Objectives: At present, the research on clear aligner of molar distalization mainly focuses on the upper jaw, while the research on mandibular molars is few.This study aims to evaluate the therapeutic effect of mandibular molars distalization with clear aligner via cone beam CT (CBCT) and Dolphin software.
Methods: Twenty cases of mandibular molars with clear aligner were included according to the inclusion and exclusion criteria. CBCT was taken before treatment (T0) and when the first molar was moved in place (T1). Dolphin software was used to measure the effectiveness of molar distalization. Three-dimensional changes in direction and the impact on the incisors and facial soft and hard tissues were evaluated.
Results: The effective rates of crown and root distalization of the second and first mandibular molars were 74%, 49%, and 71%, 47%, respectively. The second and first molars were both the distal buccal cusp with the largest distalization [(2.15 ± 0.91) mm and (1.85±1.09) mm], respectively, with significant difference between the T0 and T1 (P<0.05). The second and first molars were accompanied by depression, distal tilt, and buccal tilt with 1.06 mm, 2.10°, 2.27°, and 0.91 mm, 1.62°, and 1.91°, respectively, with significant differences between the T0 and T1 (all P<0.05). There was no obvious difference between men and women. The mandibular central incisor showed a lip-side movement of 1.02 mm, a depression of 0.82 mm, a mesial incline of 0.66°, and a crown-lip torque of 1.51° after molar distalization, with significant differences between the T0 and T1 (all P<0.001). Only the lower lip thickness increased by 0.1 cm, the length of the lower lip increased by 0.1 cm, and the ANS-ME (distance from anterior nasal spine to submental point) decreased by 0.13 cm, with significant differences between the T0 and T1 (all P<0.05).
Conclusions: Clear aligner can effectively move mandibular molars farther, the crown is more effective than the root, and it is tilted. The second mandibular molar is more effective than the first mandibular molar in its distant displacement and three-dimensional changes. Molar distalization causes minor changes in mandibular incisors and facial soft and hard tissues.
目的: 当前隐形矫治远移磨牙的相关研究主要着眼于上颌，而下颌磨牙远移研究尚少。本研究旨在通过拍摄锥形束CT(cone beam CT，CBCT)，应用Dolphin软件三维评估无托槽隐形矫治器远移下颌磨牙的疗效。方法: 根据纳入和排除标准纳入20例无托槽隐形矫治器远移下颌磨牙的病例，在治疗前(T0)和下颌第1磨牙远移到位时(T1)拍摄CBCT，运用Dolphin软件测量下颌第1、2磨牙的牙冠牙根远中移动距离，计算下颌磨牙远移有效率，同时评估三维方向变化及对下中切牙和面部软硬组织的影响。结果: 下颌第2、1磨牙牙冠和牙根远移有效率分别为74%、49%和71%、47%；下颌第2、1磨牙均为远中颊尖点远移距离最大，分别为(2.15±0.91) mm、(1.85±1.09) mm；下颌第2、1磨牙远移后伴有压低、远中倾斜、颊向倾斜，分别为1.06 mm、2.10°、2.27°和0.91 mm、1.62°、1.91°，在T0和T1之间差异均有统计学意义(均P<0.05)，下颌磨牙三维方向变化均具有统计学意义(均P<0.05)，男女性别之间差异无统计学意义(均P>0.05)；下颌中切牙在磨牙远移后表现为唇侧移动1.02 mm、压低0.82 mm、近中倾斜0.66°、冠唇向转矩1.51°，在T0和T1之间差异均有统计学意义(均P<0.001)；面部软硬组织指标中仅下唇厚度增加0.1 cm，下唇长度增加0.1 cm，下颌面高缩短0.13 cm，在T0和T1之间差异均有统计学意义(均P<0.05)。结论: 无托槽隐形矫治器能有效远移下颌磨牙，牙冠远移有效率高于牙根，为倾斜移动；下颌第2磨牙远移有效率、三维方向变化均高于下颌第1磨牙；磨牙远移使下颌切牙、面部软硬组织有少量变化。.
Keywords: clear aligner; cone beam CT; molar distalization; three-dimensional measurement.