Bedran-de-Castro Ana Karina B, Pereira Patricia N R, Thompson Jeffrey Y
Department of Operative Dentistry, Dental Research Center, School of Dentistry, University of North Carolina, Chapel Hill, NC 27599-7450, USA.
J Adhes Dent. 2004 Autumn;6(3):191-4.
The purpose of this study was to evaluate the effect of mechanical load cycling and tubule orientation on the ultimate tensile strength of crown and root dentin.
Twenty bovine teeth were cleaned and their incisal surfaces reduced, resulting in a flat surface 4 mm above the cementoenamel junction. The teeth were divided into 4 groups: G1 = control (no mechanical load cycling); G2 = 1,000,000 load cycles at 50 N; G3 = 1,000,000 load cycles at 100 N; G4 = 1,000,000 load cycles at 200 N. Sections of 0.5+/-0.1 mm thick were cut mesiodistally and the slabs further trimmed to 0.5+/-0.1 mm in an hourglass shape, according to the tubule orientation (parallel and/or perpendicular to the long axis of the tooth) in the root and crown, with a fine diamond bur to produce a cross-sectional surface area of 0.25 mm2. All specimens were then subjected to ultimate tensile strength testing at a crosshead speed of 1 mm/min. Means and standard deviations were expressed in MPa. The bond strength data were analyzed with three-way ANOVA and Fisher's PLSD test (p < 0.05).
Ultimate tensile strength values did not differ statistically significantly between the loaded group and the control. However, statistical differences existed between root and coronal dentin (p < 0.001) and between parallel and perpendicular orientation of tubules (p < 0.001), where root and sections parallel to the tubules presented higher values than coronal and perpendicular, respectively. These differences were not related to mechanical loading.
There was no effect of in vitro load cycling on ultimate tensile strength of dentin. Differences presented between ultimate tensile strength of crown vs root dentin and parallel vs perpendicular to the tubule orientation can be influenced by differences in the amount of organic and inorganic content as well as composition of the dentin matrix. It is important to consider these aspects when predicting the quality and durability of restorations according to the types of dentin and tubule orientation to be restored.
本研究旨在评估机械加载循环和小管方向对冠部和根部牙本质极限拉伸强度的影响。
清洁20颗牛牙并磨除其切端表面，在牙骨质牙釉质界上方4mm处形成一个平面。将牙齿分为4组：G1 = 对照组（无机械加载循环）；G2 = 在50N下进行1,000,000次加载循环；G3 = 在100N下进行1,000,000次加载循环；G4 = 在200N下进行1,000,000次加载循环。沿近远中方向切割厚度为0.5±0.1mm的切片，并根据根部和冠部中小管的方向（平行和/或垂直于牙齿长轴），使用精细金刚石车针将切片进一步修整成沙漏形，使其厚度为0.5±0.1mm，以产生0.25mm²的横截面积。然后所有标本在十字头速度为1mm/min的条件下进行极限拉伸强度测试。均值和标准差以MPa表示。使用三因素方差分析和Fisher's PLSD检验（p < 0.05）分析粘结强度数据。
加载组和对照组之间的极限拉伸强度值在统计学上无显著差异。然而，根部和冠部牙本质之间（p < 0.001）以及小管平行和垂直方向之间（p < 0.001）存在统计学差异，其中根部和与小管平行的切片分别呈现出比冠部和垂直方向更高的值。这些差异与机械加载无关。
体外加载循环对牙本质的极限拉伸强度没有影响。冠部与根部牙本质的极限拉伸强度以及平行与垂直于小管方向之间存在的差异，可能受牙本质基质中有机和无机成分的含量以及组成差异的影响。在根据待修复的牙本质类型和小管方向预测修复体的质量和耐久性时，考虑这些方面很重要。
