RPD Manual 11 - Removable Prosthodontics - Dalhousie University

Direct and Indirect Retainers - 48
4. "C" clasp (Hair-pin or Reverse action)
a. The retentive area (undercut) is adjacent the
occlusal rest.
b. The upper arm is a minor a connector giving
rise to tapered lower arm.
Advantages:
a. Allows use of undercut adjacent to edentulous space
Disadvantages:
a. Almost impossible to adjust
b. Non-esthetic
c. Difficult to fabricate so the upper portion of the retentive arm clears the opposing
occlusion
d. Covers extensive tooth surface and acts as a food trap
e. Insufficient flexibility on short crowns due to insufficient clasp arm length
Cast suprabulge clasps should be used in most tooth borne cases. Exceptions to this rule include:
1. Esthetic concerns. Since wrought-wire clasps can be placed into greater undercuts
(0.02") than cast clasps (0.01") they can be placed lower on teeth, allowing better
esthetics in some cases. Infrabulge clasps are also less visible.
2. Where a posterior abutment is mobile or of questionable prognosis, the treatment
plan could call for the use of the stress-breaking qualities of a wrought clasp on the
anterior abutment. This would allow the prosthesis to be converted into a distal
extension type if the weak posterior abutment should be lost.
3. Where abutments are mobile, the tooth borne segment is extensive, the use of the
stress-breaking clasps should be considered.
Disadvantages of cast suprabulge clasps:
1. Create a "pump-handle" action on the abutment teeth in distal extension cases if the
guiding plane on the distal surface is too long, with insufficient relief.
2. Some clasps can be ineffective on teeth tilted buccally or lingually
3. Some varieties cover more tooth surface than is desirable
4. Poor esthetics in the anterior region
There have been many modifications to cast suprabulge clasps. Some are too complex and
impractical for common use.