A Clinical Study of Twin-block Appliance on Treatment of Class II Division 1 Malocclusion

【Objective】To evaluate the dento-alveolar, skeletal and soft tissue changes caused by Class Ⅱ division 1 malocclusion correction in the patients treated with Twin-block appliance.【Methods】Sixteen patients in growth with Angle Class Ⅱ division 1 malocclusion and mainly with mandibular retrognathia were investigated.Lateral cephalometric X-ray was taken, and skeletal, dento-alveolar and soft tissure measurements were carried outbefore and after treatment for each patient. Two time-points of results were compared and submitted to statisticalanalysis.【Results】Changes were occurred for the growth direction and length of mandible after treatment. Overjetand overbite were decreased by 8.13 mm and 4.27 mm, respectively, while SNB, mandibular plane angle, Ar-Pogand lower facial height were increased by 1.70°and 3.47°, 4.06 mm and 2.53 mm, respectively. The maxillaryincisors has a tendency of lingual torque (P 0.05), without advancement of point A, which contributes to anincreased degree of nasal-labial angle and decreased protrusion of upper lip (P 0.01). In addition, the inclinationof lower incisors decreased slightly, although with no statistical significance, it was important to evaluate the stabilityof the lower anterior segment after treatment. 【Conclusions】 Twin-block functional appliance possesses theorthopedic effect on Angle Class Ⅱ division 1 malocclusion. When repositioning the mandible forward, it creates the force to limit maxillary growth forward as well. Simultaneously it causes the changes of dento-alveolar. All the seaspects contribute to a harmonious relationship of upper and lower jaws and a better profile.