The teeth, differing in part by their texture, from the other bones,
have also a peculiar mode of nutrition which we shall now examine. But
as the knowledge of this supposes that of the general structure of the
teeth, it is proper to explain here that structure, referring their
description to the examination of the bones of the face.
_Organization of the Teeth._
The teeth are formed by two substances, one external, of a peculiar
nature, called enamel, the other internal, which is the common base of
it, and the texture of which is the same as that of the other bones.
They have besides a cavity which contains a spongy substance, as yet
but little known.
_Hard Portion of the Teeth._
The enamel of the tooth is only seen around the crown; some anatomists
have thought that it extended a little upon the root, an opinion
founded no doubt upon the extreme whiteness that the root often has in
detached teeth, and which makes it impossible to distinguish the line
of demarcation. But a very simple experiment proves this demarcation;
it consists in macerating the tooth in diluted nitric acid. The acid
immediately attacks both the root and the crown which it softens; but
the first becomes yellow like almost all animal substances exposed to
its action, whilst the other preserves its colour, and even becomes
whiter. This experiment also proves that their respective natures are
essentially different.
The enamel, thick on the top of the crown, grows thinner towards the
root, an arrangement required by its use, which is to defend the tooth,
to support principally the efforts of mastication, which are made
especially upon the top of the crown.
This substance hard, compact, particularly when it has remained a long
time in the air, acted upon with difficulty by the file, is composed
of very close fibres, the direction of which cannot be traced. The
medullary oil does not appear to penetrate it; it does not burn, but
breaks by the action of fire, and is thus separated from the other
substance, which, exposed to heat, at first becomes black, then burns
like the other bones and gives out the same odour.
Is the enamel organized, or is it only a fluid which, oozing at
first from the external surface of the tooth, afterwards becomes
there hardened and concrete? This question is not I think easy to
be resolved. The enamel has in fact attributes which seem equally
favourable to both these opinions. On the one hand it is sensible,
like every thing that is organized; it gives us, much more evidently
than the hair or the nails, the sensation of bodies which strike it.
The diluted acids, the vegetable especially, raise its sensibility so
much, that the least touch becomes very painful a long time after their
use. The teeth are then, as we call it, on edge. On the other hand the
enamel has many characters that seem to denote a want of organization.
1st. It never inflames, or becomes the seat of any tumour, or any
alteration which softens its texture; it never experiences any
alteration, which by raising its life, renders it more sensible than in
a natural state, as happens to the hair, for example, which ordinarily
insensible, has a very great vital activity in the plica polonica. In
fact we often judge of the vitality of organs more by their morbid
alterations, than by their natural state. 2d. It appears that there
does not take place in the enamel alternate exhalation and absorption
of nutritive matters, or at least if it does, it is not sensible.
Rubbing wears away this substance, which is never replaced; this is
remarkable in old people, and in those who are in the habit of often
striking their teeth together. We know that we file the enamel like an
inorganic body, and that it is not reproduced, whilst the hair and the
nails evidently grow after being cut. File the extremity of a long bone
after amputation; fleshy granulations will soon grow upon the filed
surface; the action of the instrument will be a stimulus which will
develop the vital phenomena.
The osseous portion of the tooth composes the whole of the root and the
interior of the crown; it is formed by the compact texture, very dense,
having great resemblance to that of stone. It has none of the texture
of the cells. Its fibres, very close to each other, have various
directions, very difficult to trace, but which in general follow
that of the roots; it is necessary, in order to see this direction
perfectly, to soften the teeth in an acid.
Each tooth has a cavity situated in the crown, of the same form as the
crown, diminishing in diameter as we advance in age, communicating
externally by small canals, the number of which is equal to that of the
distinct roots of the tooth, and which open at the end of these roots.
This cavity is lined by a very delicate membrane on which the vessels
ramify, and which, with its opposite face, covers the marrow.
_Soft Portion of the Tooth._
This is a spongy substance which appears to be formed by the
interlacing of the vessels and nerves belonging to each tooth, but
the nature of which is not yet well understood; we know only that it
has a very great animal sensibility equal to that of the medullary
organ. This is proved, 1st, by the pains of carious teeth in which the
marrow is bare, and which are, as we know, extremely acute; 2d, by the
introduction of a probe into the opening occasioned by caries, this
produces no pain until it comes to the marrow, and then it is extreme;
3d, by opening a socket of a very young animal that has not yet cut its
teeth. At this age the marrow is very considerable and the tooth being
small in proportion, it is easy to raise the tooth without injuring it,
because it has as yet no root and the opening at the base of the crown
is very large. The tooth being raised and the marrow thus laid bare,
if it is irritated in any way the animal gives signs of the most acute
pain. I have often made this experiment, always easily done, on account
of the want of thickness of the osseous layers which then form the
sockets.
The teeth have remarkable sympathies, which extend not only to the
solid part, but also to the marrow. As this is much greater in
proportion in the early ages, as it is almost the predominant part
of the tooth, these sympathies are then more numerous and evident.
In these sympathies, sometimes the animal and sometimes the organic
properties are brought into action.
The sympathies of animal sensibility are evident in those pains of
which the teeth become the seat from the action of cold or moisture
upon the cutaneous system; in those produced in the face and the
head by the caries of a tooth. Fauchart relates a case of obstinate
hemicrania, which was immediately removed by the extraction of a tooth.
The sensibility of the ear and the eyes is changed in some violent
cases of tooth ache. The animal contractility is also brought into
action in the sympathies of the teeth; nothing is more frequent in
dentition, than convulsions of the voluntary muscles. Tissot speaks of
a spasm of the muscles of the jaw, which was cured by the extraction of
two carious teeth, and of a convulsion in the muscles of the neck that
occasioned death, the primitive source of which was in a decayed tooth.
The organic sympathies are not less often produced by affections of the
teeth. Spasmodic vomiting, diarrhœa, frequency of the pulse, oftentimes
involuntary evacuation of urine, phenomena, over which the sensible
organic contractility of the stomach, the intestines, the bladder and
the heart presides, are the frequent effects of dentition and violent
pains of the teeth, especially of the first. The insensible organic
contractility, and the organic sensibility are brought sympathetically
into action in the enlargements of the parotid gland, in the general
swelling of the face, in the increased secretion of saliva and
sometimes in the erysipelatous inflammations which take place from an
acute affection of the teeth.
The sympathies of the teeth often take place between the two
corresponding teeth of the same row or of the two rows. My first upper
molar tooth of the left side is a little carious; from time to time it
gives me pain, then invariably the first molar tooth of the right side
becomes as painful, though it is sound. There are other cases in which
a tooth being painful below, sympathetic pains are felt in that which
is above, and vice versa.
The structure of the teeth having been explained, let us see how their
different substances are developed. This subject of osseous nutrition
does not appear to me to have been clearly illustrated by any author.
I shall attempt to explain it better. There are two dentitions, one
is provisional and limited to the first age, the other belongs to the
whole life; each should be considered before, during, and after the
cutting of the teeth.
_First Dentition considered before Cutting._
The phenomena of dentition before the period of cutting are these; the
jaws of the fœtus are closed the whole length of their upper edge; they
appear to be homogeneous at first view; but examined in their interior,
they exhibit a row of small membranous follicles, separated by delicate
partitions, disposed like the teeth of which they are to serve as the
germ, and having the following arrangement.
The membrane which serves as a covering to the follicle forms a sac
without an opening, which lines at first all the parietes of the
socket, to which it is attached by elongations. At the place where the
vessels and nerves enter, this sac leaves the socket, becomes detached,
is folded into the form of a canal which accompanies the vascular and
nervous bundle, and afterwards spreads out upon the marrow of the tooth
which is the termination of the bundle.
It follows from this that this membrane has the general conformation of
the serous membranes, in the shape of some kinds of night-caps. It has
two portions, the one attached and lining the socket, the other loose
and covering the marrow, as for example, the pleura has a costal and a
pulmonary portion. The marrow and the vessels, though contained in its
duplicature, are in truth found without the cavity, which is lubricated
by a simple exhalation. I have found that this exhalation was like
that of the serous membranes, essentially of an albuminous nature; the
action of the nitric acid, that of alkohol and of fire incontestably
prove it. Subjected to the action of one of these agents, especially
the first, the membrane whitens immediately. The layer of albumen which
covers it becomes concrete and coagulated, as when we make a similar
experiment upon a serous surface.
The marrow, very considerable at this period, is found suspended, like
a bunch of grapes, from the extremity of the vessels and the nerves.
It is upon the medullary portion of the membrane of the follicle, and
upon the surface of its loose extremity, that the first osseous point
is developed; it soon extends, and takes precisely the form of the top
of the crown, which it is afterwards to form, that is to say, that it
is quadrilateral in the molar teeth, pointed in the canine, and wedge
shaped in the incisors. Developed at first nearest the gums, it extends
afterwards along the vascular and nervous stem, it is moulded upon it
as it approaches the part of the alveolus where it enters; so that
it exhibits on this side a concave surface which embraces the pulpy
portion of the membrane, and adheres by several vascular elongations;
and as this portion is loose, the first rudiment of the tooth floats
also in the cavity of the membrane, as we can see very well by cutting
the alveolar portion of this membrane, after having destroyed the
corresponding part of the alveolus.
The following consequences result from this kind of development; 1st.
The crown is first formed, and the root is not produced but as the
ossification in length advances upon the portion of membrane lining the
vascular and nervous bundle. 2d. As all the vessels that come to the
tooth enter at its internal surface, and as the external is entirely
free in the cavity of the membrane, the ossification in thickness
is made especially at the expense of the internal cavity which is
constantly contracting, as well as the marrow, an arrangement, the
reverse of that of the other bones, the ossification of which commences
at a point placed in the centre of the cartilage, and which at first
solid in the middle, afterwards become hollow for the medullary
cavities and those of the cells, which are always enlarging. 3d. After
the ossification of the tooth, the portion of the membrane of the
follicle which lined the alveolus, remains the same, whilst that its
portion corresponding with the marrow, originally free at the other
side, becomes adherent on this side to the whole dental cavity which it
lines, of which it forms the membrane noticed above in the article on
the structure of the teeth, and which is thus found between the marrow
and the osseous substance. 4th. The marrow of the tooth is the part
first formed, and the most considerable in the first periods of life.
It appears that the osseous substance is next formed, and that the
enamel afterwards arises on the exterior of this. I have not yet been
able to make evident the manner of its origin.
It is difficult to ascertain at what period the membraneous follicle is
formed; that of the first ossification appears to be from the fourth
to the fifth month. At the time of birth, we find the twenty teeth of
the first dentition already advanced; the whole crown is formed; the
beginning of the root appears also in the form of a broad tube, with
extremely delicate parietes, and which is constantly becoming longer
and thicker; when it reaches the bottom of the socket, the tooth
immediately appears externally as this is too narrow to contain it.
The number of teeth, less in the first than in the second dentition,
gives a peculiar form to the jaws of the fœtus and the infant,
especially to the lower one, which is less elongated in front, and
consequently wider in proportion than in the adult, in whom in order
to receive all the teeth, the alveolar border must necessarily be more
extended. This arrangement of the lower jaw has a great influence in
the expression of the physiognomy.
_First Dentition considered at the period of Cutting._
The following phenomena take place about the sixth or seventh month
after birth, very rarely sooner, still more rarely before birth, though
there are examples of this, as is proved by the history of Louis XIV.
At first the two small incisor teeth of the lower jaw appear, sometimes
together, sometimes separately; soon after the corresponding incisors
of the superior jaw. A month or two later, the four other incisors
are cut. At the end of the first year, the four canine teeth usually
appear. At the end of the second, or often later, two molar are cut
in each jaw and two others soon follow. Each cutting almost always
begins in the lower jaw. At the age of four years, four and a half,
sometimes five or six, always at a very uncertain period, there appear
below two other molars and then two above, which complete the number
of twenty-four teeth forming the first dentition; all these except the
last four fall out and are replaced by new ones.
The following is the mechanism of this first dentition; the
ossification extending constantly towards the root, the tooth can no
longer be contained in the socket; it pierces the alveolar portion of
the membrane and the mucous membrane of the mouth and an intermediate
medullary texture that separates them, with much ease, as this triple
layer gradually becomes thinner as the cutting approaches. Is this
phenomenon owing only to the mechanical pressure of the tooth? I think
that there is another cause; for observe that here the membranes are
very little raised before rupturing; whilst that in polypi and other
tumours that sometimes arise under the membrane of the gums, it is
infinitely more stretched, still it does not break, but is only lifted
up. The mechanism of the opening of the gums is not more known than the
principle of the severe accidents which are sometimes connected with
it. The sac which formed the original membrane of the follicle being
thus open, its portion which lines the socket unites to the membrane
of the mouth, becomes continuous with it and at the same time adheres
intimately to the neck of the tooth; and as during the development
of the root, the internal face of this membranous portion, at first
loose as we have seen, has gradually contracted adhesions with it, it
follows that this root is found fastened between the alveolar portion
which lines its exterior, and the medullary portion which covers the
interior; it is this which gives it solidity. As the adhesions of
the membrane increase, we can less easily distinguish it. It is rare
that in the first dentition the formation of the root is finished as
completely as in the second; its internal cavity remains also very
broad, and the marrow is more developed.
_Second Dentition considered before Cutting._
It is necessary, as in the preceding case, to distinguish the nutritive
phenomena into those which take place before, during and after the
cutting. Before the cutting, we observe by opening the jaw, a row of
dental follicles, corresponding to the row of teeth already formed,
situated below or at the side, and separated from them by little
partitions, the thickness of which is found greater in proportion as it
is examined nearer infancy.
These follicles have precisely the same arrangement as those of the
first dentition; like them they form sacs without an opening, the
alveolar portion of which is attached, and the loose medullary portion
is covered on its surface with the first osseous layers for the crown.
The manner of growth is the same; that is to say, it takes place from
the exterior to the interior, the reverse of the other bones; an
arrangement, which gives the part of the tooth immediately in contact
with foreign bodies, being the first formed, time to acquire the
solidity necessary for its functions.
As the second teeth grow, their vascular system becomes greater, and
that of the old ones diminishes; which arises from this, that the
sensibility weakened in the last, draws to them no more blood, whilst
being raised in the others, it attracts it powerfully. We observe also
that the partition of the sockets diminishes in thickness, and that
the root of the first is destroyed. This double phenomenon does not
appear to be owing to the pressure exerted by the new tooth, as then
the root would spread and become flat only; or if it experienced a
real destruction, we should find the remains of it, which we never do.
It is then probable that, it is by the absorption of the phosphate of
lime, that the partition and root disappear, nearly as we have said the
internal cavities of the cartilaginous bones are formed.
We see from this, that the ossification of the roots of the first teeth
is of short duration; it begins the last and terminates the first.
When it is of but little extent, the teeth become loose, from the want
of insertion. The disappearance of the partitions increases it. It
is at about the age of six or seven years that the shedding of them
commences; this takes place in the order in which they were cut, that
is to say, first the incisors, then the canine, and then the molars.
Observe that the last, which appeared at four years of age, are not
renewed.
_Second Dentition considered at the period of Cutting._
During the cutting of the second teeth, we observe them come out in the
same order as those with which they correspond are detached. 1st. The
eight incisors. 2d. The four canine appear. 3d. In the place of the
first molar, two new ones are cut; these afterwards have the name of
small molars. 4th. The second molar remains, as we have just said; it
is the first of the great ones. 5th. At eight or nine years of age, two
other molars appear in each jaw. 6th. Finally, at eighteen, twenty, or
thirty years, and sometimes later, a third molar is cut; this is called
the dens sapientiæ.
There is then in each jaw sixteen teeth, of which four are incisors,
two canine, two small molars, and three large ones.
Sometimes the second teeth while they are forming, instead of
appropriating to themselves the nutritive substance of the roots of the
first and their partition, leave them untouched; neither are destroyed;
and the second teeth are cut at the side of the first which remain
in their places. When this phenomenon happens, it is usually only to
a single tooth; sometimes, however, it happens to many and even all,
and then there is a double row. In general, the second teeth have a
tendency to go out at the side of the gums. When very obliquely placed,
by a defect of conformation, their crown leans forward or backward;
instead of piercing the jaw, they remain always buried in the sockets.
_Phenomena subsequent to the Cutting of the Second Teeth._
After being cut, the teeth evidently grow, 1st, in length; 2d,
in thickness. It is only the root that is enlarged in the first
direction; the crown preserves always the same dimensions; and if
in old people it appears longer, it is only because the gums have
retracted; a phenomenon which besides we very often observe in persons
who have become thin, in those who have made use of mercury, &c.
The growth in the second direction is not made without, but only
within; the canal of the root and the cavity of the body are constantly
contracting, and are finally obliterated. Then the tooth receiving no
longer the blood or the influence of the nerves, dies and falls out.
But this death appears also to be hastened by the accumulation of
osseous substance, of a very great quantity of the phosphate of lime,
which predominates there so much over the gelatine, that the principle
of life is entirely destroyed, so that in this respect, the shedding of
the teeth exhibits a phenomenon analogous to that of the shedding of
the horns of the herbivorous animals, of the calcareous shell of the
crustaceous ones, &c.
Why has nature given to the life of the teeth a shorter term than to
that of the other bones, which do not cease to exist but with the
other organs, whilst the teeth die a long time before? Is it because
the stomach becoming weak with age, the animals are thence compelled
to nourish themselves in their old age, with soft substances, adapted
to the languid state of the gastric forces? Undoubtedly in man, a
thousand causes, arising especially from the nature of the aliments,
their degree of heat and cold, the manner in which they are cooked,
their infinitely various qualities, hasten the natural period of the
death and the fall of the teeth, because by incessantly exciting
and stimulating these organs, they keep them in a state of constant
activity, which exhausts their life sooner than it otherwise would have
been. Thus a thousand causes arising from society, make the term of the
general life much shorter than that fixed by nature. But in general in
all animals, the death of the teeth precedes that of the other organs,
though they are not under the influence of society, and they masticate
only aliments destined by nature to be in contact with their teeth.
The jaws destitute of teeth in old age, contract; the sockets are
effaced; the texture of the gums becomes firmer, and mastication is
continued, though with more difficulty. In this change of conformation,
the alveolar edge is thrown back; hence the prominence of the chin
before. It diminishes in height; hence the approximation of this part
to the nose, a phenomenon that arises especially from the absence of
the teeth.