Methods 20 patients whose first mandibular molars were extracted were involved in this study, using Edgewise appliance, welding hook in mesiolingual band, cooperating II class traction, the molar space were closed in sliding. 方法对20例第一磨牙缺失的病例,采用Edgewise矫治技术,带环近中点焊舌钮或自制拉钩,适当配合II类牵引,滑动关闭磨牙间隙。
14 ( 31.82%) had a dentin fusion between the peninsula-like floor and the mesial pulp chamber wall, forming a large mesiobuccal-distal ( MB-D) orifice and a small mesiolingual orifice ( Type ⅲ). 14个半岛形髓室底和近中髓壁之间有一个牙本质带,形成一个大的近颊-远中(MB-D)根管口和一个小的近舌根管口(TypeⅢ)。