HF Acid Etching Ceramics — MFDS Part 1 MCQ

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HardDental MaterialsHF Acid Etching CeramicsMFDS Part 1

A lithium disilicate glass-ceramic onlay is tried in and confirmed not to have been pre-etched. After removal of the try-in material, conventional separate acid etching of the fitting surface is planned before silane application and adhesive resin cementation. Which acid should be used to create the required micromechanical retention?

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Correct answer: C — Hydrofluoric acid

Hydrofluoric acid is the conventional etchant for lithium disilicate, a silica-containing glass-ceramic. It preferentially dissolves part of the glassy phase, producing a microporous fitting surface that provides micromechanical retention; silane is then applied to promote chemical coupling to resin cement. Commercial protocols commonly use hydrofluoric acid at approximately 5%, often for about 20 seconds for lithium disilicate, but the restoration and etchant manufacturers’ instructions must be followed. Phosphoric acid may be used in some cleaning protocols after contamination, but it is not the conventional primary etchant for an untreated lithium disilicate surface. Citric, maleic and polyacrylic acids do not provide the required glass-ceramic etching pattern. Hydrofluoric acid is not used to etch zirconia, which lacks an etchable silica-rich glass phase.

Reference: Shoorgashti R, Ehsani SS, Ducret M, Rokhshad R. Effect of Surface Treatments on the Bond Strength of Computer-aided Design and Computer-aided Manufacturing Lithium Disilicate to Restorative Materials: A Systematic Review. European Journal of Prosthodontics and Restorative Dentistry. 2024;32(4):423-433. https://pubmed.ncbi.nlm.nih.gov/39607319/