Effects of water and water-free polar solvents on the tensile properties of demineralized dentin

Objectives. The aim of this study was to test the null hypothesis that the tensile properties of demineralized dentin are not influenced by the hydrogen bonding ability of anhydrous polar solvents. Methods. Dentin disks 0.5mm thick were prepared from mid-coronal dentin of extracted, unerupted, human third molars. 'I' beam and hour-glass shaped specimens were prepared from the disks, the ends protected with nail varnish and the central regions completely demineralized in 0.5 M EDTA for 5 days. Ultimate tensile stress (UTS) and low-strain apparent modulus of elasticity (E) were determined with the specimens immersed for 60min in water, methanol, HEMA, acetone or air prior to testing in those same media. Apparent moduli of elasticity were measured on the same specimens in a repeated measures experimental design. The results were analyzed with a one-way ANOVA on ranks, followed by Dunn's test at α = 0.05. Regression analysis examined the relationship between UTS or E and Hansen's solubility parameter for hydrogen bonding (δ_h) of each solvent. Results. The UTS of demineralized dentin in water, methanol, HEMA, acetone and air was 18(7), 29(7), 31(6), 41(13) and 146(27)MPa, x̄(SD), n = 10. Low-strain E for the same media were 11(7), 43(12), 79(21), 132(31) and 253(115)MPa. Regression analysis of UTS vs δ_h revealed a significant (p < 0.0005, r = -0.69, R² = 0.48) inverse, exponential relationship. A similar inverse relationship was obtained between low-strain E vs δ_h (p < 0.0001, r = -0.93, R² = 0.86). Significance. The tensile properties of demineralized dentin are dependent on the hydrogen bonding ability of polar solvents (δ_h). Solvents with low δ_h values may permit new interpeptide H-bonding in collagen that increases its tensile properties. Solvents with high δ_h values prevent the development of these new interpeptide H-bonds.