Hydrofluoric acid etching versus self-etching glass ceramic primer: consequences on the interface with resin cements

Abstract

Objectives: The purpose of this in vitro study was to compare the effects of traditional HF + silane (two steps process) versus self-etching glass ceramic primer (one step process) on the wettability of 2 types of CAD/CAM glass ceramics and the chemical bonding types between the ceramics and a composite cement. The tested ceramics were a leucite-reinforced feldspathic glass ceramic (IPS Empress CAD Multi) and a lithium disilicate-based glass ceramic (IPS e.max CAD). Methods and materials: Forty specimens (18 mm x 4 mm) were fabricated, twenty from each glass ceramic then sanded to alumina of 50 µm under reduced pressure of 1 bar. Each group of 20 was randomly sub divided into two groups (n = 10): Group 1 = IPS Empress CAD Multi + MEP(self-etching ceramic primer Monobond Etch&Prime, Ivoclar Vivadent); Group 2 = IPS Empress CAD Multi + 5.0% HF (IPS Ceramic Etching Gel, Ivoclar Vivadent) + MP (Monobond Plus, Ivoclar Vivadent); Group 3 = IPS e.max CAD + MEP; Group 4 = IPS e.max CAD + 5.0% HF + MP. The effect of the different surface treatments applied to the glass ceramics was compared by analysis of water contact angle measurements as well as spreading coefficients. Contact angles were determined with a Digidrop device (GBX). Contact angles and spreading coefficients for ceramics with different surface treatments were compared by ANOVA. A second analysis of variance was made to compare the two glass ceramics with identical treatments. Statistical analysis also included the Duncan post hoc test (p < 0.05). Eight additional specimens for infrared spectroscopy were assigned, four for each glass ceramic. The discs were cut longitudinally and each half received a surface treatment. After each surface treatment, a resin cement (Multilink Automix, Ivoclar Vivadent) was applied to the surface of the half-disks and photopolymerized. The samples were examined on their slice (treated ceramic + resin cement) by spectrophotometric analysis. FTIR, by peak recognition and spectral comparison, allowed to reveal the bonding types formed between the ceramic after surface treatments and the resin cement. A differential analysis was carried out to compare the spectra obtained with the 2 treatments of each of the ceramics and to highlight any differences. Results: The values of the contact angles were more favorable with HF treatment followed by MP for the two glass ceramics, the same applied to the values of the spreading coefficients (negative values). These results were even more pronounced for the IPS Empress CAD Multi. Infrared spectra of the interfaces between the two treated ceramics and the resin cement showed chemical bonds. The treatment with HF + MP increased binding more than treatment with MEP, particularly for IPS Empress CAD Multi. Conclusion: Wettability of the glass ceramics depended on surface treatment, and the ceramic structure was related to the bonding of the silane to the resin cement. This means it is important to select surface treatment as a function of ceramic material. Strong, hydrophobic interactions play an important role in the long-term durability of bonding in cement-ceramic associations.