The effects of tubule orientation on fatigue crack growth

Abstract: The fracture of restored teeth is a significant obstacle to lifelong oral health. Recent studies suggest that fatigue cracks originate at flaws introduced during cavity preparation and that fatigue crack growth is a principle cause of restored tooth fractures. In this study, the rate of fatigue crack growth in bovine dentin was estimated under mode I cyclic loading. Double cantilever beam (DCB) spec-imens were obtained from bovine molars and subjected to high cycle fatigue loading (105N 106). The fatigue crack growth rates were measured and used to estimate the crack growth exponent and coefficient according to the Paris Law. The average fatigue crack growth exponent was 4.7 0.6 for crack growth parallel to the dentin tubules, which was sig-nificantly larger than 4.3 0.5 for crack growth perpendic-ular to the tubules (t-test, CI 80%). Although the crack growth rates varied considerably, there was no significant dependence on tubule orientation or tubule density. How-ever, specific features of the fracture surfaces and tendencies for crack curving away from the tubules suggested prefer-ential fatigue crack growth perpendicular to the dentin tu-bules. Results from this study are being used to guide an experimental investigation of fatigue crack growth in hu