Which material is MOST appropriate for the final impression of a lithium disilicate (e.max) crown preparation?

Correct answer: B. Polyvinyl siloxane (addition silicone)

• A. Reversible hydrocolloid can reproduce fine detail but requires specialized conditioning and water-cooled trays, is dimensionally unstable, and has been largely superseded by PVS.
• B. CORRECT. POLYVINYL SILOXANE is the material of choice for definitive fixed prosthodontic impressions. It offers excellent dimensional stability (allowing delayed pouring and multiple pours), superb elastic recovery, high tear strength and outstanding detail reproduction — essential for capturing a clean, unambiguous crown margin. Automixing delivers consistent, void-free material.
• C. Alginate is dimensionally unstable — it undergoes syneresis and imbibition and must be poured within minutes. Its detail reproduction is inadequate for a crown margin. It is appropriate for study casts, opposing casts and provisional fabrication.
• D. Impression compound is a rigid thermoplastic used for border molding and preliminary edentulous impressions. It cannot record undercuts elastically.

Note: Contamination caution: LATEX gloves and some retraction cord chemicals INHIBIT the polymerization of PVS, producing a sticky, unset surface at the margin. Use vinyl or nitrile gloves and rinse the preparation thoroughly.