[Growth and development of the dental arch and alveolar ridge in the incisal segment from the late period of mixed dentition to the early period of permanent dentition].

The purpose of this study is to provide information on normal growth and development of the dental arch and alveolar ridge. Materials were longitudinal casts obtained from 38 children (male: 19, female: 19) with normal dentition. The casts were taken at 2-month intervals for the purpose of providing information on tooth emergence. Measurements for chronological age were taken from 11 years and 6 months to 13 years and 6 months. Measurements for dental age were taken during a period of 1 year before and 1 year after emergence of the permanent second molar. In addition to these dental age measurements, other measurements for dental age were made at each evaluation of dental arch length and basal dental arch length for a period of 1 year before and 1 year after emergence of the permanent second premolar. After a reference plane had been established and each cast had been standardized, a formcorder was used to trace 5 sagittal sections at the midline and at the region of the right and left central and lateral incisors. Growth and development of dental arch length, basal arch length, and alveolar width in both the maxilla and the mandible were measured on these 5 sagittal sections. Total dental arch length was taken to be the distance between the mesial surfaces of the permanent first molars and the labial surface of each incisor. Total basal arch length was taken to be the distance between the ridge of the posterior region of the basal arch and the most concave point of the labial basal arch. In addition to casts, lateral cephalometric films were used to measure, at ages 12, 13 and 14, changes in the vertical and horizontal dimensions of both the central incisors and the jaws and the long axes of the permanent central incisors. Results and conclusions 1. Mean growth in dental arch length 1) In the maxilla When growth was evaluated by chronological age, in 2 years, the total dental arch length decreased 1.0-1.2 mm in the region of the central incisors and 0.8-0.9 mm in the region of the lateral incisors. Evaluated by dental age based on the emergence of the permanent maxillary second premolar, up to 2 months before the emergence of that tooth, no notable changes occurred in the total dental arch length in the regions of both the central and lateral incisors. But a remarkable decrease of 0.9-1.1 mm took place thereafter.(ABSTRACT TRUNCATED AT 400 WORDS)