Full Coverage Posterior Crowns Flashcards
Reasons for full coverage
- Restores fx and morphology and aesthetics (2nd)
- Preserving remaining tooth tissues and increasing fracture resistance e.g post RCT
- Integrating with other prostheses
- Improve pt confidence and psychology
Endodontically treated teeth - indications for crowning
Weakened due to access cavity preparation
Loss of structural integrity associated with loss of roof of pulp chamber
Fragile due to loss of dentine elasticity
Cusp protection is required for…
Posteriors are restored with….
- loss of marginal ridge
- loss of substantial tooth structure
- heavily restored tooth
adhesive restorations (DIRECT RESIN COMPOSITE)
cusp-coverage cast restorations (ONLAY 3/4 CROWN) - only height reduction
full coverage restorations (CROWNS) - preparation around and on top
Design considerations
Aesthetic considerations Adjacent/opposing teeth - prognosis? Caries/restorations Periodontal tissues Pulp, RCT and periapical tissue Is tooth in function? Retention of crown - dentine bonded - ceramic crown - requires deeper prep to accommodate layers Materials
Periodontal tissue factors
Plaque control
Periodontal attachement
Alveolar bone levels
Status of periodontal disease
Pulpal death post crown prep is due to
Aggressive insult to tooth, dentine and odontoblasts
thermal damage
LA - adrenaline reduces blood supply to tooth - more likely to die
Desiccation
Bacterial contamination
Loss of vitality is BIG RISK
Crown preparation
1.2mm shoulder crown prep on posterior tooth leaves <0.7mm remaining dentine thickness
Materials used have to balance
Fx and aesthetics
FGC
PFM - metal core layered by porcelain
All ceramic
Metal (Full gold crown)
Minimal reduction - CONSERVATIVE Least aesthetic Can be adjusted intra orally Least abrasive to opposing teeth High survival rate on the long term - 90% BEYOND 10 YRS
PFMs
Metal-ceramic
Ceramic is most important on
- Metal Core
- Extensive tooth reduction (buccally)
- Aesthetics at the cost of tooth tissue
- Only the metal core is adjustable intra-orally
Buccal and labial surface
Alloys used in FGC
- Type I (Soft) Hard enough to stand up to biting forces but soft enough to burnish against margins. Used for one-surface inlays
- Type II (Medium) Less burnishable but hard enough to stand up in small, multiple surface inlays that did not include B/L surfaces.
- Type III (hard) The most commonly used type of gold for all- metal crowns and bridges. Includes the following metals: • Gold 75% • Silver 10% • Copper 10% • Palladium 3% • Zinc 2%
- Type IV (Extra hard) is used for partial denture frameworks but was not used in fixed prosthetics.
Alloys used in PFM - high noble
- High-noble alloys have a min of 60% noble metals (any combination of gold, palladium, and silver) and a min of 40% by weight of gold. Contain a small amount of tin, indium, or iron which provides for oxide layer needed to provide a chemical bond with porcelain.
Alloys used in PFM - noble alloys
- Noble alloys have a min of 25% noble metal (gold, palladium, or silver) by weight. Have high strength, durability, hardness, and ductility.
Alloys used in PFM - base metal alloys
- Base-metal alloys have <25% noble metals. Less expensive, much harder, stronger but less elastic than other alloys. Castings can be made thin and still have the rigidity needed to support porcelain.
Ideal metal for cast-dental restorations and are heavily used for PFM. Unfortunately, some of the components like nickel and beryllium, can cause allergic reactions.
All ceramic crowns - for posterior?
Most aesthetic
High strength CERAMIC CORE FOR POSTERIORS
BUT
Brittle Low tensile strength less conservative Not adjustable intra-oral Abrasive to opposing teeth (40x more than gold to enamel)
