Transverse growth of the maxilla and mandible in untreated girls with low, average, and high MP-SN angles: a longitudinal study.

INTRODUCTION

The purpose of this study was to investigate maxillary and mandibular transverse growth in untreated female subjects with low, average, and high mandibular plane angles longitudinally from ages 6 to 18.

METHODS

Eighty-one untreated white girls with low (< or = 27 degrees , n = 16), average (> 27 degrees to < 37 degrees , n = 41), and high (> or = 37 degrees , n = 24) mandibular plane angles at age 6 were selected from the Bolton-Brush and Burlington Growth Studies. For each subject, longitudinal posteroanterior cephalograms at different ages (from ages 6 to 18) were traced, and the widths of maxilla and mandible were measured. All the measurements were converted by using a magnification factor of 8.5% (the subject-to-film distance was set at 13 cm).

RESULTS

At age 6, the high-angle group had narrower maxillary and mandibular widths than the low-angle group, and this trend continued until age 18. From ages 6 to 14, maxillary width showed a steady and similar rate of increase for all 3 groups (0.90-0.95 mm per year), yet a plateau was reached at age 14 for all groups. Mandibular width increased at a steady rate (about 1.6 mm/year) for all 3 groups until age 14, and a plateau was reached for the high-angle group. For the low- and average-angle groups, mandibular growth continued from ages 14 to 18 but at a slower rate (0.85 mm and 0.39 mm per year, respectively).

CONCLUSIONS

Vertical facial patterns (with low or high mandibular plane angles) might play a strong role in the transverse growth of the maxilla and the mandible.