Janakiraman Nandakumar, Gill Pawandeep, Upadhyay Madhur, Nanda Ravindra, Uribe Flavio
a Clinical Assistant Professor, Division of Orthodontics, University of Connecticut, School of Dental Medicine, Farmington, Conn.
b Tulare, Calif.
Angle Orthod. 2016 Jan;86(1):32-8. doi: 10.2319/012815-68.1. Epub 2015 May 15.
To quantify the effects of tip-back mechanics on the maxillary first molars and incisors.
Sixteen subjects with Class II end-on malocclusion were treated with an intrusion arch to achieve distalization of the maxillary molar through tip-back mechanics. Lateral cephalograms were taken prior to molar tip-back (T1), after molar tip-back (T2), and after molar root uprighting (T3). Data were analyzed using the Friedman's and Wilcoxon signed rank tests to evaluate differences in time points (P ≤ .016).
The maxillary first molar distalized 1.53 mm (P = .001) with 6.65° (P = .001) of distal tipping and 0.86 mm (P = .001) of extrusion at T2. Minor relapse of the first molar (mesial direction) was seen at T3. The maxillary incisors flared labially 0.4 mm, and the incisor root apex moved palatally 1.19 mm (P = .005) at T2. At T3, the incisor root apex moved palatally 1.5 mm (P = .003) from T1. An angular change from T1 of 3.31° (P = .008) and 3.53° (P = .014) was seen at T2 and T3, respectively, as a result of palatal root movement of the maxillary incisors.
A significant amount of distalization of maxillary molars was attained at the crown level with tip-back mechanics. Palatal root angulation change was significant in the incisors with minimal anteroposterior movement of the incisal edge.
量化后倾力学对上颌第一磨牙和切牙的影响。
对16例安氏II类直面错牙合患者采用压低弓丝，通过后倾力学实现上颌磨牙远中移动。在磨牙后倾前（T1）、磨牙后倾后（T2）和磨牙牙根直立后（T3）拍摄头颅侧位片。采用Friedman检验和Wilcoxon符号秩检验分析数据，以评估各时间点的差异（P≤0.016）。
在T2时，上颌第一磨牙远中移动1.53mm（P = 0.001），远中倾斜6.65°（P = 0.001），伸长0.86mm（P = 0.001）。在T3时可见第一磨牙有轻微复发（向近中方向）。在T2时，上颌切牙唇向散开0.4mm，切牙根尖腭向移动1.19mm（P = 0.005）。在T3时，切牙根尖相对于T1腭向移动1.5mm（P = 0.003）。由于上颌切牙腭根移动，在T2和T3时，相对于T1分别出现3.31°（P = 0.008）和3.53°（P = 0.014）的角度变化。
后倾力学在上颌磨牙牙冠水平实现了显著的远中移动。切牙腭根角度变化显著，切缘前后向移动极小。
