Prosthodontics (Fixed and Removable)
Prosthodontics examines whether you can design a prosthesis that can be seated, cleaned, retained and maintained: preparation geometry and finish lines, connector dimensions, removable partial denture classification and component choice, and complete denture record-taking.
Fixed prosthodontics
- The path of insertion governs everything; axial taper of about 6 degrees gives retention without binding, and resistance comes from the preparation's height and taper together.
- Occlusal reduction must match the material (roughly 1.5-2 mm for metal-ceramic and low-strength ceramic, more for monolithic zirconia), and margins should sit supragingivally where possible.
- Impression with addition-cured silicone or polyether after gingival retraction; a wash technique records the finish line without tearing.
- Connector cross-section must follow the material: undersized connectors are the commonest cause of framework fracture, especially with zirconia.
Removable partial dentures
- Classify with Kennedy and apply Applegate's rules: the classification is based on the most posterior edentulous area, and a missing third molar of no prosthetic value is not counted.
- Occlusal rests are seated in prepared spoon-shaped rest seats with the floor inclined toward the marginal ridge to direct forces along the tooth's long axis.
- Tooth-borne spaces suit cast circumferential clasps; distal extension bases suit mesial rests with a stress-releasing design such as the RPI, and require an altered cast impression.
- A mandibular lingual bar needs roughly 4 mm of height, 2 mm of thickness, and its superior border about 3 mm clear of the gingival margin.
Complete dentures
- Record vertical dimension at rest and centric relation at the correct vertical dimension; border moulding establishes the functional sulcus.
- Balanced occlusion and a retentive posterior palatal seal improve stability; the neutral zone positions teeth where the tongue and cheek do not dislodge them.
- Two implants in the anterior mandible supporting a locator overdenture markedly improve retention and satisfaction.
Worked example
A Kennedy Class I mandibular arch with two canines remaining: each canine receives a mesial rest seat and an RPI-style clasp assembly, a lingual bar major connector is used, and the distal extension bases are recorded with an altered cast technique so the bases can move under load without torquing the canines.
Traps
- Counting a missing third molar in Kennedy classification.
- Designing a distal extension with rigid tooth support only.
- Forgetting that a lingual bar must be 3 mm from the gingiva.