Which of the following is NOT an elastomer impression material?

• A. Elastomer impression material
• B. Spatula
• C. Alginate
• D. Clear matrix

Answer: (C)

Elastomer impression materials are rubber-like polymers that set to a flexible, highly accurate replica with good dimensional stability. Alginate is not an elastomer; it’s an irreversible hydrocolloid impression material that sets by a chemical gelation process and tends to undergo more dimensional change with time, making it less suitable for final impressions. The spatula is merely an instrument for mixing or loading material, not a material itself, and a clear matrix refers to a supporting matrix rather than an elastomeric impression material. So the material that fits the criterion of not being an elastomer impression material is alginate.