The effect of different acid porcelain surface treatments on composite-porcelain shear bond strength

Background: A number of systems have been developed to facilitate bonding of composites to porcelain, surface conditioning methods and agents accompanied with the use of silane coupling agent have resulted in improved bond strength. This study was formulated to evaluate the effect of 37% phosphoric acid surface treatment in comparison to 1 %,5%,and 10% hydrofluoric acid on bond strength of resin composite to porcelain. Material and Methods: Specimen preparation was divided in to two phases: fabrication of metal disks (8mm diameter and 4mm thickness) and ceramic veneering. The metal specimens were obtained using lost wax technique. Thirty two ceramic fused to metal specimens were prepared, sandblasted with 50 ym aluminum oxide, and divided in to four groups of 8 samples: Group I: Etching with 1% hydrofluoric acid solution for 2 minutes .Group II: Etching with 5% hydrofluoric acid solution for 2 minutes. Group III: Etching with 10% hydrofluoric acid solution for 2 minutes. Group IV: Etching with 37% phosphoric acid gel for 15 seconds. Monobond-s, Heliobond, Resin composite (Tetric Evo Ceram, Ceramic repair .Vivadent /Ivoclar.Schaan/ Liechtenstein)were applied to each specimen according to manufacturer's instruction with the use of a plastic transparent split mold (4mm diameter and 4mm he'ight ) especially designed for this purpose, specimens were stored in 37 °C in distilled water for 24 hours before being thermocycled between 5°C and 55 °C for 100 cycles .Shear bond strength was determined by a universal testing machine(Zwick 1454 ) at a cross head speed 5 mm/minutes .One way ANOVA test and LSD test were used to analyze the bond strength. Results: Mean shear'bond strength values for the tested groups were 21.25+2.67 for group I, 23.47± 1.24 for group II, 23.68 + 2 for group III, arid 21.01 ±2.16 for group IV. One way ANOVA test showed significant differences among the tested groups. LSD test revealed that specimens treated with 5%,and 10% cone, hydrofluoric acid(group II, and group III) were significantly higher than those treated with 1% hydrofluoric acid, and 37% phosphoric acid (group I, and grouplV),while there was no significant difference between group II, and group III, also between group I, and grouplV. Conclusions: Surface preparation of the ceramic with 10% hydrofluoric acid for two minutes recorded the highest bond strength with the composite, most of specimens treated with hydrofluoric acid exhibited cohesive failure within porcelain.