Support and Indirect Retention Flashcards
Define support.
Resistance to VERTICAL load (caused by OCCLUSAL FORCES during function) directed through the denture to the underlying MUCOSA. This force is ultimately resisted by BONE.
3 different types of support
tooth
mucosa
both
4 examples of tooth support
- cingulum/ occlusal rests.
- onlays
- overdenture abutments
- connectors
How is tooth support gained?
- The PERIODONTAL LIGAMENT. Aim to apply the force through the denture then vertically down the tooth. This is transmitted through the PDL and resisted by BONE.
How do occlusal/ cingulum rests help with support?
enable us to direct the force VERTICALLY through the tooth. Extends from denture framework and sits at the marginal ridge of the tooth.
When is a rest seat needed?
- Depending on the occlusion and shape of the tooth, we may have to prepare a REST SEAT (ex. if opposing dentition occludes tightly with where we want to put the rest).
Characteristics of a rest seat
1mm deep (must sit in the ENAMEL layer), 2mm wide, smooth and rounded. This is a CAST feature, hence is captured in the impression and replicated in the model to allow CHROME CASTING.
What must be done when adding a cingulum rest on anteriors? Why?
Must cut a CINGULUM SEAT (on palatal/ lingual aspect of the tooth within the ENAMEL layer) means the rest can SIT yet not LEAN on the tooth.
When are onlays used?
- Cover a larger area of the occlusal surface.
- Used when there is more INTEROCCLUSAL SPACE (ex. significant wear on a tooth).
3 cases when overdenture abutment would be used.
- the coronal portion of a tooth is very broken down
- worn through non carious surface loss
- cannot extract tooth due to medical reasons.
2 benefits of overdenture abutments
- PRESERVE BONE (helps with denture retention).
- Overdenture abutment tooth provides support.
2 downsides of tooth support.
- Downside: If force is not coming vertically, this will MOVE the tooth.
- Downside: The less ligament and bone there is, the less support the tooth can offer AND increased load on the tooth may compromise its periodontal health. CAREFUL PERIODONTAL TREATMENT IS REQUIRED AS PART OF TREATMENT PLANNING PHASE.
2 ways of achieving mucosal support?
- Saddles: the areas which carry the prosthetic teeth.
- Connector: the part of the denture that connects all the components.
Downside of mucosal support
Mucosa has a degree of compressibility, hence when a force is applied the patient may feel slight denture movement.
How is mucosal support enhanced?
The bigger the area of mucosa we cover the greater amount of support we can achieve.
