Physical Properties Of Dental Materials Question and Answers

Physical Properties Of Dental Materials Important Notes

1. Tarnish

• Tarnish is the surface discoloration
• Occurs due to
  • Formation of calculus, plaque on the surface of the metal
  • Formation of oxides, sulfides, chlorides
    • Tarnish is the forerunner of corrosion

2. Corrosion

• Corrosion is the actual deterioration of the metal by a reaction with its environment
• Corrosion Types
  • Dry Or chemical corrosion
    • In it, the metal reacts to form oxides, chlorides, and sulfides in the absence of electrolytes
  • Wet Or electrochemical corrosion
    • It requires the presence of water or other fluid as an electrolyte
    • It has 3 types-crevice corrosion, stress, corrosion, and galvanic corrosion

3. Passivation

• Chromium, aluminum, and titanium form strong adherent oxide films on their surface to protect from corrosion
• This is called passivation

Read And Learn More: Dental Materials Question and Answers

4. Creep

• Creep is defined as time-dependent plastic deformation or strain of material under static load
• Creep Types
  • Static creep
  • Dynamic creep

5. Flow

• Flow is deformation under a small static load
• Flow describes the behavior of amorphous materials such as waxes

6. Metamerism

• Objects that appear to be color-matched under one type of light may appear very different under another light source
• This phenomenon is known as metamerism
• Different light sources used in dental procedures are
  • Daylight
  • Incandescent lamps
  • Fluorescent lamps

7. Coefficient Of Thermal Expansion

The linear coefficient of thermal expansion of some materials concerning tooth enamel are:

Physical Properties Of Dental Materials

Physical Properties Of Dental Materials Long Essays

Question 1. What are Tarnish and Corrosion? What are the causes for it? How to avoid it?
Answer:

1. Tarnish:

Tarnish Definition:

• Tarnish is surface discoloration on a metal or a slight loss or alteration of the surface finish or luster
• It is often the forerunner of corrosion

Tarnish Causes: In the oral cavity

The presence of the following on the surface of restorations

1. Deposits
   • Hard deposits like calculus or
   • Soft deposits like plaque or mucin
2. Stains produced by
   • Presence of pigment-producing bacteria
   • Use of drugs containing iron or mercury
   • Adsorbed food debris
3. A thin film of oxides, sulfides, or chlorides.

Protection Against Tarnish: It can be protected by the following measures

1. Maintaining good oral hygiene
2. Minimizing the intake of tea, coffee, or tobacco that produces stains

2. Corrosion:

Corrosion Definition: It is a process in which the deterioration of a metal is caused by a reaction with its environment

Corrosion Causes: Corrosion occurs due to

1. Water, oxygen, chloride ions, sulfides
2. Various acids such as phosphoric, acetic, and lactic acid

Corrosion Types:

1. Aqueous or Electrolytic or wet corrosion

Its subtypes are

• Galvanic corrosion
• Heterogeneous composition corrosion
• Stress corrosion
• Concentration cell corrosion

2. Dry or chemical corrosion

Protection against corrosion:

It can be protected by the following measures

1. Passivation:

• The process of formation of a strong oxide layer on its surface by metal is called Passivation
• This strong film protects the metal from corrosion
• Examples: Chromium, titanium, and aluminum are passive metals

2. Increasing noble metal content

• Gold, platinum, and palladium are examples of noble metals
• It is suggested that dental alloys must contain at least 50% of these metals
• As these metals are EMF-positive they resist corrosion better than any other metal

3. Polishing

• Well-polished restorations remove surface roughness
• This reduces the chances of concentration cell corrosion

4. Avoiding dissimilar metal restorations

• Dissimilar metals cause Galvanic corrosion
• Thus it should be avoided

Mechanical Properties Of Dental Materials

Physical Properties Of Dental Materials Short Essays

Question 1. Types of corrosion.
Answer:

Types Of Corrosion

1. Dry Corrosion Of Chemical Corrosion:

Corrosion is a non-aqueous corrosion in which the metal reacts to form oxides and sulfides in the absence of electrolytes.

Corrosion Example:

• Formation of Ag₂S in dental restorations containing silver
• Oxidation of alloy particles in dental amalgam.

2. Electrolytic or EIectrochemical Or Wet corrosion:

• It requires the presence of electrolytes
• This electrolyte supplies the ions needed at the cathode and carries away the corrosion products at the anode
• The anode undergoes an oxidation reaction with the production of free electrons
• The reduction reaction occurs at the cathode by accepting electrons from the anode
• The production of electrons should be balanced by the consumption of electrons
• During a reaction, metal with the lower electrode potential becomes the anode
• Its subtypes are

1. Galvanic Corrosion
   • It occurs due to adjacent dissimilar metal restorations
   • Example: Presence of amalgam occlusal restoration with opposing gold inlay
   • Between these two dissimilar metals, saliva acts as an electrolyte producing short-circuit
   • As a result, the patient experiences pain
   • It can be minimized by painting varnish on the surface of the amalgam restoration.
2. Heterogeneous Composition Corrosion
   • It occurs within the structure of the restoration
   • Examples: Eutectic alloys and peritectic alloys
   • Impurities in any alloy enhance corrosion
3. Stress Corrosion
   • A metal is called to be stressed when it undergoes cold working
   • If stressed and unstressed metals are contacted the stressed metals get corroded
   • The stressed metal acts as an anode while unstressed metal is a Cathode
4. Concentration Cell Corrosion Or Crevice Corrosion.
   • It occurs due to variations in the composition of the given electrolyte

Types Of Corrosion Example:

• Differences in the composition of saliva
  • The presence of food debris in between the teeth alters the composition of the saliva
  • Due to this corrosion occurs under the layer of food debris
  • It can be prevented by maintaining good oral hygiene
• Differences in oxygen concentration
  • Due to the presence of pits, the oxygen concentration of the restorations differ
  • The region at the bottom of the pit has a lower oxygen concentration
  • This region behaves as an anode while the alloy surface around the pit becomes a cathode and corrosion results

Physical Properties Of Dental Materials Short Question And Answers

Question 1. Difference between tarnish and corrosion.
Answer:

Difference Between Tarnish And Corrosion

Properties Of Dental Composites

Question 2. Creep and flow.
Answer:

1. Creep Definition:

Creep is defined as time-dependent plastic deformation or strain of material under static load or constant stress near its melting point

Creep Types:

1. Static creep: It is a time-dependent deformation produced in a completely set solid subjected to constant stress.
2. Dynamic creep: Produced when the applied stress is fluctuating

Creep May Cause

• Deformation of dental restorations like an amalgam
• Improper fit of fixed partial dentures

Creep Flow: It is used to describe the rheology of amorphous substances like waxes

Question 3. Hue, value, and chroma
Answer:

Hue, Value, And Chroma: Hue, value, and chroma are the three dimensions of the color

1. Hue
   • It describes the dominant color of an object
   • Example: red, blue, or green
2. Value
   • It is the relative lightness or darkness of the color
   • It is independent of hue
3. Chroma
   • It represents the degree of saturation of a particular color
   • It is always associated with value and hue
   • The higher the chroma, the more intense the color

Hue, Value, And Chroma Measurement:

• The color is determined by the Munsell system
• It consists of a cylinder that shows the three dimensions of color

1. Hue- Changes occur in a circumferential direction
2. Value- Increases towards the top and decreases towards the bottom
3. Chroma- It increases along the radius from an axis

Corrosion Resistance In Dental Materials

Question 4. Metamerism
Answer:

Metamerism Objects that appear to be color-matched under one type of light may appear very different under another light source.

• This phenomenon is known as Metamerism
• To overcome metamerism, it is recommended that the color-matching procedures should be carried out under two or more different light sources out of which one should be daylight
• The light sources used should be the same in the clinic as well as in the laboratory
• The different sources used in dental procedures are Daylight, incandescent lamps, and fluorescent lamps

Question 5. Coefficient of thermal expansion.
Answer:

Coefficient Of Thermal Expansion Definition: The change in length per unit of the original length of a material when its temperature is raised by lk is known as the coefficient of thermal expansion.

Coefficient of thermal expansion Significance:

• It is important in dental applications to produce cast restorations that fit and maintain the seal at a restoration margin.
• It Influences the procedures Involving wax patterns, casting metals, and crowns, placing amalgam and composite resin restorations, and preparing metal-ceramic crowns and bridges.

Question 6. Thermal conductivity.
Answer:

Thermal Conductivity Synonym: Coefficient of thermal conductivity

Thermal Conductivity Definition:

• It is the quantity of heat in calories per second that passes through a specimen 1 cm thick having a cross-sectional area of 1 cm2 when the temperature difference between the surfaces perpendicular to the heat flow of the specimen is 1 degree K.
• In general thermal conductivities increase in the following order:
  • polymers< ceramics < metals

Thermal Conductivity Significance:

• Materials having high thermal conductivity are called conductors and those with low conductivity are insulators.
• The higher the thermal conductivity, the greater the ability of the substance to transmit thermal energy
• Increased thermal conductivity induces greater pulpal sensitivity

Thermal Conductivity Value:

Thermal conductivity is measured as watt per meter per second per degree Kelvin.

Corrosion Resistance In Dental Materials

Question 7. Electrolytic corrosion
Answer:

Electrolytic Corrosion

• It requires the presence of electrolytes
• This electrolyte supplies the ions needed at the cathode and carries away the corrosion products at the anode
• The anode undergoes an oxidation reaction with the production of free electrons
• The reduction reaction occurs at the cathode by accepting electrons from the anode
• The production of electrons should be balanced by the consumption of electrons
• During a reaction, metal with the lower electrode potential becomes the anode

Its Subtypes Are:

1. Galvanic corrosion
2. Stress corrosion
3. Concentration cell corrosion
4. Heterogeneous surface composition corrosion