CURRENT CONCEPTS IN AMALGAM Date: Saturday, March 17, 2001 at 09:09:43 PM Amalgam Alloy - mixture of metals Amalgam - alloy including mercury Used for more than 150 years 100 million amalgam restorations per year in the USA for the last 20 years Billions sold with no adverse effects Components 1. Silver - Increases strength, expansion and reactivity. Decreases creep. Corrosion products are AgCl and AgS. 2. Tin - Increases reactivity and corrosion. Decreases strength and hardness. Corrosion products are SnO, SnCl, and SnS. 3. Copper - Increases strength, expansion and hardness. Decreases creep. Corrosion products are CuO and CuS. 4. Zinc - Increases plasticity, strength and the Hg:alloy ratio. Decreases creep. Causes secondary expansion. Corrosion products are ZnCl and ZnO. 5. Mercury - Wets the alloy particles. Decreases strength if in excess amounts. Implicated in toxic and allergic reactions. Types 1. Spherical - AgSnCu + Hg Æ AgHg + CuSn + AgSnCu 2. Lathe cut - AgSn + Hg Æ AgHg + SnHg + AgSn 3. Admixed - AgSn + AgCu + Hg Æ AgHg + AgSn + CuSn No gamma 2 if copper > 12%. Phases Gamma - AgSn Gamma 1 - AgHg Gamma 2 - SnHg Epsilon - CuSn Eta - CuSn Beta - AgSn Beta 1 - AgHg Beta (Galloy) - GaCu + Sn Preps - Conserve Tooth Structure Minimal width and depth: 330, 245 Only carious areas: slots, tunnels "S" curve Rounded internal angles Cavosurface at 90 Remove unsupported enamel Remove all caries past DEJ Use caries indicator if desired Retention - mechanical or bonded (controversial) Liner, base or adhesive - proper selection Adequate bulk of amalgam Wedge - good contacts, proper contour, no overhangs Minimize microleakage Functional anatomy Use proper amalgam - type, speed of set, etc. Amalgam Failures - Causes Inadequate retention Insufficient bulk for strength Failure to remove unsupported enamel Caries not removed Inadequate condensation Recurrent caries Amalgams Spherical Spheroidal Admixed Tytin Tytin FC Contour Valiant Valiant PhD Unison, Megalloy Dispersalloy Galloy Retention 1. Pins Provide best retention Place in dentin, 0.5 mm from DEJ, parallel to external surface of tooth Back off _ turn Rule of 2's 2. Internal retention/amalgam inserts Amalgapins Amalgapins Resistance comparable to pins Slots Retention less than pins Boxes Use in short clinical crowns Grooves No need for 2 mm coverage Dovetails 245 bur 2 mm deep Parallel walls Bevel optional 3. "Bonded Amalgam" Not confirmed over time - microleakage Best to attempt "sealed" amalgam Combine with accessory retention 4. Best results Combination of all three above Confirmed by current research "...amalgam bonding is an adjunct to and not a substitute for mechanical retentive form. The main advantage of conventional amalgam adhesives seems to be their ability to seal the tooth restorative interface, preventing microleakage into the dental tubules and pulp and reducing post-operative sensitivity." Cobb, et al, Am J Dent, Oct 1999 "Continuous microgaps were observed between amalgam and dentin in the specimens using no lining material and Copal varnish compared to specimens using PQ1 adhesive bonding system." Estafan, Gen Dent, March-April 2000 Bases and Liners Base - thicker and 0.5-1 mm, provides thermal protection. Used to create ideal cavity form. Liner - Minimize microleakage and protect pulp. Options: Copal resin varnish, Glass ionomer (RRGI, Compomer), Calcium hydroxide, ZOE, Zinc Phospate, Amalgam bonding agent, Dentin/enamel/universal bonding agent, Adhesive agent with filled component, Nothing, Combition of the above. Allow amalgam to contact tooth for stability. "An amalgam over a thick liner/base is like a sheet of glass on a trampoline." - Bill Robbins (UTSA) "filled adhesive resins produced higher amalgam to dentin shear bond strengths than unfilled resins, and spherical alloy produced higher bond strengths than admixed alloy" , (Diefendorfor and Reinhardt, Oper Dent, Mar-Apr 1997) Amalgam Alternatives (Not substitutes) Direct composites (Heliomolar RO, Hybrids, Condensables such as Alert, Solitaire, SureFil, Pyramid, Prodigy Condensable, Glacier, Filtek P60) Ariston pHc - "Alkaline Glass Restorative" - advertised as a non-bondable, non-retentive amalgam alternative. Is really Compoglass F as a non-etched liner followed by Tetric. Direct / Indirect or Indirect (lab) composites (Concept, Artglass, belleGlass HP, Maxxim, etc) Cast metal Porcelain inlay / onlay / veneer / full veneer crown / full porcelain crown / PFM crown CAD-CAM Metal ionomers "Alternatives" or "Substitutes"?? A true substitute has NOT been found yet. (Corbin and Kohn, JADA, Apr 1994), "If the 96 million amalgams placed in 1990 had used alternate material, would have cost $12 billion additional dollars. One time replacement of all existing amalgams in permanent posterior teeth - $248 billion" "Based on the in-vitro results presented in this study, the use of amalgam substitutes for stress bearing restorations in permanent teeth cannot be recommended without serious concerns." (Lutz and Krejc, J. Esth Dent, May 2000) Criteria when considering amalgam substitutes: service life, radiopacity, wear properties, marginal adaptation, setting expansion/contraction, technique sensitivity,potential secondary caries risk. What materials are better than amalgam in these areas? (Lutz and Krejc) Current Controversy on Mercury 1. Types: Elemental - Least toxic. Very small contribution to total body burden of Hg. Is the form found in dentistry. Lipid soluble, absorbed in lungs. Very short-lived due to rapid oxidation. Inorganic - Moderate toxicity. Formed by oxidation of elemental. Limited lipid solubility. Becomes sequestered in kidney, excreted slowly in urine. Half life ~ 60 days. Organic - Most toxic. High lipid solubility. Only from non-dental sources. 90% absorbed in gut. Accumulates in red blood cells, sequestered in CNS and liver. Not found in urine. Excreted in feces. 2. Sources of Hg: Ambient air Amalgam Food Drugs, medicines Water Occupational 3. Signs and Symptoms of Toxicity: Tremor Headache Ataxia Irritability Personality change Slowed nerve conduction Loss of memory Weight loss Insomnia Appetite loss Fatigue Gingivitis Depression Psychological distress 4. Mercury Facts: "3 to 6 occlusal amalgam surfaces and from 3 to 10 surfaces in total - had very little influence on the intra-oral release of mercury vapor, regardless of amalgam type used, nor were any effects found on mercury levels in urine and saliva." J. Dent. Res., May, 1993. "It is not known whether the vast majority of people with amalgam restorations experience any clinical effect from this small additional body burden of mercury."" PHS, Jan., 1993. "The ADA continues to support dental amalgam as a safe and effective restorative material and sees no cause for public concern about either existing or future amalgam restorations." ADA, Dec., 1990. "Thus, on the basis of current evidence, the careful use of amalgam as a posterior restorative material should continue". Brit. Dent. J., 1993. Maximum occupational daily allowance of elemental mercury - 300-500 ug/day. (NIOSH). 8-10 occlusal amalgams release 1-3 ug/day of elemental mercury. Total elemental + inorganic Hg dose from amalgam is 4 -5 ug/day (1995) No proven cure for removal of amalgams as Hg in blood is elevated for days! High copper amalgams release more Hg than conventionals. Depends on type and age of restoration. Steady state reached in 30 days. Single amalgam releases 0.03 ug/day based on a safety threshold occupational exposure of 83 ug/day. J Dent Res, May, 1995. The amount of Hg released from a restoration is directly related to the amount of Sn in the Gamma 1 (AgHg) phase. J Dent Res, July, 1995. If using high volume evacuation and water spray, operatory air Hg levels do not exceed 1 - 2 mg / m3 when placing, removing or polishing amalgam restorations. Acta Odont Scand, 1995. When steam autoclaving amalgam containing teeth or instruments containing amalgam scrap, initial venting of the autoclave produces elemental Hg levels significantly in excess of OSHA vapor ceiling levels. J. of Dent Educ, May 1996. Amalgam cost (USA): One time replacement of all existing amalgams in permanent teeth = $248 billion. JADA, April 1994 5. Dental Mercury - Environmental Concerns: Interment - graveyard drainage Cremation Extracted teeth Amalgam down sewer - amalgam traps in offices Storage of amalgam scrap - under fixer or dry? Disposal of amalgam scrap - toxic waste Hg release during autoclaving of extracted teeth Amalgam - Standards of Care Conserve tooth structure Rubber dam High copper alloy Water spray Encapsulated amalgam High volume suction Calibrated amalgamator Minimize microleakage Amalgam Notes Spherical or spheroidal - All Class I's (control microleakage) Admixed or spheroidal - Class II's unless can get good contact with spherical Use sphericals around pins and internal retention. Don't combine spherical and admixed. Pre and post-carve burnish? Use bonding agent Personal preference Repair or replace? Repair strength is 7 - 18% that of intact amalgam (Oper Dent, Jan-Feb 1998) Amalgam Research Hg - free amalgam (NIDR) Galloy (SDI) - Liquid is 62% Ga, 25% In, 13% Sn - No moisture for 18 hours - Caution against contact with conventional high Cu amalgam --- corrosion Hg - Indium - Decreases Hg vapor pressure - Decreases Hg evaporation - Surface oxides form quicker Beta 1 / Non-gamma 1 amalgam Tytin FC (spheroidal) - treated Tytin spherical particles / controlled expansion PRIMM - Poly Rigid Inorganic Matrix Material - Porous Ceramic fibers. Condensable, curable, carvable, polishable. "White amalgam" Restorations with >0.3% Zn and >12% Cu have minimal corrosion and the longest longevity. Zn and Cu act synergistically. (J. Dent Res, Nov 1997) Galloy - ".by the three year evaluation, 10% of the restored teeth suffered complete or incomplete tooth fracture. Galloy, used with either of two sealing resins, is not a suitable restorative material." (Quint Int, Jan 1999) Amalgam substitutes: "Based on the in-vitro results presented in this study, the use of amalgam substitutes for stress bearing restorations in permanent teeth cannot be recommended without serious concerns." (Lutz, J. Esth Dent, May 2000) Both gold and amalgam still have a place in restorative dentistry, particularly for restorations that are extensive and need to withstand a heavy occlusal load." (Mount, Quint Int, Sept 2000) Amalgam Opposition Vimy, Lorscheider (1995) - "an average individual with eight occlusal amalgam fillings, a total of 120 ug Hg could be released daily into the mouththe release of Hg from dental amalgam tooth fillings provides the major contribution to Hg body burdenthe use of silver in amalgam may be almost as questionable as is Hg, and this evidence suggests that it may be inappropriate to alternatively use recently developed Hg - free silver amalgamsresearch evidence does not support the notion of amalgam safetyit has the potential to induce cell or organ pathophysiology." - Interesting references, including their original sheep studies. Dietschi (PP&A, Sept 1996) - "The fragility of the remaining tooth structure surrounding large amalgam restorations results in the cracked tooth syndrome, which is well documented, and should no longer be neglected. It is not too early to declare that the use of amalgam today, where adhesive procedures can be safely applied, is unethical." ADA News, Nov 1996 -"no significantly higher levels of mercury in either the urine, blood or brain tissue of Alzheimer's patients as compared to controls" Christensen (Oper Dent, Jul 1997) - "Amalgam restorations are and will continue to be the mainstay of posterior tooth restorations for many years to come" Christensen (Lecture, Jan 1998) - "You sniff more mercury in a fish market than in a lifetime of amalgams" JADA, April 1998 - "To date, there is no evidence to suggest that mercury released from dental amalgams results in any adverse effects to health in the general population..if recommended mercury hygiene procedures are followed, the risks of any adverse health effects arising from mercury exposure in the dental office are minimal"
