Amalgam

Question 1

when is mercury vapour produced?

Answer 1

on removal of amalgam

Question 2

why would you use amalgam for a restoration?

Answer 2

not good moisture control, large occlusal load

Question 3

1895 amalgam

Answer 3

GV Black- 67% silver 27% tin 5% copper 1% zinc

Question 4

what is creep?

Answer 4

when amalgam flows out of restoration and becomes proud and occlusal loading causes fractures

Question 5

how does copper contribute to amalgam?

Answer 5

improves strength and reduces creep and corrosion. eliminates the tin mercury phase, no expansion

Question 6

what is the tin mercury phase?

Answer 6

gamma 2 phase weakest phase- causes creep.

Question 7

what happened in 1833

Answer 7

Crawcour brothers introduce amalgam to US.
Powdered silver coins mixed with mercury.
Expanded on setting

Question 8

what are operator controlled variables when using amalgam?

Answer 8

trituration
condensation
burnishing
polishing

Question 9

describe titration, overtrituration and undertrituration

Answer 9

Mixing time
refer to manufacturer
recommendations
Overtrituration
“hot” mix
sticks to capsule
decreases working / setting time
slight increase in setting contraction
Undertrituration
grainy, crumbly mix

Question 10

describe condensation for lathe cut alloys, spherical alloys and admixture alloys

Answer 10

lathe-cut alloys
small condensers 
high force
spherical alloys
large condensers 
less sensitive to amount of force
vertical / lateral with vibratory motion
admixture alloys
intermediate handling between lathe-cut and spherical

Question 11

what are the condensation rules?

Answer 11

Condenser must fit!! (outline form / isthmus - large enough for the small end of the amalgam condenser).
Place the amalgam in small increments.
Condense with heavy pressure (hear squeak).
Over pack – remove the mercury rich layer by carving.

Question 12

what are the carving rules

Answer 12

Carve back to the cavity outline.
Removes Hg rich layer.
Simulate lost anatomical form.
Aim for a smooth amalgam/enamel junction.
Do not reproduce deep fissures.
Remove gross gingival excess.
Always check that the restoration conforms to the patient’s occlusion.

Question 13

describe burnishing

Answer 13

Pre-carve
removes excess mercury
improves margin adaptation
Post-carve
improves smoothness
Combined
less leakage

Question 14

describe polishing of amalgam

Answer 14

After 24 hours of setting time.
Increased smoothness
Decreased plaque retention
Decreased corrosion
Clinically effective?
no improvement in marginal integrity
Mayhew, Oper Dent 1986
Collins, J Dent 1992
N.B. Avoid overheating

Question 15

why would you bond an amalgam?

Answer 15

When there is not enough tooth substance to allow for the retention of the amalgam – e.g. missing cusp.
To achieve a complete marginal seal – prevents ingress of bacteria – protects the pulp

Question 16

what are advantages of a bonded amalgam

Answer 16

Reduced need for preparation of retentive features in the cavity
No need to use pins
Reduced marginal leakage and postoperative sensitivity
Reinforcement of tooth structure

Question 17

disadvantages of a bonded amalgam

Answer 17

Time consuming
More expensive than traditional amalgam restoration

Lack of data on long –term clinical effectiveness

Question 18

what technique is used to place a bonded amalgam

Answer 18

Liner if appropriate
Acid etch margins
Apply prime and bond
Place ‘Rely–x– arc’ or ‘Smartcem’ (chemical cure resin-based cement) and leave uncured
Condense amalgam, carve etc.

Question 19

explain amalgam toxicity

Answer 19

Side effects are either toxic or allergic.
Toxicity – mainly from mercury (Hg).
Allergy – to any component – amalgam allergy may result in contact dermatitis, oral lichen planus etc.
Theoretical risk of foetal damage as Hg can cross the placenta.

Question 20

safety precautions when handling amalgam

Answer 20

Training

Avoid accidental spillage of mercury (most amalgam is encapsulated nowadays).

Deal with the spillage immediately (every practice should have a mercury spillage kit on premises that deals with cleaning spilt mercury).Avoid heating any spilt mercury
Appropriate storage of waste amalgam
Waste collected by approved contractor (NOT put down sink!!)
Well ventilated surgery
Aspiration, venting externally with Hg removal filter

Question 21

symptoms of mercury poisoning

Answer 21

Headaches
GI upsets
Dyspepsia
Tremors
Salivation / xerostomia
Severe gingivitis
Fatigue / irritability
Oedema of face and ankles
Character changes