RPD Master Impression Tray — ORE Part 1 MCQ
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Correct answer: C — A custom-made rigid tray with material relief
**A is correct.** A working impression for a conventional cobalt-chromium RPD should be made in a rigid custom-made tray, with relief/spacer appropriate to the selected impression material. This permits controlled, relatively uniform material thickness and more reliable reproduction of teeth, supporting tissues and functional denture-bearing areas for the master cast. A perforated stock tray with alginate is more appropriate for a preliminary impression and does not provide the same control for a definitive cast. Putty in a plastic stock tray is insufficiently controlled for this purpose. Impression compound alone is not a definitive RPD master-impression technique. Zinc oxide-eugenol can record edentulous mucosa but is rigid when set and is unsuitable where dentate undercuts must be recorded for an RPD.
Reference: Kilfeather GP, Lynch CD, Sloan AJ, Youngson CC. Quality of communication and master impressions for the fabrication of cobalt chromium removable partial dentures in general dental practice in England, Ireland and Wales in 2009. Journal of Oral Rehabilitation, 2010. https://pubmed.ncbi.nlm.nih.gov/20085617/