Removable Partial Dentures: Design and Fit

How the Kennedy classification guides removable partial denture design, the difference between suprabulge and infrabulge clasps, and the role of major connectors in distributing chewing loads.

The removable partial denture is indicated for restoring partial edentulism when fixed rehabilitation isn't feasible — due to loss of posterior support, insufficient bone quality or quantity, or anatomically inadequate abutment teeth. Its design always starts with classifying the arch according to the Kennedy system, which distinguishes four classes based on the position of edentulous spaces: Class I includes two free-end distal saddles (with no posterior support on either side), Class II a single free-end distal saddle, Class III a lateral saddle bounded by natural teeth on both sides, and Class IV an anterior saddle crossing the midline.

The structure of a removable partial denture is made up of elements with distinct functions. Major connectors link the different saddles together, maintain spatial relationships between the clasps, and distribute chewing load across the entire structure, avoiding any interference with bony prominences or mobile tissue; in the mandible, when space doesn't allow for a lingual plate, a thinner lingual bar is typically used instead. Clasps, or direct retainers, embrace the abutment tooth for at least 180 degrees and consist of three functionally distinct parts: the shoulder (rigid, connected to the rest seat), the arm (semi-rigid, joining shoulder and tip) and the tip (the flexible part that actually engages the tooth's undercut).

The Ney reference system classifies different clasp types by their geometry and clinical indication. Clasp number 1, or the Akers clasp, is symmetric and represents the simplest configuration, particularly indicated in Kennedy Class III and some subclasses. Infrabulge clasps, such as the T-clasp or Roach type, offer less complete embrace and are therefore almost never used alone, but leverage a different mechanical principle — bracing in the undercut without excessively compromising aesthetics — which makes them useful in combination with other retentive elements.

An intrinsic aesthetic limitation of visible metal clasps, often flagged by patients, has led to the development of alternatives such as precision attachments, which however require encasing the abutment tooth with a crown to adequately bear chewing loads — a solution properly falling into the combination-prosthesis category, more complex and costly but aesthetically superior. In any case, the design of the removable partial denture — connector type, number and position of clasps, presence of secondary retention — should always be determined through surveyor analysis of the plaster models, which precisely identifies the available undercuts on each abutment tooth.

On Oralzon you'll find alloys for casting partial denture frameworks, prefabricated clasps of every type, and surveying instruments needed to design a custom removable partial denture.