Surface treatments to improve the repair of acrylic and bis-acryl provisional materials.

PURPOSE: To evaluate the in vitro effects of the Composite Primer and different surface treatments on the shear bond strength (SBS) of acrylic and bis-acryl repairs with resin composite (RC).

METHODS: Acrylic (Alike) and bis-acryl (Protemp 4) blocks were prepared. Surface roughness was standardized (0.16 µm) and grit blasting was applied to half of the samples. Blocks were divided randomly into groups according to surface treatment [methyl methacrylate monomer (MMA) for 180 seconds or bonding agents (Composite Primer and Scotchbond Multi Purpose), applied alone or following MMA]. Two consistencies of RC [ regular (Filtek Z350XT and Solare composite) or flowable (Filtek Z350XT flowable and G-aenial flowable composite) ] were used to test bond repair. Cylinders (2 mm diameter) of each RC (n= 10/group) were attached to the block surface, and SBS was measured using a universal testing machine at 0.5 mm/minute. Failure (adhesive, cohesive or mixed) was assessed under ×3.5 magnification. SBS data were analyzed using factorial ANOVA, followed by Tukey post-hoc, and Weibull moduli estimation (α = 0.05).

RESULTS: The highest SBS, Weibull modulus (m) and scale parameter (σ0) were found in combined use of MMA and bonding agents (P< 0.001), regardless of the substrate, RC consistency or brand. The use of the Composite Primer and flowable RC also increased SBS (P< 0.001). Significant interaction between surface treatment and RC consistency was observed for the PMMA substrate (P< 0.001). Sandblasting did not influence SBS (P> 0.05). Adhesive failure was most prevalent (93.5%) and SBS values were significantly higher in mixed fractures (19.2± 3.8 MPa) compared to the adhesive ones (9.7± 6.0 MPa) (P< 0.001). No cohesive fracture was observed.

CLINICAL SIGNIFICANCE: Composite Primer improved the adhesion of acrylic and bis-acryl repairs, especially when a flowable composite was used. When such product is not available, the combined use of MMA and a bonding agent is necessary, increasing the number of clinical steps, cost, and time required.