Vol 5, No 2, 2003 129 Effect of 2% Chlorhexidine on Microtensile Bond Strength of Composite to Dentin Fabrício Luscino Alves de Castro a /Marcelo Ferrarezi de Andrade b / Sillas Luiz Lordello Duarte Júnior b /Luís Geraldo Vaz c / Fernando Jorge Mendes Ahid a a Doctoral student, Department of Restorative Dentistry, Araraquara School of Dentistry, UNESP, Araraquara, São Paulo, Brazil. b Assistant Professor, Department of Restorative Dentistry, Araraquara School of Dentistry, UNESP, Araraquara, São Paulo, Brazil. c Assistant Professor, Department of Dental Materials and Prosthet- ics, Araraquara School of Dentistry, UNESP, Araraquara, São Paulo, Brazil. Purpose: To evaluate the effect of 2% chlorhexidine on the microtensile bond strength of composite res- in to dentin treated with three dentin bonding systems. Materials and Methods: Flat dentinal surfaces were prepared in 24 extracted human third molars. Teeth were randomly divided into 8 distinct experimental groups according to the adhesive applied (Prime & Bond NT, Single Bond and Clearfil SE Bond), the application (yes/no) of chlorhexidine, and the time point at which it was applied (before or after acid etching the dentin). Composite resin blocks were built up over treated surfaces, and teeth were then stored in water at 37ºC for 24 h. Samples were thermocy- cled, stored under the same conditions, and then vertically sectioned, thus obtaining specimens with 1.0 ± 0.1 mm 2 cross-sectional area. Specimens were stressed in tension at 0.5 mm/min crosshead speed. Bond strength results were evaluated using a one-way ANOVA (p < 0.05). The modes of failures were verified using optical microscopy. Dentin disks were obtained from 3 additional teeth treated in the same manner for observation under SEM. The most representative samples of fractured specimens were also observed under SEM. Results: No statistically significant differences of bond strength values were found between any groups. Failures occurred mainly within the bond; exclusively adhesive fractures (adhesive-dentin) were not ob- served. Conclusion: The 2% chlorhexidine solution, applied before or after acid etching of the dentin, did not interfere with the microtensile bond strength of composite resin to the dentin treated with Prime & Bond NT, Single Bond, or Clearfil SE Bond bonding systems. J Adhes Dent 2003; 5: 129–138. Submitted for publication: 25.05.02; accepted for publication: 14.11.02. Reprint requests: Fabricio de Castro, Departamento de Odontologia Restauradora, Faculdade de Odontologia de Araraquara, UNESP, Rua Humaitá no 1680, Centro, 14801-903 Araraquara, São Paulo, Brazil. Tel: +55-16-3335-9579; 55-16-201-6388. e-mail: fabriciodecastro @hotmail.com ncomplete removal of caries-affected enamel or dentin is a problem in restorative dentistry, and secondary caries can appear if bacteria are left in the cavity after its preparation. Even when good sealing is obtained, those bacteria can multiply, cre- ating a toxin source that can diffuse to the pulp, re- sulting in irritation and inflammation. 3 A possible solution to this problem would be treating the cavity preparation with a disinfectant. Some authors recommend chlorhexidine applica- tion to the cavity prior to its restoration. 6,7 Chlor- hexidine has a broad spectrum of action; generally Gram-positive bacteria are more susceptible than Gram-negative, particularly Streptococcus mutans, which seems to be more sensitive. 7,9 I