The effect of chin cup therapy on the growth and development of the cranial base and midface.

The purpose of this study was to determine how the growth rates of certain cranial base and midfacial points and dimensions were affected by force application to the mandible by the chin cup. Control and treated samples consisting of Japanese girls with skeletal Class III relationships were analyzed. Each sample consisted of lateral cephalometric radiographs taken annually (control group) or semiannually (treated group) from early childhood through adolescence. The control sample was composed of seven persons and the treated sample of ten persons. The subjects of the treated sample were required to wear a chin cup a minimum of 12 hours per day. The total force delivered was 500 g, 250 g per side, and the direction of force was, on average, through the condyle. No other appliances were used. The results of this study indicate that the chin cup causes a closing of the cranial flexure angle N-S-Ba, inhibits posterior growth of the point basion, and imposes a vertical growth tendency on the points nasion and sella. The chin cup significantly inhibits anterior and posterior vertical maxillary growth and growth of upper anterior facial height. Because development of vertical posterior facial height is inhibited more than anterior facial height, a clockwise rotation of the maxilla occurs. The chin cup also causes flaring and a decrease in eruption rate of the maxillary incisors. It has no effect on the eruption rate of the maxillary molars, but accelerates their rate of mesial movement as compared with controls.(ABSTRACT TRUNCATED AT 250 WORDS)