Dental Ceramics Quiz
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Questions and Answers

What is the main role of organic binders in ceramic materials?

  • They increase the hardness of the material.
  • They act as pigments to add color.
  • They bond the powder particles and allow modeling. (correct)
  • They provide thermal insulation.

Which of the following statements correctly describes the disadvantages of traditional ceramic porcelain?

  • It is flexible and lightweight.
  • It experiences a firing shrinkage of 10%.
  • It is prone to extensive cracking. (correct)
  • It is soft and durable.

What occurs during the process of fritting in dental ceramics?

  • The mixture is rapidly cooled into water. (correct)
  • The glass is transformed back into a powder form.
  • The mixture is heated to a temperature above the sintering point.
  • The mixture is cooled slowly in air.

Which layer is typically the base layer in dental ceramics?

<p>Ground opaquer (C)</p> Signup and view all the answers

What is a property of the glazed ceramic masses regarding plaque retention?

<p>They do not retain plaque. (C)</p> Signup and view all the answers

What is one of the key steps in obtaining a full ceramic crown?

<p>Compaction. (B)</p> Signup and view all the answers

What is the approximate range for compressive strength in ceramics, as stated?

<p>150-900 MPa (A)</p> Signup and view all the answers

What is the primary component of the ceramics used in dental porcelain?

<p>Feldspar, quartz, and kaolin (B)</p> Signup and view all the answers

What defines dental porcelain in terms of its material composition?

<p>It essentially consists of sintered glass. (B)</p> Signup and view all the answers

Which technique can increase the firing shrinkage in ceramic mass?

<p>Brushing the material onto the die. (B)</p> Signup and view all the answers

Which property describes the brittleness of ceramics?

<p>Very low plastic strain (B)</p> Signup and view all the answers

Which intermolecular bond is characteristic of crystalline ceramics?

<p>Ionic bonds (A)</p> Signup and view all the answers

What is the purpose of milling in the context of dental ceramics?

<p>To create a very fine powder from the materials. (C)</p> Signup and view all the answers

What factor can influence the mechanical properties of ceramics?

<p>Internal irregularities and pores (D)</p> Signup and view all the answers

What is the main reason ceramics have high resistance to compression?

<p>Their crystalline structure (B)</p> Signup and view all the answers

Which of the following ceramics has the highest Vickers hardness?

<p>In-Ceram (D)</p> Signup and view all the answers

What defines the vitreous phase in ceramic materials?

<p>It maintains shape and contributes to durability. (A)</p> Signup and view all the answers

Which statement about the properties of dental ceramics is correct?

<p>They are brittle but have a high resistance to chemical factors. (C)</p> Signup and view all the answers

What is the cause of fatigue in ceramics over time?

<p>Alkaline hydrolysis of Si oxides (A)</p> Signup and view all the answers

Which type of ceramics has reduced hardness similar to dental enamel?

<p>Low-sintering ceramics (A)</p> Signup and view all the answers

What is the role of high-temperature heating in the production of ceramics?

<p>It promotes the rearrangement of atoms. (A)</p> Signup and view all the answers

Which of the following is NOT typically considered a ceramic material?

<p>Calcium carbonate (A)</p> Signup and view all the answers

Why can't the inner side of ceramics be glazed?

<p>Adaptation to the dental abutment would be lost. (B)</p> Signup and view all the answers

What is a characteristic feature of glass compared to ceramics?

<p>It exhibits a disordered atomic structure. (A)</p> Signup and view all the answers

What characterizes the glassy amorphous matrix in dental porcelain?

<p>Consists of a tetrahedral network of silica (C)</p> Signup and view all the answers

Which phase in feldspar dental ceramics primarily influences translucency?

<p>Leucite phase (B)</p> Signup and view all the answers

What is the purpose of gradually heating with the furnace door open during the firing process?

<p>To drive off excess water and combustion byproducts (A)</p> Signup and view all the answers

What effect does vacuum firing have on the porosity of ceramic materials?

<p>Decreases porosity to 0.5% (B)</p> Signup and view all the answers

What effect does sodium oxide (Na2O) have on feldspar during sintering?

<p>Reduces the melting point (C)</p> Signup and view all the answers

What is the key characteristic of glazing in ceramics?

<p>It adds a smooth, shiny, and impervious outer layer (B)</p> Signup and view all the answers

Which material can be classified as a network modifier in glass composition?

<p>K2O (C)</p> Signup and view all the answers

What is the primary role of silica in dental ceramics?

<p>Assuring mechanical strength (A)</p> Signup and view all the answers

How does the coefficient of thermal expansion (CTE) of dental porcelain compare to that of enamel?

<p>The CTE of porcelain is similar to that of enamel. (C)</p> Signup and view all the answers

What happens to ceramics during rapid cooling?

<p>They can develop fissures and cracks. (C)</p> Signup and view all the answers

What results from maintaining glass at a high temperature for an extended period?

<p>Devitrification (C)</p> Signup and view all the answers

What is the significance of the pyroplastic flow in the firing process?

<p>It decreases the viscosity of the molten glass. (B)</p> Signup and view all the answers

What happens to the structure of silica when bonded into an orderly arrangement?

<p>It forms a crystal lattice (D)</p> Signup and view all the answers

What is the main characteristic of a material that allows it to form glasses easily?

<p>Complex molecular structure (D)</p> Signup and view all the answers

What should be avoided after glazing ceramics?

<p>Mechanical working (A)</p> Signup and view all the answers

What increases the translucency of ceramics significantly during the firing process?

<p>Vacuum firing (D)</p> Signup and view all the answers

Which oxide is commonly used as an entrance for network formers in glass compositions?

<p>Sodium oxide (C)</p> Signup and view all the answers

What is the influence of potassium oxide (K2O) on the viscosity of molten feldspar?

<p>It increases viscosity (C)</p> Signup and view all the answers

What is a disadvantage of using ceramics with low firing temperatures?

<p>Reduced hardness of the material (C)</p> Signup and view all the answers

Which material is used for mechanical working of ceramics to prevent damage?

<p>Diamond burs (A)</p> Signup and view all the answers

Flashcards

What are ceramics?

Ceramics are materials made from non-metallic substances that are fired at high temperatures, resulting in a solid, hard, and brittle material. They are often used in dentistry due to their resistance to chemicals, thermal and electrical insulation, and versatility in color.

What is the chemical composition of ceramics?

The chemical makeup of ceramics includes metallic elements like Aluminum, Calcium, Magnesium, and Potassium, combined with non-metallic elements like Silicon, Oxygen, Boron, and Fluorine. These elements form oxides, nitrites, and silicates, which can exist in either amorphous (glass-like) or crystalline structures.

What types of bonds are found in ceramics?

Ceramics can have two types of intermolecular bonds: ionic bonds, which create a crystalline structure, and covalent bonds, which form an amorphous structure similar to glass. The type of bond determines the properties of the ceramic material.

How are ceramics made from clay?

Most ceramics used in dentistry are based on clay, specifically kaolin. Clay paste is molded, burned, and dehydrated, eliminating particles and forming a vitreous material (glass). The higher the temperature, the more vitreous material is formed.

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What is the structure of glass?

Glass is a material where the disordered atomic structure of a liquid state persists even at low temperatures, giving it solid properties. It's fundamentally different from crystalline ceramics, which have a more organized atomic structure.

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What are the main types of dental ceramics?

Dental ceramics are classified into two main categories: feldspathic ceramics and aluminous ceramics.

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What are the key characteristics of feldspathic ceramics?

Feldspathic ceramics are known for their high aesthetic value. They have good translucency, which allows light to pass through them, providing a natural look for dental restorations.

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What are the key characteristics of aluminous ceramics?

Aluminous ceramics are prized for their high strength and resistance to wear and tear. They are often used for dental restorations in high-stress areas, such as molars.

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Vitrification

The process of cooling a material very fast, preventing the atoms from forming an ordered structure, resulting in an amorphous solid.

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Devitrification

The rearrangement of atoms in a glass material from a disordered state to a crystalline structure, often caused by prolonged exposure to high temperatures.

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Silica glass

A type of silica glass formed by the irregular arrangement of tetrahedral SiO2 units, commonly used in dentistry.

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Polymorphism

The ability of a substance to exist in multiple crystalline forms, each with a different arrangement of atoms.

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Network formers

Chemical compounds that form the basic network structure of a glass, like silica and boron oxide.

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Network modifiers

Chemical compounds that modify the properties of a glass by disrupting the network structure, like sodium oxide and potassium oxide.

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Annealing temperature

The temperature at which a glass material softens and becomes moldable, allowing for shaping and manipulation.

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Dental porcelain

A type of ceramic material commonly used in dentistry, composed of a glassy amorphous matrix with dispersed crystalline phases, such as leucite and alumina.

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Orthoclase

A type of feldspar commonly used in dental ceramics with a high potassium oxide content, enhancing ceramics' viscosity and translucency.

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Quartz

A common ingredient in dental porcelain, a fine crystalline form of silica, contributing to mechanical strength and translucency.

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What inorganic pigments are used in dental ceramics?

Inorganic pigments are metal oxides used in dental ceramics to provide color. Copper oxide creates a green color, iron oxide gives a brown hue, cobalt oxide delivers blue, and titanium oxide results in a yellow-brown color.

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What are the roles of organic binders in dental ceramics?

Organic binders, such as starch and glucose, are key ingredients in dental ceramics. They serve as a glue, holding the powder particles together, and allow for shaping the material. Importantly, they burn off completely during firing, leaving no residue.

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What is a major disadvantage of traditional feldspathic porcelain?

Traditional feldspathic porcelain, while aesthetically pleasing, suffers from a significant drawback: a large shrinkage of 30% during sintering. This shrinkage adds complexity to the fabrication process.

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What is fritting in dental ceramics?

During the industrial production of dental ceramics, the raw material undergoes an initial heating process called fritting. This involves melting the mixture and rapidly cooling it in water, resulting in a glass-like material known as frit.

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Explain the sintering process in dental ceramics.

Sintering is a crucial step in ceramic manufacturing. The powdered material is mixed with water and organic binders, then heated to the annealing temperature of the glass component. This process allows the powder particles to fuse together, creating a solid and durable ceramic structure.

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What is the purpose of compaction in ceramic crown fabrication?

Compaction is the initial step in fabricating a ceramic crown. The ceramic mass is applied onto a die using brushing techniques. During compaction, excess water and air are removed, and the ceramic mass is prepared for the firing stage.

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What is the role of firing in ceramic crown fabrication?

Firing is an essential step in the production of dental ceramic crowns. After compaction, the ceramic crown is heated in a kiln to a specific temperature, promoting sintering and the formation of a robust, durable structure.

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Describe the function of glazing in ceramic crown production?

Glazing is the final step in the production of dental ceramic crowns, giving the crown a smooth, polished finish. During glazing, a glassy liquid material is applied to the ceramic crown and then fired, resulting in a protective layer that enhances aesthetics and durability.

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Strength

The ability of a material to withstand the applied load without breaking.

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Hardness

The ability of a material to resist scratching or indentation.

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Impact Strength

The property of a material to resist fracture under impact or sudden loading.

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Stiffness

A measure of a material's resistance to deformation under stress.

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Thermal Shock Resistance

The ability of a material to tolerate changes in temperature without cracking.

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Tensile Strength

A material's ability to resist deformation under stress.

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Compressive Strength

The amount of stress a material can withstand before it starts to break.

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Fatigue Resistance

The ability of a ceramic material to resist wear and tear over time.

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Firing (Sintering)

The process of heating ceramic materials to high temperatures to achieve desired properties. It involves gradual heating, removal of excess water and combustion byproducts, a bisque stage, and glass melting.

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Cooling Ceramics

The rapid cooling of fired ceramic materials can cause fissures and cracks, weakening the structure. To prevent this, slow cooling is crucial.

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Glazing

A smooth, shiny, and impervious outer layer applied to ceramic materials to improve their aesthetics and make them resistant to stains and liquids.

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Density of Dental Ceramics

The density of dental ceramics is a key property that affects their weight and handling. It falls between noble and non-noble alloys, making them easier to cast.

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Melting Temperature of Dental Ceramics

Dental ceramics have a high melting temperature, which is a valuable characteristic in dentistry as it allows for high-temperature firing processes.

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CTE of Dental Ceramics

The coefficient of thermal expansion (CTE) measures how a material changes in size with temperature fluctuations. In dental ceramics, it's important for compatibility with other materials used in dental restorations.

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Aesthetics of Dental Ceramics

Dental ceramics offer excellent aesthetic properties, closely mimicking the natural look of teeth. This is due to their translucency and ability to be colored.

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Translucency of Dental Ceramics

The ability of a material to allow light to pass through it. Vacuum firing enhances translucency in dental ceramics, making them appear more lifelike.

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Chemical Properties of Dental Ceramics

Dental ceramics are chemically inert and resistant to most chemicals found in the mouth. However, they can be etched by hydrofluoric acid.

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Working with Glazed Ceramics

Dental ceramics are generally durable but must be handled with care after glazing, as mechanical work can damage their structure.

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Study Notes

Dental Ceramics or Dental Porcelain

  • Dental ceramics are formed from nonmetallic materials fired at high temperatures.
  • Keramos (Greek) means pottery, referring to a product formed from earthy materials.
  • Porcelain is a type of ceramic composed of feldspar, quartz, and kaolin, fired at high temperatures. It's also known as the Venus shell.
  • Ceramics are solid masses formed from heated powders.

Properties of Ceramics

  • High melting/annealing temperature
  • Brittle (resistant to compression, not tensile strength)
  • Hard
  • Thermal and electrical insulators
  • Resistant to chemical factors
  • Wide range of colours
  • Amorphous structure = glass
  • Crystalline structure = ceramic

Molecular Structure of Ceramics

  • Metallic elements: Al, Ca, Mg, K
  • Non-metallic elements: Si, O, B, F
  • Ceramics frequently contain metalloid oxides (SiO2 – silica)
  • "Unconventional" ceramics used in dentistry: NaCl, ZnO
  • Investment materials
  • Inorganic filler of composites
  • Glass ionomer cements
  • Ceramic bonds can be ionic, forming a crystalline structure
  • Ceramic bonds can be covalent, forming an amorphous structure (glass)

Molecular Structure of Glass

  • Glass is a material where the disorderly structure of atoms from the liquid state remains at a low temperature.
  • This maintains the properties of a solid.
  • Glass = overcooled liquid. .
  • Glasses flow at room temperature (a phenomenon known as creep).
  • The material in the molten phase cools very quickly, thus preventing the atoms from forming an orderly solid structure = glass (vitrification).
  • The more complex the material's structure, the easier it is to form glasses.
  • Glasses can be formed from several grains with a very slow rate of growth.
  • Crystallization of a glass is known as devitrification.
  • Dental ceramics are mineral silicates with a complex structure.
  • Cooling rate of several degrees Celsius per hour is needed for vitrification.
  • Silica (SiO2) has a versatile three-dimensional pyramidal structure (tetrahedron).
  • Each oxygen atom (valence 2) bonds with two silicon atoms.
  • Bonding of tetrahedrons forms an ordered crystalline structure (quartz, tridymite, Cristobalite)
  • Disorderly bonding of tetrahedrons forms an amorphous structure = silica glass.
  • Network formers: Complex molecular structure (silica, silica + Al oxide, silica + feldspar, germanium oxide, boric oxide)
  • Intermediates: Cannot form glasses but can be inserted into the network (alumina)
  • Network modifiers/stabilizers: Large metallic ions, substituting covalent bonds into ionic bonds, reducing annealing/sintering temperatures while increasing strength and chemical resistance, (Na, K, Ca oxides or carbonates).

Composition of Dental Porcelain

  • Dental porcelain is a mixture of two phases:
    • A glassy amorphous matrix (pyramidal network of silica and modifiers).
    • A crystalline phase (formed by leucite, alumina, zirconia, fluoride, mica, spinell). The crystalline phase determines the mechanical, physical, chemical, and optical properties.
  • Composition differs from industrial porcelain by a higher feldspar ratio and lower quartz/kaolin ratio.
  • Typical conventional feldspar dental ceramic composition:
    • Feldspar (75%)
    • Quartz (22-25%)
    • Kaolin (0-3%)
  • Metallic oxides (SiO2, Al2O3, Na2O, K2O, CaO)

Quartz

  • Quartz is silicon dioxide (SiO2).
  • It creates a fine crystalline dispersion within the glassy phase, influencing mechanical strength and translucency (preserving shape during sintering).

Kaolin

  • Kaolin is a hydrous alumino-silicate.
  • It acts as a bonding agent in the ceramic paste, contributing to its mouldability (and water content).
  • In dental ceramics, its presence is often reduced or completely absent, replaced by other components.

Inorganic Pigments

  • Inorganic pigments are metallic oxides (e.g. Fe - brown, Cu - green, Co - blue, Ti - yellow-brown).

Organic Binders

  • Organic binders are starch and glucose used to bind the powder particles, enabling modeling, and subsequently burn out without residues.

Traditional Ceramic Porcelain (Feldspathic) Disadvantages

  • 30% sintering shrinkage
  • Stiff
  • Brittle
  • Very hard

Firing and Sintering of Dental Ceramics

  • Increase temperature until the mixture becomes liquid, all components fuse.
  • Rapid cooling to a solid glass (fritting) can cause cracking due to internal stresses.
  • Milling the solid glass to a very fine powder.

Sintering Procedure

  • Mix powder with water/special liquids (+organic binders).
  • Apply onto die and mold to tooth morphology.
  • Heat until the glass reaches annealing temperature (sintering) – powder's particles fuse together.

Technical Stages for a Full Ceramic Crown

  • Compaction
  • Firing (sintering)
  • Glazing

Compaction

  • Material is applied with brushing onto the die (potential for air and water inclusions).
  • Compaction method: vibration, spatulation, whipping, dabbing.
  • Using a mixture of different sized particles reduces the firing shrinkage.

Firing (Sintering)

  • Gradual heating (open furnace door) to drive off water and byproducts (explosion risk otherwise).
  • Furnace door is closed and the temperature increases.
  • Organic binders burning result in slight shrinkage.
  • Bisque stage: fusing process starts (fragile/porous).
  • Glass melting helps particles fuse together – initial firing shrinkage to -20%
  • Prolonging firing period can lead to morphological issues (highly glazed). Firing furnace +/- vacuum.
  • Vacuum firing: reduces porosity (5.6% - 0.5%), improves flexure strength (20-30MPa to 50-60MPa), increases translucency by 20x(minimizing pores.)
  • Slow cooling due to ceramic's poor thermal conductivity. Rapid cooling leads to fissures, reducing mechanical properties.
  • Cooling under pressure reduces existing porosities.

Glazing

  • After firing, the ceramic body possesses porosity.
  • Glazing creates a smooth, shiny, and impervious outer layer..
  • Glazing methods:
    • Apply a glazing layer and sinter at low temperature for short amount of time or.
    • Final firing stage at higher temperature with careful control = fusion of superficial layer particles

Physical Properties of Dental Porcelain

  • Medium density (1-3.8 g/cm3) – between noble and non-noble metals, heavier than polymers, facilitates casting.
  • Very high melting point can be reduced by adding stabilizers/modifiers.
  • Firing at lower temperatures reduces hardness (important for metal-ceramic attachments).

Coefficient of Thermal Expansion (CTE)

  • Reduced values ( -15 x 10-6/°C).
  • Similar CTE to enamel is advantageous.
  • CTE different from MC (12-15 x 10–6/°C) creates mechanical issues (risk of increased local temperature and cracks).
  • Ceramics can be worked with diamond burs under water cooling.

Aesthetics

  • Excellent aesthetics, resembling natural teeth.
  • Ceramics have an amorphous (isotropic), and the enamel has a crystalline (anisotropic) structure.
  • Fluorescent, translucent, and unlimited possibilities for coloring due to inorganic pigments (oxides).
  • Casting ceramics (glassy) have superior aesthetics because of the light reflection (modulus) due to mica crystals.

Translucency

  • Dicor (glassy ceramic) has higher translucency, leading to a decreasing order.
  • Empress (pressed ceramic).
  • In-Ceram Spinell, Alumina, and Zirconia have lower translucency.

Chemical Properties

  • Chemically inert, resisting the oral pH.
  • Glazing reduces solubility and water absorption.
  • Etching can only be done by fluorhydric acid. (inner layer of all-ceramic restoration)

Biological Properties

  • Glazed ceramic masses don't retain plaque.
  • Excellent biocompatibility from the patient perspective.
  • Well-tolerated by the marginal periodontium and dental tissues
  • Thermal insulator for the dental pulp.

Mechanical properties

  • High stiffness (E = 380 GPa)
  • High compressive strength (150-900 MPa).
  • Moderate tensile strength (20-60 MPa) = brittle.
  • Inner layers in tension experience micro-cracks.
  • Relatively fragile.
  • Minimal fracture strength (low values)
  • Maximum plastic strain of 0.1%.
  • Micro-cracks due to low thermal contraction coefficient.
  • Glaze coat partially fills in cracks.
  • Inner side cannot be glazed to retain adaptation to dental abutments.
  • Low Impact Strength (because it is brittle). Mechanical properties are influenced by internal/surface irregularities, uneven powder particle sizes.

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Dental Ceramics Lecture 9 PDF

Description

Test your knowledge on the properties and applications of dental ceramics. This quiz covers various topics including the role of organic binders, the disadvantages of traditional porcelain, and the techniques involved in creating ceramic crowns. Challenge yourself and deepen your understanding of this important field!

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