VOL. LX.

No. 7

C

HISTORICAL.

YSTS of the dental system are generally classified as root-cysts, follicular cysts, and multilocular cysts, and by the majority of authorities are believed to arise from anomalies and from remnants of the enamel organ. Root-cysts and follicular eysts are more frequently found in the upper jaw, while multilocular cysts and their solid forerunners are with rare exceptions found in the lower jaw.

As to their origin, root-cysts are believed to occur in connection with chronic inflammations of the peridental membrane. They are by far the most frequent. Of 416 cases of cysts which Rosenstein* observed, 394 were rootcysts, 13 follicular cysts, and 9 could not be determined. Astachoff examined

"Zur Klinik der Kieferzysten," D. Monatsschr. f. Zahnheilk., 1912, xxx, 160.

"Ueber die Pathogenese der Zahnwurzelzysten," D. Monatsschr. f. Zahnheilk., 1909, xxvii, 644.

VOL. LX.-38

98 pieces from jaws carrying gangrenous teeth, and in these found 36 root granulomas and 52 root-cysts. Not rarely the root projects into the cystic cavity; in larger cysts several roots may be found.

Follicular cysts are independent of caries of the teeth, and as a rule occur during the second dentition. They are believed to originate from dilatation of a tooth follicle or misplacement and malformation of a tooth germ. Very frequently they contain one tooth, less frequently several teeth, the crowns of which are directed toward the lumen. Sometimes the tooth is lacking in the alveolar process where the tooth like cyst is located.

Multilocular cysts belong to the class of solid epithelial tumors in the central portion of the jaw. This is simply the stage preceding the cyst formation.

Root-cysts and follicular cysts are very much alike as to their form and growth. The most characteristic feature of all is the frequent presence of squamous epithelial cells which occur as plugs or ten

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drils extending through the granulation tissue, or as a lining of the cystic cavity. They also occur in root granulomas, which so frequently develop into rootcysts. Römer,* who examined 100 specimens of root granulomas, divides them. into two distinct classes according to the presence or absence of epithelial cells. The latter type is called by him "simple granuloma," and Römer maintains that such granulomas never develop, in fact never can develop, into cysts for the very reason that they do not contain any epithelial cells.

According to most writers these epithelial cells are derived from the so-called débris épithéliaux paradentaires of Malassez, i.e. the cell clusters and cords which occur almost constantly in the peridental membrane in man and the higher animals. There is not yet absolute agreement among authors as to the origin, nature, and function of these cells. The majority of recent writers consider them. as the remains of that portion of the enamel organ which, as Hertwig and Von Brunnt have shown, normally extends downward as an epithelial sheath around the root. After the eruption of the tooth this sheath is gradually broken up by the fibers of connective tissue which extend from the alveolar periosteum to the dentin of the developing root; but remnants persist throughout life.

and Black.* These two authors are inclined to doubt the mere embryonic character of these cells. Noyes, although he accepts their embyronic origin, considers it as apparently improper and illogical to suppose that embyronic débris would persist through life, if it were useless to the organism. He is guarded in his statements concerning the possible function of these cell clusters, because of the failure of extensive attempts to discover a connection with the epithelial cells lining the gingival space, or a duct or a lumen, in these strings.

Black expresses more positive views. According to him, the epithelium of the enamel organ, as it breaks up and floats away, is absorbed and disappears completely. "These cells," he writes, "seem to have nothing whatever in common with the epithelial cells scattered in strings in the peridental membrane. They are not like them. They do not seem to be of the same quality at all." He is inclined to consider them as glandular structures. "These cells must, as a whole, be regarded as glandular. I know of no other term to apply to them, although they have no ducts and in many respects are respects are out of form as glands." Black, therefore, emphatically contends that the epithelial cells occurring in the peridental membrane are of two kinds, unrelated to each other; that those derived from the epithelial root-sheath are being absorbed and disappear completely, a process which, he claims, may be observed and confirmed by anybody who will take the pains to study it properly; and that those which persist through life in the peridental membrane are not like the other cells, but are normal to this tissue and may have a glandular function. It is, however, not clear from his statements whether there have been as conclusive studies made by him or others of this second type of cells. We are not informed when these cells appear, whether they may coexist with the first type, or whether they present any differential histological features, and no suggestions are made as to their origin.

further development. There are, on the one hand, those buds and secondary outgrowths of the enamel ridge which are exceedingly frequent during the embryonic development of the human teeth in the various developmental stages, and on

* Adloff, "Zur Frage der Herkunft des Epithels in den Wurzelzysten," D. Monatsschr. f. Zahnheilk., 1912, xxx, 188.

uterine life, and being absorbed when this function is fulfilled; cells from this sheath are remnants of a used-up organ, hence they lack the growth-energy of the other type of cells when they become active again in a granuloma or a cyst.

Black's statement, that the epithelial cells which persist in the peridental membrane through life must be regarded as glandular, is not yet supported by any

proof; but it can hardly be denied that structures which, as he contends, are normal to the peridental membrane, and constant elements in so highly an important tissue, may have some physiological function to perform. Illustrations of these cell cords in Noyes' textbook, and casual remarks in the literature, hint at the possibility that they may be in some way connected functionally with the cementum. Noyes describes them as being surrounded by an extremely delicate basement membrane. "They lie very close to the surface of the cementum, winding in and out among the fibers. They anastomose and join with each other, forming a network, the meshes of which are comparatively close in the gingival portion and comparatively wide in the apical portion." (Fig. 1.) He calls attention to the observation that "The ends of the loop toward the cementum often show enlargements which in some cases apparently lie directly in contact with the cementum." (Figs. 2 and 3.) Astachoff, who examined 98 specimens from jaws, also observed the close proximity of the epithelial "cell islands" to the cementum. In one case of a cyst he found them even in eroded depressions of the cementum. He writes of them, "They are similar to the odontoclasts, or they replace to some degree, as an epithelial sheath, the bundles and cells of the peridental membrane which are lacking here."

*

HERTWIG'S SHEATH.

It is, indeed, striking what a degree of differentiation cells of the connective tissue type may attain. The odontoblasts which are formed from the cells of the

pulp, i.e. from connective tissue cells, are high columnar cells, and resemble much more epithelial cells than the cells in Malassez débris épithéliaux paradentaires. It may be worth while to review some of the statements of embryologists concerning the structures from which these cells are considered to be derived. To Von Brunn* we owe the best description of the enamel organ and of the so-called epithelial root-sheath, which is frequently called after him "Brunn's sheath," but, as proposed by Brunn himself, more properly called Hertwig's sheath, Hertwig having described it first.

Von Brunn calls attention to the fact that in rats the summits of the crowns of the molars are free from enamel; immediately after the eruption of the teeth the dentin is already freely exposed on

the outer surface. The incisors of rodents are provided with enamel only on the front surfaces; also the summits of these teeth are enamel-free at the time of eruption. The incisors of these animals have no roots. Yet at an earlier stage of development these teeth have a complete covering of enamel epithelium like other teeth. Tomes also found that in the armadillo, whose teeth are absolutely free from enamel, the tooth anlage nevertheless begins with the formation of a complete enamel organ. In the eel and various fishes the enamel organ likewise extends very much farther than the final very small enamel cap.

The question naturally arises, What has the enamel epithelium to do in those places where subsequently no enamel is being developed? Von Brunn showed that its purpose is that of giving form to the tooth, and that the function of enamel formation is only an accessory one. He writes, "Its presence is evidently necessary in order to the odonto

* Von Brunn, loc. cit.

Tomes, quoted from Von Brunn.