2

NORMAL TYPE OF THE DENTAL ARCH.

well formed, and the positions of the teeth are regular (mere freaks of nature excepted). But from this perfectly symmetrical dental arch there develop with the growth of the permanent set some of the most astounding abnormalities.

These peculiarities of the permanent teeth it is unnecessary to describe in detail. In the departure from symmetry they assume almost every variety of position, so that it would be almost impossible for the human mind to conceive of an irregular arrangement which would not find its counterpart in nature. These variations are recognizable by every one of extended observation, and are deformities, because they are a greater or less departure from a normal standard. Such a standard can not, in the nature of things, be one shape to which all must conform or be classed as deformed.

Symmetry and harmony do not imply uniformity; and the dental arch may be developed up to the highest type of perfection, and yet there exist as great a variety of form as there would be in the faces of the aggregated beauties of the world. Races, nations, and families are thus represented without deformity.

The normal type of the dental arch I conceive to be a regular line; the arch may be wider or narrower, varying somewhat in individuals or races, but the line will be an easy, graceful curve, without break or tendency to form an angle. Within certain limits a narrow dental arch, as associated with certain features, may become the very perfection of beauty, while with another form of head and face the widest development may be equally pleasing. That which is recognized now as the standard or full measure of beauty, as well as of utility, is not unlike that which existed in the remotest historic ages, nor different from that which is now exhibited among all communities not degenerated by luxury or vice.

In 1864 Messrs. Cartwright and Coleman, of London, made an examination of some two hundred ancient skulls in

WIDTH OF ANCIENT AND MODERN JAWS.

3

the crypt of Hythe Church, Kent. Those skulls, of which there is no authentic history, further than that they had been there for centuries, were apparently of both sexes and all ages. The maxillæ presented in all instances unusually well-developed alveolar arches. The teeth were remarkable for regularity of position, only two deviations being noticed: one upper canine shut within the lower jaw on occlusion, and one bicuspid was turned upon its axis, and there might have been other slight irregularities which were unnoticed; but in no single instance was there anything seen approaching to that which, under the term "contracted arch," so commonly exists in the present day. The average width of the dental arch in those skulls, from the outside of the first molar to the corresponding point, was two and a half inches.

In 1869 Mr. John R. Mummery, of London, contributed to the Odontological Society of Great Britain the most valuable paper on this subject which I have ever read. I accord more importance to his personal examinations than I do to the observations of any man not a practical dentist. The statements of all others, even those of ethnologists, being less precise and more general in their character, must be accepted with some allowance. He examined all the available skulls of ancient races, and of modern uncivilized races, to the number of about three thousand, and tabulated more than one half of them, which were classified as follows: Ancient British, 203; Roman British, 143; Anglo-Saxon, 76; and ancient Egyptian, 36. Of modern uncivilized races: North American, 145; Polynesian, 204; East Indian, 223; African, 438; and Australian, 165.

From a careful analysis of the measurements given in his tables, I find that the average width of the dental arch, from first molar across to first molar, in the skulls of ancient races, was a trifle less than two and three eighths inches; the same measurement of the uncivilized moderns showed an average width of a trifle above two and a half inches. The

4

DEFINITION OF ABNORMALITY.

narrowest measurement given by him of any skull of any race is two and one eighth inches. The highest average of any race is nearly two and three fourths inches, and these belong to the New-Zealander, the Feejee-Islander, and the Ashantees. The narrowest average was found among the Hottentots and Bushmen of South Africa.

In these tables there is abundant evidence that the full measure and type of both dental and maxillary arches has been sustained among all races of simple habits in all ages. Dr. Nichols, a dentist, who spent twelve years in the Rocky Mountains and on the Pacific coast, during which period he examined the mouths of thousands of Indians and Chinese, informed me that he never saw an instance of irregularity of the teeth in either of those races, with but one exception, and that a displaced canine in the mouth of a ChiThe jaws of both races are universally well formed and amply developed. And this is also true of all semi-barbarous and savage races of good physical organiza

nese woman.

tion.

The standard of normality of the dental arch is a curved line expanding as it approaches the ends, and the teeth all standing on that line.

Abnormality will include such a shape of the arch as is not in harmony with the surrounding features, all crowding and twisting, and all departures from a regular line in the positions of the teeth.

In classifying the causes of irregularities, they will be placed under one of two heads-developmental or accidental; the developmental operating prior to the eruption of the crowns, and the accidental at the time of eruption or subsequently.

Almost the only answer received by the dental student as to the cause of these irregularities has been "premature extraction of the deciduous teeth," and consequent contraction of the jaw; and this answer has been almost universally accepted without a question as to its philosophy. A few

PREMATURE EXTRACTION.

5

facts have been correlated, and a conclusion arrived at as unscientific as it is erroneous.

The premature extraction theory rests upon the supposition that the jawbone contracts upon the removal of the deciduous teeth. The fact seems to have been entirely ignored that the teeth and alveolar processes are a superstructure of the jawbone, growing up on it, fulfilling their destiny, and passing away, without disturbing the foundation much more than an oak disturbs the planet upon which it has been sustained. There is a period in the history of the maxilla when it is itself an entity, and prior to hardly a trace of the subsequent superincumbent structures; and in the ordinary course of nature there comes a period at the other end of life when equally all trace of dentition is gone, and the maxillæ remain undestroyed entities.

While the proofs are conclusive that the jaws are developed independently of the teeth and alveolar processes, and that no ordinary surgical interference with the teeth or processes impedes or impairs that development, and while also it may be true that all the primary teeth may be removed long anterior to the period of eruption of the permanent ones without retarding their development or impairing their regularity, the doctrine may still be correct that the too early extraction of some of the temporary teeth in connection with a tardy development of the maxilla will be likely to result in a crowded and abnormal condition of their successors. This result is not as likely to show itself with any other teeth as with the canines.

In observing the order of eruption of the permanent set in the regular economy of nature, it will be seen that for every tooth of the deciduous set there is a permanent one lying underneath it in process of formation, and that in due time a deciduous tooth will loosen and fall out, and a permanent one will take its place.

With a normal growth of the maxillæ there will occur no interference and no irregularity. The central incisors will

6

DISORDERED ERUPTION.

first appear; then the laterals; after that the bicuspids; and lastly the canines. Each predecessor of a permanent tooth will maintain its position until about the period of the emergence of its successor. There will be no contraction of the alveoli, because there will be no opportunity for it.

But take now a disturbed or tardy development of the maxillæ instead of a normal condition, and observe the result. Remove for any cause one after another of the temporary set, or all at once, and the period of eruption will not be interfered with, but the arrangement in the arch may be impaired. The centrals will find a place without difficulty-so will the laterals; the bicuspids will be pretty certain to have sufficient room, as their diameters are generally less than their predecessors; but when these teeth are all fully erupted, it will be found in a majority of cases at the present day that the first bicuspid and the lateral are nearly or quite in contact, filling the space destined for the permanent canine, which must now emerge either anteriorly or posteriorly to its true position, showing conclusively that, if the alveolar arch had not contracted, the contiguous teeth had encroached upon the space destined for the canine and forced it out of position. In either case it is the unquestioned result of the too early removal of the deciduous canines; for no one will doubt that, had the temporary canines been allowed to remain, they would have prevented contraction of the alveoli or an encroachment on their domain. It may be argued that if the original direction of the canine was correct, it would force itself between the lateral and bicuspid, thus making way for itself; but this is against the. experience of nearly all observers, and very naturally so.

Admit the fact that from some cause or other the bicuspid and lateral come into contiguity, and from the tardiness. of the erupting canine it will find solid and unyielding roots to contend with, which will necessarily force it out of the dental arch.

Mr. Tomes relates a case in which he removed for cause