الفهرس 
IntroductionOnly 14 pages are availabe for public view
 |  | from | 126 |  |  |
| | | from | 126 | | |
Abstract
This study was conducted to evaluate the effect of time and surface treatment on shear bond strength of repaired fiber reinforced resin composite to nano-hybrid resin composite material. A total of 80 specimens were prepared from light cured FRC (everX Posterior) using a split Teflon mold with central hole 5mm in diameter and 2mm in height. They were equally assigned to two main groups according to the time of repair (24 hours and one month). The specimens of each group were stored in distilled water in the incubator at 37°C. At the end of the storage period each group was furtherly divided into five subgroups (n=8) according to the surface treatment applied: Subgroup (1): (No surface treatment). For the other subgroups the specimens were treated as follows; Subgroup (2): (Diamond coated bur, phosphoric acid etching, two step self-etch adhesive), Subgroup (3): (Diamond coated bur, phosphoric acid etching, two step self-etch adhesive, silane coupling agent), Subgroup (4): (Air abrasion, phosphoric acid etching, two step self-etch adhesive), Subgroup (5): (Air abrasion, phosphoric acid etching, two step self-etch adhesive, silane coupling agent). All steps of surface treatment were applied according to the manufacturer’s instructions. A tygon tube with 1.3 mm diameter and 2mm height was placed on the surface of fiber reinforced composite specimens and the repair nanohybrid resin composite was then applied.
All the fiber reinforced resin composite specimens with their overlying repair nanohybrid resin composite material were subjected to thermocycling for 5000 cycles which is equivalent to six months in water baths. The temperature range was 5-55°C with a dwell time 30 seconds and transfer time ten seconds. Specimens were fixed on a custom made acrylic block then, secured in a mounting lower jig of a universal testing machine. A stainless-steel wire (0.2mm diameter) was looped semi-circularly around the bonded assembly as close as possible to the bonding interface and aligned with the long axis of the upper moving jig of the universal testing machine. The shear test was done at across head speed of 1mm/min until failure. A stereomicroscope was used to evaluate the type of the fracture.
Two-way ANOVA test showed that the type of surface treatments, the time of repair and their interaction had a statistically significant effect on shear bond strength of nanohybrid resin composite repair material to fiber reinforced resin composite substrate. Regarding the time of repair, for the subgroups (1-5) that were repaired after 24 hours showed high statistically insignificant difference between each other. While for the subgroups (1, 2, 4 and 5) that were repaired after one month showed high statistically insignificant difference between them. While they all were highly statistically significant compared to (subgroup 3), which had the lowest statistically significant value of SBS (MPa). Regarding the surface treatments, the subgroups (2, 4 and 5) which were repaired after one month had a statistically significant higher values compared to those repaired after 24 hours. While for subgroups (1 and 3) there was no statistically significant difference whether they were repaired after 24 hours or after one month.
When specimens were examined under the stereomicroscope, mixed and cohesive failures were common, where fibers became prominent and detached from the surface.