Effect of Antioxidant Treatment and Delayed Bonding on Shear Bond Strength of Porcelain Laminate Veneers Bonded To Bleached Enamel (In Vitro Study)

Abstract

This study was designed to investigate the effect of antioxidant application following bleaching as well as delaying bonding after bleaching. Forty intact maxillary central incisors, free of caries were used. IPS e.max Press ingots were used to fabricate 40 ceramic discs (6 mm diameter × 4 thickness). The teeth were divided into four groups: three of which were test groups and one was control. In the three test groups, the enamel surfaces were bleached using 40% hydrogen peroxide (WHITEsmile POWER WHITENING) for 20 minutes. The control group was left unbleached.  group A “Antioxidant treatment”: (n=10) glass ceramic specimens bonded to enamel surfaces that were treated with an antioxidant following bleaching. Antioxidant of 10% sodium ascorbate was applied in the form of gel on the enamel for 10 minutes.  group B “Delayed bonding”: (n=10) glass ceramic specimens bonded to enamel surfaces after immersion in artificial saliva for one week following bleaching. The artificial saliva solution was changed twice daily during the 7-day time period.  group C “Immediate bonding”: (n=10) glass ceramic specimens bonded to enamel surfaces immediately after bleaching.  group D “Control group”: n=10 glass ceramic specimens bonded to unbleached and untreated enamel surfaces. The glass ceramic discs were bonded to the treated and untreated (control) enamel surfaces using a self-adhesive resin cement (RelyX U200) following the manufacturer‟s instructions. 65 All 40 specimens were tested after bonding and thermocycling for 600 cycles using a universal testing machine at cross-head speed of 0.5 mm/min until failure occured. The load denoting failure point was then recorded. Shear bond strength (B) values were calculated using the following formula(89): B = F×S − 1 Where: B: shear bond strength in MPa F: the load in N at failure S: the bonded area of the cylinder in mm2 S=πr2 Where: S: the bonded area of the cylinder in mm2 π: 3.14159 r: radius of the cylinder in mm Data was collected, tabulated and statistically analyzed. Results showed that there was no significant difference between shear bond strength of the antioxidant treatment group (group A), delayed bonding (group B) and that of the control group (group D). It also showed that the shear bond strength between the immediate bonding group (group C) was significantly lower than all other groups (groups A, B and D).