Acrylic Denture Porosity — MFDS Part 1 MCQ
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Correct answer: B — Monomer overheating during polymerisation because the curing temperature rose too rapidly
The correct answer is B. Rapid heating, combined with the exothermic polymerisation reaction, can overheat the monomer, particularly within a thick section where heat dissipates poorly. This produces characteristic internal gaseous porosity. Adequate flask pressure and an appropriate curing cycle reduce this risk. Excess monomer may increase residual monomer and dimensional change but does not best explain this distribution of rounded internal voids. Inadequate mixing can introduce defects or entrapped air, but it is less specifically associated with porosity concentrated in the thickest region after rapid heat curing. Autopolymerising acrylic has different residual-monomer and mechanical characteristics, but its use alone does not inevitably produce porosity. Therefore, E is incorrect.
Reference: Compagnoni MA et al. Porosity, water sorption and solubility of denture base acrylic resins polymerized conventionally or in microwave. Journal of Applied Oral Science. 2018. https://pubmed.ncbi.nlm.nih.gov/12385904/