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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  AgHg + CuSn + AgSnCu

2. Lathe cut - AgSn + Hg  AgHg + SnHg + AgSn

3. Admixed - AgSn + AgCu + Hg  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"