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DMS :( > impression materials and amalgam > Flashcards

impression materials and amalgam Flashcards

1
Q

broad ideal properties

A 
pt comfort
operator convenience
accuracy
removal and undercuts
storage
compatible with cast material
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2
Q

pt comfort

A 
non-toxic, non-irritant
acceptable taste and smell
 - gagging could distort
setting time short
removal without damage to tissues
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3
Q

operator convenience

A

easy to mix and use, quick
setting and mixing time
storage
decontaminable

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4
Q

accuracy

A

viscosity and contact angle/wettability - surface interaction
setting dimensional changes
elastic recovery
surface detail/reproduction

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5
Q

removal and undercuts

A

tear strength
rigidity
no effect on oral tissues

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6
Q

storage

A

dimensional stability
setting shrinkage
thermal expansion/contraction

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7
Q

alginate composition

A

salt of alginic acid e.g. Na/K alginate 12%
calcium sulphate 12%
trisodium phosphate 2%
filler 70%
modifiers, flavourings, chemical indicators small %

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8
Q

salt of alginic acid

A

e.g Na/K alginate
12%
reacts with Ca ions
water soluble salt

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9
Q

calcium sulphate

A

12%
provides Ca ions
reacts to form insoluble gel

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10
Q

trisodium phosphate

A

2%

delays gel formation - retarder

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11
Q

filler

A

70%

cohesion, strength

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12
Q

modifiers, flavourings, chemical indicators

A

small %

improve surface, taste, pH colour change

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13
Q

alginate setting reaction

A

Na alginate to Ca alginate
one Ca knocks out 2 Na
can’t be broken, irreversible
creation of cross-links between polymer chains

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14
Q

alginate pH change setting reaction

A

11 to 7

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15
Q

alginate delay

A

alter amount to alter setting times

trisodium phosphate preferentially reacts with Ca ions in CaSO4 until exhausted

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16
Q

alginate manipulation

A

correct powder to liquid ratio
water 18-24 degrees
perforated tray and adhesive
increased temp speeds up setting

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17
Q

removing alginate impression

A

sharp pull

elastic recovery, max tear strength

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18
Q

alginate and crosslinking

A

cross linking continues after apparent set - greater elastic properties ifs you wait for a few mins after tackiness has gone from surface

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19
Q

using large bulk of alginate

A

permanent distortion and tearing slightly reduced

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20
Q

alginate properties - pt comfort

A

non-toxic, non-irritant
acceptable taste, smell
setting time ok

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21
Q

alginate operator convenience

A 
relatively easy to use
setting time ok
storage - avoid moisture
 - prepare cast asap to avoid dimensional change
 - syneresis - release of H2O
 - imbibition - uptake of H2O
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22
Q

alginate accuracy

A

not as good as elastomers for surface reproduction
setting changes and flow ok
movement - stresses, distortion. Can create stresses if pull before properly set
not 100% elastic recovery
poor tear strength - avoid deep UCs
poor long-term dimensional stability
- moist gauze over impression to reduce distortion during transit time

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23
Q

where can’t non-elastic impression materials be used?

A

UCs

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24
Q

impression compound

A

mucocompressive
thermoplastic - no chemical reaction involved
poor dimensional stability

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25
Q

components of impression compound

A

resins
waxes
plasticisers
fillers

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26
Q

plasticisers in impression compound

A

reduce brittleness

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27
Q

fillers in impression compound

A

overcome tackiness
control degree of flow
minimise shrinkage due to thermal contraction
improve rigidity

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28
Q

colloid

A

2 phase system of fine particles (1-200nm) of one phase dispersed in another phase

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29
Q

hydrocolloid

A

if dispersing medium H2O

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30
Q

hydrocolloid 2 states

A

SOL - viscous liquid state
GEL - jelly-like consistency
- agglomeration of particles
- entangled framework of solid particles enclosing liquid by capillary forces

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31
Q

2 major categories for assessing

A

material characteristics
clinical performance
- pt acceptance, ease of use
be wary of user feedback

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32
Q

assessing properties

A 
flow/viscosity
surface detail/reproduction
contact angle/wettability
elastic recovery (%)
stiffness (flexibility)
tear strength
mixing and working time (min)

identify properties not mentioned

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33
Q

ISO standards

A

assess relevant properties of a produce to see whether it meets acceptable requirements for safe and effective use

grooves/indentations of 20/50um are replicated depending on material viscosity

don’t establish best material - designed to exclude unsafe materials from the market

but industries use them as a quality sign

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34
Q

viscosity

A

ability to flow and make close contact with tissue surfaces

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35
Q

surface wetting

A

intimate contact with tissue so all of surface is replicated

not form voids due to repulsion or moisture

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36
Q

contact angle

A

determines how well material envelops the hard/soft tissue surface
low contact angle - spread easily and adapt smoothly

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37
Q

tear strength

A

stress material will withstand before fracture

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38
Q

reproduction of surface detail

A

standard notch dimensions
A = 20um
B = 50um (ISO norm)
C = 75um

test whether material fills these notches

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39
Q

rigidity

A

stress/strain

ideally impression material low rigidity - ease its removal from UC/interdental areas

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40
Q

properties affecting accuracy

A 
viscosity
setting mechanism
TEC
 - ideally low to cope with mouth to room temp transition
hydrophobic/hydrophillic
elasticity
tear strength
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41
Q

thixotropy

A

greater accuracy of impression without excessive flow

become less viscous when subjected to an applied stress

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42
Q

reversible hydrocolloid

A

agar - no longer used
galactose sulphate, forms a colloid with H2O
better elastic recovery but needs special conditioning unit etc

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43
Q

irreversible hydrocolloid

A

alginate

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44
Q

alginate process

A 
prep
insertion
setting
removal
storage
cast prep
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45
Q

polyethers

A

mod dimensional change on setting
good elastic recovery
allergies
susceptible to moisture absorption

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46
Q

polysulfide rubber

A 
long-term dimensional change - need to pour up quickly
good elastic properties
good tear strength
bad taste
messy
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47
Q

condensation-cured silicones

A

high setting shrinkage

quite rigid

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48
Q

addition-cured silicones

A 
stability
quite rigid
excellent elastic recovery
e.g. Virtual - PVS
 - tear strength
 - elastic recovery
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49
Q

viscoelastic behaviour

A

elastic recovery takes time
- wait before you pour cast - minimise permanent deformation
if load time is less there is less overall permanent strain so lower deformation
- remove imp tray quickly with a sharp pull

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50
Q

fct of impression

A

produce accurate (dimensional and surface) replica of surface and shape of hard and soft oral tissues

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51
Q

impression

A

a negative reproduction of tissues

52
Q

tray retention

A

adhesive or perforated

53
Q

types of impression

A

single tooth
whole dentition
edentulous mouth

54
Q

mucostatic impression

A

fluid materials that prevent displacement of the STs

give impression of undisplaced mucosa

e.g. ZOE, low viscosity alginates

55
Q

mucocompressive impression

A

stiff, viscous materials that record an imp of the mucosa under load
displaced soft tissue
may produce distorted imp in edentulous pts with a flabby ridge
e.g. compound, high viscosity alginates/elastomers

56
Q

classification of impressions

A

clinical - mucostatic or mucocompressive

properties - elastic or non-elastic

57
Q

what are elastic impressions for?

A

dentate

58
Q

what are non-elastic impressions for?

A

edentulous and inter-occlusal records

59
Q

if purely elastic what will happen to the shape?

A

will change shape instantaneously

60
Q

how is the amalgam alloy formed?

A

by trituration

61
Q

amalgam constituents

A 
Ag 70%
Sn 25%
Cu 3%
Zn 1%
Hg 1%
62
Q

amalgam powder

A 
50%
Sn, Ag
Cu
Zn
(Hg - pre-amalgamated)
63
Q

amalgam liquid

A

50%

Hg - triple distilled

64
Q

Sn, Ag

A

inter metallic compound Ag3Sn. y phase

65
Q

Cu

A

strength and hardness

66
Q

Zn

A

scavenger (slag)

67
Q

classification

A

composition
- traditional
- copper enriched
particle shape and size

68
Q

particle types

A

lathe cut

spherical/spheroidal

69
Q

lathe cut

A

fill ingots

use heat tx to relieve internal stresses

70
Q

spherical/spheroidal

A

spray molten metal into inert atmosphere

71
Q

amalgam setting reaction

A

Ag3Sn + Hg - Ag3Sn + Ag2Hg3 + Sn7Hg9

72
Q

y phase

A

Ag3Sn - strongest

73
Q

y1

A

Ag2Hg3

74
Q

y2

A

Sn7Hg9

75
Q

amalgam matrix

A

y1 and y2

76
Q

unreacted particles

A

y

insufficient Hg for complete reaction

77
Q

y2 properties

A

weak and poor corrosion resistance

78
Q

higher Hg content

A

weaker amalgam as it will produce more y2

79
Q

traditional (hand-mixed) setting dimensional changes

A

initial contraction - solution of alloy particles in Hg

expansion - y1 crystallisation

80
Q

modern (mechanically mixed)

A

small contraction

solid solution of Hg in Ag3Sn

81
Q

Zinc and expansion

A

saliva/blood: Zn +H2O - ZnO + H2
bubbles - pressure build up - expansion
downward pulpal pain, upward sits proud. why Zn free

82
Q

properties depend on

A 
handling factors
 - proportioning and trituration
 - condensation - remove excess Hg
 - carving and polishing 
cavity design
product
corrosion
83
Q

factors reducing strength

A 
undermixing
too high Hg content after condensation
too low condensation pressure
slow rate of packing - increments don't bond
corrosion
creep
84
Q

properties

A 
early strength low then increases
high abrasion resistance
creep - marginal breakdown
biocompatible?
thermal properties
 - TEC x3 of tooth
 - conductivity high
doesn't bond to tooth
handling ok
poor aesthetics
radiopaque
not anticariogenic
smooth surface if polished
short placement time
85
Q

advantages of spherical particles

A 
less Hg required
higher tensile strength 
higher early compressive strength
less sensitive to condensation 
easier to carve
lower setting shrinkage
86
Q

types of amalgam

A 
Cu single
 - lowest creep
 - best compressive strength
PERMITE - non-y2
encapsulated - Hg hygiene
87
Q

indications

A

moderate and large cavities
posterior teeth
core build ups when definitive Rxs will be indirect cast Rx

88
Q

corrosion

A

y2 most electronegative - acts as anode of oxidation cell. will gradually dissolve
- weakens esp at margins
corrosion products may contribute to sealing margins

89
Q

reducing corrosion

A

Cu enriched, polishing margins

avoiding galvanic cells

90
Q

Cu enriched alloys

A

non-y2
>6% Cu
dispersion modified or single composition

91
Q

dispersion modified Cu enriched alloys

A 
Ag-Cu spheres and lathe cut alloy
y+Hg - y+y1+y2
y2+Ag-Cu - Cu6Sn5 + y1 (takes several days)
Cu6Sn5 halo around spheres
small insignificant amount of y2 remains
92
Q

single composition Cu enriched alloy

A

powder Ag-Sn-Cu

Ag-Sn-Cu + Hg - Ag-Sn-Cu + y1 + Cu6Sn5

93
Q

benefits of copper enriched alloys

A 
higher early strength
less creep
higher corrosion resistance
increased durability of margins
gets rid of y2
no Zn - no delayed expansion
94
Q

disadvantage of copper enriched alloys

A

surfaces more prone to tarnish

95
Q

contraindications

A

aesthetics important
pt history of sensitivity
can’t produce retentive cavity
would need to remove excessive healthy tooth to produce retentive cavity

96
Q

local reactions

A

lichenoid lesions
galvanic response
tooth discolouration
amalgam tattoo

97
Q

lichenoid lesions

A

T4 hypersensitivity

replace with gold/composite

98
Q

galvanic response

A

battery effect from 2 different amalgams or amalgam and cast metal
tingling

99
Q

tooth discolouration

A

corrosion products migrate into tooth surfaces - porous

100
Q

amalgam tattoo

A

fine amalgam particles migrate into ST

confuse with melanoma

101
Q

matrices

A

recreate cavity wall
allows adequate condensation
confines amalgam to cavity
<0.05mm thick

102
Q

condensation

A 
vertical and lateral pressure
expels excess mercury 
adapts material to cavity walls
reduces layering (homogeneous)
eliminates voids
103
Q

inadequate condensation

A

lack of adaptation to cavity
poor bonding between layers
inadequate Hg expression therefore removal
inferior mechanical properties

104
Q

IP caries

A 
self-retentive box prep
 - remove less tooth
 - technically demanding
proximo-occlusal prep
 - very retentive
 - destruction of tooth
105
Q

moisture contamination

A

reduced strength

increased creep, corrosion, porosity

106
Q

microleakage

A

passage of fluid and bacteria in micro gaps (10 microns) between Rx and tooth
- pulpal irritation and infection
- discolouration
- secondary caries
caused by mechanical loading and thermal stresses

107
Q

wedges

A 
adaptation of matrix at cervical margin
temp tooth separation
aids proximal contour
prevents excess amalgam gingivally
prevents movement of matrix band
108
Q

why should you always overfill ?

A

increased Hg content on surface - remove by carving

109
Q

retention form

A

features that prevent loss of Rx in any direction

110
Q

resistance form

A

features that prevent loss of material due to distortion/fracture by masticatory forces

  • sufficient depth
  • gingival floor approx 90 degrees to axial wall
111
Q

sealing and bonding

A

amalcure

no evidence of increased survival

112
Q

mechanical retention

A

grooves/dimples within cavity design

pins - Ti/SS

113
Q

placing pins

A 
Ti/SS
increase retention
into dentine in greatest bulk
never in enamel or ADJ - will crack
pack amalgam around pin
114
Q

problems with pins

A 
initial
 - stress
 - D cracking
 - sensitivity
 - risk of pin in pulp/periodontium
long-term
 - secondary caries: if Rx leaks it won't fall out, caries track down pin
115
Q

why should you never user pins with composite?

A

won’t fall out if bond fails

116
Q

Minimata convention

A

global treaty - protect human health and env from adverse effects
phase DOWN

1 - encapsulated
2 - separators - 95% or more particles
3 - authorised waste collection

117
Q

SDCEP

A

no justification on health grounds for:
- not placing amalgam
- removal of sound Rx
don’t use in U15s, pregnant or breastfeeding unless specific medical reason
- e.g. lack of cooperation and inadequate moisture control

118
Q

carving

A

recreate anatomical contour

119
Q

finishing

A

only if need to adjust
polishing considered unnecessary
- heat
- Hg risk?

120
Q

removal

A

dam and high vol aspiration
min cutting
greatest Hg release during insertion and removal

121
Q

Hg absorption

A 
vapour into lungs
contact with skin
GIT
gingiva and mucosa
D+P as metal ions?
122
Q

GV black cavity classification - 1

A

pit and fissure

123
Q

GV black cavity classification - 2

A

approximal (posterior teeth)

124
Q

GV black cavity classification - 3

A

approximal (anterior teeth)

125
Q

GV black cavity classification - 4

A

approximal involving incisal angle

126
Q

GV black cavity classification - 5

A

cervical surfaces

127
Q

GV black cavity classification - 6

A

cusp tips

DMS :( (18 decks)

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