Materials for indirect restorations Flashcards
Hove some requirements the material we use for indirect restoration should fill
- Accuracy of fit
- Strength to resist occlusal forces
- Rigidity to avoid flexure and hence cement failure
- Should have a thermal expansion coefficient similar to the tooth
- Should not attract plaque
- Should be biocompatible
Give examples of materials we can use to make crowns and bridges
- Metals
- Ceramics
- Metal ceramic
- Indirect dental composite
Name the 2 types of metals we can use to make indirect restorations
- Gold and palladium alloys
- Base metal alloys
Give examples of some Gold and palladium alloys (precious metals) we can use to make indirect restorations
- Type III gold alloy
- Silver palladium
- Palladium-silver-gold
- Gold-silver-copper-palladium
- Palladium-copper
- Palladium-tin
Which type of gold alloy do we use for indirect restorations? What are the other types used for?
We use type III for indirect restorations
Type I and II are used for inlays
Give examples of some base metal alloys we can use to make indirect restorations
- Nickel-chromium
- Nickel-chromium-berylium
- Titanium
What factors do we take into consideration when choosing an indirect restoration material?
- Cost
- Corrosive resistance
- Strength
- Stiffness
- Hardness
- Ductility
What are some of the differences between base metal alloys and precious metals (in terms of being used as a restoration)?
- Base metal alloys have a higher modulus of elasticity so they are more rigid
- Base metal alloys are less flexible
What is a major drawback of base metal alloys
You need very careful control casting conditions
Increasing concern about the biocompatible of dental alloys
Define material biocompatibility
The ability of a material to perform with an appropriate host repose in a specific application
Give some issues surrounding biocompatibility of indirect restoration materials
- Grinding and casting fumes can result in conjunctivitis, dermatitis and bronchitis
- High levels of nickel are carcinogenic
- Nickel is well known to cause contact dermatitis
Do base metals or precious metals bond better to porcelain
Precious metals bond better
How do porcelain based metal alloys work
Coping distributes stresses and provides rigid support (this inhibits propagation of cracks from small faults at the metal ceramic interface)
How is a good bond achieved between the metal and the porcelain in a metal ceramic allow?
- Mechanical retention
- Direct chemical bond can be made using ion diffusion
- mis match of the co efficient of therapy expansion can be used
What are some of the disadvantages of metal ceramic alloys
- Absence of light transmission especially in cervical and proximal areas
- Reduced depth of translucency
- Presence of fret line at gingival margin
- Some patients may have a sensitivity or be allergic to alloys
