Watanabe L G, Marshall G W, Marshall S J
Department of Restorative Dentistry, University of California, San Francisco, USA.
Dent Mater. 1996 Mar;12(2):109-15. doi: 10.1016/S0109-5641(96)80077-7.
Dentin has a highly oriented tubule structure, and the tubule number density and area fraction of intertubular dentin vary with distance from the pulp. This investigation sought to determine the influence of tubule orientation on shear strength of dentin from samples derived at various intratooth locations.
Third molars were sectioned and prepared to provide samples from two locations (center and cusp) and with one of three specific tubule orientations. In series 1, matched pairs of midcoronal samples were tested using two tubule orientations. A paired t-test was used for statistical analysis. In series 2, three samples from central and cuspal areas were tested using three different tubule orientations. A two-day ANOVA was used for statistical analysis. Each sample had dimensions of approximately 1 x 1 x 5 mm and was tested in a hydrated state by a single plane lap shear method.
The paired dentin samples of the midcoronal dentin in the two orientations had shear strengths of 72.4 +/- 15.6 MPa and 78.4 +/- 13.2 MPa, and were not significantly different (p > 0.05; paired t-test). In the second series, samples from the center location with tubules parallel to the shear plane with applied force in directions rotated by 90 degrees did not exhibit a significant difference (p > 0.05), with an average value of 53.5 +/- 9.5 MPa. Samples oriented with tubules along the long axis of the specimen and tested with shear force applied perpendicular to the tubule direction had significantly higher (p < 0.05; two-way ANOVA) shear strength (78.0 +/- 8.5 MPa). The specimens from the cusp area did not exhibit a statistically significant difference (p > 0.05; two-way ANOVA) with respect to the three orientations (83.6 +/- 8.4; +/- 13.8; 91.8 +/- 12.7 MPa). Cuspal areas were stronger than central areas in two of the three orientations tested.
Results indicated that the shear strength differs in central and cusp areas and is dependent on dentin tubule orientation in the central area. Shear strengths were much larger than values reported in shear bond strength tests. This suggests that dentin shear strength is far in excess of dentin bond strengths using shear tests, and that fractures through dentin in such result from flaws or stress concentration in the dentin.
牙本质具有高度定向的小管结构，小管数量密度和管周牙本质面积分数随与牙髓距离的变化而变化。本研究旨在确定小管取向对来自不同牙内位置的牙本质样本抗剪强度的影响。
将第三磨牙切片并制备，以提供来自两个位置（牙尖中心和牙尖）且具有三种特定小管取向之一的样本。在系列1中，使用两种小管取向对匹配的中冠样本对进行测试。采用配对t检验进行统计分析。在系列2中，使用三种不同的小管取向对来自牙尖中心和牙尖区域的三个样本进行测试。采用双向方差分析进行统计分析。每个样本的尺寸约为1×1×5mm，并通过单面搭接剪切法在水合状态下进行测试。
两种取向的中冠牙本质配对样本的抗剪强度分别为72.4±15.6MPa和78.4±13.2MPa，差异无统计学意义（p>0.05；配对t检验）。在第二个系列中，来自牙尖中心位置、小管平行于剪切平面且施加力方向旋转90度的样本之间差异无统计学意义（p>0.05），平均值为53.5±9.5MPa。小管沿样本长轴取向并在垂直于小管方向施加剪切力进行测试的样本具有显著更高的抗剪强度（p<0.05；双向方差分析）（78.0±8.5MPa）。来自牙尖区域的样本在三种取向之间差异无统计学意义（p>0.05；双向方差分析）（83.6±8.4；±13.8；91.8±12.7MPa）。在测试的三种取向中的两种中，牙尖区域比牙尖中心区域更强。
结果表明，牙尖中心和牙尖区域的抗剪强度不同，且在牙尖中心区域取决于牙本质小管取向。抗剪强度远大于剪切粘结强度测试中报道的值。这表明，使用剪切测试时，牙本质抗剪强度远超过牙本质粘结强度，并且在这种情况下牙本质中的断裂是由牙本质中的缺陷或应力集中导致的。
