RETENTION OF THE TEMPORARY CANINES.

7

from a child all of the deciduous teeth prior to the eruption of any of their successors, so that for a time the gums were edentulous; nevertheless, in due time the permanent teeth developed in perfect regularity of sequence and of symmetry. While Mr. Tomes's report shows that no abnormality followed the removal of all the teeth at once, such a result is to be feared from such a practice, and most certainly will ensue if there be not a coincident, independent, and ample development of the maxilla. Cases are coming constantly under our observation where from some cause the temporary canines have been sacrificed, the space closed up, and the permanent teeth malposed, with little hope of their ever assuming unaided their rightful positions.

From this there can be but one deduction, which is that whatever may be the inducement to remove any or all of the deciduous teeth prior to their period of shedding, the canines should be retained until there is ample evidence of the early emergence of their permanent successors, unless the health or comfort of the child would be sacrificed in so doing. But it would be far better to remove one or all of the deciduous teeth and take the risks of an irregularity in the permanent ones, than submit the child to constant suffering and consequent injury to its health by their retention.

How much of the malposition of the permanent teeth is due to the prolonged presence of the temporaries is still an unsettled point. Although absorption may be proved to be an independent process, and in no wise connected always with the progress of an erupting tooth, nevertheless the cases are so common in which the absorbed portion of the deciduous tooth corresponds accurately with the new crown as to force upon us the conviction that it is influenced by it, and therefore that if the permanent tooth had persisted in the right direction, the deciduous tooth would have become displaced.

The question naturally arises, Is the presence of the deciduous teeth the cause or the effect of the irregularity? If

8

RESULTS FROM SLIGHT CAUSES.

their presence be the cause of irregularities, then it is manifest that in this generation of malposed teeth it is our duty to anticipate the trouble, and at an early day remove them before even it is possible for them to give a wrong direction to their successors.

With the present knowledge upon the subject, there is no more evidence that the presence of the temporary tooth caused the irregularity than that the position and tendency of the permanent tooth was originally wrong. It is quite as reasonable to adopt the latter view as to suppose that the function of absorption was arrested and by that the tooth was turned aside. Whether their presence be the cause or the result of the malposition, this we know, that when a permanent tooth has erupted and its deciduous predecessor has not been removed, the immediate extraction of such tooth will go very far toward the complete correction of the deformity, thus showing that the apparent cause of the malposition of a single tooth is often the presence of a temporary

crown.

Even an unabsorbed spicula of a deciduous root will appear to cause a slight deviation in the inclination of a growing tooth, which, on coming in contact with its opponent of the other jaw at an unnatural angle, will be sufficient to cause the mal-occlusion of the entire dental economy.

A very trifling accident occurring at the period of erupting teeth will sometimes cause most serious results. The fall of a child has produced a slight inversion of an erupting central incisor, which, when further elongated, met the cutting edge of the lower centrals. It was easier and more natural for the child to throw the lower jaw forward and catch outside the upper tooth than otherwise. Thus began a habit which did not end until all the upper incisors were in like manner caught and inverted, and finally the whole dental articulation disorganized.

It would be impossible to describe and give the exact operating cause of all irregularities which could be traced to

TRANSMITTED PECULIARITIES.

9

an accidental source; they could not be ascertained short of a special anatomical examination of each individual case, which is generally out of the question.

Many of the forms of irregularity are directly traceable to inheritance, and are transmitted peculiarities. Probably in a large proportion of cases where the irregularity in a dental arch is confined to one or two teeth, the primary cause, so far as that individual is concerned, is an hereditary family peculiarity. The teeth of every person possess more or less individuality, and most of those peculiarities which stamp their individuality are inherited. The form and color of teeth, when not disturbed by abnormal influences, are derived from the same source. Whenever we find any departure from what we are apt to regard as the typal form of each tooth, or any disproportion of size in their relations to each other, we shall be likely to find them peculiarities of descent. The number of such cases which come under the observation of the dentist shows the universality of the law, that departures from a normal type are liable to be transmitted to succeeding generations, and eventually the peculiarity becomes the fixed type of the family or race.

For example, we have seen two small teeth develop between the central incisor and the canine, neither of which could be called a symmetrically formed lateral incisor, while upon the other side of the median line a single lateral incisor was well developed. This abnormality in a boy a dozen years of age was inherited from the father, in whom exactly the same kind of a deformity existed.

The transmission by inheritance of a predisposition to a defect or a deformity, is the result of the same general law of nature which gives the form and features of progenitors to their offspring. How far back in one's ancestry such peculiarities could be traced before arriving at the initial must be a matter of conjecture. The observations and the data are too limited to form an opinion.

It is a wonderful subject for contemplation that, at some

10

INFLUENCE OF CORRECTION ON OFFSPRING.

remote period in the history of our progenitors, Nature departed from her normal type, and a dwarfed lateral incisor, a twisted canine, or an undeveloped bicuspid was the result; and, following down the line of descent, we find precisely the same peculiarity appearing and reappearing-not always confined to the direct line, but continuing in the same family, by passing to the children of the brother or sister, and always presenting characteristics identical with the antecedent type. "There is an ingrafted tendency in all living organized matter to reproduce itself."

It is yet to be determined whether the correction of the irregularities of the dental organs exercises any influence upon the offspring. I am of the opinion that such deformities, even where transmitted for generations, may have the tendency stamped out by being corrected immediately on their development—that is, before the deformity has made its fixed impression upon the individual. This we might reasonably expect, because it would be assisting nature to return to its normal type.

There is one form of irregularity which is sometimes due to hereditary predisposition and sometimes to causes acting after eruption. An undue prominence of the upper incisors may be either congenital or acquired. The acquired origin is almost always a habit of thumb-sucking or its equivalent. It is not difficult, as a general thing, to make the distinction even without questioning the patient. In a protrusion of congenital origin the jaw is generally pinched in the bicuspid region, and the protrusion culminates in a pointed or V-shaped position of the central incisors. When such prominence has a mechanical or accidental origin, the whole front of the arch will be found rounded out, and the teeth pulled forward; and there will be likely to be more or less space between each of the teeth anterior to the bicuspids.

A marked case of the latter class came into my hands for treatment. It was an only child, a girl about thirteen years old, brought by her mother. The protrusion of the

incisors was considerable, and the effect upon the upper lip most marked, destroying the symmetry of the features. On remarking half inquiringly, "I wonder what could have caused that?" the mother replied with a somewhat shamed face, "I suppose it was my allowing her to nurse until she was nearly nine years old. I did not know it would hurt her teeth."

An undue prominence of the superior incisors is said to be not uncommon among idiots. And to such an extent had it been observed among that class in connection with the habit of thumb-sucking that Dr. Ballard, of London, adopted the theory that the thumb-sucking preceded, and was the cause of idiocy. A little further inquiry into the ancestry of the patient, and a better knowledge of the development of the dental organs, would have probably shown the fallacy of this theory. Subsequently Mr. Charles Tomes presented his hypothesis, attributing the deformity to a peculiarity in the development of the maxillæ at a very early period of life, and to mechanical causes operating upon the permanent teeth at the time of their eruption.

The causes operating upon the development of the maxillæ Mr. Tomes does not seem to regard in the light of a transmitted tendency, but rather to forces having their origin in the individual. The mechanical causes at work on the crowns of the teeth at the period of their eruption, forcing them inward, he believes to be the pressure of the cheek; for he says: "It will generally be found that this malformation is associated with greatly enlarged tonsils which necessitate breathing being carried on with the mouth open. Now, as every one can easily verify upon himself, the effect of the mouth being held open is to increase the tension of the soft parts about its angles, and the result of the increased pressure is to bring about a bending inward at the corresponding point, i. e., the bicuspid region; at the same time the median portion of the arch escapes the controlling pressure which would have been exercised by closed lips, and the