Relationship between ceramic primer and ceramic surface pH on the bonding of dual-cure resin cement to ceramic

Objectives. This study examined the relationship between a ceramic primer and ceramic surface pH on the microtensile bond strength of dual-cure resin cement to ceramic. Methods. Ceramic blocks (Vita Celay Blanks) were cut into multiple 3 mm-thick slices and polished using 600-grit SiC paper. Two pairs were left untreated (controls), six pairs were treated with 40% phosphoric acid (PA), six pairs were treated with 20% hydrofluoric acid (HFA), and rinsed with water for either 15, 30 or 60 s. Half the specimens were silanated with Tokuso ceramics primer (TCP) (Tokuyama) and the other half with TCP formulated without phosphate monomer (TCP-NoPM). All the pairs were bonded with Bistite II dual-cure resin cement (Tokuyama) and light-cured. After 24 h water storage at 37 °C, the bonded specimens were cut into 6×0.7×0.7 mm3 beams and their microtensile bond strengths (μTBS) determined. Failure modes were determined using a confocal laser-scanning microscope. For scanning chemical analysis, the polished slices were cut into quarters, divided into seven groups of six, and treated in a similar manner as described for the μTBS test. Surface pH was then determined using a scanning chemical microscope. For SEM examination, one ceramic quarter from each of the seven groups was used. Results. Three-way ANOVA revealed that the μTBS of TCP was significantly higher than TCP-NoPM with no acidic treatment (p<0.05). However, after treatment of the ceramic surface with either PA or HFA, and 15 s rinsing, there was a significant reduction in surface pH (p<0.05), and no significant difference in μTBS between TCP and TCP-NoPM (p>0.05). For TCP, there were no significant differences in μTBS and failure mode between the control, PA, and HFA treated groups when the water rinsing time was increased. Whereas, for TCP-NoPM and surface treatment with PA, an increase in rinsing time resulted in a significant reduction in μTBS and a significant increase in surface pH (p<0.05). Significance. Acidic treatment of the ceramic surface did not significantly increase dual-cure resin/ceramic bond strengths when the ceramic primer, TCP, was used. It is suggested that when no phosphate monomer is present in a ceramic primer, dual-cure resin cement/ceramic bond strength is dependent upon the concentration of H+ ions on the ceramic surface.