Physical Properties Of Dental Materials Question and Answers

Physical Properties Of Dental Materials Important Notes

1. Tarnish

• It 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

• It is the actual deterioration of the metal by a reaction with its environment
• 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

4. Creep

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

5. Flow

• It is deformation under a small static load
• It 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 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

Read And Learn More: Dental Materials Question and Answers

3. 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

Physical Properties Of Dental Materials Short Essays

Question 1. Types of corrosion.
Answer:

Types of corrosion

1. Dry corrosion of chemical corrosion:

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

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 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

Question 2. Creep and flow.
Answer:

1. Creep:

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 Significance:

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

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.

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