For the last ten years the writer has been using tin at the cervical margin of proximal cavities in bicuspids and molars, especially in deep cavities (now an accepted practice), and he finds that it prevents further caries oftener than any other metal or combination of metals he has ever seen used. In filling such cavities, adjust the rubber, and use a shield or matrix of such form as to just pass beyond the cervical margin; this will generally push the rubber out of the cavity, but if it does not, then form a wedge of wood and force between the metal and the adjoining tooth, thus bringing the metal against the cervical margin, and if a small film of rubber should still remain in the cavity, it may be forced out by using any flat burnisher which will reach it, or it can be dissolved out with a little chloroform. Fill from one-fourth to one-half of the cavity with tin, and complete the remainder with gold when the tooth is of good structure; this gives all the advantages of gold for an occlusal surface.

Before beginning with the gold, have the tin solid and square across the cavity, and the rest of the cavity a good retaining form, the same as for gold filling; then begin with a strip of gold slightly annealed and mallet it into the tin, but do not place too great reliance upon the connection of the metals to keep the filling in place.

On the same plan, proximal cavities in the anterior teeth can be filled, and also buccal cavities in molars, especially where they extend to the occlusal surface. The cervical margin should be well covered with tin thoroughly condensed, thus securing perfect adaptation, and a solid base for the gold with which the filling is to be completed. Time has fully demonstrated that the cervical margin is most liable to caries, and here the conservative and preservative qualities of tin make it specially applicable.

"Electrolysis demonstrates to us that no single metal can be decomposed, but when gold and tin are used in the above manner they are united at the line of contact by electrolysis. The surface of both metals is exposed to the fluids of the mouth, and the oxid of tin is deposited on the tin, by reason of the current set up by the gold; thus some atoms of tin are dissolved and firmly attached to the gold, but the tin does not penetrate the gold to any great extent." (Dr. S. B. Palmer.)

This connection of the metals assists in holding the filling in place, but it is more likely to break apart than if it was all gold. After electrolysis has taken place at the junction, it requires a cutting instrument to completely separate the tin and gold.

For filling by hand pressure, use instruments with square ends and sides, medium serrations, and of any form or size which will best reach the cavity.

For filling with the hand mallet, use instruments with medium serrations, and a steady medium blow with a four-ounce mallet; in force of blow we are guided by thickness of tin, size of plugger, and depth of serrations, strength of cavity-walls and margins, the same as in using gold. The majority of medium serrated hand mallet pluggers will work well on No. 10 tin of one, two, or three thicknesses. If the tin shows any tendency to slide, use a more deeply serrated plugger. The electro-magnetic, and mechanical (engine) mallet do not seem to work tin as well as the hand mallet or hand force, as the tendency of such numerous and rapid blows is to chop up the tin and prevent the making of a solid mass, and also injure the receiving surface of the filling. In using any kind of force, always aim to carry the material to place before delivering the pressure, or blow.

In order to obtain the best results, there must be absolute dryness, and care must be exercised, not thinking that because it is tin it will be all right. Skill is required to make good tin fillings, as well as when making good gold fillings. Always use tapes narrower than the orifice of the cavity; they are preferable to rolls or ropes. After a few trials it is thought that every one will have the same opinion. A roll or rope necessarily contains a large number of spaces, wrinkles, or irregularities, which must be obliterated by using force in order to produce a solid filling; thus more force is employed, and more time occupied in condensing a rope, than a flat tape; the individual blow in one case may not be heavier than in the other, but the rope has to be struck more blows. The idea that a rope could be fed into a cavity with a plugger faster and easier than a tape has long ago been disproved. Many of the old-fashioned non-cohesive gold foil operators used flat tapes, as did also Dr. Varney, one of the kings of modern cohesive gold operators.

The tape is made by folding any portion of a sheet of foil upon itself until a certain width and thickness is obtained. This tape is very desirable in small or proximal cavities where a roll or rope would catch on the margin and partially conceal the view.

In the form of a tape, perhaps more foil can be put in a cavity, and there may be more uniform density than when ropes are used. Tapes can also be made by folding part of a sheet of foil over a thin, narrow strip of metal. Fold the tin into tapes of different lengths, widths, and thicknesses, according to the size of the cavity; then fold the end of the tape once or twice upon itself, place it at the base of any proximal cavity, and begin to condense with a foot plugger of suitable size, and if there is a pit, groove, or undercut which it does not reach, then use an additional plugger of some other form to carry the tin to place; fold the tape back and forth across the cavity, proceeding as for cohesive gold. In small proximal cavities a very narrow tape of No. 10, one thickness, can be used successfully. For cavities in the occlusal surface, use a tape as just described, generally beginning at the bottom or distal side, but the filling can be started at any convenient place, and with more ease than when using cohesive gold. In any case if the tin has a tendency to move when starting a filling, "Ambler's left-hand assistant" is used, by slipping the ring over the second finger of the left hand, letting the point rest on the tin. This instrument is especially valuable in starting cohesive gold (see Fig. 6). This is the easiest, quickest, and best manner of making a good filling, relying upon the welding or cohesive properties of the tin.

Many operators have not tried to unite the tin and make a solid mass; they seem to think that it cannot be accomplished, but with proper pluggers and manipulation it can be done successfully.

For large occlusal or proximal cavities, the tapes may be folded into mats, or rolled into cylinders, and used on the plan of wedging or interdigitation, and good fillings can be produced by this method, but the advantage of cohesion is not obtained, and more force is required for condensing. They are, therefore, not so desirable as tapes, especially for frail teeth. When using mats or cylinders, the general form of the cavity must be depended upon to hold the filling in place. To make the most pliable cylinders, cut a strip of any desired width from a sheet of foil and roll it on a triangular broach, cutting it off at proper times, to make the cylinders of different sizes.

A cylinder roller, designed by the author, is much superior to a broach. (See Fig. 7.) When the cavity is full, go over the tin with a mallet or hand burnisher, being careful not to injure the cavity-margin. Cut down occlusal fillings with burs or carborundum wheels, and proximal fillings with sharp instruments, emery strips or disks. After partially finishing, give the filling another condensing with the burnisher, then a final trimming and moderate burnishing; by this method a hard, smooth surface is obtained.

Fillings on occlusal surfaces can be faced with No. 20 or 30 tin, and burnished or condensed, by using a burnisher in the engine, but do not rely upon the burnisher to make a good filling out of a poor one.

By trimming fillings before they get wet, any defects can be remedied by cutting them out; then with a thin tape (one or two layers of No. 10) and serrated plugger proceed with hand or mallet force to repair the same as with cohesive gold.

Another method of preparing tin for fillings is to make a flat, round sand mold; then melt chemically pure tin in a clean ladle and pour it into the mold; put this form on a lathe, and with a sharp chisel turn off thick or thin shavings, which will be found very tough and cohesive when freshly cut, but they do not retain their cohesive properties for any great length of time,—perhaps ten or twenty days, if kept in a tightly corked bottle. After more or less exposure to the air they become oxidized and do not work well, but when they are very thin they are soft, pliable, and cohesive as gold, and any size or form of filling can be made with them.

Among the uses of tin in the teeth, the writer notes the following from Dr. Herbst, of Germany: "After amputating the coronal portion of the pulp, burnish a mat of tin foil into the pulp-cavity, thus creating an absolutely air-tight covering to the root-canal containing the remainder of the pulp; this is the best material for the purpose." There has been a great deal said about this method, pro and con, notably the latter. The writer has had no practical experience with it, and it need not be understood that he indorses it.

If a pulp ever does die under tin, perhaps it will not decompose as rapidly as it otherwise would, owing to its being charged with tin-salts.

The Herbst method of filling consists in introducing and condensing tin in cavities by means of smooth, highly tempered steel engine or hand burnishers. In the engine set of instruments there is one oval end inverted cone-shaped, one pear-shaped, and one bud-shaped. The revolving burnisher is held firmly against the tin, a few seconds in a place, and moved around, especially along the margins, not running the engine too fast. Complicated cavities are converted into simple ones by using a matrix, and proximal cavities in bicuspids and molars are entered from the occlusal surface. The tin foil is cut into strips, and then made into ropes, which are cut into pieces of different lengths; the first piece must be large enough so that when it is condensed it will lie firmly in the cavity without being held; thus a piece at a time is added until the cavity is full. The hand set of burnishers has four which are pear-shaped and vary in size, and one which is rather small and roof-shaped. In filling and condensing they are rotated in the hand one-half or three-quarters of a turn.

Dr. Herbst claims a better adaptation to the walls of the cavity than by any other method. Proximal cavities in bicuspids and molars can easily be filled; the tin can be perfectly adapted against thin walls of enamel without fracturing them; less annoyance to the patient and less work for the dentist; can be done in half the time required for other methods.

Fees should be reasonably large, certainly more than for amalgam, for we can save many teeth for a longer time than they could have been preserved with cohesive gold. Many are not able to pay for gold, but they want their teeth filled and saved, and it is expected that we will do it properly and with the right kind of material; thus it is our duty in such cases to use more tin and less amalgam.

We should always take into consideration the amount of good accomplished for the patient,—the salvation of the tooth,—and if we are sure, from experience and observation, that the tin filling will last as long as a gold one in the same cavity, or longer, then the fee should be as much as for gold, with the cost of the gold deducted. The amount of the fee ought to be based upon the degree of intelligence, learning, and skill required; upon the amount of nervous energy expended; upon the draft made on the dentist's vitality; upon what benefit has been given the patient; upon the perfection of the result; and, everything else being equal, upon the time occupied; the value of this last factor being estimated in proportion to the shortness of it.