Department of Preventive and Community Dentistry, College of Dentistry, University of Iowa, Iowa City, IA 52242, USA.
Am J Orthod Dentofacial Orthop. 2011 Sep;140(3):e93-8. doi: 10.1016/j.ajodo.2011.04.017.
The primary stability of orthodontic anchorage miniscrews is believed to result from mechanical interlock, with success based upon a number of variables, including screw diameter, angle of placement, monocortical vs bicortical placement, placement through attached or unattached soft tissue, presence or absence of a pilot hole, periscrew inflammation, and maximum placement torque. The purpose of this ex-vivo study was to further explore the relationship between maximum placement torque during miniscrew placement and miniscrew resistance to movement under load.
Ninety-six titanium screws were placed into 24 hemi-maxillae and 24 hemi-mandibles from cadavers between the first and second premolars by using a digital torque screwdriver. All screws were subjected to a force parallel to the occlusal plane, pulling mesially until the miniscrews were displaced by 0.6 mm. The Spearman rank correlation test was used to evaluate whether there was an increasing or a decreasing relationship between maximum placement torque of the screws, miniscrew resistance to movement, and bone thickness. A paired-sample t test and the nonparametric Wilcoxon signed rank test were used to compare maximum placement torque, bone thickness, and miniscrew resistance to movement between coronally positioned and apically positioned screws in the maxilla and the mandible, and between screws placed in the maxilla vs screws placed in the mandible. Additionally, 1-way analysis of variance (ANOVA) with the post-hoc Tukey-Kramer test was used to determine whether there was a significant difference in miniscrew resistance to movement for screws placed with maximum torque of <5 Ncm, 5 to 10 Ncm, and >10 Ncm.
The mean difference in miniscrew resistance to movement between maximum placement torque groupings, <5 Ncm, 5 to 10 Ncm, and >10 Ncm, increased throughout the deflection range of 0.0 to 0.6 mm. As deflection increased to 0.12 to 0.33 mm, the mean resistance to movement for miniscrews with maximum placement torque of 5 to 10 Ncm was statistically greater than for screws with maximum placement torque <5 Ncm (P <0.05). As deflection increased to 0.34 to 0.60 mm, the mean resistance to movement for miniscrews with maximum placement torque of 5 to 10 Ncm and >10 Ncm was significantly greater than for screws with maximum placement torque <5 Ncm (P <0.05). At no deflection was there a significant difference in resistance to movement between the 2 miniscrew groups with higher placement torque values of 5 to 10 Ncm and >10 Ncm.
Ex vivo, the mean resistance to movement of miniscrews with higher maximum placement torque was greater than the resistance to movement of those with lower maximum placement torque.
正畸锚固微螺钉的初级稳定性被认为源于机械互锁，成功取决于许多变量，包括螺钉直径、放置角度、单皮质与双皮质放置、穿过附着或不附着的软组织放置、是否有导孔、螺钉周围炎以及最大放置扭矩。本体外研究旨在进一步探讨微螺钉放置过程中最大放置扭矩与微螺钉在负荷下抗移动能力之间的关系。
通过数字扭矩螺丝刀将 96 个钛螺钉放置于 24 个尸体上颌和下颌第一前磨牙与第二前磨牙之间的半上颌和半下颌中。所有螺钉均受到平行于咬合平面的力，向近中牵引，直到微螺钉移动 0.6mm。采用 Spearman 秩相关检验评估螺钉最大放置扭矩、微螺钉抗移动能力与骨厚度之间是否存在正相关或负相关关系。采用配对样本 t 检验和非参数 Wilcoxon 符号秩检验比较上颌和下颌中近中放置和根尖放置的螺钉以及上颌和下颌中放置的螺钉之间的最大放置扭矩、骨厚度和微螺钉抗移动能力。此外，采用单因素方差分析（ANOVA）和事后 Tukey-Kramer 检验来确定最大放置扭矩为<5 Ncm、5-10 Ncm 和>10 Ncm 时微螺钉抗移动能力是否存在显著差异。
在 0.0 至 0.6mm 的挠度范围内，微螺钉抗移动能力在最大放置扭矩分组之间的平均差异逐渐增加。当挠度增加到 0.12 至 0.33mm 时，最大放置扭矩为 5-10 Ncm 的微螺钉的平均抗移动能力显著大于最大放置扭矩<5 Ncm 的螺钉（P<0.05）。当挠度增加到 0.34 至 0.60mm 时，最大放置扭矩为 5-10 Ncm 和>10 Ncm 的微螺钉的平均抗移动能力显著大于最大放置扭矩<5 Ncm 的螺钉（P<0.05）。在无挠度时，最大放置扭矩为 5-10 Ncm 和>10 Ncm 的两组微螺钉之间的抗移动能力没有显著差异。
在体外，最大放置扭矩较高的微螺钉的平均抗移动能力大于最大放置扭矩较低的微螺钉的抗移动能力。
