Bonding Performance of Universal Adhesive Systems: Influence of surface free energy characteristics

Objectives: The purpose of this study was to evaluate the bonding performance of universal adhesive systems and the influence of surface free energy characteristics.
Methods: Three universal adhesives, GBU-500 (GB, GC), Scotchbond Universal (SB, 3M ESPE) and All Bond Universal (AB, BISCO) were used. Bovine enamel, dentin, resin composite, lucite glass-ceramic, lithium disilicate, zirconia, Au-Ag-Pd alloy and Au-Pt alloy were used as adherends. These adherends were wet ground with #600-grit SiC paper and the adhesives applied according to each manufacturer’s instructions. One set of sample was stored in 37 ℃ distilled water for 24h and other set thermal cycled for 10,000 cycles. Bond strengths of the adhesives with these adherends were measured by the notched-edge shear bond strength test (ISO 29022:2013). The surface free energies were determined by measuring the contact angles of three test liquids placed on the untreated and adhesive-treated surfaces. ANOVA and Tukey HSD tests at a level of 0.05 were done. SEM observations were also conducted.
Results: When bonding to a wide range of materials, GB consistently showed a bond strength of over 15MPa, while SB and AB greatly differed with different materials. Surface free energies of the untreated surfaces of a wide range of materials were significantly different depending on the adherends. On the other hand, the surface free energy of adhesive treated surfaces did not show any significantly difference depending on the adherends.
Conclusions: The experimental universal adhesive system (GBU-500) showed consistently high bond strength to wide range of restorative materials. The universal adhesive treatments change the surface free energy characteristics of various adherends.