Time-Dependent Effect of Refrigeration on Viscosity and Conversion Kinetics of Dental Adhesive Resins André L Faria-e-Silvaa Evandro Pivab Rafael R Moraesb AbstrAct Objectives: This study evaluated the effect of refrigeration at 4oC and post-refrigeration times (immediate, 5, 10, 15, or 20 min) on the viscosity and conversion kinetics of adhesive bonding resins. Methods: Scotchbond Dual-Cure (3M ESPE) and Clearfil SE Bond (Kuraray) were tested. Control samples were kept at 25oC for 24 h. At each post-refrigeration time, the temperature was checked with a K-type thermocouple. Viscosity measurements as a function of temperature were performed using a cone-plate viscometer. Real-time polymerization was monitored by infrared spectroscopy. Degree of conversion (DC) was calculated for each second during polymerization, and the rate of po- lymerization analyzed. Data were separately submitted to two-way ANOVA and Tukey’s test (P<.05). Results: Clearfil presented faster increase in temperature after exposure to room temperature than Scotchbond. A continuous decrease in viscosity (Pa.s) was observed for both Scotchbond (0.49, 0.34, 0.30, 0.26, 0.23, 0.23) and Clearfil (0.38, 0.37, 0.34, 0.25, 0.24, 0.22). For Scotchbond, higher final DC was detected for the control (62.7%) compared with the immediate (53.3%) and 5 min (54.7%) groups. For Clearfil, the control sample (81.4%) showed higher DC than all refrigerated groups (68.8– 69.5%). Clearfil always showed significantly higher DC than Scotchbond. Conclusions: Refrigeration presented a significant time- and material-dependent effect on the viscosity and polymerization kinetics of the bonding resins. Under clinical conditions, adhesive agents should be removed from the refrigerator at least 20 min before being used. (Eur J Dent 2010;4:150- 155) Key words: Bonding resins; Degree of conversion; Polymerization kinetics; Refrigeration; Viscosity. a Professor, Department of Dentistry, School of Dentistry, State University of Montes Claros, MG, Brasil. b Department of Restorative Dentistry, School of Dentistry, Federal University of Pelotas, RS, Brasil. Corresponding author: Prof. André L. Faria-e-Silva Department of Dentistry, School of Dentistry State Uni- versity of Montes Claros, MG, Brazil Campus Universi- tário Prof. Darcy Ribeiro, Vila Mauricéia Montes Claros, MG, Brasil - 39401-089 Phone/Fax: +55 38 3229.8284 E-mail: andrelfsilva@hotmail.com IntroductIon The main goal of the adhesion of restoratives materials to dental hard tissues is to obtain high bond strengths and a satisfactory, long-lasting seal.1-3 Over the last decade, a number of inves- tigations have reported that several factors might interfere with the bonding ability of adhesive sys- tems to enamel or dentin, including the adhesion strategy,4 conditioning time,5 solvent removal method,6,7 thickness of the adhesive layer,8 and even the environmental humidity.9,10 150 European Journal of Dentistry