Department of Mechanical Engineering, University of Maryland Baltimore County, 1000 Hilltop Circle, Baltimore, MD 21250, USA.
J Dent Res. 2011 Aug;90(8):1031-6. doi: 10.1177/0022034511408429. Epub 2011 May 31.
The fatigue crack growth resistance of dentin was characterized as a function of depth from the dentino-enamel junction. Compact tension (CT) specimens were prepared from the crowns of third molars in the deep, middle, and peripheral dentin. The microstructure was quantified in terms of the average tubule dimensions and density. Fatigue cracks were grown in-plane with the tubules and characterized in terms of the initiation and growth responses. Deep dentin exhibited the lowest resistance to the initiation of fatigue crack growth, as indicated by the stress intensity threshold (ΔK(th) ≈ 0.8 MPa•m(0.5)) and the highest incremental fatigue crack growth rate (over 1000 times that in peripheral dentin). Cracks in deep dentin underwent incremental extension under cyclic stresses that were 40% lower than those required in peripheral dentin. The average fatigue crack growth rates increased significantly with tubule density, indicating the importance of microstructure on the potential for tooth fracture. Molars with deep restorations are more likely to suffer from the cracked-tooth syndrome, because of the lower fatigue crack growth resistance of deep dentin.
牙本质的疲劳裂纹扩展阻力随距牙釉质牙本质界的深度而变化。从第三磨牙的牙冠制备紧凑拉伸（CT）标本，在深部、中部和周围牙本质中。用平均小管尺寸和密度来量化微观结构。疲劳裂纹与小管成平面生长，并根据起始和生长响应进行特征描述。深层牙本质表现出最低的疲劳裂纹扩展起始阻力，这表明其应力强度阈值（ΔK(th) ≈ 0.8 MPa•m(0.5)）和最高的增量疲劳裂纹扩展率（比周围牙本质高 1000 倍以上）。在循环应力下，深层牙本质中的裂纹经历了增量扩展，其循环应力比周围牙本质低 40%。平均疲劳裂纹扩展率随小管密度显著增加，表明微观结构对牙齿断裂的潜在可能性很重要。由于深层牙本质的疲劳裂纹扩展阻力较低，因此深度修复的磨牙更容易出现裂纹牙综合征。
