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BDS stage 2 > DMT practicals > Flashcards

DMT practicals Flashcards

(72 cards)

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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
What does the charpey impact tester consist of ?
weighted pendulum which drops down
26
What happens when the pendulum hits a specimen ?
the pendulum should fracture | the pendulum looses energy and it max acsent i sless as a result
27
What can be used to measure impact strength ?
difference between specimen height and no specimen height
28
Why can brittle materials fracture under their stress ?
they have notches which concentrate stress
29
If a notch has a large effect on impact strength it is ?
notch sensitive
30
What 2 properties are needed to determine if a material is notch sensitive ?
Ep | Ei
31
What is Ei ?
energy of initiation | energy of failure of unnotched specimens
32
What is Ep ?
energy of propagation | energy needed to fail notched specimens
33
What is the relationship between Ep and Ei in a notch senstitive material ?
Ei > Ep
34
Impact strength is also known as ?
toughness
35
How do we usually measure diametral tensile strength ?
dumb bell shaped specimens | apply tensile force
36
Why can we use conventional methods to measure tensile strenght in brittle materials ?
they would shatter
37
How do we measure diamteral tensile strength in materials ?
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
What happens as we apply more compressional stress ?
the internal forces will increase | material breaks down the diameter
39
Which types of materials can only have their diamteral tesnile strength measured ?
rigid materials | brittle materials would shatter
40
How do we calculate stress ?
force/cross sectional area
41
What is adhesion ?
attachment of one surface to another as a result of molecular attraction or interlocking with the surfaces
42
What are the 3 types of adhesion ?
chemical physical complex
43
What is chemical bonding ?
molecular attraction
44
What is physical bonding ?
interlocking of surfaces of adhesive
45
What is complex bonding ?
combination of physical and chemical
46
What are the materials used in white fillings ?
glass ionomers | composites
47
What are composite materials ?
resin based | filled with glass filler
48
Do composites bind directly to the tooth ?
no | thye need an adhesive
49
How do you apply a composite ?
acid to remove mineral content dentine is porous resin is applied and uses chemical process to infiltrate porosities composite is applied to resin
50
How does composite bind ?
physical process | resin uses chemical process
51
What are the layers in a composite filling ?
dentine resin composite
52
How do GIC set ?
acid base reaction
53
Does GIC need an adhesive ?
no | GIC binds to dentine withour need for adhesive
54
How does GIC adhere to dentine ?
chemical process
55
Does composite or GIC have a higher shear bond strenght ?
composite- as it has an adhesive
56
What are the 3 modes of failure ?
adhesive | cohesive mixed
57
What is an adhesive mode of failure ?
smooth surface | failure of interface of resin and composite
58
What is a cohesive mode of failure ?
rough surface either some composite left behind or some dentine removed
59
What is a mixed mode of failure ?
smooth and rough | mix of adhesice and cohesive
60
What do tooth coloured fillings consist of ?
glass filler | incorporated into glass matrix
61
Do tooth colured fillngs adhere directly ?
no they rely on an adhesive
62
How do composites set ?
by polymerisation
63
How can we measure the heat released in polymerisation ?
calorimeter
64
How can polymerisation be initiated ?
be mixed with an initiator | inititated by light
65
How does light polymerisation work ?
Require exposure to a visible light source
66
What is the wavelength of visible light ?
380 to 700 nm
67
Why are chemically activated polymers harder to use than light activated ?
chemcially activated have shorter working time | light activated materials have infinite working time
68
What is the disadvantage of using a curing light ?
it can only set composites to the depth the light can reach | as a result have to do composite fillings in layers
69
What are the factors affecting cure ?
distance angle depth
70
What is the relationship between the diameter of the cure tip and light intensity ?
the smaller the diameter of the light tip the higher the light intensity
71
What happens if composite is not fully polymerised ?
releases monomer that leads to insenstitvity
72
What is the relationship between energy of light polymerisation and energy of light only ?
energy of light polymerisation- energy of light= energy chemical polymerisation

BDS stage 2 (28 decks)

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