/> 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 glass

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 space, 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 labial 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 labial end is bent out of the way over

the labial surface of the adjoining tooth, as shown in Fig. 4. When the

labial 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.





It is preferable to save the labial 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 labial walls, filled by this

method, have lasted from twenty-three to thirty-seven years.