amalgam Flashcards
1
Q
how is it formed?
A
by trituration
2
Q
constituents
A
Ag 70% Sn 25% Cu 3% Zn 1% Hg 1%
3
Q
amalgam powder
A
50% Sn, Ag - intermetallic compound Ag3Sn - y phase Cu - strength and hardness Zn - scavenger (slag) (Hg - pre-amalgamated)
4
Q
amalgam liquid
A
50%
Hg - triple distilled
5
Q
classification
A
composition
- traditional
- copper enriched
particle shape and size
6
Q
equation for setting reaction chemical symbols
A
Ag3Sn + Hg - Ag3Sn + Ag2Hg3 +Sn7Hg9
7
Q
y
A
Ag3Sn
8
Q
y1
A
Ag2Hg3
9
Q
y2
A
Sn7Hg9
10
Q
equation for setting reaction y
A
y + Hg - y + y1 + y2
11
Q
why are there particles of y in the end product?
A
unreacted particles because insufficient Hg for complete reaction
12
Q
amalgam matrix
A
y1 and y2
13
Q
which is the strongest phase?
A
y
14
Q
particle types
A
spherical/spheroidal
lathe cut
15
Q
lathe cut
A
fill ingots
use heat tx to relieve internal stresses
16
Q
spherical/spheroidal
A
spray molten metal into inert atmosphere
17
Q
y2 properties
A
weak and poor corrosion resistance
18
Q
effect of higher Hg content
A
weaker amalgam as will produce more y2
19
Q
traditional (hand mixed) setting dimensional changes
A
initial contraction - solution of alloy particles in Hg
expansion - y1 crystallisation
20
Q
modern (mechanically mixed) setting dimensional changes
A
small contraction
solid solution of Hg in Ag3Sn
21
Q
zinc and expansion
A
saliva/blood: Zn + H20 - ZnO + H2
bubbles - pressure build up - expansion
downward pulpal pain, upward sits proud. Why Zn free
22
Q
properties depend on:
A
handling factors - proportioning and trituration - condensation (remove excess Hg) - carving and polishing cavity design product corrosion
23
Q
factors reducing strength
A
undermixing too high mercury content after condensation too low condensation pressure slow rate of packing - increments don't bond corrosion creep
24
Q
amalgam disadvantages
A
creep - marginal breakdown
thermal properties
doesn’t bond to tooth
aesthetics
25
amalgam advantages
```
high abrasion resistance
handling ok
radiopaque
smooth surface if polished
short placement time
```
26
advantages of spherical particles
```
less Hg required
higher tensile strength
higher early compressive strength
less sensitive to condensation
easier to carve
lower setting shrinkage
```
27
amalgam corrosion
y2 most electronegative - acts as anode of oxidation cell, will gradually dissolve
- weakens esp at margins
corrosion products may contribute to sealing margins
28
how to reduce corrosion
Cu enriched, polishing margins
| avoiding galvanic cells
29
Cu enriched alloys %
>6% Cu
| non-y2
30
types of Cu enriched alloy
dispersion modified
| single composition
31
dispersion modified Cu enriched alloy
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
32
single composition Cu enriched alloy
powder Ag-Sn-Cu
Ag-Sn-Cu + Hg - Ag-Sn-Cu + y1 + Cu6Sn5
33
benefits of copper enriched
```
higher early strength
less creep
higher corrosion resistance
increased durability of margins
gets rid of y2
no zinc - no delayed expansion
```
34
disadvantages of copper enriched
surfaces more prone to tarnish
35
encapsulated
Hg hygiene
36
indications
moderate and large cavities
posterior teeth
core build ups when definitive Rxs will be indirect cast Rx
37
contraindications
aesthetics important
pt history of sensitivity
can't produce retentive cavity
would need to remove excessive healthy tooth to produce retentive cavity
38
local reactions
lichenoid lesions
galvanic response
tooth discolouration
amalgam tattoo
39
lichenoid reactions
T4 hypersensitivity
| replace with gold/comp
40
galvanic response
battery effect from 2 diff amalgams or amalgam and cast metal
tingling
41
tooth discolouration
corrosion products migrate into tooth surfaces - porous
42
amalgam tattoo
fine amalgam particles migrate into ST
| confuse with melanoma
43
matrices
recreate cavity wall
allows adequate condensation
confines amalgam to cavity
<0.05mm thick
44
condensation
```
vertical and lateral pressure
expels excess mercury
adapts material to cavity walls
reduces layering (homogenous)
eliminates voids
```
45
inadequate condensation
lack of adaptation to cavity
poor bonding between layers
inadequate Hg expression therefore removal
inferior mechanical properties
46
moisture contamination
reduces strength
| increases creep, corrosion, porosity
47
microleakage
passage of fluid and bacteria in microgaps (10 microns) between Rx and tooth
- pulpal irritation and infection
- discolouration
- secondary caries
caused by mechanical loading and thermal stresses
48
wedges
```
adaptation of matrix at cervical margin
temp tooth separation
aids proximal contour
prevents excess amalgam gingivally
prevents movement of matrix band
```
49
why should you always overfill?
increased Hg content on surface - remove by carving
50
retention form
features that prevent loss of Rx in any direction
51
resistance form
features that prevent loss of material due to distortion or fracture by masticatory forces
- sufficient depth
- gingival floor approx 90 degrees to axial wall
52
sealing and bonding: dual cure
no evidence of increased survival
53
mechanical retention
grooves/dimples within cavity design
| pins - Ti/SS
54
pins
increase retention
into D in greatest bulk
never in E or ADJ - will crack
pack amalgam around pin
55
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
56
why should you never use pins with composites?
won't fall out if bond fails
57
minimata convention?
Global treaty to protect human health and env from adverse effects
phase down
58
amalgam legistlative rules
encapsulated
separators - at least 95% particles
authorised waste collection
59
SDCEP guidance
no justification on health grounds for:
- not placing amalgam
- removal of sound Rx
don't use in U15s, pregnant and breastfeeding unless specific medical reason e.g. lack of cooperation and inadequate moisture control
60
carving
recreate anatomical contour
61
finishing
only if need to adjust
62
polishing
considered unnecessary
heat
Hg risk?
63
removal
dam and high vol aspiration
min cutting
greatest Hg release during insertion and removal
64
Hg absorption
vapour into lungs
contact w skin
GIT
gingiva and mucosa
65
GV Black cavity classification
```
1 - pit and fissure
2 - approximal (posterior teeth)
3 - approximal (anterior teeth)
4 - approximal involving incisal angle
5 - cervical surfaces
6 - cusp tips
```
