Impression Materials — ORE Part 1 MCQ
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Correct answer: B — Addition silicone (polyvinyl siloxane/PVS)
Addition silicone (PVS) is the most accurate impression material for crown and bridge work. Systematic reviews of the literature confirm its superiority to condensation silicone, with addition silicones producing significantly smaller dimensional changes (approximately −0.08% compared to condensation silicones at −0.24% to −0.37%). This superior dimensional stability directly translates to more accurate dies and better marginal fit of castings. Addition silicone is the standard taught and used in UK dental schools for precision crown and bridge impressions. Condensation silicone (option E) is less accurate due to greater dimensional instability and release of byproducts. Alginate lacks the dimensional stability needed for precision work and has retention issues. Zinc oxide eugenol and impression compound are too rigid for recording fine detail in prepared teeth and are used only for preliminary impressions.
Reference: Johnson GH, Craig RG. Accuracy of addition silicones as a function of technique. Journal of Prosthetic Dentistry. 1986;55(2):197–203. https://pubmed.ncbi.nlm.nih.gov/3514856/; Confirmed by: Ciliberto G, et al. Dimensional Stability and Accuracy of Silicone-Based Impression Materials Using Different Impression Techniques—A Literature Review. Journal of Prosthodontics. 2017;26(7):584–589. https://pubmed.ncbi.nlm.nih.gov/28991761/