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BDS stage 2 > DMT practicals > Flashcards

DMT practicals Flashcards

1
Q

What do impression materials require ?

A

a large working time- can be mixed, loaded and set into the mouth
the time taken from the start of mixing to the material no longer being usable at room temperature

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2
Q

When a material is first set in the mouth which type of deformation should it undergo ?

A

plastic- retains the shape of the impression

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3
Q

What is the state of deformation during setting of impression materials ?

A

viscoelastic

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4
Q

What is the state of deformation when impression materials are set ?

A

elastic- cant be permenantly deformed

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5
Q

What type of deformation should occur in the working time ?

A

plastic

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6
Q

What type of deformation should happen in the setting time ?

A

elastic

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7
Q

If the recovery is 0 the material is ?

A

elastic

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8
Q

Acrylic and resin materials undergo setting by ??

A

polymerisation

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9
Q

What is polymerisation ?

A

the process by which small molecules are joined covaleltnty into large molecular chains

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10
Q

What are the dimensional changes that happen in polymerisation ?

A

monomers are usually liquid/gas and this leads to solid formation in polymerisation- increase in viscosity and contraction occurs

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11
Q

What can dimensional changes be measured with ?

A

dialtometer

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12
Q

How do denture base materials initiate polymerisation ?

A

when acrylic beads are added and they absorb water

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13
Q

What are the stages of form that denture base materials go through when polymerising ?

A

sandy stage
stringy
douhy

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14
Q

What is mixed with MMA to intitate polymerisation of denture base materials ?

A

PMMA mixed with MMA

PMMA is polymer

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15
Q

How does the dilatometer work ?

A

when the polymer is at dough stage
but into water bath that has a liquid callbrated pipette attached
rises in liquid due to volume changes in PMMA

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16
Q

What are gypsum materials used for ?

A

impression materials

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17
Q

How does gypsum set ?

A

not by polymerisation

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18
Q

What are gysum products made of ?

A

calcium sulphate hemihydrate

plaster and stone

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19
Q

What are dental plaster and stone used for ?

A

record of intra oral structures

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20
Q

How is dental plaster and stone provided and how is it set ?

A

provided as powder- mix with water

set by exo reaction

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21
Q

What happens when dental plaster mixes with water ?

A

forms calcium sulphate dihydrate
this is less soluble
precipitates out in solution

precipitation occurs until no further dihydrate to precipitate out

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22
Q

How can the setting of dental gypsum be measured ?

A

extensometer

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23
Q

How can dentures be subjected to rapidly applied stress ?

A

dropping the denture

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24
Q

What does the charpey impact tester do ?

A

provide a rapidly applied force with sufficient magnitude

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25
Q

What does the charpey impact tester consist of ?

A

weighted pendulum which drops down

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26
Q

What happens when the pendulum hits a specimen ?

A

the pendulum should fracture

the pendulum looses energy and it max acsent i sless as a result

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27
Q

What can be used to measure impact strength ?

A

difference between specimen height and no specimen height

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28
Q

Why can brittle materials fracture under their stress ?

A

they have notches which concentrate stress

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29
Q

If a notch has a large effect on impact strength it is ?

A

notch sensitive

30
Q

What 2 properties are needed to determine if a material is notch sensitive ?

A

Ep

Ei

31
Q

What is Ei ?

A

energy of initiation

energy of failure of unnotched specimens

32
Q

What is Ep ?

A

energy of propagation

energy needed to fail notched specimens

33
Q

What is the relationship between Ep and Ei in a notch senstitive material ?

A

Ei > Ep

34
Q

Impact strength is also known as ?

A

toughness

35
Q

How do we usually measure diametral tensile strength ?

A

dumb bell shaped specimens

apply tensile force

36
Q

Why can we use conventional methods to measure tensile strenght in brittle materials ?

A

they would shatter

37
Q

How do we measure diamteral tensile strength in materials ?

A

apply a compressive froce
this sets up tensile forces within the specimen that are equal and opposite direction and perpendicular to the force application

38
Q

What happens as we apply more compressional stress ?

A

the internal forces will increase

material breaks down the diameter

39
Q

Which types of materials can only have their diamteral tesnile strength measured ?

A

rigid materials

brittle materials would shatter

40
Q

How do we calculate stress ?

A

force/cross sectional area

41
Q

What is adhesion ?

A

attachment of one surface to another as a result of molecular attraction or interlocking with the surfaces

42
Q

What are the 3 types of adhesion ?

A

chemical
physical
complex

43
Q

What is chemical bonding ?

A

molecular attraction

44
Q

What is physical bonding ?

A

interlocking of surfaces of adhesive

45
Q

What is complex bonding ?

A

combination of physical and chemical

46
Q

What are the materials used in white fillings ?

A

glass ionomers

composites

47
Q

What are composite materials ?

A

resin based

filled with glass filler

48
Q

Do composites bind directly to the tooth ?

A

no

thye need an adhesive

49
Q

How do you apply a composite ?

A

acid to remove mineral content
dentine is porous
resin is applied and uses chemical process to infiltrate porosities
composite is applied to resin

50
Q

How does composite bind ?

A

physical process

resin uses chemical process

51
Q

What are the layers in a composite filling ?

A

dentine
resin
composite

52
Q

How do GIC set ?

A

acid base reaction

53
Q

Does GIC need an adhesive ?

A

no

GIC binds to dentine withour need for adhesive

54
Q

How does GIC adhere to dentine ?

A

chemical process

55
Q

Does composite or GIC have a higher shear bond strenght ?

A

composite- as it has an adhesive

56
Q

What are the 3 modes of failure ?

A

adhesive

cohesive mixed

57
Q

What is an adhesive mode of failure ?

A

smooth surface

failure of interface of resin and composite

58
Q

What is a cohesive mode of failure ?

A

rough surface
either some composite left behind
or some dentine removed

59
Q

What is a mixed mode of failure ?

A

smooth and rough

mix of adhesice and cohesive

60
Q

What do tooth coloured fillings consist of ?

A

glass filler

incorporated into glass matrix

61
Q

Do tooth colured fillngs adhere directly ?

A

no they rely on an adhesive

62
Q

How do composites set ?

A

by polymerisation

63
Q

How can we measure the heat released in polymerisation ?

A

calorimeter

64
Q

How can polymerisation be initiated ?

A

be mixed with an initiator

inititated by light

65
Q

How does light polymerisation work ?

A

Require exposure to a visible light source

66
Q

What is the wavelength of visible light ?

A

380 to 700 nm

67
Q

Why are chemically activated polymers harder to use than light activated ?

A

chemcially activated have shorter working time

light activated materials have infinite working time

68
Q

What is the disadvantage of using a curing light ?

A

it can only set composites to the depth the light can reach

as a result have to do composite fillings in layers

69
Q

What are the factors affecting cure ?

A

distance
angle
depth

70
Q

What is the relationship between the diameter of the cure tip and light intensity ?

A

the smaller the diameter of the light tip the higher the light intensity

71
Q

What happens if composite is not fully polymerised ?

A

releases monomer that leads to insenstitvity

72
Q

What is the relationship between energy of light polymerisation and energy of light only ?

A

energy of light polymerisation- energy of light= energy chemical polymerisation

BDS stage 2 (28 decks)

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