The approximate cause of these peculiarities in the incisors can hardly be said to have been demonstrated. Mr. Hutchinson thought at one time136 that they were due to a stomatitis or an alveolar periostitis, but he has since changed his mind as to that point, believing now137 that the syphilitic tooth is the result of an arrest of development in the central or first-formed portion of the dentine. The incisors being made up of these lobes or denticles, and dwarfing of the middle one taking place, the two lateral ones fall together. This accounts at once for the small size of the tooth, its shape of an inverted truncated cone, and its crescentic edge.138 If it were due to stomatitis, it would be more likely to be equally distributed, syphilis in its late manifestations being notably unsymmetrical; there would be no rational explanation of the involvement of one or two teeth while those on either side so frequently escaped; if it were mercurial stomatitis, the enamel too would be involved, as is not usually the case in the syphilitic teeth. It is possible that the central incisors are chiefly affected because they, with the first molars—also affected according to Mr. Moon—and the lower incisors—not infrequently involved—are the first-formed teeth.
136 "The physiognomonical, dental, and other peculiarities by which we recognize the subject of inherited taint when advanced beyond the period of infancy are all of them the direct consequences of special inflammations from which the patient has suffered at former periods; e.g. the synechiæ and lustreless iris of iritis; the malformed teeth of periostitis of the alveolus and dental sacs; the protuberant forehead of hydrocephalus; the flattened nose of snuffles; the pale, earthy, opaque skin of cutaneous inflammation and eruption" (Aphorisms respecting Constitutional Syphilis, 1863).
137 Proc. of Odont. Soc. of Great Britain, vol. ix., p. 248. See also ibid., pp. 241, 242, remarks of Mr. Moon; also Monthly Review of Dental Surgery, June 15, 1877.
138 The denticle theory of formation is not necessarily opposed by the fact that there is only a single undivided pulp-cavity in these incisors. Instances of the separate formation of processes of dentinal pulp while others are being used and worn away, all of them finally to unite in a common pulp-chamber, have been observed in lower animals, as in the molar of the elephant.
The most elaborate article upon syphilitic teeth which has appeared since Mr. Hutchinson's original memoir is one by Fournier,139 in which, after a very broad and comprehensive consideration of the subject, he arrives at the following conclusions: The hereditary influence of syphilis shows itself in the dental system in two ways, very unequal in point of diagnostic value—viz. first, by a retardation of evolution; second, by the arrest of growth and modifications of structure. The phenomena belonging to the second class may be grouped as follows: First, dental erosion. This is due to imperfect formation of the tooth, the result of a temporary stoppage in its development; but as it produces an appearance like that of worm-eaten wood, it has been called erosion, though in so far as the word conveys the idea of the wearing of a surface which has been previously normal, it is incorrect. The tooth affected with syphilitic erosion has never been normal. The different forms of erosion can be subdivided into groups according as they affect the face or the free edge or grinding surface of the tooth. Of those involving the face there are four types: Erosions en cupule, consisting of small excavations or cups in the surface of the crown; erosions en facettes, in which the surface presents a series of small planes, as though they had been filed; erosions en sillon when there is a linear excavation in the crown of the tooth in the shape of a transverse groove; and erosions en nappe, in which the whole surface is discolored, disorganized, and honeycombed.
139 Archives de Derm. et Syph., Sept. 25, Oct. 2, Oct. 9, 1883. A translation made by the writer may be found in the Dental Cosmos for January and February, 1884.
A second group of erosions affects the free edge of the tooth, and includes the Hutchinson teeth, with several less important varieties. Dental erosions are multiple, symmetrical, maintain the same level on the crowns of corresponding teeth, and are situated at different heights on the crowns of teeth of different classes. It is evident, therefore, that they are the result of a morbid influence of a general character. There are three theories as to their etiology: (a) that they have no relation to syphilis,140 but are always connected with infantile eclampsia; (b) that they are exclusively the result of hereditary syphilitic influence; and (c) that they are simply ordinary lesions originating from syphilis with marked frequency, and even in one form—the Hutchinson tooth—appearing to originate only from it. This latter view is the one adopted by Fournier himself. Continuing to group the symptoms due to arrest of growth and modification of structure, we have, second, microdontism, or dwarfing and stunting of the teeth—pegged teeth; third, dental amorphism, in which the teeth are strangely distorted or even transformed in type; fourth, dental vulnerability, or extreme susceptibility to all traumatic or disintegrating influences.
140 M. Magitot, Treatise on the Anomalies of the Dental System, Paris, 1877; Clinical Studies on Erosion of the Teeth considered as a Retrospective Sign of Infantile Convulsions, Paris, 1881; Castanié, Paris, 1879, Thesis No. 384; Rattier, Paris, 1879, Thesis 569; and others.
Interstitial Keratitis.—The frequency of this form of diffuse inflammation of the cornea, and the diagnostic significance which has been so positively attributed to it—and has been as positively denied—render it of special interest to the general practitioner, who is almost certain to meet with occasional cases, and should be prepared to recognize its possible relation with other, and often graver, conditions.
It begins, commonly, as a slight, diffused haziness situated in the substance of the cornea itself, usually not far from the centre, and at first affecting only one eye. This depends at this stage on the presence of a number of little distinct dots of inflammation, limited to circumscribed, almost microscopic, areas, but later, in a few days, these coalesce, and at the end of a few weeks the whole cornea will probably have become nearly or quite opaque, looking like ground glass. There is no ulceration, and but little congestion as compared with that seen in other inflammatory diseases of the eye, although in the majority of cases there is a fulness of the ciliary vessels and a little photophobia with pains around the orbit. This condition may persist for one or two months, after which the other cornea is nearly always attacked,141 and is similarly affected, although the disease is apt to pass through its different stages rather faster than in the first eye.