[Soft tissue angle evaluation of fixed Twin-Block appliance treatment and tooth extraction treatment in skeletal Class II malocclusion].

PURPOSE: This cephalometric study was designed to evaluate the soft tissue profile effects of Twin-Block combined with straight wire appliances in the treatment of skeletal Class II malocclusion with mandibular retrognathia in growing individuals by angulation. METHODS: The sample comprised 31 growing individuals with skeletal Class II and mandibular retrognathia, which were divided into 2 groups. One group (18 patients) was treated with fixed Twin-Block combined with fixed appliance， the other group (13 patients) was only treated with fixed appliance after tooth extraction. Pretreatment and posttreatment lateral cephalograms were taken before and after Twin-Block treatment and after all the fixed appliance treatment. Angular cephalometric measurements of soft tissue were analyzed statistically. Intragroup and intergroup changes of the 2 groups were evaluated by Student's t test using SPSS 15.0 software package. RESULTS: Significant difference of FH-N'Pg', G-Pn-Pg', LiSi-SN and SnLs-SiLi were discovered in both groups (P<0.05). With Twin-Block combined with fixed appliance, N'-Sn-Pg', Sn-N'-Si and Si-N'-S changed significantly, while LsSn-SN and Z angle differed significantly before and after treatment with extraction and fixed appliance. After treatment of Twin-Block combined with fixed appliance, Sn-N'-Si decreased significantly, and the difference between the change of the 2 groups was significant. Meanwhile LsSn-SN was stable in combined treatment group while it decreased greatly after extraction. CONCLUSIONS: Compared with extraction with fixed appliance treatment, Twin-Block combined with fixed appliance treatment is more favorable in promoting lower facial profile in growing skeletal Class II individuals with mandibular retrognathia.