Shetty V, Freymiller E, McBrearty D, Caputo A A
Section of Oral and Maxillofacial Surgery, UCLA School of Dentistry, 90024-1668, USA.
J Oral Maxillofac Surg. 1996 May;54(5):601-9: discussion 609-10. doi: 10.1016/s0278-2391(96)90642-4.
This study examined the effects of positional screw size and placement configuration on osteotomy site stability in a sagittal split ramal osteotomy model.
A reproducible analog of a sagittal split ramus osteotomy was developed to facilitate equitable comparisons of fixation stability. The distal segment of each analog was advanced by 7 mm and fixed bilaterally with 2.0-mm or 2.4-mm cortical screws applied in either a linear or a triangular configuration. Reduced analogs were placed in a straining frame, and simulated masticatory loads wee applied alternatively to the mandibular first molars. Ensuring osteotomy site displacements were acquired and registered by displacement transducers attached to a computer-based data acquisition program. A coordinate transformation procedure was used to convert the component displacements captured by the individual transducers into a common "instability factor" to reflect fixation stability for each construct and loading condition.
Between configurations, the magnitude of interfragmentary displacement was less when the screws were applied in a triangular than in a linear configuration (P < or = .0001). Within configurations, 2.4-mm cortical screws provided greater stability than 2.0-mm screws. The stability profiles of the 2.0-mm screws, applied in a linear configuration at the superior border, were very similar regardless of whether two or three screws were used. The loads at which the linear systems became unstable were significantly higher (P < or = .0001) than for the triangular systems. Despite the twofold or higher difference in the mean instability factor of the individual test constructs, the SDs for each construct were only one tenth to one fifth of the corresponding means.
None of the internal screw systems were grossly unstable when used to stabilize ramal osteotomies. Other conditions, including quality and strength of investing bone, being equal, cortical screws placed in a triangular configuration provide greater stability than screws placed in a linear configuration. Osteotomy sites stabilized by 2.4-mm screws are more stable than those stabilized by 2.0-mm screws. It does not matter whether two or three screws are applied at the superior border in a linear configuration, provided that the outer screws are an inch apart. The model system has a very good measurement precision and has important implications in optimizing fixation device design and placement configuration.
本研究在矢状劈开下颌支截骨模型中，探讨位置螺钉尺寸和放置构型对截骨部位稳定性的影响。
建立一种可重复的矢状劈开下颌支截骨模拟模型，以利于对固定稳定性进行公平比较。每个模拟模型的远心段向前推进7mm，并用2.0mm或2.4mm皮质骨螺钉以线性或三角形构型双侧固定。将缩小后的模拟模型置于应变框架中，交替对下颌第一磨牙施加模拟咀嚼负荷。通过连接到基于计算机的数据采集程序的位移传感器获取并记录截骨部位的位移。采用坐标变换程序将各个传感器捕获的分量位移转换为一个共同的“不稳定因子”，以反映每种结构和加载条件下的固定稳定性。
在不同构型之间，螺钉以三角形构型放置时骨折块间位移的幅度小于以线性构型放置时（P≤0.0001）。在相同构型内，2.4mm皮质骨螺钉比2.0mm螺钉提供更高的稳定性。在上缘以线性构型应用2.0mm螺钉时，无论使用两枚还是三枚螺钉，其稳定性情况非常相似。线性系统变得不稳定时的负荷显著高于三角形系统（P≤0.0001）。尽管各个测试结构的平均不稳定因子存在两倍或更高的差异，但每个结构的标准差仅为相应平均值的十分之一到五分之一。
当用于稳定下颌支截骨时，没有一种内固定螺钉系统会出现严重不稳定。在其他条件（包括覆盖骨的质量和强度）相同的情况下，以三角形构型放置的皮质骨螺钉比以线性构型放置的螺钉提供更高的稳定性。用2.4mm螺钉稳定的截骨部位比用2.0mm螺钉稳定的截骨部位更稳定。在上缘以线性构型应用两枚或三枚螺钉时，只要外侧螺钉相距1英寸，其效果并无差异。该模型系统具有非常好的测量精度，对优化固定装置设计和放置构型具有重要意义。
