الفهرس 
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Abstract
This study was conducted to evaluate the effect of various types, placement techniques and aging of composite resin on the fracture resistance of premolars with restored MOD cavities. A total of 40 sound upper premolars with standardized MOD cavities were used for this study. Specimens (n=40) were randomly divided into two main groups (n=20) according to the type (consistency) of resin composite restoration. Then, each group of them will be divided into two subgroups (n=10) according to the technique of placement of the resin composite restoration and each subgroup will be further divided into two divisions (n=5) according to the effect of thermocycling.
G1 (Incremental G-aenial posterior) as the control group, G2 (Bulk-fill EverXposterior + G-aenial posterior), G3 (Incremental G-aenial Universal Injectable), G4 (Bulk-fill EverXflow + G-aenial posterior). Half the number of each of those 4 groups (n=5), a total of (n=20) were randomly chosen and thermocycled for 5000 cycles (between 5 and 55 °C with a dwell time of 30 s and a transfer time of 15 s).
Specimens were individually mounted on a computer-controlled material testing machine (Instron 3345) with a load cell of 5 kN and the maximum load to produce fracture in Newton (N).
Statistical analysis was performed using the three-way ANOVA test and Bonferroni-corrected Mann-Whitney U test. The results of this study showed that the bulk-fill packable SFRC (EverXposterior) had the highest fracture resistance value (1129.83±112.15)N in the non-aged groups and the bulk-fill flowable SFRC (EverXflow) had the highest fracture resistance value (1504.92±5.46)N in the aged groups. While, the control (group 1), had the lowest value of fracture resistance (681.68±51.15)N in the aged groups.
Summary and Conclusions
Conclusions:
Within the limitations of this study, the following conclusions could be suggested:
1- The flowable resin composite materials had a higher value of fracture resistance than the packable resin composite materials after aging, Additionally, the bulk-fill flowable short fiber reinforced composite material showed the highest value of fracture resistance among all other restorative materials.
2- The bulk-filling technique, especially with short fiber reinforced composites, showed improved fracture resistance values than the incremental conventional technique.
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3- Thermocycling at (5000 cycles) deteriorates the fracture resistance of packable resin composite materials while it enhanced the fracture resistance of the flowable resin composite materials.
Recommendations:
1- The flowable resin composite materials might be very promising in restoring upper premolars with MOD cavities, especially the bulk-fill flowable short fiber reinforced composite material.
2- The bulk-fill short fiber reinforced composites, used as restoration of premolars with MOD cavities, could have a significant reinforcing effect on the treated teeth more than the incremental conventional technique.
3- Aging could have a significant influence on decreasing the fracture resistance of packable resin composite materials while increasing the fracture resistance of the flowable resin composite materials.