EFFECT OF DIFFERENT REPAIR PROTOCOLS ON BOND STRENGTH TO DIRECT AND INDIRECT RESIN COMPOSITE

Objective: This study was carried out to investigate the effect of different surface treatment protocols on bond strength of nano-composite as a repair material to two types of resin composite either direct composite or indirect resin composite blocks for CEREC system.
 
Materials and methods: Total of 80 composite discs were prepared and were divided into two main groups (40 each) according to the type of composite used (C), nano-filled composite (C1) and composite blocks for CEREC system (C2). All specimens were aged for one month in a distilled water solution at 370C. Each group was sub-divided into  four subgroups (10 each) according to the surface treatment protocol (T) that was done on the  discs, either no treatment (T0) (control), application of  Ortho phosphoric acid (T1), Hydrofluoric acid (T2) and Sandblasting(T3) . Each sub group was subdivided into two classes (5 each) according to silane application (S1) or without (S0). Nanofilled resin composite (Filtek Z350 XT, 3M ESPE) was used as a repair material. Microshear bond strength testing (μ-SBS) was done using Universal testing machine. Failure modes of the fractured specimens were analyzed using scanning electron microscope (SEM). μ-SBS results were analyzed using ANOVA, Tukey’s post-hoc and Student t-tests.
 
Results: The indirect resin composite of the hydrofluoric acid group with silane showed the highest µ-Shear bond strength mean value (31.35±5.1) while the direct composite of the etchant group with no silane showed the lowest µ-Shear bond strength mean value (20.8±4.5). Regarding the composite type, C2 recorded statistically significant (P<0.05) higher µ-shear bond strength mean value (27.05±6.1 MPa) than C1  (23.82±6.2 MPa). Regarding the surface treatment, T3  recorded statistically non-significant (P>0.05) highest µ-shear bond strength mean value (26.72±0.78 MPa) followed by T1  (25.77±2.55 MPa) then T2  (24.71±1.44 MPa) while T0  recorded statistically non- significant (P>0.05) lowest µ-shear bond strength mean value (24.54±1.7 MPa). Regarding the silane application, S1  recorded statistically non-significant (P>0.05) higher µ-shear bond strength mean value (26.28±1.57MPa) than S0(24.59±1.66MPa).
 
Conclusions:   The Cojet treatment of the resin composite improved the bond strength of different types of resin composite .The type of resin composite used for repair influences the bond strength to the repaired resin composite. Silane application to repaired resin composite affects the bond strength to it with different treatment protocols.