When dentin is air-dried after etching, the primer solution must be able to re-expand the matrix for proper resin infiltration. Solvation of dried dentin is dependent on the ability of the primer to interact with the dentin matrix. Objectives: This study tested the effect of several HEMA/solvent experimental primers on the bond strength to dentin. Methods: Flat dentin surfaces were etched with 35% phosphoric acid for 20s, rinsed and air-dried for 30s. The surfaces were primed with a 35% HEMA (H) mixed with either 65% water, methanol, ethanol, propanol or butanol as solvents (v/v solutions) for 60s and bonded with a 4-META/TBBO bonding agent (Amalgambond, Parkell). Resin (Z-100, 3M) build ups were constructed incrementally and the teeth stored for 24h at 37^oC. The teeth were longitudinally sectioned to obtain bonded beams of 0.8 mm². They were tested in a microtensile mode at 1.0 mm/min. Untested specimens were prepared for TEM analysis of the interface. Results:

Primer	H / Water	H / Methanol	H / Ethanol	H / Propanol	H / Butanol
Bond Strength MPa ± SD (N)	31.1±12.5 (19) b	33.5±12.6 (20) b	47.9±10.6 (20) a	16.1±12.8 (14) c	14.5±9.7 (13) c

ANOVA showed that bond strength was dependent on the solvent used in the experimental primers (p<0.05). TEM revealed differences in the morphology of the hybrid layers created by various primers. Propanol and Butanol groups showed a higher percentage of specimens that failed before testing. Conclusions: Bond strengths were dependent on the solvent used in the primer. Supported by 300481/95-0, CNPq, and 01/06140-1, FAPESP.