الفهرس 
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Abstract
This study was conducted to evaluate the effect of different surface treatment protocols after different time lapsed on the repair bond strength of HVGIC. Eighty half hourglass slabs of Fuji IX (GC Corporation, Tokyo, Japan) were constructed in a specially designed copper mold, while other 10 whole hourglass slabs were acting as the control group. The 80 half hourglass slabs were then divided into four groups (20 each) according to the different surface treatments applied (Group I: The repair material was added after substrate was left to set against air. Group II: The repair material added after substrate was left to set against matrix. Group III: The repair material added after substrate was exposed to grinding. Group IV: The repair material added after substrate was exposed to both grinding and conditioning with 25% PAA (3M ESPE AG, Germany)). Each group was further divided into 2 subgroups (10 each) according to the time lapsed (Subgroup 1: the repair material was added at five min from the start of mixing of the substrate material. Subgroup 2: the repair material was added at ten min from the start of mixing of the substrate material). The repaired slabs were then covered with a varnish (GC corporation, Tokyo, Japan) and kept for 24 h in a humid condition. The TBS for the cohesive and repaired slabs was then evaluated using a universal testing machine at a crosshead speed 0.5mm/min. All fractured surfaces were evaluated to assess the type of failure. Then data were collected and analyzed using two-way ANOVA. Statistical analysis was carried out using SPSS program (SPSS, 2008). The results of two-way ANOVA showed that the type of surface treatment employed, the time lapsed and their interactions got a statistically significant effect on the repair bond strength evaluated.
Fracture mode of all samples was analyzed using stereo-microscope at x25 magnification. The analysis of the failure mode showed that 33.75 % were cohesive, 23.75% were adhesive and 42.5 % were showing mixed failure.