Brasileiro Bernardo Ferreira, Grotta-Grempel Rafael, Ambrosano Glaucia Maria Bovi, Passeri Luis Augusto
College of Dentistry, Federal University of Sergipe, Aracaju, Sergipe, Brazil.
J Oral Maxillofac Surg. 2012 Apr;70(4):941-51. doi: 10.1016/j.joms.2011.02.106. Epub 2011 Jul 14.
The aim of this study was to evaluate the biomechanical features of 3 different methods of rigid internal fixation for sagittal split ramus osteotomy for mandibular setback in vitro.
Sixty polyurethane replicas of human hemimandibles were used as substrates, simulating a 5-mm setback surgery by sagittal split ramus osteotomy. These replicas served to reproduce 3 different techniques of fixation, including 1) a 4-hole plate and 4 monocortical screws (miniplate group), 2) a 4-hole plate and 4 monocortical screws with 1 additional bicortical positional screw (hybrid group), and 3) 3 bicortical positional screws in a traditional inverted-L pattern (inverted-L group). After fixation, hemimandibles were adapted to a test support and subjected to lateral torsional forces on the buccal molar surface and vertical cantilever loading on the incisal edge with an Instron 4411 mechanical testing unit. Peak loadings at 1, 3, 5, and 10 mm of displacement were recorded. Means and standard deviation were analyzed using analysis of variance and Tukey test with a 5% level of significance, and failures during tests were recorded.
Regardless of the amount of displacement and direction of force, the miniplate group always showed the lowest load peak scores (P < .01) compared with the other fixation techniques. The hybrid group demonstrated behavior similar to the inverted-L group in lateral and vertical forces at any loading displacement (P > .05). Molar load tests required more force than incisal load tests to promote the same displacement in the mandibular setback model (P < .05).
For mandibular setback surgery of 5 mm, this study concluded that the fixation technique based on the miniplate group was significantly less rigid than the fixation observed in the hybrid and inverted-L groups. Mechanically, adding 1 bicortical positional screw in the retromolar region in the miniplate technique may achieve the same stabilization offered by inverted-L fixation for mandibular sagittal split ramus osteotomy setback surgery in vitro.
本研究旨在评估三种不同的坚固内固定方法用于下颌支矢状劈开截骨术后退下颌骨的体外生物力学特征。
使用60个聚氨酯材质的人半下颌骨复制品作为实验对象，模拟通过下颌支矢状劈开截骨术进行5毫米后退手术。这些复制品用于重现三种不同的固定技术，包括1）一块4孔钢板和4枚单皮质螺钉（微型钢板组），2）一块4孔钢板和4枚单皮质螺钉外加1枚双皮质定位螺钉（混合组），以及3）以传统倒L形排列的3枚双皮质定位螺钉（倒L形组）。固定后，将半下颌骨安装到测试支架上，使用Instron 4411力学测试装置在颊侧磨牙表面施加侧向扭力，并在切缘施加垂直悬臂加载。记录位移为1、3、5和10毫米时的峰值载荷。采用方差分析和Tukey检验分析均值和标准差，显著性水平为5%，并记录测试过程中的失败情况。
无论位移量和力的方向如何，与其他固定技术相比，微型钢板组始终显示出最低的载荷峰值分数（P <.01）。在任何加载位移下，混合组在侧向和垂直力方面的表现与倒L形组相似（P >.05）。在下颌骨后退模型中，磨牙载荷测试比切缘载荷测试需要更大的力才能产生相同的位移（P <.05）。
对于5毫米的下颌骨后退手术，本研究得出结论，基于微型钢板组的固定技术明显不如混合组和倒L形组的固定牢固。从力学角度来看，在微型钢板技术的磨牙后区增加1枚双皮质定位螺钉，在体外可实现与倒L形固定用于下颌支矢状劈开截骨术后退手术相同的稳定性。
