"If we compare tin with amalgam, we must certainly decide in favor of the former and give it preference; as if it is packed and condensed as perfectly as may be, we know just what such fillings will do every time.

We know that there will be no changes or leakage of the fillings at the margins; whereas, with amalgam, the rule is shrinkage of the ma.s.s, and consequently the admission of moisture around the filling, the result being further decay. It is not contended that this is always the result with amalgam, but it is the general rule; yet we must use amalgam, as there are not a few cases where it is the best that we can do; but it is to be hoped, and I think it may be said, that as manipulative skill advances, amalgam will be less and less used. For so-called temporary work, very often I prefer tin to gutta-percha, as it makes a much more reliable edge and lasts longer, even when placed and packed without great care."--_N. Y. Odon. Society Proceedings_, page 51, 1894.

One of the main reasons which induced the writer to begin the use of tin foil (_Stannum Foliatum_) for filling teeth, in 1867, was the fact that amalgam filling failures were being presented daily. Believing that tin could do no worse, but probably would do better, we banished amalgam from the office for the succeeding seven years, using in the place of it tin, oxychlorid, and gutta-percha. Since that time we have seen no good reason for abandoning the use of tin, as time has proved it worthy of great confidence. There is no better dental litmus to distinguish the conservative from the progressive dentist.

If we take a retrospective view and consider what tin foil was thirty years ago, we do not wonder that so many operators failed to make tight, good-wearing fillings. As it came from the manufacturer it looked fairly bright, but after being exposed to the air for a short time it a.s.sumed a light bra.s.sy color, and lost what small amount of integrity it originally possessed. This tin was not properly refined before beating, or something was put on the foil while beating, so that it did not have the clean, bright surface and cohesive quality which our best foil now has. No. 4 was commonly used, but it would cut and crumble in the most provoking manner. Fillings were made by using mats, cylinders, tapes, and ropes, with hand-pressure, on the plan for manipulating non-cohesive gold foil, but it was difficult to insert a respectable approximal filling.

From the best information obtainable, the writer believes that Marcus Bull (the predecessor of Abbey) was the first to manufacture and sell tin foil in the United States, as he began the manufacture of gold foil at Hartford in 1812.

Several years ago a radical change came about in the preparation of tin foil, for which the manufacturer should have his share of the credit, even if the dentist did ask for something better, for the quality depends largely upon the kind and condition of the tin used and on the method of manufacture.

For making tin foil for filling teeth, the purest Banca tin that can be obtained is used. The tin is melted in a crucible under a cover of powdered charcoal. It is then cast into a bar and rolled to the desired thickness, so that if No. 6 foil is to be made, a piece one and one-half (1-1/2) inches square would weigh nine grains. This ribbon is then cut into lengths of about four feet, and spread on a smooth board slanted, so that the end rests in a vat of clean water.

Then apply to the exposed surface of the ribbon diluted muriatic acid, and immediately wash with a strong solution of ammonia. Turn the ribbon and treat the other side in the same way. It is then washed and rubbed dry. The object of using the acid is to remove stains and whiten the tin, and the ammonia is used to neutralize the effect of the acid.

The strips are then cut into pieces one and a half inch square, filled into a cutch and beaten to about three inches square. It is then removed from the cutch and filled into a mold, and further beaten to the desired size. When the ragged edges are trimmed off, the foil is ready for booking.

It takes skill and experience to beat tin foil, for it is not nearly as malleable as gold; up to No. 20 it is usually beaten, but higher numbers are prepared by rolling. In each case the process is similar to that employed in preparing gold foil. The number on the book is supposed to indicate the weight or thickness of the leaf. On the lower numbers the paper of the book leaves its impression.

On weighing sheets of tin foil from different manufacturers a remarkable discrepancy was found between the number on the book and the number of grains in a sheet, viz: Nos. 3, 4, 5, weighed 7 gr. each; No. 6, 9 gr.; No. 8, from 9 to 18 gr.; No. 10, from 14 to 15 gr.; No. 20, 18 gr. In some instances the sheets in the same book varied three grains. We submit that it would be largely to the advantage of both manufacturer and dentist to have the number and the grains correspond. No dentist wishes to purchase No. 8 and find that he has No. 18; no one could sell gold foil under like circ.u.mstances. Of the different makes tested, White's came the nearest to being correct. The extra tough foil which can now be obtained is chemically pure, and with it we can begin at the base of any cavity, and with mallet or hand force produce a filling which will be one compact ma.s.s, so that it can be cut and filed; yet in finishing, it will not bear so severe treatment as cohesive gold. Always handle tin foil with clean pliers, never with the fingers; and prepare only what is needed for each case, keeping the remainder in the book placed in the envelope in which it is sold, otherwise extraneous matter collects upon it, and it will oxidize _slightly_ when exposed to the air for a _great_ length of time.

Before using tin foil, a few prefer to thoroughly crumple it in the hands or napkin, under the impression that they thus make it more pliable and easier to manipulate.

A piece of blue litmus paper moistened and moved over a sheet of tin foil will occasionally give an acid reaction, probably owing to the acid with which it is cleaned before beating not having been thoroughly removed. Foil held under the surface of distilled water and boiled for five minutes, then left until the water is cold, removed and dried, shows it has been annealed, which makes it work easily, but not as hard a filling can be made from it as before boiling.

In selecting and using this material for filling, we are able fully to protect the cavity; and if we understand the material, and how to manipulate it, we will surely succeed. This statement demands serious attention, and appeals to every one who is anxious to practice for the best interests of his patients; then let us make a thorough study of the merits of the method and material.

Until recently, the term cohesion had but one special meaning to dentists, and that as applied to gold for filling teeth; being understood as the property by which layers of this metal could be united without force so as to be inseparable. The writer claims that good tin foil in proper condition is cohesive when force is applied, and can be used for filling teeth in the same manner in which cohesive gold foil is used. This claim has been confirmed by several dentists, as noted in another part of this volume.

Cohesion is the power to resist separation, and it acts at insensible distances. The integral particles of a body are held together by cohesion, the const.i.tuent parts are united by affinity.

The attraction between atoms of pure tin represents cohesion. Marble is composed of lime and carbonic acid, which are united and held together by affinity.

The condition which obtains in the tin may be called cohesion, adhesion, welding, or interdigitation, but the fact remains that layers of tin foil can be driven together into a solid ma.s.s, making a tight filling with less malleting than is required for gold; if it is overmalleted, the receiving surface is injured.

On account of its pliability it is easily adapted to the walls and margins, and a perfect fit is made, thus preventing capillary action and preventing further caries. Of all the metals used for filling it is the best tooth-preserver and the most compatible with tooth-substance, and the facility with which a saving filling can be made largely commends it.

Tin has great possibilities, and has already gained a high position as a filling-material. Upon the knowledge we possess of the possibilities and limitations of tin as a filling-material, and our ability to apply that knowledge, will largely depend our success in preserving teeth.

It is a good material for filling many cavities in the temporary teeth, and children will bear having it used, because it can be placed quickly, and but little force is required to condense one or two layers of No. 10 foil. The dentin in young teeth has a large proportion of organic material, for which reason, if caries takes place, many believe it is hastened by thermal changes. Gold fillings in such teeth might prevent complete calcification, on account of the gold being so good a conductor; but if tin is used, there is much more probability of calcification taking place, because of its low conductivity and its therapeutic influence. It does not change its shape after being packed into a cavity. Under tin, teeth are calcified and saved by the deposit of lime-salts from the contents of the dentinal tubuli. This is termed progressive calcification.

Like other organs of the human body, the teeth are more or less subject to const.i.tutional change. The condition in which we find tooth-structure which needs repairing or restoring should be a sure indicator to us in choosing a filling-material. Up to the age of fourteen, and sometimes later, we find many teeth which are quite chalky. In some mouths also, at this period, the fluids are in such a condition that oxychlorid and oxyphosphate do not last long; for some reason amalgam soon fails, while gutta-percha is quickly worn out on an occlusal surface. In all such cases we recommend tin, even in the anterior teeth, for as the patient advances in years the tooth-structure usually becomes more dense, so that, if desirable, the fillings can be removed, and good saving operations can be made with gold. By treating cases in this manner very little, if any, tooth-structure is lost.

The teeth of the inhabitants of Mexico and Guatemala are characteristic of their nervous and nervo-lymphatic temperaments; children ten years of age often have twenty-eight permanent teeth, and they are generally soft or chalky, but our dentists there report good success in saving them with tin.

In filling this cla.s.s of teeth, we should be very careful not to use force enough to injure the cavity-margin, for if this occurs, a leaky filling will probably be the result. Still, we have seen some cases where _slight_ imperfections at the margin, which occurred at the time of the filling or afterward, did no harm, because the deposit of tin oxid filled up the ends of the tubuli, thus preventing caries. We believe that this bar to the progress of caries is set up more frequently when tin is used than with any other metal under like conditions.

CHAPTER V.

In some mouths tin does not discolor, but retains a clean, unpolished tin color, yet when there is a sesquioxid of the metal formed, fillings present a grayish appearance. In the same mouth some fillings will be discolored, while others are not. As a general rule, proximal fillings are most liable to show discoloration. Perhaps one reason is that on occlusal and buccal surfaces they are subject to more friction from mastication, movements of the cheeks, and the use of the brush.

We have seen a large number of fillings which were not blackened, yet were saving the teeth perfectly, thus proving to a certainty that blackening of tin in the tooth-cavity is not absolutely essential in order to obtain its salvatory effects as a filling-material.

Where there is considerable decomposition of food which produces sulfuretted hydrogen, the sulfid of tin may be formed on and around the fillings; it is of a yellowish or brownish color, and as an antiseptic is in such cases desirable. To offset the discoloration, we find that the sulfid is insoluble, and fills the ends of the tubuli, thus lending its aid in preventing further caries. A sulfid is a combination of sulfur with a metal or other body. A tin solution acted on by sulfuretted hydrogen (H_{2}S) produces a dark-brown precipitate (SnS), stannous salt, which is soluble in ammonium sulfid (NH_{4})_{2}S_{2}; this being precipitated, gives (SnS_{2}) stannic salt, which is yellow.

Brown precipitates are formed by both hydrogen sulfid and ammonium sulfid, in stannous solutions. Yellow precipitates are formed by hydrogen sulfid and ammonium sulfid in stannic solutions. The yellow shade is very seldom seen on tin fillings; the dark brown is more common.

An oxid is a combination of oxygen with a metal or base dest.i.tute of an acid. In oxidation the oxygen that enters into combination is not sufficient to form an acid. The protoxid of tin (SnO) is black, and can be obtained from chlorid of tin, or by _long_ exposure of tin to the atmosphere. The oxygen in the saliva helps to blacken the tin, and the metallic oxid penetrates the dentin more or less, acting as a protection, because it is insoluble. Oxygen is the only element which forms compounds with all others, and is the type of electro-negative bodies; it combines with all metals, therefore with tin, and in many cases only the metal is discolored, and not the tooth. Steam boilers are made tight by oxidation.

Where there is complete oxidation, the tooth is blackened to but a very slight depth, and the oxid fills the ends of the tubuli, thus affording an additional barrier to the entrance of caries. The filling itself will prevent caries, but oxidation acts as an a.s.sistant.

"In the mouth, a suboxid is more likely to be formed than a protoxid, but both are black; sulfur and oxygen are capable of acting on tin under favorable circ.u.mstances, such as warmth, moisture, full contact, condensation of elements, and their nascent conditions; the first three are always present in the mouth. The protosulfuret of tin is black."

(Dr. George Watt.) Others give the color as bluish-gray, nearly black.

Experiments show that slight galvanic currents exist between fillings of dissimilar metals in the mouth, and practical experience demonstrates that these currents occasionally produce serious results.

Direct galvanic currents do not decompose normal teeth by true electrolysis, but acids resulting from decomposition of food and fluids react upon the lime const.i.tuents of the teeth and promote secondary caries.

When two metals are so situated in the mouth that the mucous membrane forms a connecting conductor and the fluids are capable of acting on one metal, galvanic action is established sufficient to decompose any of the binary compounds contained in these fluids; the liberated nitrogen and hydrogen form ammonia, which being exposed to the action of oxygen is decomposed and nitric oxid formed, resulting in nitric acid. We also have in the mouth air, moisture, and decomposing nitrogenous food to a.s.sist in the production of nitric acid.

"Galvanic action is more likely to develop hydrochloric acid, for the chlorids of sodium and pota.s.sium are present in the normal saliva and mucus, and when decomposed their chlorin unites with the hydrogen derived from the water of the saliva." (Dr. George Watt.)

The fact should also be noted that both nitric and hydrochloric acids are administered as medicine, and often a.s.sist in producing decay.

When there is a battery formed in a mouth containing tin fillings and gold fillings, and the fluids of the mouth are the exciting media, tin will be the positive element and gold the negative element; thus when they form the voltaic pair, the tin becomes coated or oxidized and the current practically ceases.

There is more or less therapeutical and chemical action in cavities filled with tin, and its compatibility and prophylactic behavior as a filling-material depends partly upon the chemical action which occurs.

Some dentists fill sensitive cavities with tin, in order to secure gentle galvanic action, which they believe to be therapeutic, solidifying the tooth-structure.

"Tin possesses antiseptic properties which do not pertain to gold for arresting decay in frail teeth; it not only arrests caries mechanically, but in chalky (imperfect) structure acts as an antacid element in arresting the galvanic current set up between the tooth-structure and filling-material." (Dr. S. B. Palmer.) If the metal is acted on, the tooth is comparatively safe; if the reverse, it is more or less destroyed. The galvanic taste can be produced by placing a piece of silver on the tongue and a steel pen or piece of zinc under it; then bring the edges of the two pieces together for a short time, rinse the saliva around in the mouth, and the peculiar flavor will be detected.

"In 1820 attention was called to the injurious effects of the galvanic current on the teeth, and dentists were advised never to use tin and amalgam in the same mouth.

"A constant galvanic action is kept up in the mouth when more than one kind of metal is used in filling teeth, and galvanism is often the cause of extensive injury to the teeth. The most remarkable case I ever saw was that of a lady for whom I filled several teeth with tin. After a time decay took place around some of the fillings. I removed them and began to refill, but there was so much pain I could not proceed. I found that by holding a steel plugger an inch from the tooth I could give her a violent galvanic shock. I observed that the exhalation of the breath increased the evolution of galvanism." (Dr. L. Mackall, _American Journal of Dental Science_, 1839.)

"When a faulty tooth in the upper jaw had been stopped from its side with tin, the interstice between it and the adjoining tooth being quite inconsiderable, while the upper surface of a tooth not immediately beneath it in the lower jaw was stopped with the same metal, I have known a galvanic shock regularly communicated from one tooth to the other when by the movement of jaws or cheeks they were brought near together." (Dr. E. Parmly, _American Journal of Dental Science_, 1839.)

"An interesting debate here sprung up on the action where two metals are used in one filling, such as gold and tin, the saliva acting as a medium, and where the baser metal is oxidized by exhalents and by imbibition through the bony tooth-structure." (Pennsylvania Society of Dental Surgeons, 1848.)

"A patient came to me and complained of pain in the teeth. Upon examination I found an amalgam filling next to one of tin. With a file I made a V-shaped separation, when they experienced immediate relief from pain." (Dr. Nevill, _American Journal of Dental Science_, 1867.)

In regard to the decay of teeth being dependent on galvanic action present in the mouth, Dr. Chase, in 1880, claimed that a tooth filled with gold would necessarily become carious again at the margin of the cavity, wherever the acid secretions constantly bathe the filling and tooth-substance. A tooth filled with amalgam succ.u.mbs to this electro-chemical process less rapidly, while one filled with tin still longer escapes destruction. The comparative rapidity with which teeth filled with gold, amalgam, or tin, are destroyed is expressed by the numbers 100, 67, 50. He prepared pieces of ivory of equal shape and size, bored a hole in each, and filled them. After they had been exposed to the action of an acid for one week, they had decreased in weight,--viz, piece filled with gold, 0.06; amalgam, 0.04; tin, 0.03.

"With tin and gold, some have the superst.i.tion that the electricity attendant upon such a filling will in some way be injurious to the tooth; it matters not which is on the outside, when rolled and used as non-cohesive cylinders each appears. We say that neither experimentally, theoretically, nor practically can any good or bad result be expected from the electrical action of a tin-gold filling on tooth-bone, and neither will the pulp be disturbed." (Dr. W. D. Miller, _Independent Pract.i.tioner_, August, 1884.)

"When the bottom of a cavity is filled with tin which is tightly (completely) covered with gold, there is _practically_ no galvanic action and there is no current generated by contact of tin and gold,--_i.e._, no current leaves the filling to affect the dentin. That portion of tin which forms the base is more positive than a full tin filling would be. The effect is to cause the surface exposed to dentin to oxidize more than tin would do alone; in that there is a benefit. In very porous dentin there is enough moisture to oxidize the tin, by reason of the current set up by the gold." (Dr. S. B. Palmer.)