Restorative - Bridges/crowns Flashcards
What is Ante’s law?
The root surface area of abutment tooth should be equal to or greater than that of the tooth being replaced with Pontic.
What bridge is better for cases of mal-alignment?
Fixed moveable - reduces risk of excessive tooth tissue removal and pulpal damage
Indicated for use when abutment teeth are not parallel.
What is the most mechanically unsound bridge design?
Cantilevers - all load is transmitted onto sole abutment tooth
What type of cantilever bridge carries the lowest risk of failure?
Posterior bridge with large single abutment design mesial Pontic (mesial cantilever with distal abutment)
However, for 3 and 4 distal cantilever may be more advantageous due to antes law.
When would you use a spring cantilever bridge?
When there is spacing anteriorly e.g. central missing - the 6 would be abutment and a bar would come over to the space meaning no metal is seen anteriorly.
In RBB’s, what is the thickness or retainer and what material is used?
Nickel chromium/CoCr should be at least 0.7mm to achieve adequate rigidity.
How is the fitting surface for a RBB prepared?
Prepare fitting surface by sandblasting with 50micron aluminium oxide (Al203)
What is the 5 and 10yr surgical rates of RBB compared to conventional bridges?
RBB:
5yr 88%; 10yr 44%
Conventional:
94%
What cements should be used for metal conventional bridges?
RMGI:
- Relyx, adhesive resin or GI, zinc phosphate
What cements should be used for metal ceramic substructure bridges?
RMGI:
- relyx, adhesive resin or GI, zinc phosphate
What cements should be used for adhesive bridges?
Panavia 21
- adhesive resin cement that cures when oxygen is excluded
What cements should be used for ceramic adhesive resin bridges?
Relyx Unicem or nexus (adhesive universal resin cement)
What prep is required for a MCC?
Non functional cusps: 2mm Functional cusps: 2.5mm Incisal: 1.5-2mm Axial: 1-1.5mm Shoulder 1.2-1.3mm Between 10-20degree taper
What prep is required for a metal crown?
Non functional cusps: >1mm
Functional cusps: >1.5mm
Thickness at least 0.5mm
Chamfer 0.3-0.5mm 10degree taper
What prep is required for ceramic crowns?
Non functional cusps: 2mm
Functional cusps: 2.5mm
Occlusal: 1.5-2mm
Shoulder/heavy chamfer 1mm
What type of resin bonded bridge design would give the best prognosis?
Distal cantilever anterior bridge
How is porcelain used when creating all ceramic crowns and veneers?
Porcelain is fired into refractory die
What type of crown has metal that acts as a heat sink reducing tendency for porcelain to crack on cooling?
Metal ceramic crowns
What crown is constructed over a platinum foil matrix?
Porcelain jacket crown
What crown involves sintering which increases the coping strength prior to veneering with feldspathic porcelain?
Zirconia supported crown
What type of crown has colour and characterisation provided by surface tinting with a tendency to chip off?
Cast glass crown (dicor)
What component helps to minimise creep in amalgam?
Copper (Cu)
What component acts as oxygen scavenger in amalgam?
Zinc
What is the role of a dentine conditioner (phosphoric acid)?
To dissolve the smear layer and demineralise the surface mineral exposing a collagenous matrix and the dentine tubules
What is the purpose of the Denar self centring Facebow?
To locate the maxillary cast to the articular hinge axis in a similar way to the relative location of the maxilla to the mandible hinge axis.
Protection of a polyaklenoate restoration immediately after placement is best achieved by?
Use of a barrier such as unfilled resin or varnish is best for protecting GIC restorations from imbibition/
Why should a conventional GIC be covered and finished delayed for at least 24 hours?
Silaceous hydrogel is sensitive for moisture imbibition and desication
