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CONS > Amalgum > Flashcards

Amalgum Flashcards

1
Q

What is amalgam

A

An alloy containing mercury

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2
Q

What is an alloy?

A

A mixture of 2 or more metals in which the primary constituent is a metal

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3
Q

What are the constituents of amalgam?

A

Mercury
Silver
Tin
Copper
Trace elements (zinc, silver, palladium)

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4
Q

What are the types of amalgam and what is conventional amalgam?

A

Several types of amalgam alloy. They all contain tin, most have copper and some have zinc
Conventional amalgam is 67-74 percent silver, 25-28 percent tin, 2 percent zinc, 3 percent mercury

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5
Q

What does silver do?

A

Increases strength and hardness

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6
Q

What does tin do?

A

Increases plasticity- aids amalgamation process due to its high affinity for mercury

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7
Q

What does copper do?

A

Reduces plasticity
Increases strength and hardness

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8
Q

What does tin do?

A

Not needed by prevents oxidation during manufacture

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9
Q

What does mercury do?

A

Activates the reaction- the only metal that can bind to metals in such away that the material can be easily manipulated into the cavity

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10
Q

Palladium

A

Reduces corrosion and increases lustre

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11
Q

Indium

A

Reduces creep

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12
Q

Classification of amalgam

A

Copper content- low copper content 0-6 percent high copper content > 6-13 percent
Zinc content- zinc containing more than 0.01-2 percent, non-zinc <0.01 percent
Shape of alloy particles- spherical, lathe cut or admixed

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13
Q

What are the key properties of amalgam

A

Strength-
Corrosion
Creep
Thermal properties

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14
Q

Strength

A

Compressive strength>over tensile strength: note amalgam is weak in thin sections
Affected by: type of alloy, shape and size of particle, amount of mercury and manipulation of the mix
Gamma phase 2 is the weakest so you want to limit this phase, compress into cavity so that unreacted core of particles are packed closely together and mercury rich layer is brought to the surface and removed.

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15
Q

Corrosion

A

Heterogenous, multiphase structure
May eventually form a seal
Can be accelerated in a ‘Galvanic cell’

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16
Q

Creep

A

The flow is caused by loads acting over long periods
Leads to unsupported enamel over the cavity margin, further weakened by corrosion, leads to ditching of margins

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17
Q

Thermal properties

A

High value of thermal conductivity
Coefficient of thermal expansion 3x that of dentine

18
Q

Advantages of amalgam

A

Strength
Ease of handling and placement (less technique and moisture sensitive than other materials)
Wear resistant
Longevity
Cost effective
Reduced marginal leakage (marginal seal improves due to slowed corrosion over time)

19
Q

Disadvantages of amalgam

A

Poor aesthetics (not tooth coloured)
Does not adhere to tooth structure
Galvanic effects
High thermal conductivity
Controversy over biocompatibility

20
Q

Clinical uses of amalgam

A

Large posterior restorations
Where occlusal forces are high
Deep interproximal boxes
Cavities where moisture control is likely to be difficult
As a core material (Nayyer core)

21
Q

Placement of amalgam- cavity preparation requirements

A

Must be retentive- use of undercuts
Bucco palatal/lingual width important in long term survival (avoid using amalgam in thin sections)
Must be sufficient enough to withstand considerable condensation forces used during packing/placement
Cavo-surface angle must be 90 degrees in order to generate an amalgam surface angle of 90 degrees (Avoid using amalgam in thin sections)

22
Q

What are the other options for amalgam placement?

A

Slots, locks and grooves

23
Q

Talk about grooves and locks

A

Retentive groove in dentine whose lengths are in the horizontal plane
Locks in the vertical plane

24
Q

Talk about1) dentine pins and 2) their considerations

A

Self threaded dentine pins, stainless steel, placed using a contra angled handpiece with a small round bur.
Pin hole smaller than the pin
Inter pin distance important
Nature of dentine important
Consider tooth alignment, age of pulp chamber.

Pin size/characteristics
Pin location
Pin number
Pin angulation
Pin hole prep

25
Q

Complications with dentine pins

A

Pin breakage
Loose pins
Heat generation 80 degrees
Dentine crazing-microfracture
Perforation into pulpal space

26
Q

What are the liners used with amalgam?

A

RGMI liners
Calcium hydroxide
Calcium silicates

27
Q

Summary of rules for amalgum preparations?

A

Remove all caries at the EDJ
Remove all gross caries and access the cavity base
2mm occlusal-gingival thickness of amalgum
No unsupported enamel (90 degrees cavo surface angle)
Break proximal contacts
Adequate retention and resistance form
Box and isthmus should each be self retentive
Flat occlusal floor

28
Q

What to consider in amalgum placement?

A

Significant packing pressure is required
Correct condensation should result in reduction overall mercury content
Vertical and lateral condensation is required
Small vs large pluggers
Should see a ‘puddle’ of mercury if sufficient force is used.

29
Q

What to remember when carving and shaping the restoration?

A

Pack amalgum against the cusps, not just in an apical direction
Use a probe to define the marginal ridge
Discoid cleoid/ wards carver to contour the fissure pattern
Remove excess and smooth with a damp cotton roll

30
Q

Finishing

A

Amalgum cannot be finished immediately after placement
Fine diamonds/amalgam finishing burs to remove excess or redefine fissure pattern (24 hours after placement)
Brown/Green Shofu points to obtain lustre
Use for only short periods and keep tooth wet to avoid excessive generation of heat

31
Q

Why finish an amalgum restoration?

A

Aids marginal integrity
Reduces plaque accumulation
Improves appearance?

32
Q

Bonded amalgum restorations-technique?

A

Walls are prepared as for placement of composite restorations
Tooth isolated with vaselined matrix band
Etch, wash, lightly dry and then coat with a thin layer of bond
Amalgam is packed into cavity so that amalgam and air-inhibited layer of the adhesive resin set at the same time and develop a mechanical interlock

33
Q

What are the advantages of bonded amalgum restorations?

A

Increased amalgam retention
Conservation of tooth structure
Reduced microleakage
Fracture resistance of tooth reinforced initially. However, research suggests breakdown of bond after approx. 1 year.
May reduce post-op sensitivity by sealing the dentine tubules

34
Q

Bonded amalgum restorations disadvantages

A

Few long term studies on longevity
Bond may breakdown over time
Uniform placement of bond on cavity walls is difficult
Longer chairside time
Expensive materials

35
Q

Clinical indications of bonded amalgum restorations

A

Useful for large multi-surface amalgams
Amalgam repairs
Not recommended for routine amalgam cavities with sufficient mechanical retention and undercuts

36
Q

Does adding adhesive designed to bond dental amalgam fillings to teeth make the fillings perform better and last longer than fillings without it? Cochrane OH group March 2016

A

Authors’ conclusions:

There is no evidence to either claim or refute a difference in survival between bonded and non-bonded amalgam restorations

37
Q

Longevity

A

Studies report 50 percent survival times for class I II III restorations
High copper amalgums have a much higher survival rate 5 years at 97

38
Q

Causes of failure of amalgum restorations

A

Recurrent caries (5-50 percent)
Marginal ditching
Excessive creep
Bulk fracture
Loss of retention
Failure rates increase with the size of restoration

39
Q

How to reduce failure from amalgum restorations

A

Reduce caries risk (prevention)
Use high copper blended amalgum
Careful cavity design

40
Q

Controversy around amalgum

A

Well known toxicity of mercury
Studies have linked amalgum with health problems like Alzheimer’s, MS, immune system dysfunction, behavioural problems

However there is little to no evidence linking systemic illness with amalgum

41
Q

How to manage the risk of amalgum?

A

The patient-
Estimates of daily total amalgam associated mercury intakes are well below threshold levels to which all workers can be exposed to on a daily basis without any adverse effects (set by the World Health Organisation at 25μg/m3).

The dentist and assistant-
The World Health Organisation has set the threshold limit value (TLV) for short term occupational exposure at 500μg/m3 of mercury vapour.
During placement, removal levels highest – with strict adherence to guidelines TLV not exceeded

42
Q

When should amalgum not be used?

A

Confirmed allergy to mercury
1% of the population have true allergies to mercury
Reactions may be local or widespread
Those suspected of having an allergy should receive patch testing

In Pregnancy/breast feeding- current NHS guidance
Patients under 15 years (can be used with justifications)

CONS (10 decks)

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