Flexural strength of dual cured composite resin cements polymerized with different light sources


Aim: To determine the flexural strength of dual cured composite resin cements polymerized with LED light and Quartz-tungsten halogen light and to determine the effect of curing and storage time on the flexural strength. Materials and Methods: feldspathic porcelain (IPS InLine) used to produce uniform disc-shaped specimens (10mm diameter and 1.5mm thickness ). An electronic caliper was used to confirm precise specimen dimensions. Vita shade 2A was selected. One commercial dual-polymerizing composite resin cement was used (Variolink II; Ivoclar Vivadent ). The resin cement was placed in brass molds 8 ×6× 2 mm in size that lined with a teflon used to prepared the specimens to determine flexural strength. After insertion of the resin cements a glass slab was pressed over the mold and removed any expressed materials around the margins of the mold. A mylar strip (0.07 mm) was used to prevent adhesion of the resin cement to ceramic disk. Two types of light source were used: Quartz-tungsten halogen light and LED. The specimens divided into 8 groups (10 specimens for each). For each light source the curing time done for 20 and 60 sec. and the specimens either tested 15min. after curing or after 24hrs. Measurements for the 3-point flexural strength test were performed at a constant crosshead speed of 1 mm/min. Statistical data analysis was performed by three-way ANOVA and Duncan Multiple Range Tests to determine the significant group. Results: three- way ANOVA indicated there is no statistical significant differences between the two light sources (p>0.05), were as there is statistically significance between the flexural strength of specimen cured for 60 sec. and tested after 24hrs more than other groups (p<0.05). Conclusions: adequate curing time with 60sec. and instruction for the patient not to use of the restoration until at least 24hrs after the insertion of the restoration is advocated