Removable Prosthodontics - Removable Partial Dentures
Removable partial denture prosthodontics tests classification, design, and the biomechanics of sharing load between teeth and mucosa. The exam expects you to justify every component rather than list clasps.
Core rules
- Apply Applegate's rules: classify by the most posterior edentulous area; modifications are counted, not the number of missing teeth.
- Kennedy I is bilateral distal extension; II is unilateral distal extension; III is bounded posterior; IV is anterior.
- Rest seats must be prepared into enamel or restoration, not on an incline; they direct load along the long axis.
- Use guide planes and a surveyor to create a single path of insertion.
- For distal extension, consider a mesial rest and proximal plate/I-bar design to reduce torque on the abutment.
Worked example
A mandibular Kennedy II modification 1 case has a terminal molar abutment. You prepare a mesial occlusal rest, a distal guide plane, and an I-bar. Reasoning: the mesial rest converts the abutment into a Class I lever less than a distal rest; the I-bar contacts the tooth near the height of contour and disengages during function.
Traps
A rest on a steep incline produces orthodontic force. A clasp placed too high is unretentive; too low causes gingival impingement. Ignoring the surveyor creates a nonseating framework. A rigid major connector crossing movable tissue causes ulceration. Extending the base without an altered cast can overload the ridge.