Influence of Light Intensity on Surface Free Energy and Dentin Bond Strength of Core Build-up Resins

Abstract

SUMMARY Objective We examined the influence of light intensity on surface free energy characteristics and dentin bond strength of dual-cure direct core build-up resin systems. Methods Two commercially available dual-cure direct core build-up resin systems, Clearfil DC Core Automix with Clearfil Bond SE One and UniFil Core EM with Self-Etching Bond, were studied. Bovine mandibular incisors were mounted in acrylic resin and the facial dentin surfaces were wet ground on 600-grit silicon carbide paper. Adhesives were applied to dentin surfaces and cured with light intensities of 0 (no irradiation), 200, 400, and 600 mW/cm2. The surface free energy of the adhesives (five samples per group) was determined by measuring the contact angles of three test liquids placed on the cured adhesives. To determine the strength of the dentin bond, the core build-up resin pastes were condensed into the mold on the adhesive-treated dentin surfaces according to the methods described for the surface free energy measurement. The resin pastes were cured with the same light intensities as those used for the adhesives. Ten specimens per group were stored in water maintained at 37°C for 24 hours, after which they were shear tested at a crosshead speed of 1.0 mm/minute in a universal testing machine. Two-way analysis of variance (ANOVA) and a Tukey-Kramer test were performed, with the significance level set at 0.05. Results The surface free energies of the adhesive-treated dentin surfaces decreased with an increase in the light intensity of the curing unit. Two-way ANOVA revealed that the type of core build-up system and the light intensity significantly influence the bond strength, although there was no significant interaction between the two factors. The highest bond strengths were achieved when the resin pastes were cured with the strongest light intensity for all the core build-up systems. When polymerized with a light intensity of 200 mW/cm2 or less, significantly lower bond strengths were observed. Conclusions The data suggest that the dentin bond strength of core build-up systems are still affected by the light intensity of the curing unit, which is based on the surface free energy of the adhesives. On the basis of the results and limitations of the test conditions used in this study, it appears that a light intensity of >400 mW/cm2 may be required for achieving the optimal dentin bond strength.

Influence of duration of phosphoric acid pre‐etching on bond durability of universal adhesives and surface free‐energy characteristics of enamel

“…The surface free‐energy values ( γ S ) of the specimens with phosphoric acid pre‐etching were significantly higher than those of the specimens with and without a smear layer. Optimal wettability is important to enable the adhesive materials to spread across the entire adherend surface and establish adhesion . Theoretically, phosphoric acid pre‐etching creates more porosity on enamel surfaces and increases both the bonding area and the wettability of the substrate, permitting resin to infiltrate more deeply into the phosphoric acid pre‐etched enamel surface than into surfaces not pre‐etched .…”

Influence of light intensity on surface-free energy and dentin bond strength of single-step self-etch adhesives

“…Reportedly, the γS d values of many oxidized surfaces measured using this method are approximately 40 mN/m 12,15,19) , whereas those of surfaces coated with polytetrafluoroethylene are around 20 mN/m.…”

Light-Curing Units

“…Omitting any description of the method or an analysis of the light received by the RBC, many simply state that the restoration was light cured for xx seconds. Light curing an RBC is more complicated than this statement implies (Ferracane 2013;Leprince et al 2013;Strassler 2013;, and certain aspects of the process have been shown to greatly affect the outcome (Rueggeberg et al 1994;Ferracane et al 1997;Fan et al 2002;Vandewalle et al 2004;Xu et al 2006;Rueggeberg et al 2009;Ferracane et al 2013;Leprince et al 2013;Shortall et al 2013;Bortolotto et al 2014;Shimizu et al 2015).…”