Microshear Bond Strength of Repaired Composite after Different Surface Treatments

Objectives: To determine the influence of two mechanical surface treatments and bleaching on the microshear bond strength of repaired resin composite using two different adhesive systems. Methods: Thirty circular discs (1cm diameter x 2mm thickness) of Herculite Ultra (HU) resin composite (Kerr) were made. Six specimens were used as control, while the other 24 discs were aged in distilled water for 6 months. The aged discs were assigned into 2 groups (n=12), one group was bleached using Colgate Simply White Night Clear, while the other was not bleached. Both groups were stored in distilled water for two weeks then subdivided into 2 subgroups according to the used mechanical surface treatment, either diamond fissure point or air abrasion with 25 µm AI203 particles for 10 seconds. Etch and rinse adhesive [OptiBond FL (OBFL), Kerr] and self-etch adhesive [OptiBond All.In.One (OB), Kerr] were used to bond the control and the treated composite substrates to the new resin composite. HU composite resin was used for composite cylinders build up (0.9mm diameter x 0.5mm height). Three composite cylinders were constructed on each treated surface (n=9). Lloyd universal testing machine was used to test microshear bond strength at crosshead speed of 0.5 mm/minute. The data were statistically analyzed using One-way ANOVA and Tukey's test (P≤ 0.05). Results: After aging, the mean microshear bond strength of OBFL (25.3 MPa) showed statistically significantly higher value than OB (22.47 MPa). Diamond point surface treatment showed the lowest mean microshear bond strength value (20 MPa). There was no statistically significant difference in the microshear bond strength values between bleached (23.77 MPa) and non-bleached (24 MPa) specimens. Conclusions: Under the test conditions, air abrasion of aged composite provided better microshear bond strength, whereas bleaching had no effect. Etch and rinse adhesive offered better microshear bond strength for the repaired composite.