Removable Prosthodontic Technology: Denture Design, Occlusion Rims, Articulation, Processing, Repairs and Relines
Removable Prosthodontic Technology
This domain tests fabrication of complete and removable partial dentures: design rules, record bases and occlusion rims, articulation and occlusal records, acrylic processing, and the repair and reline procedures that come back to the laboratory.
Design and record rules
- Partial dentures: classify by Kennedy and apply Applegate's rules - the classification is based on the most posterior edentulous area, and an unerupted or crowned tooth that will not be replaced is not counted. Rests seat on prepared rest seats; a lingual plate is used when the soft tissue cannot support a bar.
- Occlusion rims: the maxillary rim is shaped to support the lip (anterior height about 20–22 mm) and the occlusal plane is set parallel to the interpupillary line and Camper's plane. Vertical dimension is established before centric relation is recorded.
- Articulation: a facebow transfers the maxillary cast; centric relation records transfer the mandibular cast. Balanced occlusion in complete dentures requires anterior, working and balancing contacts.
- Processing: the denture is packed at the dough stage and cured in water. A typical cycle is 74 °C for 8–9 hours, or 74 °C for 1.5 hours then 100 °C for 1 hour. Linear polymerisation shrinkage of PMMA is roughly 0.4–0.5%, partly offset by stone expansion.
- Repairs and relines: flask the fractured parts, use a separating medium and clear the fracture line, then pack repair resin. Chairside relines use autopolymerising resin; laboratory relines use heat-cured resin for better colour stability and lower residual monomer.
Worked example
A technician places a flask directly into boiling water for a full cure. The resulting denture base shows bubbles and a rough-fitting intaglio. Reasoning: the resin's surface sets first, then the interior polymerises and the monomer boils where the temperature exceeded its boiling point before polymerisation completed - classic processing porosity. The correct cycle raises the temperature slowly so that polymerisation keeps pace with heating, keeping the dough soft and letting the flask cool slowly before deflasking.
Traps that cost marks
Mixing Kennedy classes, packing at the sandy or stringy stage instead of the dough stage, and curing too fast or deflasking while hot, which produces distortion rather than porosity.