Restorative & Materials · patient case question
Which cement is indicated for the lithium disilicate crown?
Patient case: Cementing a glass-ceramic crown
Patient: Female, 41 years old
Chief Complaint: “I am here to have the permanent crown fitted on my front tooth.”
Background: Healthy. Tooth #9 was root treated and restored with a fibre post and composite core. The definitive restoration is a pressed glass-ceramic crown.
Findings: The preparation has a 2 mm ferrule and adequate retention form. A feldspathic veneer for the adjacent tooth #8 is being processed at the same appointment. The crown try-in is satisfactory.
Show answer and explanation
Correct answer: B. Adhesive resin cement
- A. Zinc phosphate is a conventional luting cement with no adhesive capability whatsoever. It works purely by mechanical interlocking and depends entirely on the retention form of the preparation. It remains acceptable under full metal and zirconia crowns, but it does nothing for a glass ceramic.
- B. CORRECT. Glass ceramics derive a substantial part of their clinical strength from being ADHESIVELY BONDED to tooth structure: the resin supports the relatively brittle ceramic from within and limits crack propagation. The full protocol is hydrofluoric etch, rinse, silane, then an adhesive resin cement. Resin-modified glass ionomer is a defensible alternative for a lithium disilicate CROWN with adequate thickness and good retention form, but resin cement is mandatory for thin restorations such as veneers and for preparations with limited retention.
- C. Zinc oxide eugenol is a temporary and sedative cement. Critically, EUGENOL INHIBITS RESIN POLYMERISATION — so it must not even be used provisionally on a preparation that will later receive a resin-bonded restoration, or the definitive bond is compromised.
- D. Polycarboxylate bonds chemically to calcium in tooth structure and is notably kind to the pulp, but it is weak, relatively soluble, and it does not bond to ceramic.
Note: The contrast worth carrying: ZIRCONIA needs no hydrofluoric acid and no silane — it is air-abraded and primed with an MDP-containing agent, then luted with self-adhesive resin or resin-modified glass ionomer. Metal-ceramic and gold can be cemented conventionally. Match the cement to the substrate, not to habit.
Practice Restorative & Materials questions Restorative & Materials study notes