FESEM analysis of a HF-etched high-density lithium disilicate ceramic

Objectives: Study the effect of hydrofluoric acid (HF) on the ultra-morphology of a new lithium disilicate ceramic (LD, GC Initial LiSi Press).
Methods: Four ingots were pressed in proprietary investment following the program recommended by the respective manufacturer. After cooling, specimens were wet polished up to 1200-grit SiC paper and cleaned ultrasonically with distilled water. Specimens were divided in 4 identical areas and assigned to the following groups (n=4): (1) Polished surface used as control; (2) surface roughened by blasting with glass beads (Rolloblast, Renfert) under 4-bar pressure; (3) as in group 2, followed by 5%HF (IPS Ceramic Etching Gel, Ivoclar Vivadent) for 20 sec; (4) as in group 2, followed by 9%HF (Porcelain Etch, Ultradent Products) for 20 sec. Specimens were cleaned ultrasonically with distilled water for 180 sec, air dried, mounted on aluminum stubs, sputter-coated with Au-Pd, and observed under a FESEM (JSM-6701F, JEOL) at magnifications of 2,000X to 30,000X.
Results: The morphology of the control group showed a smooth surface without retentive features. Blasting with glass beads (Group 2) resulted in an irregular surface area exposing LD crystals and glass-ceramic, without a ceramic etching pattern. Both 5%HF (Group 3) and 9%HF (Group 4) resulted in a characteristic honeycomb etching pattern in glass matrix that preserved the integrity of LD crystals. 9%HF resulted in a slightly deeper etching pattern than that of 5%HF, with an array of exposed LD crystals supported by glass matrix. No obvious over-etched ceramic was detected for the HF groups. In general, 5%HF (Group 3) resulted in a more superficial etching pattern than 9%HF (Group 4).
Conclusions: Within the limitations of this ultra-morphological study, 5%HF and 9HF can be used to prepare this LD substrate for bonding. However, 9%HF resulted in a more pronounced LD etching pattern.