Abstract
In this systematic review, we aimed to assess the current evidence regarding the effectiveness of functional treatment with both removable and fixed appliances to normalize the external soft tissue for skeletal class II adolescent individuals. We performed a broad electronic search to retrieve relevant studies from nine databases to identify randomized controlled trials (RCTs) and controlled clinical trials (CCTs) that investigated soft tissue changes following functional treatment and evaluated the changes using 2D lateral cephalometric radiographs and 3D-optical surface laser scanning. A total of three RCTs and eight CCTs were included. Ages ranged from 11 to 16 years with the fixed functional appliances, and from eight to 12 years with the removable ones, including 689 skeletal class II patients. Version 2 of Cochran's risk-of-bias (RoB2), and the risk of bias in non-randomized studies of interventions (ROBIN-I) were used to assess the risk of bias for the included papers. Of the 11 eligible studies, three studies were included in the meta-analysis to assess the upper and lower lip position in relation to the E-line (Ricketts's aesthetic line) in addition to the nasolabial angle. The meta-analysis showed that the upper lip retracted after functional treatment with Twin-block in relation to E-line (mean difference (MD) = -1.93; 95% CI: -2.37, -1.50; p < 0.00001; χ² = 5.43; p = 0.07; I(2) = 63%), while the lower lip position did not change after functional treatment with Twin-block in relation to E-line (MD = 0.03; 95% CI: -0.56, 0.61; p = 0.92; χ² = 1.74; p = 0.42; I(2) = 0%). The nasolabial angle increased after Twin-block treatment (MD = 5.75; 95% CI: 4.57, 6.93; p < 0.00001; χ² = 6.77; p = 0.03; I(2) = 70%). The mentolabial angle and Z-angle also increased after functional therapy, where the facial convexity angle decreased, regardless of the functional devices used. On the other hand, using the 3D-optical surface laser scanning showed that the upper lip length and the commissural width did not change following therapy, but the lower lip increased in length, as well as the total face height. More high-quality RCTs are required to obtain accurate evidence in this field.