Dental Ceramics 1

Question 1

what are dental ceramics?

Answer 1

Compounds of oxygen with lighter metals or metalloids

Non-metallic, inorganic in nature

Consist mainly of glasses, porcelains, glass-ceramics

Exhibit different chemical, mechanical, physical, and thermal properties than metals and polymers

Generally, they are brittle, temperature resistant, and do not react with most liquids, gases, alkalis or acids. They are excellent electrical and thermal insulators

Question 2

what is a silicate ceramic?

Answer 2

Silicate ceramics:
Characterized by a an amorphous glass phase and a porous structure.

Consists mainly of SiO2 with small additions of crystalline Al2O3, MgO, ZrO2, and other oxides.

Example: Dental porcelains

Question 3

what are oxide ceramics?

Answer 3

2) Oxide Ceramics:
Contain a principal crystalline phase such as Al2O3, MgO, Thorium Oxide (ThO2), or ZrO2 , with or without a small glass phase content

ZrO2 is of major importance as a dental oxide ceramic because it has a high fracture toughness. However, it can not be used in the pure state because of cracks developing during sintering due to phase transformation from tetragonal to monoclinic structure. Thus, MgO, Y2O3, CaO, and CeO are added to suppress this transformation.

Question 4

what are non-oxide ceramics?

Answer 4

3) Non-Oxide Ceramics:
Examples: TiB2, ZrB2, SiC, TiC, and Si3N4

They are not practical for use in dentistry due to their high processing temperatures, complex processing methods, and unaesthetic color and opacity

Question 5

what are glass ceramics?

Answer 5

4) Glass Ceramics:
A ceramic consisting of a glass matrix phase and at least one crystal phase

The crystal phase pursues a process of nucleation and growth inside the glass matrix

Example: Dicor glass-ceramic

Question 6

what are the 8 classifications of dental ceramic products?

Answer 6

Dental ceramics are commercially available as: core ceramic, liner ceramic, margin ceramic, opaque dentin ceramic, enamel ceramic, stain ceramic, glaze ceramic, and addition ceramic

These products can be classified according to their:
1. Use (anterior, posterior, crowns, veneers, stain ceramic, glaze ceramic, FPD (fixed partial denture, etc…)

2. Composition (pure alumina, pure zirconia, silica glass, etc…)
3. Processing method (sintering, CAD-CAM, etc…)
4. Firing temperature (low-fusing, medium-fusing, and high-fusing)
   5) Microstructure (glass, crystalline, or crystal- containing glass)
   6) Translucency (opaque, translucent, transparent)
   7) Fracture resistance
   8) Abrasiveness

Question 7

what are 8 ceramic processing methods?

Answer 7

1. Condensation
2. Hot pressing
3. Casting
4. Slip-casting
5. CAM (starting with a high quality ceramic ingot)
6. CAM (starting with a partially sintered ceramic block
7. Copy milling
8. Milling of dry-pressed powder on enlarged die

Question 8

For metal-ceramic prostheses, what is base metal alloy?

Answer 8

High Noble: must contain ≥ 40 wt% Au and ≥ 60 wt% noble metal elements such as Pt, Pd, etc..

Noble: must contain ≥ 25 wt % of noble metal elements

Predominantly Base Metal: Contains < 25 wt% of noble metal elements

Question 9

what is the composition of dental porcelains?

Answer 9

Typical ingredients are SiO2, Al2O3, CaO, NaO, K2O, B2O3, and an increased alkali content

Soda, potash, and leucite are necessary to increase the thermal coefficient of expansion to a level compatible with the alloy coping

Metallic opacifiers are added to conceal underlying alloy

Silica can exist in four different forms: crystalline quartz, crystalline cristobalite, crystalline tridymite, and noncrystalline fused silica

Question 10

what are glass modifiers?

Answer 10

Alkali metal ions such as Na, K, and Ca are added to produce dental porcelains with different firing temperatures

Dental porcelains are classified according to their firing temperatures

	High fusing (1300oC)
	Medium fusing (1101 – 1300oC)
	Low fusing (850 – 1100oC)
	Ultra-low fusing (<850oC)

Question 11

what is the composition of feldspathic porcelains and what are they used for and why can it not be classified as glass-ceramics?

Answer 11

Potassium feldspar (K2O) and sodium feldspar (Na2O) are natural minerals. They contain Al2O3 and SiO2

Used in making porcelains for metal-ceramic crowns

Potassium feldspar mixed with other metal oxides and fired at a high temperature forms leucite and a glass phase that softens and binds the porcelain powder together (liquid phase sintering)

Cannot be classified as glass-ceramics because crystal formation does not occur through controlled nucleation, formation and growth mechanisms

Question 12

what are the 4 types of processes to produce a metal coping for metal-ceramic prostheses?

Answer 12

There are 4 types of processes to produce a metal coping for metal-ceramic prostheses:

1. Electrodeposition of of gold or other metal on a duplicate die
2. Burnishing and heat-treating metal foils on a die
3. CAD/CAM processing of a metal ingot
4. Casting through the lost-wax process