Electricity generated by heat is called thermo-electricity. If a cavity with continuous walls is half filled with tin and completed with gold, or half filled with silver and completed with gold, and the junctions of the metal are at 20-1/2 C. and 19-1/2 C., if the electrical action between the tin and gold be 1.1, the action between the silver and gold will be 1.8, thus showing the action in silver and gold to be nearly two-thirds more than in the tin and gold, a deduction which favors the tin and gold.

Rubbing two different substances together is a common method of producing an electric charge. Is there not more electricity generated during mastication on metal fillings than when the jaws are at rest?

Friction brings into close contact numerous particles of two bodies, and perhaps the electrical action going on more or less all the time through gold fillings (especially when other metals are in the mouth) accounts for a powdered condition of the dentin which is sometimes found under cohesive gold fillings, but not under tin.

CHAPTER VI.

White caries, the most formidable variety known, may be produced by nitric acid, and in these cases all the components of the tooth are acted upon and disintegrated as far as the action extends. In proximal cavities attacked by this kind of caries, separate freely on the lingual side, and fill with tin. When such fillings have been removed the dentin has been found somewhat discolored and greatly solidified as compared to its former condition; this solidification or calcification is more frequent under tin than gold, which is partly due to the tin as a poor conductor of heat. Nature will not restore the lost part, but will do the next best thing--solidify the dentin. In some cases, under tin, the pulp gradually recedes, and the pulp-cavity is obliterated by secondary dentin. In other cases the pulps had partly calcified under tin. It has been known for years that tin would be tolerated in large cavities very near the pulp without causing any trouble, and one reason for this is its low conducting power. Attention is called to the fact that gold is nearly four times as good a conductor of heat as tin, and more than six times as good a conductor of electricity. Where tin fillings are subject to a large amount of attrition, they wear away sooner or later, but this is not such a great detriment, for they can easily be repaired or replaced, and owing to the concave form produced by wear the patient is liable to know when a large amount has been worn away. That portion against the wall of the cavity is the last removed by wear, so that further caries is prevented so long as there is any reasonable amount of tin left. If at this time the tooth has become sufficiently solidified, proper anchorage can be cut in the tin or tooth, one or both, as judgment dictates, and the filling completed with gold. A tin filling, confined by four rather frail walls, may condense upon itself, but it is so soft and adaptable that the force which condenses it continually secures the readaptation at the margin; thus there will be no leakage or caries for years. Owing to its softness and pliability, it may be driven into or onto the tubuli to completely close them from outside moisture, and with a hand burnisher the tin can be made to take such a hold on dry, rough tubuli that a cutting instrument is necessary to remove all traces of it.

Tin foil has been found in the market that under a magnifying gla.s.s showed innumerable tiny black specks, which, upon being touched with an instrument, crumbled away, leaving a hole through the foil. More than likely, some of the failures can be attributed to the use of such foil.

Good tough foil, well condensed by hand or mallet force, stays against the walls of a cavity and makes a tight filling, and ought to be called as near perfect as any filling, because it preserves the tooth, and gives a surface which will wear from five to twenty years, depending upon the size and location of the cavity and tooth-structure. Buccal cavities in the first permanent molars, and lingual cavities in the superior incisors, filled for children from six to eight years of age, are still in good condition after a period of twenty years. Perhaps the limit is reached in the following cases, all in the mouths of _dentists_: One filling forty years old; one forty-two; four on the occlusal surface, fifty; in the latter case gold had been used in other cavities and had failed several times. Lingual cavities in molars and bicuspids can be perfectly preserved with tin. Tapes of No. 10 foil, from one to three thicknesses, can be welded together and will cohere as well or better than semi-cohesive gold foil, and it can be manipulated more rapidly; therefore, if desirable, any degree of contour can be produced, but the contour will not have the hardness or strength of gold, so in many cases it would not be practicable to make extensive contours with tin, owing to its physical characteristics.

No. 10 will answer for all cases, and it is not as liable to be torn or cut by the plugger as a lower number, but one need not be restricted to it, as good fillings can be made with Nos. 4, 6, or 8. More teeth can be saved with tin than with any other metal or metals, and the average dentist will do better with tin than with gold. It is invaluable when the patient is limited for time or means, and also for filling the first permanent molars, where we so often find poor calcification of tooth-structure. In cases of orthodontia, where caries has attacked a large number of teeth, it is well to fill with tin, and await further developments as to irregularity and caries.

If cavities are of a good general retaining form, that will be sufficient to hold the filling in place; but if not, then cut slight opposing angles, grooves, or pits. Cavities are generally prepared the same as for gold, except where there is a great deal of force brought upon the filling; then the grooves or pits may be a little larger; still, many cavities can be well filled with less excavating than required for gold, and proximal cavities in bicuspids and molars, where there is sufficient s.p.a.ce, can be filled without removing the occlusal surface, and here especially should the cavities be cut square into the teeth, so as not to leave a feather edge of tin when the filling is finished, as that would invite further caries and prove an obstruction to cleansing the filling with floss.

In proximal cavities involving the occlusal surface, cut the cervical portion down to a strong square base, with a slight pit, undercut, or angle, at the buccal and lingual corners; where there is sufficient material, a slight groove across the base, far enough from the margin so that it will not be broken out, can be made in place of the pit, undercut, or angle; then cut a groove in the buccal and lingual side (one or both, according to the amount of material there is to work upon), extending from the base to the occlusal surface; in most of these cases the occlusal grooves or pits would have to be excavated on account of caries; thus there would be additional opportunity for anchorage. In place of the grooves the cavity may be of the dovetail form. In nearly all proximal cavities in bicuspids and molars, some form of metal shield, or matrix, is of great advantage, as they prevent the tin from crushing or sliding out. By driving the tin firmly against the metal, a well-condensed surface is secured; and as the metal yields a little, we can with a bevel or thin plugger force the tin slightly between the metal and the margin of the cavity, thus making sure of a tight filling, with plenty of material to finish well. After removing the metal, condense with thin burnishers and complete the finish the same as for gold. Where no shield or matrix is used, or where it is used and removed before completing the filling, it is often desirable to trim the cervical border, for in either case there is more light and room to work when only a portion of the cavity has been filled. Tin cuts so much easier than gold, it is more readily trimmed down level with all cervical margins.

Be sure that all margins are made perfect as the work progresses, and if the cavity is deep and a wide shield shuts out the light, then use a narrow one, which can be moved toward the occlusal surface from time to time.

In filling the anterior teeth when the l.a.b.i.al wall is gone, and the lingual wall intact or nearly so, use a piece of thin metal three-quarters of an inch long and wide enough to cover the cavity in the tooth to be filled, insert it between the teeth, and bend the lingual end over the cavity; the l.a.b.i.al end is bent out of the way over the l.a.b.i.al surface of the adjoining tooth, as shown in Fig. 4. When the l.a.b.i.al wall is intact or nearly so, access to the cavity should be obtained from the lingual side, and in this case the bending of the shield would be reversed, as shown in Fig. 5. The shield is not absolutely essential, but it helps support the tin, and also keeps a separation.

[Ill.u.s.tration: FIG. 4.]

[Ill.u.s.tration: FIG. 5.]

It is preferable to save the l.a.b.i.al wall and line it with (say) five layers of No. 4 semi-cohesive gold folded into a mat and extended to the outer edge of the cavity; this gives the tooth a lighter shade, and bicuspids or molars can be filled in the same manner. Cases are on record where incisors with translucent l.a.b.i.al walls, filled by this method, have lasted from twenty-three to thirty-seven years.

CHAPTER VII.

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 pa.s.s 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 a.s.sists 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 ma.s.s, 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 s.p.a.ces, 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 a.s.sistant" 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 ma.s.s; they seem to think that it cannot be accomplished, but with proper pluggers and manipulation it can be done successfully.

[Ill.u.s.tration: FIG. 6.]

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 tr.i.m.m.i.n.g 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.

[Ill.u.s.tration: FIG. 7.]

By tr.i.m.m.i.n.g 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-ca.n.a.l 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.

CHAPTER VIII.

Dr. Robinson's Fibrous and Textile Metallic Filling is a shredded metallic alloy, mostly tin, and has the appearance of woven or felt foil. It is prepared in a machine invented by the doctor especially for the purpose, and he gives directions for using as follows: "Cut the material into strips running with the selvage, and fill as you would with soft foil; use it in all surrounding walls, and finish with a mallet burnisher. Where the surface comes to hard wear, weld on gold with long, sharp serrated pluggers, and finish the same as with gold fillings. The advantage over gold for cervical, buccal, and lingual walls is the perfect ease with which it is adapted, and it can be burnished so as to be absolutely impervious to moisture. Sharp, coa.r.s.e-serrated pluggers are particularly desirable when using hand pressure." It comes in one-half-ounce boxes, filled with sheets less than two inches square; the thin ones are used for filling, and the thick ones make good linings for vulcanite.