Effect of Solvent on Enamel Bond Strengths with Universal Adhesives

Objectives: To compare the effect of solvent in universal adhesives on enamel shear bond strengths (SBS).
Methods: Crowns of 64 bovine mandibular incisors were embedded in acrylic resin, wet-polished up to 600-grit SiC paper and assigned to 3 universal adhesives (UAs) with different solvents (n=16): (1) Ethanol-based UA (ADU, AdheSE Universal, Ivoclar Vivadent); (2) Isopropanol-based UA (PBU, Prime&Bond Universal, Dentsply); and (3) Acetone-based UA (OPT, OptiBond Universal, Kerr Co.). A non-solvated hydrophobic resin (HEL, Heliobond, Ivoclar Vivadent) was used as control. A double-sided tape with a 2.5 mm-diameter perforation was placed over the enamel surface to delimit the bonding area. The adhesive procedures were performed under X2.5 magnification. Enamel was etched with 37.5% H₃PO₄ (Kerr Gel Etchant, Kerr Co.) for 15 sec, rinsed with water and air-dried. The adhesives were applied according to the respective manufacturer's instruction The specimens were positioned onto the Ultradent Bonding Assembly (Ultradent Products Inc.). After adhesive application, composite cylinders (Filtek Z250, 3M) were built-up using the Ultradent mold (internal diameter=2.4 mm; height=2.5 mm). Composite was light cured (40 sec/increment, 40J/cm²) keeping the light tip in contact with the mold. Specimens were stored in water (24h/37°C). A knife-edged metallic rod (Ø=2.8mm semi-circular notch) loaded the composite cylinders (Instron 4444, 1mm/min) until fracture. Mode of failure was analyzed with optical microscopy (Í40): A) Adhesive; M) Mixed; CR) Cohesive in resin composite; CE) Cohesive in enamel. Statistics included one-way ANOVA and post-hoc test (α=95%).
Results: Mean SBS [MPa±(SD)] and failure mode are displayed in Table. HEL resulted in four pre-testing failures (0 MPa):
Conclusions: All UAs resulted in statistically higher enamel SBS than the non-solvated hydrophobic resin regardless of the solvent in their composition.