Objectives: To determine the Knoop microhardness (KMH) of bovine enamel after grinding, acid treatment and resin infiltration with different adhesive systems. Methods: flat (4000grit) enamel surfaces of 3mm thick from bovine incisors were divided in 5 groups: 1) 36% Phosphoric acid etching (PAE) and infiltration with Prime&Bond NT; 2) PAE and infiltration with Single Bond; 3) application of Prompt-L-Pop; 4) application of Etch & Prime 3.0; 5) application of Clearfil SE Bond. After grinding, etching and infiltrating MH was measured with a KMH tester using 30g load. Self-etching primers were eliminated from surfaces with ethanol solutions prior to KMH test of etched surfaces and reapplied before testing infiltrated surfaces. Infiltrated surfaces were carefully ground in order to remove the adhesive layer and obtain infiltrated enamel. Results were analysed by ANOVA and Student Newman Keuls tests (p<0.05). Results: Means and standard deviations (SD) of KMH (KNH) are shown in the table. Same letter indicates no differences in columns and number in files. Conclusions: PAE decreased KMH more than self-etching primers. The highest KMH values were obtained after resin infiltration with SB and CSEB. (CICYT/FEDER:MAT2001-2843-CO2.RED CYTED VIII.J)

	Ground	Etched	Infiltrated
1. PBNT	302 (16) A1	158 (41) A2	186 (40) A3
2. SB	304 (10) A1	140(38) A2	238 (47) B3
3. PLP	301 (11) A1	196(31) B2	172 (31) A3
4. EP	301 (12) A1	247 (50) C2	188 (41) A3
5. CSEB	307 (11) A1	181 (44) B2	222(37) B3