CARIES OF HUMAN TEETH. 
BY 
FRANK ABBOTT, M.D. 
[REPRINTED FROM THE DENTAL COSMOS.] CARIES OF HUMAN TEETH. 
By FRANK ABBOTT, M.D., 
PROFESSOR OF OPERATIVE DENTISTRY AND DENTAL THERAPEUTICS IN THE NEW YORK 
COLLEGE OF DENTISTRY. 
(Read before the New York Odontographical Society, December 17, 1878, and 
January 21, 1879.) 
For some years I have held opinions differing more or less from 
those of any writer upon this subject, but have expressed them on 
but few occasions, except in my lectures before the class at the college. 
Not feeling secure in the views I entertained, however, I concluded 
to thoroughly investigate the subject, to either prove my theories 
correct or abandon them for the facts which I expected to establish. 
Very much to my gratification, my researches have confirmed my 
former views, with very little if any variance. Notwithstanding the 
fact that nearly all investigators for many years past, whose writings 
we have had access to, have accounted for the decay of teeth in what 
apparently seemed to the profession a satisfactory way, still there 
were practical facts which led me to view the subject differently, 
and which it was difficult to account for from their stand-point. 
These facts I have attempted to account for in this paper. I have 
been careful to make no statement which I am not able to prove to 
any one who will take the trouble to carefully study the specimens 
under the microscope. 
Before entering upon the consideration of the subject, however, I 
wish briefly to recapitulate what has recently been discovered by Dr. 
C. F. W. Bodecker in the minute structure of human teeth. The 
reasons why I do so are, that not only are my own researches cor- 
roborative of Bodecker’s discoveries, but a full understanding of the 
morbid processes is possible only upon a correct knowledge of the 
normal conditions. 
Since Dr. C. Heitzmann brought to evidence that, with the exception 
of dry horny tissue (epidermis, nails, and hair), all other tissues of 
the living body were endowed with life, and that the presence of living 2 
CARIES OP HUMAN TEETH. 
matter was demonstrable not only in the formerly so-called cells, but 
also in the basis-substance (matrix), the question arose whether a 
normal tooth, attached to a living body, was not possessed of this 
same living matter in itself. It was to be expected, judging from the 
phenomena of growth, of decay, of restitution, etc., that a tooth 
was provided with such living matter just as well as bone, which 
it resembles so greatly in its minute structure. But the full evidence 
of its presence in the tissues of the tooth was first demonstrated by 
the above-quoted gentleman. 
The dentine is traversed by innumerable canaliculi, which ramifi- 
cate both toward the enamel and the cement. Each canaliculus con- 
tains a delicate fiber of living matter, which is in direct connection 
with the protoplasmic formations within the pulp-cavity, with the 
offshoots of the cement-corpuscles, and the fibers between the enamel- 
rods. Every dentine-fiber sends innumerable delicate conical threads 
through the cavity of the canaliculus into the basis-substance be- 
tween the canaliculi, where a very minute network of living matter 
is present, uniting the dentinal fibers with each other throughout the 
whole tissue of the dentine. The basis-substance is analogous to 
that of hone, therefore glue-giving, and at the same time infiltrated 
with lime-salts. Around each dentinal canaliculus the basis-sub- 
stance is denser than between the canaliculi. 
The cement is identical in every respect with hone; its basis- 
substance is traversed by larger cavities, which contain nucleated 
protoplasmic bodies,—the cement-corpuscles. From these arise larger 
offshoots in a radiated arrangement, and the protoplasmic body as 
well as all its larger ramifying offshoots send delicate offshoots of 
living matter into the basis-substance, which latter is pierced by a 
network of living matter, this being in uninterrupted connection 
with the network within the basis-substance of the dentine, the 
boundary being termed, formerly, the interglobular space; by Dr. 
Bodecker, “ interzonal layer.” 
The enamel is provided between its polyhedral rods with very 
slender fibers of living matter, which also send extremely delicate 
offshoots into the basis-substance of the rods. Such offshoots traverse 
the cement-substance between the rods, and form an extremely minute 
network of living matter within the rods themselves, its meshes 
being occupied by dense depositions of lime-salts. 
Again, the network of living matter of the enamel is in direct 
union with that of the dentine, and, on the neck of the tooth, with 
the network of the cement. From these facts it necessarily follows 
that we must consider a tooth which is normal in its structure, and 
in close connection through the periosteum with the jaws, as a 
living body; consequently, it follows that morbid processes will result 
in a reaction of the living matter in the tooth just as well as in bone CARIES OP HUMAN TEETH. 
3 
or any other living tissue of the body. What this reaction essentially 
consists in during the process termed caries I have, to my own satis- 
faction at least, pretty clearly settled. And it occurs to me that, 
through my researches, new stand-points have been revealed of con- 
siderable value, both for abstract science and practical use. 
Methods.—The results recently obtained with regard to the minute 
structure of the teeth have been arrived at by new methods. As a 
matter of course, dried specimens of teeth, formerly almost exclu- 
sively in use, did not reveal any of the soft parts within the hard 
dental tissues. Only a frame of the tissue was left, and we may 
readily understand why the investigations of the carious process as 
yet have not passed above hypotheses and speculations. 
For preparing dentine and cement, there is no better method known 
than slow decalcification by means of a one per cent, solution of 
chromic acid. In my experience large quantities of this solution are 
needed for a few teeth. A few drops of hydrochloric acid may be 
added to the chromic acid solution every other day, in order to hasten 
the decalcifying process. And the solution itself should be changed 
frequently, say once every week. The process of decalcification 
ought to proceed very slowly; so much so, that at least two months 
should be required for preparing the superficial layers of the tooth for 
cutting with a razor. 
The teeth thus prepared I imbedded in paraffin, with a small 
quantity of wax added, after the water had been extracted from 
them by strong alcohol. The sections obtained from such speci- 
mens I stained with carmine, this being, in my experience, the best 
method for the demonstration of the carious condition of the tooth. 
After this I mounted the specimens in glycerin, diluted one-half 
with distilled water, and lastly inclosed them with ordinary asphalt 
varnish. 
The enamel of teeth prepared in the foregoing manner can never 
be cut, because it becomes extremely brittle; therefore, I was obliged 
to resort for its examination to the method first practiced by Dr. 
Bodecker, which essentially consists in splitting perfectly fresh teeth, 
by means of a saw, into thin lamellae, and grinding these down to 
the necessary thinness, always under water. The thin slices should 
be kept for decalcification, for twenty-four hours, in a very dilute 
solution of chromic acid. A saturation of this solution of over one- 
half of one per cent, in my opinion is deleterious to the enamel, which 
if completely decalcified shows only a minute network of living matter, 
as I first have observed, but no trace of the enamel-rods and prisms. 
A little practice will enable any one to obtain ground specimens 
of a whole tooth, of such extreme delicacy that they are fit for even 
the highest magnifying powers over one thousand. A perfectly 
transparent condition should be the main property of a specimen of 4 
CARIES OF HUMAN TEETH. 
a carious tooth, because only with such specimens are we enabled to 
study the minutest changes of the tissues to our satisfaction. Ground 
specimens can be stained with carmine and mounted in the same way 
as those obtained by cutting. 
The former method of mounting specimens of teeth in damar 
varnish or Canada balsam has proved so very unsatisfactory, owing 
to the high degree of the clearing process, that it has been abandoned 
by our best microscopists. This method was good enough for dry 
specimens of teeth, in which the compartments in the dentine and 
enamel were filled with filth and air; but as we nowadays wish to 
see more of the soft tissues within the hard framework, we employ 
the only reliable methods as yet discovered, as described above. 
Etiology.—Although the examination of a carious tooth can reveal 
the cause of the disease only to a limited degree, I do not hesitate 
to express my conviction in this respect, on the foundation of twenty 
years of practical experience. 
There is not the slightest doubt in my mind as to the origin of 
caries of teeth. The first lesion under all circumstances is due to 
the action of an acid, which in a merely chemical way dissolves out 
the lime-salts from the enamel. No doubt quite a strong acid is neces- 
sary for decalcification of so solid a tissue as the enamel of a tooth. 
And the question often arises, Where does this acid come from ? 
First let us take into consideration the starting-points of the morbid 
process. I fear no contradiction on the part of my professional brethren 
when I say caries never begins on the smooth surfaces of a tooth, which 
are exposed to the friction of mastication, but always starts on points 
which, owing to their anatomical structure, form receptacles for food, 
etc., or on points between the teeth where, owing to want of cleanli- 
ness, decaying material can accumulate. It is therefore not to the 
friction between the single teeth (Salter) (which, as we know, is 
possible to a certain extent in the normal condition), but to the acid 
generated from the decaying material retained between the two 
flat or concave surfaces which the teeth present to each other, that 
the beginning of the destruction of enamel is due. 
That this decaying material may be sought for and found in the 
food 1 think will hardly admit of a doubt; and, as it occurs to me, 
mainly in such kinds of food as through their decomposition are apt 
to produce an acid, not very strong, perhaps, in itself, but possessing 
a high degree of affinity for lime-salts, viz., lactic acid. 
First among the varieties of food ranks meat, which by putrefaction 
may produce free lactic acid; next are the saccharine materials; and 
last the amylaceous, which being converted into dextrine by the 
action of the saliva, may be transformed, if brought in contact with 
putrefying meat, into lactic acid. There is no doubt that the or- 
ganic portion of teeth, as it advances to the stage of decomposition CARIES OF HUMAN TEETH. 
5 
in the process of caries, plays a very important part in the formation 
of this acid. 
Perhaps the sour decomposition is assisted locally by the action of 
micrococci and leptothrix; although these organisms are known to 
prosper only in alkaline, and not in acid fluids. These vegetable 
organisms are present in innumerable quantities on the healthiest 
gum; tartar is crowded with them. And even in the highest degrees 
of development of tartar caries is absent. In fact, when decayed 
cavities in teeth become filled with tartar, the carious process is as 
effectually stopped as it is possible for it to be when such cavities are 
filled in the most perfect manner, with gold or any other favorite 
material. Hence I do not consider the views of those authors correct 
who claim that micrococci and leptothrix play any important part in 
producing, or even supporting, the carious process. 
I fully concur, however, with the views of those who claim that the 
resistance of the teeth against caries, owing to their amount of lime- 
salts, greatly varies in different people. The hue of the teeth, as is 
well known, is indicative to some extent of their amount of lime- 
salts. The microscope shows a considerable variety, with regard to 
the presence or the degree of density, of that layer of the basis-sub- 
stance surrounding the dentinal canaliculi. E. Neumann first drew 
attention to this layer, which sometimes is so dense and so well de- 
fined, owing to its greater refracting power than that of the basis- 
substance between the canaliculi, that it may be regarded almost as 
a protecting sheath to the living matter within the canaliculi. This 
layer is well marked even in fossil teeth; it resists somewhat the 
action of strong acids and alkalies, but it is almost completely 
absent in a number of carious teeth which I have examined. I have 
also remarked that different teeth, treated exactly in the same manner 
with chromic acid solution, become soft in a markedly shorter space 
of time than others. The general health or constitution may have 
considerable influence upon the quantity of lime-salts deposited in 
the basis-substance of the teeth, although it has been claimed that 
people of so-called scrofulous and tuberculous constitutions on the 
average have better teeth than strong and vigorous persons. 
Nations of high civilization, which inevitably leads to bodily and 
mental deprivation, as a rule have a greater percentage of carious 
teeth than those of a low degree of culture, or with no culture at 
all. 
However this may be, the fact that caries of the teeth begins as a 
chemical process scarcely will, in my opinion, be questioned. On a 
dead tooth, natural or artificial, as well as on teeth manufactured 
from the dentine of the elephant or the hippopotamus, the process 
will remain, under all circumstances, a chemical one, assisted only by 
the putrefying remains of the organic material of the tooth; while 6 
CARIES OF HUMAN TEETH. 
on a live tooth either acute or chronic reaction-changes take place, 
which I intend presently to consider. 
Caries of Enamel. 
The clinical phenomenon of caries, in its very origin, consists essen- 
tially in a discoloration of the enamel. A whitish or grayish spot on 
the surface of the enamel is indicative to an experienced eye of the 
beginning of decay, which spot proves when touched with an instru- 
ment to be soft and crumbly. Often a brown spot is visible on the 
enamel as a sign of the softening process. The less pigmentation 
present, the more rapid is the process of decay. On the contrary, 
the more distinct the discoloration, the slower is the softening process. 
Nay, dark-brown spots may be present in the enamel for many years 
without being followed by softening. The brown discoloration, as 
such, cannot be considered as an essential feature of caries of enamel, 
but it usually accompanies the carious process, and does so the surer 
the slower the morbid process runs. On microscopic specimens we 
meet with decayed pits in enamel without any discoloration of this 
tissue. On other specimens we have a very marked orange or brown 
hue on the decayed part as well as in its neighborhood, and some- 
times scattered specks are to be seen some considerable distance from 
the diseased part. The brown discoloration is located in the basis- 
substance of the enamel-rods, the outlines of which are much more 
marked than when in a healthy condition. The interstices between 
the rods here are plainly visible even with a magnifying power of 
only five hundred diameters. This power will reveal delicate beaded 
fibers of living matter within the interstices, which in healthy enamel 
can be seen distinctly with a power of eight, hundred to one thousand 
only. Besides the discoloration, no material changes are seen on the 
enamel-rods. 
What process the pigmentation of the enamel is due to I cannot 
say, but it occurs to me that we have no right to look upon this 
process as a merely chemical reaction upon the basis-substance of the 
rods. That in fact it is the basis-substance holding the pigment, and 
not the lime-salts deposited therein, is proven by specimens from which 
the lime-salts have been extracted to a considerable extent by chromic 
acid, and which still show the brown stain. I dare say that this 
brown discoloration is a strong proof of the presence of life in the 
enamel, as in teeth where the pulps are dead such stains never appear, 
nor can they be produced by artificial means. The process of decay 
in the enamel can best be studied on superficial erosions of the same, 
a sample of which I have illustrated. In this instance the brown 
discoloration of the decayed part was but trifling, and entirely ab- CARIES OF HUMAN TEETH. 
7 
sent in its vicinity, so that we have to consider it as a case of acute 
caries. 
Fig. 1. 
We see at E, E, Fig. 1, the unchanged enamel partly deprived of its 
lime-salts. Toward the periphery a zone appears in which the enamel- 
rods are spotted, evidently owing to their partial decalcification. 
Close to this and immediately below the decayed part (see P, P) a 
zone is visible in which the enamel is granular, and looks precisely like 
normal enamel from which, by a somewhat stronger solution of chromic 
acid, the lime-salts have been dissolved out. Here the protoplasmic 
condition of the enamel is re-established simply by decalcification, 
and there is no doubt that this is the very condition of the enamel 
by which the white spot is produced upon the surface while the tooth 
is still in the jaw. On the boundary of the enamel we see a shallow 
depression (C) filled with protoplasmic bodies, which represent either 
complete enamel-prisms or lumps of such prisms. All these proto- 
plasmic formations are united with each other by delicate threads; they 
exhibit but a slight brown discoloration, they readily imbibe carmine, 
and if the specimen be stained with a half per cent, solution of chlo- 
ride of gold these bodies assume a dark-blue tinge, while the un- 
changed enamel is hut little affected by this reagent. On the outermost 
layer we see several flat epithelial bodies (_ZV) attached to the proto- 
plasm, which in the transverse section look irregularly spindle-shaped, 
and are evidently the remnants of the so-called Nasmyth’s membrane, 
or enamel-cuticle, sunken down with the decaying protoplasm. On 
the level of the enamel we also recognize such flat epithelia (_L, Ii). 
Beneath them on the right side of the drawing there is present a zone 
of decalcified enamel, while on the left side the division into proto- 
plasmic bodies is fully accomplished. 8 
CARIES OF HUMAN TEETH. 
Not a trace of micrococci or of leptothrix is visible in or above 
the decayed pit of the enamel, which again proves that these or- 
ganisms do not play any important part in the process of caries; 
at least, do not materially interfere with the tooth in its normal 
condition. 
The way in which the caries proceeds downward is plainly shown 
by the figure. There are small, irregular, bay-like excavations on its 
boundary, and in the midst of the decayed part a wedge-shaped 
elongation is running downward into the softened enamel. The 
shape in which caries appears in the enamel is, however, greatly vary- 
ing. Besides the wedge shape as illustrated in the wood-cut, the 
forms in which caries proceeds are shallow or conical excavations, ex- 
cavations with abrupt walls, fissures, and grooves. On the bottom of 
the main excavation we sometimes see a smaller cavity, it being in a 
narrow or wide communication with the main decayed mass. 
Besides the peculiar medullary elements forming the contents of a 
carious cavity of the enamel in its initial stage, I not very rarely have 
met with dark-brown, irregularly-shaped clusters filling the whole 
cavity. How such changes of medullary corpuscles. are produced I 
am unable to say, although it seems to be kindred to the so-called 
colloid or hyaloid metamorphosis which we observe in other tissues, 
the only difference being that in caries the colloid clusters are deeply 
saturated with a uniform brown pigment, the origin of which, as 
mentioned above, is unknown. 
Caries of Dentine. 
Upon examining a large number of teeth with carious dentine, we 
are struck by conditions to the presence of which no observer has as 
yet drawn attention. Sometimes the dentine, attacked by caries, 
looks but little changed on its periphery. A narrow zone of yellowish 
color forms the boundary toward irregular, shallow excavations (see 
Fig. 2, letter a). At other times, besides the bay-like excavations on 
the periphery, there are visible elongations, cylindrical, conical, pear- 
shaped, or leaf-like, passing down into the dentine in varying depths 
(see Fig. 2, letter b). There is no doubt that this form of decaj7- of 
the dentine occurs with the least preliminary changes of the tissues; 
it evidently runs a slow course, and I think I am justified in calling 
this form of caries chronic. It seems evident that decay of a tooth 
assumes an acute or chronic form just in proportion to its perfect or 
imperfect calcification. Dead teeth in which the pulps have been de- 
stroyed either by necrosis as a natural process, or by artificial means 
with caustics, very frequently run this kind of slow or chronic deca}U 
The decay of artificial teeth, either human or ivory, in all probability CARIES OF HUMAN TEETH. 
9 
Fro. 2. 
runs either an aeute or chronic course, according to the amount of 
lime-salts infiltrated into the glue-giving basis-substance. 
I have examined a piece of a hippopotamus tooth which for a 
period of about one year was worn in the mouth of a patient, and a 
spot became decayed about the size of a hemp-seed. I softened this 
piece with chromic acid solution, imbedded it in paraffin and wax, and 
cut thin sections with a razor. On the bottom of the decayed pit 
numerous conical spots appeared running downward into the dentine, 
characterized by the absence of coloring matter in specimens stained 
with carmine. No material change besides was observable; even the 
dentinal canaliculi did not look enlarged. The bottom of the carious 
cavity was covered with a layer of finely-granular, evidently disin- 
tegrated organic material, and above this the ordinary masses filling 
carious cavities in teeth, viz., micrococci and leptothrix, were visible. 
In chronic caries merely a chemical process takes place, assisted 
by putrefaction of the organic constituents of the tooth. Here first 
the solution of the lime-salts of the dentine takes place, either along 
the bay-like excavations or in the shape of longitudinal depressions. 
No reaction whatever follows this process. The glue-giving basis- 
substance being deprived of its lime-salts shows a yellow discoloration, 
and only traces of the dentinal canaliculi. The basis-substance then 
breaks down into an indistinct granular mass, which is immediately 
filled with a new growth of low vegetable organisms, viz., micrococci 
and leptothrix. 
My specimens plainly show that these organisms are not the ad- 
vance-guard in the process of decay. The first change that takes 
place is exposure of the basis-substance by the chemical action of 
some acid, independent of the named organisms which come to view 
only after complete disintegration of the basis-substance. I never 
have seen the penetration of these organisms into the dentinal can- 
aliculi before a thorough deealcification of the basis-substance had 
taken place. No doubt, however, the decayed mass itself may be 
crowded with such organisms which they seem to form with. In the 10 
CARIES OF HUMAN TEETH. 
great majority of my specimens I have met with formations on the 
diseased boundary of the dentine which demonstrate a considerable 
degree of reaction, produced by the irritating power of the same 
agent to which the lime-salts of the dentine yield. In fact, this was 
the case in all teeth which were alive when attacked by the carious 
process, or rather when removed from the jaws. On the boundary 
of this process we see irregularly-shaped elongations running a certain 
depth into the tissue of the dentine. The more superficial the elon- 
gations are, the surer the morbid process may be termed a slow one; 
and, on the contrary, the deeper the elongations, the more certain we 
may be that the morbid process has advanced rapidly. The elonga- 
tions mainty have the shape of fissures filled with a dark granular 
material, if viewed with a low power. These fissures run independ- 
ently of the direction of the dentinal canaliculi; nay, very often 
cross them (see Fig. 3, letters a a). In the specimens they look as 
a rule as if communicating with each other, and also directly or in- 
directly with the decayed outer surface. Sometimes the fissures look 
completely isolated, though we may assume that they are separated 
from the communication with analogous and more superficial forma- 
tions only by the method of preparation, viz., cutting into thin 
lamellae. 
Fig. 3. 
On the surface of the carious portion of dentine we see irregular 
cavities filled with the same granular mass that is present in the fis- 
sures, consisting evidently of debris of the former tissue, together, CARIES OE HUMAN TEETH. 
11 
perhaps, with micrococci, and very often fine thread-like leptothrix. 
The more rapidly the destruction of the dentine has advanced, the 
more irregular islands of dentine are left on the surface (see Fig. 3, 
letters b b). 
In our figure the decay evidently has proceeded rapidly; hence the 
remnants of the former dentine, recognizable by the presence of the 
canaliculi, are very small and irregular on the outer periphery of the 
dentine. 
The outermost portion of the decayed part is, as a rule, brittle, and 
crumbles away in chromic acid specimens. Where it is left it shows 
a crowd of leptothrix and micrococci, without any distinctly recog- 
nizable remnants of the former tissue. On the boundary of the 
carious portion we, as mentioned above, meet with a yellow discolor- 
ation of the dentine, evidently produced by a chemical agent, which 
first dissolves out the lime-salts from the dentine, and in turn liquefies 
the glue-giving basis-substance. In live teeth the yellow discoloration 
usually takes place in the shape of longitudinal strings of different 
diameters, running mainly parallel with the longitudinal direction of 
the dentinal canaliculi. Hay, we often see single yellow strings run- 
ning from the bottom of a carious cavity in the enamel through the 
whole depth of the dentine to the pulp-chambers (see Fig. 3, letters 
c c). The best method for demonstrating these strings is doubtless 
the staining of chromic acid specimens in an ammoniacal solution of 
carmine. While the unchanged dentine readily takes up the carmine, 
the strings, the deep yellow color of which is undoubtedly due to the 
action of the chromic acid, remain unstained. 
With a power of about five hundred diameters, we recognize under 
the microscope, in longitudinal section of the dentine, that sometimes 
the yellow discoloration has taken place only within the limits of a 
few dentinal canaliculi, while at other times quite a number of these 
have undergone discoloration. Still sharper defined is the yellow 
discoloration on transverse sections. Here we see that mainly the 
canaliculi and their immediate neighborhood have taken up the yel- 
low color in the shape of sharply-circumscribed dots, which are the 
larger the nearer they approach to the periphery of the decayed part. 
The basis-substance between these yellow spots has taken up more 
or less carmine. Let us examine such a cross-section with a magni- 
fying power of one thousand diameters under the microscope. 
At a certain distance from the decay the canaliculi look unchanged, 
and each contains the central transverse section of the dentinal fiber 
with its delicate radiated offshoots (see Fig. 4, letter a). Nearer to 
the decay we meet with moderately-enlarged canaliculi, the center 
of which is occupied by a cluster of protoplasm, the granules and 
threads of which have readily taken up the carmine (see Fig. 4, b 6). 
One step farther we find the canaliculi considerably enlarged, to double 12 
CARIES OF HUMAN TEETH. 
or treble their original size, and they are filled with yellow proto- 
plasm, plainly exhibiting the net-like arrangement of the living matter 
(see Fig. 4, c c). The most peripheral granules send delicate conical 
Fig. 4. 
offshoots through the surrounding light space toward the unchanged 
basis-substance. In some of the enlarged canaliculi accumulations 
of living matter are seen fully in the shape of nuclei; sometimes two 
or more such nuclei may be seen surrounded by a varying amount of 
protoplasm (see Fig. 4, d d). Still nearer to the decay the canaliculi 
are enlarged to ten or fifteen times their original diameter, and the 
cavities thus produced are all filled with a partly-nucleated protoplasm 
(see Fig. 4, e e). Between the roundish cavities we meet with longi- 
tudinal cavities, arising from the confluence of several cavities in one 
main direction (see Fig. 4,/). The cavities continue increasing in 
size, and form large spaces, with rounded, bay-like boundaries, between 
which only scanty traces of unchanged basis-substance are left (see 
Fig. 4, g g). Lastly, the basis-substance has entirely disappeared, and 
only protoplasm is visible in its place, either in the shape of multi- 
nuclear layers or of irregular so-called medullary elements with rather 
faint marks of division (see Fig. 4, h h). Nearest to the periphery CARIES OF HUMAN TEETH. 
13 
the protoplasm does not exhibit any form elements, but looks like a 
disintegrated granular mass, probably intermixed with or replaced 
by micrococci. I say probably, inasmuch as all good histologists 
agree, nowadays, that the diagnosis of micrococci is possible only 
when they are clustered together, which is not always demonstrable 
even in the thoroughly-decayed mass. 
We have a series of changes of the dentine fibers, and the surround- 
ing basis-substance of the dentine before us, which I have not the least 
doubt is the normal procedure of the transformation of dentine by the 
carious process. 
Fig. 5. 
Figure 5 is an oblique section, and illustrates exactly the same 
changes from a tooth attacked by a less acute caries, perhaps owing 
to its greater solidity or more perfect calcification. Here a relatively 
small number of dentinal canaliculi are enlarged and filled with pro- 
toplasm (see Fig 5, a a). The center of the protoplasmic bodies is 
occupied by one or two nuclei, which look as if they originated 
from the former dentinal fiber. On the periphery of the dentine 
there are regular nests filled with protoplasmic formations of the 
above description, partly broken down into medullary elements (see 
Fig. 5, b b). On other parts, on the contrary, the transformation of 
the basis-substance into protoplasm has even preceded the changes 
of the dentinal fibers (see Fig. 5, c). The canaliculi are not noticeably 
enlarged; the dentinal fibers are either unchanged or slightly swollen, 14 
CARIES OF HUMAN TEETH. 
and more granular than in the normal condition; while outside these 
we have a thoroughly decalcified and liquefied basis-substance, which 
means a reappearance of the network of the living matter before 
the stage of disintegration. 
Caries of Cement 
So long as the gums are in their normal condition and position 
caries does not begin in the cement, but if the gums have receded 
from any cause, thus exposing the cement which covers the necks 
of the teeth, it may then begin to decay. I never have had an op- 
portunity of examining primary caries of cement under the micro- 
scope, but of caries of this tissue advanced from within, viz., from de- 
cayed dentine, I have several specimens. The microscope reveals in 
these specimens a more or less advanced decay, which in its essential 
features is fully analogous to caries of the dentine when in a live 
condition; in other words, it is an inflammatory process. On the 
boundary of the caries we see, besides unchanged cement-corpuscles 
(see Fig. 6, a a), those which have been enlarged and transformed 
into medullary or inflammatory elements (see Fig. 6, b b). Nay, 
I have observed that the lacunae holding the protoplasmic body 
were partly unchanged, while a part participated in the inflammatory 
process (see Fig. 6, c c). 
The enlargement of the cement-corpuscles is evidently not due to 
a direct swelling of the protoplasm itself, but to a liquefaction of the 
surrounding basis-substance, in which the protoplasmic condition, 
and with this also the medullary elements which have participated 
in the formation of the basis-substance, reappears. The inflamed 
portions of the cement look granular with lower powers of the mi- 
croscope, but high powers reveal the net-like structure of the living 
matter, and the formation of irregular polyhedral elements which 
are separated from each other by a light, narrow seam, this being 
traversed by extremely delicate uniting threads. 
The history of development of bone demonstrates that this tissue 
originates from medullary elements, the so-called osteoblasts, which 
partly remain unchanged, and as such form the bone-corpuscles, while 
their greater part is transformed into basis-substance (Waldeyer). 
The history of the development of the cement has not as yet been 
studied, but we have good reasons for assuming that it develops in a 
way identical with that of bone, as both tissues are identical in their 
structure, and exhibit identical results when inflamed. 
Dr. C. Heitzmann has drawn attention to the fact that the proto- 
plasm of the medullary elements, when transformed into glue-giving 
basis-substance, does not altogether perish. It is only the fluid, non- 
living part of the protoplasm which, by chemical changes, is trans- CARIES OF HUMAN TEETH. 
15 
formed into glue; the living part of the protoplasm, on the contrary, 
remains unchanged, and is simply concealed by the refracting power 
of the glue-giving basis-substance. That this view is a correct one 
the investigator named has proven by the appearances in inflamed 
bone, and I can fully corroborate his views from my observations on 
inflamed cement. 
Fig. 6. 
Virchow’s view that the bone-corpuscles swell and divide into 
inflammatory elements by being converted into proliferating mother 
cells, is in my opinion wrong. No proliferation is demonstrable in 
the earliest stages of inflammation of the cement. Nothing but 
a decalcification, and thereafter a liquefaction, of the glue-giving 
basis-substance takes place in order to bring to view the very same 
medullary elements which once have shared in the formation of 
the cement. The inflammatory reaction in the cement-corpuscle 
itself may be so slight that (as mentioned above) a part of this pro- 
toplasm may look almost unchanged, while another part toward the 
decalcified basis-substance gives an appearance identical with that 
of the surrounding liquefied basis-substance. The result of this 
process is a transformation of the tissue of the cement into medullary 
or inflammatory elements (see Fig. 6, d d). These remain in con- 
nection with each other by delicate threads of living matter, but 
at last become disintegrated, and give, together with micrococci 
and leptothrix threads, a decayed mass, just as well as enamel and 
dentine. CARIES OF HUMAN TEETH. 
Results.—After having examined teeth attacked by the carious 
process, microscopically, from the mouths of over thirty different 
persons, I can sum up the results of my researches in the following 
aphorisms: 
I. In enamel, caries in its earliest stage is a chemical process. 
After the lime-salts are dissolved out, and the basis-substance liquefied, 
the protoplasm reappears, and breaks apart into small, irregularly- 
shaped so-called medullary or embryonal bodies. 
II. Caries of dentine consists in a decalcification, and in turn a 
dissolution, of the glue-giving basis-substance, around the canaliculi 
as well as between them. The living matter contained in the canal- 
iculi is transformed into nucleated protoplasmic bodies, which, together 
with protoplasmic bodies originating from the living matter in the 
basis-substance, form the so-called indifferent or inflammatory tissue. 
III. Cement, if attacked by caries, exhibits first all phenomena 
known to be present in the early stages of inflammation of bone. 
The protoplasmic cement-corpuscles, as well as the basis-substance 
after its decalcification and liquefaction, produce indifferent or inflam- 
matory elements. 
IV. The indifferent elements originating through the carious 
process from enamel, dentine, and cement do not proceed in new for- 
mation of living matter, but become disintegrated and transformed 
into a mass crowded with micrococci and leptothrix. 
Y. Caries of a living tooth, therefore, is an inflammatory process, 
which, beginning as a chemical process, in turn reduces the tissues of 
the tooth into embryonic or medullary elements, evidently the same as 
during the development of the tooth have shared in its formation; and 
its development and intensity are in direct proportion to the amount 
of living matter which they contain, as compared with other tissues. 
YI. The medullary elements, owing to want of nutrition and to 
continuous irritation, become necrosed, and the seat of a lively new 
growth of organisms common to all decomposing organic material. 
YII. Micrococci and leptothrix by no means produce caries; they 
do not penetrate the cavities in the basis-substance of the tissues of 
the tooth, but appear only as secondary formations, owing to the 
decay of the medullary elements. 
YIII. In dead and artificial teeth caries is a chemical process, 
assisted only by the decomposition of the glue-giving basis-substance 
of dentine and cement. 
History. 
John Hunter, “ Diseases of the Teeth,” etc., 1778, says: “ The 
most common disease to which the teeth are exposed is such a decay 
as would appear to deserve the name of mortification. But there CARIES OP HUMAN TEETH. 
17 
is something more, for the simple death of the part would produce 
but little effect, as we find that teeth are not subject to putrefaction 
after death, and therefore I am apt to suspect that during life there 
is some operation going on which produces a change in the diseased 
part.” 
Joseph Fox, “ The History and Treatment of the Diseases of the 
Teeth and Gums,” 1806, says: “ The diseases to which the teeth are 
subject are similar to those which affect bones in general, and in like 
manner they have their origin in inflammation. The teeth differ only 
from bones in not possessing sufficient living power to effect the 
process of exfoliation.” 
Thomas Bell, “ Anatomy, Physiology, and Diseases of Teeth,” 1831, 
under the heading of “ Gangrene of the Teeth, commonly called 
Caries,” says: “ The most common disease to which the teeth are 
liable is that which has hitherto been universally known under the 
name of caries,—a name which, although authorized both by English 
and Continental writers, is in this instance totally misapplied. It is, 
in fact, calculated essentially to mislead, as the disease has not the 
slightest analogy to true caries of bone. The perpetuation of so 
obvious an error as this is surely more than the most fastidious oppo- 
nent of innovation could require. I propose, therefore, to substitute 
for it the term gangrene of the teeth, a word which expresses the real 
nature of the disease. It may be defined as mortification of any part 
of a tooth, producing gradual decomposition of its substance.” 
Farther on he says: “ Still, however, the true proximate cause of 
dental gangrene is inflammation. And the following appears to me 
to be the manner in which it takes place. When, from cold or from 
any other cause, a tooth becomes inflamed, the part which suffers the 
most severely is unable, from its possessing comparatively but a small 
degree of vital power, to recover from the effects of inflammation, 
and mortification of that part is the consequence. That the bony 
structure of the teeth is liable to inflammation, appears not only 
from the identity of the symptoms which take place in them, when 
exposed to causes likely to produce it, with those which are observed 
in the other bones when inflamed, but more conclusively still from 
the fact, already mentioned,, that teeth are occasionally found in 
which distinct patches, injected with the red particles of blood, have 
been produced by this cause after the continuance of severe pain.” 
Dr. E. Magitot, “ Treatise on Dental Caries” (English translation 
by Dr. T. H. Chandler, 1878), in his general conclusions says: 
“ I. Dental Caries is a purely chemical alteration of the enamel and 
ivory of the teeth. Dental Caries is one. The varieties of form and 
color depend upon simple secondary variations in the nature of the 
altering cause, the progress, and the duration of the malady. 
“ Lesions of the enamel consist, after the removal of the cuticle, in 18 
CARIES OF HUMAN TEETH. 
a purely passive chemical disorganization of the prisms composing 
its tissue. 
“ Lesions of the ivory, consisting likewise in a chemical decomposi- 
tion of its elements, may sometimes, though rarely, remain passive; 
but most frequently they determine in the tissue phenomena of re- 
action that manifest themselves by the appearance of a cone or white 
zone, formed by a mass of canalicules obliterated in consequence of a 
formation of secondary dentine. 
“ The tooth attacked by caries does not remain passive and inert, 
but may in some measure undertake to resist its action by the 
phenomena of condensing dentification of the ivory. 
“The agent of dental caries is the saliva, become the medium of acid 
fermentation, or the vehicle of foreign substances susceptible of alter- 
ing directly the tissues of the ivory and the enamel. Caries can be 
caused artificially by imitating the conditions of alteration that the 
mouth itself may present. It then offers the same characteristics as 
the morbid caries, with the exception of the phenomena of the organic 
resistance. 
“ The intimate mechanism of the production of caries is a simple 
solution of the mineral and calcareous salts which enter into the 
constitution of the enamel and of the ivory, by the agent of new 
formation.” 
Drs. Leber and Eottenstein, “ Dental Caries and its Causes,” 1873, 
say: “We have already several times remarked that the action of 
acids alone does not account for all the phenomena which appear in 
caries of the teeth. It is true that acids, even very much diluted, can 
attack the dental tissue; but we find in their mode of action differ- 
ences Avhich distinguish them from the phenomena and from the pro- 
gress of dental caries. The acids attack first the enamel and rapidly 
change it to a chalky mass; later on their action is felt in a marked 
manner upon the dentine, which becomes more transparent, and, in 
fine, as if cartilaginous, by the very slow but progressive loss of its 
calcareous salts. 
“ Caries, on the contrary, proceeds slowly in the enamel; it is much 
swifter in the dentine, where it proceeds promptly along the can- 
aliculi. This difference of progress must be attributed to the partici- 
pation of the fungi in the work of the caries. The elements of the 
fungus glide easily into the interior of the canaliculi, which they 
dilate, and thus favor the passage of the acids into the deeper parts; 
these same elements cannot penetrate a compact enamel, or at least 
they enter more slowly, and only when the elements which form it 
have been greatly changed by the action of acids. . . . For them 
(the leptothrix) to be able to penetrate thus, it is mscessary that the 
teeth be in a suitable condition; the enamel and the dentine must have 
lost their density by the action of acids. It seems that the fungi are CARIES OF HUMAN TEETH. 
19 
not able to penetrate an enamel of normal consistence. The dentine 
itself, in its normal condition of density, offers great difficulties to 
their entrance, and we are not yet sure that the leptothrix could 
triumph over this resistance. ... We cannot decide at present if the 
leptothrix is able to penetrate sound dentine when from any abnormal 
circumstance it happens to be denuded; but if the enamel or the 
dentine are become less resistant at any point through the action of 
acids, or if at the surface of the dentine a loss of substance has occurred, 
then the elements of the fungus can pass into the interior of the dental 
tissues and produce by their extension, especially in the dentine, effects 
of softening and destruction much more rapid than the action of acids 
alone is able to accomplish.” 
Carl Wedl, “Pathology of the Teeth,” 1872, says: “It was quite 
natural to transfer to the teeth the signification implied in the expres- 
sion £ Caries of boneindeed, the fundamental phenomena, namely, 
the destruction of the hard tissues, offered a striking analogy. In 
their development, however, the two processes by no means present 
such an identity. Caries of bone, as is well known, is an inflamma- 
tory process (osteitis) which originates in the soft parts of the bone 
and erodes its hard tissue. This is not the case with the carious 
process in the teeth, which commences in the hard tissues and spreads 
to the vascularized and nervous dental pulp. Upon close investigation 
the latter px-ocess is found to be so entirely distinct from the former 
that the attempt has repeatedly been made to expunge altogether 
from the nomenclature of diseases of the teeth the expression ‘ Caries 
of the teeth.’ 
“ Notwithstanding the fact that our knowledge is advancing, unques- 
tionably, with the continual addition to the auxiliary means at our 
command for carrying on the work, it must, however, be acknowl- 
edged that a theory with regard to caries with a thoroughly scientific 
basis in all its details is still wanting. . . . 
“ In sections made in a direction transverse to the axes of the radi- 
ating dentinal canals, a greater or less number of canals are met 
with whose limiting walls (the so-called dentinal sheaths) describe 
unusually large circles, and whose cavities are replete with a mass 
which has in some places a homogeneous, in others a molecular ap- 
pearance, and forms convex projections beyond the surface of the 
section. The transverse diameters of the widened and filled canals 
vary, some being at least three times as large as others. The inter- 
tubular tissue presents a molecular cloudiness, and is beset with grains 
having the appearance of fat. In sections made parallel to the long 
axes of the canals they are quite clearly seen to be unequally filled 
by the foreign mass, since they present manifold varicosities and con- 
strictions, which also explain the variations in the diameters of the 
widened canals. . . . 20 
CARIES OF HUMAN TEETH. 
“ Since we know that an interchange of material takes place in the 
dentine and cement during life, as is proved by the occurrence of 
atrophies, hypertrophies, and new formations, and that the dentine 
possesses a degree of sensibility, we cannot reject absolutely the idea 
of a reaction on the part of both hard tissues against the effects of 
external agents. 
“ Some authors seem to have had an intimation of this idea, since 
they were inclined to consider the textural changes in carious dentine 
as vital processes. There can be no doubt that the sensibility, some- 
times increasing to actual pain, of the dentine, when deprived of its 
protecting covering, is a vital action, and that this becomes dimin- 
ished when the most sensitive, the peripheral portion, is destroyed by 
an external agent. These facts, however, are by no means sufficient 
to enable us to draw a conclusion in favor of the reactionary power 
of dentine in parts which are attacked by caries. . . . 
“ In consequence of the decomposition of the secretions, acids are 
formed which extract the calcareous salts from the hard tissue, and 
give rise to a disintegration of the affected portions of the latter, in 
which no inflammatory reaction occurs.” 
Tomes, “ System of Dental Surgery,” 1873, says : “ Although dental 
caries has been investigated and described by all who have written 
upon the subject of Dental Surgery, from the earliest period when 
disorders of the teeth first attracted attention down to the present 
time, yet it can scarcely be said that the nature of the disease is 
perfectly understood, for even now two hypotheses prevail. In one 
the disease is assumed to be no disease whatever, but merely the re- 
sult of chemical solution of the dental tissues, and therefore depend- 
ent both in its origin and its progress on the uncontrolled action of 
physical and chemical laws. According to the other hypothesis, the 
fact that teeth are part of a living organism, if not essential to the 
origin of the mischief, at all events profoundly modifies its progress. 
Much has been written in favor of each of these views, and yet the 
subject cannot by any means be held to be settled.” 
In the appendix to this work we find the following “conclusions,” 
viz.: 
That caries is an effect of external causes in which so-called “vital” 
forces play no part. That it is due to the solvent action of acids which 
have been generated by fermentation going on in the mouth, the buccal 
mucus probably having no small share in the matter; and when once 
the disintegrating process is established at some congenitally defective 
point, the accumulations of food and secretions in the cavity will in- 
tensify the mischief by furnishing fresh supplies of acids.