[A new fixed Twin-block appliance in the treatment of adolescent patients with skeletal Class Ⅱ malocclusion].

Purpose: To evaluate the clinical effect of a new fixed Twin-block on adolescent patients with skeletal ClassⅡ malocclusion.

Methods: Twenty-one patients aged 10-13 years with skeletal ClassⅡ malocclusion with mandibular retrusion were chosen for functional treatment using a new fixed Twin-block. Before and after treatment, panoramic and cephalometric films were taken, and the observation indexes were measured and recorded.

Results: There was no loosening or destruction of the appliance during treatment, the mean duration of treatment was (11.42±1.78) months. The position of the mandible(SNB), the length of the mandible (Co-Gn), nasolabial angle (Cm-Sn-UL), condylar sagittal position(Pcd-S), the lower labial protrusion distances (LL-SnPg') were significantly increased (P＜0.05) after treatment, and the relative position of the maxilla and mandible (ANB), Y-axis angle(SGn/FH), the inclination of the maxillary incisors (U1/SN), and the depth of the mental-labial sulcus (Si-LLPg') reduced(P＜0.05). Maxillary position(SNA), posterior mandibular position(S Vert-Co), mandibular length(Go'-Me), the mandibular incisor inclination (IMPA), and upper and lower mesial incisor angles(U1/L1), protrusion of the upper lip (UL-SnPg') were changed but without significant difference(P＞0.05). The vertically orientated measurements of the vertical position of the lower dentition(Ll-MP), L6-MP, the vertical distance of the upper and posterior teeth (U6-PP), anterior height (N-Me), facial height index(S-Go'/N-Me), and mandibular plane angle (MP/SN) did not change significantly(P＞0.05), while the posterior height(S-Go'), the vertical position of the upper dentition(U1-PP), occlusal plane angle (SN/OP), mandible height (Ar-Go'), the mandible ramus height(Co-Go) was increased significantly (P＜0.05).

Conclusions: New fixed Twin-block significantly promotes mandibular growth and provides effective vertical control, improves the facial profile by retracting the maxillary incisors, and the clinical effect is reliable.