Spontaneous Changes in the Incisor Relationship following Extraction of Lower First Permanent Molars

Abstract

The spontaneous changes in overbite, overjet and incisor inclinations during the first year following extraction of both lower first permanent molars were investigated in 43 (19M, 24F) patients whose ages ranged from 8–14 years at the time of extraction. The changes were measured on 90° left lateral cephalometric radiographs taken before extraction and approximately 12 months later. On average, there was a tendency for the overbite and overjet to increase with associated retroclination of lower and proclination of upper incisors. The range of the changes was relatively large. When the overbite showed an appreciable increase during the period of observation, pre-existing proclination of upper or lower incisors and an increased overbite or overjet were the most frequent findings. Remarkably, a previously increased overjet seemed to be a better indicator of an overbite that would increase than was the Previous overbite itself. In most cases showing a previously normal overbite or overjet, the overjet after extraction remained stable. Correlation of the overbite and overjet together against the changes in overbite proved disappointing from the prognostic standpoint except that previously incomplete overbites almost invariably increased.