Dental Amalgam

Objectives Differentiate between amalgam alloy and amalgam Describe the function of major elements in amalgam Describe the effect of moisture contamination on dental amalgam Describe acceptable mercury hygiene practices Explain the trituration and setting processes Describe the reactions involved in both conventional and high-copper amalgams Describe the self-sealing property of amalgam

Definitions Amalgam alloy Dental Amalgam The powdered metal before it is mixed with mercury Dental Amalgam Powdered metal mixed with mercury used to restore teeth Amalgamation Combining mercury with an alloy of silver, tin, and copper Trituration Mechanical mixing of amalgam alloy particles with mercury to achieve amalgamation

Advantages of Dental Amalgam Tough, wear resistant Long lasting Cost-effective Self-sealing margins as material corrodes Least technique-sensitive material Might work in wet, contaminated field Life expectancy of the material depends on patient’s diet & OH and on the size of the restoration

Definitions cont. Condensation Ditching Use of mechanical or hand instruments to place or condense the amalgam mass into the cavity preparation Ditching Gradual deterioration of amalgam at the tooth-restoration interface Microleakage may occur

Composition of Modern Amalgam Mercury Forms workable mass Silver Increases setting expansion and strength Tin Helps amalgamation Decreases expansion Copper Increases strength, hardness & setting expansion; redness Zinc Minimizes oxidation Palladium Whitens

Conventional (low copper) alloy Black’s composition 65% silver (Ag) 25% tin (Sn) 5% copper (Cu) 1% zinc (Zn) (sometimes)

Setting Reaction of Low Copper Amalgam γ + Hg γ + γ1 + γ2 γ = Ag-Sn alloy γ1 = Ag-Hg phase γ2 = Sn-Hg phase Mercury is absorbed by the alloy particles and dissolves the surfaces of them Liquid mercury becomes saturated with silver & tin and the Ag-Hg and Sn-Hg precipitate until solid mass results – may take as long as 24 hours to completely harden

High Copper High Copper Dental Amalgam > 6% Copper Almost universally used today Higher strength Higher corrosion resistance Less marginal breakdown Low creep Types of high copper Admixed, blended Dispersion

Admixed versus Single Composition Dispersion alloys Oldest type of high Cu Alloy powder is a mixture of two alloys Mix of spherical and lathe-cut particles Various sizes Adapt better to cavity walls Produce better contacts

Single Composition Alloy powder contains powder particles of one composition Spherical or comminuted Require less mercury for mixing Require less condensation force 60% of dentists use admixed 40% of dentists use spherical

Spherical High Copper Amalgam Tytin is good example

Zinc versus Non-zinc Zinc aids in minimizing the oxidation of other metals present in the alloy during the manufacturing process Zinc-containing Zinc in excess of .01% Non-zinc Zinc less than .01%

Definitions-Physical Properties Excessive expansion Put pressure on pulp, protrusion of restoration or fracture Excessive contraction Pulls away from the cavity walls Permits leakage between tooth and restoration Strength Gains strength in 1 wk. Variables Trituration Residual Mercury Porosity Creep Deforms under a constant load

Physical Properties cont. Tarnish = Surface discoloration Can be removed by polishing Corrosion Loss of surface by chemical attack Affects surface and subsurface Deterioration by chemical or electrochemical action

Mercury Content and Function Refers to the amount of mercury in the amalgam mix 40-50% mercury in mix is common Liquid which provides the “plastic” mass so that the alloy can be inserted into cavity preparation Acts as a matrix material to bind alloy particles

Manipulative Variables Original alloy-mercury ratio of the mix Amount of trituration Pressure and technique of condensation Time elapsed during mixing and condensation Mercury content highest at margins

Excessive vs. Insufficient Mercury Effects of excessive mercury Serious loss of strength Increase in creep and marginal breakdown Effects of insufficient mercury Stiff, grainy mix that is difficult to condense Final restoration probably contains voids that decrease strength

Trituration time Varies with brand of alloy, alloy-mercury ratio, size of the mix, type of amalgamator, and speed setting Undertrituration Grainy mix with excess mercury Overtrituration Excessive heat production Causes mix to set up too quickly

Triturator Ivoclar Vivodent Silamat S5

Effects of Moisture Contamination Excessive expansion Moisture and zinc Liberates hydrogen gas within the amalgam mass which leads to delayed expansion beginning at 1 week and continues for months Protruding restorations lead to: secondary caries at overhang, corrosion, loss of strength, postoperative pain from pressure

Finishing and Polishing After carving, amalgam is smoothed by burnishing it with a ball burnisher Polishing Reduces surface roughness, eliminates pits from carving Increases life of restoration if done periodically by preventing tarnish & corrosion

Marginal Breakdown In time, most amalgam margins become chipped or ditched Most likely in the following Alloys with high creep values Alloys with high mercury content in marginal areas Areas of flash due to incorrect finishing technique

Types of failures Secondary or recurrent caries Bulk fracture Marginal breakdown Excessive dimensional change Excessive tarnish and corrosion

Cracked Tooth Syndrome

Bonded Amalgams Rationale For Amalgam Bonding Adhesively prepared tooth surface Bonding agent Amalgam is packed directly into the uncured resin cement, forcing the glass filler in the resin cement to intermingle with the amalgam. These materials harden together in an interlocking matrix that provides tremendous bond strength of amalgam to dentin, increases the strength of the restored tooth and reduces microleakage and sensitivity

Amalgam Bonding ResiLute Resin Cement (one example) Chemically bonds to the DenTASTIC Adhesive Primer Micromechanically bonds to the amalgam, locking in the amalgam and increasing the strength of the restored tooth. ResiLute is dual cure, fluoride releasing and is available in both universal and clear shades.

Safety of the Patient Primary concern is whether mercury can produce local or systemic toxic effects Major controversy between 1988 and 1991 National Institute of Health announced in 1991 that amalgam is safe and effective except for those few people who have a true allergic reaction to mercury or other components of amalgam

Mercury and Safety of Dental Office Staff Prevention Ventilation of office No carpet For spills use a mercury-spill kit Vacuum cleaners should not be used for spills Hazard when inhaled during mixing Can lead to a cumulative toxic effect Vapor is colorless, odorless and tasteless Can be absorbed through skin

Precautions cont. In cases of skin contact, wash with soap and water Excess mercury (which includes waste amalgam) should be collected & stored Capsules should be tightly capped Triturators should have hoods over arms Use pre-proportioned capsules When cutting amalgam-water spray and suction needed Wear gloves and mask Periodic monitoring of exposure levels