blasts' being properly placed, namely, against its inner surface; it forms the matrix for the later dentin substance. When the odontoblasts are placed in the proper position, when the first dentin layer is formed and in this way the shape of the tooth secured, the enamel epithelium has played its part for this portion of the tooth; now the fixation and fastening of the tooth can begin, and the connective tissue performing this work may destroy the mold." "I must emphasize in particular," he states, "that the first odontoblasts are always found at some distance from the free border of the epithelial sheath, and that from this I draw the conclusion that the presence of the epithelial sheath is the conditio sine qua non for the formation and arrangement of the odontoblasts, and thus of the dentin itself."

Quite novel are the views which Fischer* holds in regard to the ultimate fate of the enamel epithelial sheath. He claims that this epithelium, after having fulfilled its mission of enamel formation, by no means is resorbed and disappears or forms the enamel cuticle, as believed by some authors, but it continues to differentiate and becomes again typical epithelium of the mucous membrane. As the crown of the tooth breaks through, the flanks of the persisting enamel epithelial sheath try to establish a communication with the proliferated external epithelium of the mucous membrane, after having sent forward short buds and plugs into the surrounding connective tissue. The cylindrical matrix of the youngest enamel epithelium gradually passes over into the older cubical cell form, while the layer of ameloblasts, which is still present at the time of the perforation of the tooth, exchanges its cylindrical form with the cubical only later. Co-operating with the external epithelium, it finally produces the tissue proliferation which forms the later papilla of the gingiva. He states that the

*Fischer, "Beiträge zum Durchbruch der bleibenden Zähne und der Resorption des Milchgebisses," Anatomische Hefte, 1909, Xxxviii, 617.

importance of this "return" of the enamel epithelium to the mother tissue, of this "new characteristic" of all epithelium involved in the development of the teeth, is particularly emphasized when we consider the activity of the epithelium from the phylogenetic standpoint.

The most primitive form of dentition consists in a bulging out or an evagination of the epidermis into which a papilla of mesodermal connective tissue pushes from beneath. In the lower jaw of the pike we find for the first time the tendency of the epithelium to grow downward or to invaginate into the mesodermal tissue as a tooth germ, but without ever losing the connection with the mother epithelium. In amphibia we have both simple epithelial evaginations and invaginations into the depth, which, however, always remain in continuity with the mucous membrane. In reptilia the line of teeth may separate completely from the epithelium of the jaw, leaving only a few rudiments.

In all higher vertebræ the epithelium forming the teeth is regularly being snared off from the mucous membrane for a definite time, but when its mission is fulfilled it is differentiated back into the mother tissue. Remnants of epithelium may, nevertheless, be left in the depth of the jaw and persist as indifferent cells. These correspond to Malassez' débris épithéliaux paradentaires. These are, however, not differently sized collections, scattered irregularly and independent of one another, as represented by Malassez and his followers, but constitute a large wide-meshed network, which is being formed as the cementoblasts break through an originally solid epithelial sheath. This epithelium wound like a net around the root, and which morphologically belongs to the epithelium of the mucous membrane, may have retained enough regenerative energy so that in a case of cyst formation it may line the cystic cavity.

Apparently Fischer stands alone with his view of a return of the epithelial cells to the mother tissue-morphologically and functionally like it.

Granting that the epithelial cords of

Indeed, his illustrations strikingly reveal the seeming continuation of the direction of such cords from the depth of the membrane to the mucous membrane. (Fig. 4.)

ORIGIN OF EPITHELIAL CELLS IN ROOT

CYSTS.

While by the majority of writers the theory is adhered to that the epithelial cells occurring in root-cysts and root granulomas originate from the cell cords. within the peridental membrane, an entirely different view is held by Grawitz.* This author believes that epithelial cells lining cysts are always derived from the squamous epithelium of the mucous. membrane of the mouth. Every cyst begins with abscess formation within the granulation tissue. Epithelization of the cavity does not take place unless the pus reaches the surface of the mucous membrane through a fistulous tract. If this does occur, the squamous epithelium of the mouth grows downward and covers the wall of the duct as well as that of the cystic cavity. A closed cyst is formed if the fistula heals after it has been lined. According to him only the genuine odontogenous cystomas are derived from embryonic enamel epithelium.

Adloff and Schuster cite cases which they believe speak in favor of such an origin. Schuster, however, believes that the epithelial invasion from the squamous epithelium of the mouth does not necessarily depend on the formation of a fistula. Distal portions of proliferated papillary bodies of the mucous membrane may be snared off by the connective tissue and remain as an epithelial cell nest in the peridental membrane, and give rise to an epithelial invasion of a granuloma or cyst. He points out that if cell remnants of the enamel organ are the origin of the epithelial cells in cysts and granulomas, the structure of this organ

should be found reproduced to some extent. This is strikingly the case in cystomas, while the epithelial cells in a root-cyst show a marked resemblance to those of the mucous membrane.

The majority of writers, however, consider as untenable the views held by Grawitz. Astachoff, who examined specimens from 98 jaws with the teeth in situ, did not find a single case which might be used as proof of this theory, Dependorff points out that the epithelium appears in the granuloma early, before a cavity formation sets in, and that in fresh melting-down processes in encapsulated granulomas the tendency of pus to break through is rarely observed; the encapsulated focus remains restricted. and is soon surrounded by epithelial cell tracts.

Perthes advances the following arguments in refutation of Grawitz' theory: (1) The occurrence of epithelium in completely solid granulomas excludes the supposition that it owes its existence to the lining of an abscess. (2) The free movability of the mucous membrane over the cyst and the absence of a fistulous tract speak against it. (3) From clinical experience it is observed that a root-cyst never develops from a chronic abscess with a fistula. (4) Growth of a cyst such as is observed could not be accounted for if there were a communication from the cyst to the oral cavity, since the content of the cyst would be poured out constantly or at intervals.

While there is still such division of opinion in regard to the origin of the epithelium in root-cysts, authors generally agree concerning the genesis of follicular cysts and cystomas. The former, although in form and growth very similar to the root-cysts, have some characteristic features which make the origin rather obvious; the location, the time of development, and the content speak for an embryonic starting-point, namely, a

misplaced or malformed tooth anlage. As to the latter, we may, from their his

*Astachoff. loc. cit. Dependorf, loc. cit.

Perthes, quoted from Schuster, loc. cit.

tological structure, rightfully believe that the epithelium in these tumors is derived from the enamel organ, the structure of which is strikingly reproduced in the tumor tissue.

ETIOLOGY OF ROOT-CYSTS.

Root-cysts result from chronic inflammations of the peridental membrane. The first impulse is given by inflammatory changes of the connective tissue, which are due to various influences, mechanical and chemical, but chiefly bacterial. Moorehead, in his extensive clinical experiences, found root-cysts almost invariably to arise from infected tooth-roots. He calls this type "infection cyst," in order to emphasize the distinction from follicular cysts which develop in the absence of caries of the teeth and apparently are unrelated to infectious processes of any kind. Proell* considers the granulation tissue which is being formed as a measure of protection on the part of the tissue surrounding the tooth against bacterial invasion. next phase is the effect of the granulation tissue on the epithelial cells in the peridental membrane, which are in a state of repose as long as the root membrane is perfectly healthy, but awake from their slumber when this is altered.

The

Partsch has seen distinct changes take place in these epithelial cells under the influence of an inflammation of the connective tissue. Vascular loops formed in the course of hyperplastic changes push out toward the cell nests and force them to give up their globular form, so that they lie like a cap over the loops. Dependorf believes he has seen the beginning proliferation of the resting epithelium. The former may occur before the formation of granulation tissue; the latter only sets in when this is present. Wherever degenerative processes occur

* Proell, "Zur Mikroskopie der Granulome und Zahnwurzelzysten," D. Monatsschr. f. Zahnheilk., 1911, xxix, 161.

Partsch, "Zur Pathogenese der Zahnwurzelzysten," Allg. mediz. Centralzeit., 1910, lxxix, 20.

Dependorf, loc. cit.

in the granulation tissue, the epithelium shows the tendency to surround and encapsulate such foci. This is the beginning of cyst formation. Strands grow out from this epithelial layer into the granulation tissue and encircle and snare off other regions which, being cut off from the surrounding tissue, are poorly nourished, and hence the tissue undergoes degenerative processes. When these are complete the epithelial barrier is also dissolved and the detritus added to the cystic content. Some authors are emphatic in stating that the cyst begins chiefly through participation of the connective tissue, others that it begins with degenerative processes in the epithelium.

The peculiar behavior of the connective tissue toward the epithelial cells and vice versa produces most varied and often very strange pictures, which have given rise to various comparisons. Proell likens it to a mucous polypus, which seizes an object with its two main arms and incorporates it; when the two arms have closed around an area of granulation tissue a cyst is being formed. Witzel* compares such region of proliferation to a bath sponge, the supporting scaffold of which is the epithelium, while granulation tissue fills the alveoli. Römert speaks of "Epithelglocken," epithelial bells. Dreuw and Rumpel lay stress on the islands of connective tissue marked off by the epithelial cells, which they call "Plasmominseln," inasmuch as they are filled with plasma cells.

As to the fluid which occupies the cyst, Fischer believes it is due to mucinous softening of the surrounding connective tissue; a cyst fluid proper is formed which passes through the epithelial layer and fills a space lined with epithelial cells. Also an inflammatory

* Witzel, “Ueber Zahnwurzelzysten, deren Entstehung, Ursache und Behandlung," D. Monatsschr. f. Zahnheilk., 1896, xiv, 305.

Römer, "Epithelgranulome in Zahnwurzelzysten," Handb. d. Zahnheilk., 1909, ii, 676.

Fischer, "Experimentelle Unterschungen über die Entwicklung folliculärer Zysten," D. Monatsschr. f. Zahnheilk., 1911, xxix, 188.

exudate may diffuse through the thin cellular wall, according to him. Partsch disputes the formation of a cyst by liquidation of the epithelial cells, as Dependorf claims. If this were the case we should find epithelial cells in some form of transition or degeneration within the cystic cavity; this, however, is never observed. He holds the view that fluid accumulates in the space between the root and the granuloma, and thus a cyst is formed. This is not admitted by others on the ground that under these conditions the bare root should be found in every cyst.

An examination of a number of cysts such as I have made during the past year is peculiarly fascinating on account. of the great variety of the histological features which they present. No two cysts are alike. Certain elements appear in nearly all of them, such as epithelial cells and plasma cells, but chameleonlike they change their appearance continually, and with almost every specimen we find differences in the arrangement, the location, the amount present, the size, and the staining qualities. The alterations are sometimes so marked, the disguise so complete, that it is often extremely difficult, if not almost impossible, to identify them.

which was lined with ciliated epithelial cells on the inner and outer wall; there was no fistulous tract in his case. Both authors are of the opinion that these cells were derived from the lining of the maxillary sinus. According to Adloff, fistulæ are present in all cysts at some time; the absence of one in Proell's case simply indicates that it had healed completely. pletely. Although he admits that the cells of the body in general retain with great persistence their specific properties, he considers the squamous and cubical cells in his two specimens as being derived from the same source, i.e. the ciliated cylindrical cells of the antrum, a transition having gradually taken place from the ciliated cylindrical to the squamous type.

Römer, who observed a cyst lined on the inside with ciliated and squamous epithelial cells, objects to this conception of a transition of one type of cells to another, and believes that, in addition to Malassez' epithelial remnants, aberrant epithelial germs of the antrum could be taken into account. It would seem that the possibility of such an origin cannot be absolutely denied in Adloff's cases. One of these was associated with some noteworthy peculiarities. In a girl sixteen years of age the upper first molar had three roots, to each of which a granuloma was attached; two of these were of the simple kind, the third was the cyst described by him. He admits that the epithelium in the two former, as in all granulomas, was derived from the epitheoriginated from the antrum, and he lial remnants; in the last, he believes, it

states that "Thus for the first time the

proof has been given that an epithelization of a granuloma may take place from the outside." "It is very remarkable," he continues, "that squamous epithelium analogous to that of the mucous membrane of the mouth has never yet been demonstrated on the outer wall of a cyst."

From these considerations the questions arise as to why an outside lining is so extremely rare; whether a fistulous opening is necessary to invite a growing downward of the epithelium, or whether,