EFFECT OF ANTIOXIDANT TREATMENT AND DELAYED BONDING ON SHEAR BOND STRENGTH OF PORCELAIN LAMINATE VENEERS BONDED TO BLEACHED ENAMEL (IN VITRO STUDY)
AbstractIntroduction: Porcelain laminate veneers are sometimes necessary after bleaching in patients requiring marked change in tooth color. Bonding following bleaching has been shown to be compromised. The use of an antioxidant agent and delayed bonding could improve bonding.Aim of the study: was to evaluate the effect of antioxidant treatment and delayed bonding, one week after bleaching, on the shear bond strength of porcelain laminate veneers bonded to bleached enamel in comparison with immediate bonding after bleaching.Methodology: Forty freshly extracted maxillary central incisors with flat enamel surfaces were prepared and divided into four groups (n=10/group). Three test groups were bleached with 40% hydrogen peroxide (Power Whitening) and one control group was left as unbleached enamel. Forty glass ceramic discs were fabricated using IPS e.max Press to be bonded to the enamel surface. Group A:antioxidant treated specimens. Bleached specimens were treated with an antioxidant agent, 10% sodium ascorbate, for 10 minutes then glass ceramic discs were bonded to the specimens. Group B:delayed bonded specimens. Bleached specimens were stored in artificial saliva for 7 days then glass ceramic discs were bonded to the specimens. Group C: immediate bonded specimens. Glass ceramic discs were immediately bonded to bleached specimens. Group D:control group. Glass ceramic discs were bonded to unbleached specimens. Dual cured resin cement (RelyX U200) was used for bonding. Following bonding, the specimens were thermocycled for 600 cycles corresponding to one clinical year service then tested for shear bond strength using a universal testing machine at a crosshead speed of 0.5 mm/min. Bond failure analysis was evaluated for the specimens using a stereomicroscope and random samples were chosen to be tested under a scanning electron microscope.Results: No significant difference was found between the control, delayed bonding and antioxidant treated group (p<0.001). Immediately bonded group showed significantly lower mean bond strength with glass ceramic discs than all groups (p<0.001).Conclusions: It is recommended to delay bonding for one week after bleaching or use 10% sodium ascorbate to reverse bleaching.