RESUMEN
PURPOSE: To investigate the therapeutic effect of modified fixed Twin-block on patients whose mandible was retruded and anterior overjet was normal. METHODS: Thirty-six adolescents with mandibular retrusion and normal anterior overjet were selected. The goal of occlusal reconstruction was to move the soft tissue pogonion forward to the zero meridian(0°). Fixed Twin-block combined with the mini-implants on the mandibular buccal shelf was used to promote mandibular growth. After 12 months, the appliances were removed step by step to observe the stability of the jaw relationship. Fixed orthodontic treatment was performed to achieve ideal occlusion and coordinated profile. SPSS 13.0 software package was used for Student's t test. RESULTS: The length of mandibular body increased significantly which facilitated the forward movement of the soft tissue pogonion, and the profile changed from convex to straight. Comparison of the results before and after Twin-block treatment showed that Co-Gn, SNB, U1-SN, U6-0°, U1-0°, U1-L1, anterior overbite, anterior overjet, Pog's-0°, L1-0° and lower anterior facial height changed significantly (Pï¼0.05). Comparison of the results before and after fixed orthodontic treatment showed that PP-MP, SN-MP, U6-0°, IMPA, L1-0°,U1-SN, U1-L1, anterior overbite and overjet changed significantly(Pï¼0.05). CONCLUSIONS: Modified fixed Twin-block combined with mini-implants on the mandibular buccal shelf can effectively stimulate the mandibular growth and improve the lateral profile of patients with mandibular retrusion and normal overjet.