الفهرس 
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Abstract
This study aimed to evaluate the effects of addition of FGO with four concentrations, to conventional GICs, on their surface microhardness, compressive strength, antimicrobial effects, either after 24 h or after thermocycling (equivalent to 1 year). Fluoride ion release was also evaluated after storage in deionized water for 1, 7 days and 1, 3, and 6 months’ time intervals versus their equivalent thermal cycles.
Fluorinated graphene oxide powder was prepared from fluorinated graphite powder (Sigma Aldrich™) using improved Hummer’s method. After characterization with XRD, FTIR, and TEM, FGO powder was added to three Fuji IX powder bottles using mechanical blending method with three concentrations (1 wt. % FGO, 2.5 wt. % FGO, and 5 wt. % FGO) forming three groups (group 2, 3, and 4 respectively), in addition to the conventional GICs control group (group 1).
Sample size calculation resulted in total number of specimens being 64 specimens, to increase the power of the study, a total of 320 specimens were prepared (80 specimens for each concentration and 80 specimens for each test). For surface microhardness, compressive strength, and antibacterial effects, half the number of specimens (40 specimens) were subjected to thermocycling (equivalent to 1 year) being 10,000 thermal cycles between 5 °C and 55 °C with 15 s dwell time and 10 s transfer time. While for fluoride ion release 40 specimens were tested after different storage times in deionized water, and the other 40 specimens were tested after their equivalent thermal cycles.
For SMH, compressive strength, and antimicrobial activity tests, results were calculated using two-way ANOVA, p-values were adjusted for multiple comparisons using Bonferroni correction.
For SMH test, specimens with dimensions 10 mm diameter and 2 mm thickness were tested using Vickers microhardness test. For 24 h, only 5 wt. % FGO (group 4) showed increased SMH values. While thermocycling adversely affected all groups with no significant differences between them.
For compressive strength test, specimens with dimensions 4 mm diameter and 6 mm height were prepared according to ISO Guidelines No. 9917–1:2007 (E), and were tested using a universal testing machine (Instron 3365; Massachusetts, UK) (Figure 9) with a crosshead speed of 0.5 mm/min. For 24 h groups, groups 3 and 4 showed the highest values, while thermocycling adversely affected all groups with group 4 having more pronounced adverse effects than group 3.
After compressive strength test, SEM was used to characterize the fractured surfaces of specimens to evaluate the homogenous distribution of FGO in GICs.
For antimicrobial activity tests against each Streptococcus mutans and Candida albicans, specimens’ dimensions 30 mm x 30 mm x 1 mm were tested using pellicle sticking method. For both 24 h and thermo-cycled groups, all groups showed increased antimicrobial activity with increase in FGO concentration, which was not affected by thermocycling.
For fluoride ion release test, results were calculated using three-way mixed model ANOVA, P-values were adjusted for multiple comparisons using Bonferroni correction.
For fluoride ion release test, specimens with dimensions 10 mm diameter and 2 mm thickness were prepared to be stored in deionized water and placed in plastic tubes (CELLSTAR® polypropylene tubes), fluoride release was evaluated using fluoride ion selective electrode. Half the number of specimens were tested after each 1, 7 days as well as 1, 3, and 6 months after renewal of the deionized water after each time interval. And the other half were tested after their equivalent thermal cycles (20, 140, 600, 1800, and 3600 respectively). Results showed that after both aging simulation procedures, that after 1 day, and 7 days, groups 3 and 4 showed the highest results. And after 1 month, and 3 months, group 4 showed the highest results. And after 6 months, all groups were comparable.
While comparing both aging procedures, no significant differences were found between all tested groups after all time intervals.
For cumulative fluoride ion release, after 1 and 7 days immersion time and for the equivalent thermocycles, groups 4 and 3 showed the highest fluoride release with no significant difference between them. And after 1, 3 and 6 months, group 4 exhibited the highest cumulative fluoride release values. Groups 1 and 2 showed the lowest cumulative fluoride release values at all time intervals and equivalent thermocycles.