临床使用时间对正畸镍钛弓丝机械性能的影响

目的评价临床使用时间的长短对弓丝机械性能的影响。方法选取山东大学口腔医学院正畸科同一时期内收治的30例上颌后牙段基本无拥挤的非拔牙矫治患者，利用三点弯曲试验装置（MTS Tytron 250， USA），检测未经使用、使用4周、8周及12周的镍钛弓丝在37?℃下的应力应变关系，应用单因素方差分析及q检验，比较4组弓丝的滞后值、平台期的载荷值。结果未经使用的弓丝平台期应力值为(1.54±0.05)N，滞后值为(0.47±0.05)N；使用4周后分别为(1.35±0.03)N和(0.61±0.03)N；使用8周之后分别为(1.38±0.07)N和(0.46±0.07)N；使用12周之后分别为(1.02±0.04)N和(0.34±0.04)N。通过单因素方差分析及q检验，每组的平台期应力值和滞后值之间均存在明显的差异（P＜0.05）。结论随着临床使用时间的增加，镍钛丝的性能有所衰减，但是使用后的镍钛矫正弓丝仍然具有超弹性。

Time effect on the mechanical properties of orthodontic NT arch wires

To evaluate the time effect on mechanical properties of orthodontic arch wires. Methods30 non extraction patients treated in the department of orthodontics in Shandong University in the same time period were enrolled in this study. The three point bending test was used to measure the strain and stress of arch wires at 37?℃. One way ANOVA and q test were used to compare the lag values and platform stresses. ResultsThe platform stress of the control group was 1.54±0.05N and the lag value was 0.47±0.05N. The platform stress of wires with a 4 week usage was 1.35±0.03N and the lag value was 0.61±0.03N. The platform stress of wires used for 8 weeks was 1.38±0.07N and the lag value was 0.46±0.07N. The platform stress of wires used for 12 weeks was 1.02±0.04N and the lag value was 0.34±0.04N. By one way ANOVA and q test, there were significant differences between each group（P＜0.05）. ConclusionWith the increment of use time, the properties of arch wires are attenuated, but their elasticity is still good.