NO762009L - - Google Patents

Description

Dental bonding agent.

Dental repairs usually consist of a metal core or frame on which porcelain is placed on the visible plates for aesthetic reasons. For many years, gold has been the basic structural metal for the production of such metal frames or cores. Due to the price of gold, however, many attempts have been made to arrive at base metal alloys that could be used instead of gold. Such compositions appear e.g. of the U.S. Patents Nos. 1,736,053, 2,089,587, 2,156,757, 2,134,423, 2,162,252, 2,631,095, 3,121,629, 3,464,817, 3,544,315, 3,685,115, 3,716,718, 3716,718 and 3,834,024, and in standard dental literature such as e.g. Skinner and Phillips: "The Science and Dental Materials", page 582, sixth edition W.B. Saunders Co., Philadelphia and London, 1967, and Morrey and Nelson: "Dental Sciences Handbook", page 168, American Dental Association and National Institute of Dental Research, U.S. Government Printing Office, Washington, D.C., 19 70. Suitable alloys are usually

on a nickel or cobalt basis, and in particular nickel alloys.

When such base metal alloys can be used as frameworks to be coated with porcelain, the porcelain is usually fired directly onto the metal surface and held in place by mechanical bonding. To achieve mechanical bonding, a roughening of the metal surface is required. Suitable roughening to achieve this metallic bond is very difficult to implement. Moreover, mechanical binding is not always sufficient to withstand the daily stresses,

and it therefore not infrequently happens that the porcelain comes loose. the metal core in whole or in part. It is therefore desirable to arrive at a binder that is resistant to such a solution.

The present invention is directed to the binder and in particular to compositions and methods for joining dental porcelain with a frame of base metal alloy. When the dental porcelain is to be joined to the metal frame using the binders according to the present invention, a strong bond is formed which resists peeling of the porcelain under much higher stress than without such a binder. Moreover, the ingredients are free of compounds that cause tissue disruption or toxicity problems.

The binder composition according to the present invention consists of: (1) a metal/porcelain/adhesive consisting of powdered aluminum mixed with powdered glass which has a melting temperature in the range 950-1010°C, preferably approx. 980°C, and (2) a mixing medium or carrier which is a compound capable of emitting a reducing atmosphere during firing of the adhesive or binder. The glass used is a mixture of non-crystalline oxides as commonly known in the field and as described in more detail later. The carrier medium can be an inert medium with no other function than as a carrier medium, and the reducing atmosphere that is necessary during the burning or sintering of the binder can be provided by separately supplied gas, however, a preferred embodiment of the invention includes that the reducing atmosphere is provided by means of the carrier medium. The term "binder composition" includes, in the present context, both the binding component and the carrier medium. The terms "bond-forming component" and the like refer to the aluminum-glass mixture. The terms "core", "frame", "substrate", "substrate", "structure" and the like in connection with "metal" mean the same thing and refer to the dental structure to be coated with porcelain.

According to a preferred embodiment of the invention, the bond-forming component is a mixture of aluminum and glass which melts in the range 977-988°C. The aluminum is available as a powder so fine that it passes a 400 mesh sieve, and is preferably in the form of a powder with a particle size of 20 microns or finer. The glass is a mixture of non-crystalline oxides comprising silicon dioxide, aluminum oxide, sodium oxide, calcium oxide and magnesium oxide, it may contain one or more of the following oxides: tin oxide, potassium oxide, lithium oxide, boron oxide, titanium oxide, barium oxide, zirconium oxide, etc. The amounts of the first mentioned oxides which can be called essential oxides, can vary significantly depending on whether there are non-essential oxides and possibly their quantity. Thus, the essential oxides may be present in amounts (by weight) as follows: 47-74% silicon dioxide, 1-16% alumina, 3-17% sodium oxide, 0.6-6% calcium oxide and 0.4-4% magnesium oxide. The other oxides can be found in the following amounts: 0-12% potassium oxide, 0.25% tin oxide, 0.5% lithium oxide, 0-2% boron oxide and 0-2% barium oxide. The preferred glasses are those where the oxide composition falls within the following weight limits: 47-63% silicon dioxide, 9-25% tin oxide, 10-14% aluminum oxide, 8.5-10% potassium oxide,

3-5% sodium oxide, 0.6-13% calcium oxide, 0.4-0.8% magnesium oxide, and 0-5% lithium oxide. Many suitable glasses are commercially available such as glass, porcelain, ceramic oxides etc. Other glass compositions can be produced by dry mixing the suitable oxides

in proper quantities, melt the mixture into a frit, pour the frit into water, dry and grind the mixture to a suitable fineness, as known in the field. The glass composition is ground to a particle size powder that passes a 165 mesh sieve (about 60 microns) or finer. The particle size for both aluminum and the glass is mainly based on the most finely divided powders which are

few at present. When finer powders become available, these should be used.

The carrier medium in the new preparations according to the invention is liquid organic silicon compounds (organosilicon compounds) such as silicone oil, silane etc. Suitable liquid organic silicon compounds should provide suitable liquid painting properties after incorporation into the binder powder mixture. Preferably, organic liquid silicon compounds have a viscosity of

4- 40 centistokes at 25°C or 6-17 centistokes at 37°C, or 45-85 Saybolt seconds. These organosilicon compounds will provide a reducing atmosphere, while providing the appropriate flow in the mixture.

In preparations consisting of a powdered mixture

of aluminum and glass in liquid organic silicon compound, the exact amount of liquid carrier used in the powder mixture is not critical. Usually such large amounts of liquid organic silicon compound are used that the suitable fluidity for paint on metal surfaces is achieved. Liquid with viscosity

tet in the range 6-17 centistokes at 37°C will give preparations with suitable grinding properties by combining one part by weight of solid binder mixture and 0.25-0.75 parts by weight of liquid. Usually the solids content of the preparation is 60-80% by weight.

The relative amounts between aluminum and glass are important. The aluminum component can make up from 40-79 percent by weight of the total dry matter mixture and the rest is a glass component. Good results are achieved with a 50:50 mixture of aluminum and glass.

The binder composition can be prepared by carefully mixing the binder components and the carrier medium in a suitable manner to form a completely uniform slurry. Preferably, the solids, i.e. aluminum and glass powders, are premixed, and the powder mixture is then thoroughly mixed with a liquid organosilium compound. The preparation can be pre-mixed on site before use or powder mixture and liquid can be pre-mixed, that is, the entire preparation can be pre-mixed. The composition can be used by dental technicians with normal equipment

The present invention also relates to the use of a binder preparation according to the present invention to achieve secure adhesion or binding of the dental porcelain to the metal core. A preferred embodiment consists in using the above-mentioned new binder composition in admixture with a carrier medium which provides a reducing atmosphere. However, the invention also includes the use of other means which deliver a reducing or non-oxidizing inert atmosphere, where the carrier component is only an inert liquid with suitable flow properties.

According to the method of the present invention for joining the dental porcelain with a metal core, the new binder mixture is applied evenly to the relevant surface of the metal core which has been produced in the usual way, e.g. by sling casting, and which is thoroughly cleaned with diluted acid and/or sandpaper, and the coated core is then fired in air at a temperature of 650-1040°C in a special oven. The coated and burnt metal core is taken out of the oven, allowed to cool and cleaned by brushing off loose material and ultrasonic washing with hot water, and then drying. Porcelain mesh is applied and the resulting porcelain-coated metal core is fired in the usual way.

During the execution of these steps, the binder mixture is applied in a known manner. Generally, painting with a brush is appropriate. Good results are achieved whether the coating mass can be qualitatively described as thick, thin or medium. It is crucial and important that all surfaces are coated evenly with the binder composition.

During firing, the firing temperature and time can be varied. According to a common dental technician method, the coated metal core is placed in an oven preheated to 650 oC and heated rapidly in air to a maximum temperature between 980-1040°C, with a heating rate of 50-55°C/min. Preferably, the maximum temperature is in the range 1004-1016°C. The total heating time when heating takes place in this way is less than 15 minutes. Alternatively, the heating can take place at a lower temperature for longer

period of time.

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

The step of cleaning the coated metal after burning on the binder is also important and decisive for achieving good adhesion between porcelain and metal. When the cleaning step is omitted, it is often found that the porcelain cracks. Cleaning with a brush and ultrasound in water seems to give the best results, although other methods that remove non-adherent components can also be used.

The porcelain is applied to the binder-coated metal surface in a suitable way, e.g. as is usually applied to porcelain without a binder. Preferred methods are painting with a brush or coating with a spatula. After applying the porcelain, the porcelain is fired at the correct temperature adapted to the particular porcelain, forming a metal. The firing can take place at temperatures within a wider temperature range of 870-1095°C. A further coating of porcelain is then applied which is fired in a known manner to complete the dental work, and during this a bond is formed between the metal and the porcelain which thereby becomes resistant to cracking and peeling due to mechanical stress. The binder composition according to the invention is adapted to metal alloys and porcelain which are suitable for use together without a binder.

The metal alloys which are best suited for use with binder compositions according to the invention are nickel- and cobalt-based alloys, especially chrome-nickel alloys. Representative alloys can be found in the previously mentioned patents and the dental literature on base metal alloys. Other alloys as a binder.-the composition can be used with are commercially available under different brands. Additional alloys with which the present composition can be successfully used are found in U.S. Pat. patent application no. 546,642/1975.

The porcelain to be joined with the dental alloy can be any porcelain suitable for use with the chosen alloy. By "porcelain" is meant the dental porcelain that is known in the field, also including dental glass. Typically, such porcelain contains silicon oxide, aluminum oxide, potassium oxide, sodium oxide and smaller amounts of other oxides. Normally, the first porcelain layer is opaque porcelain. Opaque porcelain reduces the tendency for metal to seep through the final coating. Opaque porcelain is commercially available and contains in the oxide mixture either zirconium, tin oxide, titanium oxide or zirconium silicate as an opacifying agent. The opaque porcelain is normally coated with a relatively thick layer or several layers of compact porcelain, usually followed by a final layer or outer layer of chewing porcelain on the tip. The compact or building porcelain is commercially available as gum porcelain or white porcelain (also called (US) dentine) and may have a smaller amount of opacifying agent, and the chewing porcelain usually has a similar composition to the building porcelain without opacifying agent. In all coatings after the first, the porcelain is joined to the porcelain. In the first coating, the porcelain is bonded to the metal and the problems to be solved with the help of the present binder preparation exist at the porcelain/metal interface. It is thus only the porcelain that is to be joined with metal that is of interest in carrying out the present invention. Since the porcelain to be joined to the metal in current practice is opaque porcelain, the type of porcelain to be joined to the metal using the present binder will usually be opaque porcelain, although the invention is not limited to this.

Types of porcelain that are advantageously used are feldspar porcelain, which has a similar oxide content to the glass component in it

in-

present binder. Typical porcelain preparations can be found in standard works such as Skinner and Phillips, "referred to earlier, and compositions for several porcelain types in the trade can be found on page 60 of Jean-Marc Meyer, "Contributions to 1'Etude de la Liaison Céramo-metallique des Porcelaines cuites sur Alliages en Prosthése Dentair" (contribution to the study of the ceramic-metallic bond between porcelain and metal alloys in dental prostheses) Thesis, University of Geneva 1971.

Suitable porcelain types include those described

in the U.S. patent no. 3,052,982, with the following oxide content: 61-67. 8% SiO2, 11.7-17.1% Al2O3, 0.1-2.6% CaO, 0.1-1.8% MgO, 2.37-9.6% Na2O, and 6.7-19.3% K2O . This composition can be modified by adding lithium oxide in amounts up to 5% and/or opacifying agents in amounts from 0.05 to approx. 25% and the other oxides are reduced accordingly. Suitable, opaque porcelain types can have oxides in the following approximate proportions: Si02447^63%, Al2°310-14%, CaO 0.6-1.3%, K288?5-11.0%, Na20 1.5-5% , MgO 0.4-0.8% and SnO29-25%. The present invention is not directed at the porcelain's chemical composition and thus any known dental porcelain or porcelain preparation can be used. Some of the well-known porcelains in the trade are "CERAMCO" opaque porcelain, "CERAMCO" gum porcelain, "BIOBOND" opaque porcelain, "BIOBOND" construction porcelain, "VITA" porcelain etc.

The choice of porcelain with regard to exact installation depends to a greater extent on the metal alloy that is to be coated with the porcelain than on the existing binder. In order for the binder to have the advantageous properties described, it is a prerequisite that the choice of porcelain is adapted to the metal alloy used in the core or substrate. Thus, the thermal expansion properties of the porcelain should be adapted to the alloys. It is known that a meaningful simple expansion coefficient cannot be obtained for porcelain to the same extent as for metal over a wide temperature range of 65-600°C and that valid expansion coefficients can only be established for a narrower temperature range. Empirical methods are therefore often used to select the porcelain for a particular alloy after prior determination of expansion coefficients. The method for selecting a porcelain in connection with a particular alloy does not form part of the present invention, but when a suitable pair of porcelain and me ta 11 eg er Ing is to be joined, the use of the present*-new binder will greatly increase the bonding force . Even the porcelain/metal bond, which according to previous standards would be considered good, seems to be largely insufficient in light of the present invention.

The superior strength of the bond achieved by

with the help of the present binder preparation can be demonstrated qualitatively and quantitatively. Thus, when a mechanical stress, such as a hammer blow is applied to crowns or test disks coated with porcelain using the binder according to the invention, essentially no peeling occurs in the flat porcelain/metal, whereas when you strike such a sample without a binder, the porcelain will most often peel cleanly from the metal .

The bond strength in the contact surface can be further demonstrated by cutting a groove in the porcelain surface, inserting a knife blade into the crack and twisting. Crowns or discs made without bonding agent will completely or substantially peel off and separate at the porcelain/metal surface when this unusual force is applied, while crowns made using the existing bonding agent are intact in the joint. Even when extra-ordinary stresses are therefore continued, the porcelain/metal bond remains intact and fractures occur instead in the porcelain mass.

The bond strength can also be demonstrated quantitatively. However, the measured numbers may vary depending on the particular combination of alloy and porcelain, the method of measuring the bonding force or the treatment of the metal surface prior to bonding. Therefore, when the bond strength is measured as the force required to separate a metal rod from a porcelain disc joined along the circumference around such a rod, the quantitative figures will be higher than when the bond strength is measured as the force required to separate porcelain bonds between the end surfaces of two rods . Furthermore, the porcelain/metal bonding force is usually greater when the porcelain is applied to a sandblasted surface than when applied to a polished or an untreated surface. Regardless of the quantitative measurement values, however, it is found that for a chosen combination of alloy and porcelain, the bonding force will be unexpectedly much greater when binder preparations according to the invention are used.

The beneficial effect of the binder preparation according to the invention seems to be connected with their ability to provide a bond-forming component in elemental and oxidized form at the right time in the contact surface. The reducing atmosphere initially ensures that the binding component is in elemental form. With continued heating, it is assumed that a favorable part of the binder component turns into oxidized form which can then react with the porcelain during the subsequent porcelain firing step. However, when the heating takes place over a longer period of time or when the temperature exceeds 1065°C, it is found that the binding force is reduced by the subsequent application of porcelain and firing. However, the invention is not limited to any particular theory. Regardless of the explanation of what happens in the contact surface, a superior bond is achieved by using the present preparation.

The following examples shall illustrate the invention without being construed as limiting.

Example I

A binder with the following composition is produced by carefully mixing their components:

Preparation I

The resulting component is a fine slurry suitable for painting on metal. The binder preparation is painted on flat discs of base metal alloy.

The metal alloy has the following composition extracted in % by weight: 81.3% nickel, 19.1% chromium, 4.0% silicon, 4.1% molybdenum and 1.4% boron and is described in patent application U.S. No. 546,642/ 1975.

The ground discs are dried in the door opening of the melting furnace and then heated in the furnace at 650-1010°C. The discs are taken out. the oven and cool on the counter. After cooling, the slices are brushed with a toothbrush and water to remove loose particles<p>and cleaned in ultrasound for 5 min. with warm water and dried. CERAMCO opaque porcelain is then applied to the surface and fired as described by the manufacturer. A layer of CERAMCO gum porcelain is also applied and fired. Each sample is then cut through the porcelain layer with a "DEDICO" type cutting wheel which forms a notch and a screwdriver is placed in the notch, then turned to try to loosen the porcelain. The porcelain is resistant to dissolution from the metal.

Example II

In a similar way, a binder with the following composition is produced:

Composition II

The slurry is suitable for application to metal surfaces when painting.

The bond strength between metal and porcelain by using the above binder composition is measured mechanically in the following way: Pieces measuring 1 cm in length and 9 mm in diameter are made from base metal alloy (composition described in example I). A pair of cylindrical pieces are used for each experiment. Each pair is polished at one end with sandpaper. Binder is then applied to the polished ends and fired in the oven, preheated to 650°C where the temperature is later increased in air at a speed of 50-55°C to 1010°C. After reaching 1010°C, the pieces are removed from the oven and cooled on the counter.

The test cylinders are cleaned as described in example I,

and dried. A layer of opaque porcelain (same as in example I) is then applied to the binder-coated surface and fired at 650-927°C in vacuum (- approx. 74 cm Hg), and from 930-1010°C in air.

A second layer of the same opaque porcelain is then applied, and the porcelain-coated surfaces are joined together. Enough porcelain is applied so that when the porcelain-coated ends lie next to each other, there is a certain excess along the circumference which compensates for the shrinkage during firing. The joined test cylinders are heated in the oven at 650-930°C in vacuum and from 930-1010°C in air. After reaching 1010°C, the samples are held at this temperature for 2 min.

Comparison samples that have not had a binder applied are prepared by (a) polishing one end of each pair as described above, (b) painting opaque porcelain with the same composition on the polished ends and firing, and (c) applying a new porcelain layer, joining the two ends and firing, so that the methods used differed only in that the steps of applying and firing the binder were omitted.

The excess porcelain on the test and control samples is worn off so that the diameter of the porcelain surface is the same as that of the metal.

The pieces are then inserted into an INSTRON instrument to determine the mechanical properties. Due to the small size of the test pieces, special adapters are used to hold the samples while some of the measurements take place. The tests used are the following: Tensile strength: The test is placed directly in the INSTRON instrument and the force required to break the sample is measured using tensile forces at each end of the sample.

Shear force: The samples are placed in a holder that consists

of two bars with an opening through each bar, the openings can be placed directly opposite each other while retaining the sample.

The sample is placed so that the porcelain/metal contact surface coincides with the contact surface between the two holding rods which are pulled in opposite directions. The holding device is placed in the INSTRON instrument and the force required to break the sample apart is measured.

Twisting: The samples are placed in a holder that holds one end while a twisting force is applied to the other, after which the holder is placed in the INSTRON instrument and measured

the relative twisting force (torsion force) that is required

y to break the sample apart. The torsional force set here is calculated as a number based on the load required to twist the pieces apart multiplied by the distance from the sample where the force is applied.

Three-point loading: The specimen is placed in a special three-point loading apparatus mounted on the INSTRON instrument, and the required compressive force that causes failure in the metal/porcelain interface is measured.

Impact resistance: A device is made that consists of two metal rods that are held side by side. The rods are hinged in such a way that one can be fully rotated, while the other is held firmly in a vertical position. The sample is held on the fixed rod with a part projecting over the edge of the first rod in such a direction that it will be in the way of the second rod when it is turned. The second rod is swung out with measured force and the relative force required to induce fracture is set up. The impact strength is measured here as a number based on the linear distance traveled by a moving rod of constant weight to induce fracture in the sample. The difference between the numbers for the control sample and the experimental samples is assumed to be of greater importance than the real numerical values. The results are set out in Table I.

Example II

In a similar way, a binder is made with the composition shown below:

Composition III

The composition is applied to a pure metal core of base metal alloy with the same composition as stated in example I. The painted metal core is dried, fired, cleaned and coated with porcelain with the same composition as stated in example I. One cuts through the porcelain layers and applies a twisting force as described in example I. The porcelain is found to break into pieces, but the metal/porcelain contact surface is intact.

Example IV

Aluminum powder and one or more glass compositions (all of which consist of an oxide mixture) are carefully mixed with silicone oil to form a binder preparation in the form of a smooth slurry. The amount of oxide components in the glass and the relative amount of organosilicon compounds are listed in Table II.

The composition is used for measuring blending properties in the same way as described in example I. Thus, the preparations are painted on flat discs of nickel-chromium alloy with the same composition as in example I, the painted discs are fired, the porcelain is applied (CERAMCO kopak) and fired on the discs which .forming the test pieces. The porcelain layer is cut across and torsional forces are applied as described, in order to judge the bond as good or bad. If no solution occurs in the metal/porcelain surface and the fracture occurs in the porcelain, the bond is considered to be

•in

good, if the layer loosens, the binding force is poor. The binding forces in all samples with binding agent preparation according to table II,

is rated: good.

Example V

In the same way as described in examples I, III and IV, binder compositions are prepared as shown below:

Composition IV

Composition V Composition VI

Separately, the compositions are applied to a pure metal core or base metal alloy substrate having the following weight composition: 71.3% nickel, 19.1% chromium, 4.6% silicon, 3.7% molybdenum and 1.3% boron, which constitutes the item in the U.S. patent application no. 546,642/1975.

The coated metal is fired as described in example I and then the porcelain is applied in the same order as described in example I.

The samples show good adhesion pearl/metal.

Example VII

Similarly, a binder is prepared by mixing 2 g of aluminum powder (20 microns), 2 g of glass powder (same oxide content as in Example I) and sufficient (1.5-2.5 ml) silicone oil (GE #69) to form a thick and light mortar mixture.

The composition is used to join porcelain with a sample piece of nickel-chromium alloy with the same content as described in example I.

The test pieces are prepared for testing in a similar way to example II except for the following: Ten pairs of test pieces are used without affecting the surface of the alloy before applying binder (untreated surface).

the other ten pairs of bits are ground with a diamond wheel before applying adhesive (ground surface). After applying the binder, the pieces are fired, cleaned, coated with porcelain and fired in the same way as before.

The pieces undergo tests in the INSTRON instrument to measure the resistance to three-point loading as described. The following results are obtained:

Untreated surface 858 kg/cm<2>

Grinded surface 728 kg/cm<2.>

Claims (7)

1. Bonding agent suitable for joining the dental porcelain to a metal core of non-noble metal alloy in a dental repair, characterized by 4 a). a bond-forming component of powdered aluminum mixed with powdered glass with a melting range of approx. 950-1010°C and (b) a carrier medium in the form of a liquid organosilicon compound which is capable of emitting a reducing atmosphere at a temperature of approx. 650-1040°G, where the glass is a mixture of oxides in the following weight ratio: 47-74% silicon dioxide, 1-16% aluminum oxide, 3-17% sodium oxide, 0.6-6% calcium oxide and 0.4-4% magnesium oxide . 2. Composition as stated in claim 1, characterized in that the glass may additionally contain one or more of the following oxides: in approximate weight ratios: 0-12% potassium oxide, 0-25% tin oxide, 0-5% lithium oxide, 0-2% boron oxide and 0-2% barium oxide. 3. Composition as stated in claim 1, characterized in that the carrier medium is silicone oil. ' 4. Composition as stated in claim 1, characterized in that the glass melts in the range 977-988°C. 5. Composition for joining the dental porcelain with a metal core of base metal alloy consisting of a mixture of powdered aluminum and powdered glass, in silicone oil as carrier medium, where for each part of solid binder mixture there is from 0.75-1225 parts by volume of liquid and where the glass is a mixture of oxides in the following weight ratio: 47-74% silicon dioxide, 1-16% aluminum oxide, 3-17% sodium oxide, 0.6-6% calcium oxide and 0.4-4% magnesium oxide. 6. Composition as specified in claim 5, characterized in that the aluminum/glass ratio is from approx. 2.3:1 to approx. 1:1.5. 7. Procedure for joining dental porcelain with a metal core in dental repair work, characterized by: 1) applies to the cleaned metal core a substantially uniform coating of a binder composition consisting of (a) a bond-forming component of powdered aluminum mixed with powdered glass having a melting temperature within 950-1010°C and containing the following components by weight: 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 medium in the form of an organosilicon compound which can emit a reducing atmosphere with temperatures between approx. 650 and 1040°C, 2) burning of the coated metal core by rapid heating from approx. 650°C to a maximum temperature containing 980-1040°C, 3) 3) cleaning of the coated and burnt surface and 4) application of the porcelain to the cleaned surface followed by firing.