الفهرس | Only 14 pages are availabe for public view |
Abstract Summary The current study was designed to investigate the effect of preheating of composite resin on intrapulpal temperature (IPT) and dentin microtensile bond strength (µTBS). For the IPT testing, 36 molar teeth were used to obtain discs by removing the occlusal enamel to expose the superfacial/middle dentin surface (1 disc/tooth) of different thicknesses (0.5mm,1mm,1.5mm). The discs were divided into three groups (n=8) according to the temperature applied on microhybrid P60 composite resin either at room temperature or 54 ℃ or 68 ℃ using a CalsetTM device. IPT was measured at baseline, after application of the preheated composite, after the first curing cycle for composite and finally after the second curing time using K-type thermocouple. For the µTBS testing, 16 molar teeth were used to obtain beams through removing the occlusal enamel parallel to cementoenamel junction to expose the dentin. The teeth were divided according to the type of composite resin either microhycrid (P60) or nanohybrid (Z250). These 2 groups were subdivided into 4 subgroups according to the number of preheating cycles either no heating, one preheating cycle at 68 ℃, two preheating cycles at 68 ℃ or three preheating cycles at 68 ℃ (2 teeth/group). Meta® BIOMED Etchant and Single bonding Agent™ was applied to the exposed dentin according to the manufacturer’s instructuctions then each type of composite resins was applied in 2 increments (1.5 mm each) and cured at 0 mm distance for 40 seconds. Each specimen was sectioned into beams (8/group). The beams were subjected to µTBS test, the failed specimens were examined after testing and the failure mode was recorded whether adhesive, cohesive or mixed. Summary 84 The final results of the current study revealed that whenever the dentin thickness decreased, the IPT increased but it did not affect the pulp cells. Regarding the temperature of the composite to be placed, there was no difference between all groups; 37 ℃, 54 ℃ and 68 ℃. Increasing the temperature to 68 ℃ increased the µTBS to dentin in case of P60 microhybrid resin composite which was increased with the second preheating cycle but did not further increase with a third heating cycle. On the other hand, with Z250 nanohybrid resin composite, preheating did not affect the µTBS with any cycles of preheating compared to the room temperature. Repeated heating cycles affected the degree of conversion of P60 resin composite rather than Z250, this was reflected in the mode of failure where in P60 specimen, the adhesive mode of failure showed dominance, while in C0 was more frequent. On the other hand, the failure mode of Z250 was similar in all tested groups. |