Objectives: To determine the stiffening rate of demineralized dentin matrix subjected to different neat solvents. Methods: Dentin beams of approximately 0.8 mm X 0.7 mm X 8.0 mm were obtained from human third molars. They had their ends covered with resin composite leaving a middle exposed length of 4.0 mm (Gauge lenght) to be demineralized in 0.5M EDTA (pH 7.0) for 7 days. The specimens were individually gripped to a Vitrodyne machine, pre-loaded to 10 g and stressed in tension up to 5% strain for 30 cycles (20 min) at 0.6 mm/min while immersed in water (control). Then, water was replaced by either acetone, methanol, ethanol, propanol or butanol, and the specimen subjected to the same cyclic protocol. The maximum modulus of elasticity (E) 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. ANOVA was used for comparisons. Results: E values are in MPa ± SD, N=5.

Solvent	E / min	E Max cycle 1	E Max cycle 15	E Max cycle 30
Water	-0.00069±0.00029a	0.109±0.025a	0.100±0.026a	0.094±0.023a
Acetone	0.00944±0.00255b	0.185±0.034a	0.284±0.043b	0.374±0.061b
Methanol	0.00600±0.00175b	0.213±0.042a	0.292±0.068b	0.333±0.071b
Ethanol	0.00811±0.00274b	0.155±0.058a	0.248±0.089b	0.317±0.110b
Propanol	0.00541±0.00195b	0.190±0.103a	0.246±0.109b	0.298±0.132b
Butanol	0.00238±0.00462a	0.169±0.072a	0.172±0.068a	0.217±0.085b

Regression analysis showed that E increased significantly with time for all water-free solvents (R²=0.8 to 0.99). Stiffening rate was higher for acetone and ethanol, intermediate for methanol and propanol and lower for butanol (p<0.05). Conclusions: The stiffening rate of demineralized dentin matrix is both time and solvent dependent. Supported by CNPq 300481/95-0, FAPESP 01/06140-1 and 01/07250-5.