Ceramics Flashcards
Definition of ceramic
Simple compounds of metallic and non-metallic elements e.g. almost all solids that are neither metals nor polymers.
Definition of glass
A material e.g. ceramic or polymer, that has been cooled to a rigid condition without crystallising.
Crystalline define
Exhibit long range and periodic anatomic order
Amorphous define
Lack of long-range atomic order (glasses)
Important properties of ceramics
- Flexural strength: forces that are applied as ceramics are brittle, they can chip
- Fracture toughness: how strong the material is
- Chemical solubility: otherwise will start dissolving
- Antagonistic wear
- Translucency: how they appear
What are the 3 types of all ceramic systems?
- Polycrystalline (oxide) ceramics - without a glass phase e.g. Procera Al2O3/ZrO2, Cercon, lAVA
- Glass-infiltrated ceramics (With a glass phase) e.g. In Ceram Al2O3/ZrO2
- Glass ceramics (with a glass phase) e.g. Empress I/II
Which type of ceramic system is the most aesthetic?
Glass ceramic
Which type of ceramic system is the most strongest?
Polycrystalline (oxide) ceramics
What are glass ceramics used for?
Inlays and onlays, veneers, anterior single crowns
What are glass infiltrated ceramics used for?
Substructures for anterior and posterior single crowns
Systems for glass infiltrated ceramics
In-Ceram (Alumina Al2O3)
In-Ceram Spinnell (Al2O3+MgO2)
In-Ceram Zirconia (Al2O3+ZrO2)
What are oxide ceramics used for?
AlZr Cores for anterior and posterior crowns
Zr anterior and posterior bridgework
What is the most common cause of failure in all ceramic restorations?
Fracture
Why do porcelains fracture?
- No moveable defects/dislocations (as in metals) to dissipate stress
- Flaw leads to stress concentrations, especially with tensile forces
- If a crack starts to propagate, less stress required to continue propagation and the crack accelerated quickly
- Fracture stress determined by the largest flaw
Traditional (Feldspathic) Porcelain disadvantages
- Fracture resistance low
- Construction technique sensitive: shrinking due to fusing when fired, skill level required to achieve good aesthetics
- Hardness
What are some areas of development to counteract disadvantages of traditional ceramic restorations?
2 Solutions: provide support for using a stronger substrate or produce ceramics that are stronger and tougher.
1. Better fracture resistance: laminate to metal to decrease influence of internal flaws, adapted to substructure,
Dispersion strengthening of glasses: alumina added to glass to increase strength and high strength crystalline ceramics as a core
Leucite-reinforce glass ceramics e.g. IPS Impress
Indications: crowns, inlays, onlays and veneers
