Influence of different etching protocols on the reliability of resin bonding to CAD/CAM feldspathic porcelain

Abstract Objectives To evaluate the effects of different acid etching times on the mechanical strength of dental porcelain as well as the influence on the reliability of resin bonded CAD/CAM porcelain veneer. Material and Methods Rectangular CAM/CAM feldspathic porcelain (Mark II, Vita Zahnfabrik) specimens (12 mm×10 mm×4 mm) were prepared and polished with silicon carbide abrasive paper under running water. All the samples were randomly divided into four groups according to the corresponding etching protocols: control group (without any treatment), group A (etched with a gel etchant containing 5% hydrofluoric acid for 30 s and rinsed with de-ionized water), group B (etched for 1 min and rinsed), group C (etched for 2 min and rinsed). After silanization, resin stubs were adhered on porcelain surface. There are 25 resin–porcelain samples prepared in each group and subjected to the shear bond strength testing. Weibull analysis was conducted to evaluate of the reliability of resin–porcelain bonding. For each of the etching method, eight additional porcelain samples (3 mm×2 mm×10 mm) were prepared and etched. Then, surface roughness (Ra), microhardness (Vickers Hardness) and biaxial flexural strengths were measured on these porcelain specimens. Energy dispersive X-ray spectrometry technique was used to assess the changes in surface chemical composition after etching and the surface topography was recorded under atomic force microscope (AFM) and scanning electron microscopy (SEM). Results The reliability of resin to CAD/CAM porcelain bonding was decreased with the increase in HF etching time. The application of HF etching for 30 s decreased the Vickers hardness number (HV) significantly from 651.6 (control group) to 488.7 (group A). With the extension of etching time, the Vickers hardness number was further reduced to 430.1 (group B) and 305.7 (group C). However, the biaxial flexural strengths of these four groups were not statistically significant different (p>0.05). AFM revealed the porous structures on the porcelain surface at microscopic level. Conclusions The application of HF to etch the CAD/CAM feldspathic porcelain surface reduced the microhardness number. Etching with 5% hydrofluoric acid on dental porcelain for more than 1 min might impair the reliability of resin bonded porcelain veneer.