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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
components of impression compound
resins waxes plasticisers fillers
26
plasticisers in impression compound
reduce brittleness
27
fillers in impression compound
overcome tackiness control degree of flow minimise shrinkage due to thermal contraction improve rigidity
28
colloid
2 phase system of fine particles (1-200nm) of one phase dispersed in another phase
29
hydrocolloid
if dispersing medium H2O
30
hydrocolloid 2 states
SOL - viscous liquid state GEL - jelly-like consistency - agglomeration of particles - entangled framework of solid particles enclosing liquid by capillary forces
31
2 major categories for assessing
material characteristics clinical performance - pt acceptance, ease of use be wary of user feedback
32
assessing properties
``` flow/viscosity surface detail/reproduction contact angle/wettability elastic recovery (%) stiffness (flexibility) tear strength mixing and working time (min) ``` identify properties not mentioned
33
ISO standards
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
34
viscosity
ability to flow and make close contact with tissue surfaces
35
surface wetting
intimate contact with tissue so all of surface is replicated not form voids due to repulsion or moisture
36
contact angle
determines how well material envelops the hard/soft tissue surface low contact angle - spread easily and adapt smoothly
37
tear strength
stress material will withstand before fracture
38
reproduction of surface detail
standard notch dimensions A = 20um B = 50um (ISO norm) C = 75um test whether material fills these notches
39
rigidity
stress/strain | ideally impression material low rigidity - ease its removal from UC/interdental areas
40
properties affecting accuracy
``` viscosity setting mechanism TEC - ideally low to cope with mouth to room temp transition hydrophobic/hydrophillic elasticity tear strength ```
41
thixotropy
greater accuracy of impression without excessive flow | become less viscous when subjected to an applied stress
42
reversible hydrocolloid
agar - no longer used galactose sulphate, forms a colloid with H2O better elastic recovery but needs special conditioning unit etc
43
irreversible hydrocolloid
alginate
44
alginate process
``` prep insertion setting removal storage cast prep ```
45
polyethers
mod dimensional change on setting good elastic recovery allergies susceptible to moisture absorption
46
polysulfide rubber
``` long-term dimensional change - need to pour up quickly good elastic properties good tear strength bad taste messy ```
47
condensation-cured silicones
high setting shrinkage | quite rigid
48
addition-cured silicones
``` stability quite rigid excellent elastic recovery e.g. Virtual - PVS - tear strength - elastic recovery ```
49
viscoelastic behaviour
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
50
fct of impression
produce accurate (dimensional and surface) replica of surface and shape of hard and soft oral tissues
51
impression
a negative reproduction of tissues
52
tray retention
adhesive or perforated
53
types of impression
single tooth whole dentition edentulous mouth
54
mucostatic impression
fluid materials that prevent displacement of the STs give impression of undisplaced mucosa e.g. ZOE, low viscosity alginates
55
mucocompressive impression
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
classification of impressions
clinical - mucostatic or mucocompressive | properties - elastic or non-elastic
57
what are elastic impressions for?
dentate
58
what are non-elastic impressions for?
edentulous and inter-occlusal records
59
if purely elastic what will happen to the shape?
will change shape instantaneously
60
how is the amalgam alloy formed?
by trituration
61
amalgam constituents
``` Ag 70% Sn 25% Cu 3% Zn 1% Hg 1% ```
62
amalgam powder
``` 50% Sn, Ag Cu Zn (Hg - pre-amalgamated) ```
63
amalgam liquid
50% | Hg - triple distilled
64
Sn, Ag
inter metallic compound Ag3Sn. y phase
65
Cu
strength and hardness
66
Zn
scavenger (slag)
67
classification
composition - traditional - copper enriched particle shape and size
68
particle types
lathe cut | spherical/spheroidal
69
lathe cut
fill ingots | use heat tx to relieve internal stresses
70
spherical/spheroidal
spray molten metal into inert atmosphere
71
amalgam setting reaction
Ag3Sn + Hg - Ag3Sn + Ag2Hg3 + Sn7Hg9
72
y phase
Ag3Sn - strongest
73
y1
Ag2Hg3
74
y2
Sn7Hg9
75
amalgam matrix
y1 and y2
76
unreacted particles
y | insufficient Hg for complete reaction
77
y2 properties
weak and poor corrosion resistance
78
higher Hg content
weaker amalgam as it will produce more y2
79
traditional (hand-mixed) setting dimensional changes
initial contraction - solution of alloy particles in Hg | expansion - y1 crystallisation
80
modern (mechanically mixed)
small contraction | solid solution of Hg in Ag3Sn
81
Zinc and expansion
saliva/blood: Zn +H2O - ZnO + H2 bubbles - pressure build up - expansion downward pulpal pain, upward sits proud. why Zn free
82
properties depend on
``` handling factors - proportioning and trituration - condensation - remove excess Hg - carving and polishing cavity design product corrosion ```
83
factors reducing strength
``` undermixing too high Hg content after condensation too low condensation pressure slow rate of packing - increments don't bond corrosion creep ```
84
properties
``` 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
advantages of spherical particles
``` less Hg required higher tensile strength higher early compressive strength less sensitive to condensation easier to carve lower setting shrinkage ```
86
types of amalgam
``` Cu single - lowest creep - best compressive strength PERMITE - non-y2 encapsulated - Hg hygiene ```
87
indications
moderate and large cavities posterior teeth core build ups when definitive Rxs will be indirect cast Rx
88
corrosion
y2 most electronegative - acts as anode of oxidation cell. will gradually dissolve - weakens esp at margins corrosion products may contribute to sealing margins
89
reducing corrosion
Cu enriched, polishing margins | avoiding galvanic cells
90
Cu enriched alloys
non-y2 >6% Cu dispersion modified or single composition
91
dispersion modified Cu enriched alloys
``` 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
single composition Cu enriched alloy
powder Ag-Sn-Cu Ag-Sn-Cu + Hg - Ag-Sn-Cu + y1 + Cu6Sn5
93
benefits of copper enriched alloys
``` higher early strength less creep higher corrosion resistance increased durability of margins gets rid of y2 no Zn - no delayed expansion ```
94
disadvantage of copper enriched alloys
surfaces more prone to tarnish
95
contraindications
aesthetics important pt history of sensitivity can't produce retentive cavity would need to remove excessive healthy tooth to produce retentive cavity
96
local reactions
lichenoid lesions galvanic response tooth discolouration amalgam tattoo
97
lichenoid lesions
T4 hypersensitivity | replace with gold/composite
98
galvanic response
battery effect from 2 different amalgams or amalgam and cast metal tingling
99
tooth discolouration
corrosion products migrate into tooth surfaces - porous
100
amalgam tattoo
fine amalgam particles migrate into ST | confuse with melanoma
101
matrices
recreate cavity wall allows adequate condensation confines amalgam to cavity <0.05mm thick
102
condensation
``` vertical and lateral pressure expels excess mercury adapts material to cavity walls reduces layering (homogeneous) eliminates voids ```
103
inadequate condensation
lack of adaptation to cavity poor bonding between layers inadequate Hg expression therefore removal inferior mechanical properties
104
IP caries
``` self-retentive box prep - remove less tooth - technically demanding proximo-occlusal prep - very retentive - destruction of tooth ```
105
moisture contamination
reduced strength | increased creep, corrosion, porosity
106
microleakage
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
wedges
``` adaptation of matrix at cervical margin temp tooth separation aids proximal contour prevents excess amalgam gingivally prevents movement of matrix band ```
108
why should you always overfill ?
increased Hg content on surface - remove by carving
109
retention form
features that prevent loss of Rx in any direction
110
resistance form
features that prevent loss of material due to distortion/fracture by masticatory forces - sufficient depth - gingival floor approx 90 degrees to axial wall
111
sealing and bonding
amalcure | no evidence of increased survival
112
mechanical retention
grooves/dimples within cavity design | pins - Ti/SS
113
placing pins
``` Ti/SS increase retention into dentine in greatest bulk never in enamel or ADJ - will crack pack amalgam around pin ```
114
problems with pins
``` 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
why should you never user pins with composite?
won't fall out if bond fails
116
Minimata convention
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
SDCEP
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
carving
recreate anatomical contour
119
finishing
only if need to adjust polishing considered unnecessary - heat - Hg risk?
120
removal
dam and high vol aspiration min cutting greatest Hg release during insertion and removal
121
Hg absorption
``` vapour into lungs contact with skin GIT gingiva and mucosa D+P as metal ions? ```
122
GV black cavity classification - 1
pit and fissure
123
GV black cavity classification - 2
approximal (posterior teeth)
124
GV black cavity classification - 3
approximal (anterior teeth)
125
GV black cavity classification - 4
approximal involving incisal angle
126
GV black cavity classification - 5
cervical surfaces
127
GV black cavity classification - 6
cusp tips

DMS :( (18 decks)

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