Restorative & Materials · single question
Which luting cement exhibits HYGROSCOPIC EXPANSION after setting?
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Correct answer: D. Resin-modified glass ionomer
- A. Zinc oxide-eugenol shows minimal expansion and is used as a provisional cement.
- B. Polycarboxylate is dimensionally stable and chelates to calcium in tooth structure.
- C. Zinc phosphate contracts slightly on setting and is dimensionally stable thereafter.
- D. Correct. RESIN-MODIFIED GLASS IONOMER contains HEMA, which ABSORBS WATER and causes the set cement to EXPAND. This can partially compensate for polymerisation shrinkage and improve marginal seal, but it is also a genuine clinical hazard: hygroscopic expansion inside a rigid, non-yielding all-ceramic crown has been implicated in post-cementation crown FRACTURE. For this reason RMGI is generally avoided under thin all-ceramic restorations.
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