Physiological Tooth Migration and its Significance for the Development of Occlusion

Abstract

The comparative and biometrical examination of serial casts made of 60 dentitions before, during and after eruption of the permanent incisors demonstrated the following findings: Expansion of the dental arches in the anterior region, to accommodate the larger successional incisors into proper alignment, was brought about by a lateral and frontal alveolar growth during the time of the eruption of these teeth. The mean increase in intercanine width was greater in the upper arches than in the lower ones, and again greater in previously closed upper or lower deciduous arches than in previously spaced ones. In the mandibular arches the strongest impulse of lateral growth was noted during the eruption of the lateral incisors. In the maxillary arches this occurred during the eruption of the central incisors. An occasional "secondary" spacing of the upper deciduous anteriors took place when the still undeveloped maxillary arch was somewhat widened upon eruption of the permanent lower central incisors. Spaced deciduous arches generally produced favorable alignment of the permanent incisors while about 40% of the arches without spaces produced crowded anteriors. Forward extension of the arches was measured from a line connecting the distals of the cuspids. The averages revealed no difference between previously spaced and closed arches but were 1 mm. greater for the upper arches than for lower ones. According to tooth measurements on the plaster reproductions this difference between the maxillary and mandibular forward extension could not be credited to a greater increase in thickness of the crowns of the upper permanent incisor over that of the lower ones. It was interpreted as an expression of an evolutionary tendency toward a lessened forward growth of the mandibular alveolar process.