CA1053408A

CA1053408A - Dental bonding agents

Info

Publication number: CA1053408A
Application number: CA254,627A
Authority: CA
Inventors: Pei Sung; James Lee-You
Original assignee: Johnson and Johnson
Current assignee: Johnson and Johnson
Priority date: 1975-06-13
Filing date: 1976-06-11
Publication date: 1979-05-01
Also published as: PT65223A; FR2313912B1; DK264776A; BE842895A; FR2313912A1; GB1529267A; AU498842B2; FI761681A; JPS51151734A; DE2626092A1; SE7606673L; NO762009L; PT65223B; NL7606412A; BR7603803A; AU1490876A; ZA763492B; ES448828A1

Abstract

Abstract of the Disclosure A bonding agent composition for use in dental restorations for bonding porcelain to the metal core or framework, especially framework of non-precious metal alloys. The bonding agent composition comprises: (a) a bond-forming component comprising a powdered mixture of aluminum and a glass which fuses at a temperature in the range of from about 1750°F to about 1850°F and (b) ? liquid carrier. The carrier is preferably one capable of ? viding a reducing atmosphere at temperatures within the range of from about 1200°F to about 1900°F. The bonding agent composition is applied to a metal core which is to be faced with porcelain and heated from about 1200°F. to a temperature in the range of about 1750°F. to 1900°F. to produce a very strong bond at the interface resistant to separation of the porcelain by stresses placed upon the restoration during use.

Description

~o 5340 8 CER 15 DESCRIPTION OF THE INVENTION
.

Dental restoration generally comprise a metal core or framework to which porcelain is bonded on the visible surfaces for esthetic reasons. For many years gold has been the basic structur~l metal for preparing the metal core or framework. However, because of the cost of gold, many attempts have been made to devise non-precious metal alloys which could be used in place of gold. Such compositions are illustrated, for example, by U.S. Patent Nos. 1,736,053;

2,o89,587; 2,156,757; 2,134,423; 2,162,252, 2,631,095, 3,121,629,

3,464,817; 3,544,315; 3J685,115; 3,716,418; 3,761,728; and 3,834,024, and ln standard dental literature such as Sk~nner and Phillips, "TH~: SCIENCE 0~ DENTAL MAq~ERLALS," p. 582, Sixth edition, W. B. Saunders Com~any, Philadelphia and London, 1967 and Morrey and Nelson, "DENTAL SCIENCES H~NDBOOK," p. 168, ~erican Dental Association and National Institute of Dental Research, U.S. Government Printing Office, Washington~ D.C., 1970. Suitable alloys are generally nickel or cobalt-based alloys~ particularly, nlckel-chromium alloys.
, When such non-precious metal alloys are to be employed as a framework or core to be faced with porcelain, generally the porcelain is fired directly onto the metal surface and is held there by mechanical bonding. To produce mechanical bonding, a surface roughening of the metal is required.
Appropriate roughening for mechanical bonding is extremely difficult. Moreover~ mechanical bonding is not always adequate to endure the stresses of daily use and a separation of the porcelain from the metal framework in whole or in part lQ534~`8 ~E~ l~?

frequently occurs. It is desirable to provide a bond resistant to such separation.

The present invention is directed to bonding agents and more particularly, it relates to compositions and methods for bondingdentalporcelain to a non-precious metal alloy ~ramework. When dental porcelain is bonded to the metal framework using the bonding agents of the present invention, a strong bond is formed which is able to resist separation of the porcelain under far greater stresses than ln the absence of bonding agent. Moreover, the components are free of materials which cause tissue necrosis or present toxicity problems.

, The bonding agent composition of the present invention comprises: (1) a metal to porcelain bond forming component consisting of powdered aluminum in admixture with a powdered glass, said glass being characterized by fusing at a temperature in the range of about 1750F. to 1850F.
preferably about 1800F. with (2) a carrier componen~ which is a substance capable of providing a reducing atmosphere during the firing or baking of the bonding agent. Glass as herein employed is a mixture of non-crystalllne oxides as ls generally understood in the art and hereinafter more fully described. The carrier may be an inert carrier having no function than as a carrier and the reducing atmosphere necessary during the baking or firing of~the bonding agent provlded by separately supplied reducing gases; however, "` ~Q534(~t~

the preferred embodiment of the present invention contemplates the reducing atmosphere to be supplied by the carrier component.
The expression "bonding agent composition" as herein employed refers to both the bonding-forming component and carrier. The expressions "bond-forming component" and "bond-forming agent"
refer to the aluminum-glass mixture. The expressions "core", "framework", "substrate", and "structure" when employed with "metal" are intended to have the same significance and refer to the dental structure which is to be faced with porcelain.
Broadly, the invention relates to a bonding agent composition suitable for bonding dental porcelain to a metallic core of a non-precious metal alloy in a dental restoration comprising (a) a bond-forming component of powdered aluminum in admixture with a powdered glass fusing at temperatures in the range of from about 1750F. to about 1850F., and (b) a carrier component comprising a liquid organo-silicon compound capable of providing a reducing atmosphere at temperatures of from about 1200F. to about 1900F., wherein said glass is of a mixture of oxides which include the following in approximate weight percent: 47-74% silicon dioxide; 1-16% aluminum oxide;
3-17% sodium oxide; 0.6-6% calcium oxide; and 0.4-4% magnesium oxide.
In a preferred embodiment of the present invention, the bond-forming component is a mixture of aluminum and a glass fusing within the range 1790 to 1810F. The aluminum is in the form of a powder capable of passing through a 400 mesh screen and is preferably in the form of a powder of particle size of 20 microns or finer. The glasses are a mixture of non-crystalline oxides which include silicon dioxide, aluminum oxide, sodium oxide, calcium oxide and magnesium oxide; it may contain one or more of the follow-~ _ 4-ios3~08 ing oxides: stannic oxide, potassium oxide, lithium oxide, boron oxide, titanium oxide, barium oxide, zirconium oxide, etc. The amounts of the first-named oxides which may be called the essential oxides may vary significantly depending on the presence of and/or amount of the latter or non-essential oxides. Thus, the essential oxides may be present in amounts (by weight) as follows: a~out 47-74%

i - 4a -1 053~08 silicon dioxide, 1-16~ aluminum oxide~ 3-17~ sodium oxide, o.6 to 6~o calcium oxide and 0.4-4% magnesium oxide. The other oxides may be present in amounts as follows: 0-12% potassium oxide, 0-25% stannic oxide, 0-5% llthium oxlde, 0-2% boron oxide and 0-2% barium oxide. The preferred glasses are those in which the oxide compo~ition may be within the following ranges in percent by welght: 47-63% silicon dioxide; 9-25% stannic oxide; 10-14% aluminum oxide; 8.5-10% potassium oxide; 3-5%
sodium oxide; 0.6-.13% calcium oxide; o.4-o.8~ magnesium oxide;
and 0-5% lithium oxide. Many suitable glasses are available commercially as glassl porcelaln, ceramic oxides, etc. Other glass compositions may be prepared by dry blending the appropriate oxides in appropriaté amounts, fusing the mixture to a frit~ quenching with water, drying and ball-mil~ng to appropriate fineness as known in the art. The glass compositions arç powders of particle size such as would pass through a 165-mesh screen (about 60 microns) or finer. The particle slze of both the aluminum and the glass compositions are based primariIy on the finest currently-available powders. When flner powders become available, such would be desirable.

The carrier component of the novel bonding agent composi-tions of the present invention are liquid organic silicon (organosilicon) compounds such as silicone oil, silane, etc.
Suitable liquid organic silicon compounds are those which maintain appropriate fluid paint-on characteristics after incorporation of the bonding agent component powder. Preferred organic silicon liquids are those having a viscosity range of from about 4 to 40 centistokes at 25C. or 6 to 17 centistokes 105340~3 lC~0 1~. or 45-85 Saybolt seconds. These organosilicon compounds, in addition to providing appropriate fluidity properties, also provide a reducing atmosphere.

In compositions comprising a powdered mixture of aluminum and a glass in a liquid organic silicon compound, the exact amount of liquld carrier to be employed with the powdered mixture is not critical. Generally, such amounts of liquid organosilicon compound is employed as to provide the appropriate fluidity for painting on metal surfaces.
Employing liquids havlng a ~iscosity in the range of about 6 to 17 centistokes at 100F, compositions having æuitable paint-on properties may be prepared by comblning for each part by weight of solid bonding component mixture from 0.25 to o.75 parts by volume of liquid~ Usually the solids content of the composition is from about 60~ to 80% by weight.

The relative amounts of aluminum and glass are important. The alumlnum component may constitute from about 40 to about 70 percent of the total solids mlxture, the balance being the glass component. Good results are obtained with a 50:50 mixture of aluminum to glass.

The bonding agent compos~tion may be prepared by intimately admixing the bond-forming component and the carrier component in any suitabl~ manner tO obtain a substantially uniform slurry composltion. Preferably, the solids, i.e. J the aluminum and glass powders, are pre-blended and the powder blend intimately admixed with the liquid organosllicon compound. The preparation of the compositlon by admixing may be carried out just prlor to use or the powder blend and llquid may be premixedJ i.e., the -slurry compositlon may be pre-prepared. The composltion may be employed by dental technlcians employing conventional techniques, The present invention i8 also concerned with employing the bonding agent compoæition o~ the present in~ention to securely adhere or bond dental porcelain to a metal core. A
preferred embodiment contemplates the use of the above-described novel bonding composition in admixture with a carrler component whlch provides a reducing atmosphere.
However, the present inventlon embraces the employment of other means for providing a reducing or a non-oxidizlng inert atmoæphere and the carrier component belng merely an inert liquid of approprlate fluid properties.

In accordance with the method of the present invention of bonding dental porcelain to a metal core or framework, the novel bonding agent composition is applied uniformly to the appropriate ~urface of the metal core which has been prepared employing conventional techniques such aæ the Loæt Wax Technique and which has been thoroughly cleaned such as with dilute acid and/or sandpaper, and the coated metal core then baked in air in the temperature range of about 1200F to about 1900F. in a .

~ 053408 CER 15 dental porcelain furnace. The coated and fired metal core is removed from the furnace, allowed to cool and then cleaned by brushing off loose material and washing ultrasonically with warm water and thereafter dried. The porcelain is then applied and the resulting porcelain-coated metal core or framework fired in a conventional manner.

In carrying out the first of the foregoing steps, the bonding agent composition is applied in any suitable manner.
Generally, painting on with a brush is convenient. Good results are obtained whether the coating may be described ; qualitatively as thi~k, thin or medium. It is critical and es8ential that all surfaces be evenly coated with the bonding agent composition.

In carrying out the baking step, the exact temperature and time of heating may be varied. In a method con~enient for use by dental technicians, the coated metal core is placed - in a furnace preheated to l200F. and rapidly heated in air to a maximum temperature in the range of-from about 1800F. to about 1900F. at a rate of heating of about 90-100F. per minute. PreferablyJ the maximum temperature is in the range of from about 1840F. to about 1860F. The total heating time when thé heating is carried out in this manner is less fifteen minu-tes. Alterna-tively, heating may be carried out at a lower temperature for a longer period.

When the baking step is to be carried out in a non-oxidizing (reducing or inert) atmosphere which is to be provided by a source other than the carrier component, the furnace is filled with a reducing or inert gas such as hydrogen, nitrogen,.methane~ carbon monoxide, argonJ etc.
during heating. The coated metal core is heated as above described.

The step of cleaning the surface of the coated metal after baking on the bonding agent is also critical and essential ~o the obtaining of good adherence of porcelain to the metal.
~hen the cleaning step is omitted cracking of the porcel~in is seen to occur Cleaning with a brush and then ultrasonically . with water appears tQ give the best results although other methods which remove non-adhering materials may al80 be employed.

The porcelain is applied to the.bonding agent coated metal surface~in any appropriate manner normally employed to coat metal surfaces in theabsence of a b~nding agent. Pre-~erred methods are painting on with a brush or coating with a spatula. After application of the porcelain, the porcelain i8 fired.at temperatures appropriate for the particular porcelain and metal employed. Thus,.it may be carried out at any appropriate temperature range within the broader limits of from about 1600F. to about 2000F. Thereafter, addltional coatings f porcelain may be applied and fired in a conventional manner to complete the production of the dental restoration in which a bond is formed between the metal and porcelain which is resistant to separation on application of mechanlcal stresses.

The bo ~ g agent compositions of the present inven-tion are adapted to be employed with metal alloys and porcelains which are suitable for use together in the absence of a bonding a~ent.
Metal alloys for which the bonding agent compositions of the present invention are most useful are the nickel and cobalt based alloys, particularly the nickel-chromium alloys.
Representative alloys are found in the aforementioned patents and dental literature on non-precious metal alloys. Other alloys with which the bonding agent composition may be employed are available under various trade names. Still other alloys with which the bonding agent compositions are usefully employed are the subject matter of Canadian application No. 244,988 filed January 30, 1976.
The porcelain which is to be bonded to the dental alloy may be any porcelain appropriate to be employed with the alloy chosen. By "porcelain" is meant dental porcelain as known in the art and embraces dental glasses. They generally contain silicon oxide, aluminum oxide, potassium oxide, sodium oxide, and minor amounts of other oxides. Normally, the porcelain covering which is first applied to the metal is an opaque porce-lain. An opaque porcelain reduces the tendency of the metal to be seen through the final coating. Opaque porcelains are available commercially and include in the oxide composition either zirconium oxide, tin oxide, titanium oxide, or zirconium sili-cate as an opaquing agent. The opaque porcelain is normally coated with a relatively thick layer or layers of body porce-lain followed usually by a final layer or coating at the tips of incisal porcelain. The body porcelain is available commer-cially as gingival or body porcelain (sometimes called dentine)and may have a small amount of opaquing agent, and incisal por-1053~8 celain is usually of similar composition as body porcelain with-Ollt opaquing agent. In all coatings subsequent to the first coating, porcelain is bonded to porcelain. In the first coating, porcelain is bonded to metal and the problems to be solved by the bonding agent composition of the present invention are with the porcelain-to-metal relationship. Thus, it is solely the por-celain which is to be bonded to metal which is of concern in the practice of the present invention. Since under present prac-tice, the porcelain which is bonded to metal is that understood in the art as opaque porcelain, the porcelains which are to be bonded to metal by the bonding agent compositions generally are opaque porcelains although not limited thereto, Procelains which are advantageously bonded are feld-spathic porcelains and are similar in oxide content to the glass component of the instant bonding agent. Typical porcelain com-positions are found in standard references such as Skinner and Phillips, "THE SCIENCE OF DENTAL MATERIALS," p. 518, W.B. Saun-ders Company, Philadelphia and London 1967; the compositions of several commercial porcelains are listed on Page 60 of Jean-Marc Meyer, "Contributions a l'Etude de la Liaison Céramo-metallique des Porcelaines cuites sur Alliages en Prothèse Dentaire,ll Thesis, University of Geneva, 1971. Suitable porcelains include those having compositio~s described in U.S. Patent 3,052,982 of the following oxide content: 61-67.8% SiO2; 11.7-17.1% A1203; 0.1 -2.6% CaO, 0.1-1.8% MgO, 2.37-9.6% Na20 and 6.7-19.3% K20. The foregoing composition may be modified to include lithium oxide in amounts up to 5% and/or opaquing agent in amounts from about 0.05 to about 25% and the other oxides reduced or modified. Suit-able opaque porcelains may have the oxides inthe following approx-3~ imate ranges: SiO2 47 to 63%; A12O3 10 to 14%; CaO 0.6 to 1.3%;
K20 8.5 to 11%; Na20 1.5 to 5%; MgO 0.4 to 0.8%; and Sn02 9 to 25%. The present invention is not directed to the chemical 1053~08 compostion of the porcelain; thus, any commercially-available dental porcelain or porcelain compositions prepared by a skilled artisan may be employed. Some of the commercially-available porcelains include CERAMCO* Opaque Porcelain, CERAMO* Gingival Porcelain, BIOBOND* Opaque Porcelain, BIOBOND** Body Porcelain, VITA*** Porcelain, etc.
The selection of the porcelain in terms of exact com-position is dependent to a greater degree on the metal alloy substrate which is to be faced with the porcelain than on the instant bonding agent. For the bonding agent to have the advan-tageous properties provided by the present invention, it is ex-pected that the selection of the porcelain be appropriate for the metal alloy core or substrate employed. Thus, the thermal expansion properties of porcelain should be compatible or reason-ably matched with that of the alloy. It is recognized that a meaningful single coefficient of expansion is not obtainable for porcelain as it is for metal over the broad temperature range of about 25 to 600C. and that coefficients of expansion values are valid only for a narrow range of temperatures. Frequently, therefore, after preliminary determination of the coefficients of expansion, empirical methods are employed for the selection of the porcelain to be employed with the, particular alloy. The method of selection of porcelain for use with a particular alloy is not part of the present invention, but when a reasonably "matched" porcelain and metal alloy are to be bonded together, the use of the present novel bonding agent greatly enhances the bonding properties. Thus, even porcelain-to-metal bonds which by previous standards would be considered to be good bonding appear greatly inadequate when seen in the light of the present invention.

* Trademark of Johnson & Johnson or Affiliated Company ** Trademark of Dentsply International, Inc., York, Pennsylvania.
*** Trademark of Vita Zehnfabrick, Saechiagen, West Germany ~053~(38 The greatly superior strength of the bond provided by the bonding agent compositions of the present invention may be demonstrated qualitatively and quantitatively. Thus, when mechanical stress such as a hammer blow is applied to crowns or test disks faced with porcelain prepared by employing a bonding agent of the present invention, there is substantially little or no separation at the porcelain-to-metal interface whereas when it is applied to those prepared without use of bond-ing agent, the porcelain tends to separate cleanly from the metal.
The strength of the bond at the interface may be fur-ther demonstrated by cutting or sawing a slit on the porcelain face, inserting a flat bar or knife blade into said slit and applying torsional force. The crowns or disks prepared without use of the bonding agent completely or substantially completely separate at the porcelain-metal interface on application of this unusual force while the crowns prepared by the use of the bond-ing agent of the present invention remain securely bonded. Thus, even when extraordinary stresses are applied, the porcelain-to-metal bond remains intact and fracture or fractures occur insteadwithin the porcelain structure.
The bond strength may also be demonstrated quantitati-vely. However, the actual values may vary depending on the par-ticular alloy and porcelain combination, on the method of deter-mining bond strength, or on the treatment of metal surface prior to bonding. Thus, when the bond strength is measured as a force required to separate a metal rod from a porcelain disc bonded circumferentially around such rod, the quantitative values are found to be higher than when the bond strength is measured as a force required to separate porcelain bonds between the end faces of two rods. Also~ the porcelain to metal bond strength values generally are higher when porcelain is applied to a sand-blaste(l - 13 ~

~53~(~8 surface than when applied to a polished surace or even to an untreated surface. However, whatever quantitative values may be a.ssigned, it is found that for any particular combination of alloy and porcelain, bonding strength is unexpectedly superior when the bonding agent compositions of the present invention are em-ployed.
The success of the bonding agent composition of the present invention appears to be associated with the ability to provide a bond forming component in elemental and oxidized forms at appropriate times at the interface region. The provi-sion of a reducing atmosphere insures the presence initially of the bond forming component in the elemental form. On continued heating, conversion of a desirable portion of the bonding com ponent to an oxidized form is believed to take place which can subsequently react with the porcelain during the porcelain firing step. However, when the heating is over an extended period or exceeds about 1950F., the bonding power is found to have been diminished when subsequently porcelain is applied and fired. The invention, however, is not limited to any particular theory. Re-gardless of what explanation may be advanced as to what happens at the interface, a superior bond is obtained by the employment.
of the bonding agent composition of the instant invention.
The following examples illustrate the invention, but are not to be construed as limiting:
EXAMPLE I
A bonding agent having the composition set forth below is prepared by intimately mixing together the components.
COMPOSITION I
Aluminum powder (-400 mesh) 2 grams Glass 2 grams ~0534~8 SiO2 49.64% by weight A123 12.04% by weight Na20 3.60% by weight CaO 0.76% by weight MgO 0.48% by weight K20 8.40% by weight SnO2 21~0~/o by weight Li20 1.19% by weight B203 0 . l~/o by weight ~e23 0.013% by weight BaO 0.14% by weight Silicone Oil*about 1.5 milliliters The resulting composition is a fine slurry suitable for painting on metal. The foregoing bonding agent composition is painted on flat disks of a non-precious metal alloy. The alloy employed is of the following composition in weight percent: 71.3%
nickel; 19.1% chromium, 4.~/0 silicon, 4.1% molybdenum; and 1.4%
boron and is the subject matter of Canadian application No. 244, 988, filed January 30, 1976.
The painted disks are dried at the door of a dental furnace and then heated in the furnace at temperatures of from 1200F. to 18~0F. in air. The disks are removed from the furnace and bench cooled. After cooling, the disks are brushed with a toothbrush and water to remove loose particles of bonding agent and then ultrasonically cleaned for 5 minutes with warm water and dried~ CERAMCO* Opaque Porcelain is then applied to the surface and fired according to manufacturer's directions. A
layer of CERAMCO* Gingival Porcelain is also applied and fired.
Thereafter, each specimen is cut through the porcelain layer with a DEDICO** Cut Off Wheel to form a slit, and a screwdriver placed in the slit and torsional force applied to attempt to pry off *Silicone Oil - GE No. 69, viscosity 6-17 centistokes 100F, density 8 lbs./gal. GE No. 69 is a TrademarX.
*CERAMCO - Trademark of Johnson & Johnson ** DEDICO - Trademark 1053~ 8 the porcelain. The porcelain is resistant to separation from the metal.

- 15a -EXAMPL$ II

In a similar manner, a bonding agent of the following composition 1~ prepared.

COMPOSITIO~ II

Aluminum powder 2 grams Glass* 2 gr~m~
Sillcon Oil (GE #69~ 2.5 mllllllters *Same oxlde content as in Composltion I.

The composi~ion 1s a slurry sultable ~or applying on metal surfaces by palnting.

The strength of bon~ formed between metal and O porcelain by employing the foregoing b~ndlng agent composition is determlned by tests measuring mechanlcal properties in the following manner:

.
Employing the no~-precious metaI alloy (o~ composition described ln Exa~ple I), slugs which are 1 centlmeter ln length and 3/8 inch ln diameter, are prepared. For each test, a pair of slugs are employed. Each pair of slugs are poli6hed on one end with sandpaper. The bonding agent is then applied to the pol~shed ends and baked by placing in a furnace preheated to 1~00F. and the temperature raised in air at a rate of 90-100F. and the temperature raised in alr at a rate of 90-100~./minute to 1850F. On reaching 1850F, the slugs are removed from th~ ~rnace and bench-cooled.

10534(~8 The test slugs are cleaned in a manner similar to that described in Example I and dried. Thereafter, a layer of opaque porcelain (same as that employed in Example I) is applied to the bonding agent covered surface and fired by heating from 1200F. to 1700F. in vacuum (about 29 inches of mercury) and from 1700F. to 1850F. in air.

Then, a second layer of the same opaque porcelain is applied and the porcelaln covered surfaces are ~oined together~
Enough porcelain is applied so that when the porcelain-covered 1~ ends are joined, theré iB sufficient porcelain to extend beyond the perlphery, the excess compensating for the 8hrinkage which occurs on firing. The ~oined slugs (test specimens) are heated in a furnace at temperatures of from 1200F to 1700F in vacuum and from 1700F. to 1850F. in air. After reaching 1850F., the ~pecimens are maintained at that temperature for 2 minutes.

Control specimens, employing no bonding agent are prepared by (a) polishing one end of each pair as above described for the test 6pecimens; (b) applying opaque porcela1n o~ the same composition as for the test specimens to the polished ends and firing; and (c) applying a second layer of porcelain, ~oining the two ends and firing; the procedure differing only in the omission of the steps of applying and baking on of the bondlng agent.

10534(~8 The excess porcelain on the test and control specimens are ground off so that the diameter of the porcelain portion is of the same dimension as that of the metal.

The slugs are then employed for testlng mechanical properties in the INSTRON Instrument. In view of the small size of the test specimens special adapter~ are prepared for retaining the specimens while carrying out certain of the measur~ments. The tests employed are as follows:

Tensile Strength: The specimens are placed directly in the INSTRON and the force necessary to ~racture the specimen by exerting a pulling force at opposite ends of the specimen are noted, Shear: The specimens are placed in an adapter compris-ing two bars with an orlfice penetrating through each bar, the orifices are capable of being aligned above one another and retaining the specimen. The specimen is positioned so that the porcelain-to-metal interface coincides with the interface of the two adapter bars which are to be pulled in opposite direct~ons. The adapter is placed in the INSTRON and the force necessary to ~racture the specimen is measured.

Torsion: The specimens are placed in an adapter which is designed to hold one end stationary while a twisting force is applied to the othsr end and the adapter is placed in the ~NSTRON and the relative torsional force necessary to fracture the specimen is determined and recorded as levels. Torsional level as herein employed is a calculated number based on the load necessary to fracture the specimen multiplied by the distance from the specimen at which the force is applied.

T~ree-Point Loading: The specimens are placed in a special three-point loading apparatus mounted on the INSTRON
and the compression force necessary to cau6e failure at the metal-porcelain interface read on the INSTRON.

Impact Testing: A device is prepared consi~ting of two metal bars whlch are held side-by-side. These bars are hinged in such a manner that one bar is fully rotatable while the other is held stationary in a vertical position.
The test specimen is held on the stationary bar with a portion extending over the edge of the first bar in a direction such that it would be in the path of the second bar when the latter is rotated. The secon~ bar then is swung at a measured force and the relative force necesæary to cause fracture is determined. Impact level as herein employed is a number based on the linear distance travelled by a moving bar of constant weight to cause fracture of the test specimen.
The difference between the values for the control specimen and the test specimens are considered to be of greater significance than the actual numerical values. The results are seen in Table I.

` 1053~08 TABLE I
Mechanlcal Properties*
Tensile Shear 3-Point Stren~th Strength Torsion Loading Impact Specimen (psi~ (psi) (psi) (level) Test ~onding agent) 5019 5889 3.056 10206 7.6 Control (no bond- 1781 - 2815 1.678 4153 3.6 ing agent) *Test specimens - a~erage of seven to ten determinations.
Control specimens - average of flve to elght determinations (except tenslle ætrength;average of two determinations).

EXAMPLE II

In a slmilar manner, a bonding agent having the composltion set forth below i8 prepared.

COMP~SITION III
Aluminum Powder t-400 mesh) 3 grams Glass* 2 grams Silicone Oil (GE #69) 2 mllliliters *Same çomposition as glass of Compositlon I.
.

The composition is applied to a clean metal core of a non-precious metal alloy of the same composition as set forth in Example I. The painted metal core is then dried, baked, cleaned and faced with porcelains of the same compositions as employed in Example I.

The porcelain layers are then cut and torsional force applied as descrlbed in Example I. It i~ found that there is fracture of the porcelain but the metal-to-porcelain interface remainsintact.

EXAMPLE IV

Aluminum powder and one or more glass compositions (each consisting of a mixture Or oxides) are lntimately mlxed together with silicone:oll to obtain bonding agent compositions as substantially uniform slurries. The amounts of aluminum, each oxide component of the glass, and the ~olume of organo-silicon compound in the ~arious composltions are 11sted in Table II.

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_ ~ ~ i ri ~ O

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~ ~ * * * * * * ** * ** * ** ** ** 00~
e~ b O O O O O O O O O O O O11~ ~: O O
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The compositions are employed to test for bonding properties in a manner similar to that described in Example I.
Thus, the compositions are painted on flat disks of a nickel-chromium alloy of the same composition as that described in Example I, the painted disks baked, then porcelaln (CERAMC0*
opa~ue) applied and fused onto the disks to obtain test specimens. The porcelain layer 1s cut and torsional force applied as previously described and the bond assessed as good or bad. If there is no separation at the metal-porcelain interface and the fracture occurs in the porcelain, the bonding is considered Good; if there is separati4n at the interface, the bonding is considered Bad.

The bonds in all the speclmens employing the bonding -agent compositions llsted in Table II are rated Good.

- EXAMPLE V ' , In a manner similar to that described ln Examples I, III, and IV, bonding agent composltions having the following compositions are prepared.

*Trademar~F Johnson & Johnson or Subsidiary.

.
~3 ~os340s COMPOSITION IV

Aluminum powder (-20 microns) 2 grams Glass 2 grams SiO2 68~ by weight A1203 3-% by weight Na20 16% by weight CaO 6.o% by weight MgO 4.0~ by weight K20 0.5% by weight B203 1.5% by weight BaO 2.0~o by weight Silicone Oil (GE #69) 1.5 milliliters COMPOSITION V
Aluminum powder (-20 microns) 2 grams I Glass 2 grams SiO2 74% by weight A1203 1.0% by weight Na20 16.5% by weight CaO 5.0% by weight MgO 3.5~ by weight Silicone Oil 1.5 milliliters . . .
2~

/~S3Yo8 - - ~PO-SITION VI
Aluminum powder (-20 microns) 1.6 grams Glass 2.4 grams SiO2 65.1% by weight A12O3 13.3% by weight Na20 6.07% by weight CaO 1.37% by weight MgO 0.92% by weight K2O 9.78% by weight SnO2 0.05% by weight Li2o 1.01% by weight Fe2O3 0.015% by weight Silicone Oil 2.0 milliliters In separate operations, the compositions are applied to a clean metal core or substrate of non-precious metal alloy of the following composition in weight percent:
71.3% nickel; 19.1% chromium; 4.6% silicon; 3.7% molybdenum:
and 1.3% boron and is the subject matter of Canadian applica-tion No. 244,988, filed January 30, 1976.
The coated metal is baked in the manner described in Example I. Thereafte~, the coated metal is faced with por-celain employing the same porcelains and procedures described in Example I.
~he samples show good adhesion of porcelain to metal.

2~

EXAMPLE VII

In a similar manner, a bonding agent is prepared by mixing together 2 grams of aluminum powder (20 microns), 2 grams of glass powder (same oxide content as in Composition I) and a sufficient amount (1.5 -2.5 milliliters) of silicone oil (GE #69) to produce a thick easily paintable composition.

The composition is employed to bond porcelain to slugs of a nickel-chromium alloy of the same composition as described in Example I.

The 61ugs are prepared for testing in a manner similar to that described in Example II except as follows:

Ten pairs of slugs are employed without modifying the surfaces of the alloy before applying the bonding agent (As received surface). In ten other pa~rs of slugs, the surfaces are ground with a diamond wheel prior to applying the bonding agent (Ground surface). After application of the bonding agent, the slugs are baked, cleaned, coated with porcelain and fired in a manner similar to that previously described.

The slugs are then tested in the Instron testing instru-ment for three-point loading as previously described. The results are as follows:

As received surface 12,205 p.s.i.
Ground surface 10,364 p.s.i.

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:-

1. A bonding agent composition suitable for bonding dental porcelain to a metallic core of a non-precious metal alloy in a dental restoration comprising (a) a bond-forming component of powdered aluminum in admixture with a powdered glass fusing at temperatures in the range of from about 1750°F. to about 1850°F., and (b) a carrier component comprising a liquid organo-silicon compound capable of providing a reducing atmosphere at temperatures of from about 1200°F. to about 1900°F., wherein said glass is of a mixture of oxides which include the following in approximate weight percent: 47-74% silicon dioxide; 1-16% aluminum oxide;
3-17% sodium oxide; 0.6-6% calcium oxide; and 0.4-4%
magnesium oxide.

2. A composition according to Claim 1, in which the glass may contain in addition one or more of the following oxides in approximate weight percent: 0-12% potassium oxide;
0-25% stannic oxide, 0-5% lithium oxide; 0-2% boron oxide and 0-2% barium oxide.

3. A composition according to Claim 1, in which the carrier is silicone oil.

4. A composition according to Claim 1, in which the glass fuses within the range 1790° - 1810°F.

5. A bonding agent composition for bonding a dental porcelain to a metallic core of a non-precious metal alloy comprising a mixture of powdered aluminum and powdered glass in silicone oil as carrier, wherein for each part of solid bonding component mixture there is present from about 0.75 to 1.25 parts by volume of liquid; wherein said glass is a mixture of oxides which include the following in approximate weight percent: 47-74% silicon dioxide; 1-16% aluminum oxide, 3-17% sodium oxide; 0.6-6% calcium oxide; and 0.4-4% magnesium oxide.

6. A composition according to Claim 5 wherein the ratio of aluminum to glass is from about 2.3:1 to about 1:1.5.

7. A method of bonding dental porcelain to a metal core of a dental restoration comprising:
1) applying to a cleaned metal core, a substantially uniform coating of a bonding agent composition comprising (a) a bond forming component comprising powdered aluminum in admixture with a powdered glass fusing at temperatures in the range of from about 1750°F. to about 1850°F and comprising the following in approximate weight percent: 47-74% silicon dioxide; 1-16% aluminum oxide; 3-17% sodium oxide; 0.6-6% calcium oxide;
and 0.4-4% magnesium oxide; and (b) a carrier component comprising an organosilicon compound capable of providing a reducing atmosphere at temperatures of from about 1200°F. to about 1900°F.;
2) baking the coated metal core by rapidly heating from a temperature of about 1200°F. to a maximum temperature in the range of from about 1800°F. to about 1900°F.;

3) cleaning the coated and baked surfaces and 4) applying porcelain to the cleaned surface and firing.