Part 26

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.