Evaluation of the effects of different mechanical surface treatments on surface roughness to improve repair bond strength of aged composite restoration


Background: Some clinical situation may require the repair of aged composite. The higher degree of resin conversion
rate may prove to be disadvantages if a repair procedure based on covalent bonding from unreacted
methacrylate group is attempted. This in vitro study evaluated the effects of different mechanical surface treatments
(ST) on surface roughness measurement (SRM) to improve repair shear bond strength (SBS) of aged composite
restoration and determine the mode of bond failure.
Materials and methods: Forty composite (Dyract® EXRTRA)samples for SBS test & twelve samples for SRM were
constructed & aged for 6 months in DD water at 37°C & randomly allocated into 4 groups(Gp) according to
mechanical ST; Gp-I(control):no mechanical ST. Gp-II: pumice polishing. Gp-III: Soflex disc polishing. Gp-IV: Diamond
disc roughening. After that all samples etched by H3PO4, SRM were measured, then intermediate adhesive (Prime &
Bond® NT) were applied, followed by repair composite material (Dyract® EXRTRA).After 24hr. storage &
thermocycling, the repair joint subjected to SBS test and the failure sites were examined to determine the mode of
failure. The data were statistically analyzed using one-way ANOVA and LSD - tests. Chi-square(X²) was used to test
the difference in the failure site. Statistical significance was accepted if p-value < 0.05.
Results: one-way ANOVA indicated that SRM values varied significantly (P<0.05).LSD-test showed that
significantly(P<0.001) superior mean SRM was obtained by Gp-IV(diamond) (0.38 ±0.06 &#956;m), followed by Gp-II(
pumicing)(0.16 ±0.01 &#956;m) that had significantly(P<0.05) higher mean SRM than Gp-I (control)(0.11 ±0.04 &#956;m), but
there are no significant difference (P=0.074) between Gp-II(pumicing)(0.16±0.01&#956;m) and Gp-III(Soflex)(0.12±0.2
&#956;m)and between Gp-I(control)&Gp-III(Soflex) (P=0.582). Also one-way ANOVA revealed that ST had a significant
(P<0.05) influence on repair SBS.LSD-test showed that both Gp-III(Soflex) & Gp-IV(diamond) resulted in repair
SBS(19.40±2.90Mpa and18.57±2.17Mpa, respectively) that were significantly (P<0.05) superior to both GP-I(control)
and Gp-II(pumicing) (13.14±1.91Mpa and15.14±2.07Mpa, respectively), while there are no significant difference
(P=0.059) between Gp-I(control) & Gp-II(pumicing) and also between Gp-III(Soflex) & Gp-IV(Diamond)(P=0.423).
Conclusion: Surface treatments of aged composite are important for adhesion of new composite restorations.
Roughening the composite adhesion area with diamond disc or polishing with Soflex disc can provide statistically
significant increase in SBS. Pumice polishing ST although it provides significant increase in SRM, but did not reveal
significant changes in repair SBS.
Key Words: Composite; Repair; Surface treatment; Surface roughness; Bond strength. (J Bagh Coll Dentistry