Effects of surface treatments and cement types on the bond strength of porcelain-to-porcelain repair.

PURPOSE The purpose of this in vitro study was to evaluate the effects of four surface treatments and two resin cements on the repair bond strength of a ceramic primer. MATERIALS AND METHODS Eighty-eight pairs of disks (10 and 5 mm in diameter, 3 mm thickness) were prepared from heat-pressed feldspar ceramics (GC Initial IQ). After being stored in mucin-artificial saliva for 2 weeks, the 10-mm disks were divided into four surface treatment groups (n = 22) and then treated as follows: (1) no treatment (control); (2) 40% phosphoric acid; (3) 5% hydrofluoric acid + acid neutralizer + 40% phosphoric acid; (4) silica coating (CoJet-sand) + 40% phosphoric acid. The 5-mm disks were treated with 5% hydrofluoric acid + 40% phosphoric acid. The two sizes of porcelain disks, excluding the control group, were primed with Clearfil Ceramic Primer. The specimens in each group were further divided into two subgroups of 11 each, and bonded with Clearfil Esthetic Cement (CEC) or Panavia F 2.0 Cement (PFC). The specimens were stored in distilled water at 37°C for 24 hours, thermocycled for 3000 cycles at 5 to 55°C, and stored at 37°C for an additional 7 days. Shear bond strength (SBS) was measured with a universal testing machine at a 0.5 mm/min crosshead speed until fracture. Statistical analysis of the results was carried out with a two-way ANOVA and Tukey HSD test (α = 0.05). Debonded specimen surfaces were examined under an optical microscope to determine the mode of failure. RESULTS The statistical analysis showed that the SBS was significantly affected by surface treatment and resin cement (p < 0.05). For treatment groups bonded with CEC, the SBS (MPa) values were (1) 2.64 ± 1.1, (2) 13.31 ± 3.6, (3) 18.88 ± 2.6, (4) 14.27 ± 2.7, while for treatment groups cemented with PFC, the SBS (MPa) values were (1) 3.04 ± 1.1, (2) 16.44 ± 3.3, (3) 20.52 ± 2.2, and (4) 16.24 ± 2.9. All control specimens exhibited adhesive failures, while mixed types of failures were observed in phosphoric acid-treated groups. The other groups revealed mainly cohesive and mixed failures. CONCLUSIONS Combined surface treatment of etching with hydrofluoric acid and phosphoric acid provides the highest bond strengths to porcelain. Also, PFC exhibited higher SBS than CEC did.