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Chemistry > Direct Dental Restorative Materials: Dental Amalgam W6 > Flashcards

Direct Dental Restorative Materials: Dental Amalgam W6 Flashcards

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1
Q

What is the difference between an alloy, amalgam and dental amalgam

A

Alloy: Combination of >1 metals

Amalgam: Alloy of HG + 1 or more other metals ie. Alloy with Hg in it

Dental Amalgam: Mix of liquid Hg with solid alloy particles (mainly Ag, Sn and Cu) = Amalgam Alloy

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2
Q

What are the advantages of Amalgam

A
  • Good toughness and wear resistance
  • Good compressive strength (for stress bearing areas)
  • Good longevity
  • Pervents Marginal leakage
  • Easy to use
  • Economical
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3
Q

What are the disadvantages of Amalgam

A
  • Not aesthetically pleasing
  • Brittle
  • Loss of sound tooth structure (if small restoration req.)
  • Discolouration of tooth structure
  • Metallic taste
  • Corrosion and galvanism
  • Limited support for weakened tooth structure
  • Concerns about waste disposal and Hg toxicity
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4
Q

What are the indications and contraindications of Amalgam

A

Indications
- Class 1, 2, 3 and 5 in unaestetic areas or moderate to large restorations
- As core build up - for crowns and bridges
- Restorations covering cusps - using pins
- Restorations with a heavy occlusal contact
- Restorations that cannot be isolated easily
- in teeth acting as abutments (anchors of bridge) for removal appliances

Contraindications
- Anterior teeth or anywhere aesthetic
- Small-moderate class 1,2,6 that can be well isolated

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5
Q

How can you classify amalgams?

A

By…
# of alloy metals
unmixed or admixed alloys
particle shape
amount of Zn
particle size
copper content*
noble metals
generation of development

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6
Q

What are the main components of dental analgam alloy*

A

Main components…
Silver (Ag)
Tin (Sn)
Copper (Cu) - 13-30% high Cu alloy, <5% low Cu alloy

Lesser amounts of…
Indium, Palladium, Platinum, Zinc (>0.01% = labelled as zinc containing), Mercury

Note: amalgam as a whole main component = Hg - 50%

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7
Q

Describe the various shapes of dental amalgams (Cu classified)

A

Low Cu Alloys
Lathe-cut or spherical particles

High Cu Alloys
Unicompositional - spherical particles
Admixed - irregular spherical ie. different sizes but same composition or mixture of particles (Ag+Sn vs Ag+Cu) = MOST PROMINENT NOW

Differences in shape lead to different compositions

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8
Q

Besides Hg, __ is the next major component of dental amalgam. What are the benefits of including it?

A

Ag (Silver)
- ⅔ of amalgam alloy
- Increases strength, expansion on setting and resistance to corrosion

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9
Q

___ is the second largest alloy component of dental amalgam, why do we include it and what are the drawbacks?

A

Tin (Sn)
- ¼ of Amalgam alloy
- Causes setting contraction, decreases stength and resistance to corrosion
- Readily combines with Hg to form Y2 - contributes to failure

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10
Q

Cu, Zn and In/Pd are present as alloy components of dental amalgam. What are the benfits of including them?

A

Copper (Cu) - preferred
- Increases hardness, strength and setting expansion

Zinc (Zn) - not preferred
- During manifacture it decreases the oxidation of other alloys and decreases marginal failure
- Causes delay in setting expansion

Indium (In)/Palladium (Pd)
- Increases plasticity and resistance to deformation

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11
Q

What happens in the amalgamation reaction for low-copper amalgam?*

A

Ag3Sn + Hg -> Ag3Sn (Y) + Ag2Hg3 (Y1) + Sn8Hg (Y2)

Tituration mixes Ag3Sn with Hg = Ag2Hg3 (Y1) + removal of surface oxides that could have formed on alloy particles
Y2 = Sn8Hg (phase we dont want!)

Early in working time = few Y1 and Y2 = soft, condensable, carvable
Late in working time = more Y1 and Y2 = harder and stronger

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12
Q

Which phases are favourable/unfavourable in an amalgamation reaction - low copper amalgam

A

Y (Ag3Sn): 27-35% - strongest, most corrosion resistant

Y1 (Ag2Hg3): 54-56% - somewhat strong and corrosion resistant, but brittle. The matrix phase that holds this multi phase material together

Y2 (Sn8Hg): 11-13% - weakest and most corrosion prone

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13
Q

What is the main difference between a low copper amalgam and a high copper amalgam ie. how does this effect the phases that are present?

A

Increased Cu % = no Y2 phase

instead Sn + Cu form multiple products (ie. Sn is completely occupied by the Cu)

= increased strength, corrosion resistance, decerased marginal breakdown

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14
Q

What is Creep?

A

A slow change in shape caused by compression - Sliding of Y1 grains.
-> presence of Y2 predicts the extent of marginal fracture ie. High copper (no Y2) = low creep value

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15
Q

What are the changes in Amalgam during formation? Ie. Dimensional changes

A

Stage 1: Initial contraction (within first 20 mins)
-> Alloy particles dissolve in Hg = contraction

Stage 2: Expansion
-> formation and growth of crystal matrix around unconsumed alloy particles

Stage 3: Limited delayed contraction (after 6-8h)
-> If contamination with H20 occurs with Zn containing alloy = dimesional changes = sensitivity

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16
Q

How do dimentional changes differ in Low-high copper alloys

A

High-copper admix = smallest dimentional change
Low-copper lathe-cut alloy = largest dimentional change

17
Q

Delays in expansion cause…

A

Post-operative sensititiy
Protrusion of restoration from cavity
Microleakage
Perforations
Increased flow and creep

  • can occur 10-12 days following placement
18
Q

What are the factors that affect dimensional changes?

A

Particle size and shape (homogeneous=smoother=coat with Hg easier=faster amalgamation=limited expansion)

Hg content (more expansion when high Hg)

Manipulation

19
Q

Corrosion definition in relation to amalgams…

A

Progressive destruction of a metal by chemical or electrochemical reactions in the environment
= increased porosity, reduced marginal integrity, decreased strength, release of metallic products into oral cavity

20
Q

What factors affect manipulation (& performance) of amalgam

A

Manufacturing
- Alloy composition; Hg content, particle size, shape, distribution. Alloy form (powder, tablet, capsule)

Dentist
- Trituration (technique, speed and time, too much tituration), Condensation, burnishing and carving, finishing and polishing

21
Q

Define condensation (in relation to amalgam manipulation)

A

Incremental placement and compression of amalgam into cavity prep = removes excess Hg, adapts to prep walls, reduce voids = homogeneous mass
- Within 3 minutes following tritration

22
Q

What are the objectives of burnishing and carving amalgam

A

Removes overhangs, restore physiological contours, maintain interproximal contacts

Burnishing: reduces size and number of voids, excess Hg at surface discarded

23
Q

When does finishing and polishing occur for amalgam and what are the objectives

A

24 hours after restoration is placed (to allow fully set)
- reduce concentration of stress, minimise corrosion, prevent adherance of plaque = extend lifespan of restoration

24
Q

What are the 3 different forms of Hg and relative toxicity issues

A

Elemental - liquid (No issues) and vapour (absorbed=Issue)

Inorganic - low toxicity, harmless if swallowed

Organic - toxic at low concentrations (not used for amalgam)

Hg released from dental procedures does not elict toxic reactions as it is not enough (small quantity)

25
Q

Mecury release is greatest in… (low or high copper amalgams?)

A

Low copper (lots of Tin) = increased corrosion and porosities

26
Q

What are some of the signs that the Hg filling isnt biocompatiple

A

Immediate response: rash on face and limbs, dematitis

Long term response: oral lichen planus, erosive areas on tongue or mucosa adjacent to restorations and amalgam tattoo if excess Hg not removed (dark silver spot on gingiva)

27
Q

What are some of the precautions taken when working with Hg

A

Well ventilated workplace = fresh air exchange
Only use capsules
Amalgamator has enclosed arm
Non-absorbent floor coverings = easy to clean
Gloves

Chemistry (7 decks)

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