Bond strengths
of high-palladium
R. E. Lorenzana, D.D.S.,* L. A. Chambless, and R. S. Staffanou, D.D.S., M.S.**** Baylor
College
of Dentistry,
Dallas,
D.D.S.,**
content alloys V. A. Marker,
Ph.D.,***
Tex.
Palladium-based alloys have had a significant import on the fabrication of ceramometal restorations. This article compares the bond strengths of four palladiumbased alloys with that of a high-noble alloy. Tests were designed to closely represent clinical situations. Bond strengths of the palladium alloys compared favorably with the high-noble metals; palladium alloys containing up to 2% gold were the best. (J PROSTHET DENT 1990;64:677-80.)
T
base alloys have had a significant impact on the fabrication of ceramometal restorations. This project compares the porcelain bond strength of four high-palladium alloys to the bond strength of a highgold content ceramic alloy. Anusavice et a1.l have analyzed the complexity of the ceramometal bond and have indicated that a shear test constitutes the ideal measurement, but that several different tests should be used. Two types of bond strength tests were performed in this study, (1) a shear test and (2) a three-point flexure test. These tests most closely represent the clinical situation. he new
MATERIAL
palladium
AND
METHODS
The ceramic-metal bond strengths of specimens made from palladium-rich alloys were evaluated and compared to the bond strengths of specimens made with a type IV gold alloy. The materials used in these tests are listed in Table I. Two experimental procedures were used to determine the bond strengths, (1) a three-point flexure test and (2) a shear bond strength test.
Specimen
preparation
Patterns for the metal specimens were cut from sheets of acrylic resin (Temporary Splint Material, Buffalo Dental Mfg. Co., Brooklyn, N.Y.). For the flexure tests, 10 patterns for each alloy were made to the dimensions of 20 X 10 X 0.5 mm. Another 10 patterns for each alloy were prepared to a size of 15 x 3 x 2 mm, for the shear bonding test. To ensure uniformity, the acrylic resin patterns were invested (Hi-Temp Investment, Whip Mix Corp., Louisville, Ky.) in groups of 10 and cast by use of an induction casting maching (Unitek, Monrovia, Calif.). The surfaces of all of the specimens were treated according to the manufacturers’ recommendations before application of the ceramic. Jigs were designed so that the total surface area and the location of the ceramic were standardized on all specimens. Each specimen received an opaque layer (0.5 mm) and a body layer (1.5 or 3 mm) of ceramic. A diagram of the specimen designed for flexure testing is shown in Fig. 1. The design of the specimen used for shear bond testing is shown in Fig. 2.
*Assistant Professor,Department of Fixed Prosthodontics. **Associate Professor,Department of Fixed Prosthodontics. ***Associate ****Professor tics. 10/l/22731
Table
I.
Professor, Department of Dental Materials. and Chairman, Department of Fixed Prosthodon-
Materials
used in study
Composition
Metal alloys PGC 78%’
Pd, 2% AU pd, 2% Au Pd, 0% Au
Tribute PTM
68% 88%
Option SMG-2
79% Pd, 2% Au 87% Au, 7% Pt, 5% Pd
Ceramic Vita
THE
JOURNAL
;
Manufacturer
Englehard Co., Carteret, N.J. Sterngold, Mt. Vernon, N.Y. J. F. Jelenko, New Rochelle, N.Y. J. M. Ney Bloomfield, Conn. J. M. Ney
Unitek
OF PROSTHETIC
DENTISTRY
Corp.,
Monrovia,
Calif.
1. Diagram of ceramometal specimen in three-point flexure test. M, Metal; P, porcelain; F, force.
Fig.
677
LORENZANAETAL
Fig. 2. Diagram of ceramometal specimen in shear bond test. M, Metal; P, porcelain; A, acrylic; F, force.
Table
II.
Results from three-point flexure test Load
(lb)
BRS
tween materials, the load at failure and the modulus of elasticity were used to calculate a strength parameter (BRS) from the following equation?
x lo+’
Specimen
x
SD
x
SD
Option Tribute PGC
7.9
0.9
3.1
7.6 7.4 5.6 5.5
1.1
2.1
1.2 0.9 1.1
1.8 2.3 1.6
0.4 0.3 0.3 0.4 0.3
maximum
SMG-2 F’TM 88 p < 0.05; Load
CD, 1.6; BRS CD, 0.7.
The ceramic layers were fired under vacuum (1 atmosphere). Starting at 700’ C, the temperature was programmed to increase at 33’ per minute until a temperature of 920” was reached. The vacuum was released and the specimens were removed from the furnace. After the specimens were bench cooled, the opaque layer and then the body layer of the ceramic were applied and fired under vacuum in the same manner up to 940’ C. All ceramic procedures were performed by one clinical researcher to ensure uniformity of the specimens. For the shear bonding test, the porcelain was embedded in acrylic resin so that the specimen could be mounted in the test apparatus.
Bond
strength
tests
The ceramic-metal bond strengths of the completed specimens were evaluated by use of the flexure test and the shear bond strength test. Each of these bond strength tests produces different stress concentrations in the specimens and thus provides unique information on the bond strength.’ For the flexure strength test, the specimens were placed in the bending apparatus with the ceramic positioned on the side opposite the applied load (Fig. 2). The force was applied at a constant rate of 0.5 mm/min with the Universal testing machine (Instron Model 1250, Instron Corp., Canton, Mass.). For analysis and comparison be-
676
BRS = modulus
strength
of elasticity
+ S E
In this equation the bond strength ratio (BRS) is proportional to the maximum shear stress (S) and inversely proportional to the modulus of elasticity (E) of the material. The shear bond test specimens were tested in a parallel shear test (Fig. 2). Again the universal testing machine was used to apply a load at the constant rate. As indicated in Fig. 2, the force was applied to the interface of the ceramic-metal specimen. This procedure has been shown to produce lessvariability in the resu1ts.l For this test method the shear force was computed with the following equation:3 z=yG This equation shows the shear stress (T) is proportional to the shear modulus (G) and the shear strain (7). Strength data were subjected to an analysis variance, a Scheffe critical difference test, and regression analysis.
Management
of surface
roughness
After the tests, the specimens were examined to determine whether failure occurred at the interface or as a tensile fracture in the ceramic. In addition, the average surface roughness of the fractured interface surface (Ro) and the noninterface surface (RM) were measured with a profilometer (Surftest R III, Mitutoyo Mfg. Co., Ltd., Tokyo, Japan). A ratio (R&M) of these values was used to indicate the relative surface roughness and to compensate for any inherent roughness of the different alloys. The surfaceroughness ratios were compared with the bond strength results for all five alloys by use of regression analysis.
RESULTS The results from the flexure strength testing are given in Table II. Compared with the type IV gold alloy specimens,
DECEMBER1990
VOLUME64
NUMBER6
BOND
STRENGTHS
OF HIGH-PALLADIUM
0 0
ALLOYS
OPTION
.
TRIBUTE
H TRIBUTE
A PGC V PTM-88 8,
0
=
0
10
20 SHEAR
BOND
OF PROSTHETIC
V
PTM-00 -4
cl
T 40
30
STRENGTH
(MPa)
3. Graph illustrates correlation between flexure test and shear bond test.
the loads produced by the flexure test were significantly greater for specimens from .three of the alloys rich in Pd (Option, Tribute, and PGC). However, when the results were normalized by the modulus values, only specimens from one alloy, Option, produced a BRS value significantly greater than the BRS values for the type IV gold alloy specimens or the alloy specimens rich in Pd. The BRS value for SMG-2 from this study was slightly higher (2.3 x 10v3) than the previously reported value (1.4 X 10-3).2 This discrepancy could be the result of differences in specimen design and should not affect the comparison between the specimen tested in this study. The BRS values calculated from the flexure test were compared with the shear bond strengths (Table III). For this test, the specimens made from Tribute alloy exhibited significantly higher ceramic-metal bond strengths. Fig. 3 shows that the correlation was much higher between the shear bond strengths and the flexure loads (r = 0.87) than with BRS values (r = 0.39). Regardless of the evaluation method, the bond strength results for specimens of the Pd rich alloy, PTM-88, were consistently the lowest. PTM 88 alloy contains no gold as do the other alloys, a factor that may have an affect on the bond strength. A comparison of the BRS values and the surface roughness ratio produced a correlation of 0.97 (Table III). The surface roughness ratio provided an indication of the amount of ceramic adhering to the metal after failure. Thus, k/RM values exceeding 1 meant that the debonded ceramic-metal interface surface was rougher than the noninterface surface. There was no significant difference in the measured surface roughness ratios for specimens made from Option, SMG-2, and Tribute alloys (Table III). These large ratios (2.3 to 1.6) suggested that the debonding was
JOURNAL
PGC
/ / ’
THE
A
A,”
z
Fig.
OPTION
DENTISTRY
Table III. Comparison of bond strengths determined by flexure test, shear bond test, and surface roughness measurements Ems Specimen
Option SMG 2 Tribute PGC PTM 88
x 10-s
Shear strength
bond (MPa)
Surface ratio
roughness (&/RM)
x
SD
x
SD
x
SD
3.1
0.4 0.4 0.3 0.3 0.3
23.5 31.1 23.3 11.7
4.6 5.5 2.5 3.6
2.3 1.7 1.6 1.2 0.9
0.7 0.1 0.2 0.5 0.4
2.3 2.1 1.8 1.6
p < 0.05; BRS CD, 0.7; shear bond strength CD, 0.9.
CD, 6.2; surface roughness
ratio
not a completely adhesive failure and for some of the Pdrich alloy specimens the ceramic-metal failure was similar to that observed on specimens made from the type IV gold alloy. Only PTM-88 alloy specimens exhibited a surface roughness ratio of less than 1, which is consistent with the low bond strengths measured for these specimens.
DISCUSSION The ceramic-metal bond strengths of the specimens made with the Pd rich alloys Option, PGC, and Tribute were comparable to and, in one case, better than the ceramic-metal bond strength of the type IV gold alloy specimens. In addition to similarity in bond strengths, the amount of ceramic remaining on the debonded surface and the surface roughness evaluations emphasized the similarity between the ceramic-metal bond failure of specimens made from the Pd rich and the type IV gold alloys. The one 679
LOBENZANA
exception was found in specimens made with PTM-88 alloy, which was consistent with results from the previous studies.4 Since the PTM-88 alloy had a significantly different composition than the other Pd rich alloys, it is possible that the weaker bond strength was due to a less-adherent metal oxide. This explanation was supported by the surface roughness evaluation. The surface roughness of 0.94 for PTM-88 alloy specimens indicated that the debonded surface was smoother than the surface not exposed to ceramic. The rationale for this result was that the ceramic-metal failure occurred at the metal-oxide interface. It seems that the surface roughness ratio was a fairly accurate predictor of the ceramic-metal bond strength. The good correlation of the BRS and R&M values provided evidence that roughness measurements might be a reliable indicator of bond strengths. The surface roughness test method would be beneficial for discriminating between ceramic-metal bond strengths of alloys that are not well characterized or are without elastic modulus.
SUMMARY
ET AL
However, when the flexure strength loads were normalized by the modulus of elasticity to compensate for different stiffness of the alloys, only specimens of one Pd rich alloy, Option, had a significantly greater bond strength. This indicated the importance of knowing the relative stiffness of the different test alloys in order to achieve an accurate assessment of the bond strength that reflects the clinical situation. REFERENCES 1. Anusavice
KJ, DeHoff PH, Fairhurst CW. Comparative evaluation of ceramic-metal bond tests using finite element stress analysis. J Dent Res 1980;59:608-13. 2. Schaffer SP. An approach to determining the bond strength of ceramometal systems. J PROSTHET DENT 1982;48:282-4. 3. Van Vlack LH. Elements of materials science and engineering. 3rd ed. Reading, Mass: Addition-Wesley Pub1 Co, 1975;177-80. 4. Lorensana RE, Chambless LA, Marker VA, Staffanou RS. Ceramometal bond strengths of four palladium-rich alloys. [Abstract]. J Dent Res 1985;54:585. Reprint
requests
to:
DR. ROBERT S. STAFFANOU BAYLOR COLLEGE OF DENTISTRY 3302 GASTON AVE. DALLAS, TX 75246
The loads measured from the flexure bond strength test and the shear bond strength test produced similar results.
Evaluation of the electrolytic nickel-chromium base alloy restorations Herbert University Wattens,
SchBffer, of Innsbruck, Austria
Dr.Med.,* School
etching depth of a used in resin-bonded cast
and Anton Piffer**
of Dentistry,
Innsbruck,
Austria;
and
Swarovski
D. & Co.,
This study examined the relation of the electrolytic etching depth of a nickelchromium base alloy to the etching time. Cast samples (22 mm long, 4 mm wide, 1.6 mm thick) were etched in the Eltrokor etching unit, using Korolyt A as the etching solution with a constant current density of 400 mA/cm2. On each sample an approximately 3 mm long area was etched for 5,7,9, and 11 minutes. Between each etched area, a field of approximately 2 mm long remained unetched. The surface of each sample was scanned with a protllometer. The distance of the compensation plane of the scanned etched profile to the unetched areas was then measured for each etching time. The average etched depth with an etching time of 5 minutes is 30.4 pm (SD 2.39); with a time of 7 minutes the depth is 44 pm (SD 3.49); with a time of 9 minutes the depth is 59.8 gm (SD 4.10); and with an etching time of 11 minutes the depth is 72.9 gm (SD 2.94). Taking the average of all etching depths per etching time, the average loss of substance is 6.409 pm per minute etching time. (J PROSTHET DENT 1990;64:680-3.)
*Assistant Professor, Department of Restorative Dentistry, University of Innsbruck, School of Dentistry. **Physicist, Department of Research and Development, Swarovski D. & Co. 10/l/22012 680
A
fter 15 years of research and development, resinbonded fixed prosthesis are established as a treatment of partial edentulism. The components in the bonding system (metal, composite resin, and enamel) have been examined in various studies.le4 The crucial criteria for long-term sucDECEMBER
1990
VOLUME
64
NUMBER
6
of high-palladium
R. E. Lorenzana, D.D.S.,* L. A. Chambless, and R. S. Staffanou, D.D.S., M.S.**** Baylor
College
of Dentistry,
Dallas,
D.D.S.,**
content alloys V. A. Marker,
Ph.D.,***
Tex.
Palladium-based alloys have had a significant import on the fabrication of ceramometal restorations. This article compares the bond strengths of four palladiumbased alloys with that of a high-noble alloy. Tests were designed to closely represent clinical situations. Bond strengths of the palladium alloys compared favorably with the high-noble metals; palladium alloys containing up to 2% gold were the best. (J PROSTHET DENT 1990;64:677-80.)
T
base alloys have had a significant impact on the fabrication of ceramometal restorations. This project compares the porcelain bond strength of four high-palladium alloys to the bond strength of a highgold content ceramic alloy. Anusavice et a1.l have analyzed the complexity of the ceramometal bond and have indicated that a shear test constitutes the ideal measurement, but that several different tests should be used. Two types of bond strength tests were performed in this study, (1) a shear test and (2) a three-point flexure test. These tests most closely represent the clinical situation. he new
MATERIAL
palladium
AND
METHODS
The ceramic-metal bond strengths of specimens made from palladium-rich alloys were evaluated and compared to the bond strengths of specimens made with a type IV gold alloy. The materials used in these tests are listed in Table I. Two experimental procedures were used to determine the bond strengths, (1) a three-point flexure test and (2) a shear bond strength test.
Specimen
preparation
Patterns for the metal specimens were cut from sheets of acrylic resin (Temporary Splint Material, Buffalo Dental Mfg. Co., Brooklyn, N.Y.). For the flexure tests, 10 patterns for each alloy were made to the dimensions of 20 X 10 X 0.5 mm. Another 10 patterns for each alloy were prepared to a size of 15 x 3 x 2 mm, for the shear bonding test. To ensure uniformity, the acrylic resin patterns were invested (Hi-Temp Investment, Whip Mix Corp., Louisville, Ky.) in groups of 10 and cast by use of an induction casting maching (Unitek, Monrovia, Calif.). The surfaces of all of the specimens were treated according to the manufacturers’ recommendations before application of the ceramic. Jigs were designed so that the total surface area and the location of the ceramic were standardized on all specimens. Each specimen received an opaque layer (0.5 mm) and a body layer (1.5 or 3 mm) of ceramic. A diagram of the specimen designed for flexure testing is shown in Fig. 1. The design of the specimen used for shear bond testing is shown in Fig. 2.
*Assistant Professor,Department of Fixed Prosthodontics. **Associate Professor,Department of Fixed Prosthodontics. ***Associate ****Professor tics. 10/l/22731
Table
I.
Professor, Department of Dental Materials. and Chairman, Department of Fixed Prosthodon-
Materials
used in study
Composition
Metal alloys PGC 78%’
Pd, 2% AU pd, 2% Au Pd, 0% Au
Tribute PTM
68% 88%
Option SMG-2
79% Pd, 2% Au 87% Au, 7% Pt, 5% Pd
Ceramic Vita
THE
JOURNAL
;
Manufacturer
Englehard Co., Carteret, N.J. Sterngold, Mt. Vernon, N.Y. J. F. Jelenko, New Rochelle, N.Y. J. M. Ney Bloomfield, Conn. J. M. Ney
Unitek
OF PROSTHETIC
DENTISTRY
Corp.,
Monrovia,
Calif.
1. Diagram of ceramometal specimen in three-point flexure test. M, Metal; P, porcelain; F, force.
Fig.
677
LORENZANAETAL
Fig. 2. Diagram of ceramometal specimen in shear bond test. M, Metal; P, porcelain; A, acrylic; F, force.
Table
II.
Results from three-point flexure test Load
(lb)
BRS
tween materials, the load at failure and the modulus of elasticity were used to calculate a strength parameter (BRS) from the following equation?
x lo+’
Specimen
x
SD
x
SD
Option Tribute PGC
7.9
0.9
3.1
7.6 7.4 5.6 5.5
1.1
2.1
1.2 0.9 1.1
1.8 2.3 1.6
0.4 0.3 0.3 0.4 0.3
maximum
SMG-2 F’TM 88 p < 0.05; Load
CD, 1.6; BRS CD, 0.7.
The ceramic layers were fired under vacuum (1 atmosphere). Starting at 700’ C, the temperature was programmed to increase at 33’ per minute until a temperature of 920” was reached. The vacuum was released and the specimens were removed from the furnace. After the specimens were bench cooled, the opaque layer and then the body layer of the ceramic were applied and fired under vacuum in the same manner up to 940’ C. All ceramic procedures were performed by one clinical researcher to ensure uniformity of the specimens. For the shear bonding test, the porcelain was embedded in acrylic resin so that the specimen could be mounted in the test apparatus.
Bond
strength
tests
The ceramic-metal bond strengths of the completed specimens were evaluated by use of the flexure test and the shear bond strength test. Each of these bond strength tests produces different stress concentrations in the specimens and thus provides unique information on the bond strength.’ For the flexure strength test, the specimens were placed in the bending apparatus with the ceramic positioned on the side opposite the applied load (Fig. 2). The force was applied at a constant rate of 0.5 mm/min with the Universal testing machine (Instron Model 1250, Instron Corp., Canton, Mass.). For analysis and comparison be-
676
BRS = modulus
strength
of elasticity
+ S E
In this equation the bond strength ratio (BRS) is proportional to the maximum shear stress (S) and inversely proportional to the modulus of elasticity (E) of the material. The shear bond test specimens were tested in a parallel shear test (Fig. 2). Again the universal testing machine was used to apply a load at the constant rate. As indicated in Fig. 2, the force was applied to the interface of the ceramic-metal specimen. This procedure has been shown to produce lessvariability in the resu1ts.l For this test method the shear force was computed with the following equation:3 z=yG This equation shows the shear stress (T) is proportional to the shear modulus (G) and the shear strain (7). Strength data were subjected to an analysis variance, a Scheffe critical difference test, and regression analysis.
Management
of surface
roughness
After the tests, the specimens were examined to determine whether failure occurred at the interface or as a tensile fracture in the ceramic. In addition, the average surface roughness of the fractured interface surface (Ro) and the noninterface surface (RM) were measured with a profilometer (Surftest R III, Mitutoyo Mfg. Co., Ltd., Tokyo, Japan). A ratio (R&M) of these values was used to indicate the relative surface roughness and to compensate for any inherent roughness of the different alloys. The surfaceroughness ratios were compared with the bond strength results for all five alloys by use of regression analysis.
RESULTS The results from the flexure strength testing are given in Table II. Compared with the type IV gold alloy specimens,
DECEMBER1990
VOLUME64
NUMBER6
BOND
STRENGTHS
OF HIGH-PALLADIUM
0 0
ALLOYS
OPTION
.
TRIBUTE
H TRIBUTE
A PGC V PTM-88 8,
0
=
0
10
20 SHEAR
BOND
OF PROSTHETIC
V
PTM-00 -4
cl
T 40
30
STRENGTH
(MPa)
3. Graph illustrates correlation between flexure test and shear bond test.
the loads produced by the flexure test were significantly greater for specimens from .three of the alloys rich in Pd (Option, Tribute, and PGC). However, when the results were normalized by the modulus values, only specimens from one alloy, Option, produced a BRS value significantly greater than the BRS values for the type IV gold alloy specimens or the alloy specimens rich in Pd. The BRS value for SMG-2 from this study was slightly higher (2.3 x 10v3) than the previously reported value (1.4 X 10-3).2 This discrepancy could be the result of differences in specimen design and should not affect the comparison between the specimen tested in this study. The BRS values calculated from the flexure test were compared with the shear bond strengths (Table III). For this test, the specimens made from Tribute alloy exhibited significantly higher ceramic-metal bond strengths. Fig. 3 shows that the correlation was much higher between the shear bond strengths and the flexure loads (r = 0.87) than with BRS values (r = 0.39). Regardless of the evaluation method, the bond strength results for specimens of the Pd rich alloy, PTM-88, were consistently the lowest. PTM 88 alloy contains no gold as do the other alloys, a factor that may have an affect on the bond strength. A comparison of the BRS values and the surface roughness ratio produced a correlation of 0.97 (Table III). The surface roughness ratio provided an indication of the amount of ceramic adhering to the metal after failure. Thus, k/RM values exceeding 1 meant that the debonded ceramic-metal interface surface was rougher than the noninterface surface. There was no significant difference in the measured surface roughness ratios for specimens made from Option, SMG-2, and Tribute alloys (Table III). These large ratios (2.3 to 1.6) suggested that the debonding was
JOURNAL
PGC
/ / ’
THE
A
A,”
z
Fig.
OPTION
DENTISTRY
Table III. Comparison of bond strengths determined by flexure test, shear bond test, and surface roughness measurements Ems Specimen
Option SMG 2 Tribute PGC PTM 88
x 10-s
Shear strength
bond (MPa)
Surface ratio
roughness (&/RM)
x
SD
x
SD
x
SD
3.1
0.4 0.4 0.3 0.3 0.3
23.5 31.1 23.3 11.7
4.6 5.5 2.5 3.6
2.3 1.7 1.6 1.2 0.9
0.7 0.1 0.2 0.5 0.4
2.3 2.1 1.8 1.6
p < 0.05; BRS CD, 0.7; shear bond strength CD, 0.9.
CD, 6.2; surface roughness
ratio
not a completely adhesive failure and for some of the Pdrich alloy specimens the ceramic-metal failure was similar to that observed on specimens made from the type IV gold alloy. Only PTM-88 alloy specimens exhibited a surface roughness ratio of less than 1, which is consistent with the low bond strengths measured for these specimens.
DISCUSSION The ceramic-metal bond strengths of the specimens made with the Pd rich alloys Option, PGC, and Tribute were comparable to and, in one case, better than the ceramic-metal bond strength of the type IV gold alloy specimens. In addition to similarity in bond strengths, the amount of ceramic remaining on the debonded surface and the surface roughness evaluations emphasized the similarity between the ceramic-metal bond failure of specimens made from the Pd rich and the type IV gold alloys. The one 679
LOBENZANA
exception was found in specimens made with PTM-88 alloy, which was consistent with results from the previous studies.4 Since the PTM-88 alloy had a significantly different composition than the other Pd rich alloys, it is possible that the weaker bond strength was due to a less-adherent metal oxide. This explanation was supported by the surface roughness evaluation. The surface roughness of 0.94 for PTM-88 alloy specimens indicated that the debonded surface was smoother than the surface not exposed to ceramic. The rationale for this result was that the ceramic-metal failure occurred at the metal-oxide interface. It seems that the surface roughness ratio was a fairly accurate predictor of the ceramic-metal bond strength. The good correlation of the BRS and R&M values provided evidence that roughness measurements might be a reliable indicator of bond strengths. The surface roughness test method would be beneficial for discriminating between ceramic-metal bond strengths of alloys that are not well characterized or are without elastic modulus.
SUMMARY
ET AL
However, when the flexure strength loads were normalized by the modulus of elasticity to compensate for different stiffness of the alloys, only specimens of one Pd rich alloy, Option, had a significantly greater bond strength. This indicated the importance of knowing the relative stiffness of the different test alloys in order to achieve an accurate assessment of the bond strength that reflects the clinical situation. REFERENCES 1. Anusavice
KJ, DeHoff PH, Fairhurst CW. Comparative evaluation of ceramic-metal bond tests using finite element stress analysis. J Dent Res 1980;59:608-13. 2. Schaffer SP. An approach to determining the bond strength of ceramometal systems. J PROSTHET DENT 1982;48:282-4. 3. Van Vlack LH. Elements of materials science and engineering. 3rd ed. Reading, Mass: Addition-Wesley Pub1 Co, 1975;177-80. 4. Lorensana RE, Chambless LA, Marker VA, Staffanou RS. Ceramometal bond strengths of four palladium-rich alloys. [Abstract]. J Dent Res 1985;54:585. Reprint
requests
to:
DR. ROBERT S. STAFFANOU BAYLOR COLLEGE OF DENTISTRY 3302 GASTON AVE. DALLAS, TX 75246
The loads measured from the flexure bond strength test and the shear bond strength test produced similar results.
Evaluation of the electrolytic nickel-chromium base alloy restorations Herbert University Wattens,
SchBffer, of Innsbruck, Austria
Dr.Med.,* School
etching depth of a used in resin-bonded cast
and Anton Piffer**
of Dentistry,
Innsbruck,
Austria;
and
Swarovski
D. & Co.,
This study examined the relation of the electrolytic etching depth of a nickelchromium base alloy to the etching time. Cast samples (22 mm long, 4 mm wide, 1.6 mm thick) were etched in the Eltrokor etching unit, using Korolyt A as the etching solution with a constant current density of 400 mA/cm2. On each sample an approximately 3 mm long area was etched for 5,7,9, and 11 minutes. Between each etched area, a field of approximately 2 mm long remained unetched. The surface of each sample was scanned with a protllometer. The distance of the compensation plane of the scanned etched profile to the unetched areas was then measured for each etching time. The average etched depth with an etching time of 5 minutes is 30.4 pm (SD 2.39); with a time of 7 minutes the depth is 44 pm (SD 3.49); with a time of 9 minutes the depth is 59.8 gm (SD 4.10); and with an etching time of 11 minutes the depth is 72.9 gm (SD 2.94). Taking the average of all etching depths per etching time, the average loss of substance is 6.409 pm per minute etching time. (J PROSTHET DENT 1990;64:680-3.)
*Assistant Professor, Department of Restorative Dentistry, University of Innsbruck, School of Dentistry. **Physicist, Department of Research and Development, Swarovski D. & Co. 10/l/22012 680
A
fter 15 years of research and development, resinbonded fixed prosthesis are established as a treatment of partial edentulism. The components in the bonding system (metal, composite resin, and enamel) have been examined in various studies.le4 The crucial criteria for long-term sucDECEMBER
1990
VOLUME
64
NUMBER
6
