusions from mean age 8.8 to 17.8 years (before and after pubertal growth) were analyzed and compared with the Bolton norms. There was no statistically significant difference in mandibular growth between the Class II samples and the Bolton norms upon cross-sectional comparison. In the Class II subjects, forward growth of the mandible was greater than that of the maxilla by 4.36 mm on average; the dentoalveolar complex moved forward relative to the maxillary basal bone (point A) 2.16 mm and moved backward relative to the mandibular basal bone (pogonion) 2.28 mm; a strong linear relationship (almost a 1:1 ratio) existed between mandibular forward growth and dentoalveolar complex movement (r = 0.881; y = 0.976 x + 0.183). Results indicated that the effect of forward growth of the mandible, which could potentially bring the lower dentition forward, vanished into the adaptation movements of the dentoalveolar complex through intercuspal locking. Disarticulating the occlusion to minimize the effects of the adaptive mechanism and taking advantage of normal mandibular forward growth could be fundamental biological bases in treating Class II malocclusions in growing patients.

Class II malocclusion: mandibular retrusion or maxillary protrusion?

This study was undertaken to evaluate whether the majority of Class II skeletal patterns are mandibular retrusive or maxillary protrusive and also to compare four maxillary sagittal cephalometric indicators and four mandibular sagittal cephalometric indicators in a skeletal Class II sample. The Fishman SMA method was used to stratify the subjects into 11 maturity levels. Computerized cephalometric programs selected the subjects and compared the different indicators for each subject. The results indicate a wide diversity in the evaluation of maxillary protrusion and mandibular retrusion in these subjects. The Downs facial angle indicated that only 27.0% of the sample had mandibular retrusion. The angle NA-FH indicates that 56.3% of the sample had maxillary protrusion. These findings are in marked contrast to those evaluated by some of the other indicators. Preliminary data from this study was presented at a combined meeting of the Orthodontic Society of the Cote D'Azur and the North Atlantic Component of the E.H. Angle Society of Orthodontists, Nice, France, October 1990 and at the annual meeting of the North Atlantic Component of the E.H. Angle Society of Orthodontists, Philadelphia, April 1991.