Thermal Expansion — ORE Part 1 MCQ

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HardDental MaterialsThermal ExpansionORE Part 1

A provisional restoration is made from an unfilled acrylic resin. Compared with the other materials below, which material has the greatest coefficient of linear thermal expansion and is therefore most susceptible to thermally induced mismatch at a tooth–restoration margin?

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Correct answer: E — Unfilled acrylic resin

E. Unfilled acrylic resin is correct. Acrylic polymers have a high coefficient of linear thermal expansion, and the absence of inorganic filler is crucial: filler reduces expansion in resin-based materials. Thus, an unfilled acrylic restoration undergoes greater temperature-related dimensional change than tooth tissue, increasing the risk of marginal mismatch during thermal cycling. Dental amalgam and cast gold alloy expand less than unfilled acrylic, despite having higher coefficients than enamel and dentine. Porcelain has a comparatively low coefficient selected for compatibility with its supporting framework where relevant. Conventional glass-ionomer cement is also much less thermally expansive than an unfilled acrylic resin. Do not confuse this mechanism with polymerisation shrinkage: both can impair marginal adaptation, but the question asks specifically about thermal expansion.

Reference: Sideridou I, Achilias DS, Kyrikou E. Thermal expansion characteristics of light-cured dental resins and resin composites. Biomaterials. 2004;25(15):3087-3097. https://pubmed.ncbi.nlm.nih.gov/14967543/