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Dental Materials > Elastic Impression Materials Pt. 3 > Flashcards

Elastic Impression Materials Pt. 3 Flashcards

1
Q

What is a colloid

A

A heterogeneous mixture of two phases where are the two phases are not readily differentiated

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2
Q

What are the types of hydrocolloids impression material

A
  1. Reversible agar
  2. irreversible alginate
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3
Q

What are the intermolecular bonds between molecules in gel formation during cooling in reversible hydrocolloids

A
  1. Van Der walls forces
  2. hydrogen bonds
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4
Q

How are the molecules in irreversible hydrochlorides bonded

A

Cross-links between polysaccharide chains

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5
Q

What is Agar

A

It is a complex polysaccharide (galactose sulphate)

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6
Q

What is the composition of reversible hydrocolid Agar 

A
  1. 15% colloidal suspension of Agar water
  2. Borax
  3. Potassium sulphate
  4. Glycerine
  5. Alkylbenzonate
  6. Thymol
  7. Fillers and pigment
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7
Q

What is the function of borax in Agar

A

It gives body to the gel and it retards setting

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8
Q

What is the function of potassium sulphate in Agar

A

To counteract the effects of borax alternative is dipping the impression in solution of Accelerator

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9
Q

What is the structure of the molecules in Agar

A

Helical structure consisting of hydrogen bonding

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10
Q

Classify agar 

A
  1. Type one - high consistency
  2. Type two - medium consistency
  3. type three - low consistency
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11
Q

What is the property that allows agar to be removed from undercuts

A

Viscoelasticity

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12
Q

The amount of permanent deformation exhibited by viscoelastic impression material agar depends on what

A
  1. Severity of undercuts
  2. the time for the materials under stress during removal of the impression
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13
Q

Which areas are Difficult to record using Agar 

A

Inter-proximal and sub gingival areas

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14
Q

What are the properties of Agar

A
  1. Low Viscosity
  2. can record undercuts
  3. flexible
  4. poor mechanical properties
  5. tears at low stress
  6. Poor dimensional stability
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15
Q

What is syneresis

A

Squeezing of water from between polysaccharide chains

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16
Q

What is imbibition 

A

In the presence of access water agar gel may absorb water

17
Q

What does syneresis do to Agar

A

Cause shrinkage And effects accuracy

18
Q

What does imbibition due to water Gel agar 

A

Separation of polysaccharide chains and swelling of impression 

19
Q

What are the uses of Agar

A
  1. Impression of partial denture, crown and bridge
  2. used as a duplicating material to duplicate casts
20
Q

What are the Advantages of Agar 

A
  1. Material in contact with Tray sets first
  2. Uptake of moisture
  3. Reproduce finer details
  4. Used for model duplication
  5. Flexible
  6. reusable
21
Q

What are the disadvantages of Agar

A
  1. Dimensionally unstable
  2. impression cannot be electroplated
  3. low tear strength
  4. specialized equipment is required
  5. unacceptable to reuse
22
Q

Why is it unacceptable to reuse Agar

A
  1. Cross infection control
  2. Alteration of materials physical properties
  3. incorporation of small chips of dental stone 
23
Q

What is the composition of alginates

A
  1. Sodium or potassium salt of alginic acid
  2. gypsum
  3. NA3 PO4
  4. inert filler
  5. reaction indicator
24
Q

What affect does warm water have on alginate manipulation

A

Warm water reduces working time and setting time by accelerating the rate of cross-linking

25
Q

Which part of Alginate sets first in the tray 

A

The material adjacent to the oral tissues sets more rapidly than the cooler tray wall

26
Q

What are the properties of alginate

A
  1. Viscosity
  2. accuracy
  3. viscoelasticity
27
Q

Describe the decontamination of alginate impression

A

Aqueous solution of sodium hypochlorate or aldehyde (formaldehyde or glutaraldehyde) for 10 minutes

28
Q

What are the applications of alginate

A
  1. Impression for complete and partial dentures and orthodontic appliances
  2. Study models
  3. duplicating material
29
Q

What are the advantages of alginate

A
  1. Low cost
  2. easy to mix and manipulate
  3. gives good surface details even in the presence of saliva
  4. flexibility
  5. minimum requirement of equipment
30
Q

What are the disadvantages of alginate

A
  1. Cannot be electroplated
  2. Poor tear strength
  3. cannot be corrected
  4. not recommended where high level of accuracy is needed
31
Q

What is the purpose of alkylbenzonate, Thymol and glycerine in agar 

A

Preservative
bacteriocidal
plasticizer

32
Q

What is the function of fillers in Agar

A

Controls strength, viscosity and rigidity

Dental Materials (4 decks)

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