Surface Pre-treatment Effects Composite-to-composite Bond Strength

Objectives: Despite over 40-years of clinical use there are still no clear guidelines on what pre-treatment is required in order to repair fractured composite restorations predictably. Here, we compare the in vitro efficacy of three common surface pre-treatments on the shear bond strength (SBS) of composite repairs.
Methods: Disc specimens (diameter=12mm, thickness=3mm, n=45) were fabricated from five commercially available composites (table 1) using custom-made resin moulds. Specimens were polymerised for 40s on both faces (Coltolux LED, 500mW/cm²) and then left to condition for 24-hours in distilled water at 37°C. Specimens were divided into 3 treatment groups:
Group1: Polished for 60s (P600, SiC paper)
Group2: As group1, plus etched for 15s (36% H₃PO₄, Conditioner 36, DeTrey)
Group3: As group2, plus treated with a bonding agent as per manufacturer’s instructions (Optibond Solo Plus, Kerr)
For each group, fresh composite of the same brand was then applied to the treated surface (5mm diameter, 5 mm height) and polymerised for 40 seconds before incubating at 37°C for 24 hours in distilled water. SBS was then measured for each group (1mm/min, Instron 5567) and representative specimens of G1 and G2 profiled (Surftest SV-2000, Mitutoyo).
Results: Polishing the surface in isolation resulted in a low SBS for all materials. While acid-etching resulted in no increase in Ra for any composite (P>0.05, Kruskal-Wallis) the SBS increased for most composites (P<0.05, ANOVA), suggesting that some sub-micron roughening must have occurred. Group3 could not be profiled but the SBS significantly increased for all groups compared to group2 and group1 (P<0.05).
Conclusions: Within the limits of this study, simply polishing composites prior to repair resulted in a low SBS. To optimise SBS, both etching and applying a bonding agent were required. Further work is required to consider the compound effect of composite aging and bonding dissimilar composites together.