Amalgam Flashcards
when is mercury vapour produced?
on removal of amalgam
why would you use amalgam for a restoration?
not good moisture control, large occlusal load
1895 amalgam
GV Black- 67% silver 27% tin 5% copper 1% zinc
what is creep?
when amalgam flows out of restoration and becomes proud and occlusal loading causes fractures
how does copper contribute to amalgam?
improves strength and reduces creep and corrosion. eliminates the tin mercury phase, no expansion
what is the tin mercury phase?
gamma 2 phase weakest phase- causes creep.
what happened in 1833
Crawcour brothers introduce amalgam to US.
Powdered silver coins mixed with mercury.
Expanded on setting
what are operator controlled variables when using amalgam?
trituration
condensation
burnishing
polishing
describe titration, overtrituration and undertrituration
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
describe condensation for lathe cut alloys, spherical alloys and admixture alloys
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
what are the condensation rules?
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.
what are the carving rules
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.
describe burnishing
Pre-carve removes excess mercury improves margin adaptation Post-carve improves smoothness Combined less leakage
describe polishing of amalgam
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
why would you bond an amalgam?
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
what are advantages of a bonded amalgam
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
disadvantages of a bonded amalgam
Time consuming
More expensive than traditional amalgam restoration
Lack of data on long –term clinical effectiveness
what technique is used to place a bonded amalgam
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.
explain amalgam toxicity
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.
safety precautions when handling amalgam
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
symptoms of mercury poisoning
Headaches GI upsets Dyspepsia Tremors Salivation / xerostomia Severe gingivitis Fatigue / irritability Oedema of face and ankles Character changes
