Chin development as a result of differential jaw growth.

INTRODUCTION

During facial growth, the maxilla and mandible translate downward and forward. Although the forward displacement of the maxilla is less than that of the mandible, the interarch relationship of the teeth in the sagittal view during growth remains essentially unchanged. Interdigitation is thought to provide a compensatory (tooth movement) mechanism for maintaining the pattern of occlusion during growth: the maxillary teeth move anteriorly relative to the maxilla while the mandibular teeth move posteriorly relative to the basilar mandible. The purpose of this study was to investigate the hypothesis that the human chin develops as a result of this process.

METHODS

Twenty-five untreated subjects from the Iowa Facial Growth Study with Class I normal occlusion were randomly selected based on availability of cephalograms at T1 (mean = 8.32 yr) and T2 (mean = 19.90 yr). Measurements of growth (T2 minus T1) parallel to the Frankfort horizontal (FH) for the maxilla, maxillary dentition, mandible, mandibular dentition, and pogonion (Pg) were made.

RESULTS

Relative to Pg (a stable bony landmark), B-point moved posteriorly, on average 2.34 mm during growth, and bony chin development (B-point to Pg) increased concomitantly. Similarly, the mandibular and maxillary incisors moved posteriorly relative to Pg 2.53 mm and 2.76 mm, respectively. A-point, relative to Pg, moved posteriorly 4.47 mm during growth.

CONCLUSIONS

Bony chin development during facial growth occurs, in part, from differential jaw growth and compensatory dentoalveolar movements.