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 (11⁄2) 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 circumstances. 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 mass, 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.