FESEM characterization of lithium disilicate treated with hydrofluoric acid

Objectives: To compare the ultra-morphology of lithium disilicate (LD, IPS e.max CAD, Ivoclar Vivadent) bonding substrates after etching with different concentrations of hydrofluoric acid (HF).
Methods: Twenty-eight rectangular sections (4x4x1mm³) were obtained from LD blocks. LD specimens were fired following the crystallization program recommended by the manufacturer. After cooling, specimens were wet polished up to 1200-grit SiC paper and cleaned ultrasonically with distilled water. Specimens were randomly assigned to 7 groups (n=4): IVO=5.0% HF (IPS Ceramic Etching Gel, Ivoclar Vivadent); VIT=5.0% HF (Vita Ceramics Etch, VITA Zahnfabrik); FGM=5.0% HF (Condac Porcelana, FGM); ULT= HF 9.0% (Porcelain Etch, Ultradent); BIS=9.5% HF (Porcelain Etchant, Bisco); PRM=9.6% HF (Premier Porcelain Etch Gel, Premier); and PLP=9.6% HF (Porcelain Etch Gel, Pulpdent). For all groups HF etching time was 20 sec as per the LD manufacturer’s instructions. Untreated areas from each specimen were used as controls. Specimens were cleaned ultrasonically with distilled water for 180 sec, air dried, mounted on aluminum stubs, sputter-coated with gold-palladium, and observed under a FESEM (S-4700, Hitachi) at magnifications from 10,000X to 40,000X.
Results: The morphology of non-treated polished LD showed a smooth surface without any retentive features, both from top view and in cross-sectional view. All HF gels resulted in microporosities on the LD surface. The deepest etching pattern was obtained with BIS, PRM and VIT. LD specimens treated with IVO and FGM displayed a better-defined etching pattern when compared with ULT and PLP, which displayed the least pronounced etching pattern with residual surface deposits resembling a precipitate.
Conclusions: Within the limitations this study, the ultra-morphology of etched LD surfaces depends on the specific HF gel used. For the low concentration HF gels, VIT is the most aggressive, which may be explained by the inclusion of <10% sulfuric acid in its composition.