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Need to Know > dental material science need to know > Flashcards

dental material science need to know Flashcards

1
Q

explain gaseous porosity

A

voids in the material occurring when PMMA is cured fast
monomer boils
usually happens in a thicker section of the acrylic

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2
Q

what are the constitutes of gutta-percher?

A

20% GP
65% zinc oxide
10% radiopacifier
5% plasticiser

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3
Q

what are the properties of non-setting calcium hydroxide?

A

high pH- antimicrobial factors
hydrolysis pf LPS reduce inflammatory potential
removal of tissue debris

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4
Q

what are the constitutes of stainless steel?

A

72% iron
18% chromium
8% nickel
1.7% titanium
0.3% carbon

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5
Q

what is work hardening?

A

work done on metal below its recrystallisation temperature causes slip
slip= dislocations collect ar grain boundaries hence stronger, harder material
the hard wire is made by drawing the metal in a cold state through a series of dies of successively smaller diameter
this makes it stronger and gives it spring properties

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6
Q

define springiness

A

can undergo large defelctions without permanent deformation

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7
Q

give disadvantages of self cure PMMA

A

poor mechanical properties
not suitable for pts w residual monomer allergy

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8
Q

What is the use of a cavity base?

A

to minimise bulk of material

blocks out undercuts

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9
Q

what kind of reaction takes place when mixing the base and catalyst for calcium hydroxide?

A

chelation reaction

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10
Q

what is the use of a cavity lining material

A

thin coat of material over the dentine and pulp

has pallative effect

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11
Q

what reaction occurs in ZOE cement

A

acid base reaction

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12
Q

what is the composition of the base for calcium hydroxde lining material?

A
  • calcium hydroxide
  • zinc oxide
  • plasticiser
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13
Q

what chemicals react in ZOE cement and what is formed

A

ZnO and eugenol form zinc eugenolate

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14
Q

what is the strongest ZOE and why

A

EBA ZOE due to addition of quartz and aluminium

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15
Q

what takes part in the chelation reaction when mixing caclium hydroxide?

A

base- zinc oxide
catalyst- butylene glycol disalicylate

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16
Q

what pH is calcium hydroxide?

A

pH 12

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17
Q

what are uses of ZOE cement

A

lining material
temporary restoration
Root canal sealer - slow set 24 hours

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18
Q

what is the advantage of calcium hydroxide being highly alkaline?

A

kills bacteria

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19
Q

what are properties of ZOE

A

rapid set
good working time
low thermal conductivity
radiopaque
High soluble

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20
Q

name 4 properties of calcium hydroxide

A
  • soluble
  • alkaline
  • irritant- stimulate tertiary dentine formation
  • radiopaque
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21
Q

explain advantage and disadvantage of ZOE’s solubility

A

advantage - eugenol is continually released which releives pain

disadvantage - soluble in water so eugenol is released and this inhibits setting of resin materials

eugenol also discolours resin materials

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22
Q

what is a contraindication of using ZOE

A

cannot place under a composite restoration as it affects bonding

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23
Q

when should calcium hydroxide be used?

A

as a direct or indirect pulp cap under deep restorations

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24
Q

why does calcium hydroxide need to be covered with a RMGIC?

A

soluble- prevents dissolution

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25
Q

what kind of bond is formed when etching an GIC?

A

micromechanical bond

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26
Q

What type of ZOE is least soluble resin modified or normal

A

resin modified so can use under amalgam filling

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27
Q

What form of cement is the least soluble

A

RMGIC

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28
Q

What is a contraindication of using GI near the pulp

A

any unreacted HEMA is cytotoxic to the pulp

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29
Q

list ideal properties of lining materials

A
  • pulpal protection
  • therapeutic
  • radiopaque
  • bond to dentine
  • low solubility
  • cariostatic
  • low thermal expansion and conductivity
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30
Q

how can a lining material give pulpal protection?

A
  • thermal- exothermic reaction of composite/heat conducted through metal restorations
  • chemical- unreacted chemicals/pH of restorative materials
  • bacterial- against microleakage
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31
Q

what property of GI makes it bettern than other lining materials

A

It bonds to enamel and dentine forming a better marginal seal

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32
Q

how does RMGI kill bacteria

A

polymerisation of RMGI releases cytotoxic enzymes

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33
Q

what does it mean if a lining material is “therapeutic”?

A
  • reduces inflammation
  • promotes healing
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34
Q

what is the significance of a lining material being radiopaque?

A

can be viewed radiogrpahically if displaced from tooth
allows for microleakage to be seen radiographically

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35
Q

explain the thermal properties of GI and their significance

A

thermal conductivity is less than dentine (RMGI and GI)
thermal expansion is similar to dentine (GI)

during exposure to heat the GI will react similarly to dentine which will maintain seal of material

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36
Q

give an example of how a lining material can be cariostatic?

A

release fluoride

37
Q

Explain GI interaction with dentine tubules and its significance

A

GI seals dentine tubules

this decreases micro-leakage and decreases sensitivity

38
Q

what is the reason for using a lining material in a pt with reversible pulpititis?

A

pallitave care- eases the pts symptoms

39
Q

What is an advantage of using GI over other cements

A

it releases fluoride = CARIOSTATIC

40
Q

What does the initial gradient on a graph show

A

young’s (elastic) Modulus

41
Q

what type of alloy is stainless steel?

A

wrought alloy- can be cold worked

42
Q

What is indicated by the change in gradient on the stress strain curve

A

the proportional limit

43
Q

what are the components of stainless steel?

A
  • 72% iron
  • 18% chromium
  • 8% nickel
  • 1.7% titanium
  • 0.3% carbon
44
Q

what is the role of chromium in stainless steel?

A

corosion resistance

45
Q

what is the role of nickel in stainless steel?

A

corosion resistance
increase strength

46
Q

What is proportional limit and explain it

A

The stress applied before a material behaves inelastically

> proportional limit will result in deformation
< proportional limit - the material will return to the original shape

47
Q

what is the role of titanium in stainless steel?

A

prevents precipitation of chromium carbide at grain boundaries

48
Q

what does the end of a line in the stress strain curve show?

A

fracture stress

49
Q

What is translucency

A

Ability for light to pass through a material but be scattered, at one of the surfaces or internally, leading to blurring of transmitted light

50
Q

give 3 properties of stainless steel

A
  • springiness
  • ductile
  • corrosion resistant
51
Q

how does weld decay affect stainless steel?

A

makes it brittle

52
Q

What is opalescence

A

the ability of translucent material to appear blue in reflected light and orange/yellow in transmitted light

53
Q

define springiness

A

the ability to undergo large deflection WITHOUT deformation

54
Q

what makes steel classed as “stainless” steel?

A

contians at least 12% chromium

55
Q

Define cold working

A

Shaping a material below its recrystallisation temperature

56
Q

Define slip

A

Defects in a grain move to grain boundaries this results in fewer defects in the lattice structure

57
Q

what does it mean by classing iron as ‘allotropic’?

A

undergoes 2 solid state changes due to temperature

58
Q

What is an alloy

A

2 or more metals that form a common lattice structure and are soluble in one another

59
Q

define creep

A

repetitive small forces that cause gradual dimensional change

60
Q

define Fatigue

A

Repetitive small stresses that because fracture

61
Q

what are the 2 types of acrylic used in dentistry?

A

self cure
heat cure

62
Q

give an advantage of heat cure PMMA

A

has a higher molecular weight than self cure
this means better mechanical properties

63
Q

what are ideal properties of luting agents

A

low viscosity - increases as it sets

low film thickness - <25 um

easy to use

Radiopaque

Good marginal seal

Low solubility

Cariostatic

Non-toxic

High compressive strength

High hardness

64
Q

give a disadvantage of heat cure PMMA

A

gaseous porosity occurs if cured too fast
results in process taking far to long to avoid this

65
Q

What does dual cure material mean

A

cured by:
- light
- cures on its own by REDOX reaction

66
Q

what are the ideal properties of acrylic?

A
  • non-toxic
  • non-irritant
  • unaffected by oral fluids
  • high softening temperature
  • low density- lightweight
  • low thermal conductivity
67
Q

What are issues with HEMA

A
  • cytotoxic to the pulp
  • swells
68
Q

when can you not use RMGI as a cement

A

for porcelain - it swells cracking the crown
for posts - it will swell and split the root

69
Q

give an advantage of self cure PMMA

A

polymerisation doesnt require heat- less thermal contraction means a better fitting denture

70
Q

RMGI does not bond to indirect restorations so what chemical is needed

A

composite luting agent

71
Q

how does dentine bonding agent bond composite luting agent to the tooth

A

hydrophilic end bonds to tooth
hydrophobic end bonds to composite

72
Q

give 2 disadvantages of self cure PMMA

A

polymerisation is less efficiant, meaning there are more unreacted monomers
irritant/allergy issues

lower molecular weight= reduced transverse strength

73
Q

how can self cure PMMA dentures become oversized?

A

they absorb water and expand

74
Q

what is free radical polymerisation?

A

chemical union of 2 molecules to form a larger molecule without elimination of the smaller molecule

75
Q

How does composite luting agent bond to indirect restorations

A

chemical bond forms between C=C

micro-mechanical bond forms between composite luting agent and the rough inside surface of indirect restoration

76
Q

what type of bonds are present in the molecules that undergo free radical polymerisation?

A

C=C

77
Q

How do you improve bonding to porcelain

A

etch the surface with hydrofluric acid

78
Q

what are the 4 stages of free radical polymerisation?

A

activation
initiation
propagation
termination

79
Q

What is required to bond composite luting agent to porcelain/ceramics

A

Silane coupling agent

80
Q

How does silane coupling agent bond to composite luting agent and porcelain/ceramics

A

C=C bonds from silane coupling agent react with similar groups in the composite luting agents

hydroxyl groups in the silane coupling agent react with oxide groups on the porcelain surface

81
Q

What is needed to bond composite luting agent to metal

A

Metal bonding agent

82
Q

What are examples of metal bonding agents

A

MDP and 4-META

83
Q

What is important when using compoosite luting agent to bond to metal

A

must use a self cure composite as light cannot penetrate through metal

84
Q

How does metal bonding agent bond metal to composite luting agent

A

C=C bonds in metal bonding agent react with similar groups in the composite luting agent

Acid end of metal bonding agent reacts with metal oxide

85
Q

What is a self adhesive composite resin

A

composite luting material with metal bonding agent in it

86
Q

What is an example of a Self adhesive composite resin luting agent

A

Panavia

87
Q

How do you bond an indirect retention to the tooth

A

Tooth

DBA

Composite luting Agent

Indirect retention

88
Q

How do you bond porcelain/ceramic to the tooth

A

Tooth

DBA

Composite luting agent

Silane coupling agent

Porcelain/Ceramic

89
Q

How do you bond metal to the tooth

A

Tooth

DBA

Composite luting agent

Metal bonding agent

Metal

Need to Know (21 decks)

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