中文摘要：

目的：检测磨牙冠部中央区釉牙本质交界（dentin-enamel junction,DEJ）和牙本质的极限抗拉强度（ultimate tensilestrength,UTS）及断裂面分析。方法：第三磨牙牙合面分层堆积树脂,沿颊舌方向切割成厚度为1 mm的薄片后,用金刚砂车针打磨成截面积大约为1 mm×1 mm的哑铃型试件。测试磨牙中央区DEJ、牙本质浅层、牙本质中层、牙本质深层垂直和水平向的极限抗拉强度。所有试件断口扫描电镜观察。结果：牙本质不同层面的UTS呈各向异性,由牙本质浅层至牙本质深层UTS递减（P〈0.05）,釉牙本质交界区域和牙本质中层的UTS无统计学差异（P〉0.05）;断口扫描电镜观察表明管周牙本质、管间牙本质显示不在同一平面的断裂形式,牙本质和牙釉质断裂过程中裂纹进展方向改变,大多数DEJ试件的裂纹常发生在牙釉质侧。结论：磨牙冠部牙本质抵抗水平向断裂的能力强,DEJ对釉质裂纹的扩展有一定的抑制作用。

英文摘要：

Objective：To determine the ultimate tensile strength（UTS） of molar coronal dentin and the dentin-enamel junction（DEJ） area,and analyze its fracture surface.Methods： A resin composite block was built up on the human third molar occlusal surface.Slice the teeth buccolingually to obtain slices about 1mm thick.Each slice was then trimmed to a dumbbell-shaped specimen with a fine diamond bur,and to reduce a cross sectional area of about 1mm×1mm.DEJ,superficial dentin,middle dentin and deep dentin specimens were obtained from the midcoronal for tensile testing vertically and horizontally.The fracture surfaces were observed by scanning electron microscope.Results：The UTS of dentin at different levels was anisotropic and decrease from superficial dentin to deep dentin（P0.05）.The UTS of DEJ and middle dentin showed no significant difference（P0.05）.SEM micrographs：Fractures did not occur in one single plane along the peritubular dentin and intertubular dentin.The direction of fracture crack was changed in the dentin and enamel.Most DEJ specimens fractured in the nearby enamel.Conclusions：The dentin of molar crown showed higher ability to resistant fracture in the horizontal direction.The dentin-enamel junction provided a crack-arrest barrier for flaws formed in the brittle enamel.