Faria-e-Silva, Piva, Moraes profiles were detected for the 10, 15, and 20 min post-refrigeration times; the immediate and 5 min times showed lower Rpmax compared with all other groups. In contrast, for Clearfil, all post-refriger- ation times showed lower R max values compared p with the control group. Comparing the bonding resins, the R was slightly slower and higher R max p p values were usually detected for Clearfil. dIscussIon The fundamental principle of bonding to enam- el and dentin relies on a micromechanical inter- locking in which the inorganic phase of the demin- eralized substrate is exchanged by the adhesive resin. The bonding resin should be able to fully penetrate into the etched substrate and polymer- ize in loco, and therefore it must present proper fluidity to permit its infiltration. The results of this study demonstrated that the refrigeration of the bonding resins dramatically increased their vis- cosity, and similar values to those of the non-re- frigerated sample were detected only 20 min after removing the materials from refrigeration. Thus, the hypothesis tested for viscosity was confirmed. Despite the similarity in viscosity of the con- trol samples of each bonding resin, Scotchbond showed a higher increase in viscosity due to re- frigeration than Clearfil, which also showed faster increase in temperature after refrigeration. One possible explanation for this is related to the role of the components in the formulation. Both adhe- sives present Bis-GMA, a very viscous, high molec- ular weight monomer. However, while the diluent monomer for Scotchbond is the dimethacrylate TEGDMA, Clearfil contains the monomethacrylate HEMA as the main diluent, which has lower viscos- ity. Distinct ratios between Bis-GMA and diluent is one of the factors that might be responsible for the differences in viscosity. Another factor is the presence of fillers, which increases the viscosity of Clearfil. The fact that both materials presented similar viscosities at room temperature suggests that Scotchbond has a higher amount of Bis-GMA, which could explain the increased viscosity during refrigeration compared with Clearfil. Another observation was that the decrease in viscosity over the course of time was dependent on the material tested. Although Clearfil showed Figure 2. Profiles of polymerization kinetics for Scotchbond. Significantly higher final DC was detected for the control in comparison with the immediate and 5 min post-refrigeration groups, while similar DC was observed for the times 10, 15, and 20 min compared with the control sample. Table 2. Means (standard deviations) for viscosity and degree of conversion. Figure 3. Profiles of polymerization kinetics for Clearfil. The control sample showed significantly higher final DC than all post-refrigeration groups. Group Immediate 5 min 10 min 15 min 20 min April 2010 - Vol.4 Viscosity (Pa.s) Degree of conversion (%) Scotchbond 0.487 (.006) A,a 0.336 (.005) B,b 0.295 (.006) B,c 0.257 (.004) A,d 0.234 (.003) A,e Clearfil 0.376 (.007) B,a 0.367 (.003) A,a 0.338 (.006) A,b 0.254 (.005) A,c 0.238 (.006) A,d Scotchbond 53.3 (3.1) B,c 54.7 (2.4) B,bc 57.6 (2.6) B,ab 59.4 (3.4) B,a 59.5 (4.1) B,a Clearfil 68.8 (5.0) A,b 68.9 (4.8) A,b 69.1 (6.0) A,b 69.2 (3.6) A,b 69.5 (3.2) A,b Control 0.226 (.003) A,e 0.224 (.004) A,e 62.7 (3.3) B,a 81.4 (6.7) A,a Means followed by distinct letters in the same line, and small letters in the same column, are significantly different at P<.05. 153 European Journal of Dentistry