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Thermal Expansion Coefficient — MFDS Part 1 MCQ

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ModerateDental MaterialsThermal Expansion CoefficientMFDS Part 1

A posterior resin-composite restoration is repeatedly exposed to hot and cold drinks. Its coefficient of thermal expansion is substantially greater than that of the adjacent enamel and dentine. Which effect is most directly expected from this mismatch over repeated thermal cycles?

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Correct answer: C — Differential dimensional change at the interface, promoting loss of marginal integrity and microleakage

Option C is correct. When a restoration and the surrounding tooth have substantially different coefficients of thermal expansion, hot and cold exposure makes them expand and contract by different amounts. Repeated differential movement can stress the tooth–restoration interface, impair marginal integrity and promote microleakage. Thermal conductivity, addressed by B, governs the rate of heat transfer rather than dimensional change. Water sorption and hygroscopic expansion in C depend mainly on material composition and the oral environment. Polymerisation contraction in D occurs during curing and is distinct from subsequent thermal expansion and contraction. Radiopacity in E is determined primarily by the material's elemental composition, particularly the inclusion of radiopaque fillers.

Reference: Tan CL, Santini A. Marginal microleakage around class V cavities restored with glass ceramic inserts of different coefficients of thermal expansion. Journal of Clinical Dentistry. 2005;16(1):26–31. https://pubmed.ncbi.nlm.nih.gov/15974221/