SECTION V.

ANATOMY, HISTOLOGY, AND MICROSCOPY.

On Certain Disputed Points in the Development and Histology of the Teeth.

PAPER BY J. L. WILLIAMS, OF THE SECTION.

R. President and Gentlemen of the American Dental Associa

MR. President me thought which has been uppermost in my mind

since the chairman of Section V. invited me to read a paper at this time has been in the form of a query, whether there would really be sufficient interest in this subject, on the part of the Association, to warrant my occupying the necessary time to present the theme. Perhaps I ought not to have been troubled with such misgivings, but while it affords me a genuine pleasure to present to the profession the results of my labors in this direction, yet I think those matters which have a direct relation to the details of our daily office practice have a more decided interest for the most of us, and I have no desire to force myself upon an unwilling audience. I must conclude, however, that if the dental profession desires to know anything concerning this subject, it desires to know the truth; and the fact that I have been charged by those holding high positions as teachers with theorizing somewhat upon these matters and making statements which are not supported by facts is, in itself, perhaps, sufficient reason for my desire to present such evidence as I have in support of my position before the representative dental organization of the world. I shall therefore take up only such points in the history of the development of the teeth as are in dispute at the present time.

It would seem hardly necessary for me to disclaim any feeling of animosity or antagonism for the sake of disputation alone. I suppose I possess a certain amount of that intellectual pride which is common to humanity, and from which springs the gratification arising from the belief that the opinions which we hold are correct,

yet I am certain that I would trample such pride in the dust instantly if I saw that it stood in the way of my acceptance of the truth. I must assume that my highly-esteemed friend, Prof. J. E. Garretson, and others who have criticised my views are equally desirous with myself of knowing the truth; and while I suppose their belief in the certainty and security of their position has been productive of a feeling of magnanimous commiseration on their part for me, yet, if I have not completely lost all ability to interpret facts and perceive truth, I shall to-night present such evidence of the correctness of what I have previously said upon this subject as shall place my position beyond all possibility of disproof or doubt.

This subject is one which must depend largely upon illustration for its intelligent presentation. This being true, there appears the possibility of the imagination of the artist entering as an important factor in the work of illustration. This becomes especially important when there is great difficulty in tracing the continuity and relation of tissues. We have a striking example of this in Dr. Abbott's chart representing a section of a central incisor with its surrounding tissues. In this chart the odontoblasts are represented as round or oval plastids or cells, between which the dentinal fibrillæ pass to a connection with non-medullated nerve-fibres,—an error which has arisen from the extreme difficulty of preparing specimens in which the continuity of the tissues can be traced. This led me to look for an artist in whose illustrations there should be an absence of all sentiment and imagination, who should be no respecter of persons, and the truthfulness of whose work no one should dare question. In the pure sunlight of heaven, whose swift pencils wrought many of the illustrations which I shall present to-night in a space of time not exceeding the interval between the diastole and systole of a human heart, I found the agent to do my work. While the possibilities of photography are limited, within that limit there is nothing but the truth pure and simple. The photo-micrographs presented to-night were all made from actual sections cut from the jaws of human and animal embryos. The sections from which the phototographs were made will be placed under the microscope for your examination after the reading of the paper. I invite the most critical examination of these slides, knowing that the more critically they are examined the clearer will appear the elucidation attempted upon the screen. In fact, I desire to depend upon what shall appear upon the screen only so far as is necessary to make plain what can really be seen under the microscope. I must add just a few words

about the quality of the photo-micrographs. They were made without either a heliostat, substage, or a bull's-eye condenser, all of which accessories I should have had, but could not procure them in time for the work. They are not, therefore, quite as sharp and brilliant as I could wish, but perhaps sharp enough to prick some of the imaginative and "philosophical" bubbles of my critics. I have here on the desk before me a reprint from the Dental Practitioner. The title of the paper is "Development of Enamel Similar to other Epidermoid Structures." The paper presents a ludicrous and also a sad aspect. Ludicrous, in that the accidents due to a lack of skill on the part of the gentleman who mounted the specimen from which the drawings were taken are made to do duty as an explanation of a preconceived hypothesis which never had any foundation in fact. Sad, in that so little is really known concerning the histo-genesis of the teeth; that it is possible for a man to present such a paper as this to the profession without ruining his reputation as a histologist; and more lamentable still is it to find this dignified nonsense indorsed by the president of the Philadelphia Clinical Society, "an expert pathological and histological microscopist, and a gentleman whose learning and scientific attainments will not be questioned," says the author of the paper; all of which may be true as applied to the gentleman in his legitimate sphere, but the little that appears in this paper contains evidence that his opinion concerning the formation of enamel is of no value whatever.

During the discussion following the paper which I read before the New England Dental Society, at Providence, last October, it was privately remarked that it really was a matter of little importance whether this theory or that of the development of the teeth were true. It would probably be entirely out of place for me to discuss that question here. I must believe that gentlemen who travel the length and breadth of a continent to confer with each other concerning what is latest and best in the thought and practice of their chosen profession do regard this subject as one of the important foundations upon which the scientific status of dentistry rests. man who does not admit this has a very narrow and dwarfed conception of the possibilities of modern dentistry. Do you think Dr. Atkinson would have dared undertake that brilliant operation which has resulted in the union of several fractured teeth, but for his knowledge of the minute structure and functions of the tooth-pulp? Most assuredly not. Under all circumstances, the man who is master of the situation is the one who best understands the nature and

The

resources of the material which he has in hand. This being admitted, then it is a matter of vast importance that we know who is right and what is true about tooth-structure and development. It is a matter of importance that students should be correctly taught concerning these subjects.

It is the object of this paper to point out four important fallacies which are taught at the present day concerning the development and structure of the teeth. To this end I shall demonstrate that the teeth are not developed as papillæ in a groove; that there is an enamel-pulp or organ which has a definite function; that the formation of enamel is from the line of its union with the dentine outward, and that the odontoblasts are of the nature of ganglionic elements, sending processes outward into the dentine, backward into the substance of the pulp, and probably also laterally connecting them with each other. In answer to the query why these points have not been established before, I can only say that the subject is an exceedingly difficult one to investigate, and, so far as I know, the specimens which are presented for your examination to-night are the first and only ones which have ever been produced showing the natural relations of all the dental tissues to each other and to their surrounding tissues without break in their continuity. It has cost me years of study and experiment and the expenditure of hundreds of dollars to accomplish the work the results of which I am to show you to-night. You will pardon me, therefore, for my disposition not to readily yield what this long course of study has taught me to those who pin their faith to "philosophical" deductions, or a few worthless microscopical specimens sent them by some commercial dealer. The fact that I have already criticised Prof. Garretson's hypothesis of the development of the teeth, and that the author of the paper referred to is chief of the clinical staff of the Hospital of Oral Surgery of Philadelphia, of which Prof. Garretson is the surgeon in charge, leads me to believe that this brochure is in the line of a defense of Prof. Garretson. The photo-micrographs at hand enable me to refute the teaching of Prof. Garretson and others, that the teeth are developed as papillæ in a groove, which is called the "primitive dental groove," in a much more effective manner than I was able to do in my review of his address in the New England Journal of Dentistry, and the more recent series of articles in the Dental Cosmos. As an evidence that I desire to render full and complete justice to Prof. Garretson and my distinguished opponents, I propose to present photo-micrographs which I think I may safely

claim are equal, if not superior, to any illustrations which have ever been produced in support of their hypothesis. I shall first, then, proceed to show you actual photographs of sections of the jaws of human embryos, which present the "primitive dental groove" of Prof. Garretson and the older writers with diagramatic clearness.

You have on the screen (Plate I., Fig. 1) a photograph from a section cut through the face of a human embryo at about the eighth or ninth week of intra-uterine existence.

Here we have the "primitive dental groove" in which is seen the developing tooth-germ with the so-called "tunica reflexa" about folding over it, leaving the space in which the enamel is developed. Does it not seem to be a perfect illustration of the hypothesis? It may be a "thing of beauty" for the moment to those who have fondly cherished a belief in a "primitive dental groove," but it certainly is not destined to be a "joy forever." The photograph is from one of the first specimens which I prepared, and was mounted several years ago. Every process in its preparation was carefully conducted according to the authority of "the most celebrated and expert slide-makers of Europe," and with what results? Why, all of the delicate superstructure above the so-called "basement membrane,” including the enamel-pulp, was destroyed, leaving the appearance as shown. The slide possesses no value whatever. I say no value; but perhaps it may be said to have an historic value, in precisely the sense that the implements of the stone age, while possessing no intrinsic worth, yet have an historical value, as showing the benighted condition the race was once in and the progress which has been made since that time. Let me now call your attention to photomicrographs taken from specimens mounted after different and better methods.

This view (Plate I., Fig. 2) shows the first observable differentiation which marks the commencement of the process of dentition. In former papers upon this subject I have said that "if an imaginary line be drawn through the cuboidal layer of epithelial cells directly over the position which will be occupied by the future jaws of the embryo, it will represent the first observable indication of the development of the teeth. These cells, in obedience to the law of typal requirement, begin to proliferate and increase rapidly in size. This growth forces the columnar layer downward and the flat layer upward. This upward bulging forms a band running around the entire surface of the jaw, and is the bourrelet of Legros and Magitot, while the downward curving of the columnar layer gives, in