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Degree of Conversion — MFDS Part 1 MCQ

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HardDental MaterialsDegree of ConversionMFDS Part 1

Fourier-transform infrared spectroscopy is used to assess a light-cured dimethacrylate composite. The ratio of the aliphatic methacrylate C=C absorbance peak to an unchanged aromatic reference peak is 1.24 before curing and 0.47 after curing. Which interpretation is correct?

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Correct answer: D — 62.1% of the aliphatic methacrylate C=C bonds were converted

The correct answer is D. Degree of conversion is the proportion of reactive methacrylate carbon–carbon double bonds consumed during polymerisation. The aromatic peak acts as an internal reference because it remains essentially unchanged. Here, the proportion remaining is 0.47/1.24 = 0.379, so conversion is 1 − 0.379 = 0.621, or 62.1%. Option A mistakes the residual fraction for the converted fraction, while C reverses the interpretation of the calculated value. Filler loading and absorbed radiant exposure can influence polymerisation but are separate material or curing parameters and are not measured by this calculation. Degree of conversion is also distinct from depth of cure.

Reference: Galvão MR et al. Evaluation of degree of conversion and hardness of dental composites photo-activated with different light guide tips. European Journal of Dentistry. 2013;7(1):86–93. https://pubmed.ncbi.nlm.nih.gov/3949822/