You Z H, Bell W H, Schneiderman E D, Ashman R B
Department of Oral and Maxillofacial Surgery, Baylor College of Dentistry, Dallas, TX.
J Oral Maxillofac Surg. 1994 Dec;52(12):1293-302. doi: 10.1016/0278-2391(94)90052-3.
To evaluate systematically the biomechanical properties of 13 popular screw designs, ranging from 0.8 to 2.0 mm in diameter.
Screws were characterized in terms of external, core, and drill diameter; cutting flute and head design; material; pitch, thread depth; and height of shank (unthreaded portion) and shank with plate. They were tested in standardized bone specimens (2 x 2.5cm slabs of fresh bovine femur) 1, 2, 3, and 4-mm thick. For each screw-bone thickness combination, 10 trials were conducted to determine push-out force (POF) and another 10 trials to determine insertion (IT) and maximum torque (MT) yielding a total of 1,040 tests.
Among the 13 different screws, in 1-mm thick bone, both the lowest (108.5 N) and highest (294.9 N) POF were created by 2-mm screws (P < .001); that with the lowest POF had a long unthreaded shank and pitch, that with highest POF had a short unthreaded shank and pitch. Screws with 0.8- to 1.5-mm diameters showed no differences in POF. The 2-mm screw with the lowest POF also had the lowest MT in 1-mm thick bone compared with the other 2-mm screws (P < .001). In thicker bones (> 2 mm), two 2-mm screws showed 30% to 50% lower MT than the other same size screws (P < .001) because their head slots stripped easily. When all screws were considered together for a particular bone thickness, torque was strongly predicted by screw diameter (MT: r = .94, P < .001; IT: r = 0.92, P < .001). Screws with the same diameters varied significantly in IT because of differences in self-tapping cutting flute design.
External diameter, unthreaded shank height, head slot, and self-tapping cutting flute design had the greatest impact on screw strength and efficiency in thin cortical bone. Thread depth, core diameter, and metal type did not affect performance significantly. Under these highly standardized in vitro conditions, the ideal 2-mm screw has an unthreaded shank that is as short as possible, and the pitch is about 0.8 mm. Additional aspects of a clinical situation beside holding strength must, however, be considered when choosing a screw.
系统评估13种常见螺钉设计的生物力学性能，这些螺钉直径从0.8毫米到2.0毫米不等。
对螺钉的表征包括外径、内径和钻孔直径；切削槽和头部设计；材料；螺距、螺纹深度；以及杆部（无螺纹部分）和带钢板的杆部高度。在标准化的骨标本（2×2.5厘米厚的新鲜牛股骨切片）中对其进行测试，骨标本厚度分别为1、2、3和4毫米。对于每种螺钉 - 骨厚度组合，进行10次试验以确定推出力（POF），另外10次试验以确定插入力（IT）和最大扭矩（MT），总共进行1040次测试。
在13种不同的螺钉中，在1毫米厚的骨中，2毫米螺钉产生了最低（108.5牛）和最高（294.9牛）的推出力（P <.001）；推出力最低的螺钉具有长的无螺纹杆部和螺距，推出力最高的螺钉具有短的无螺纹杆部和螺距。直径为0.8至1.5毫米的螺钉在推出力方面没有差异。与其他2毫米螺钉相比，推出力最低的2毫米螺钉在1毫米厚的骨中也具有最低的最大扭矩（P <.001）。在较厚的骨（> 2毫米）中，两种2毫米螺钉的最大扭矩比其他相同尺寸的螺钉低30%至50%（P <.001），因为它们的头部槽容易剥离。当考虑特定骨厚度下的所有螺钉时，扭矩与螺钉直径密切相关（最大扭矩：r = 0.94，P <.001；插入力：r = 0.92，P <.001）。由于自攻切削槽设计的差异，相同直径的螺钉在插入力方面有显著差异。
外径、无螺纹杆部高度、头部槽和自攻切削槽设计对薄皮质骨中螺钉的强度和效率影响最大。螺纹深度、内径和金属类型对性能没有显著影响。在这些高度标准化的体外条件下，理想的2毫米螺钉具有尽可能短的无螺纹杆部，螺距约为0.8毫米。然而，在选择螺钉时，除了握持强度外，还必须考虑临床情况的其他方面。
