Ceramic Materials pt 1

Question 1

Ceramics Definition

Answer 1

Inorganic, non-metallic solids that contain metal, non-metal and metalloid atoms held in ionic and covalent bond (usually oxides)

Question 2

Silica Glass

Answer 2

SiO4 tetrahedron, primary component of dental procelain

Question 3

Microstructure of dental Porcelain

Answer 3

Primarily glass w/ some crystalline residuals

• noncrystalline or amorphous silicate-glass

and/or

crystalline silicates - quartz/crystobilite, leucite

Question 4

(De)Strengthening Mechanisms of Ceramics

Answer 4

Flaws act as stress concentrators/magnifiers: Fabrication defects and surface flaws

Question 5

Stress Concentration

Answer 5

Low locally applied stresses = very high effective local stress

Question 6

Dental Crowns - Location of major stresses in anterior crowns

Answer 6

Directly under contact

Hoop stress around circumference

Question 7

Fabrication Defects

Answer 7

Sintered powders introduce voids

Casting and pressing result in potentially less flaws

Question 8

Surface Flaws

Answer 8

Grinding can introduce flaws (polishing/re-glazing is critical)

Usually failure occurs from largest flaws

Question 9

Chemical Strengthening of Ceramics

Answer 9

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

Question 10

Glazing and polishing of Ceramics

Answer 10

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

Question 11

Preventing Stress Corrosion

Answer 11

Ceramics are weaker when fracture occurs in water, water reacts w/ ceramics

Ceramic fused to metal foil (captek) can reduce

Question 12

Crystalline Reinforcement

Answer 12

Most common method

Introduce crystalline content in glassy matrix to deflect cracks

Question 13

Crystalline Reinforced Materials

Answer 13

Glass ceramics such as:

Leucite-reinforced (Empress, 35-45% crystals)

Lithium disilicate (eMax, most commonly used, 70% crystals)

Question 14

Glass Ceramics

Answer 14

Moderate Strength

Good translucency

Can use for full thickness restorations

Formed by pressing, machining or sintered powder

No shrinkage = good fit

Question 15

Monolithic ACC Fabrication Pros and Cons

Answer 15

+ 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

Question 16

Minimal Cutback ACC Fabrication Pros and Cons

Answer 16

+ Maximize strength of crown

+ More detail where needed

+ Color gradation not limited to surface

+ Recontouring after cementation doesnt eliminate shade

• Added lab cost

Question 17

Monolithic Fabrication Technique

Answer 17

Full contour w/ surface stains

Less labor intense

Can have excellent outcomes

Full contour strength of material

“Moderate strength translucent ceramic”

Question 18

Minimal Cutback Fabrication Technique

Answer 18

“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)