The shear bond strength of freshly added composite resin to a repaired chemically bleached composite.

The purpose of this in-vitro study was to evaluate the shear bond
strength (SBS) of a repaired chemically bleached composite using a freshly added composite material. Materials and Methods: Forty composite disk specimens were prepared using a (8X3mm) Teflon mold. All specimens were stored in saline solution for 2 months. The specimens were divided into four groups (10 each) according to the instance of new composite addition. A Teflon mold (5X3mm) was used for adding the new composite disk by packing of the new composite to the previously cured disk. Group A (the control group) new composite was added to non-bleached composite . While group B fresh composite was added immediately after bleaching, group C it was added 1 week after bleaching, and group D it was added 2 weeks after bleaching.chemical bleaching was used. The SBS between the two composite disks was measured using Instron universal testing machine. Results: ANOVA test revealed statistically significant difference between the four groups (p<0.001), with the highest mean shear stress values recorded in group A followed by D then group C, while the lowest recorded in group B. Pairwise Posthok test revealed highly statistically significant difference between group B vs. A and D (p<0.001*). Statistically significant differences were found between groups A & B versus C. Non-significant differences were recorded between groups A&C versus group D. Conclusions: Teeth bleaching significantly decreases SBS in composite repair . Postponing the composite repair after bleaching procedure has a major role in regaining the desired SBS.