Polysulphide Electroplating — MFDS Part 1 MCQ

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HardDental MaterialsPolysulphide ElectroplatingMFDS Part 1

A laboratory receives a conventional elastomeric impression from which a silver-electroplated metallic die is to be produced. The impression material is a mercaptan rubber with high tear energy but comparatively high permanent deformation after stretching. Which material is described?

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Correct answer: E — Polysulphide

The correct answer is E, polysulphide. Polysulphides are mercaptan-rubber impression materials and can be used to produce silver-electroplated dies. They have high tear energy and tolerate substantial stretching before tearing, but exhibit more permanent deformation than addition silicone or polyether. Addition silicone and polyether are elastomers with better elastic recovery; importantly, selected formulations can also be electroplated, so electroplating alone would not distinguish them. Alginate is an irreversible hydrocolloid, while impression compound is a thermoplastic, non-elastomeric material. The combined chemical and mechanical features therefore make polysulphide the single best answer.

Reference: Crispin BJ, Watson JF, Bauer JG, Frawley KR. Silver-plated dies. Part I: Platability of impression materials. Journal of Prosthetic Dentistry. 1984;51(5):631-636. https://pubmed.ncbi.nlm.nih.gov/6374118/