الفهرس 
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Abstract
The present in-vitro study was done to investigate two goals:
Firstly, degree of conversion was determined and compared between two bulk-fill flowable composites and two conventional flowable composites. A total number of 28 cylindrical specimens 6mm in diameter and 4mm in thickness were fabricated from cured flowable composites using Teflon split mould. Twenty eight specimens were divided into four groups; each group contained 7 specimens according to the tested materials.
group I: FiltekTM bulkfill flowable composite.
group II: FiltekTM Z350XT universal flowable composite.
group III: Smart dentine replacement (SDR)TM.
group IV: X-FlowTM.
Bulk-fill flowable composite applied in one increment of 4mm and conventional flowable composite applied in two increments of 2mm each then cured according to manufacturer instructions. Degree of conversion was evaluated using Fourier Transform Infra-red Spectroscopy.
All data were collected, tabulated and statistically analyzed using one way ANOVA-F test for comparison between more than two groups, and Post hoc test (Tukey) for pair wise comparison.
Secondly microleakage was evaluated in class V cavity preparations restored with two Bulk-fill flowable composites (SDR and Filtek bulkfill flowable), and two conventional flowable composite (X-Flow and filtek Z350XT flowable).
Forty four human permanent molars teeth were randomly divided into four groups with 11 teeth per group according to the materials applied as in degree of conversion determinations. Class V cavities with 4mm mesio-distal width,4 mm depth, and 2mm occluso-cervical length were prepared, with the cervical border 1mm above the cement-enamel junction on the buccal surface.
The bonding agents and flowable composites were applied and cured with respect to their groups according to manufacturer’s instructions. All the restored molars were thermocycled for 500 cycles between temperatures of 5°C and 55ºC with dwell time of 30 sec. The roots apices were sealed with sticky wax and the specimens were coated with nail polish varnish except 2mm around the restoration margins.
The molar teeth were immersed in 0.5 % Basic fuchsin dye at 37°C for 24 hours then washed in water. Each tooth was sectioned longitudinally in a bucco-lingual direction through the center of the tooth
The sectioned specimens were observed with stereomicroscope at 40X magnification and were scored for degree of dye penetration at occlusal and gingival margins. All data were collected, tabulated, and the statistical analysis was done between the four groups using Kruskal Wallis test, and Mann Whitney test for pair wise comparison.
Regarding degree of conversion determination, ANOVA-F test revealed statistical significant difference among the four groups (p <0.001). SDR (bulk-fill flowable composite) in group III recorded the highest mean DC (57.97) in comparison to the other three groups, whereas Filtek Z350xt (conventional flowable composite) in group II with mean 38.89 recorded the lowest DC.
With respect to microleakage scores at the occlusal margins, Kruskal Wallis test proved no significant difference among the four groups with (p=0.563). SDR (bulkfill flowable composite) in group III recorded the lowest mean microleakage scores (0.18) among the four groups, whereas X-flow (conventional flowable composite) in group IV showed the highest mean of microleakage scores (0.45). Mann Whitney test showed that no significant difference between the lowest and the highest groups (group III and group IV respectively), with p=0.18.
With respect to microleakage scores at the gingival margins, Kruskal Wallis test proved no significant difference among the four groups with (p=0.243). SDR (bulk fill flowable composite) in group III recorded the lowest mean microleakage scores (0.36) among the four groups, whereas Filtek Z350XT (conventional flowable composite) in group II showed the highest mean of microleakage scores (1.18). Mann Whitney test showed that no significant difference between the lowest and the highest groups (group III and group II respectively), with p=0.080.