الفهرس 
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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.