# Denture Base Resins > Denture base resins for BDS Dental Materials — PMMA powder-liquid chemistry, dough stage, curing cycles, porosity types and residual monomer. - Canonical URL: https://prepelephant.com/topics/bds/dental-materials/denture-base-resins - Exam / course: BDS · Subject: Dental Materials - Publisher: PrepElephant (https://prepelephant.com) — Prepared and reviewed by the PrepElephant Academic Review Team - First published: 2026-10-02 - Last updated: 2026-10-02 - How to cite: "Denture Base Resins", PrepElephant, https://prepelephant.com/topics/bds/dental-materials/denture-base-resins ## Direct answer A denture base is polymethyl methacrylate formed at the chairside bench: polymer powder (PMMA beads with benzoyl peroxide initiator and pigments) meets monomer liquid (methyl methacrylate with a hydroquinone inhibitor, plasticiser and cross-linking ethylene glycol dimethacrylate), passes through sandy, stringy and doughy stages, and is packed under pressure into a flask to be heat-cured — classically at 74°C for eight hours, or a shorter cycle finishing with a boil. The two classic examination problems are porosity — gaseous, contraction or water types with distinct causes — and residual monomer, an irritant and allergen worst in cold-cure acrylics. Powder-liquid chemistry, the dough-stage test and the porosity table are the chapter's scoring core. ## What you must remember - Powder components: PMMA prepolymerised beads, benzoyl peroxide initiator, cadmium-free pigments and fibres for tissue match; liquid components: MMA monomer, hydroquinone inhibitor (to prevent premature set in the bottle), dibutyl phthalate plasticiser, ethylene glycol dimethacrylate cross-linker. - Mixing stages in order: sandy → stringy/sticky → dough (packed) → rubbery → hardened; the dough is judged when the mix no longer sticks to a gloved finger and pulls off cleanly. - Curing modes: heat cure in a water bath (74°C for 8 hours conventional, or a short cycle with a terminal 100°C boil that drives conversion up); chemical cure with a tertiary amine activator for repairs and chairside relines; light-activated urethane systems; microwave and fluid-pour techniques. - Polymerisation shrinkage of about 6–7% volumetric (roughly 0.5% linear) is partly offset by water sorption expansion of the finished base — one reason dentures tighten after a week in the mouth. - Porosity, by type: gaseous — monomer boils (MMA's boiling point 100.8°C) when the cure runs too hot or too fast; contraction — packing before the dough stage or insufficient pressure, so material cannot feed the shrinking mass; water — contamination by moisture or wet gypsum, leaving voids. - Residual monomer falls with complete curing and rises steeply in autopolymerised and direct-reline acrylics — the usual culprit in denture-induced stomatitis, burning mouths and contact allergy; management is thorough processing, water immersion before fitting, or laboratory reline. - Crazing — fine surface cracks — follows solvent exposure or stress in the presence of alcohol; warpage comes from uneven cooling or relaxation of stresses on release from the flask. - Technique notes: compression moulding in a denture flask remains standard, injection moulding reduces porosity and improves fit; direct chairside relines exotherm and can injure mucosa, so thin sections matter. ## A bubbly denture decoded A technician presents a processed complete denture studded with voids across the thickest palatal region, and the porosity table diagnoses it by geography. Voids concentrated in the bulky centre mean gaseous porosity: the resin mass, a poor thermal conductor, overheated internally — cured too fast or too hot, boiling the monomer (100.8°C) inside a setting mass. Voids along the flanges and between teeth mean contraction porosity: the flask was packed while the mix was still stringy, or pressure was insufficient, so the shrinking polymer had no plastic mass to feed the gaps. A scattered mottling near the tissue surface implicates wet gypsum or moisture contamination. Each cause carries its own prevention — slower cure with a terminal boil only at the end; pack at dough under adequate pressure; dry, uncontaminated moulds. The same denture teaches the finishing sequence and its hazards. It bench-cools under pressure to avoid warping stresses, is deflasked carefully, finished with acrylic burs and pumice, and polished — heat from careless polishing can distort a flange the way a cure can. If the patient instead returns a week after fitting with a burning, erythematous palate, the differential runs between candidal stomatitis and residual-monomer irritation of a rushed cold-cure reline; the monomer history question settles it, and a laboratory-processed reline settles the patient. ## Exam favourites in acrylics The stages-in-order stem is guaranteed, with the dough-stage test ("no stick to a gloved finger, pulls clean") as the discriminator. The porosity matching stem pairs cause with type: over-rapid heating — gaseous; premature packing — contraction; moisture — water. The 100.8°C figure for MMA's boiling point anchors the gaseous story, and the 74°C-for-8-hours schedule anchors the cure. Residual monomer questions ask which acrylic has most (cold-cure) and what it causes (mucosal irritation and allergy). Vivas extend to why hydroquinone sits in the liquid (inhibitor), why the denture tightens after a week (water sorption expansion), and the hazards of chairside relines — monomer burn and thermal injury to mucosa from the exotherm, managed with thin sections and warning. ## Frequently asked questions ### List the stages of an acrylic mix from powder-liquid to set. Sandy, stringy or sticky, dough, rubbery and hardened — with packing performed only at the dough stage, tested by clean separation from a gloved finger. ### Why does gaseous porosity occur and at what temperature? Methyl methacrylate boils at 100.8°C; a cure that overheats the thick resin mass — too fast or too hot — boils monomer inside it, leaving voids in the thickest regions. ### What causes contraction porosity in a processed denture? Packing before the dough stage or insufficient mould pressure: the polymerising mass shrinks without plastic material to feed the shrinkage, leaving voids along flanges and between teeth. ### Which type of acrylic contains the most residual monomer, and what does it cause? Autopolymerised (cold-cure) acrylics, used for repairs and chairside relines; residual monomer irritates and sensitises mucosa — burning, erythema and allergic contact reactions.