Clasp Design
Direct retainers may come in various designs:
- Cast circumferential clasp (suprabulge)
- Akers'
- Half and half
- Back-action
- Ring clasp
- Wrought wire clasp
- Roach clasp (infrabulge)
- I-bar
- T-bar
- Y-bar
- 7-bar
Both cast circumferential and wrought wire clasps are suprabulge clasps, in that they engage an undercut on the tooth by originating coronal to the height of contour, while Roach clasps are infrabulge clasps and engage undercuts by approaching from the gingival.
In addition there are a couple of specific theories which include the clasp design:
- RPI: mesial rest, distolingual guide plate, I-bar
- Described by Kratochvil in 1963 and modified by Kroll in 1973
- An illustration of the RPI design function
- RPA: mesial rest, distolingual guide plate, Akers' clasp-style retentive arm
- RPC: mesial rest, distolingual guide plate, other type of cast circumferential clasp
- So named in response to the RPI Philosophy introduced by Kratochvil and Kroll
Read more about this topic: Removable Partial Denture
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