[Clinical study of the effect of fixed Twin-block on adolescent skeletal Class Ⅱ malocclusion].

Purpose: To evaluate the retention ability of fixed Twin-block appliance and its clinical effect on adolescent skeletal ClassⅡmalocclusion.

Methods: Twenty-six skeletal ClassⅡdivision 1 adolescents (M:12, F: 14; age:11~13 years, average: 11.8 years) were chosen and fixed Twin-block appliance was used to guide the mandibular protrusion for one year. Before and after treatment, cephalometric films were taken to observe the skeletal, dental and soft tissue changes. Graphpad Prism 6.0 software was used for Student's t test.

Results: There was no loosening or destruction of the appliance during the treatment and the profile of all cases was improved significantly. The indexes that showed significant difference(P<0.05) included the mandibular length and position (Co-Gn, SNB, ANB, Pog-VL, Pos-VL) , the inclination and position of the maxillary incisors(U1-VL, U1-SN), the sagittal position of the mandibular dentition(L1-VL, L6-VL). The indexes that showed insignificant difference(P>0.05) included the mandibular plane(MP-SN), the length and position of the maxilla (SNA, A-VL) , the vertical position of the maxillary incisor(U1-HL), the position of the maxillary posterior teeth(U6-VL, U6-HL), the mandibular incisor inclination(IMPA) and the vertical position of the mandibular dentition(L6-MP,L1-MP).

Conclusions: Fixed Twin-block appliance can enhance the mandibular anchorage, effectively promote the mandibular growth and improve the facial profile.