Ceramic Materials pt 1 Flashcards
Ceramics Definition
Inorganic, non-metallic solids that contain metal, non-metal and metalloid atoms held in ionic and covalent bond (usually oxides)
Silica Glass
SiO4 tetrahedron, primary component of dental procelain
Microstructure of dental Porcelain
Primarily glass w/ some crystalline residuals
- noncrystalline or amorphous silicate-glass
and/or
crystalline silicates - quartz/crystobilite, leucite
(De)Strengthening Mechanisms of Ceramics
Flaws act as stress concentrators/magnifiers: Fabrication defects and surface flaws
Stress Concentration
Low locally applied stresses = very high effective local stress
Dental Crowns - Location of major stresses in anterior crowns
Directly under contact
Hoop stress around circumference
Fabrication Defects
Sintered powders introduce voids
Casting and pressing result in potentially less flaws
Surface Flaws
Grinding can introduce flaws (polishing/re-glazing is critical)
Usually failure occurs from largest flaws
Chemical Strengthening of Ceramics
Puts surface of ceramic in compression (pre-stress)
Ion exchange - Substitute small interstitial ions w/ larger interstitial ions to put glass surface in compression
Not really used in dentistry
Glazing and polishing of Ceramics
Self-Glazing: tends to heal any existing surface flaws
Surface glazes can be designed to cool so they are under surface compression to improve strength
Preventing Stress Corrosion
Ceramics are weaker when fracture occurs in water, water reacts w/ ceramics
Ceramic fused to metal foil (captek) can reduce
Crystalline Reinforcement
Most common method
Introduce crystalline content in glassy matrix to deflect cracks
Crystalline Reinforced Materials
Glass ceramics such as:
Leucite-reinforced (Empress, 35-45% crystals)
Lithium disilicate (eMax, most commonly used, 70% crystals)
Glass Ceramics
Moderate Strength
Good translucency
Can use for full thickness restorations
Formed by pressing, machining or sintered powder
No shrinkage = good fit
Monolithic ACC Fabrication Pros and Cons
+ Maximizes strength of crown where needed (lingual/incisal)
+ Characterize surface shade w/ glazes and stains
+ Single base shade used
- Recontouring after cementation can eliminate shade if most is from stain
Minimal Cutback ACC Fabrication Pros and Cons
+ Maximize strength of crown
+ More detail where needed
+ Color gradation not limited to surface
+ Recontouring after cementation doesnt eliminate shade
- Added lab cost
Monolithic Fabrication Technique
Full contour w/ surface stains
Less labor intense
Can have excellent outcomes
Full contour strength of material
“Moderate strength translucent ceramic”
Minimal Cutback Fabrication Technique
“Porcelain only in critical esthetic area”
More labor intense (more expensive)
Can have excellent clinical outcomes
Full contour strength of material in high stress areas (lingual/occlusal)
