Methods: Extracted human teeth were sectioned, ground to expose superficial dentin and embedded in acrylic. Indirect composite cylinders, 3mmX4mm (Premise, Kerr) were polymerized under nitrogen pressure. The cylinders were then bonded to dentin using either Clearfil Esthetic cement (Kuraray) or RelyX Unicem cement (3M ESPE) according to manufacturer's instructions. The specimens were cured contacting the cylinder using one of three curing lights, Flash Lite Magna (Discus), Valo (Ultradent), Optilux 501 (Kerr), Half of the specimens were thermocycled for 500 cycles at 5-55°C and the remaining were stored at 37°C for 24 hours prior to shear strength testing using an Instron machine. Data was analyzed by one-way ANOVA and Tukey's post hoc test at the 0.05 level of significance.
Results: Mean shear bond strengths in megapascals (MPa) for non thermocycled and thermocycled, respectively were: Flash Lite Magna 10.41, 7.58; Valo 14.26, 12.57; Optilux 501 12.43, 8.42. Mean shear bond strengths for nonthermocycled and thermocycled cements were: Clearfil 14.81, 10.0; RelyX Unicem 9.93, 9.05; respectively. Significant differences were found between: the Valo and Optilux 501 (p=.026), Valo and Magna (p=.001). Significant differences were also found between the two cements (p=.007) and thermocycled versus non thermocycled results (p=.014).
Conclusions: The Valo curing light showed significantly higher bond strengths amongst the three lights evaluated, while Clearfil cement outperformed RelyX Unicem. Thermocycling significantly lowered the bond strengths of indirect resins for all light and cement combinations. Supported in part by Kerr, Kuraray, and 3M ESPE.