The effect of a novel self-etching ceramic primer on shear bond strength of milled lithium disilicate to resin cement
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Purpose: The purpose of this in vitro study was to evaluate the effect of a novel self-etching ceramic primer on the shear bond strength of lithium disilicate glass ceramic to a resin cement, in comparison to the conventional two-step etch and prime ceramic conditioning method. The study further evaluated the effect of artificial aging with thermocycling and the effect of over-etching lithium disilicate glass ceramic on its shear bond strength to a resin cement. Material and methods: One hundred and forty-four composite resin rods (2.5mm in diameter and 3mm in length) were fabricated from a nano-hybrid resin composite using a polypropylene mold, then light polymerized with a light-emitting diode. One hundred and forty-four ceramic specimens (15x13x3mm) were sectioned from lithium disilicate glass ceramic blocks, crystallized, mounted in autopolymerizing acrylic resin mold, and then polished using silicon carbide papers. The ceramic specimens were divided into 6 groups based on the surface treatment regimen before bonding: 1) acid etching (A), 2) silanation (S), 3) acid etching and silanation (A/S), 4) self-etching ceramic primer (SEP), 5) two applications of self-etching ceramic primer (2SEP), 6) acid etching and self-etching ceramic primer (A/SEP). Surface treatment followed the manufacturers’ instructions for respective products. Composite resin rods were cemented to the ceramic discs with a resin cement. Each group was then divided into 2 subgroups based on the aging conditions: 1) 24 hours of storage in an incubator at 37°C and 100% humidity, and 2) 24 hours of moist storage followed by 10,000 thermocycles (5°C and 55°C, 15s dwell time). The specimens were loaded to failure in a universal loading apparatus for shear bond strength. Data were analyzed with 2-way ANOVA (α=0.05); and fracture modes were determined by examination under a light microscope. Results: Two-way ANOVA demonstrated a significant effect of surface treatment and aging condition on the shear bond strength of lithium disilicate ceramic to resin cement (p<0.0001). Further, a significant interaction between surface treatment and aging conditions was detected (p<0.0001). At 24hrs, acid etching only (A) group had significantly lower bond strength than all other groups (p<0.05). There was no statistically significant difference in bond strength found among the S, A/S, SEP, 2SEP, and A/SEP groups (p>0.05). After thermocycling, mean shear bond strength for all groups were reduced. The acid etching only (A) and silanation (S) only groups had significantly lower bond strength means compared to all other groups (p<0.05). Mean shear bond strength for the self-etching ceramic primer (SEP) group was statistically significantly lower than those of A/S, 2SEP, and A/SEP groups (p<0.05). Conclusions: After thermocycling, shear bond strength of the self-etching ceramic primer group was significantly lower than that of the two-step etch and prime conditioning method group. However, shear bond strength value of the one-step self-etching ceramic primer group fell within a clinically acceptable range for clinical performance, suggesting that etching and priming of silicate ceramics may be combined into one step. Over-etching of lithium disilicate glass ceramic in the one-step conditioning method did not adversely affect its bond strength to the resin cement.