Developmental changes in alignment of the lower labial segment.

The purpose of this study was to examine changes in lower incisor alignment at various developmental stages, from the time of eruption to the established permanent dentition and to try to predict the degree of crowding in the permanent dentition from that observed at earlier developmental stages. Forty-eight subjects (20 male, 28 female) with intact mandibular arches were selected from the Belfast growth study records. The lower incisor space condition was measured at each of four developmental stages: (1) initial eruption of the lower permanent incisors; (2) initial eruption of the permanent canines; (3) initial eruption of the second molars; (4) 3 years after eruption of the second molars. Differences in lower incisor space condition between each developmental stage were investigated and correlation analyses between the space conditions at each stage were carried out. On average, crowding of the lower incisors decreased to a statistically significant degree (- 0.9 mm) between stages 1 and 2, and increased between stages 3 and 4 (0.4 mm). Significant correlation coefficients between space condition at each developmental stage were found, but were considered unreliable as predictors of lower incisor crowding in the mature dentition.