PRODUCT NAMES AND MANUFACTURERS

NPG, NPG + 2Aalba Dent Inc., 400 WattDrive, Cordelia, Calif. 94585, 1-800-227-1332,www.aalbadent.com

Argenco 83, Argenco 77, Argenco 75, Argenco68Argen Precious Metals, 5855 Oberlin Drive,San Diego, Calif. 92121-4718, 1-800-255-5524,www.argen.com

Ney-Oro A-1, Ney-Oro B-2, Ney-Oro B-2G, Ney-Oro G-3Dentsply Ceramco, 6 Terri Lane,Burlington, N.J. 08016, 1-800-487-0100, www.ceramco.com

Harmony Soft, Harmony Medium, HarmonyHard, Harmony Extra-HardIvoclar Vivadent Inc.Bendererstrasse 2, FL-9494, Schaan, Liechtenstein,1-800-533-6825, www.ivoclar.com

Modulay, Firmilay, Laboratory-33, Midas, Rajah,Forticast, Jel-4, Jelenko No. 7, SturdicastJelenkoDental Health Products, 99 Business Park Drive,Armonk, N.Y. 10504, 1-800-431-1785,www.jelenko.com

Rx A, Rx B, Rx Jeneric IV, Rx Jeneric C, RxMidacast, Rx Ory, Rx C+Pentron LaboratoryTechnologies, LLC, 53 North Plains IndustrialRoad, Wallingford, Conn. 06492, 1-800-243-3969,www.jeneric.com

Sterngold S, Sterngold 1, Sterngold 2, SterngoldB, Sterngold 3Sterngold ImplaMed, 23 FrankMossberg Drive, Attleboro, Mass. 02703, 1-800-243-9942, www.sterngold-implamed.com

The Accepted casting alloys listed above weresubmitted according to American National Stand-ards Institute/American Dental Association, orANSI/ADA, Specification No. 5 for Dental CastingAlloys.1 This specification classifies four types ofdental casting alloys according to hardness. Hard-ness increases with higher base-metal content.dType I is the classification for low-strength cast-ings that are subject to very slight stress (such asinlays).dType II is the classification for medium-strengthcastings that are subject to moderate stress (such asinlays and onlays).dType III is the classification for high-strengthcastings that are subject to high stress (such asonlays, thin cast backings, pontics, full crowns, sad-dles, thick-veneer crowns and short-span fixed par-tial dentures).dType IV is the classification for extrahigh-

758 JADA, Vol. 133, June 2002

strength castings that are subject to very highstress and thin cross section (such as saddles, bars,clasps, thimbles, unit castings, thin-veneer crowns,long-span fixed partial dentures and removable par-tial denture frameworks).

CONSIDERATIONS FOR ACCEPTANCE

ANSI/ADA Specification No. 5 for Dental CastingAlloys1 provides a classification of and specifiesrequirements and test methods for dental castingalloys used in the fabrication of dental restorationsand appliances. All Accepted casting alloys mustmeet the requirements of this specification, whichare outlined below.

SAFETY AND EFFICACY DATA

The composition of the alloy must be within 0.5 per-cent of the weight reported by the manufacturer or0.1 percent of the weight if designated a hazardouselement by the National Institute for OccupationalSafety and Health or the World Health Organiza-tion. Mechanical properties are evaluated by mea-suring yield strength (in megapascals), elongation(percentage) and hardness. Annealed and hardenedsamples are evaluated for yield strength and elon-gation. Hardness, identified by Vickers number,must be within 10 percent of the value designatedby the manufacturer. Physical properties are deter-mined by the melting range, which must be within20 C of that specified by the manufacturer. Thecasting temperature and color also must be specified.

Alloys must demonstrate biocompatibility by con-ducting toxicity testing according to ANSI/ADA doc-ument no. 41, which describes recommended stan-dard practices for biological evaluation of dentalmaterials.2 This testing requirements include cyto-toxicity testing that evaluates cell death in L929 orHeLa cell cultures exposed to the alloy, hemolysistesting in rabbit blood and mutagenicity testingconducted according to the Ames test.

Corrosion testing must be completed for newalloys by comparing their performance to alloys thathave been in use successfully for at least five years.The corrosion test is a static immersion test that isperformed by immersing samples in an acidic solu-tion at 37 C for seven days. The sample is removedand the residual solution is analyzed for metal ionrelease. Additionally, testing must be conducted todetermine the potential of the alloy to tarnish. Tar-nish testing is a cyclic immersion test conductedusing a solution of sodium sulfide hydrate. Thesample is dipped in the test solution for 10 to 15

DENTAL PRODUCT SPOTLIGHT

Dental casting alloys

The Dental Product Spotlight appears in JADA each month to help dentists stay current on new products entering the marketplace and receiving the ADA Seal of Acceptance. These reports are prepared by the ADA Division of Science, in cooperation with TheJournal of the American Dental Association. All rights reserved.

Copyright 2002 American Dental Association. All rights reserved.

JADA, Vol. 133, June 2002 759

D E N T A L P R O D U C T S P O T L I G H T

seconds every minute. The alloy samples then arevisually analyzed with regard to color, reflectivityand roughness.

Both the manufacturer and the ADA laboratoryconduct testing according to specification no. 5 forADA Acceptance.

USES

Casting alloys are used for inlays of all classes, aswell as for individual partial- and full-coverage

restorations and frameworks for fixed and remov-able partial dentures. These alloys also can be usedfor restoration posts and cores and for splints.

1. American National Standards Institute/American Dental Associa-tion. Specification no. 5 for dental casting alloys. Chicago: AmericanDental Association; 1998.

2. American National Standards Institute/American Dental Associa-tion. Biological evaluation of dental materials. ANSI/ADA document 41and 41a. New York: American National Standards Institute; 2001.

Biocompatibility ofdental alloys

In the early years of the ADA Acceptance pro-gram, composition was considered to be one ofthe most important aspects when consideringthe acceptability of a casting alloy for dentalapplications. At that time, most dental alloycompositions were based on gold, which is known tobe extremely resistant to corrosion, as discussedbelow. However, advances in biomaterials researchover the past 20 years, and the increase in the priceof gold in the early 1980s, led to diversification ofthe elements used in dental alloys, so that typicalalloys are now based on gold, palladium, silver,nickel, cobalt or titanium.1,2 Because of the varietyof alloys available, it is not practical to base stan-dards on alloy composition, and, therefore, there hasbeen a national and international movement towardthe establishment of standards that use perfor-mance as the criterion for evaluating alloys used indental applications. An important step in movingtoward a more performance-based standard fordental alloys was to remove the compositionrequirements and make the classification systemmore clinically relevant. As mentioned in the DentalProduct Spotlight on page 758, the current classifi-cation system for dental casting alloys is brokendown into Types I through IV based on the alloysmechanical and physical properties.

Before an alloy can be classified according to itsmechanical and physical properties, however, it firstmust be evaluated for its reactivity in the oralcavity, which is governed by thermodynamic princi-ples and electrochemical reaction kinetics. Thismeans that when an alloy is placed in the oralcavity, the alloy-saliva system will be driven towarda state of equilibrium (thermodynamic equilibrium).At equilibrium, the alloy either will remain stable inits elemental form or oxidize into its ionic form.

High-noble alloys (gold, platinum and palladium)are stable in their elemental form. On the otherhand, most base metal alloys, such as titanium andcobalt-chrome, are stable in the oral environment asa result of passive oxide layers that cover their sur-face. These oxide layers act as a corrosion barrier.The potential for corrosion is important in the bio-compatibility of an alloy. Corrosion can produce ion-ized elements that interact with biological tissues.Therefore, corrosion increases the risk of toxicity,making it desirable to balance corrosion againstclinical performance when choosing an alloy.

Alloys used in dentistry usually contain at leastfour metals and often more, making the issue of bio-compatibility complex. Elements making up analloy are not necessarily released in proportion totheir percent weight; other factors can influencehow much of a particular element is released.1 Forexample, the structure of an alloy may be single-phase (homogeneous) or multiphase (heteroge-neous). This phase structure can be important tothe corrosive properties of an alloy. Other factorsfound to affect corrosion are pH and the presence ofproteins. For example, nickel is released fromnickel-chromium alloys to a much greater extent inan acidic environment,3 and the presence of proteinsin saline was found to enhance the release of silver,copper, palladium and zinc compared with a salinesolution alone (the opposite was found for nickel).4

To select the most biocompatible alloy, dentistsshould familiarize themselves with the corrosionproperties of the alloys they use and should con-sider use of high-noble and single-phase noblealloys that generally are the most biocompatible.

1. Wataha JC. Biocompatibility of dental casting alloys: a review. JProsthet Dent 2000;83:223-34.

2. Leinfelder KF. An evaluation of casting alloys used for restorativeprocedures. JADA 1997;128:37-45.

3. Brune D. Metal release from dental biomaterials. Biomaterials1986;7:163-75.

4. Wataha JC, Nelson SK, Lockwood PE. Elemental release fromdental casting alloys into biological media with and without protein.Dent Mater 2001;17:409-14.

Copyright 2002 American Dental Association. All rights reserved.