ANNEALING GOLD FOIL
“In more recent years, I have gotten to use more gold foil than I did perhaps ten years ago, because of the failure of the silicates I put in myself and the failure of the silicates put in by the hands of others. . . . I am getting back to gold foil, and I think more men, as time goes on, will be glad to get back to gold foil, which has stood the grueling test of many years of time."
DR. WILLIAM DWIGHT TRACY
MORGAN, HASTINGS & COMPANY
DIVISION OF HASTINGS & CO., INC.
North Front Street • Philadelphia. Pa. 19122
World's Oldest and
Largest Manufacturers of Filling Golds exclusively
In making a restoration with cohesive Gold Foil, annealing is really the initial step. As an operation, it is simplicity itself; but its consequences are basic and far-reaching. If it has been done improperly, even a restoration that is apparently successful will ultimately fail — according to the failure of the annealing.
Why ANNEAL Gold Foil?
The annealing of Gold Foil is not a process to alter its molecular state. Gold Foil, when absolutely pure, is cohesive inherently - is inherently capable of uniting throughout the mass. Its laminae will stick together on mere contact. It is this unique property that makes it possible to weld it in the cold state.
But its purity is impaired easily, so that it either is no longer capable of cohering or can cohere only imperfectly, making it impossible to weld it successfully in the human mouth. Even mere exposure to the air may so contaminate its surface as to destroy its cohesiveness, and hence weldability, altogether. Gold Foil must therefore be expressly protected and, just before use, have its surface thoroughly cleansed. It is for the purpose of the latter — to drive off all volatile impurities — that Gold Foil is subjected to annealing. And its annealing is thus simply and wholly a cleansing operation.
What CONTAMINATES Gold Foil?
Gold Foil may so easily be contaminated on mere exposure to the air because the atmosphere almost always contains gases that are attracted to its surface. They attach themselves by molecular attraction, depositing a film of salts that coat its surface and render it incapable of cohering. Some of these adhesive gases, being volatile, can be driven off by heat. They are the neutral and the alkaline gases, such as carbonic-acid gas and ammoniacal gas. Annealing drives them off completely, rendering the surface chemically clean again and restoring the inherent cohesiveness. Others, however — the acid gases, such as the sulphurous and the phosphorous group — cannot be volatilized by heat. Their salts are fixed, and consequently remain condensed upon the surface, rendering Gold Foil irretrievably incohesive.
Of the gases that are deleterious irretrievably, those of common occurrence in the dental office are sulphuric-acid gas, phosphoric-acid gas, and sulphureted-hydrogen gas.
Sulphuric-acid gas is given off by the sulphur of ignited matches, and is constantly exhaled by all rubber goods. A prolific source of this gas is that of the trimming and finishing of rubber dentures, vulcanizing, and the various other dental operations using rubber. And in towns and cities where sulphurous coal is burned or paper is manufactured, it is extensively present in the general atmosphere.
Phosphoric-acid gas too is given off by ignited matches, either by the phosphorus in the tips or, in the case of "safety matches," by the phosphorus-treated surface on which they are struck. It is thrown off also by the spontaneous combustion of phosphureted-hydrogen gas, which is a product of the decomposition of animal or vegetable matter.
Sulphureted-hydrogen gas is another product of such decomposition. It is very common in the general atmosphere.
Still other airborne contaminators, even of more common occurrence, are those of dust and moisture.
Lastly, Gold Foil may be contaminated also by any solid or liquid that can impart to its surface an adhesive impurity on contact. Mercury, in particular, is to be guarded against. So is also moisture from the skin of the hands. So, while the restoration is being made, is also saliva.
How TO PROTECT Gold Foil
The protection of Gold Foil from contaminative solids and liquids is obviously an ordinary affair. Likewise the neutral and the alkaline gases present no special problem —inasmuch as annealing drives them off completely. But with the gases that are deleterious irretrievably, the case is quite different. Destroying as they do the cohesiveness of Gold Foil so that it cannot be restored even by annealing, they must be prevented from settling on its surface at all. And with their occurrence in the dental office so common, that isn't likely to be successful with anything like ordinary precautions.
An express and thoroughly efficacious way of protecting Gold Foil from contamination by such gases is that of coating it, as a preventive, with a film of alkaline salts. This protective film, usually of ammonia, prevents deleterious gases from condensing directly on the Foil. Instead, these gases combine with ammonia, as an alkaline base, to form other salts, and they are neutralized by it when it is present in excess. They are then driven off by annealing as easily as any neutral or alkaline gas.
Such protection is generally effected by the simple means of keeping with Gold Foil, as in a drawer,*
* It is best for the Gold Foil in the drawer not to be loose. It should be kept, either in the original container or in a satisfactory substitute, tightly corked. And it is inadvisable to keep with it, in the same drawer, such articles as vulcanite, rubber dams, etc.
a small bottle of ammonia loosely corked. Equally satisfactory is a small sponge, or
a cotton roll, saturated with spirits of ammonia and, to avoid staining, kept in an open small bottle.
When the operator prepares forms of his own — pellets, ropes, etc. — and the Foil is handled with the fingers, it is advisable always to wear chamois finger-tips. This will provide complete protection from moisture on the skin.
AIM and METHODS of ANNEALING
From the foregoing, it is plain that the annealing of Gold Foil presupposes its express protection, and that the general aim of annealing is to drive off its surface all atmospheric moisture and whatever film has been formed by the protective alkaline gas in combination with gases that may have settled afterward.
PROPER ANNEALING is then a matter of heating Gold Foil long enough, at a given temperature, to volatilize all moisture and gases, of cleansing all its surface, of avoiding injury to the Foil in the process, and of guarding it against all contamination, from the start of its annealing to its condensation in the cavity.
UNDERANNEALING is to be avoided. It leaves impurities on the Foil, which prevent its thorough condensation. and thus cause the restoration, eventually, to pit and flake. OVER-ANNEALING is to be avoided no less. It scorches the Foil, shriveling the fine edges, and rendering it generally harsh and unworkable — with the same harmful consequences as those of underannealing. It can be the cause of some of the difficulty encountered, especially by beginners, in seating the first third of a Gold Foil restoration. And scorched Foil will not burnish properly. As to CONTAMINATION of Gold Foil during or after annealing, it may be as harmful, obviously, as contamination before annealing.
Gold Foil can be annealed, in general, by either of two methods: (1) piece by piece, in an open flame; or (2) in bulk, on a tray or some other suitable receptacle. Each has its advantages and disadvantages, and either is capable of giving satisfactory results.
To ascertain current annealing practices, Morgan, Hastings & Co. recently sent out a questionnaire to dentists in various parts of the country. The answers received were divided between the two methods about evenly: those from dentists who annealed piece by piece totaled 247, while those from dentists who annealed in bulk totaled 234. Many an operator quite naturally believed his favorite method to be superior; and there were in each group about an equal number of those who reported having had satisfactory results for as long as 20 years. On the other hand, there were in each group also those who had tried the alternative method and found it less satisfactory. Then again, there were some who, according to circumstances, now used one, then the other, with equally good results.
And so it seems reasonable to conclude that either method is sufficiently satisfactory in itself and that success depends entirely on its being employed with understanding and care. The choice is thus a question simply of the operator's personal predilection. He would evidently do well to adopt the one that is more to his liking.
The two methods of annealing are described in what follows — which also further summarizes the findings of the aforementioned questionnaire.
ANNEALING PIECE by PIECE
The method of annealing piece by piece consists in picking up each piece of Gold Foil, of whatever form, individually, heating it directly in an open flame, and placing it in the cavity.
The instrument best adapted for carrying the Foil is one with a fine, smooth point. Pliers, even with the smallest beaks, are less practical. The part of the Foil that is covered by the beaks is annealed less thoroughly than the part that is exposed to the flame fully, necessitating a second annealing, for which the position of the grasp must be changed so as to expose fully the part insufficiently annealed the first time. Not only does this take longer; it increases the hazard that a portion of the Foil may be overannealed.
The instruments used for the purpose are ingeniously various. Particularly excellent is one devised by Dr. Charles E. Woodbury. Its nichrome point is easily kept sharp and smooth; in contrast to that of steel, which soon becomes carbonized and rough. It is better also than one of gold or platinum, which tends to dull easily, and to stick to the heated Foil. An instrument of Dr. Woodbury's specifications can be made by the operator simply by sharpening and smoothening one end of a piece of 16-gauge nichrome wire, bending it like an explorer, and setting the other end into a broach-holder.
A similar instrument in common use is made by flattening and sharpening an old stainless-steel explorer to a spear-like point. Or, with a Joe Dandy disk, the flattened explorer is made into a tiny fork. Some employ, set into a broach-holder, an old broach with its barbs clipped off, or a piece of iridio-platinum wire with one end sharpened. The latter is usually bent like an explorer. Other operators, mostly those working without an assistant, pick up the Foil on the point of the condenser.*
* The term "condenser" is here adopted in place of "plugger" at the instance of Dr. James Mark Prime, as well as in recognition of its growing favor with members of Gold Foil study clubs generally. Its advocates argue that it describes the real purpose of the instrument more accurately than "plugger"; an opinion with which it is easy to go along.
Whatever the instrument, its point should be nonoxidizing, and it should pick up the Foil so as neither to crush it nor to cover any portion of it. And it should obviously be cleaned just before use. Simply scrub it with a stiff nail-brush dipped in alcohol, and then dry it thoroughly with a towel.
The fuel for the flame may be alcohol or gas (the latter may be natural or manufactured). Alcohol is widely preferred; gas is believed to be more intense, also more carbonizing. The alcohol, whether from wood or from grain, should be chemically pure. Denatured alcohol is seldom satisfactory; most denaturing agents yield an overplus of carbon and are contaminating. An increasingly popular brand of alcohol is that known as Methanol.
When the annealing is done with an alcohol lamp, the flame should be moderately strong, of a clear light-blue color, and free from soot. This requires not only that the alcohol be right, but that the lamp be thoroughly clean, and that the wick not be up too high. In lighting the lamp, the match is not to touch the wick, or else enough sulphur may stick to it to contaminate the Foil during annealing. Apply the flame of the match to the extreme edge of the wick. Or light a toothpick with the match, and then light the lamp with the toothpick. In any case, the charred part of the wick is to be trimmed off after each annealing. Some remove it by rubbing the wick with a towel.
The Foil is passed through the flame at the tip of the inner cone — neither close to the wick nor through the upper portion of the outer cone. Either of the latter may contaminate it with carbon. It is passed through the flame - not held — at a rate that will bring every particle to a dull red. If kept in the flame till it shows a bright glow, it is liable to be overannealed before it can be withdrawn. Heating it to a dull red usually takes no longer than the count of two. The exact length of time depends on the size of the piece and on the intensity of the flame. Gauging it, is entirely a matter of feel, which comes with experience.
When annealing with a Bunsen gas burner, be sure to have a reducing flame, and turn it down to about an inch high. Pass the Foil through the middle of the flame, somewhat more quickly than through an alcohol flame.
Whatever the fuel, the hazard of open-flame heating is not so much that of underannealing as that of overannealing. One must always guard against it. If a piece comes out of the flame looking the least bit shriveled, it is doubtless scorched, and is best discarded.
Every annealed piece, in all open-flame annealing, is carried-from the flame direct to the cavity. This has the important advantage of precluding all possible contamination of the Foil after annealing, whether by atmospheric moisture or gases or by substances that can contaminate it on contact. A common procedure is as follows. While malleting an annealed piece with one hand, the assistant picks up a fresh piece with the other. When the condensation of the former is finished, she then anneals the latter and carries it to the cavity. And so on till the restoration is completed. On reaching the cavity, the Foil should have cooled sufficiently not to cause any painful reaction. Its cooling can be hastened by waving it in the air for an instant.
Other operators have the assistant anneal a piece immediately after placing one in the cavity. While the latter is being malleted, the former, on the foil-carrier, is then cooling.
According to the most recent reports, the method of annealing piece by piece is increasingly giving way to that with an electric annealer, described below.
ANNEALING in BULK
Annealing in bulk is done by spreading a number of pieces of Gold Foil, of whatever form, on a tray or some other suitable receptacle, heating them through the latter, and placing them in the cavity one by one.
Of the various receptacles in common use, mica, as a sheet or a disk, was formerly a standby. When used as a sheet, its size averages about four inches square, and it is held over the flame, of an alcohol lamp or a Bunsen burner, with ordinary cotton-pliers. About 10 pieces of Foil, spread out so that no two pieces touch each other, are laid out in the central portion of the sheet; the flame, which is to be of a clear light-blue color, is turned on fairly strong; and the mica is then held over it, with-out quite touching it, until it (the mica) turns a dull red. The actual annealing time is about five or six seconds. The exact length of time varies, of course, with the intensity of the heat and with the size of the different pieces. The annealed Foil is removed to a clean, dry napkin or a clean piece of chamois skin, from which it is carried to the cavity piece by piece.
The mica should be sound and clean. Mica that has begun to check or flake is an unnecessary hazard. The condenser should be cleaned just before picking up the first piece. As previously suggested, simply scrub it with a stiff nail-brush dipped in alcohol, and then dry it thoroughly with a towel.
More operators, of those answering the aforementioned questionnaire, have reported difficulty with this mode of annealing than the total number of the operators who have found difficulty with each of the other procedures. The reasons are various. First of all, there is the hazard of simultaneous over-annealing and underannealing. Because the degree of heat reaching the different pieces is not uniform, those farthest from the hottest point of the flame may remain insufficiently heated even though those directly over it are already overheated. To minimize this troublesome variation, some operators, instead of holding the mica in one position, pass it, slowly, over the flame to and fro, distributing the heat more evenly throughout the surface.
There is another disadvantage, after annealing. It is rather difficult to remove the Foil to the napkin or the chamois skin without some of the pieces sticking together.
Still another disadvantage, also after annealing, concerns the possible contamination of the Foil while lying on the napkin or the chamois skin, waiting to be placed in the cavity. Even when it is hot, it may be contaminated by dust or acid gases; while as soon as it has cooled, it may be contaminated also by moisture or volatile gases.
When the weather is humid, atmospheric moisture should be guarded against especially. And while the Foil is thus exposed, it is best not to light a match. Also, if there is any odor of smoke coming in from the outside, it is well to close the windows, shutting out the contaminative sulphides that abound in the smoke of coal or oil.
MICA ANNEALING TRAY: Mica is used also to form what is known as a mica annealing tray. The latter consists of a metal stand designed to be mounted on an alcohol lamp or a Bunsen burner and of a disk of mica that fits as its top. The underside of the mica comes to within an inch or so of the flame.
As many as 20 pieces of Gold Foil, spread out so that no two pieces touch each other, may be placed on the tray at a time. The flame is turned on a bit stronger than under a plain sheet of mica, and the Foil is heated till the mica begins to show a tinge of red. The average annealing time is about five minutes. The flame is then turned down a little and left on till the Foil is used up. The annealed Foil is carried from the tray direct to the cavity, with the pieces in the center of the tray picked up first and the outer ones last. Additional batches are annealed in the same way, with care being taken to limit the final batch to the estimated number of pieces still required to complete the restoration.
The mica tray has obvious advantages over the sheet of mica held with pliers. For one thing, it allows more pieces to be annealed at a time. Secondly, its slower heating tends to reduce variations in the degree of heat reaching the different pieces, thus reducing the hazard of simultaneous overannealing and underannealing. Furthermore, carrying the annealed Foil from the tray direct to the cavity — without first removing it, in a mass, elsewhere— excludes the handling that could cause some pieces to stick together. And keeping the Foil warm till it is used up, safeguards it against moisture and volatile gases. Acid gases, however, are still a danger. So is of course also dust.
The care with respect to the cleanliness of the mica and the condenser should obviously be exercised here too.
There are also other annealing devices for mounting on an alcohol lamp or a Bunsen burner. Instead of a mica tray, they have a tray of PORCELAIN, ENAMELED METAL, or SOAP-STONE. The procedure is the same as that with the mica tray in all respects but one. Being less conductive of heat, these trays
require, variously, both a stronger flame and longer heating. The annealing time ranges from 10 to 20 minutes, when the flame is turned down so as merely to keep the Foil warm.
ELECTRIC ANNEALER: Still another and the latest means of annealing in bulk is that of an electrical device designed
expressly for the purpose. Electric annealers vary, but they all have in common, principally, an outer metal shell housing a heating element, a tray over the latter to hold the Gold Foil, and a lid that fits over the tray. They all operate directly from an ordinary electric outlet.
As many pieces of Gold Foil may be placed on the tray as it will hold loosely — without any two pieces touching each other. To prevent their sliding and sticking together, the tray of a recent electric annealer provides individual compartments for each piece of Foil. The current is turned on after the Foil is in place, and, with the lid off, is left on till the Foil turns a dull red or begins to adhere to the clean condenser on mere contact. The actual annealing time is, variously, from 10 to 20 minutes, depending on the maximum degree of heat the particular make of annealer is capable of generating and on the time required to attain it. One, for example, capable of attaining a maximum temperature of 650 degrees centigrade in six minutes, will drive off all moisture and volatile gases, even of the larger pieces, in about 10 minutes. The annealed Foil is carried from the tray, piece by piece, direct to the cavity.
As with the other means of annealing in bulk, it is advisable to keep the annealed Foil warm till it is used up. Some electric annealers have for the purpose a rheosat, which permits the current to be regulated downward. But even one that has no rheostat, provided that its maximum temperature does not exceed 700 degrees centigrade, may be left on — in full — with-out any hazard of overannealing. In the latter case, however, it is necessary that the current be turned off altogether in ample time for the tray to cool before annealing the next batch. Laying out Foil on a tray that is hot, is extremely difficult.
Regardless of a rheostat, an excellent way of using up a batch of annealed Foil is to start at one end of the annealer and pick up each piece in a regular order, until there remains only about a quarter of the batch. Then lay out a new batch and again turn the current on in full. While the remainder of the annealed Foil is being condensed in the cavity, the fresh Foil is thus getting annealed.
Annealed Foil that remains after the restoration is completed, is left on the annealer for the next restoration. Such Foil cannot be returned to its usual container, because it would stick together beyond separation. Reannealing does it no harm. But there is of course the hazard of its being contaminated by gases that are deleterious irretrievably. Since the only protection from them, even though not altogether unfailing, is that afforded by the lid that fits over the tray, it is important to replace it, tightly, as soon as the annealer is not in use. And if the tray has no individual compartments for each piece of Foil, there is the further hazard that even a slight jarring of the annealer may cause some pieces to slide and stick together.
Of all the means of annealing in bulk, the electric annealer is far and away the best; and, in consequence, is steadily gaining in favor. It is the simplest, the neatest, and by far the most convenient. Because its heat can be controlled more accurately, there is no hazard of underannealing. For this reason and particularly because its heat is less intense, there is also no hazard of overannealing. For both these reasons and particularly because its heat is uniform throughout, there is likewise no hazard of simultaneous overannealing and underannealing.
However, not even the electric annealer is wholly free from the disadvantages common to the other means of annealing in bulk. Some are inseparable from heating a number of pieces at a time, and then using them piece by piece, and so are inherent in the method itself.
For one thing, there is the hazard of contamination after annealing, while the Foil is on the tray, waiting to be used. As has already been noted, it may be contaminated even when hot — by dust or acid gases.
Secondly, there is the difficulty of estimating in advance the exact quantity of Gold Foil that will be required to make a given restoration. In the words of a leading operator: "It is difficult, if not impossible, to predetermine the exact quantity of gold, in the various sizes, that will be required for a given operation. If the quantity annealed at first is insufficient, there is a decided likelihood, since both my assistant and myself are but human, of our yielding to the urge of getting the restoration completed and the patient dismissed, and so of failing to heat some of the additional pellets long enough to anneal them fully. This may sound like a confession, but I believe that an investigation of this point would disclose that we should be running only true to form."
On the other hand, if the quantity annealed is more than what is actually needed, there is the disadvantage of having to leave the unused part on the tray, protected from airborne contaminators only by its lid. While far less of a hazard than with any other means of annealing in bulk, this is obviously some disadvantage still.
COPYRIGHT, 1955, BY MORGAN, HASTINGS & CO. • PRINTED IN U. S. A.
is the symbol of a century-old firm devoted to making one thing only—Filling Golds. Since 1820, to five generations of dentists, it has been more than a trade-mark. It is a faith-mark and a guide-mark. Dentists believe in it, and look for it when buying Filling Golds, because it identifies the finest products of their kind — world-famous, and the best that sound standards, pride in quality, and over a century of experience can produce.
Scanned and edited by Dr. John R. Sechena