Apparent bond strength of nonnoble alloy-porcelain combinations

Apparent bond strength combinations E. E. Quinones,

D.M.D.,*

U.

Activity,

S. Army

Dental

S. G. Vermilyea, Walter

Reed

Army

Medical

of nonnoble D.M.D., Center,

N

onnoble alloys presently comprise a sizable portion of the ceramometal alloy market.’ The low price of these alloys is their major attraction. This advantage, however, can be negated by inexperienced handling.’ In addition, the clinical successof ceramometal restorations is often predicated on the strength and integrity of the porcelainalloy bond. The bond strength values may be influenced by the alloy composition, the prefired alloy surface preparation, the rate of cooling of the porcelain, and the type of bond strength test used.3-8 The nonnoble alloys are often marketed for use with a specified porcelain and/or bonding or conditioning agent to provide optimal bond strengths. At least one study has indicated that the so-called metal conditioners have little effect on apparent bond strength values associated with some alloys.’ The present study was conducted to determine the effect of different porcelains on the porcelain-alloy bond strength of five commercially available nonnoble alloys. MATERIAL

AND

METHODS

The test alloys included Rexillium III (Jeneric Gold Co., Wallingford, Conn.), Pentillium (Pentron Corp., Wallingford, Conn.), Co-Span (Vaupel Dental Inc., Houston, Tex.), Bak-On-NP (Ceramco Inc., East Windsor, N. J.), and Unibond (Unitek Corp., Monrovia, Calif.). The opaque porcelains used were Biobond (Dentsply International Inc., York, Pa.), Vita VMKG8-Paint-on 88 (Unitek Corp.), Ceramco (Ceramco C:ommercial rruterials and equipment are identified in this report to specify the txperimental procedure. Such identification does not imply oflicial recommendation or endorsement or that the materials and equipment are necessarily the best available for the purpose. Furthermore, the opinions expressed herein are those of the authors and are no, to be construed as those of the Army Medical Lkpartment. *Lieutenant C:olonel, USA, DC; Senior Resident, Fixed Prosthodontics Service. **Lieutenant Colonel, USA, DC; Junior Resident, Removable Prosthodontics Service. Formerly, Chief, Dental Materials Branch, U.S. Army Institute of Dental Research, Washington, D.@. ***Ck~lonel. USA, DC:; Commander, U.S. Army Dental Activity, Nuremburg, West Germany. Formerly, Chief, Fixed Prosthodontirs Service.

THE

JOURNAL

OF PROSTHETIC

DENTISTRY

M.S.,** Washington,

alloy-porcelain

and W. H. Griswold,

D.D.S.***

D.C.

Inc.), and Will-Ceram (Williams Gold Refining, Buffalo, N.Y.). Forty cast metal disks (‘/ X %6 inch) were made from each alloy. The surfaces of the disks were finished on 240 grit metallographic paper, ultrasonically cleaned in distilled water, and dried in air. The castings from each alloy were divided into four groups of 10 disks each. Each group received one of the test porcelains, thereby providing 10 test specimens for each porcelain. The porcelains were applied and fired in accordance with their respective manufacturer’s instructions to include degassing and air abrading the metal where indicated. No metal conditioner or bonding agent was used with any of the porcelain-alloy combinations. The porcelain-alloy bond strengths were determined by the parallel shear method of Civjan et al.’ Porcelain cylinders (‘/s = ‘/z inch) were formed in paper tubes affixed perpendicularly to the disk surface. The porcelain was mixed with distilled water and the slurry vibrated into the tubes. Excess liquid was removed by capillary action into tissue paper. The specimens were placed in an oven at 1200” F until combustion of the paper tube was complete; then the specimens were subjected to the firing cycle prescribed by the porcelain manufacturer. The specimens were cooled to room temperature under a glass cover. The ceramic portion of each porcelain-metal couple was embedded in ?&-inch cube of autopolymerizing resin (Fastray, Harry J. Bosworth Co., Skokie, Ill.). Each cube was mounted in an aluminum fixture for added support, and the entire assembly was placed on a constant displacement rate testing machine (Universal Testing Machine, Instron Corp., Canton, Mass.). Samples were loaded diametrically at a crosshead speed of 0.02 inch/min. Details of the loading device and fixtures are described elsewhere.” The strength of the porcelainmetal bond was calculated on the basis of the ultimate load at shear failure per unit area of apparent porcelainmetal contact. Specimens were examined under lowpower magnification, and the type of failure was determined according to O’Brien’s classification.” The data were subjected to analysis of variance, and means were compared using Scheffe’s method at the 5% level of significance. 359

QUINONES,

Table I. Apparent

porcelain-alloy Biobond

--

Rexillium Pentillium Co-Span Bak-On-NP Unibond *SchefTe’s

III

were

(in pounds

GRISWOLD

per square inch)*

Vita

Ceramco

Will-Ceram

SD

Mean

SD

Mean

SD

Mean

SD

1900 2000

500 500

4600 4500

500 1000

5200 3700

500

4000

800

MOO

4400 1300 4500

WO 1200

2500

1200 1700 1100

3300

700 600

5000 1200

600 800

5200 4300 -.-~-___-..-...~

1000 1000

4800 4tW

'f!iO mi

calculated

LO he 1500 and

1300 I)\, for alloys

RESULTS The apparent bond strengths of the porcelain-alloy combinations are shown in Table I. The range of apparent bond strengths was delineated by Biobond porcelain-Rexillium III alloy (1900 psi) and Ceramco porcelain-Co-Span alloy (5400 psi). With Rexillium III, Pentillium, and Bak-On-NP alloys the bond strength values with Vita, Ceramco, and Will-Ceram porcelains were statistically equivalent (p > .05) but significantly higher than those obtained with Biobond porcelain. Co-Span alloy with Biobond porcelain gave bond strength values that were significantly lower than those obtained with the other porcelains, whereas Ceramco porcelain gave values higher than those obtained with Vita porcelain. Regardless of the porcelain used, the bond strength values with Unibond alloy were statistically equivalent. Examination of the fracture surfaces of the specimens revealed the following distribution of failure types: type V failure (within the metal oxide), 43%; type IV (at the metal-metal oxide junction), 22%; type III (within the porcelain), 23%; type II (at the metal oxide-porcelain junction), 8%. No correlation could be made between the type of failure and the bond strength values. DISCUSSION The strength and integrity of a ceramometal bond is predicated on the development of a thin adherent oxide on the substrate metal and it’s chemical interaction with the constituents of the ceramic veneer.7 These complex interactions depend on such factors as the porcelain condensation technique, the amount and distribution of porosity in the porcelain, and the specific porcelain-alloy combination. From the available data it appears that Vita, Ceramco, or Will-Ceram porcelains can be used with any of the alloys tested in this study. The statistical differences observed among the alloys with these porcelains may not be significant clinically. The coefficients of variation (15% to 52%) are reflections of the factors cited previously and the variability inherent in the test method. Biobond porcelain gave bond strength values consistent with those of the other porcelain-alloy combinations 360

AND

Mean

4100 allowances

bond strengths

VERMILYEA,

and upaque

porcelains.

_-_-

i iOu

.

respectivei\.

only when Unibond alloy was used. Other Biobond porcelain-alloy combinations gave lower bond strength values than those obtained with the same alloy in combination with Vita, Ceramco, or Will-Ceram porrelains. A common feature of these alloys is the presence of beryllium. It has been suggested that beryllium may act as a reducing agent for chromium and nickel oxides and inhibit diffusion of these elements into the porcelain.” !‘ This lack of diffusion may preclude the establishment of an adequate ceramometal bond.” In addition, the preoxidation process (that is, the degassing cycle) tends to form a surface oxide that limits the diffusion of beryllium into the oxide layer and stabilizes the alloy surface during the porcelainization process.I2 Ideally, this oxide forms a monomolecular layer, which is part of the metal and part of the glass.* Excessive thickness of the oxide layer may diminish the bond strength by permitting fracture through the oxide.‘” The so-called metal conditioners or bonding agents function to absorb excess oxides formed on the surface of the alloy and/or to provide oxidizing elements for the formation of appropriate stable oxides for bonding with the ceramic veneer during firing.“’ Conditioning agents were not used in this study. It may be that the use of Biobond porcelain with these alloys necessitates the use of bonding or conditioning materials prior to porcelain application to achieve predictable results. SUMMARY

AND

CONCLUSIONS

The apparent bond strengths of four porcelains and five nonnoble alloys were determined. On the basis of the data, the following conclusions can be drawn: 1. The use of Vita, Ceramco, or Will-Ceram porcelains with Rexillium III, Pentillium, or Bak-On-NP alloy gave similar bond strength values. 2. With the exception of Unibond alloy, the bond strength values obtained with Biobond porcelain were lower than those obtained with the other porcelain materials. 3. The ceramometal bond strength values obtained with Unibond alloy were similar with all of the porcelains tested. The continued availability of a bewildering array of SEPTEMBER

1985

VOLUME

54

NUMBER

3

ALLOY-PORCELAIN

BOND

STRENGTH

8.

new alloys and porcelains suggests the urgent need for research designed to determine the bonding mechanisms and compatibility of various porcelain-alloy combinations. The data from this investigation provide criteria for the rational selection of bond strength-compatible porcelains and alloys for clinical use.

IO.

REFERENCES

Il.

I.

2. 3.

4.

hicCrary. J. N.: Economics of alloy selection. In: Alternatives to Gold Alloys in Dentistry. DHEW pub1 No. (NIH) 77-1277, 1977, p 1 I. Stevens. I. : Some aspects of nonprecious metal alloys for ceramic restorations. Aust Dent J 22:l 1, 1977. Lubovich. R. P., and Goodkind R. J.: Bond strength studies of precious, semiprecious and nonprecious ceramic metal alloys with two porcelains. J PROSTHI:T DENT 37:288, 1977. Malhotra, M. S., and Maickel, L. B.: Shear bond strength of porcelain-fused-to-alloys of varying noble metal contents. J PKOSTHE I DEFT

5.

6.

7.

44~405,

12.

13. 14.

1980.

Civjan, S., Huget, E. F., DeSimon, L. B., and Risinger, R.: Determination of apparent bond strength of alloy-porcelain systrms. Int Assoc Dent Res Program Abstr 53:742, 1974. Guinn III, J. W., Griswold, W. H., and Vermilyea, S. G.: The elfert of waling rate on the apparent bond strength of porcelainmetal couples. J PROSTHE.I- DENT 48~551, 1982. Broom. hf. P., and Pask, J. A.: Role of “adherence oxides” in thr development of chemical bonding at glass-metal interfaces. J Am Ceram Sot 49: I, 1966.

Experimental etched-metal Timothy Stephen

comparison between perforated resin-bonded retainers

Brady, D.D.S., Asterios T. Rasmussen, Ph.D.**

Case Western Reserve University,

Doukoudakis,

School of Dentistry,

A

*Associate **Assistant

Professor, Professor,

JOURNAL

Department Department

OF PROSTHETIC

of Fixed of Oral

Prosthodontirs. Biology.

DENTISTRY

and

D.D.S., M.S.,* and

Cleveland,

cid-etch fixed partial dentures with metal frameworks have been widely used by dentists during the last decade. Rochette’ introduced the acid-etch retainers to the dental profession. Perforated cast-gold retainers were attached to the lingual surfaces of the abutment teeth using the acid-etch technique and Sevriton (Ash USA Div., Dentsply International, York, Pa.) cement.2 The framework was secured by cement-filled countersunk perforations placed through the retainer portion of the framework. The improvement of etching procedures’, 4 and composite materials increased clinical use of the acid-etch retainers.

THE

9.

Pask, J. A.: Fundamentals of wetting and bonding between ceramics and metals. In: Alternatives to Gold Alloys in Dentistry. DHEW pub1 No. (NIH) 77-1277. 1977. p 235. Bowers, J. E., Vermilyea, S. G., and Griswold. W. iI.: The ell’ect of metal conditioners on porcelain-alloy bond strength. ~J PROS‘I‘I~EI L)EN’I (Submitted for publication). O’Brien, W J.: Dental porcelains. In Craig, R. C;., editor: Dental hlaterials Review. ,\nn .\rbor, 1977 L’niversirv 01 Michigan Press, p 123. Fairhurst, (1. W.: hletal surface preparation and bonding agents in porcelain-metal systems. In: Altcrnalivcs to Gold ,\lloys in Dentistry. DHEW pub1 No. (NIH) 77-1277. 1977. p 225. Peter-Williams, T. R.: A Study of Base hletal-Crramic Interface Reactions. Thesis. Indiana L!niversit\. School of Dentistry, 1976. Lacy, .4. M.: The chemical nature of dental porcelain. Dent Clin North Am 21:661, 1977. Goeller, I., Meyer, J. M., and Nally, J. N.: Comparative study 01 three coating agents and their influence on bond strength of porcelain-fused-to-gold alloys. J PRO.l’tiE.T DLNT 28:504, 1972.

Ohio

In 1977 Howe and Denehy’ demonstrated acid-etched fixed partial dentures as a means of replacing missing anterior teeth. Since then, perforated metal retainers have been used in various types of dental treatment.l.6-12 In 1982 Livaditis and Thompson’3 introduced electrolytically etched castings for retention of resin-bonded retainers. The inside surface of the casting was etched to form metal tags that engaged the composite resin. Both the perforated and electrolytically etched framework designs are now commonly used by dentists but there are advantages and disadvantages with both techniques. There is a dearth of literature comparing the retention of the two framework designs. The purpose of this study was to compare the 361