Digital surveying replaces the eye
In an analogue workflow the cast is surveyed on a table and undercuts are judged visually. In CAD the same analysis is measured: the software reports undercut depth in millimetres at any point on the abutment, for a given path of insertion, and the path itself can be rotated and re-evaluated in seconds.
That matters because clasp retention is a function of undercut depth and clasp material. Choosing a 0.25 mm undercut for a cast cobalt-chrome clasp is a decision, not a guess — and the software confirms the undercut is actually there.
Path of insertion drives everything else
The path of insertion is fixed before any component is drawn, because it determines guide plane positions, which undercuts are usable, how much blockout is needed and where the framework can be relieved. Changing it later means redesigning the framework, not adjusting it.
A good path balances retention, aesthetics (keeping visible clasp arms off the buccal of anterior abutments where possible) and ease of insertion for the patient.
Components of the framework
Each part of an RPD framework has a defined job:
- Major connector — rigidity; sized in cross-section rather than in bulk, with relief where the mucosa needs it
- Minor connectors — join components to the major connector and transmit force to the rests
- Rests — direct vertical support onto prepared rest seats, keeping load off the soft tissue
- Retentive clasp arms — engage the measured undercut; flexibility matched to material and length
- Reciprocal arms and guide planes — resist the horizontal force the retentive arm generates
- Mesh or lattice retention — mechanical hold for the acrylic saddles and the denture teeth
Clasp selection by Kennedy class
The classification changes the mechanics, and the design follows:
- Kennedy Class I and II (free-end saddles) — designs that allow controlled movement of the saddle, with rests placed to avoid torquing the terminal abutment
- Kennedy Class III (tooth-supported) — straightforward circumferential clasping, load carried by the abutments
- Kennedy Class IV (anterior span) — aesthetic clasp placement and careful indirect retention posteriorly
Output: printed pattern or direct metal
The finished framework can be produced two ways. A castable pattern is printed and invested for conventional casting, which suits labs already equipped for casting. Direct metal laser sintering produces the cobalt-chrome framework straight from the file and removes the casting step.
Either way the file is the same design; only the compensation and support parameters differ. Metal-free thermoplastic partials are designed with different clasp geometry and thickness, since the material flexes far more.
What to send us
A digital RPD design starts from a full, clean arch scan:
- Full arch scan including the edentulous ridges and the sulcus depth
- Antagonist scan and bite registration
- Any surveyed crowns or telescopic abutments already planned
- Your preferences: material, connector type, and whether you will cast or sinter
Approval before production
Before the framework file is released we send screenshots showing the survey lines, the path of insertion, clasp positions and the connector outline. You approve the design on screen, where a change costs nothing, rather than after the metal exists.
See our RPD framework design service for turnaround and pricing.