Mechanical properties of metal-ceramic alloys at high temperature C.L. Chew1 R.D. Norman =* G.P. Stewart =

1Department of Prosthetic Dentistry School of Dentistry National University of Singapore Singapore 0511 =Department of Restorative Dentistry School of Dental Medicine Southern Illinois University 2800 College Avenue Alton, IL 62002 Received March 20, 1989 Accepted July 27, 1990 *To whom reprint requests should be addressed Dent Mater 6:223-227, October, 1990 Abstract-Four alloys used for the construction of porcelain-fused-to-metal restorations were tested at high temperatures (1000°C) so that loss of properties could be ascertained. In addition, thin flat plates of metal (30 x 11 x 1 mm) with a 9-ram recess and a metal thickness of 0.35 mm were processed for porcelain application and distortion measured at 15 points along the surface prior to and following each firing cycle. Yield and ultimate tensile strengths and elongation were determined on specimens at room temperature and at 1000°C. None of the alloys tested showed a great amount of distortion during the various firing cycles, yet they showed increased change with each successive heating. The greatest distortion occurred with Jelenko "0" alloy. When the mechanical properties were compared, there was a marked loss of both yield and ultimate strength values for each alloy (Jelenko "O"-Y.S., 95.64%, U.T.S., 96.22%; OlympiaY.S., 95.08%, U.T.S., 96.76%; TempoY.S., 91.23%, U.T.S., 93.46%; Biobond II-Y.S., 83.72%, U.T.S., 86.21%). Percent elongation increased by 272% with Biobond II and 370% with Jelenko "0", whereas Tempo and Olympia increased by 120 and 155%. It is apparentthat the palladium-based alloy and the nickelchromium-based alloy have higher mechanical properties at the temperature where porcelain will be applied.

he introduction of the metal-ceramic restoration in the mid-1950's provided a system which combined the strength of the metal substrate and the esthetics of porcelain. Initially, these alloys were made of high gold content to which a base metal was added to alter grain size (Shell and Nielsen, 1962), to provide an oxidizable surface (Tuccillo and Nielsen, 1967), and to control thermal expansion (Shell and Nielsen, 1962; Anthony et al., 1970). By the late 1960's, the cost of gold and the fluctuation within the market caused manufacturers and researchers to seek other systems. Low-content-gold alloys, palladium-based alloys, and, eventually, base-metal alloys were fabricated for this purpose. Considerable research has been directed toward the investigation of the properties of these alloys. These studies include casting a c c u r a c y (Strating et al., 1981; Moffa et al., 1973; Vincent et al., 1977), corrosion resistance (Hodge, 1977; Landesman et al., 1981), effects of heat treatment (Meyer et al., 1979; Vermilyea et al., 1980), and castability of the metals (Vincent et al., 1977; Presswood et al., 1980; Wight et al., 1980; Asgar and Arfaei, 1985). Of considerable interest has been the effect of firing cycles on mechanical properties. O'Brien et al. (1964) studied hardness of two gold alloys before and after heat treatment with a resultant increase in values. Fairhurst and Leinfelder (1966) reported similar results after 14eating specimens to 1000°C and testing them at room temperature. Leinfelder et al. (1969) tested other gold alloys showing higher hardness after high heat treatment. German (1980) felt that this hardness was a result of a Fepttype compound. Other physical properties have been studied by O'Brien et al. (1964); Fairhurst and Leinfelder (1966); Leinfelder et al. (1969); Moffa et al. (1973);


Civjan et al. (1975); Huget et al. (1977); Meyer et al. (1979); German (1980); and Vermilyea et al. (1980). Sag and creep were also studied by Shell and Nielsen (1962); Lugassy and Kumamoto (1974); Anusavice et al. (1979, 1985); Bertolotti and Moffa (1980); and Lugassy et al. (1983). It would seem that information is needed on properties of representative alloys at high temperatures, especially that reached when porcelain is applied. Metal sag should be determined on specimens where thin (0.3 mm) sections exist for porcelain application. Therefore, it is the purpose of this study to measure sag and strength properties of four alloys used for porcelain-fused-to-metal restorations at 1000°C. MATERIALS AND METHODS

Four commercially available metalceramic alloys representing a crosssection of the types of alloys used were selected for the study (Table 1).

Sag and creep t e s t . - T h e specimens were designed to reflect dimensional changes that may occur after each porcelain firing cycle and would include any mismatch between porcelain and metal that might occur. A piece of flat base-plate wax measuring 30 x 11 x 1 mm was used. A disk of wax having a diameter of 9 mm was removed from its center. The base of this hole was then covered with a thin piece of wax of 0.35-ram thickness. This resultant total wax pattern was sprued and invested in phosphate-bonded investment (WhipMix Corp., Louisville, ICY') according to the manufacturer's directions. Patterns to be cast in Biobond II were invested in carbon-free phosphate-bonded investment (Whip-Mix Corp., Louisville, KY). The metals were melted by torch, and the investments were heated to 800°C prior to being cast. Casting was accomplished by the use of a conventional Dental Materials/October 1990 223



Alloy Jelenko '0'






Biobond II

Nickel-chromium .~

Manufacturer J.F. Jelenko Armonk, NY J.F. Jelenko Armonk, NY J.M. Ney Co. Bloomfield, CT Dentsply Int'l. York, PA

30.Omm I

i I

i I

i iI














11.0mm _


.,z,. 0.3ram


Fig. I. Configuration of cast specimen with center space for porcelain application.

÷ 6

÷ 7

.÷ 8


/ ~.12 /


÷ 13

Fig. 2. Numbered points of reference for measurement of metal distortion. 25,0



2 . 5 mm

8.0mm .

J I" - 4 . S m m



16.0 mm

Fig. 3. Dimensions of the cast tensile test specimens.

broken-arm centrifugal machine. The castings were bench-cooled for 30 min before being removed from the investment. Each casting was made smooth with 400-grit Emery paper so that the top surface would be made flat. The f'mal dimension of the metal specimen was 30 x 11 x 0.9 mm. The

thickness of the circular base was 0.33 mm. The porcelain specimen area had a thickness of 1.23 mm and a 1-mm diameter (Fig. 1). On the back of the base of the specimen, 15 points were marked to serve as reference points for measurements of whatever dimensionai change may occur (Fig. 2).


Three specimens were made from each of the four alloys. For the goldcontaining alloys, 50% of new metal was used, while 60% of new metal was used for the other alloys. The "as cast" specimen was placed flat on a glass slab with the back of the base facing upward. A strain gauge with a sharp pin attached to it was used to make the measurements. The strain gauge was clamped in a f'Lxed position in relation to the glass slab. The point of the pin was lowered to come into contact with the reference points on the specimens, and the readings on the strain gauge were recorded. These readings sel-ve as the baselines. Porcelain (Williams Gold, Buffalo, NY) was baked onto the circular portion of the specimen as follows. Oxidation: The specimen was placed on two supports set 26 mm apart with the circular end facing upward. This was set at the door of an oven that was pre-heated to 540°C for one min before being placed into the muffle of the oven. The temperature of the oven was raised at the rate of 40°C per minute until the oven temperature reached 985°C, at which time the specimen was removed and benchcooled under a glass beaker. Opaque bake: Opaque porcelain was applied to the base and sides of the circular section. The specimen was then placed at the door of the pre-heated oven (540°C) for one min before being moved into the muffle of the oven. Vacuum was applied, and the temperature of the oven was raised at the rate of 40°C per min until it reached 960°C. At this temperature, the vacuum was released, and the specimen was removed and benchcooled under a glass beaker. Body and incisal bake: Porcelain was condensed into the circular section until it was flush with the surface of the specimen. It was then fired as before. Glazing: Glazing was done in air by means of the porcelain firing cycle described above. However, the specimen was left in the oven for one min at a temperature of 960°C before being removed. After each of the firing procedures, the specimen was replaced on the glass slab, and new readings on

the strain gauge at the 15 reference points were recorded. The dEferences between these sets of values and those of the baselines would indicate the amount of dimensional change that occurred after each firing cycle.

Tensile test.-The specimens were made similar to those described by Nicholls and Lemm (1985). The shape and dimensions are shown in Fig. 3. The wax patterns were made by injection of molten wax into a warm split-metal mold so that consistent dirsensions would be ensured. These wax patterns were invested in the same p h o s p h a t e - b o n d e d investments used for the sag and creep specimens. The amount of new metal used for each casting was as previously described. The casting was bench-cooled for 30 min before being divested. The specimens were made from each alloy. The ultimate tensile strengths of the specimens were measured in the Instron Testing Machine (Model 1123, Instron Corp., Canton, MA) with a load cell capacity of 1000 Kg. The test specimens were held by specially machined grips made of MARM246 metal and were able to withstand the testing temperature. Five specimens of each alloy were tested at room temperature. The specimens were properly aligned between the two stainless steel grips, and the tensile strengths were measured at a cross-head speed of 5 mm per min. Data were calculated from the chart paper. The remaining five specimens of each alloy were tested at a temperature of 1000°C. The specimens were placed between the grips, and the furnace was closed. The furnace had been pre-heated to 300°C. The temperature of the furnace was raised at the rate of 60°C per man to 1000°C. The specimens were heat-soaked for one min at 1000°C -+ 5°C before being tested. A cross-head speed of 5 mm per min was selected for high-temp e r a t u r e testing. The percentage elongation and the yield strength (0.5% offset) were calculated fi'om the stress-strain curve obtained on the chart paper print-out. Statistical analysis was by means of ANOVA and Scheff6's Multiple Comparison Test.

RESULTS The sag Jelenko in Table greatest

and creep test data for the " 0 " specimens are shown 2. These data represent the deviation from baseline and

present three main patterns: positions 1, 5, 6, 10, 11, and 15 near the supports (A); positions 2, 4, 7, 9, 12, and 14 midway between the supports and the mid-points (B); and


SAG AND CREEPTESTRESULTSFOR JELENKO"0" AFTERFIRINGSTEPS(ram) Position Oxidation Opaque Body Glaze 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

0.050(0.016) 0.075(0.023) 0.075(0.018) 0.075(0.006) 0.050(0.011) 0.050(0.008) 0.080(0.005) 0.080(0.018) 0.085(0.011) 0.070(0.000) 0.060(0.018) 0.075(0.006) 0.075(0.014) 0.070(0.008) 0.060(0.009)

0.055(0.015) 0.075(0.016) 0.085(0.017) 0.075(0.004) 0.045(0.009) 0.060(0.015) 0.090(0.018) 0.100(0.009) 0.060(0.018) 0.075(0.021) 0.065(0.006) 0.085(0.004) 0.090(0.006) 0.085(0.015) 0.060(0.013)

0.070(0.011) 0.080(0.005) 0.100(0.017) 0.085(0.011) 0.050(0.014) 0.050(0.014) 0.080(0.004) 0.095(0.020) 0.090(0.016) 0.080(0.011) 0.060(0.010) 0.085(0.006) 0.110(0.012) 0.110(0.005) 0.095(0.011)

0.090(0.012) 0.115(0.024) 0.150(0.007) 0.115(0.011) 0.060(0.009) 0.065(0.021) 0.105(0.011) 0.135(0.011) 0.130(0.010) 0.095(0.007) 0.060(0.016) 0.110(0.014) 0.140(0.015) 0.145(0.018) 0.110(0.017)



A g C

0.057(0.011) 0.075(0.012) 0.077(0.018)

0.060(0.014) 0.078(0.016) 0.092(0.010)

0.068(0.017) 0.088(0.012) 0.102(0.018)

0.080(0.019) 0.120(0.018) 0.142(0.014)


0.009(0.009) 0.013(0.009) 0.023(0.009)

0.011(0.008) 0.014(0.011) 0.027(0.007)

0.013(0.011) 0.016(0.011) 0.022(0.011)

0.015(0.011) 0.027(0.010) 0.035(0.014)


0.028(0.020) 0.015(0.021) 0.020(0.015)

0.023(0.016) 0.018(0.015) 0.015(0.014)

0.033(0.022) 0.017(0.016) 0.012(0.017)

0.037(0.019) 0.022(0.014) 0.013(0.018)

A 0.004(0.007) 0.009(0.009) 0.013(0.010) a 0.007(0.007) 0.008(0.006) 0.008(0.008) C 0.007(0.006) 0.012(0.014) 0.010(0.016) Position A representsthe outermost six measurementson the specimens. Position B representsthe second six measurementson the specimens. Position C represents the three middle measurementson the specimens.

0.013(0.010) 0.008(0.007) 0.012(0.013)






22°C Ultimate Yield Tensile Specimen Strength Strength 1 361.82 MPa 459.42MPa 2 343.35 441.49 3 366.49 466.49 4 401.78 498.33 5 412.18 511.58 Mean 377.12 475.46 S.D. 28.83 28.81 Percent of As-cast Value

Physical Properties

1000°C Ultimate Percent Yield Tensile Elongation Strength Strength 11.38% 16.38MPa 18.58MPa 12.88 16.38 18.38 13.88 16.78 17.78 12.75 15.58 17.58 11.75 17.18 17.58 12.53 16.46 17.98 0.99 0.59 0.47 4.36% 3.78%

Percent Elongation 43.12% 37.50 44.38 52.50 40.00 43.50 5.70 370.21%

Dental Materials~October 1990


the middle of the specimens 3, 8, ~nd 13 (C). Since these data are [~easonably consistent, the values of the groups above have been combined for all materials, and these appear in Table 3. In all cases, the data are stated as differences between baseline and a specific firing cycle expressed in millimeters. Accuracy of the measuring equipment is 0.005 mm. The results of the tensile tests are found in Tables 6 through 9 for :/elenko "0", Olympia, ~empo, and Biobond II. Data are presented for

specimens run at. both room temperature and 1000°C. Statistical evaluations of the data were conducted by use of ANOVA, and multiple comparisons were run by use of the Scheff4's Test. Although the statistical comparisons were made for each position on the sag specimens, data reported here represent the displacement at the maximum points (positions 3, 8, 13) for each of the four alloys. These data appear in Table 8. The results of Scheff4's Test for the tensile test specimens are found in Table 9.


, , 22oc Ultimate Yield Tensile Percent Yield Specimen Strength Strength Elongation Strength 1 459.94 MPa 783.61MPa 21.50% 24.37MPa 2 489.38 761.83 19.38 20.37 3 478.97 752.06 23.25 22.97 4 467.72 753.91 18.88 23.97 5 453.03 747.81 18.25 23.97 Mean 469.81 759.84 20.25 23.13 S.D. 14.58 14.22 2.07 1.63 Percent of As-castValue 4.92%

1000°C Ultimate Tensile Strength 26.17MPa 20.77 25.97 25.57 24.77 24.65 2.23 3.24%

Percent Elongation 25.63% 20.00 40.62 52.50 18.13 31.38 14.74 154.96%

1000oC Ultimate Percent Yield Tensile Elongation Strength Strength 14.51% 52.93MPa 54.93MPa 18.12 39.95 50.43 16.90 45.94 48.94 15.70 41.94 46.94 15.13 52.93 55.93 16.07 46.74 51.43 1.44 6.05 3.87 8.77% 6.54%

Percent Elongation 11.25% 28.75 25.63 18.75 11.88 19.25 7.90 119.79%

TABLE 6 TENSILETEST RESULTSFORTEMPO 22°C Ultimate Yield Tensile Specimen StreAgth Strength 1 529.29 MPa 792.63MPa 2 533.29 785.00 3 527.32 803.29 4 539.32 756.90 5 535.32 792.63 Mean 532.91 786.09 S.D. 5.03 17.57 Pe~ent of As-castValue



Ultimate Yield





1 611.29 MPa 2 555.32 3 561.25 4 573.32 5 606.32 Mean 581.50 S.D. 25.82 Percent of As-castValue

823.32MPa 801.29 793.83 844.29 821.89 816.92 19.94

Ultimate Percent


Elongation Strength 11.88% 10.75 10.28 11.94 12.06 11.38 0.81

97.87MPa 95.87 89.88 91.88 97.88 94.68 3.63 16.28%


Percent Elongation

115.85MPa 113.85 107.86 107.86 117.84 112.65 4.60 13.79%

51.25% 41.25 18.13 24.38 20.00 31.00 14.54 272.41%




The results of the sag and creep test show that only the specimens made from Jelenko "0" alloy were displaced to a degree whereby clinical effects might be observed. Although no attempt was made to evaluate possible mismatch between porcelain and metal, previous data would indicate that the system used here would minimize such effects. Furthermore, there was a significant change in sag and creep during each phase of the firing cycle for this alloy-which was a result of temperature, not mismatch. However, even in this situation only a 0.5% displacement occurred, which may be below the visual assurance. All of the other alloys were at a 0.1% or less displacement when the alloys were heated to 1000°C and cycled through the firing process for porcelain application. It is recognized that a change in specimen design might affect these results. For example, a continuous 0.33-mm porcelain space across the ll-mm specimen would greatly weaken this sample and allow g r e a t e r distortion to occur. Nevertheless, the test does differentiate among alloy systems. Of more interest is the g r e a t change in mechanical properties tested at 1000°C. The loss of 95%+ strength in some alloys at this temperature should cause concern. Of particular interest are the size and design of specimens used for porcelain application. In the past, only esthetics and pulpal protection have been considered. This study points out the need for the amount of metal and its location to be evaluated. CONCLUSIONS

Of the four alloy systems used, the high-gold alloy had the greatest distortion and the g r e a t e s t loss of strength at high temperature. There was a loss of strength for the other three alloys, with the low-gold alloys showing change near that seen with the high-gold but with little distortion. Both the palladium-based and the nickel-chromium alloys had low distortion and higher strengths at high temperature. REFERENCES

ANTHONY, D.H.; BURNETT,A.P.; SMITH, D.L.; and BROOKS,M.S. (1970): Shear

Test for Measuring Bonding in Cast Gold Alloy-Porcelain Composites, J Dent Res 49: 27-33. A~USAV]CE, K.J.; RINGLE, R.D.; and WEBER, R. (1979): Dynamic Measurement of Porcelain-Fused-to-Metal Alloy Sag Resistance, IADR Progr & Abst 58: No. 686. ANUSAVICE, K.J.; SHEN, C.; HASHINGER, D.; and TwIccs, S.W. (1985): Interactive Effect of Stress and Temperature on Creep of PFM Alloys, J Dent Res 64: 1094-1099. AsG~, K. and ARFAEI, A.H. (1985): Castability of Crown and Bridge Alloys, J Prosthet Dent 54: 60-65. BERTOLOTTI, R.C. and MOFFA, J.P. (1980): Creep Rate of Porcelain-Bonding Alloys as a Function of Temperature, J Dent Res 59: 2062-2065. CIVJAN, S.; HUGET, E.F.; DVIVEDI, H.; and COSNER,H.J., JR. (1975): Further Studies on Gold Alloys Used in the Fabrication of Porcelain-Fused-toMetal Restorations, J A m Dent Assoc 90: 659-665. FAIRHURST, C.W. and LEINFELDER, K.F. (1966): Heat Treating Porcelain Enameled Restorations, J Prosthet Dent 16: 554-556. GERMAN, R.M. (1980): Hardening Reactions in a High-gold Content Ceramometal Alloy, J Dent Res 59: 19601965. HODGES,R.J. (1977): The Corrosion Resistance of Gold and Base-Metal Alloys. In: Proceedings: Alternatives to Gold Alloys in Dentistry, T.M. Valega, Ed., Washington, DC: US Department of Health, Education and Welfare, pp. 106-137. HUGET, E.F.; DVIVEDI, H.; and COSNER, H.E., JR. (1977): Properties of Two Nickel-Chromium Crown and Bridge Alloys for Porcelain Veneering, J A m Dent Assoe 94: 87-90. LANDESMAN, H.M.; GENNARO, G.C.; and MARTINOFF,J.T. (1981): An 18-Month Clinical Evaluation of Semi-Precious and Non-Precious Alloy Restorations, J Prosthet Dent 46: 161-166. LEINFELDER, K.F.; SERVAIS, W.J.; and 0'BRIEN, W.J. (1969): Mechanical Properties of High Fusing Gold Alloys, J Prosthet Dent 21: 523-528. LUGASSY, A.A. and KUMAMOTO, Y. (1974): Creep of Alloys Used in Porcelain-Fused-to-Metal Restoration, IADR Progr & Abstr 53: No. 740. LUGASSY, A.A.; MOFFA, J.P.; and WATANABE, L. (1983): Study of the Creep Rate of Ceramo Alloys, J Dent Res 62: 286, Abst. No. 1056 (AADR). MEYER, J.M.; PAYiU~, J.; and HALLY, J.H. (1979): Evaluation of Alternative


3 8 13

0.075(0.018)'] 0.080(0.018)J* 0.075(0.014).]

0.085(0.017)] 0.100(0.009)|* 0.090(0.006)1

3 8 13

0.025(0.009)] 0.025(0.004) / 0.020(0.003)J

0.025(0.006)] 0.030(0.002)| 0.025(0.006)J

3 8 13

0.015(0.017)] 0.025(0.007)| 0.020(0.008)J

0.020(0.017)] 0.010(0.003)| 0.015(0.009)1



0.100(0.017)'] 0.095(0.020)J* 0.110(0.012)1

0.150(0.007)] 0.135(0.011)|* 0.140(0.0t5)J

0.025(0.006)] 0.035(0.005)| 0.020(0.007)1

0.035(0.007)] 0.045(0.006)| 0.025(0.009)J

0.015(0.021)] 0.005(0.004)| 0.015(0.006)1

0.051(0.018)] 0.005(0.005)| 0.020(0.007)J

0.020(0.010)] 0.005(0.005)| 0.005(0.005)J

0.020(0.0!1)] 0.005(0.005)| 0.010(0.004)J


3 0.010(0.007)] 0.020(0.009)] 8 0.005(0.001)| 0.010(0.007)| 13 0.005(0.004)J 0.005(0.004)J ] No significant difference (probability level, 0.05). * Significant difference (probability level, 0.05).

Specimen Jelenko "0" Olympia

TABLE 9 STATISTICALANALYSIS OF TENSILETEST SPECIMENS 22°C 1000°C Ultimate Ultimate Yield Tensile Percent Yield Tensile Strength Strength Elongation Strength Strength * * 1 -1 ] j

Biobond II ] .J * Significant difference (probability level, 0.05). ] No significant difference (probability level, 0.05). ] No significant difference between materials at ends of brackets. Alloys to Precious Ceramic Alloys, J Oral Rehabil 6: 291-230. MOFFA, J.P.; LUCASSY, A.A.; GUCKES, A.D.; and GETTLEMAN,L. (1973): An Evaluation of Non-precious Alloys for Use with Porcelain Veneers. Part I. Physical Properties, J Prosthet Dent 30: 424-431. NICHOLLS, J.I. and LEMM, R.W. (1985): Tensile Strength of Presoldered and Postsoldered Joints, J Prosthet Dent 53: 476-482. O'BRIEN, W.J.; KRING, J.E.; and RYGE, G. (1964): Heat Treatment of Alloys to be Used for the Fused Porcelain Technique, J Prosthet Dent 14: 955--960. PRESSWOOD, R.G.; SKJONSKY, H.S.; HOPLEINS, G.; PRESSWOOD,T.L.; and PENDLETON,M. (1980): A Base-Metal Alloy for Ceramometal Restorations, J Prosthet Dent 44: 624-629. SHELL, J.S. and NIELSEN, J.P. (1962): Study of the Bond Between Gold and Porcelain, J Dent Res 41: 1424-1437.



* .

* ,

Percent Elongation

]i, I .J

STRATING, H.; PAMEIJER, C.H.; and GILDENHUYS,R.R. (1981): Evaluation of the Marginal Integrity of Ceramometal Restorations. Part I, J Prosthet Dent 46: 59-65. TUCCILLO,J.J. and NIELSEN,J.P. (1967): Creep and Sag Properties of a Porcelain-Gold Alloy, J Dent Res 46: 579583. VERMILYEA, S.C.; HUGET, E.F.; and VILEA, J.M. (1980): 0bselwations on Gold-Palladium-Silver and Gold-Palladium Alloys,J Prosthet Dent 44: 294299. VINCENT, P.F.; STEVEN, L.; and BASFORD,K.E. (1977): A Comparison of the Casting Ability of Precious and Non-Precious Alloys for Porcelain Veneering, J Prosthet Dent 37: 527-536. WIGHT, T.A.; GRISIUS, R.J.; and GAUGLER,R.W. (1980): Evaluation of Three Variables Affecting the Casting of Base Metal Alloys, J Prosthet Dent 43: 415-418.

Dental Materials~October 1990 227

Mechanical properties of metal-ceramic alloys at high temperature.

Four alloys used for the construction of porcelain-fused-to-metal restorations were tested at high temperatures (1000 degrees C) so that loss of prope...
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