Removable Partial Denture: Clasps
On 05-10-2020 | Read time about 5 Minutes
Direct retainer is a component of removal partial dentures (RPD), which is used to retain and prevent dislodgement, consisting of a clasp assembly or precision attachment. Depending on their placement inside (within) the abutment tooth or outside (surrounding) the abutment, direct retainers can be broadly classified as:
Types of Clasps
- Suprabulge (originate above the survey line) or Occlusally approaching clasp or Circumferential or Akers Clasp
- Infrabulge (originate below the survey line) or Gingivally approaching clasp or Bar Clasp
Types of Suprabulge or Occlusally approaching clasps
Simple circlet clasp
- Widely used clasp
- Clasp of choice in tooth supported RPD. E.g: Kennedy Class III
- Encircles nearly the entire abutment tooth
- Covers a large area of tooth surface, therefore requiring meticulous hygiene
- Mostly indicated in tipped mandibular molar
This design is most frequently used in cases of unilateral edentulous span of an unmodified Kennedy Class II or Class III partial denture, on the side of the arch where there is no edentulous space.
A combination clasp is a circumferential retainer for a removable dental prosthesis that has a cast reciprocal arm and a wrought wire retentive clasp (GPT8).
It consists of a wrought wire retentive arm and a cast reciprocal arm.
The combination of a wrought alloy and cast alloy gives it the name ‘combination clasp’.
- It is indicated on an abutment adjacent to a distal extension base where only a mesiobuccal undercut exists on the abutment.
- It is used when maximum flexibility is desirable, such as on an abutment tooth adjacent to a distal extension base or where a large tissue undercut or on a weak abutment when a bar-type direct retainer is contraindicated.
The patient may be taught to avoid distortion of the wrought wire by explaining how to remove a partial denture- the fingernail should always be applied to its point of origin, where it is held rigid by the casting, rather than to the flexible terminal end. Often, lingual retention may be used rather than buccal retention, especially on a mandibular abutment, so that the patient never touches the wrought- wire arm during removal of the denture. Instead, removal may be accomplished by lifting against the cast reciprocal arm located on the buccal side of the tooth.