الفهرس 
Resin compositesOnly 14 pages are availabe for public view
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Abstract
The aim of this study was to evaluate a bulk fill flowable composite based on the stress decreasing technology and compare it to a conventional flowable one in relevance to degree of conversion, mini-flexure strength and induced cuspal strain during polymerization.
The specimens for DC and mFS were prepared and divided according to the resin composite material used into 2 different groups bulk-fill flowable composite (BFC) and conventional flowable composite (CFC). Each group was further subdivided into 3 subgroups according to the packing technique into 2mm single increment group, 4mm bulk packing group and 4 mm incremental packing group. For each subgroup, half the number of specimens was tested after 24 hours while the other half were tested after 6 months.
The degree of conversion was evaluated using FTIR spectrometer, while the mini-flexure strength test was performed using a universal testing machine. Analysis of the induced cuspal strain during polymerization of the two tested flowable composites was assessed by strain gages.
Results of this study revealed a significantly higher DC values for the conventional flowable composite CFC compared to the bulk fill flowable composite BFC after 24 hours storage in all experimental conditions except the 4mm bulk packing group. However, after 6 month storage duration the DC values of BFC were higher than CFC in all experimental conditions except for the 4mm incremental packing group where both showed no significant difference.
Regarding the effect of different packing techniques on the DC values after 24 hours storage time, no significant difference was found between different packing techniques for both CFC and BFC. While after 6 months storage time the 4 mm incremental packing group of BFC showed the significantly lowest DC values compared to the other subgroups. On the other hand the 4mm bulk packing group of CFC after 6 months showed the least significant DC values in comparison to other groups.
Regarding the effect of storage time, after 6 months DC results showed a significant decrease for CFC group compared to the 24 hours results in all experimental conditions. While no significant difference was found between both storage times for the BFC group.
The mini-flexure strength results after 24 hours showed an insignificant difference between both material types CFC and BFC when bulk packed in a single 2mm and 4mm increment. While BFC showed a significantly lower mFS values compared to CFC when packed incrementally in a 4 mm thickness. On the other hand after 6 months storage time CFC revealed a significantly lower mFS results compared to BFC in all experimental conditions.
Comparing different packing techniques and its effect on the mFS results revealed insignificant difference between different packing techniques after 24 hours for the CFC group. The 4 mm incremental packing subgroups showed the significant lowest mFS values in comparison to other subgroups at both storage times for BFC group. While CFC after 6 months showed the lowest mFS values when bulk packed in a 4 mm thickness compared to other experimental conditions.
Regarding the effect of storage time on the mini-flexure strength results, BFC showed insignificant difference between both storage times in all experimental conditions. While CFC after 6 months showed a significant decrease in mini-flexure strength results compared to the 24 hours results.
Induced cuspal strain during polymerization showed a significant higher strain values for CFC compared to BFC.