chapter 6: amalgam and direct gold

amalgam

metal alloy with mercury as one of the elements

in dentistry, equal parts of a powdered metal alloy and liquid mercury. most commonly supplied in a capsule

direct restorative material held in place with mechanical retention

cavity prep is overfilled and then condensed and carved

setting takes place during trituration, condensing, and carving

amalgamator/triturator

machine used to mix powdered alloy and liquid mercury (performs amalgamation/trituration)

lathe-cut alloys

particles of amalgam made by grinding metal

firmer, easier to use for interproximal restorations

spherical alloys

particles of amalgam made my spraying molten metal into an inert atmosphere- droplets cool into spheres

softer, sets faster because less mercury is used (takes less mercury to wet the surface)

packes better

admixed/blended alloy

mixture of lathe-cut and spherical alloys

advantages of using dental amalgam

tough, wear resistant, long-lasting

cost effective (but as the price of silver goes up, so does amalgam)

seals margins- margins fill with the corroded material from the amalgam and seal the interface (not necessarily a good predictor of recurrent decay) (not failed unless decay is under)

works well in a wet environment (not very technique sensitive)

longevity of material- depends on size of filling, client diet, and oral hygiene

history of dental amalgam

initially developed in France in the 1800’s

high-copper amalgam was introduced 1960

1920- US gov developed standard test for amalgam

low-copper amalgam and components

not used much today

65% silver- causes setting expansion and increased strength and corrosion resistance

25% tin- causes setting contraction and decreases strength and corrosion resistance

<6% copper- same as silver when supplied in a low copper alloy

1% zinc- reduces oxidation of the other metals

other materials- gold, palladium, indium, mercury

*less mercury, the stronger the finished product

low copper amalgam microstructure phases

tin and mercury is the weakest

low copper amalgam setting reaction

mercury + alloy → dissolve → new solid forms and sets in about 24 hours

high-copper dental amalgam and types

most are superior to low-copper b/c eliminated the tin mercury phase (less corrosion)

admix- blended, mixture of lathe-cut and spherical particles

spherical- single composition, high-copper, spherical

high copper amalgam setting reaction

10%-30% copper

tin reacts with copper

no Sn-Hg reaction product

manufacturer controlled factors affecting handling and performance

alloy composition and shape

particle size and distribution

rate of setting reaction

supplies as powder, powder pressed into a tablet, capsule (powder and tablet require the addition of liquid mercury)

dentist controlled factors affecting handling and performance

addition of precise amount of mercury when not using a premeasured capsule

trituration: over- crumbly, hard to pack, can cause voids, shorter working time

• under- mushy and grainy, hard to pack

• properly- cohesive, smooth, plasticy mass

oral cavity factors affecting handling and performance

condensation- avoid saliva contamination

anatomical form- avoid interproximal contacts and overhanging margins (marginal defects increase chance of recurrent decay)

dimensional change

want minimal change in dimension after condensation to decrease risk of leakage and postop sensitivity

affected by: mercury/alloy ratio, trituration and condensation techniques

strength

greater at 24 hours for all types

high compressive strength, low shear anf tensile strength

should be 1.5 mm thick

needs to be supported by tooth structure

creep

setting expansion

in high copper amalgam the phase that causes this has been eliminated

corrosion (oxidation)

occurs when two dissimilar metals exist in the mouth (amalgam has more than two metals)

acid environment promotes corrosion

can occur on surface and within the restoration

corrosion by-products fill an open margin and seal the margin

more susceptible to fracture

indications of decay

darkened, gray hue

use of dental amalgam

cost effective

used in class I, II, V, and VI carious lesions

can be used in cingulum pits in anterior teeth

used as core or build up before crown

on top of a cavity varnish- reduces leakage

effect of moisture

zinc-containing amalgam is more affected by moisture than non-zinc

zinc reacts with water → hydrogen gas and causes a delayed expansion of the amalgam → increased corrosion and reduced longevity

finishing and polishing

provides proper contour and margins are continuous w tooth

smooth surface discourages plaque accumulation

mercury toxicity

toxic to kidneys, lungs, and CNS

high vapor pressure, evaporates at room temperature and absorbed by lungs (most likely route of entry)

not a concern for clients

T or F: it is unethical for dentists to recommend replacing amalgam for aesthetic and health concerns

T- only recommend if they are failing or if patient wants them replaced

dentists have lost their license for recommending clients replace amalgam fillings due to health concerns

direct gold restorations

used for small restorations

Class I, II, III, and V restorations and to repair gold crowns

lacks strength of other metallics

products for direct gold restorations

mat, rope, foil, and other products

covered in chemical protectant that must be burned off with ethyl alcohol torch (annealing)

labor intensive to condense and carve

easily contaminated before making it into the mouth