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DMS > Amalgam > Flashcards

Amalgam Flashcards

1
Q

what are amalgams two main components mixed to make the material

A

mix of liquid mercury and powdered silver, tin, copper and other metals

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2
Q

function of each material in amalgam

A
  1. silver-tin compound (react with Hg forming amalgam)
  2. copper (>strength & hardness)
  3. zinc (scavenger, oxidises and removes slag)
  4. Hg in powder (speeds up reaction)
  5. liquid Hg
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3
Q

particle types in amalgam and their benefits

A
  1. lathe cut
  2. spherical
    - less Hg required
    - >tensile strength
    - > early compressive strength
    - easier to carve
    - less sensitive to condensation technique
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4
Q

setting reaction of amalgam

A

gamma phase 1 (Y1)
- first amalgam matrix molecule (Ag2Hg3)
- binds/incapsulates gamma and gamma 2 particles
- good corrosion resistance (CR)
gama phase 2 (Y2)
- second amalgam matrix molecule (Sn7Hg9)
- weak and bad CR
gamma phase (Y)
- unreacted particles (Ag3Sn)
- good Strength and CR

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5
Q

negative of zinc in amalgam

A

reacts with water to form H2 bubbles causing expansion of material

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6
Q

what is creep of a dental material and why bad for restorations

A

repeatedly applied low stresses (bellow elastic limit) causing material to flow thus permanent deformation
- causes edges of restoration to stand high, break (ditched margins) and allow microleakage

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7
Q

two types of amalgam and two types of the modern version

A
  1. traditional
  2. modern copper enriched
    i. dispersion modified
    ii. single composition types
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8
Q

Describe what ‘dispersion modified’ copper enriched amalgam is

A
  • no gamma 2 phase also (replaced with Cu)
  • spheres and lathe cut
  • two reactions (dispersion modified reaction)
    - silver tin forms halo around silver copper (instead of traditional Y2 SnHg formation alone)
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9
Q

describe what ‘single composition type’ of copper enriched amalgam is

A
  • no gamma 2 phase also
  • spherical OR Lathe cut
  • copper integrated into silver tin particles
    single setting reaction (single composition formulation reaction)
  • gamma 1 encases unreacted silver tin and copper tin (replacing gamma 2)
  • strongest and least creep (BEST OVERALL)
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10
Q

benefits of copper enriched

A
  • higher early strength
  • less creep
  • higher corrosion resistance
  • > durability of margins
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11
Q

lifetime of amalgam restoration

A

4-5 years but can be >10

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12
Q

what material has most similar thermal expansion to dentine and enamel, but sadly has a high thermal conductivity and diffusivity

A

amalgam

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13
Q

general negatives of amalgam

A
  • aesthetics
  • mercury toxicity (env. and patient)
  • no bonding (leakage)
  • corrosion
  • high thermal diffusivity
  • local sensitivity reactions (lichenoid lesions)
  • cavity prep may require excessive removal of sound tooth
  • tooth discolouration
  • amalgam tattoo
  • galvanic response
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14
Q

general positives of amalgam

A 
strong 
hard 
durable 
radiopaque 
user friendly 
long term
quick 
good load bearing
self setting
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15
Q

when use amalgam

A

medium to large posterior restoration

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16
Q

when not to use amalgam

A
  • aesthetics important to patient
  • history of mercury sensitivity
  • too little tooth remaining
  • would have to remove too much healthy tooth
  • pit/small fissure caries
17
Q

two methods of cavity prep for amalgam

A
  1. retentive (no undercut required)

2. resistance (undercut everywhere with flat bottom)

18
Q

additional methods of extra retention in amalgam restorations

A
  1. mechanical
    - grooves or dimples in cavity design
    - pins used
    - placed in only dentine and amalgam packed around for large cavities
    - too many negatives (failed restoration wont fall out so secondary caries free to form, initial stress to tooth and temp. changes can crack dentine)
19
Q

purpose of condensation in placement of amalgam

A
  • brings mercury to top to be carved off

- packs to shape of cavity

DMS (8 decks)

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