Dental Amalgam and Alloys

• Dental amalgam is a metallic restoration material
• It is composed of a mixture of silver and other metals with mercury.
• Silver amalgam was developed in Europe in the 1820s, introduced in the United States in the 1830s.
• Amalgam has been successfully used for over 170 years and is cost-effective, however, it is unaesthetic and does not bond to tooth tissues.
• Dental Amalgam Alloy contains solid metals of silver, tin, copper, and zinc
• Dental amalgam is the product when mercury is combined with alloys to form a plastic mass,

Dental Alloys

• Definition: a combination of metals
• Amalgamation is the joining of an alloy with mercury
• Trituration mixes the alloy and mercury with an amalgamator/triturator
• Dental alloy composition:
  • Silver: 40-70%
  • Tin: 2%
  • Copper: 5-30%
  • Zinc: 1% or less

Classification of Dental Amalgam Alloy

• Based on the number of alloyed metals:
  • Binary alloys contain silver and tin.
  • Ternary alloys contain silver, tin, and copper.
  • Quaternary alloys contain silver, tin, copper, and zinc or indium.
• Based on copper content:
  • Low copper alloys contain 2%-6% copper by weight
  • High copper alloys contain 12% - 30% copper by weight.
• Based on zinc content:
  • Zinc-containing alloys contain zinc in the range of 0.01% to 1%.
  • Zinc-free alloys contain less than 0.01% of zinc. -Based on shape of alloy particles:
  • Lathe cut alloy particles are irregular in shape.
  • Spherical alloy particles have a smooth spherical shape.
• Based on composition of the alloy:
  • Single or uni-compositional alloys
  • Admixed alloys

Constituents of Dental Amalgam Alloy Powder

• Silver comprises 65% by weight, increasing strength and expansion.
• Tin comprises 29% by weight, decreasing expansion and strength, and increasing setting time.
• Copper increases strength, reduces tarnish and corrosion, and reduces creep.
• Zinc provides better clinical performance and is used in manufacturing.
• Indium decreases surface tension, reduces creep and marginal breakdown, and increases strength.
• Palladium reduces corrosion and gives greater luster.
• Mercury activates reaction.

Advantages of Dental Amalgam

• Easy insertion and adaptation to cavity preparation
• Limited dimensional change
• Remains plastic long enough for placement and carving
• Good compressive strength
• Limits marginal leakage
• Withstands oral environment without irritating the host.

Disadvantages of Dental Amalgam

• Composed of approximately 50% mercury
• Poor tooth color match
• Tarnishes
• Fractures if not supported by sufficient bulk
• High thermal conductivity
• Is a controversial material
• Use is not recommended for anterior primary tooth restorations
• Use is not recommended for patients with kidney dysfunction, known allergies to mercury, and pregnant women should not have amalgam removed

Composition of Amalgam

• Low copper amalgam:
  • Silver: 68% to 72%
  • Tin: 26% to 37%
  • Copper: 4% to 5%
  • Zinc: 0% to 1%
• High copper amalgam:
  • Silver: 40% to 70%
  • Tin: 15% to 30%
  • Copper: 8% to 28%
  • Zinc: 0% to 1%

Types of Dental Amalgam

• Low-copper alloy
• High-copper alloys are frequently used in dentistry.
• Alloys are classified according to particle shape:
  • Lathe-cut particles have large crystals and are subject to corrosion.
  • Spherical particles consist of small round particles, are strong and quick setting, easier to condense, and have improved carving and polishing properties.
  • Admix alloys combine spherical and lathe-cut particles.

Components of Amalgam - Mercury

• It is poisonous.
• Exposure can occur through skin contact, mercury vapor, or mercury dust contacting mucous membranes.
• Hazard: methods for monitoring levels, handling, and disposing of excess dental amalgam safely must be understood.
• Mercury is a dense metal that is liquid at room temperature.
• Historically, mercury was mixed with alloy using a mortar and pestle and excess material was squeezed out with a cheesecloth.
• Now, alloy and mercury are sealed in a disposable capsule in 600 mg, appropriate for a single surface restoration, or 800mg for a larger restoration.

Care Guidelines

• Storage: in specific places and kept in manufacturer-sealed packages until moved to the operatory.
• Workplace: a specific place is allocated for mixing and storing.
• Handling: done in described workplace above.
• Clinical procedures: use safety glasses, snug fitting masks, gloves, and high-volume oral evacuation continuously during the procedure.
• Waste amalgam: store in a glass or plastic bottle with an air-tight lid and covered with mercury vapor suppressant.
• Cleaning equipment: vacuum cleaner bags and air filter in office heating/cooling.
• Waste disposal: used rubber dams and anything else that the amalgam has touched should be placed in a closed container.
• General cleaning: mercury vapor suppressant is recommended for routine cleaning.
• Squeeze cloths: squeezing amalgam in a squeeze cloth is no longer practiced.
• Mercury spillage: spills should be cleaned up immediately.

Mercury Spill Clean-Up

• Put on rubber, nitrile, or latex gloves.
• If there are any broken pieces of glass or sharp objects, pick them up with care and place on a paper towel in a zip lock bag.
• Use a squeegee or cardboard to gather visible mercury beads using slow sweeping motions.
• Use a flashlight close to the floor in a darkened room to find additional mercury.
• Mercury can move surprising distances on hard-flat surfaces; inspect the entire room.
• Use the eyedropper to collect or draw up the mercury beads.
• Slowly and carefully squeeze mercury onto a damp paper towel and place in a zip lock bag.
• After removing larger beads, put shaving cream on a small paint brush and gently "dot" the affected area to pick up smaller hard-to-see beads, or use sticky tape.
• Place the paint brush or duct tape in a ziplock bag.
• Label the bag as directed by your local health or fire department
• It is optional to use commercially available powdered sulfur to absorb the beads that are too small to see.
• The sulfur makes the mercury easier to see since there may be a color change from yellow to brown.
• The sulfur binds the mercury for easy removal and suppresses vapor.
• Commercialized sulfur may be supplied as mercury vapor absorbent in mercury spill kits, which can be purchased from laboratory, chemical supply and hazardous materials response supply manufacturers.
• Caution: powdered sulfur may stain fabrics a dark color and can be moderately toxic if you breathe it in.
• If you choose not to use powdered sulfur, you may want to request services of a contractor to screen for mercury vapors.
• Consult your local environmental or health agency for contractors.
• Place all materials used with the cleanup in a trash bag containing mercury beads and objects.
• Secure trash bag and label as directed by local health or fire department.
• Contact your local health department, municipal waste authority, or your local fire department for proper disposal.
• Keep the area well-ventilated for at least 24 hours after cleanup, keep pets and children out, and seek medical attention if sickness occurs.

Effects of Mercury Contamination

• Chronic/long-term exposure
  • Irritability
  • Excessive Saliva
  • Loosened Teeth
  • Periodontal Disorders
  • Slurred Speech
  • Tremors
  • Staggering
  • Erectile Dysfunction
• Acute exposure (within 30 minutes)
  • Metallic Taste
  • Thirst
  • Nausea
  • Vomiting
  • Severe Abdominal Pain
  • Bloody Diarrhea
  • Renal Failure
• Mercury is hazardous.
• There is no treatment for mercury poisoning except the administration of agents to eliminate process from the body.
• You can work safely with it with respect and appreciation

Purposes of Alloy Components

• Silver: gives high luster and silver appearance, increases the strength, durability, expansion, and decreases the flow and set time
• Tin: decreases the expansion, strength, and hardness, and increases flow, set time, and workability
• Copper: adds strength and resistance to corrosion, decreases marginal failure, and is longer lasting
• Zinc: combines with oxygen and other impurities present in the alloy but contributes to the excess expansion

Alloy Particles' Shape and Size

• Can affect the handling characteristics of amalgam.
• They may be in the form of:
  • Filings which are fine, irregular shaped particles
  • Spheres which are round particles varying in size
  • Dispersed/admix alloy, a combo of above, comes in different packaging types.
• Favored alloys are the ones with small particle size because:
  • Allows more thorough wetting of the alloy with the mercury therefore, less mercury needed.
  • Means rapid hardening with greater early strength
  • Results in less amalgam expansion
  • Easier to adapt into cavity preparations when condensing -Results in a more smoothly carved amalgam that is less prone to tarnish or corrode

Dental Amalgam

• Dental alloy + mercury = dental amalgam.
• Mercury wets the alloy particles to make a plastic, moldable mix.
• Mercury/alloy ratio makes upt 43-54% of the amalgam
• High mercury makes amalgam with increased expansion, more tarnish and corrosion, and decreased strength.
• Two types of dental amalgam are low copper amalgam, which is conventional, and high copper amalgam, which was developed in the 1960's, it is preferred, and requires slightly less mercury.
• Uses of amalgam: restoring permanent and deciduous posterior teeth, restoring distal surfaces of cuspids when preparation is from the lingual, building up a tooth prior to a crown, and sealing the apex of a tooth after root tip is removed (apicoectomy).

Properties

• Shrinkage: a small amount as amalgam sets, then corrosion occurs in the first few months and produces particles to create a seal
• Creep: occurs during mastication. Low creep is related to low marginal breakdown.
• Expansion: results in overhangs and protruding restorations, affecting periodontal health.
• Strength & Elasticity: strong enough to withstand chewing forces and fairly elastic, but low tensile strength (fractures when pulled or bent)
• Thermal Conductivity: protect pulp with a liner and/or base in deep preps

Strength of Dental Amalgam

• Amalgam strength must be high enough to resist forces placed upon it.
• Restoration shouldn't be subjected to chewing before sufficient strength develops.
• Manipulation of amalgam affects the strength of the final restoration if there is under/over trituration, poor condensation.
• Creep happens from repeated chewing.
• Creep is dimensional change, less than 3% is recommended.

Dimensional Change of Dental Amalgam

• Net contraction or expansion of amalgam.
• Freshly mixed amalgam should neither expand or contract when condensed into cavity preparation.
• Improper manipulation alters the dimensional change: -Expansion may cause protrusion or post sensitivity -Contraction may leave gaps between the tooth margin and restoration

Tarnish and Corrosion of Dental Amalgam

• Discolored and deteriorated restoration
• With tarnish, the chemical reaction between the amalgam and oral environment is restricted to the amalgam surface.
• Corrosion results from chemical reactions that penetrate restoration & cause failure.
• Tarnish and corrosion occur on amalgams with rough surfaces; polish surfaces reduce these problems.

Factors that Influence Amalgam Properties

• Trituration Time
• Under-trituration results in:
  • Dry amalgam and poor condensation
  • Fast set and porous amalgam
  • Corrosion and marginal breakdown
  • Less strength and shorter life.
• Over-trituration results in runny amalgam.
• Moisture contamination contributes to the expansion and causes corrosion.
• Can be avoided by:
  • Rinsing and drying completely
  • Use hand protection when handling amalgam
  • Wear dry gloves -Tarnish – surface discoloration of silver
• Corrosion – chemical deterioration of the metal causing the amalgam to darken and become pitted

Amalgam Restoration Failure

• Most common causes: secondary decay, marginal breakdown, and bulk fracture related to inappropriate cavity design.
• Factors that cause failures: moisture contamination, improper mixing, and incorrect mercury to alloy ratio.
• Oral environment or dentist's technique contributes to failure: corrosion for galvanism, poor finishing, poor condensing, incorrect prep design, over-filled preps.
• Manipulation of amalgam often comes in pre-capsulated amalgam in single, double, or triple mixes called spills which are color coded or numbered.
• Avoid sitting mix more than 3 ½ minutes after mixing to avoid deterioration.
• Trituration is the mixing process designed to disrupt the film of oxide so the mercury will contact the alloy particles. -An amalgamator mixes. -Always judge the appearance of the amalgam: Undertrituration can cause dry/dull mixes and less strength, while over- triturating causes shiny/wet mixes and increased creep.

Undertrituration

• It is a serious error that leads to: -Mix appearing dry dull and sandy -More expansion -More tarnish and corrosion -High residual mercury content -Reduced strength -Increased fracture

Overtrituration

• This causes: -Reduced working time with rapid set -Mix appearing shiny, wet, and soft -Decreased Strength -Higher Contraction -Increased Creep
• Follow instructions for mixing amalgam, under-trituration can cause dry amalgam that condenses poorly and over-trituration can cause runny amalgam.
• Each increment is condensed to remove excess mercury and the amalgam is overfilled so the rich mercury surface can be trimmed away.
• Mixed amalgam is placed in amalgam well, carried to tooth, and placed.
• Carve filling to reproduce the tooth's anatomy by using hand instrument.
• Avoid carving until the amalgam is hard to avoid pulling away from its margins.
• Burnishing smooth surfaces to finish and minimize corrosion which must be finished later with polishing burs abrasive disks within 24 hrs
• Successful amalgam depends on proper trituration, condensation, carving, and finishing.
• Pre-capsulated amalgam has greatly reduced mercury risk.