Effect of surface treatment on roughness and bond strength of a heat-pressed ceramic

Statement of problem. Bonding ceramic restorations to tooth structure relies on treatment of the ceramic intaglio surface, selection of a suitable resin luting agent, and appropriate treatment of prepared tooth structure. Various ceramic surface treatments have been advocated which produce different topographies and bond strengths, but little information is available to identify the interaction between the resulting surface topography and bond strength. Purpose. The purpose of this in vitro study was to evaluate the effect of surface treatments on surface roughness and bond strength to dentin and enamel of a commercially available heat-pressed dental ceramic (IPS Empress). Material and methods. One hundred heat-pressed ceramic disks were fabricated according to the manufacturer's recommendations. Specimens were divided into 5 groups (n=20) and treated with I of the following: (1) etching with 9.5% hydrofluoric acid, (2) 50%, or (3) 60% orthophosphoric acid and airborne-particle abrasion with (4) 50-mu m, or (5) 250-mu m alumina for 10 seconds. Morphological changes obtained with the surface treatments were investigated with a surface texture analyzer on half of the treated specimens. Two additional specimens from each group were treated and prepared for scanning electron microscopy. The specimens were then used for a bond strength test. The treated specimens were silanated and luted with a composite resin luting agent (Nexus 2) to enamel (n=50) and dentin (n=50) surfaces with 10 specimens for each treatment group. The luted specimens were loaded to failure in a universal testing machine in the shear mode with a crosshead speed of 0.05 mm/min. The data were analyzed with 1-way ANOVA followed by the Ryan-Einot-Gabriel-Welsch Multiple Range Test (alpha=.05). Results. Surface treatments resulted in significant differences for surface topography and shear bond strength (P<.001). Mean surface roughness (Ra) (SD) was (2.54 (0.21) mu m) for ceramic surfaces treated with 50-mu m aluminum powder. Treatment of ceramic specimens with 50% orthophosphoric acid appeared to result In a smoother surface (1.02 (0.38) mu m). The highest mean bond strength (SD) to enamel (14.7 (0.6) MPa) and dentin (8.2 (1.5) MPa) was associated with hydrofluoric acid etching. The lowest mean bond strength (SD) to enamel (2.7 (0.8) MPa) and dentin (1.5 (0.1) MPa) was recorded for 50% phosphoric acid. Conclusions. Hydrofluoric acid treatment resulted in the generation of pores and grooves that produced the greatest bond strength between the ceramic and tooth dentin and enamel. Orthophosphoric acid treatment was the least effective surface treatment method evaluated. The results are applicable to only the all-ceramic/luting system evaluated.