Alginate Water-Powder Ratio — MFDS Part 1 MCQ
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Correct answer: E — Lower viscosity and lower tear strength
Explanation lettering: D = shown as A · C = shown as B · E = shown as C · B = shown as D · A = shown as E
The correct answer is A. Adding excess water reduces the powder-to-water ratio. Experimental evidence shows that lower powder-to-water ratios produce alginate mixes with lower viscosity and lower tear strength. The more fluid mix may appear easier to load or seat, but the set impression is mechanically weaker and more liable to tear in thin sections or around undercuts. Conversely, increasing the proportion of powder raises both viscosity and tear strength, so B, C and D each incorrectly reverse one or both effects. E is incorrect because the ratio measurably affects the material's rheological and mechanical properties. The manufacturer's specified proportions should therefore be measured accurately rather than adjusted to obtain a preferred consistency.
Reference: Abdelraouf RM, Bayoumi RE, Hamdy TM. Effect of Powder/Water Ratio Variation on Viscosity, Tear Strength and Detail Reproduction of Dental Alginate Impression Material (In Vitro and Clinical Study). Polymers. 2021;13(17):2923. https://pubmed.ncbi.nlm.nih.gov/34502963/