[Interfacial strength and microleakage pattern of paired visible light cured composites]

The clinical build up of visible light cured restorations in many cases is performed by layering different types of composites to obtain enhanced characteristics. The purpose of this study was to evaluate the interfacial strength and microleakage pattern of paired light-cured restorations. Two small particle (SP), two pure hybrid (HB) and two microfilled materials (MF) were selected. Cylindrical molds were used to prepare double layer specimens for the groups SP-HB, SP-MF, HB-MF and the controls. The last group was comprised of double layer specimens respectively. All the samples were immersed in normal saline at 37 degrees C and divided in two series. The first series included samples immersed in normal saline for 24 h and accelerated aged for 1 h in saline at 37 degrees C plus 1000 times thermal cycling between 5 degrees-60 degrees C. These samples were sheared off at 0.005 inch/min cross-head speed. The second series was composed of the samples subjected to the some experimental conditions but tested for their interfacial microleakage pattern utilizing the silver nitrate technique. According to the results pairing SP-MF, SP-HB increases interfacial strength compared to MF-MF, and HB-HB. The combination of HB-MF results in no statistical significance from MF-MF or HB-HB. Minimal leakage was detected in some cases but did not correlate to bond strength values.