Finishing And Polishing Materials Essay Question And Answers

Finishing And Polishing Materials Important Notes

1. Polishing agents

Finishing And Polishing Materials Polishing Agents

2. Rake angle

  • It is the angle between the rake face and the radial line
  • Positive Rake Angle – Radial line is ahead of the rake face
  • Negative Rake Angle – The rake face is ahead of the radial line
  • Zero Rake Angle – The rake face and radial line coincide

Finishing And Polishing Materials Long Essays

Question 1. Enumerate materials and methods while polishing chromium-cobalt alloys and acrylic resin.
Answer:

Polishing:

It is a process of providing lustre or gloss on a material surface

Polishing Agents Used:

  • Natural
  • Arkansas stone, chalk, corundum, diamond, emery, garnet, pumice, quartz, sand, tripoli, zirconium silicate
  • Manufactured or synthetic agents
  • Silicon carbide, aluminium oxide, synthetic diamond, rouge, tin oxide

Polishing of Cobalt-Chromium Alloys:

  • Electrolytic polishing is done
  • It is an electrochemical process
  • The alloy to be polished is made anode of an electrolytic cell
  • Current is passed
  • Some of the anode is dissolved leaving a bright surface

Polishing of Cobalt-Chromium Alloys Advantages:

  • Very little material is removed
  • The Fit of the denture remains unaltered

Polishing For Acrylic Resin:

  • Acrylic resin is a relatively soft materials
  • Contour with tungsten carbide bur and sandpaper
  • This leaves large scratches
  • Remove scratches using a rubber point
  • Apply pumice over the canvas buff wheel
  • Preliminary polishing is done
  • Clean the work
  • Apply Tripoli or a mixture of chalk and alcohol with a rag wheel
  • Hold the work firmly without excessive pressure
  • Repeat this over the entire surface till the surface is bright and well polished
  • Clean the work

Question 2. State various abrasives used in dentistry
(or)
What are the different types of abrasives and polishing agents?
Answer:

Abrasive and Polishing Agents:

Finishing And Polishing Materials Abrasive And Polishing Agents

Question 3. Classify dental burs. State their functions
Answer:

Dental Burs:

It is defined as a rotary cutting instrument with cutting heads of various shapes and two or more sharp-edged blades, used as a rotary grinder.

Dental Burs Classification:

  • According to their mode of attachment to the handpiece
    • Latch type
    • Friction grip type
  • According to their composition
    • Stainless steel
    • Tungsten carbide
    • Combination
  • According to their motion
    • Right bur-revolves clockwise
    • Left bur- revolves anticlockwise
  • According to the length of their head
    • Long
    • Short
    • Regular
  • According to their use
    • Cutting burs
    • For finishing and polishing

Read And Learn More: Dental Materials Question and Answers

  • According to their shapes
    • Round
    • Pear shaped
    • Inverted cone
    • Wheel shaped
    • Tapering fissure
    • Straight fissure

Dental Burs Functions:

Finishing And Polishing Materials Dental Burs Functions

Question 4. What are the rake angle and clearance angle?
Answer:

Rake Angle:

Rake Angle Definition:

It is the angle between the rake face and the radial line

Positive Rake Angle:

When the radial line leads the face so that the rake angle is on the inside of the radial line, the rake angle is said to be positive

Zero Rake Angle:

  • Where the radial line and the face contour correspond the rake angle is zero
  • In such an instance, the bur tooth is said to have zero radial rake angle

Negative Rake Angle:

If the face is beyond or leading the radial line in reference to the direction of rotation, the angle formed between the face and the radial line is called the negative rake angle

Finishing And Polishing Materials Three Types Of Rake Angles

Clearance Angle:

The angle between the back of the tooth and the work is known as the clearance angle.

Fishing And Polishing Materials

Finishing And Polishing Materials Short Essays

Question 1. Describe the action of abrasives and state the requirements of abrasive materials
Answer:

The action of Abrasives:

  • The action of abrasive is essentially a cutting action
  • An abrasive tool has many abrasive points that are not arranged in an ordered pattern
  • Thus innumerable random scratches are produced
  • Each tiny particles present a sharp edge that cuts through the surface similar to a chisel
  • A shaving is formed which crushes to a fine powder
  • This powder clogs the abrasive tool and thus frequent cleaning is required

Abrasives Requirements:

  • Abrasives Shape
    • It should be irregular in shape
    • Round smooth surfaces are poor abrasives
    • While irregular and jagged particles are more effective
  • Abrasives Hardness

Abrasive should be harder than the work it abrades

  • Abrasives Strength
    • It possesses a high-impact strength
    • The abrasive particle should fracture rather than dull out
    • Fracture of an abrasive is also helpful in shedding the debris accumulated from the work
    • They are most effective when used on brittle tooth enamel
  • Abrasives Attrition Resistance:

They should have attrition resistance

Question 2. Define abrasive and polishing agents. Give examples of each.
Answer:

Abrasive Agent:

  • A hard substance used for grinding, finishing or polishing a less hard substance is called abrasive agent
  • Examples- emery, diamond, rouge, etc.

Polishing Agent:

  • It is an agent used in the process of providing lustre or gloss on the material surface
  • Example- polishing cakes, pumice, etc.

Question 3. Dental bur design
Answer:

Dental bur design

  • The design of the bur includes the following a Blade or cutting edge
  • It is in contact with the horizontal line or face
  • Tooth face
    • The sides of the tooth ahead of the cutting edge in the direction of the rotation is the tooth face
  • Back of the tooth
    • The opposite of the bur tooth is the back of the tooth
  • Rake angle
    • It is the angle between the rake face and the radial line
  • Positive rake angle
    • When the radial line leads the face so that the rake angle is on the inside of the radial line, the rake angle is said to be positive
  • Zero rake angle
    • Where the radial line and the face contour correspond the rake angle is zero
    • In such an instance, the bur tooth is said to have zero radial rake angle
  • Negative rake angle
    • If the face is beyond or leading the radial line in reference to the direction of rotation, the angle formed between the face and the radial line is called the negative rake angle
  • Clearance angle
    • The angle between the back of the tooth and the work is known as the clearance angle
    • The clearance angle of most burs is straight and clearly defined
  • Tooth angle
    • It is the measurement between the face and the back
  • Flute or chip space
    • It is the space between successive teeth
    • The number of teeth in a bur is 6 or 8
    • Dental burs provide a negative rake angle

Question 4. Polishing of metals
Answer:

Polishing of Amalgam:

Finishing And Polishing Materials Polishing Of Amalgam

Polishing of Gold Alloys:

Finishing And Polishing Materials Polishing Of Gold Alloys

Question 5. Factors affecting cutting efficiency of dental burs.
Answer:

1. Dental burs Reduced use of crosscuts

  • Crosscuts are provided at low speed to increase cutting efficiency
  • Crosscuts used at high speed produce unduly rough surfaces

2. Dental burs Extended heads on fissure burs

Extended head length of burs is used

3. Dental burs Rounding of sharp tip angles

    • Sharp tip results in
    • High-stress concentration
    • Increases the tendency for the tooth to fracture
  • Rounded corners results in
    • Lower stresses in restored teeth
    • Enhances strength of tooth
    • Preserves vital dentin
    • Facilitates adaptation of restorative material

4. Dental burs Rake angle

A negative rake angle minimizes fracture of the cutting edge

5. Dental burs Edge angle

Increased edge angle reinforces the cutting edge

6. Dental burs Clearance angle

  • Eliminates rubbing friction of the clearance face
  • Provides a stop to prevent the bur edge from digging into the tooth structure
  • Provides adequate flute space

Finishing And Polishing Materials Short Question And Answers

Question 1. Abrasives used in dentistry
Answer:

Abrasives used in dentistry

  • Natural
  • Arkansas stone, chalk, corundum, diamond, emery, garnet, pumice, quartz, sand, tripoli, zirconium silicate
  • Manufactured or synthetic agents
  • Silicon carbide, aluminium oxide, synthetic diamond, rouge, tin oxide

Question 2. Dentrifices
Answer:

Abrasives used in dentistry

  • Popularly known as toothpaste, these are agents used with a toothbrush to cleanse and polish natural teeth.
  • They should have maximum cleansing efficiency the minimum tooth abrasion.

Dentrifices Functions:

  • Assist the toothbrush to mechanically remove stains, debris and soft deposits from the tooth.
  • To impart a polished surface to the tooth.
  • They help to reduce care and maintain healthy gingiva. Improve aesthetics and reduce mouth odours.

Question 3. Pumice
Answer:

Pumice

  • It’s a type of abrasive
  • It is a highly siliceous material of volcanic origin and is used as an abrasive or polishing agent depending upon the particle size.
  • Its use ranges from smoothening dentures to polishing teeth in the mouth.
  • Flour of pumice extremely fine-grained derivated used for polishing enamel

Question 4. Diamond abrasive
Answer:

Diamond abrasive

  1. The hardest and most effective abrasive for tooth enamel is composed of diamond chips
  2. The chips are impregnated in a binder or plated onto a metal shank to form the diamond stones and discs, which are very popular in the dental profession

Question 5. Bonded abrasives
Answer:

Bonded abrasives

  • Bonded abrasives consist of abrasive particles incorporated through a binder to form grinding tools such as points, wheels, separating discs, coated thin discs, and a wide variety of other abrasive shapes.
  • Particles are bonded by four general methods.
  1. Sintering
  2. Vitreous bonding (glass or ceramic).
  3. Resinous bonding (usually phenolic resins).
  4. Rubber bonding (latex-based silicone-based rubber).
  5. Because most of the rubber wheels, cups, and points contain latex, a known allergen, all residues must be removed from the polished surface

Question 6. Rouge
Answer:

Rouge

  • It is a type of abrasive agent used in dentistry.
  • Rouge is a fine red powder composed of iron oxide.
  • Is used in a cake form.
  • It may be impregnated on paper or cloth known as ‘crocus cloth’.
  • It is an excellent polishing agent for gold and Nobel metal alloys. But is likely to be dirty to handle.

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