الفهرس 
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Abstract
The present in vitro study was designed to investigate the aging effect on the micro-tensile bond strength and nanoleakage of bulk fill resin composite versus a
conventionally incrementally applied resin composite. Materials used in this study were X-tra fil® (Packable bulk fill resin composite), X-tra base® (Flowable bulk fill resin composite), Grandio®SO (Nano
hybrid resin composite) and Solobond® M (light-curing total-etch bond).
Methods: a total number of 45 extracted caries free human permanent molars were selected to prepare specimens for the micro-tensile bond strength (µTBS) and nanoleakage testing. Teeth were mounted in acrylic blocks to hold them in Isomet
for sectioning and flattening the occlusal surface. Teeth were randomly divided into three groups (C) according to type of resin composite material which used for restoring the teeth. where nanohybrid resin composite (Grandio SO®) was used as the control group (C1), Packable bulk fil resin composite (X-tra fil®) was used for restoring teeth in C2 group used for restoring teeth in C3 group. Each group was further subdivided into 3 subgroups (N=5) according to the water storage time, where in subgroup 1; teeth were stored for 24 hours, subgroup 2; teeth were stored for 3 months while for subgroup 3; teeth were stored for 6 months. Teeth of each subgroup were stored separately in distilled water at room temperature in a light tightly-sealed plastic container, labeled according to time of assessment. Each specimen were serially sectioned perpendicular to the bonded interface using the low speed diamond saw under water spray coolant for preparation of one slab for nanoleakage test and beams (0.9±0.1 mm in thickness and 7±1 mm in length) for micro-tensile testing. The prepared beams were tested individually using a universal testing machine. Maximum tensile stresses were recorded in megapascals (MPa). For nanoleakage Summary and Conclusion 60 testing the prepared slabs were immersed in prepared ammoniacal silver nitrate tracer solution for 24 h in a black photo-film container to ensure total darkness. The slabs then were rinsed with distilled water and immersed in photo-developing
solution for eight hours before nanoleakage evaluation using scaning electron microscope (SEM). The percentage distribution of metallic silver particles at the < adhesive/tooth substrate interface was calculated with a digital image analysis software (NIH ImageJ 1.60, Scion, and Frederick, MD, USA) in a selected area on each image. >Results: for μTBS, after 24 hours of water storage the X-tra base® showed a higher statistically significant μTBS to dentin (33.82 ±9.84 MPa) than did the other two types of resin composites. After three months the X-tra fil® showed the lowest mean value of μTBS (10.90 ± 5.66 MPa), meanwhile, after six months of water storage Grandio®SO showed the highest mean value of μTBS (15.85 ± 6.76 MPa). >Regardless of the time the X-tra fil® showed the lowest mean of μTBS (15.07 ± >11.73 MPa), while there is no significant difference between the X-tra base® and
Grandio®SO. Also the water aging adversely affect μTBS values which deceased gradually by time. For nanoleakage the results showed no statistically significant difference between he three types of resin composites, while aging showed statistically significant increase in distribution of metallic silver particles percentage at the adhesive/tooth
substrate interface.
Summar .