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DMS :( > amalgam > Flashcards

amalgam Flashcards

1
Q

how is it formed?

A

by trituration

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2
Q

constituents

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

amalgam powder

A 
50%
Sn, Ag - intermetallic compound Ag3Sn - y phase
Cu - strength and hardness
Zn - scavenger (slag)
(Hg - pre-amalgamated)
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4
Q

amalgam liquid

A

50%

Hg - triple distilled

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5
Q

classification

A

composition
- traditional
- copper enriched
particle shape and size

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6
Q

equation for setting reaction chemical symbols

A

Ag3Sn + Hg - Ag3Sn + Ag2Hg3 +Sn7Hg9

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7
Q

y

A

Ag3Sn

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8
Q

y1

A

Ag2Hg3

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9
Q

y2

A

Sn7Hg9

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10
Q

equation for setting reaction y

A

y + Hg - y + y1 + y2

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11
Q

why are there particles of y in the end product?

A

unreacted particles because insufficient Hg for complete reaction

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12
Q

amalgam matrix

A

y1 and y2

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13
Q

which is the strongest phase?

A

y

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14
Q

particle types

A

spherical/spheroidal

lathe cut

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15
Q

lathe cut

A

fill ingots

use heat tx to relieve internal stresses

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16
Q

spherical/spheroidal

A

spray molten metal into inert atmosphere

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17
Q

y2 properties

A

weak and poor corrosion resistance

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18
Q

effect of higher Hg content

A

weaker amalgam as will produce more y2

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19
Q

traditional (hand mixed) setting dimensional changes

A

initial contraction - solution of alloy particles in Hg

expansion - y1 crystallisation

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20
Q

modern (mechanically mixed) setting dimensional changes

A

small contraction

solid solution of Hg in Ag3Sn

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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

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22
Q

properties depend on:

A 
handling factors
 - proportioning and trituration
 - condensation (remove excess Hg)
 - carving and polishing
cavity design
product
corrosion
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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
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24
Q

amalgam disadvantages

A

creep - marginal breakdown
thermal properties
doesn’t bond to tooth
aesthetics

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25
Q

amalgam advantages

A 
high abrasion resistance
handling ok
radiopaque
smooth surface if polished
short placement time
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26
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
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27
Q

amalgam 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

28
Q

how to reduce corrosion

A

Cu enriched, polishing margins

avoiding galvanic cells

29
Q

Cu enriched alloys %

A

> 6% Cu

non-y2

30
Q

types of Cu enriched alloy

A

dispersion modified

single composition

31
Q

dispersion modified Cu enriched alloy

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

32
Q

single composition Cu enriched alloy

A

powder Ag-Sn-Cu

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

33
Q

benefits of copper enriched

A 
higher early strength
less creep
higher corrosion resistance
increased durability of margins
gets rid of y2
no zinc - no delayed expansion
34
Q

disadvantages of copper enriched

A

surfaces more prone to tarnish

35
Q

encapsulated

A

Hg hygiene

36
Q

indications

A

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

37
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

38
Q

local reactions

A

lichenoid lesions
galvanic response
tooth discolouration
amalgam tattoo

39
Q

lichenoid reactions

A

T4 hypersensitivity

replace with gold/comp

40
Q

galvanic response

A

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

41
Q

tooth discolouration

A

corrosion products migrate into tooth surfaces - porous

42
Q

amalgam tattoo

A

fine amalgam particles migrate into ST

confuse with melanoma

43
Q

matrices

A

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

44
Q

condensation

A 
vertical and lateral pressure
expels excess mercury
adapts material to cavity walls
reduces layering (homogenous)
eliminates voids
45
Q

inadequate condensation

A

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

46
Q

moisture contamination

A

reduces strength

increases creep, corrosion, porosity

47
Q

microleakage

A

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
Q

wedges

A 
adaptation of matrix at cervical margin
temp tooth separation
aids proximal contour
prevents excess amalgam gingivally
prevents movement of matrix band
49
Q

why should you always overfill?

A

increased Hg content on surface - remove by carving

50
Q

retention form

A

features that prevent loss of Rx in any direction

51
Q

resistance form

A

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
Q

sealing and bonding: dual cure

A

no evidence of increased survival

53
Q

mechanical retention

A

grooves/dimples within cavity design

pins - Ti/SS

54
Q

pins

A

increase retention
into D in greatest bulk
never in E or ADJ - will crack
pack amalgam around pin

55
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

56
Q

why should you never use pins with composites?

A

won’t fall out if bond fails

57
Q

minimata convention?

A

Global treaty to protect human health and env from adverse effects
phase down

58
Q

amalgam legistlative rules

A

encapsulated
separators - at least 95% particles
authorised waste collection

59
Q

SDCEP guidance

A

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
Q

carving

A

recreate anatomical contour

61
Q

finishing

A

only if need to adjust

62
Q

polishing

A

considered unnecessary
heat
Hg risk?

63
Q

removal

A

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

64
Q

Hg absorption

A

vapour into lungs
contact w skin
GIT
gingiva and mucosa

65
Q

GV Black cavity classification

A 
1 - pit and fissure
2 - approximal (posterior teeth)
3 - approximal (anterior teeth)
4 - approximal involving incisal angle
5 - cervical surfaces
6 - cusp tips

DMS :( (18 decks)

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