Which Kennedy classification requires an indirect retainer to resist rotation?

Which Kennedy classification requires an indirect retainer to resist rotation?

• A. Class III
• B. Class I or II
• C. Class IV
• D. Class II

Answer: (B)

The need for an indirect retainer arises when a denture has a long lever arm that makes it want to rotate around the remaining abutment teeth. This situation occurs in Kennedy Class I and Class II designs, where there is a posterior edentulous area (unopposed span) and the denture is at risk of rotating about the anterior rests or fulcrum line under functional loads. An indirect retainer provides a counter-moment to resist that rotation, typically by incorporating an anterior rest or projection connected to the anterior teeth so that loading on the posterior edentulous area creates a stabilizing force. In Class III or Class IV designs, there are sufficient abutments and supports to resist rotation with the direct retainers and major connector, so an indirect retainer is not routinely required. So, the classification that requires an indirect retainer to resist rotation is the one with posterior edentulous areas on both sides or on one side (Class I or Class II).

The need for an indirect retainer arises when a denture has a long lever arm that makes it want to rotate around the remaining abutment teeth. This situation occurs in Kennedy Class I and Class II designs, where there is a posterior edentulous area (unopposed span) and the denture is at risk of rotating about the anterior rests or fulcrum line under functional loads. An indirect retainer provides a counter-moment to resist that rotation, typically by incorporating an anterior rest or projection connected to the anterior teeth so that loading on the posterior edentulous area creates a stabilizing force.

In Class III or Class IV designs, there are sufficient abutments and supports to resist rotation with the direct retainers and major connector, so an indirect retainer is not routinely required.

So, the classification that requires an indirect retainer to resist rotation is the one with posterior edentulous areas on both sides or on one side (Class I or Class II).