The Treatment Effect Of Class â…¡ Division 1 Malocclusion With Twin-block Appliance: A Cephalometric Study

Objective: To investigate the skeletal, dental and facial changes produced by the Twin-block appliance excluding the influence of natural growth, thereby, it is more objective, actual and accurate to reflect the treatment effect, and provide clinical and theoretical basis for the early functional therapy of class II division I malocclusion.Method: The study consisted of 30 children with class II division 1 malocclusion and retrognathic mandible. One group (9 boys, 7 girls, average 11.5years old) was treated with Twin-block appliance for average 14 months, the other group (8 boys, 7 girls, average 11 years old) children was observed for 13 months without treatment. The cephalometric data of two groups before and after treatment or control was analyzed statistically. Result: 1. After treated with the Twin-block appliance, the mandible unit length(Ar-Po) increased by 6.48mm,the ramus height(Ar-Go) increased by 4.59mm,the mandibular body length(Go-Gn) increased by 3.61mm. The SNB angle increased by 1.86o; The anterior facial height and posteriorfacial height increased obviously, but the angle of mandibular plane was stable. The upper incisor retroclined 10.31o,the lower incisor proclined by 4.28 o ,the lower molar moved mesially by 2.73mm, overbite decreased by 3.12mm, all of which were statistically significant comparing with the control group(p<0.05). Overjet was corrected by 4.76mm,of which 61% was due to dental effect and 39% due to skeletal effect. Molar relationship was corrected by 5.02mm,of which 75% was due to dental effect and 25% due to skeletal effect.2. After observation of 13 months, the maxilla vertical location (A-CFH),the mandibular total length (Ar-Po), the mandibular body length (Go-Gn), the mandibular plane angle(MP-SN) significantly increased, and the SNB angle decreased, N-Me and ANS-Me increased, the upper incisor proclined and the overjet increased, all of which were statistically significant (p<0.05).Conclusion: 1.The functional treatment with Twin-block appliance, significantly increased the mandibular unit length, the ramus height and the mandibular body length. The chin moved forward, which increased the SNB degree and decreased the ANB degree. Deep overbite,deep overjet,molar relation and Class II profile were improved greatly,which indicate that Twin-block appliance promote the mandibular growth sagittally and vertically, the correction of Class II skeletal relation and soft tissue profile can be achieved.2. The treatment with Twin-block appliance can make the upper incisor retroclined and the lower incisor proclined , The problems of teeth and arch could not resolved by functional appliance , which often need treat with fixed appliance at the second stage.3. After 13 months of observation, the mandibular length increased and the mandibular plane angle showed clockwise rotation. The skeletal relation and soft tissue profile were not improved in the control group but showed a trend of getting severe. It suggest that the treatment of Class II division 1 patient should start timely, in order to prevent the malocclusion from getting severe.