Carvalho R M, Fernandes C A, Villanueva R, Wang L, Pashley D H
Department of Operative Dentistry, Endodontics and Dental Materials, Bauru School of Dentistry, USP, Brazil.
J Adhes Dent. 2001 Winter;3(4):309-14.
This study investigated the ultimate tensile strength (UTS) of human dentin as a function of tubule orientation and density.
Slabs of dentin (ca 0.7 mm thick) were obtained from human third molars by either transversally or longitudinally sectioning the crowns with an Isomet saw. The slabs were gently trimmed to reduce the central area of the coronal dentin to a cross-sectional area of approximately 0.5 mm2. The longitudinally sectioned slabs were either trimmed from the mesial and distal sides or from the occlusal and pulpal aspects to permit the tensile load to be applied either parallel or perpendicular to the tubule orientation. The transversally sectioned specimens were obtained at several distances from the pulp and were used to evaluate the effects of tubule density. The trimmed specimens were tested in tension on a Kratos testing machine at 0.5 mm/min. After failure, the UTS of each was calculated and expressed in MPa. The fractured ends of the transversally sectioned specimens were viewed under SEM to calculate the number of tubules per mm2 at the site of fracture, and its relation with the UTS was investigated by regression analysis.
The UTS of dentin is higher when the load is applied perpendicular to the tubule orientation (80 +/- 13 MPa) than when applied parallel to tubule orientation (58 +/- 11 MPa, p < 0.05). There was a tendency for dentin to be weaker as the number of tubules at the site of fracture increased, although this relationship was not statistically significant (R2 = 0.051, p > 0.05).
The UTS of dentin is dependent on the tubule direction. Dentin tends to be weaker as the number of tubules per area increases.
本研究调查了人类牙本质的极限拉伸强度（UTS）与小管方向和密度的关系。
通过使用Isomet锯横向或纵向切割人类第三磨牙的牙冠来获取牙本质薄片（约0.7毫米厚）。将薄片轻轻修整，把牙冠中部牙本质区域的横截面积减小至约0.5平方毫米。纵向切割的薄片要么从近中侧和远中侧修整，要么从咬合面和牙髓面修整，以使拉伸载荷能够平行或垂直于小管方向施加。横向切割的标本从距牙髓不同距离处获取，用于评估小管密度的影响。将修整后的标本在Kratos测试机上以0.5毫米/分钟的速度进行拉伸测试。破坏后，计算每个标本的UTS并以MPa表示。在扫描电子显微镜（SEM）下观察横向切割标本的断裂端，计算断裂部位每平方毫米的小管数量，并通过回归分析研究其与UTS的关系。
当载荷垂直于小管方向施加时，牙本质的UTS（80±13MPa）高于平行于小管方向施加时（58±11MPa，p<0.05）。尽管这种关系无统计学意义（R2 = 0.051，p>0.05），但随着断裂部位小管数量的增加，牙本质有变弱的趋势。
牙本质的UTS取决于小管方向。随着单位面积内小管数量的增加，牙本质往往会变弱。
