Indications for Crowns and the Preoperative Assessment Flashcards
What is a crown?
A full coverage extra- coronal restoration.
What kind of restoration is a crown? (direct or indirect)
Indirect - made in the lab.
7 indications for crowns?
- Repeated failure of a direct plastic restoration.
- Difficulty achieving adequate contour, contact point and occlusal contacts with a direct restoration.
- Minimize risk of tooth fracture.
- Aesthetics.
- To include design characteristics to accommodate a metal-based removable prosthesis.
- Bridge abutment.
- Replacement of an existing crown.
2 ways in which a direct restoration can fail?
- Fracture.
- Debond.
why are inadequate occlusal contacts bad?
Increased risk of restoration FRACTURE and subsequent MICROLEAKAGE and SECONDARY CARIES.
4 materials a crown can be made from?
- Gold alloy (precious metal alloy).
- Ceramic.
- Metal bonded to ceramic.
- Non precious metal alloys (ex. cobalt chromium, nickel chromium).
Why are inadequate contact points bad?
- Increased FOOD PACKING.
- Difficult to CLEAN and MAINTAIN –> SECONDARY CARIES/ PERIODONTAL DISEASE.
Why are long/ broad contact points bad?
HARDER to CLEAN –> Increased risk of PERIODONTAL DISEASE + SECONDARY CARIES.
3 advantages of a crown compared to a direct restoration?
- Occlusal pattern can be made to conform to existing occlusion or to a reorganized occlusion.
- Can take into account guidance on excursive movements.
- Can be made with ideal contact points and appropriate contour.
What teeth are unrestorable (3)?
- Cracked tooth: crown to root extension.
- Split tooth: crown and root.
- Vertical root fracture.
- ANY CRACK THAT HAS EXTENDED ONTO THE ROOT SURFACE IS UNRESTORABLE.
When does a fractured cusp often occur (what clinical situation)? Why does this occur?
- LARGE restorations surrounded by THIN PIECES OF BONE.
- Occlusal forces cause WEDGING FORCES which PUSH OUT ONTO THE REMAINING CUSPS.
What can be used to prevent a fractured cusp? How?
- Can use a CROWN.
- Ensures forces propagate along the LONG AXIS of the tooth and thus PREVENT PROPAGATION OF CRACKS.
What did lucarotti find the survival of molar tooth to reintervention with regard to type of restoration to be for MOD amalgam vs crown at 15 years?
- MOD: 34.
- Crown: 60.
What is a cracked tooth?
Tooth that is cracked but remains in a SINGLE PIECE.
- Can be into enamel, dentine or pulp.
What can be used to stop crack propagation in a cracked tooth?
a CROWN (prevent crack from reaching pulp where it will allow ingress of bacteria and thus infection).
What are telescopic dentures?
DOUBLE CROWN DENTURES - Consist of double crowns
- Primary/inner crown: Cemented to the abutment.
- Secondary/ outer crown: Attached to the denture.
2 ways in which crowns can be used with removable prostheses?
- Rest seat preparations for denture.
- Telescopic/ double crown dentures.