PHYSIOLOGICAL TOOTH MIGRATION AND ITS SIGNIFICANCE FOR THE DEVELOPMENT OF OCCLUSION

I. THE BIOGENETIC COURSE OF THE DECIDUOUS 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 study was made to learn the extent and rate of physiological tooth migration and the mechanism which determines the development of occlusion. This is the first of four papers and deals with the development of the deciduous dentition from 3 to 5 years. Plaster reproductions of the deciduous dental arches of 30 children taken seriatim at various developmental stages were measured and examined for changes in morphology. The findings may be summarized as follows:

1. After the deciduous dental arches were completely formed, their sagittal and transversal dimensions were not altered except when subjected to inadequate environmental influences.

2. Two consistent morphological arch forms of deciduous dentures were found; the arches were either continuously spaced or continuously closed. Spaces in the deciduous denture were not developmental, but congenital. Closed arches were on an average narrower transversally than spaced ones.

3. The spaced arches frequently exhibited two distinct diastemata; one between the mandibular deciduous canine and first deciduous molar and the other between the maxillary second deciduous incisor and deciduous canine. These were interpreted as "primate spaces."

4. The terminal plane of the arches in occlusion remained constant.

5. Vertical growth of the alveolar processes concomitant with the development of the successional tooth germs and sagittal growth concomitant with the development of the accessional tooth germs was observed.

6. The present concept of physiological changes of the deciduous dental arches through spacing and through mesial shifting of the mandibular teeth was not confirmed by the above observations.