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BDS2 CLINICAL Dental Materials > Impression Materials > Flashcards

Impression Materials Flashcards

(74 cards)

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1
Q

What is the function of impression materials

A

To produce an accurate replica of the surface and shape of hard and soft oral tissues

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2
Q

What is an impression

A

a negative reproduction of tissues

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3
Q

What is dental stone used to do

A

fill impressions to produce a positive replica (stone cast) which represents the position, shape, size and orientation of each tooth

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4
Q

What are dental stone casts used for

A

evaluating dentition when orthodontic, occlusal or other problems involved
in laboratory fabrication of restorations and prostheses

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5
Q

What does the treatment properties hinge on

A

the quality and accuracy of the initial impression

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6
Q

What does the impression material require

A

Impression materials with the right properties

clinician with good technique

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7
Q

What are the classifications of impression materials based on

A

Clinical

Properties

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8
Q

What are the clinical classification

A

mucostatic

mucocompressive

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9
Q

What are the properties

A

elastic

non elastic

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10
Q

What are mucostatic impression materials

A

zinc oxide eugenol, low viscosity alginates

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11
Q

What do mucostatic impression materials do

A

fluid materials that displace the soft tissues slightly

give an impression of the undisplased mucosa

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12
Q

What are mucocompressive impression materials

A

impression compound
high viscosity alginates
elastomers

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13
Q

What do mucocompressive materials do

A

viscous materials that record an impression of the mucosa under load i.e give an impression of displaced soft tissues

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14
Q

What happens to the impression material during removal

A

it undergoes elastic strain and has to change shape to overcome the bulbosity of the tooth

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15
Q

What do we want the impression material to do after removal

A

change back to its original shape making it truly elastic

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16
Q

What is it called when the impression material never returns to its original shape

A

permanent strain
it does not recover
making the impression inaccurate

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17
Q

What should be done to try and decrease the permanent deformation

A

keep the load time less by removing with a sharp pull so there is less overall permanent strain

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18
Q

What are the two types of elastic materials

A

hydrocolloids

elastomers

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19
Q

What are the elastomers

A

polysulphides
polyethers
silicones

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20
Q

What are the hydrocolloids

A

agar (reversible (lab duplicating) but no longer used

alginate - irreversible

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21
Q

What are the elastomers

A

polysulphides
polyethers
silicones (conventional and addition cured)

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22
Q

What happens to non elastic material on removal

A

don’t recover well

either deform/fracture

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23
Q

What is the impression process

A 
preparation
insertion
setting 
removal
storage 
cast prep
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24
Q

What happens in preparation

A

mixing
chemical reaction
heat
to result in a material that slows and takes up shape/space available

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25
What happens in insertion
pick a tray | need adhesive maybe
26
What happens in setting
chemical polymerisation cooling (only some) to form a solid replica
27
What happens in storage
need to see how quickly the impression needs to be poured before the dimensional changes become significant but should wait a bit to allow elastic recovery
28
What are the ideal properties needed for
accuracy patient operator
29
What are the properties for accuracy
``` flow setting changes removal storage decontamination compatible with cast material viscosity setting mechanism thermal expansion coefficient hydrophobic/hydrophilic elasticity tear strength ```
30
What is the ideal property for flow
that it can flow over the dentition and make intimate contact with the surfaces and record surface detail
31
What is the ideal property regarding setting changes
we don't want it to shrink nor expand, we want it to remain the same dimension
32
What is the ideal property for removal
no effect on oral tissues no change dimensionally complete elastic recovery
33
What are the ideal properties for storage
does not change dimensionally over time (moisture) - a weak point for alginates
34
What are the ideal properties for decontamination
dimensions and surfaces unaltered
35
Why is viscosity important
determines the ability to flow over surface and so level of detail recorded
36
What is the ideal property for setting mechanism
does physical/chemical process = dimensional contraction
37
What is the ideal property for thermal expansion coefficient
ideally low | to cope with mouth to room temperature transition
38
What is the ideal property for hydrophobic/hydrophilic
affects surface contact because saliva will be present on the tooth
39
What is the ideal property for elasticity
elastic/viscoleastic behavior | for undercuts so that it won't fracture
40
What is the ideal property of tear strength
withstand tearing when removed especially from undercuts
41
What are the ideal properties for patient comfort
non-toxic acceptable taste and smell short setting time removable with damage to oral tissues
42
What are the ideal properties for operator convenience
quick, simple technique convenient working/setting times must be able to be decontaminated cost (inexpensive) is a consideration BUT not a property
43
What is a colloid
two phase system of fine particles (1-200nm) of one phase dispersed in another phase
44
What is a hydrocolloid
colloid dispersed in water
45
What are the two states of a hydrocolloid
sol | gel
46
What is the sol phase
viscous liquid state
47
What is the gel phase
jelly like consistency
48
What is the gel phase due to
agglomeration of particles | entangled framework of solid particles enclosing liquid by capillary forces
49
What is the composition of alginate
``` salt of alginic acid calcium sulphate trisodium phosphate filler modifiers flavourings chemical indicators ```
50
What is the function of the salt of alginic acid
it reacts with calcium ions
51
What is the function of calcium sulphate
provides calcium ions
52
What is the function of trisodium phosphate
delays gel formation
53
What is the function of filler
for cohesion and strength
54
What is the function of modifiers, flavourings and chemical indicators
improve the surface taste pH color change (to show transition from sol to gel)
55
How does trisodium phosphate delay the setting reaction
calcium ions interact with the phosphate ions and it is only when the phosphate ions are used up that the remaining calcium ions react with sodium alginate
56
What happens in the setting reaction
there is long cross linked fibril entangling undissolved particles
57
What is the setting reaction
2NanAlg + nCaSO4 --> nNa2SO4 + CanALg
58
How does calcium ions result in cross linking
because they're divalent
59
What is the alginate delay
trisodium phosphate preferentially reacts with Ca ions in CaSO4 then 2NanAlg reacts with Ca ions
60
How can alginate be manipulated
``` use correct powder/liquid ratio use water at 18-24 degrees use perforated tray and adhesive remove impression with a sharp pull use in bulk ```
61
Why does alginate have greater elastic properties if a minute or two is waited
cross linking continues after apparent set
62
Why does alginate set quicker on soft tissues
because an increased temp speeds up setting
63
Why should a bigger bulk of alginate be used (5mm)
as permanent distortion and tearing is slightly reduced
64
What features of alginate allow for patients comfort
non toxic, non irritant acceptable taste and smell setting time is ok
65
What features of alginate allow for operator convenience
easy to use okay setting time storage - need to avoid moisture but should be left with damp gauze. prepare cast ASAP
66
what is syneresis
release of water
67
what is imbibition
uptake of water
68
What is the issue with storage of alginate
it can release water but also take on water | could distort it
69
How is the flow for alginate
okay
70
How is the setting changes for alginate
ok
71
What happens if the patient is moving during setting
can result in internal stresses that lead to distortion
72
How is the elastic property of alginate
not 100% elastic recovery
73
How is the tear strength of alginate
poor avoid deep undercuts use in bulk
74
How is the storage of alginate
syneresis or imbibition may effect dimensions/accuracy

BDS2 CLINICAL Dental Materials (15 decks)

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