Posterior Full Coverage Crowns I and II Flashcards
Why restore a compromised tooth?
Restoring function and aesthetics
Restore structural integrity and resisting fracture
Integrity with other prosthesis
Why crown root filled teeth?
Weakened tooth due to access cavity prep
Loss of structural integrity associated with loss of roof of the pulp chamber
Loss of dentine elasticity
When is cuspal protection of posteriors needed?
Loss of marginal ridges
Loss of substantial tooth structure
Heavily restored teeth
How to achieve cuspal protection?
Adhesive restorations (direct resin composite)
Cusp coverage cast restorations (onlay, 3/4 crown)
Full coverage restoration (crown)
When are crowns used to achieve integrity with other structures (example)?
Place crowns on abutment teeth to incorporate the RPD
What design considerations are made with posterior crowns?
Is the tooth in function Appearance Adjacent teeth Periodontal tissues Pulp Retention of the crown to the tooth Materials Cost
What to consider with periodontal tissues with posterior crowns?
Plaque control Periodontal attachment Alveolar bone levels Status of periodontal disease Mobility
Pulpal death following crown preps due to?
Aggressive insult to tooth, dentine and odontoblasts Thermal damage LA Desiccation Bacterial contamination
Around 10-20% of pulps necrose after crown prep - warn pt before of loss of vitality
What does a 1.2mm shoulder crown prep on a posterior tooth leave?
1.2mm shoulder crown prep on a posterior tooth leaves less than or 0.7mm remaining dentine thickness
Posterior crown materials?
Metal
Metal ceramic
Ceramic
Features of metal (full gold) crowns?
Minimal tooth reduction as strong
Least aesthetic
Can be adjusted intraorally (occlusion)
Gold alloy types?
Type 1 - soft gold
- can withstand biting forces
- soft enough to burnish against margins of cavity
- main use - one surface inlays
Type 2 - medium gold
- less burnishable
- hard enough to stand up in small
- multiple surface inlays that do not include buccal or lingual surfaces
Type III - hard gold
- Most common for all metal crowns and bridges
- Gold 75%, silver 10%, copper 10%, palladium 3% and zinc 2%
Type IV - extra hard
- Used for partial denture frameworks but not used in fixed prosthetics
Survival of a gold crown?
97% at 9 yrs
94.1% for >40 yrs
Metal-ceramic crown features?
Metal core
Extensive buccal tooth reduction
Aesthetics at the cost of tooth tissue
Only the metal component can be adjusted intra-orally
PFM alloy types?
High noble alloys have a minimum of 60% noble metals and min of 40% by weight of gold Noble alloys (gold, palladium, silver) contain at least 25% by weight noble metal - high strength, durability, hardness and ductility
Base metal alloys
- Contain less than 25% noble metal
- Much harder, stronger and twice the elasticity of high noble and noble metal alloys
- Casting can be made thinner - still rigid and can support porcelain
- Contain nickel and beryllium - allergic reactions
Metal ceramic and all ceramic crown survival?
Systematic review:
5 yr survival 93.3% of all ceramic crowns
95.6% for metal ceramic crowns
All ceramic crown features?
High strength ceramic core Most aesthetic Low edge strength Requires extensive reduction Intra-oral adjustment not possible
All ceramic crowns survival rate?
5 yr fracture rate of 4.4%
Molars - higher fracture rate than premolar crowns
Principles of tooth preparations for crowns?
Preservation of tooth structure Retention and Resistance Structural durability Marginal integrity Preservation of periodontim
Retention form of retention?
Prevents dislodgement of the crown in an axial direction
Resistance form of retention?
Prevents dislodgement of the crown due to rotation from a lateral load
What should the tooth prep design be?
Well defined and well finished
Clear finish line visible
Ceramic margins should be a butt-joint rounded shoulder
All prep line angles and point angles are best rounded
What should the tooth prep be for all ceramic crowns?
Minimal occlusal reduction - 1.5mm
>2mm in areas of stress
5 degree taper
Shoulder margin
What should the occlusal reduction reflect?
The morphology of the tooth and the functional pathways of the occlusion
Features of a PFM crown prep?
Chamfer Lingual axial reduction Wing Functional cusp bevel Planar occlusal reduction Facial axial reduction Shoulder Gingival bevel
Posterior crowns - stage 1 of clinical stages?
Pre-op clinical and radiographic assessment
Further investigations, study models, diagnostic wax up
Tx planning
Informed consent
Clinical stage 2 - posterior crowns?
Tooth build up and preparation Impression Occlusal record Temporisation Fabrication (lab stage)
Posterior crowns - clinical stage III?
Removal of temp crown Try in of definitive crown Cementation of definitive crown Occlusal check Review
