Which type of denture base acrylic is LEAST porous?

Correct answer: B. Heat-cured

• A. Light-cured acrylic depends on light penetration, which limits depth of cure and leaves inconsistency through the thickness of the material.
• B. CORRECT. HEAT-CURED polymethyl methacrylate achieves the highest degree of conversion and the lowest residual monomer, giving the DENSEST, least porous material with the best strength, colour stability and dimensional accuracy. Porosity is minimised because the controlled, gradual heating cycle allows polymerisation to complete before the monomer can boil, and because the material is processed under pressure in a flask.
• C. Microwave curing gives properties approaching heat cure but is more prone to porosity from uneven heating within the mass.
• D. Self-cured acrylic polymerises at room temperature via a chemical initiator, giving a LOWER degree of conversion, HIGHER residual monomer, more porosity, and weaker mechanical properties. It is used for repairs, relines and orthodontic appliances.

Note: Porosity matters clinically: a porous denture base absorbs fluid, harbours Candida, discolours, and is weaker. Higher residual monomer in self-cured resin is also the main cause of acrylic-related mucosal irritation.