Dental Amalgam

Status of Dental Amalgam in 2009

Amalgam & Resin Composite for posterior restorations – use in the U.S. use of amalgam has declined significantly amalgam 88.4% of all direct posterior restorations (1990) amalgam 60.6% of all direct posterior restorations (1999) Berthold M. Restoratives Trend data shows shift in use of materials. ADA News. Vol 33; 2002:1, 10-11.

Amalgam & Resin Composite for posterior restorations – use in the U.S. 71 million posterior amalgams (1999) 46 million posterior resin composites (1999) amalgam is still by far the most widely used material for posterior restorations Berthold M. Restoratives Trend data shows shift in use of materials. ADA News. Vol 33; 2002:1, 10-11.

all schools teach Class I resin composites Amalgam & Resin Composite for posterior restorations – use in the U.S. dental school all schools teach Class I resin composites less acceptance as restoration becomes larger and more complex only 30% teach resin composite for 3-surface Class II in molars (1997) 1 68% teach resin composite for 3-surface Class II in molars (2005) 2 1 Mjor IA, Wilson NH. J Am Dent Assoc 1998;129(10):1415-1421. 2 Lynch CD, McConnell RJ, Wilson NH. J Am Dent Assoc 2006;137(5):619-625.

80% of schools: amalgam is taught first (2005) Amalgam & Resin Composite for posterior restorations – use in the U.S. dental school 80% of schools: amalgam is taught first (2005) 60% of posterior restorations placed by students are amalgam (2005) Lynch CD, McConnell RJ, Wilson NH. J Am Dent Assoc 2006;137(5):619-625.

Amalgam & Resin Composite for posterior restorations – use in the English speaking world Canada very like U.S. in UK 16% of 654 general dentists ‘often’ or ‘always’ used resin composite in posterior restorations (2001) 1 In Australia 41% of 560 general dentists ‘often’ or ‘always’ used resin composite in posterior restorations (2002) 2 1 Burke FJ, Wilson NH, Cheung SW, Mjor IA. J Dent 2001;29(5):317-324. 2 Burke FJ, McHugh S, Randall RC, Meyers IA, Pitt J, Hall AC.. Aust Dent J 2004;49(4):185-191.

Many dentists don’t use amalgam at all (2002 data) Amalgam & Resin Composite for posterior restorations – use in the Scandinavia Many dentists don’t use amalgam at all (2002 data) 72% of Finnish dentists 60% of Swedish dentists 12% of Danish dentists 8% of Norwegian dentists Ylinen K, Lofroth G. Acta Odontol Scand 2002;60(5):315-320.

Jordan: amalgam used predominantly Brazil: like North America Amalgam & Resin Composite for posterior restorations – use in other places Jordan: amalgam used predominantly Brazil: like North America Japan: very few amalgams placed Other countries: little in the published literature; guess is that most of the world uses amalgam like U.S. Ylinen K, Lofroth G. Acta Odontol Scand 2002;60(5):315-320.

In 2008 Scandinavian countries began banning amalgam. Amalgam Regulation In 1990s, anti-amalgam websites and newsletters rumor that amalgam had been banned in Europe, especially in Sweden and Germany Not true. Until 2008 there was very little legislation limiting the use of amalgam anywhere in the world. 1,2 In 2008 Scandinavian countries began banning amalgam. 1 Wahl MJ.. Quintessence Int 2001;32(7):525-535. 2 Burke FJ. J Dent 2004;32(5):343-350.

Amalgam Regulation - recommendations to dentists that amalgam not be placed in pregnant women (Sweden, Norway, Austria, and Germany) that amalgam not be placed in patients with renal impairment (Germany) in most of the world, dentists have received no such recommendations Burke FJ. J Dent 2004;32(5):343-350.

Amalgam Regulation - Norway & Denmark Norway banned dental amalgam beginning 1/1/08. Ban by regulation – a bit surprising. Denmark is phasing out amalgam – allow only in permanent molar teeth where there is evidence that amalgam will outlast a resin composite. New regulation were to take effect in October of 2008.

Amalgam Regulation - the situation in Sweden Sweden is making an all out effort to outlaw all use of mercury – regulations to do this are already in effect after delaying including dental amalgam in the ban several times, the ban dental amalgam was finally set to go into force 6/1/09 not too big a change; amalgam is already used very little. The Swedish National Health system has not reimbursed dentists for amalgam restorations since 1999 Burke FJ. J Dent 2004;32(5):343-350.

leakage decreases with time simple to place Amalgam - advantages strong enough wear resistant enough leakage decreases with time simple to place durable (1/2 fail in 7 – 15 years) initially inexpensive – cost effective

Leakage of amalgam restorations with time 1 mo This self sealing behavior may be one of the reasons for the success of amalgam restorations. 3 mo 6 mo

Amalgam - disadvantages silver color – can tarnish to black poor initial seal thermal and electrical conductor corrodes

bulk fracture can occur Amalgam - disadvantages Weak in tension & shear margins fracture bulk fracture can occur

Development of amalgam 1818 – Paris dentist Louis Regnart suggests use of amalgam to restore teeth Another Parisian dentist, August Omesine Taveau popularized it

Development of amalgam - 2 Crawcours – five brothers & their sons Poorly educated, claimed to have learned about amalgam in France 1790 – 1830: Crawcours were itinerant dentists in Northern England Claimed to be able to save teeth with a new material “Royal Mineral Succedaneum”

Development of amalgam - 3 1833 two of the Crawcour brothers travel to the U.S. 1834 they were “chased out” of the U.S. 1843 – American Society of Dental Surgeons declares use of amalgam malpractice

Development of amalgam - 3 1843 – 1895 alloy powder gradually improved, culminating with the research of G.V. Black The major change was the addition of tin (Sn) to the silver (Ag) in the powder

Powder is based on the composition Ag3Sn, an intermetallic compound Low Copper Amalgam Powder is based on the composition Ag3Sn, an intermetallic compound β Ag-Sn  Ag-Sn

intermetallic compound: usually stable over a narrow range of composition centered around a composition that is a whole number ratio of the elements (e.g., A3B, A2B, AB, AB2, AB3) can be thought of as involving a mixture of covalent and metallic bonding ordered – usually remain ordered from room temperature to their melting temperature

Random Solid Solution (Disordered) Gold Copper Random Solid Solution (Disordered)

Intermetallic Compound (Ordered) Gold Copper Intermetallic Compound (Ordered)

Powder is based on the composition Ag3Sn, an intermetallic compound Low Copper Amalgam Powder is based on the composition Ag3Sn, an intermetallic compound Also contains zinc (Zn) Mixed with 53 – 60 wt. % mercury Extra Hg was squeezed out (“expressed”) during condensation.

(Ag - Sn alloys particles) + Hg low - copper amalgam: (Ag - Sn alloys particles) + Hg = 1 (Ag - Hg) + 2 (Sn - Hg) + (partially consumed particles)

 Ag - Sn Ag3Sn b Ag - Sn Ag5Sn  Cu - Sn Cu3Sn phases in particles: Intermetallic compound b Ag - Sn Ag5Sn Solid solution  Cu - Sn Cu3Sn Intermetallic compound Intermetallic compounds are brittle. Consequently, the particles are brittle.

1 (Ag - Hg) Ag2Hg3 2 (Sn - Hg) Sn7Hg matrix phases: Intermetallic compound 2 (Sn - Hg) Sn7Hg ??? The predominant matrix phase, 1, is intermetallic and, consequently, is brittle. Since both the partially consumed particles and matrix phase are brittle, amalgam will be brittle.

Reaction mechanism – low-copper amalgam: Very plastic Very plastic Silver & tin dissolve into liquid mercury. After silver reaches saturation, 1 Ag-Hg crystals nucleate & grow.

Reaction mechanism – low-copper amalgam: Plastic Carveable solid  crystal continue to grow. As they grow they consume the liquid Hg. When tin reaches saturation in Hg, 2 crystals nucleate & grow. Both types of crystals continue to grow until all the mercury is con- sumed. Matrix is mostly 1, but also contains 2 and voids.

Microstructure – low-Cu amalgam: P - Ag-Sn G1 - 1 (Ag-Hg) G2 - 2 (Sn-Hg) E -  Cu-Sn V - voids

 Ag - Sn Ag3Sn β Ag - Sn Ag5Sn  Cu - Sn Cu3Sn phases in particles: Intermetallic compound β Ag - Sn Ag5Sn Solid solution  Cu - Sn Cu3Sn Intermetallic compound

1 (Ag - Hg) Ag2Hg3  2 (Sn - Hg) Sn7Hg matrix phases: Intermetallic compound 1 (Ag - Hg) Ag2Hg3  2 (Sn - Hg) Sn7Hg ???

1 (Ag - Hg) Ag2Hg3 < 60 vol. % 2 (Sn - Hg) Sn7Hg < 10 vol. % matrix phases: 1 (Ag - Hg) Ag2Hg3 < 60 vol. % 2 (Sn - Hg) Sn7Hg < 10 vol. %

High – copper Amalgams

High-Cu Amalgams - types: admixed single composition

Development of High-Cu Amalgams: admixed amalgam invented – Innes & Youdelis 1962 less marginal fracture in admixed high Cu amalgam restorations – Mahler et al., 1970.

after 8 years; Osborne et al. 1980 fractured margins less marginal fracture fractured margins admixed high-Cu amalgam low copper amalgam low copper amalgam after 8 years; Osborne et al. 1980

Admixed High-Cu Amalgams – Powder Types: irregular (Ag-Sn alloy) + spherical (Ag-Cu) irregular (Ag-Sn alloy) + spherical (Ag-Sn-Cu)

Admixed High-Cu Amalgam powder Dispersalloy Au-Cu Ag-Sn spherical particles Au-Cu lathe-cut particles Ag-Sn 30 um

(Ag - Cu alloys particles) + Hg admixed amalgam: (Ag - Sn alloy particles) + (Ag - Cu alloys particles) + Hg = 1 (Ag - Hg)  (Cu-Sn) + (partially consumed particles) +

1 (Ag - Hg) Ag2Hg3 2 (Sn - Hg) Sn7Hg  (Cu-Sn) Cu6Sn5 matrix phases: corrosion resistant weak 1 (Ag - Hg) Ag2Hg3 corrodes very weak 2 (Sn - Hg) Sn7Hg  (Cu-Sn) Cu6Sn5 corrodes less fairly strong

Microstructure – Admixed High-Cu Amalgam: G1 - 1 (Ag-Hg) P - Ag-Sn E -  Cu-Sn V - voids R -  + 1 D – Ag-Cu alloy

1 (Ag - Hg) Ag2Hg3 < 60 vol. %  (Cu-Sn) Cu6Sn5 < 10 vol. % matrix phases: 1 (Ag - Hg) Ag2Hg3 < 60 vol. %  (Cu-Sn) Cu6Sn5 < 10 vol. %

High-Cu Amalgams - types: admixed single composition

Single Composition High-Cu Amalgams: Invented by Kamal Asgar in 1974

Single Composition High-Cu Amalgam – types: Spherical – Ag-Sn-Cu Irregular – Ag-Sn-Cu

Single Composition High-Copper Amalgam Tytin 30 um

single - composition amalgam: (Ag - Sn - Cu alloys particles) + Hg = 1 (Ag - Hg)  (Cu-Sn) + (partially consumed particles) +

Microstructure of single-composition high-copper amalgam: 1 (Ag - Hg) – the matrix phase unconsumed alloy (Ag-Cu-Sn) particles  (Cu-Sn) particles

Compressive strength after seven days: low - copper 350 MPa admixed 430 MPa single - composition 500 MPa

Tensile strength after seven days: low - copper 50 - 75 MPa admixed 50 - 75 MPa single - composition 50 - 75 MPa

DB Mahler’s marginal fracture rating system: 1 3 5 7 2 4 6 11 7 9 8 10

Marginal Fracture of Amalgam Restorations Mahler et al. J Oral Rehab 1979;6:391-398.

Creep Test - ADA Specification No. 1

Static creep: Time-dependent plastic deformation that occurs when a material is placed under a constant load that is less than the its yield strength.

Creep Test - ADA Specification No. 1 cylinder: 8 mm high by 4 mm in diameter temperature: 37o C stress: 35.85 MPa

Creep Test - ADA Specification No. 1 (height 4th hr) - (height 1st hour) initial height x 100

ADA Creep Beech & Brockhurst. Aust Dent J 1982; 27:306-309.

ADA Creep Values of Amalgam Types

Correlation between marginal fracture & creep ( 10 - 6 / sec ) Vrijhoef & Letzel J Oral Rehab 1986;13:299 - 303.

one-hour compressive strength Beech & Brockhurst. Aust Dent J 1982; 27:306-309.

One-hour Compressive Strength of Amalgam Types

Posterior Amalgam Restorations - Longevity Manhard & Hickel (2004) reviewed 41 clinical studies of amalgam & 50 of resin composite. annual failure rates: amalgam: 0 – 7.4% / yr resin composite: 0 – 9.0% / yr average failure rate of combined studies amalgam: 3.0% / yr resin composite: 2.2% / yr Not statistically different Manhart J, Chen H, Hamm G, Hickel R. Oper Dent 2004;29(5):481-508.

Posterior Amalgam Restorations - Longevity Manhard & Hickel (2004) reviewed 41 clinical studies of amalgam & 50 of resin composite. problems: too many short terms studies – exclude failure mechanisms whose probability increases with time (e.g. caries, bulk fracture, marginal fracture) combine studies performed in general practice with studies performed in optimum settings. Manhart J, Chen H, Hamm G, Hickel R. Oper Dent 2004;29(5):481-508.

Longevity Testing – Test settings general practice – dental offices, public health clinics, lots of clinicians, operators uncalibrated, patients from everywhere – works against longevity optimum settings – often dental schools, few operators, operators calibrated, selected patients – promotes longevity Wilson NH. Oper Dent 1990;15(4):149-155. Mjor IA, Jokstad A, Qvist V. Int Dent J 1990;40(1):11-17.

Longevity Testing – Types of studies longitudinal studies prospective – can tightly control variables; often optimum settings; can study aspects of general practice too retrospective – rely of patient charts or insurance databases; often used in general practice settings cross sectional – a ‘snap shop’ of restorations placed or replaced over a short period; usually used to study general practices

Longevity Testing – Test settings general practice – dental offices, public health clinics, lots of clinicians, operators uncalibrated, patients from everywhere – works against longevity optimum settings – often dental schools, few operators, operators calibrated, selected patients – promotes longevity Wilson NH. Oper Dent 1990;15(4):149-155. Mjor IA, Jokstad A, Qvist V. Int Dent J 1990;40(1):11-17.

65.8 years (3244 restorations; combined studies; 5 – 15 years) 1 Longevity Testing – median survival times posterior amalgams longitudinal prospective - optimum settings 65.8 years (3244 restorations; combined studies; 5 – 15 years) 1 57.5 years (181 restorations; 13 years) 2 69.0 years (53 restorations; 8 years) 3 1. Letzel H, van 't Hof MA, Marshall GW, Marshall SJ.J Dent Res 1997;76(11):1787-1798. 2. Osborne JW, Norman RD. Dent Mater 1990;6(3):189-194. 3. Collins CJ, Bryant RW, Hodge KL. J Dent 1998;26(4):311-317.

14.4 years (1345 restorations; 0 – 17 years) 1 Longevity Testing – median survival times posterior amalgams longitudinal retrospective - general practice settings 14.4 years (1345 restorations; 0 – 17 years) 1 11.9 years (76,418 restorations; 0 - 12 years) 2 1. Dawson AS, Smales RJ. Aust Dent J 1992;37(3):196-200. 70. 2. Lucarotti PS, Holder RL, Burke FJ. J Dent 2005;33(10):805-815.

1990 - 2001 data from UK’s General Dental Service’s database: Longevity Testing – median survival times posterior amalgams longitudinal retrospective general practice 1990 - 2001 data from UK’s General Dental Service’s database: Single surface amalgams: 11.9 years (16,680 restorations) 1 DO & MO amalgams: 9.8 years (16,680 restorations) 1 MOD amalgams: 8.8 years (147,087 restorations) 1 1. Lucarotti PS, Holder RL, Burke FJ. J Dent 2005;33(10):805-815.

Class II amalgams: 44.1 years (1213 restora-tions – 15 years) 1 Longevity Testing – median survival times posterior amalgams longitudinal prospective optimum settings – Class II only - Class II amalgams: 44.1 years (1213 restora-tions – 15 years) 1 Class II amalgams: 25.0 years (469 restora-tions – 9.5 years) 2 Class II amalgams: 27.6 years (664 restora-tions – 15 years) 3 1. Gruythuysen RJ, Kreulen CM, Tobi H, van Amerongen E, Akerboom HB. Community Dent Oral Epidemiol 1996;24(3):207-210. 2. Jokstad A, Mjor IA. Acta Odontol Scand 1991;49(1):47-63. 3. Smales RJ. Oper Dent 1991;16(1):17-20.

44.3 years (~ 80 restorations; 10 years) 1 Longevity Testing – median survival times posterior RCs longitudinal prospective - optimum settings - 1 44.3 years (~ 80 restorations; 10 years) 1 24.4 years (55 restorations; 8 years) 2 26.0 years (52 restorations; 8 years) 2 43.0 years (54 restorations; 8 years) 2 Lundin SA, Koch G. Swed Dent J 1999;23(5-6) 3. Collins CJ, Bryant RW, Hodge KL. J Dent 1998;26(4):311-317.

19.4 years (194 restorations; 10 years) 1 Longevity Testing – median survival times posterior RCs longitudinal prospective - optimum settings - 2 19.4 years (194 restorations; 10 years) 1 20.2 years (34 restorations; 11 years) 2 35.4 years (100 restorations; 17 years) 3 34.4 years (56 restorations; 11 years) 4 1. Gaengler P, Hoyer I, Montag R. J Adhes Dent 2001;3(2):185-194. 2. van Dijken JW.. J Dent 2000;28(5):299-306. 3. Wilder AD, Jr., May KN, Jr., Bayne SC, Taylor DF, Leinfelder KF J Esthet Dent 1999;11(3):135-142. 4. Pallesen U, Qvist V. Clin Oral Investig 2003;7(2):71-79.

Longevity Testing – median survival times posterior RCs longitudinal retrospective general practice settings No long term studies

The End