What is the primary function of an indirect retainer in a distal-extension removable partial denture?

The indirect retainer is a component of a Kennedy Class I or Class II removable partial denture that prevents the distal extension base from rotating away from (lifting off) the supporting tissues. When functional forces tend to lift the distal extension base, the indirect retainer — placed on a tooth anterior to the fulcrum line — acts as a counterbalance through lever mechanics to resist this rotation. This is distinct from direct retention, which is provided by the clasp assemblies. The effectiveness of an indirect retainer increases the further it is placed from the fulcrum line.