Faria-e-Silva, Piva, Moraes Another factor that might affect the perfor- Temperature mance of adhesive agents is their temperature The temperature of the bonding resins at each during polymerization. Manufacturers usually rec- post-refrigeration time was measured using a ommend that dental adhesive resins be stored at K-type thermocouple connected to a digital ther- room temperature to prevent early evaporation of mometer (Tecpel Co. Ltd., Taipei, Taiwan). The the solvent. However, they are commonly refriger- thermocouple tip (0.2 mm diameter) was placed ated to extend their shelf life, and dentists usu- into the bottle for 5 s and the temperature record- ally take the materials from the refrigerator and ed. Two measurements were performed after re- use them immediately under clinical conditions. frigeration and equilibration cycles and averaged. As the temperature potentially interferes with the All analyses were performed under controlled viscosity and the ability of the solution to penetrate temperature (25±1°C) and humidity (60±5%) con- into the substrate, as well with the reactivity of the ditions. monomers,11,12 it is likely that this process may af- fect the efficacy of bonding agents. Viscosity Few studies have reported the influence of Viscosity measurements for the control and all refrigeration on the performance of bonding post-refrigeration times of both adhesive agents agents,13-16 and conflicting results are described were performed using a cone-plate digital vis- in literature. Spohr et al16 detected no significant cometer (CAP2000+; Brookfield, Middleboro, MA, differences in bond strength between specimens USA). A constant 5 µL volume of the bonding so- at room temperature and refrigerated specimens lutions was dispensed in the equipment operat- for etch-and-rinse systems, while Pazzinato et ing under the following settings: temperature of al15 reported that the environmental temperature 25°C, speed of 200 rpm, shear rate of 1 s-1, and can influence the rate of spreading of the adhesive run time of 15 s. Three specimens were tested for system in clinically relevant times and may influ- each material/post-refrigeration time condition. ence adhesive thickness on cavity walls as well. The refrigeration and equilibration cycles were While these studies usually concentrate on evalu- conducted after placing the adhesive resins back ating bond strengths, there is no report in the lit- into the refrigerator for 24 h. Data were computed erature regarding the effect of refrigeration on the in Pa.s and submitted to two-way ANOVA (materi- polymerization mechanism or viscosity of dental al vs. post-refrigeration time) followed by Tukey’s adhesive resins. test (P<.05). The purpose of this study was to evaluate the effect of refrigeration at 4oC and post-refrigera- Real-time infrared spectroscopy tion times (immediate, 5, 10, 15, or 20 min) on the The real-time polymerization was evaluated by viscosity and conversion kinetics of bonding res- Fourier transform infrared spectroscopy (Pres- ins. The hypothesis tested was that refrigeration tige21; Shimadzu, Tokyo, Japan) as previously would have a time-dependent influence on both described,17 using an attenuated total reflectance viscosity and polymerization. device composed of a horizontal ZnSe crystal. A constant volume (5 µL) of bonding solution was MAtErIALs And MEtHods dispensed onto the crystal and photo-activated for The bonding resins of two adhesive systems 20 s using a quartz-tungsten-halogen light unit were evaluated: Scotchbond Dual-Cure (3M ESPE, (Optilux501; Demetron Kerr, Orange, CA, USA) St. Paul, MN, USA) and Clearfil SE Bond (Kuraray, with 600 mW.cm-2 irradiance. The polymerization Tokyo, Japan). The primer solutions were not test- reaction was monitored in real time for 1 min us- ed. Materials compositions are shown in Table 1. ing Happ-Genzel apodization, collecting spectra in tvChiosencmotrsoaitltyesraainamdlspplaoetlsy2mw5oeeCrreifzoadrtei2of4innhek.dinTbehyteicebsvoaanlfduteianrtgiknaeggebeponintthgs t8hcem1−618.0Wtioth1t5h4is0 scemtu−1pr,aonngee,swpeitchtrau mres(oonluetisocnanof) were stored under refrigeration at 4oC for 24 h. Af- every second was acquired. Three specimens ter removing the materials from the refrigerator, were tested for each material/post-refrigeration different post-refrigeration times were tested: im- time condition. The refrigeration and equilibration mediate, 5, 10, 15, and 20 min. cycles were conducted after placing the adhesive April 2010 - Vol.4 151 European Journal of Dentistry