Amalgum

Question 1

What is amalgam

Answer 1

An alloy containing mercury

Question 2

What is an alloy?

Answer 2

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

Question 3

What are the constituents of amalgam?

Answer 3

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

Question 4

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

Answer 4

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

Question 5

What does silver do?

Answer 5

Increases strength and hardness

Question 6

What does tin do?

Answer 6

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

Question 7

What does copper do?

Answer 7

Reduces plasticity
Increases strength and hardness

Question 8

What does tin do?

Answer 8

Not needed by prevents oxidation during manufacture

Question 9

What does mercury do?

Answer 9

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

Question 10

Palladium

Answer 10

Reduces corrosion and increases lustre

Question 11

Indium

Answer 11

Reduces creep

Question 12

Classification of amalgam

Answer 12

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

Question 13

What are the key properties of amalgam

Answer 13

Strength-
Corrosion
Creep
Thermal properties

Question 14

Strength

Answer 14

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.

Question 15

Corrosion

Answer 15

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

Question 16

Creep

Answer 16

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

Question 17

Thermal properties

Answer 17

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

Question 18

Advantages of amalgam

Answer 18

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)

Question 19

Disadvantages of amalgam

Answer 19

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

Question 20

Clinical uses of amalgam

Answer 20

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)

Question 21

Placement of amalgam- cavity preparation requirements

Answer 21

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)

Question 22

What are the other options for amalgam placement?

Answer 22

Slots, locks and grooves

Question 23

Talk about grooves and locks

Answer 23

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

Question 24

Talk about1) dentine pins and 2) their considerations

Answer 24

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

Question 25

Complications with dentine pins

Answer 25

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

Question 26

What are the liners used with amalgam?

Answer 26

RGMI liners Calcium hydroxide Calcium silicates

Question 27

Summary of rules for amalgum preparations?

Answer 27

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

Question 28

What to consider in amalgum placement?

Answer 28

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.

Question 29

What to remember when carving and shaping the restoration?

Answer 29

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

Question 30

Finishing

Answer 30

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

Question 31

Why finish an amalgum restoration?

Answer 31

Aids marginal integrity Reduces plaque accumulation Improves appearance?

Question 32

Bonded amalgum restorations-technique?

Answer 32

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

Question 33

What are the advantages of bonded amalgum restorations?

Answer 33

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

Question 34

Bonded amalgum restorations disadvantages

Answer 34

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

Question 35

Clinical indications of bonded amalgum restorations

Answer 35

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

Question 36

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

Answer 36

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

Question 37

Longevity

Answer 37

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

Question 38

Causes of failure of amalgum restorations

Answer 38

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

Question 39

How to reduce failure from amalgum restorations

Answer 39

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

Question 40

Controversy around amalgum

Answer 40

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

Question 41

How to manage the risk of amalgum?

Answer 41

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

Question 42

When should amalgum not be used?

Answer 42

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)