PHYSIOLOGICAL TOOTH MIGRATION AND ITS SIGNIFICANCE FOR THE DEVELOPMENT OF OCCLUSION

II. THE BIOGENESIS OF ACCESSIONAL DENTITION

¹ Division of Dental Medicine, College of Dentistry, and The George Williams Hooper Foundation for Medical Research, University of California, San Francisco, Calif.

A further clinical study of the development of occlusion in 60 children by means of serial plaster reproductions of the dental arches was made. Through comparative measurements, three different biologic mechanisms of normal occlusal adjustment of the accessional teeth were found:

1. The occurrence of a terminal plane forming a mesial step in the deciduous denture allowed the first permanent molars to erupt directly into proper occlusion without altering the position of the neighboring teeth.

2. The presence of a mandibular primate space and a straight terminal plane was conducive to proper molar occlusion by means of an early mesial shift of the mandibular deciduous molars into the primate space upon eruption of the lower first permanent molar.

3. Closed deciduous arches and a straight terminal plane resulted in a transitory end-to-bnd relationship of the first permanent molars. Proper occlusion was effected through a late mesial shift of the mandibular permanent first molars subsequent to the shedding of the deciduous second molars.

Migration of the lower deciduous and permanent molars constituted the physiological measure to secure proper occlusion of the permanent molars. There was no mesial shift of the mandible as indicated by the unchanged anteroposterior relationship of the opposing deciduous cuspids. Function and attrition had less bearing on the molar adjustment than widely assumed. The anatomical pattern of the deciduous arches controlled the ability of the deciduous and permanent molars to migrate mesially as a result of the eruptive force of the accessional teeth.