Dental Ceramics Classification, Composition, Properties

Dental Ceramics Important Notes

1. Dental Ceramics

• It is a compound of metallic and nonmetallic compounds
• They are most suitable as tooth-colored restorative materials
• They have high compressive strength and low tensile strength
• It is insoluble and impermeable to oral fluids
• Bonding of porcelain to metal occurs by both chemical and mechanical bonding

2. Dental Ceramics Classification

3. Dental Ceramics Composition

4. Dental Ceramics Metallic oxides

They are added to obtain various shades

5. Dental Ceramics Feldspar

• They act as basic glass former, flux, matrix, and surface glaze
• It undergoes incongruent melting at 1150-1530°C
• It forms leucite crystals

Read And Learn More: Dental Materials Question and Answers

6. Dental Ceramics Glazing

• It is a process that gives a smooth and glossy surface, enhances esthetics, and helps in hygiene
• Glazed porcelain is stronger than unglazed porcelain
• The self-glaze is more permanent than the applied glaze

7. Dental Ceramics CAD-CAM

• Computer-Aided Design and Computer Aided Machining
• It is used to prepare metal and ceramic inlays and crowns without the need for impression and casting procedure

8. Dental Ceramics Stages of firing

Dental Ceramics Long Essays

Question 1. Classify dental casting alloys. Describe mechanical properties and add a note on dental ceramics
Answer:

Classification of Dental Casting Alloys:

• According to use
  • Alloys for all metal and resin veneer restoration
  • Alloys for metal-ceramic restoration
  • Alloys for removable dentures
• According to the yield strength and percent elongation
  • Type 1- soft
  • Type 2- medium
  • Type 3- hard
  • Type 4- extra hard
• According to nobility
  • High noble metal alloys
  • Noble metal alloys
  • Predominantly base metal alloys
  • Base metal
• According to the major elements
  • Gold alloys
  • Silver alloys
  • Palladium alloys
  • Nickel alloys

• • Cobalt alloys
  • Titanium alloys
• According to the three major elements
  • Gold-palladium-silver
  • Palladium-silver-tin
  • Nickel-chromium-molybdenum
• According to the number of alloys present
  • Binary
  • Tertiary
  • Quaternary

Dental Ceramics:

It is an inorganic compound with nonmetallic properties typically consisting of oxygen and one or more metallic or semi-metallic elements that are formulated to produce the whole or part of ceramic-based dental prosthesis

Dental Ceramics Classification:

• According to the firing temperature
  • High fusing
  • Medium fusing
  • Low fusing
  • Ultra-low fusing
• According to the type
  • Feldspathic porcelains
  • Leucite-reinforced glass ceramics
  • Alumina reinforced porcelain
  • Zirconia reinforced ceramics
• According to the function of the restoration
  • Core ceramics
  • Opaque ceramic
  • Veneering ceramic
• According to microstructure
  • Glass-ceramic
  • Crystalline ceramic
  • Crystal containing ceramic
• According to the fabrication process
  • Condensable ceramics
  • Heat pressed ceramic
  • Castable ceramic
  • Machinable ceramics

Dental Ceramics Composition:

Dental Ceramics Properties:

• Strength
• Glazed porcelain is stronger than ground porcelain
• Compressive strength- 331 MPa
• Low tensile, shear, and flexure strength
• Modulus of elasticity- 69 GPa
• Surface hardness- 460 KHN
• Wear resistance
• More resistant to wear
• Thermal properties
• Low thermal conductivity
• Coefficient of thermal expansion- 6.4-7.8 * 10 6/ °C
• Specific gravity
• 2.242
• Dimensional stability
• It is dimensionally stable after firing.
• Chemical stability
• Insoluble and impermeable to oral fluids
• Esthetics properties
• Excellent esthetics
• Biocompatibility
• Biocompatible with the oral tissues

Dental Ceramics Uses:

• Single unit crown
• Porcelain jacket crown
• Metal ceramic crown
• Castable glass ceramic crown
• Porcelain veneer for crowns and bridges
• Artificial teeth
• Inlays and Onlays
• Ceramic brackets used in orthodontic
• Implants, bioglasses

Question 2. Classify dental porcelains. Describe the methods of condensation and firing procedures
Answer:

Dental porcelains Classification:

• According to the type
  • Feldspathic porcelains
  • Leucite-reinforced glass ceramics
  • Alumina reinforced porcelain
  • Zirconia reinforced ceramics

Dental porcelains Condensation:

The process of packing the powder particles together and removing the excess water is called condensation

Condensation Purpose:

• Packs the particles together
• Minimizes porosity
• Improves strength
• Reduces firing shrinkage
• Removes excess water

Condensation Methods:

• Vibration
• Mild vibration by tapping or running serrated instrument
• The ultrasonic vibrator is also present
• Vibration brings out excess water to the surface which is blotted using absorbent paper
• Spatulation
• A small spatula is used to apply and smooth wet porcelain
• Dry powder
• It is placed on the opposite side of a wet increment

Dental porcelains Firing:

• The process of sintering and fusing the particles of the condensed mass is known as firing
• It is done in a porcelain furnace

Firing Method:

Firing Stages:

Question 3. What are metal-ceramic restorations? What are the ideal requirements for metal-ceramic restorations? Mention its composition.
Answer:

Metal Ceramic Restoration:

Metal ceramic restorations are those alloys that are compatible with porcelain and capable of bonding to it

Metal Ceramic Restoration Ideal Requirements:

• Its melting temperature should be higher than porcelain firing temperatures
• It should be able to resist creep
• Its coefficient of thermal expansion should be compatible with that of porcelain
• It should have a high stiffness
• It should not stain or discolor porcelain

Metal Ceramic Restoration Composition:

Dental Ceramics Short Essays

Question 1. Requirements of metal-ceramic alloys
Answer:

Requirements of metal-ceramic alloys

• Its melting temperature should be higher than porcelain firing temperatures
• It should be able to resist creep
• Its coefficient of thermal expansion should be compatible With that of porcelain
• It should have a high stiffness
• It should not stain or discolor porcelain

Question 2. Aluminous porcelain and its advantages
Answer:

Aluminous porcelain 

• Aluminous porcelain was developed by McLean in 1965
• It contains increased alumina content compared to conventional porcelain

Aluminous porcelain Use:

• Used in the construction of the core layer of the porcelain jacket crown
• Conventional body and enamel porcelain are then condensed over it

Aluminous porcelain Advantages:

• More esthetic
• Strength is twice that of conventional porcelain
• Less expensive
• Requires less removal of tooth structure

Question 3. Chrome-cobalt alloy
Answer:

Chrome-cobalt alloy

• They possess high strength
• Have excellent corrosion resistance
• They are bright luster, hard, strong alloy

Chrome-cobalt alloy Application:

• Denture base
• Cast removable partial denture
• Crown and fixed partial dentures
• Bar connectors

Chrome-cobalt alloy Composition:

Question 4. Drawbacks and benefits of metal Ceramics
Answer:

Metal Ceramics Drawbacks:

• Less flexibility
• High modulus of elasticity
• Low tensile strength
• Sufficient bulk of metal is required
• The shape of the crown out in line with the anatomic form of adjacent teeth

Metal Ceramics Benefits:

• Permanent esthetic quality
• Good resistance to fracture
• No wear occurs by abrasion
• No staining
• Less tooth preparation required

Question 5. Dicor
Answer:

Dicor

• Dicor is the first commercially available castable ceramic material for dental use
• It was developed by Dentsply International
• It is a castable glass that is formed into an inlay, facial veneer, or full crown restoration by a lost wax casting process similar to that employed for metals
• It is not used nowadays because of
• Very low tensile strength
• Tends to fracture easily
• More amount of tooth preparation is required

Question 6. Methods of strengthening Dental porcelain.
Answer:

1. Development of residual compressive stress

• Ion exchange or chemical tempering
• Involves the exchange of larger potassium ions for the smaller sodium ions
• Thermal tempering
• Involves cooling the surface while it is hot and in a molten state
• Thermal compatibility
• The coefficient of thermal contraction of metal is slightly larger than porcelain e This mismatch increases the strength of porcelain

2. Disruption of crack propagation

• Dispersion of crystalline phase
• Transformation toughening with partially stabilized zirconia

Dental Ceramics Short Question And Answers

Question 1. Aluminous porcelain
Answer:

Aluminous porcelain

• Aluminous porcelain was developed by McLean in 1965
• It contains increased alumina content compared to conventional porcelain

Aluminous porcelain Use:

• Used in the construction of the core layer of the porcelain jacket crown
• Conventional body and enamel porcelain are then condensed over it

Question 2. Condensation and firing of porcelain
Answer:

Porcelain Condensation:

The process of packing the powder particles together and removing the excess water is called condensation

Condensation Purpose:

• Packs the particles together
• Minimizes porosity
• Improves strength
• Reduces firing shrinkage
• Removes excess water

Porcelain Firing

• The process of sintering and fusing the particles of the condensed mass is known as firing
• It is done in a porcelain furnace

Question 3. Ceramic crown
Answer:

Ceramic crown Advantages:

• Superior esthetics
• Excellent translucency
• Requires slightly more preparation of the facial surface
• The appearance can be influenced and modified by selecting different colors of luting agents

Ceramic crown Disadvantages:

• Reduced strength
• Difficult to maintain a well-finished margin
• Cannot be used on extensively damaged teeth
• Need large connectors
• This leads to the impingement of the interdental papilla
• Wear of opposing teeth

Question 4. Glazing
Answer:

Glazing Uses:

• To obtain a smooth glossy surface
• To enhance aesthetics
• To reduce crack propagation
• The strength of glazed porcelain is much more than unglazed porcelain

Glazing Types:

• Overglaze
  • Glaze powder is mixed with a special liquid
  • The firing temperature is low
  • Chemical durability is low o Has high flux content
  • Contains more glass modifiers
  • Imparts glossy surface
• Self glaze
  • Restoration is subjected to a controlled heating
  • All the constituents are completely melted to form a single-phase glass
  • Has a high fusion temperature

Glazing Objectives:

• Enhances aesthetics
• Enhances hygiene
• Improves strength
• Reduces wear of opposing teeth

Question 5. Castable ceramics
(or)
Advantages of castable ceramics
Answer:

Castable ceramics

• Ease of fabrication
• Improved esthetics
• Minimal processing shrinkage
• Good marginal fit
• Moderately high flexural strength
• Low thermal expansion
• Minimal abrasiveness

Question 6. Role of feldspar in porcelain
Answer:

Role of feldspar in porcelain

• It acts as a flux, matrix, and surface glaze
• When it is mixed with metal oxides and fried at high temperatures it can form a glass phase that is able to soften and flow slightly
• During firing feldspar fuses and acts as a matrix and binds silica and kaolin

Question 7. Types of glazes
Answer:

Types of glazes

• Overglaze
• Glaze powder is mixed with a special liquid
• The firing temperature is low
• Chemical durability is low e Has high flux content
• Contains more glass modifiers o Imparts glossy surface
• Self glaze
• Restoration is subjected to a controlled heating
• All the constituents are completely melted to form a single-phase glass
• Has a high fusion temperature

Question 8. Uses of glazing
Answer:

Uses of glazing

• To obtain a smooth glossy surface
• To enhance aesthetics.
• To reduce crack propagation
• The strength of glazed porcelain is much more than unglazed porcelain

Question 9. Porcelain condensation techniques.
Answer:

Porcelain condensation techniques

• Vibration
• Mild vibration by tapping or running serrated instrument
• An ultrasonic vibrator is also present
• Vibration brings out excess water to the surface which is blotted using absorbent paper
• Spatulation
• A small spatula is used to apply and smooth wet porcelain
• Dry powder
• It is placed on the opposite side of a wet increment

Question 10. Classification of dental casting alloys.
Answer:

1. Dental casting alloys According to use

• Alloys for all metal and resin veneer restoration
• Alloys for metal-ceramic restoration
• Alloys for removable dentures

2. Dental casting alloys According to the yield strength and percent elongation

• Type 1 – soft
• Type 2 – medium
• Type 3 – hard
• Type 4 – extra hard

3. Dental casting alloys According to the nobility

• High noble metal alloys
• Noble metal alloys
• Predominantly base metal alloys
• Base metal

4. Dental casting alloys According to the major elements

• Gold alloys
• Silver alloys
• Palladium alloys
• Nickel alloys
• Cobalt alloys
• Titanium alloys

5. Dental casting alloys According to the three major elements

• Gold-palladium-silver
• Palladium-silver-tin
• Nickel-chromium-molybdenum

6. Dental casting alloys According to the number of alloys present

• Binary
• Tertiary
• Quaternary