Effects of solvents on the early stage stiffening rate of demineralized dentin matrix

OBJECTIVES: To monitor the stiffening rate of demineralized dentin matrix at the early stages after exposure to different neat solvents. METHODS: Dentin beams approximately 0.8x0.7x8.0 mm were obtained from human third molars. After covering their ends with resin composite, the middle exposed length of 4.0mm (gauge-length) was demineralized in 0.5 M EDTA (pH 7.0) for 7 days. The specimens were gripped by a testing machine, pre-loaded to 10 g and cyclically stressed in tension to 5% strain, for 30 repeated cycles (total 20 min) at 0.6 mm/min while immersed in water (control). Then, water was replaced by either 100% acetone, methanol, ethanol, propanol, HEMA or air and the specimens subjected to the same cyclic protocol. The maximum apparent modulus of elasticity (E(Max)) was calculated for every cycle, plotted as a function of time and subjected to regression analysis. Stiffening rate was calculated as changes in E (min). Regression analysis examined the relationship between E and time for each solvent. Data were analyzed by one-way ANOVA and Student-Newman-Keuls test at alpha=0.05. RESULTS: Regression analysis showed that E increased significantly with time in all water-free solvents (R2=0.8-0.99). Stiffening rate was higher for acetone (0.9 MPa/min) and ethanol (0.8 MPa/min), intermediate for air (0.7 MPa/min), methanol (0.6 MPa/min) and propanol (0.5 MPa/min), lower for HEMA (0.2 MPa/min) and practically none for water (0.07 MPa/min) with p<0.05. CONCLUSIONS: The solvent-induced stiffening rate of demineralized dentin matrix is both time and solvent-dependent. The ability of solvents to promptly stiffen the demineralized dentin matrix may be important in maintaining the resin-infiltrated matrix expanded during the solvent evaporation stage of resin bonding.