Tin is second in importance in alloys for amalgam, as it increases plasticity, prevents discoloration, reduces conductivity and edge strength, retards setting, favors spheroiding, therefore should not be the controlling metal.
It will be noticed that when cavities are lined with tin foil, it only constitutes a small part of the filling, and that it has not been melted with the other metals in the alloy before being amalgamated.
A thick mat of tin has been recommended as a partial non-conductor under amalgam fillings.
Plastic tin can be made by pouring mercury into melted tin, or by mixing the fillings with mercury at ordinary temperatures; it has a whitish color, and if there is not too much mercury it occurs in the form of a brittle granular mass of cubical crystals. Generally amalgams of tin and mercury do not harden sufficiently, but forty-eight parts of mercury and one hundred of tin make a fairly good filling, said to have a therapeutical value; it should not be washed or squeezed before using, and "is not a chemical combination."
"Tin unites with mercury in atomic proportions, forming a weak crystalline compound." (Dr. E. C. Kirk.)
Mercury and tin readily unite as an amalgam under ordinary circumstances, and form a definite chemical compound having the formula Sn_{2}Hg. (Hodgen.)
Another preparation of tin is known as stannous gold; it is manufactured in heavy sheets and used the same as cohesive gold foil, and can be easily manipulated, for it is rather plastic.
Crystal tin for taking the place of tin foil:
"Take chemically pure hydrochloric acid and dissolve tin foil in it until a saturated solution is obtained; this may be done speedily by heating the acid to a boiling point, or the same thing can be accomplished in a few hours with the acid cold; it is then chlorid of tin. It is then poured into a clean vessel and an equal quantity of distilled water added; then a clean strip of zinc is plunged into the solution, and tin crystals are deposited on the zinc; when there is sufficient thickness on the zinc, remove both, and slip the crystals off from the zinc into pure water, clean the zinc thoroughly, and reinsert for another coating. The character of the crystallization will be modified by the extent of the dilution of the solution in the first place. Wash the tin in pure water until all traces of the acid are removed, or a few drops of ammonia can be added to neutralize the acid.
It was suggested that it would be desirable to have some acid remain in the tin for filling teeth in which there is no sensitive dentin. We have put in a few fillings, and it works beautifully, and makes firmer fillings than foil. It must be kept in water (probably alcohol is better). It is pure tin, unites perfectly, and works easier than foil."
(Dr. Taft, _Dental Register of the West_, 1859.)
For some years it was considered the best practice to enlarge all root-canals and fill them with gold; in many of these cases the crown cavities were filled with tin.
Tin has been used for filling root-canals, but should there happen to be any leakage through the foramen or tooth-structure, the tin will discolor, and there may be infiltration into the crown, thus causing discoloration, which might be objectionable if the crown was filled with gold. Chloro-percha, gutta-percha, and oxychlorid of zinc are much better for this purpose.
The apical quarter of a canal has been filled with tin, and the remainder with cement. Tin can be used for filling root-canals. Roll on a broach small triangular pieces of the foil into very small cone-shaped cylinders, carry to place, then withdraw the broach, and force in the cylinder with the same or a larger broach; sometimes it is necessary to use another broach, to push the cylinder off from the one on which it is rolled. Another method is to carry and pack into the canal by means of a broach, very narrow strips of No. 10 or 20 foil; or the apical third of the canal could be filled with gold and the rest with tin.
"About four years ago I concluded to try tin for filling root-canals; then I began to look for patients whose general health was good, who had strong, hardy-looking teeth, and kept their mouths in good condition. I found one who answered all my requirements, with a molar to be filled, and they would not have it filled with gold, or could not, on account of the expense. I filled the canals with tin and the crown with amalgam.
After filling thirty-eight molars in this way I stopped for developments. In six or seven weeks a lady returned with an inferior molar abscessed, but at the time it was filled the circumstances were such that it could not be properly treated. In nine months a gentleman for whom I had filled four molars returned with an inferior one abscessed. This is the sum-total of abscessed teeth where tin was used in the root-canals, at the end of four years. The others are in good condition, as I have seen them every six months. The roots were treated from four to six weeks with carbolic acid before filling." (Dr. A. W.
Harlan, _Missouri Dental Journal_, 1872.)
"Tin foil is just as good as gold for filling root-canals, as it is entirely innocuous and sufficiently indestructible, while its softness and pliability commend it. Where gold is to be used for the crown, it is better to fill the bulbous portion of the pulp-cavity with gold also, so as to weld these portions of gold together. The success of Dr. Harlan's treatment was about equal to what might be expected from the same number of teeth where the canals had been filled with gold." (Editor, _Missouri Journal_.)
Shavings turned from a disk of pure tin have been used in combination with Watts's sponge gold for filling teeth, either by making a portion of the filling from each metal or using them indiscriminately.
A mat of tin foil dipped in chloro-percha can be used to cap an exposed pulp, or a concave tin disk can be used for the same purpose. A mat of tin has been used over a slight exposure of the pulp, because of its slight conduction of heat and cold, thus avoiding much thermal irritation and stimulating recuperation.
Some use Robinson's fibrous material as a surface for tin fillings, thinking that it is harder and will wear longer because of the erroneous notion that it has platinum in it.
CHAPTER IX.
Tin has been recommended for temporary fillings in sensitive cavities, because it is soft and easily packed in contact with the walls, has therapeutic value, and after a time, when the temporary filling is removed, the cavity is not as sensitive as formerly.
It has been observed that starting gold in a sensitive cavity causes pain, but starting tin in the same place seldom does.
As long as tin preserves its integrity it preserves the tooth, therefore tin fillings should not be repaired with amalgam, as their integrity may be destroyed. Cavities can be partly filled with tin and completed with sponge, fibrous, or crystalloid gold, after the manner described for beginning with tin and finishing with gold foil.
"I advocated tin at the cervical wall, cervico-lingual and cervico-buccal angles to the thickness of 24 plate. Then complete the filling with gold. Some of my most successful efforts in saving soft teeth have been made in this way. This method has great value over gold for the whole filling, but there are two objections to it: First, it imparts to the cervical border the color and appearance of decay, so that in three cases where an instrument passed readily into the tin I have removed the fillings, without any necessity for it, not even finding any softening of the margins. Second, its use requires the same conditions of dryness, shape of cavity, delicate manipulation, inconvenience to patient, and strain upon the operator as when gold is used alone." (Dr. D. D. Smith, _Dental Cosmos_, 1883.) He admits that this method saves _soft_ teeth and also cervical margins. Do not those two very important factors more than counterbalance the color, and oversight of the dentist?
Dryness is an essential in making the best filling with any material, and the time and strain consumed by the majority of operators in filling with tin is not more than one-half what it is in using gold.
"I use tin at the cervical margin of all proximal cavities in bicuspids and molars. I prepare a matrix of orange-wood to suit each case, letting it cover about one-third of the cavity, then fill with tin condensed by hand force and automatic mallet; now split the matrix and carefully remove it piece by piece, so as not to disturb the tin; then trim and finish this part of the filling. Make another wooden matrix, which covers the tin and remainder of the cavity, and fit it snugly to place.
Use a coarsely serrated plugger and begin packing non-cohesive gold into the tin, letting it fill about one-third more of the cavity; then complete the last third (surface) with cohesive gold. I have tested this method for twenty years, and it has given me splendid results. I always tell patients that there will appear sooner or later a slight discoloration near the gum, which must not be mistaken for caries." (Dr.
A. P. Burkhart.)
Another use for tin in the operating-room is found in Screven's "Gutta-percha-coated Tin Foil," a cohesive, antiseptic non-conductor, of which the inventor says: "Cement fillings that have been kept dry for ten hours after mixing will be much harder than those soon exposed to moisture, and they will retain that hardness though exposed to moisture afterward. This preparation will keep a filling perfectly dry in the mouth, and when removed the filling will be found hard as stone. There is nothing better for lining cavities, holding nerve-caps in position, holding a preparation in place when devitalizing a pulp where the tooth is so much broken away as to make it difficult to prevent a filling showing through the enamel, and for many other purposes."
High-heat gutta-percha has been used as a base in deep occlusal, buccal, and approximal cavities, completing the fillings with tin. Occlusal cavities may be filled with tin; then after the filling is condensed and finished, drill out the center and fill with cohesive gold, not cutting away the tin so as to expose the margin; such fillings wear well, as much of the attritial force comes on the gold portion of the filling.
With the exception of the part in brackets, the following article is from the _British Journal_, May, 1887:
"If a person eats an oyster stew at 130 F., a gold filling would carry the difference between the temperature of the stew and that of the mouth, 130 - 98 = 32, almost undiminished to the bottom of the cavity; allowing 2 of diminution, then the cavity around the gold filling has assumed 128; now the person feels warm and drinks ice-water at 32.
Taking into consideration the specific heat of the gold filling, it will assume about 40, which it carries with a diminution of the cold of about 4,--that is, as if it was 44,--into the interior of the cavity; then the cavity will assume 44, the difference within one-tenth of a minute being 128 - 44 = 84, a change which would produce a violent inflammation in any organ which was not accustomed to it. This derangement in the tooth means interruption of circulation, and young teeth will be most affected.
"Thermal effect depends on heat-conducting power [gold is nearly four times as good a conductor of heat as tin] and also on specific heat, so the more the latter approaches that of the tooth the less it is liable to produce sudden changes [thus favoring tin]. Specific heat manifests itself by the speed of changes, while the heat-conducting power influences the intensity [then the intensity of heat in a gold filling would be three or four times as much as in a tin filling]. In speed gold produces this change in one-tenth of a minute" [tin in one-fifth,--that is, gold absorbs heat and expands about twice as fast as tin].
In 1838 Dr. J. D. White introduced sharp-wedge-shaped instruments for filling teeth, and he claims to have been the first to use them; they pack laterally as well as downward, and present as small a surface to the filling as possible, so that the greatest effect may be produced upon a given surface with a given power. Rolls of either tin or gold are made by cutting any desirable portion from a sheet of No. 4 foil; cut this portion once transversely, place on a napkin or piece of chamois, then with a spatula fold a very narrow portion of the edge once upon itself; then with the spatula resting on the thickened edge draw the spatula away from it with gentle pressure, and the foil will follow in a roll.
[Illustration: FIG. 9.]
The old method of using rolls, ropes, and tapes or strips is the same, but we will describe one method of using tapes. (See Fig. 9.) A _strip_ is a single thickness of foil in ribbon form; a strip folded lengthwise once, twice, or more forms a _tape_ of two, four, or more thicknesses of foil. The tin foil should be cut into strips and folded into tapes proportioned in width and thickness to the size of the cavity. One end of the tape is carried to the bottom of the cavity and then forced against the side opposite the point where we intend to finish; now remove the wedge-shaped plugger and catch the tape outside of the cavity, and fold another portion against that already introduced, letting all the folds extend from the bottom to a little beyond the margin. Proceed in this manner, with care and sufficient force, until the cavity is full, using for the last folds a small instrument.
Condense the surface with a large plugger, then go over it carefully with a small instrument, and if any part yields, force in a wedge-shaped plugger and fill the opening in above-described manner; condense, burnish, and trim alternately until the surface is level with the cavity-margin. By extending the folds from the orifice to the base of the cavity, the liability of the tin to crumble or come out is effectually prevented, and by putting it in with a wedge-shaped plugger it is pressed out into all depressions of the walls.
A later method of filling with tape or rope is to use wedge-shaped pluggers with sharp serrations, filling the _ends_ of the cavity, and as the two parts approach each other that next to the wall should be in advance of the rest, thus an opening will be left in the center which can be filled with a smaller tape or rope.
Another old method: Take a piece of foil and roll it into a hard ball; then gradually work it into the cavity, being careful to have sufficient around the margin.
Still another suggested method: Roll a piece of foil into a loose ball, place it in the cavity, and pass a wedge-shaped plugger into its center.
This has the effect of spreading the tin toward the walls of the cavity, the opening to be filled with folds in a way already described. The wedge is used as often as it can be made to enter, filling each opening with folds; then condense the surface, trim, and burnish.
[Illustration: FIG. 10.]
The English give the Americans the credit of first using cylinders.
Anyhow, Dr. Clark, of New Orleans, in 1855, used them made from non-cohesive gold, and also from gold and tin in alternate layers. (See Fig. 10.)
Cylinders were used which were a little longer than the depth of the cavity, introduced with wedge-shaped pluggers around the walls, each one being closely adapted to the margin; then another row was added, which was forced firmly against the preceding, continuing this process until the cavity was full. The wedge, having a smooth end and sides, is forced into the center so as to drive the tin toward the sides of the cavity, being careful not to split the tooth; the opening is then filled with a cylinder. Now force a smaller-sized wedge into the center of the last cylinder, and into the opening introduce another cylinder, proceeding in this manner until the filling is solid. Then condense the ends of the cylinders, trim, and burnish. For the same operation more recent pluggers are wedge-shaped, with sharp, deep serrations. In these cases the filling is retained by the general form of the cavity and wedging within a certain limit, and not by cohesion of the different parts. For a time tin cylinders were prepared and put on sale at the dental depots.
As far as we are aware, the first tin foil made use of in operative technics was by Dr. F. S. Whitslar, who removed a disk of German silver from an ivory knife-handle in 1845, then used hand pressure to fill the cavity with tin. In the college course of operative technics tin foil can be used, almost to the exclusion of gold foil, to demonstrate the manipulation of both cohesive and non-cohesive gold. Shavings scraped from a bar of tin are also useful in operative technics; they are more cohesive than foil.