Morphogenetic response to activator treatment

Abstract

E xperiments on growing primates have demonstrated that changes induced in the posture of the mandible may cause dental malocclusion.7 Class II, Division 1 malocclusions have been produced by lowering the postural position of the mandible relative to the maxilla which, in turn, caused extrusion of maxillary buccal teeth. In similar experiments, in which no extrusion of the maxillary buccal teeth was allowed, a lowering of the mandible did not result in a Class II malocclusion. The findings from these experiments indicate that the relative eruption of the posterior teeth is an important factor in the establishment of molar relationships. These results constitute the basis of the present clinical study. The purpose of this investigation was to change a Class II molar relationship into neutral occlusion by reversing the effects demonstrated in the primate experiments. This was achieved by impeding the vertical development in the maxillary molar region and concurrently stimulating vertical development in the mandibular molar segments. Correction of a Class II molar relationship by nightly use of a removable orthodontic appliance is a generally accepted procedure.1-41 6p * However, the design of the appliance has been as varied as the interpretation of its effects. For the present experiment, a removable appliance, which was a modification of the conventional activator, was designed. Theoretically, this appliance cquld elicit a series of morphogenetic responses which might contribute to the correction of the Class II malocclusion. Five hypotheses were formulated which, singly or in combination, might explain the structural changes in the transformation from a Class II to a Class I dental occlusion :