PubMed · 13231165
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B BILY. 1954. [Notes on dentinogenesis imperfecta].. https://pubmed.ncbi.nlm.nih.gov/13231165/
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As cyclic fatigue is considered to be a major cause of clinical tooth fractures, achieving a comprehensive understanding of the fatigue behavior of dentin is of importance. In this note, the fatigue behavior of human dentin is examined in the context of the Kitagawa-Takahashi diagram to define the limiting conditions for fatigue failure. Specifically, this approach incorporates two limiting threshold criteria for fatigue: (i) a threshold stress for fatigue failure, specifically the smooth-bar (unnotched) fatigue endurance strength, at small crack sizes and (ii) a threshold stress-intensity range for fatigue-crack growth at larger crack sizes. The approach provides a "bridge" between the traditional fatigue life and fracture mechanics based damage-tolerant approaches to fatigue-life estimation, and as such defines a "failure envelope" of applied stresses and flaw sizes where fatigue failure is likely in dentin This approach may also be applied to fatigue failure in human cortical bone (i.e. clinical "stress fractures"), which exhibits similar fatigue behavior characteristics, and in principle may aid clinicians in making quantitative evaluations of the risk of fractures in mineralized tissues.
For a description of light propagation in biological tissue it is usually assumed that tissue is a random medium. We report a pronounced light guiding effect in cubes of human dentin that cannot be described by this standard model. Monte Carlo simulations which consider the microstructure of dentin are performed and successfully compared to experiments. Contrary to explanations so far, we show that light guiding is due to scattering by the tissue's microstructure. Exploiting this concept, light can be guided in arbitrary directions or locations without involving reflections or wave effects.