Semiprecious

A preliminary

alloys

for cast rBstoyEIpions:

report

John W. Dale, B.D.S., D.D.S., M.D.%,*

and John B. Moser, MSc.,

Northwestern

Chicago,

University

Dental

School,

Ph.D.**

Ill.

M

anufacturers of semiprecious dental alloys promote these alloys as useful substitutes for gold alloys in restorative dentistry. To be clinically acceptable a dental casting alloy must (1) be capable of being accurately cast, burnished, and adjusted with available dental instruments, (2) resist occlusal forces, and (3) not tarnish or corrode in the oral environment. This article describes an in vitro study of five semiprecious alloys (Table I) . Each alloy was selected because it could be cast by a technique similar to that used with gold dental alloys. They were tested for accuracy of fit, marginal adaptation, ease of polishing, and corrosion. Few studies of semiprecious alloys have been published.l, 2 Our in vitro evaluation was made to determine whether semiprecious alloys, most of which have a silver-palladium base, should be used in the mouth.

MATERIALS AND METHODS Five recently extracted premolar teeth were prepared for mesio-occlusal inlays. The preparations were waxed directly and the patterns were immediately vacuuminvested. Five wax patterns were made on an MOD National Bureau of Standards die and these also were immediately vacuum-invested. One wax pattern from a tooth and one pattern from the MOD die were invested to be cast in each alloy to be investigated. Those patterns to be cast in Forticast,? Alborium,? Paladin 3,$ and Stemgold 66$ were vacuum-invested in Kerr Luster Cast.8 The invested patterns were allowed to bench-set for 30 minutes and then were placed in a burnout furnace for 70 minutes at 900’ F. before casting. The patterns to be cast in Williams dloy// *Visiting Associate Professor, Fixed Prosthodontics. **Associate Professor, Biological Materials. tJ. F. Jelenko & Co., New Rochelle, N. Y. SSterndent Corp., Mt. Vernon, N. Y. IKerr Mfg. Co., Romulus, Mich. /I Williams

Gold

Refining

Co.,

Inc.,

Buffalo,

N. Y.

627

628

Dale

J. Prosthet. Dent. December. 1977

and Moser

Table I. Physical properties of evaluated alloys* Alloy

Alborium Forticast Paladin 3 Sterngold 66 Williams WLW

Manufacturer

J. F. Jelenko & Co., New Rochelle, N. Y. J. F. Jelenko & Co., New Rochelle, N. Y. Stemdent Corp., Mt. Vernon N. Y. Sterndent Corp., Mt. Vernon, N. Y. Williams Gold Refining Co., Inc., Buffalo, N. Y.

Vickers hardness

Per cent elongation

Melting range (” F.)

180

10

1,705-l ,870

195

18

1,790-1,810

140

15

1,700-l ,800

159

12

1,730-l ,810

150

5

1,915-2,070

*Supplied by manufacturers. were vacuum-invested in Jelenko Complete,* were allowed to bench-set for 45 minutes, and then were heat-soaked at 1,350° F. for 60 minutes. All units were sandblasted after casting to remove any remaining investment. The manufacturers’ instructions were followed at all times with all materials that were used. A dental laboratory technician invested the patterns and we cast the inlays. Each sandblasted casting was placed on a tooth or die for observation and evaluation of dimensional change. Each casting was examined in situ under a binocular microscopet for marginal adaption and then the cervical margins were photographed$ at 30x magnification (Figs. 1 and 2). A 2 pennyweight specimen of each alloy was polished with 4/O emery paper after being mounted in an acrylic resin base fitted with contact electrodes. Each specimen was then immersed in Ringer’s solution. Polarization was usually begun at a potential approximate to the open-circuit corrosion potential. Succeeding potential increases were 50 mv. ; a period of 5 minutes elapsed at each potential setting before a current reading was taken. Constant controlled potentials were maintained using a Wenking potenti0stat.g The generated current was measured and recorded on a strip-chart recorder. The electrolyte was constantly exposed to the atmosphere and kept at a room temperature of 25 ? lo C. RESULTS AND DISCUSSION Clinically all of the castings made on the Class II preparations showed accurate fit and marginal integrity; no deficiencies could be found with a sharp explorer. Under microscopic examination the Williams WLW hard casting showed signs of slight shrinkage at the margins, but the other castings were extremely accurate. All of the castings on the National Bureau of Standards die were satisfactory except the Williams WLW alloy, which again showed slight shrinkage. All of the castings could be highly polished using conventional polishing tech* J.E. Jelenko & Co., New Rochelle, N. Y. tBausch & Lomb, Inc., Rochester, N. Y. $Polaroid Land instrument camera, Model EDlO, Polaroid Corp., Cambridge, Mass. $Type 70 TSl, Brinkman Instruments, Westbury, N. Y.

Semiprecious alloys

for

cast restorationr

629

Pig. 1. Cervical margins of three castings: A, the Paladin 3 tooth-alloy margin at 30x magnification showing a cervical margin and a portion of an axial margin; B, the Alborium tooth-alloy margin at 30x magnification showing a cervical margin after polishing; the margin is accurate; C, the Williams WLW hard die-alloy casting at 30x magnification showing the cervical margin and a portion of an axial margin. niques and polishing did not affect their marginal integrity. The low percentage of elongation and the hardness of the alloys made it extremely difficuit to burnish the margins. Fig. 3 shows the potentiostatic anode polarization curves of the five semiprecious and a type III casting alloy? were alloys. Curves for a base-metal gold substitute” obtained from previous evaluations.3 The in vitro behavior of the castings under the experimental conditions should give an accurate indication of corrosion behavior in the mouth.4-s Voltage curves that tend to be parallel to the abscissa (horizontal) indicate regions of activity, especially when they occur at active potentials, i.e., potentials situated in the upper part of the potential-vs.-current plot. Curves tending to be parallel to the ordinate (vertical) indicate regions of passivity. Curves in the upper right of Fig. 3 starting from a strongly negative open-circuit potential represent alloys that are more prone to corrosion than those represented in the lower left of the diagram. The shaded area in Fig. 3 indicates the range of the anode polarization measure*Howmedica III, Austenal Prod., Chicago, Ill. tProcast, J. Aderer, Inc., New York, N. Y.

630

Dale

and

J. Prosthet. Dent. December, 1977

Moser

Fig. 2. Forticast die -alloy casting portion of a cervical margin.

at

10x

magnification

axial

margin

and

a

GOLDJY

a.

I 1

*loxi

1

,O-6

IO-

,

Comparison

of

sentially silver-palladium

I

4

CUVENT

3.

an entire

-1

g +eoo-

Fig.

showing

potentiostatic

lo0061~~

anode

I 2

I I@ O

IO

2

(MAKM~)

polarization

behaviors

of

semiprecious

alloys

(es-

based) with base-metal and gold alloys.

(AG-PD) fixed prosthodontic alloys. The data are compared with those from a typical nonprecious metal alloy based on the nickelchromium system* and a type III casting gold.? alloys exhibited potential-current relationships intermediate All five semiprecious to those of base alloys and noble alloys. These semiprecious alloys were active in the range between 0 and +400 to +500 mv. and then became passive as the current density approached 1 ma. per square centimeter. The relatively low current densities of the active regions and the uniformly passive behavior in the noble potential region indicate that little corrosion should be expected in the oral environment. ments of the five silver-palladium

*Howmedica +Procast,

III, J, Aderer,

Austenal Inc.,

Prod., New

York,

Chicago, N. Y.

111.

Volume

Number

38

Semiprecious

6

alloys

for

cast

restorations

631

CONCLUSION A previous clinical evaluation indicated that semiprecious metals had a definite place in the construction of dowels and cores in endodontically treated teeth.2 The results from the present in vitro study suggest that those alloys do have a place in the fabrication of single castings as types III and IV gold alloy substitutes. Although when compared with a type III gold alloy the behavior of the semiprecious alloys tested was less like that of a noble alloy, the semiprecious alloys appeared less active than the base-metal alloy. This suggests that the semiprecious alloys should be acceptably resistant to corrosion in the oral environment. We would like to acknowledge Dr. G. I. Brinsden, Dr. E. H. Greener, Chairman of Biological Materials, for allowing us to conduct this study.

Chairman Northwestern

of Fixed Prosthodontics, University Dental

and School,

References I. 2. 3. 4. 5. 6.

7. 8.

Huget, E. F., and Civjan, S.: Status Report on Palladium-Silver-Based Crown and Bridge Alloys, J. Am. Dent. Assoc. 89: 383-385, 1974. Dale, J. W., and Moser, J.: A Clinical Evaluation of Semiprecious Alloys for Dowels and Cores, J. PROSTHET. DENT. 38: 161-164, 1977. Moser, J.: Unpublished data. Watson, J. F., and Wolcott, R. B.: A Method for the Control of Galvanism, J. PROSTHET. DENT. 35: 279-282, 1976. Sarkar, N. K., and Greener, E. H.: In Vitro Corrosion Resistance of New Dental Alloys, Biomater. Med. Devices Artif. Organs 1: 121-129, 1973. Acharya, A., Sandrik, J. L., Wragg, L. E., and Greener, E. H.: Correlation of Microstructures and Open Circuit Potentials of Gold-Iron Alloys With Their in Vivo Corrosion Behavior, J. Biomed. Mater. Res. 2: 407-427, 1968. Hoar, T. P., and Mears, D. C.: Corrosion-Resistant Alloys in Chloride Solutions: Materials for Surgical Implants, Proc. R. Sot. Lond. 294(A) : 486-510, 1966. Greener, E. H., Harcourt, J. K., and Lautenschlager, E. P.: Materials Science in Dentistry, Baltimore, 1972, The Williams & Wilkins Company, p. 363. DR. DALE 203 RAMSGATE RD. SANS SOUCI 2219 NEW SOUTH WALES,

AUSTRALIA

DR. MOSER NORTHWESTERN UNIVERSITY DENTAL SCHOOL 311 E. CHICAGO AVE. CHICAGO, ILL. 60611