Dental Amalgam أ.م. مثنى شعبان رجب جامعة تكريت كلية طب االسنان

Transcription

1 Dental Amalgam Definitions Amalgam Any alloy that contains mercury Amalgamation Combining mercury with an alloy of silver, tin, and copper Amalgam alloy Trituration Mechanical mixing of amalgam alloy particles with mercury to achieve amalgamation Condensation 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 Dramatic changes in the past 20 years Predominate constituents Silver Increases setting expansion and strength Tin Helps amalgamation Decreases expansion Other constituents Copper Increases strength, hardness, and setting expansion; redness Zinc Minimizes oxidation Palladium Whitens Mercury Forms workable mass Tradition Amalgam (Low Copper) Spherical or Lathe-cut 1

2 66-73% silver 25-29% tin 6% cupper 2% zinc 3% mercury Spherical vs. Lathe-cut Spherical Spherical particles µ in size Lathe-cut Different shaped particles 0-70 µ in size High Copper Amalgam Greater than 6% copper Almost universally used today Higher strength Higher corrosion resistance Less marginal breakdown Low creep Types of high copper Admixed Single composition Admixed Composition Dispersion ( Blended) alloys Oldest type of high copper Alloy powder is a mixture of powders of two alloys Mix of spherical and comminuted 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 Zinc versus Non-zinc Zinc aids in minimizing the oxidation of other metals present in the alloy during the manufacturing process Zinc-containing 2

3 Zinc in excess of.01% Non-zinc Zinc less than.01% Physical Properties Excessive expansion Put pressure on pulp, protrusion of restoration or fracture Excessive contraction Pulls away from the cavity walls Permits gross leakage between tooth and restoration Strength Gains strength in 1 week Variables Trituration Residual Mercury Porosity Creep Deforms under a constant load Tarnish Surface discoloration Deposit of surface film that produces discoloration Can be removed by polishing Corrosion Loss of surface by chemical attack Effects 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 versus Insufficient Mercury Effects of excessive mercury 3

4 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 Finishing and Polishing Finishing 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 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 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 4

5 Marginal breakdown Excessive dimensional change Excessive tarnish and corrosion Hazard when inhaled during mixing o Can lead to an accumulative toxic effect o Vapor is colorless, odorless and tastless Can be absorbed through skin High incidence of miscarriages in staff Prevention Ventilation of office No carpet For spills use a mercury-spill kit Vacuum cleaners should not be used for spills In cases of skin contact, wash with soap and water Excess mercury (which includes waste amalgam) should be collected & stored Use glycerin or x-ray fixer solution Capsules should be tightly capped Amalgamators 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 5