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Year 2 > dental materials > Flashcards

dental materials Flashcards

1
Q

Describe the different treatments of calcium sulphate dihydrate (Gypsum) to form plaster, stone and improved stone

A

Plaster: heated at 120 degrees C = beta-hemihydrate

Stone: autoclave= heat and pressure of 120-130 degrees C forming alpha-hemihydrate

Improved Stone: heated in solution of 30% CaCl2

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2
Q

how much heat must be applied to calcium sulphate dihydrate (Gypsum) for it to form an insoluble anhydride?

A

above 200 degrees C

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3
Q

Which additives act as accelerators in Gypsum and how?

A

K2SO4 : encourages crystal growth, accelerates setting reaction and reduces overall expansion

CaSO4.2H2O : provides additional nucleation sites for crystal growth

<20% NaCl : provides additional nucleation sites and increases reaction rate + reduced observed expansion

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4
Q

Name some additives which retard the setting of Gypsum products

A

> 20% NaCl : slows down reaction rate by depositing crystals and preventing growth

Borax : counteracts the increased rate of setting

Potassium citrate : interfere with crystal formation

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5
Q

which factor increases setting time for gypsum products?

a) decreased water amount
b) increased spatulation rate
c) increased temeprature
d) decreased spatulation time

A

d) decreased spatulation time

(increased water intake also increases setting time)

(increasing the spatulation time lowers the setting time)

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6
Q

which factors increases expansion of gypsum products upon setting?

a) increased water amount
b) increased spatulation rate
c) increased temeprature
d) increased spatulation time

A

d) increased spatulation time

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7
Q

Which additives retards setting of gypsum products?

a) K2SO4
b) Borax
c) CaSO4.2H20
d) < 20% NaCl
e) potassium citrate

A

b) Borax
AND
e) potassium citrate

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8
Q

Regarding gypsum products, what is hygroscopic expansion?

A

increased expansion by immersing material in water while setting

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9
Q

Regarding gypsum products, why is expansion an important feature?

A

ensures crowns and dentures are not too tight of a fit

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10
Q

What are the compositional differences between Low-Cu amalgam and HIgh-Cu amalgam?

A

low: less copper
more silver, tin and zinc

high: more copper
less silver, tin and zinc plus palladium and indium

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11
Q

In amalgam, what is the function of silver?

A

increases strength, tarnish and corrosion resistance and expansion

decreases flow and creep ad setting tme

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12
Q

In amalgma, what is the function of Tin?

A

increases setting time, flow and creep

decreases strength, expansion and corrosion resistance

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13
Q

In amalgam, what is the function of copper?

A

increases strength, hardness, expansion and corrosion and tarnish resistance

decreases flow and creep and setting time

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14
Q

In amalgam, what is the function of zinc?

A

decreases oxidation of other metals

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15
Q

In amalgam, what is the function of palladium?

A

increases tarnish and corrosion resistance and strength

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16
Q

In amalgam, what is the function of indium?

A

increases strength

decreases flow and creep, and surface tension = less mercury required

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17
Q

In amalgams, which phase is the weakest phase?

A

the mercury based phases

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18
Q

why are spherical particles in amalgam better than lathe-cut?

A

spherical particles require less mercury to wet the surface and therefore result in the overall amalgam having less mercury based phases.

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19
Q

True or false:

amalgam reaction is never complete

A

TRUE

set amalgam contains unreacted Ag3Sn in the matrix

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20
Q

True or false:

the higher the mercury content of amalgams, the higher the expansion

A

TRUE

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21
Q

what are the advantages of amalgam?

A
  • long lasting
  • high compressive strength
  • good wear resistance
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22
Q

what are the disadvantages of amalgam?

A
  • non adhesive (mechanical retention)
  • thermal conductivity and diffusivity
  • electrical conductivity = galvanic effects
  • poor aesthetics
  • viscoelastic = creep
  • marginal creep (due to higher thermal expansion coefficient
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23
Q

In amalgams, how is the marginal seal formed?

A

over time, corrosion products fill up the marginal gap that is produced as a result of the difference in coefficient of thermal expansion between tooth and amalgam

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24
Q

How does alginate set upon addition of water?

A

Through Chemical cross-linking between two polymer chains via Ca

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25
Q

Which component is added as a retarding agent in alginates?

a) Diatomaceous earth
b) CaSO4
c) Na3PO4
d) Sodium silicofluoride
e) Magnesium oxide

A

c) Na3PO4

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26
Q

Which component is added as a pH controller in alginates?

a) Diatomaceous earth
b) CaSO4
c) Na3PO4
d) Sodium silicofluoride
e) Magnesium oxide

A

d) Sodium silicofluoride
AND
e) Magnesium oxide

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27
Q

Which component is the cross-linking agent in alginates?

a) Diatomaceous earth
b) CaSO4
c) Na3PO4
d) Sodium silicofluoride
e) Magnesium oxide

A

b) CaSO4

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28
Q

Which component is used as a filler for body and strength in alginates?

a) Diatomaceous earth
b) CaSO4
c) Na3PO4
d) Sodium silicofluoride
e) Magnesium oxide

A

a) Diatomaceous earth

29
Q

In the setting reaction of alginates, what ion suppresses the cross-linking reaction?

a) Ca
b) Na
c) PO4
d) SO4
e) Mg

A

c) PO4

30
Q

In alginates, which ion forms the cross-links between the polymer chains?

a) Ca
b) Na
c) PO4
d) SO4
e) Mg

A

a) Ca

31
Q

Why is the pH of the final set alginate important to maintain close to neutral?

A

Alkalinity/acidity of the set gel will give a poor plaster/stone surface

32
Q

What are the disadvantages of alginates?

A
  • Loss of water = shrinkage and poor dimensional stability
  • Immersing alginates in water = initial expansion then shrinkage
  • poor tear strength
  • highly viscoelastic (requires snap-removal technique)
  • doesn’t adhere well to tray (requires mechanical locking features)
33
Q

What is the difference of the setting process between alginates and agar?

A

alginates set upon formation of cross-links = chemical process and thus is irreversible

agar sets upon a physical process and therefore is a reversible process.

34
Q

List 10 desirable qualities of an ideal impression material

A
  • pleasant odour, taste and colour
  • adequate strength (so does not tear when removing from mouth)
  • readily wets oral tissues
  • economically commensurate
  • satisfactory texture and consistency
  • adequate shelf life
  • compatible with cast and dye materials
  • readily disinfects without loss of accuracy
  • free of toxic/ irritant constituents
  • easy to use
35
Q

What are the uses of elastomers?

A

as elastomers have good strength and dimensional stability, they are used to produce accurate replicas of teeth and supporting tissues:

for construction of dentures, crowns , bridges and inlays

36
Q

With regards to elastomer impression materials, which impression material sets quicker, light-bodied or heavy-bodied material?

A

Light-bodied - it has less filler

37
Q

When taking impressions using elastomers, what is the difference in the one-step and two step technique?

A

One-step: the light-bodied material is syringed onto teeth with the heavy-bodied material in the tray being placed on top immediately

Two-step: the heavy-bodied material is used to take an impression first, then the light-bodied material is placed onto teeth and the heavy-bodied impression tray is reinserted onto the teeth

38
Q

What are the advantages and disadvantages of using elastomers for impressions?

A

ADVANTAGES:
-the light-bodied materials can record fine details needed for crowns etc

DISADVANTAGES:
-for one stage technique: the two pastes have to be mixed simultaneously

-for two stage technique: the time taken is longer

39
Q

What are the different types of elastomer impression materials?

A
  • addition silicones
  • condensation silicones
  • polyether (impregnum penta)
  • polysulphides
40
Q

Which one is more dimensionally stable and why? : addition silicones or condensation silicones?

A

addition silicones are the most stable as they result in no loss of molecules. In condensation reactions , there is a loss of a small molecule resulting in greater shrinkage of the material

41
Q

which product is NOT found in condensation silicones?

a) inert filler
b) silicone polymer with OH terminals
c) alkyl silicate (tetraethoxy orthosilicate)
d) dibutyle tin dilaurate
e) silicone oligomer with Si-H groups

A

e) silicone oligomer with Si-H groups

this is found in the catalyst paste of ADDITION silicones

42
Q

List the disadvantages of using condensation silicones as impression materials

A
  • shrinkage ( although still better than alginates)
  • hydrophobic material therefore requires incorporation of detergents to increase wettability
  • incorporation of hydrophilic compounds = expansion upon immersion of disinfecting agents
  • limited shelf life ( mainly with liquid catalyst)
  • erratic setting behaviour if liquid catalyst used
43
Q

List the advantages of Condensation silicones for using as impressions

A
  • Stronger + better dimensional stability in comparison to alginates
  • more elastic than polysulphides and polyethenes
  • adequate tear strength and elongation
44
Q

List the advantages of addition silicones as impression materials

A
  • Best dimensional stability ( shrinkage of less than 0/05% in 24hrs)
  • very good elastic recovery
45
Q

List the disadvantages of addition silicone impression material

A
  • Less elongation and tear strength in comparison to condensation silicones however still adequate
  • hydrophobic material = needs detergents to increase wettability
  • incorporation of hydrophilic material = expansion upon immersion in disinfecting solution
  • free water in plaster can react with unreacted Si-h groups releasing hydrogen and resulting in a porous mould = requires at least 30 mins before being casted
  • setting can be seriously impaired if handled with natural rubber gloves
46
Q

True or false,

once the impression is taken using polyether (impregum penta) it should be wrapped up in a damp napkin before storing.

A

FALSE

the material swells in prolonged contact with water or water vapour

47
Q

List the advantages of using impregum penta (polyether) as in impression material

A
  • Good dimensional stability in AIR
  • Quick setting time compared to polysulphides
  • Clean to handle and odourless
48
Q

List the disadvantages of using impregum penta (polyether) for taking impressions

A
  • Poor dimensional stability on prolonged contact with water / water vapour
  • Permanent deformation
  • original impregum material was very stiff and had 50% elongation = tearing upon removal
49
Q

How does the reaction take place upon setting for impregum penta (polyethers) impression materials?

A

Cationic (addition) reaction via ring opening of imino group

50
Q

What are the advantages and disadvantages of using polysulphide impression materials?

A

ADVANTAGES:

  • strongest impression material

DISADVANTAGES:

  • unpleasant odour
  • slow setting
  • dimensional stability (shrinkage of 0.1-0.2%)
  • messy handling
  • elastic recovery not as good as silicone and polyether
51
Q

Which component in polysulphide impression material is the cross-linking agent?

a) plasticiser
b) sulphur
c) lead dioxide
d) stearic /oleic acid
e) polysulphides

A

c) lead dioxide

52
Q

What is the role of triglycerides in polyethers?

A

triglycerides are added to increase intrinsic viscosity

53
Q

Which reaction takes place upon setting of polysulphides impression materials?

A

condensation reaction

54
Q

In addition silicones, which component is the cross-linking agent?

a) silicone oligomer with Si-H groups
b) silicone polymer with OH terminal
c) platinum salt
d) dibutyl tin dilaurate
e) alkyl silicate (tetraethoxy orthosilicate)

A

a) silicone oligomer with Si-H groups

55
Q

Which compound is the cross-linking agent in condensation silicones?

a) silicone oligomer with Si-H groups
b) silicone polymer with OH terminal
c) platinum salt
d) dibutyl tin dilaurate
e) alkyl silicate (tetraethoxy orthosilicate)

A

e) alkyl silicate (tetraethoxy orthosilicate)

56
Q

Which component is the catalyst in condensation silicones?

a) silicone oligomer with Si-H groups
b) silicone polymer with OH terminal
c) platinum salt
d) dibutyl tin dilaurate
e) alkyl silicate (tetraethoxy orthosilicate)

A

d) dibutyl tin dilaurate

57
Q

Which component is a catalyst in addition silicones?

a) silicone oligomer with Si-H groups
b) silicone polymer with OH terminal
c) platinum salt
d) dibutyl tin dilaurate
e) alkyl silicate (tetraethoxy orthosilicate)

A

c) platinum salt

58
Q

Name the types of non-elastic impression materials

A
  • impression plaster
  • impression compound
  • zinc oxide/eugenol
59
Q

What does ‘mucocompressive’ and ‘mucostatic’ impression material mean?

A

mucocompressive material refers to one that displaces soft tissue (buccal and lingual)

mucostatic impression material refers to a material that does not displace soft tissues

60
Q

When are non-elastic impression materials used?

A

in endentulous cases

61
Q

Which material is mucostatic and which is mucocompressive :

a) impression plaster
b) impression compound
c) zinc eugenol/oxide

A

a) impression plaster = mucostatic
b) impression compound = mucocompressive
c) zinc eugenol/oxide = mucostatic

62
Q

Why are diluents added to composites?

A

To increase flow of material and improve handling characteristics

63
Q

Which statement is incorrect regarding filler particles within composites ?

a) increase mechanical properties
b) increase wear resistance
c) increase coefficient of thermal expansion
d) decrease polymerisation shrinkage
e) increase control of aesthetics

A

c) increase coefficient of thermal expansion

fillers DECREASE the coefficient of thermal expansion

64
Q

Why is coupling agent added to composites?

A

To bond the organic resin and filler particles together

the organic resin is hydrophobic, whereas the filler particles are hydrophilic

65
Q

Why is acid etching required when using composites?

A

Acid etching removes the pellicle layer and surface enamel layer, reducing the surface energy and thus improving wettability of the adhesive.

It also increases surface roughness, increasing the surface area for micro-mechanical retention

66
Q

In acid base reactions, which statement is false regarding setting reactions?

a) the smaller the particle size, the faster the setting reaction
b) the smaller the particle size, the slower the setting reaction
c) the greater the powder amount, the faster the setting reaction
d) the higher the temperature, the faster the setting reaction

A

b) the smaller the particle size, the slower the setting reaction

67
Q

Which two acid-base cements chemically adhere onto the tooth?

a) GIC and calcium hydroxide
b) GIC and ZOE
c) GIC and zinc polycarboxylate
d) Zinc phosphate and GIC
e) Zinc phosphate and EBAs

A

c) GIC and zinc polycarboxylate

68
Q

What is the difference between liquid components of zinc phosphate and zinc polycarboxylate cements?

A

zinc phosphate liquid component is phosphoric acid

zinc polycarboxylate liquid component is polyacrylic acid

69
Q

List the uses of acid base cements(5 marks)

A
  • permanent/temporary fillings
  • cavity liner
  • permanent or temporary luting of crowns/bridges
  • attachment of orthodontic appliances
  • root canal sealer

Year 2 (10 decks)

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