الفهرس 
IntroductionOnly 14 pages are availabe for public view
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Abstract
This in vitro study was carried out to evaluate and compare the shear bond strength and microleakage of flowable composite and flowable compomer against that of hybrid composite after two different aging intervals. Shear bond strength test: This study was performed on 60 extracted sound permanent upper human molars embedded in selfpolymerizing acrylic resin and supported by plastic mounting cylinders. The occlusal surface of each tooth was ground flat to expose enough dentin surface area. Then the teeth were divided into 3 groups according to the tested restorative material (flowable composite, flowable compomer and hybrid composite). The restoration samples of each restorative material were prepared on the corresponding teeth utilizing a stainless steel split mold with a standard central hole of 3mm dimension in diameter and height. After preparation of the restoration samples of all materials, all tooth specimens were subjected to thermalcycling (between 5 ?c to 55 ?c for 500 cycles using 30 seconds dwell time) and stored in distilled water at 37 ?c till the time of testing. Then each group was subdivided into 2 subgroups relative to the testing time to early (after 48 hours) and delayed (after 2 months). The shear test was conducted using LLOYD universal testing machine, with shear force range of 0 to 2500 N and crosshead speed of 2 mm/minute. ?Measurement of the shear bond strength was evaluated by dividing the exerted force at the moment of failure by the bonded surface area. The results were tabulated and subjected to statistical analysis using one way (ANOVA) and Student ttest. Microleakege test: This part of study was undertaken on 60 extracted sound permanent human upper premolars. A standardized trapezoidal class V cavity preparation with dimensions of 3mm for the occlusal wall and 2mm for the cervical and proximal walls was prepared on the buccal surface of each tooth with the gingival margin in the cementum. The teeth were divided into 3 groups according to the tested restorative material (flowable composite, flowable compomer and hybrid composite). The teeth of each group were restored with the corresponding material, subjected to thermalcycling (between 5 ?c to 55 ?c for 500 cycles using 30 seconds dwell time) and stored in distilled water at 37 ?c till the time of testing. Then each group was subdivided into 2 subgroups relative to the testing time to early (after 48 hours) and delayed (after 2 months). All teeth were painted with 2 layers of molten ulility wax except 1mm around the restored cavity margins. Then the teeth were immersed in 2% methanol solution of Liclman dye for 24 hours. Upon removal from the dye, each tooth was sectioned longitudinally at the center of the restoration and each half was examined under stereomicroscope at X20 magnification for the extent of dye penetration in tenth of millimeters. The results were tabulated and subjected to statistical analysis using one way (ANOVA) and Student ttest. The conclusions of the present study was: (1) Flowable composite revealed the highest shear bond strength to dentin at both 48 hours and 2 month aging intervals. (2) Flowable compomer revealed the least shear bond strength to dentin and maximum microleakage at the cervical wall after 48 hours and 2 month aging intervals. (3) Hybrid composite showed intermediate shear bond strength and microleakage between flowable composite and flowable compomer. (4) Aging for 2 months in water adversely affect the shear bond strength of all the tested restorative materials. (5) The sealing ability of the tested restorative materials seemed to be enhanced by aging in water up to 2 months as evident by decrease in microleakage. (6) Flowable compomer and hybrid composite showed better sealing ability to enamel than dentin/cementum margins, while flowable composite sustained the same sealing ability at both margins. (7) Further studies are encouraged for use of flowable composite in conjunction with other types of hybrid composite in such cases where enamel is missin