Flaw Sensitivity of Dentin: Importance of Depth and Microstructure

Flaw sensitivity and damage tolerance are commonly used in describing the mechanical behavior of structural materials. However, these terms are seldom used in referring to the behavior of dentin and enamel, despite their importance to the success of clinical practices. Objective: To evaluate the strength and apparent flaw sensitivity of coronal dentin, and to assess differences related to dentin depth and the chemical composition. Methods: Rectangular beams (N=60) were sectioned from the coronal dentin of molars from patients of 17≤age≤27. Four groups were examined including two groups of nominally flaw-free beams prepared from inner (near the pulp) and outer (near the DEJ) dentin, as well as two groups from these regions with a single “surface flaw” made by indentation. The flexure strength, and the strain and energy to fracture of the groups were quantified using Weibull statistics. Fourier Transform Infrared Microspectroscopy in Reflectance Mode (FTIR-RM) was used to examine the relative mineral and collagen contents. Results: The average elastic modulus (p ≤ 0.05), flexural strength (p ≤ 0.005), and strain (p ≤ 0.005) and energy to fracture (p ≤ 0.001) of the inner dentin were significantly lower than those properties of outer dentin. Although the indentation surface flaws did not cause a significant reduction in strength, results from the Weibull analyses suggested that the inner dentin exhibited a larger intrinsic flaw size distribution. Conclusion: The region with the highest mineral/collagen ratio and lowest collagen content exhibited the lowest strength and energy to fracture. There is a greater likelihood for tooth fracture to initiate from deep restorations due to an increase in stress within regions of lower damage tolerance and a larger distribution of intrinsic flaws. (Supported by the National Institutes of Health (NIDCR DE016904), the NSF (BES 0238237) and by a fellowship to DH Wang from Kyungnam University)