Discoloration Of Tin And Decomposition Of Food

In some mouths tin does not discolor, but retains a clean, unpolished

tin color, yet when there is a sesquioxid of the metal formed, fillings

present a grayish appearance. In the same mouth some fillings will be

discolored, while others are not. As a general rule, proximal fillings

are most liable to show discoloration. Perhaps one reason is that on

occlusal and buccal surfaces they are subject to more friction from

ma tication, movements of the cheeks, and the use of the brush.



We have seen a large number of fillings which were not blackened, yet

were saving the teeth perfectly, thus proving to a certainty that

blackening of tin in the tooth-cavity is not absolutely essential in

order to obtain its salvatory effects as a filling-material.



Where there is considerable decomposition of food which produces

sulfuretted hydrogen, the sulfid of tin may be formed on and around the

fillings; it is of a yellowish or brownish color, and as an antiseptic

is in such cases desirable. To offset the discoloration, we find that

the sulfid is insoluble, and fills the ends of the tubuli, thus lending

its aid in preventing further caries. A sulfid is a combination of

sulfur with a metal or other body. A tin solution acted on by

sulfuretted hydrogen (H{2}S) produces a dark-brown precipitate (SnS),

stannous salt, which is soluble in ammonium sulfid (NH{4}){2}S{2};

this being precipitated, gives (SnS{2}) stannic salt, which is yellow.

Brown precipitates are formed by both hydrogen sulfid and ammonium

sulfid, in stannous solutions. Yellow precipitates are formed by

hydrogen sulfid and ammonium sulfid in stannic solutions. The yellow

shade is very seldom seen on tin fillings; the dark brown is more

common.



An oxid is a combination of oxygen with a metal or base destitute of an

acid. In oxidation the oxygen that enters into combination is not

sufficient to form an acid. The protoxid of tin (SnO) is black, and can

be obtained from chlorid of tin, or by long exposure of tin to the

atmosphere. The oxygen in the saliva helps to blacken the tin, and the

metallic oxid penetrates the dentin more or less, acting as a

protection, because it is insoluble. Oxygen is the only element which

forms compounds with all others, and is the type of electro-negative

bodies; it combines with all metals, therefore with tin, and in many

cases only the metal is discolored, and not the tooth. Steam boilers are

made tight by oxidation.



Where there is complete oxidation, the tooth is blackened to but a very

slight depth, and the oxid fills the ends of the tubuli, thus affording

an additional barrier to the entrance of caries. The filling itself will

prevent caries, but oxidation acts as an assistant.



"In the mouth, a suboxid is more likely to be formed than a protoxid,

but both are black; sulfur and oxygen are capable of acting on tin under

favorable circumstances, such as warmth, moisture, full contact,

condensation of elements, and their nascent conditions; the first three

are always present in the mouth. The protosulfuret of tin is black."

(Dr. George Watt.) Others give the color as bluish-gray, nearly black.



Experiments show that slight galvanic currents exist between fillings of

dissimilar metals in the mouth, and practical experience demonstrates

that these currents occasionally produce serious results.



Direct galvanic currents do not decompose normal teeth by true

electrolysis, but acids resulting from decomposition of food and fluids

react upon the lime constituents of the teeth and promote secondary

caries.



When two metals are so situated in the mouth that the mucous membrane

forms a connecting conductor and the fluids are capable of acting on

one metal, galvanic action is established sufficient to decompose any of

the binary compounds contained in these fluids; the liberated nitrogen

and hydrogen form ammonia, which being exposed to the action of oxygen

is decomposed and nitric oxid formed, resulting in nitric acid. We also

have in the mouth air, moisture, and decomposing nitrogenous food to

assist in the production of nitric acid.



"Galvanic action is more likely to develop hydrochloric acid, for the

chlorids of sodium and potassium are present in the normal saliva and

mucus, and when decomposed their chlorin unites with the hydrogen

derived from the water of the saliva." (Dr. George Watt.)



The fact should also be noted that both nitric and hydrochloric acids

are administered as medicine, and often assist in producing decay.



When there is a battery formed in a mouth containing tin fillings and

gold fillings, and the fluids of the mouth are the exciting media, tin

will be the positive element and gold the negative element; thus when

they form the voltaic pair, the tin becomes coated or oxidized and the

current practically ceases.



There is more or less therapeutical and chemical action in cavities

filled with tin, and its compatibility and prophylactic behavior as a

filling-material depends partly upon the chemical action which occurs.



Some dentists fill sensitive cavities with tin, in order to secure

gentle galvanic action, which they believe to be therapeutic,

solidifying the tooth-structure.



"Tin possesses antiseptic properties which do not pertain to gold for

arresting decay in frail teeth; it not only arrests caries mechanically,

but in chalky (imperfect) structure acts as an antacid element in

arresting the galvanic current set up between the tooth-structure and

filling-material." (Dr. S. B. Palmer.) If the metal is acted on, the

tooth is comparatively safe; if the reverse, it is more or less

destroyed. The galvanic taste can be produced by placing a piece of

silver on the tongue and a steel pen or piece of zinc under it; then

bring the edges of the two pieces together for a short time, rinse the

saliva around in the mouth, and the peculiar flavor will be detected.



"In 1820 attention was called to the injurious effects of the galvanic

current on the teeth, and dentists were advised never to use tin and

amalgam in the same mouth.



"A constant galvanic action is kept up in the mouth when more than one

kind of metal is used in filling teeth, and galvanism is often the

cause of extensive injury to the teeth. The most remarkable case I ever

saw was that of a lady for whom I filled several teeth with tin. After a

time decay took place around some of the fillings. I removed them and

began to refill, but there was so much pain I could not proceed. I found

that by holding a steel plugger an inch from the tooth I could give her

a violent galvanic shock. I observed that the exhalation of the breath

increased the evolution of galvanism." (Dr. L. Mackall, American

Journal of Dental Science, 1839.)



"When a faulty tooth in the upper jaw had been stopped from its side

with tin, the interstice between it and the adjoining tooth being quite

inconsiderable, while the upper surface of a tooth not immediately

beneath it in the lower jaw was stopped with the same metal, I have

known a galvanic shock regularly communicated from one tooth to the

other when by the movement of jaws or cheeks they were brought near

together." (Dr. E. Parmly, American Journal of Dental Science, 1839.)



"An interesting debate here sprung up on the action where two metals are

used in one filling, such as gold and tin, the saliva acting as a

medium, and where the baser metal is oxidized by exhalents and by

imbibition through the bony tooth-structure." (Pennsylvania Society of

Dental Surgeons, 1848.)



"A patient came to me and complained of pain in the teeth. Upon

examination I found an amalgam filling next to one of tin. With a file I

made a V-shaped separation, when they experienced immediate relief from

pain." (Dr. Nevill, American Journal of Dental Science, 1867.)



In regard to the decay of teeth being dependent on galvanic action

present in the mouth, Dr. Chase, in 1880, claimed that a tooth filled

with gold would necessarily become carious again at the margin of the

cavity, wherever the acid secretions constantly bathe the filling and

tooth-substance. A tooth filled with amalgam succumbs to this

electro-chemical process less rapidly, while one filled with tin still

longer escapes destruction. The comparative rapidity with which teeth

filled with gold, amalgam, or tin, are destroyed is expressed by the

numbers 100, 67, 50. He prepared pieces of ivory of equal shape and

size, bored a hole in each, and filled them. After they had been exposed

to the action of an acid for one week, they had decreased in

weight,--viz, piece filled with gold, 0.06; amalgam, 0.04; tin, 0.03.



"With tin and gold, some have the superstition that the electricity

attendant upon such a filling will in some way be injurious to the

tooth; it matters not which is on the outside, when rolled and used as

non-cohesive cylinders each appears. We say that neither experimentally,

theoretically, nor practically can any good or bad result be expected

from the electrical action of a tin-gold filling on tooth-bone, and

neither will the pulp be disturbed." (Dr. W. D. Miller, Independent

Practitioner, August, 1884.)



"When the bottom of a cavity is filled with tin which is tightly

(completely) covered with gold, there is practically no galvanic

action and there is no current generated by contact of tin and

gold,--i.e., no current leaves the filling to affect the dentin. That

portion of tin which forms the base is more positive than a full tin

filling would be. The effect is to cause the surface exposed to dentin

to oxidize more than tin would do alone; in that there is a benefit. In

very porous dentin there is enough moisture to oxidize the tin, by

reason of the current set up by the gold." (Dr. S. B. Palmer.)



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 deg. C. and 19-1/2 deg. 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.