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idiosyncrasy is frequently present, which, by being intensified, may give rise to unfortunate mental or physical defects." But consanguinity, pernicious and powerful as it is for evil, by multiplying family weaknesses or diseases in offspring, is not the only cause of the augmentation of deleterious predispositions. Persons not related by blood may be possessed of "taints" or idiosyncrasies or defects of organs or tissues so similar that, by combination in offspring, they will lead to excessive exaggeration. In regard to the teeth, this will have an especial effect, owing to their peculiar susceptibility.
But let us here notice what Dr. Norman W. Kingsley says upon this subject. He writes that " many of the forms of irregularity with which we are familiar are directly traceable to inheritance and transmitted peculiarities. Especially is this true when it 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 features which stamp their individuality are hereditary. The form and color of the teeth, when not disturbed by abnormal influences, are derived from the same source. Any departure from typal form is a peculiarity of descent, as well as any predisposition to defect or deformity. It is a most wonderful subject for contemplation that at some remote period in the history of our progenitors, when nature departed from the normal type to produce, say, a deformed lateral incisor, a twisted cuspid, or to suppress a lateral or a third molar,—that, following down the line of descent, we find precisely the same peculiarity appearing and reappearing in the same line, and again not in the line, but in different branches of the family." Defects of structure, as well as of form and arrangement, are also transmitted more or less directly. Thus, we know that children frequently have the same defects upon the same teeth which the parent possessed, and that they become carious, and are lost at the same age; or, owing to the increased ratio of deficiency of structure by inheritance, are lost earlier in the child. A minute defect of contour, fissures, extra cusps on 'lingual or palatal surfaces, peg-like teeth, total absence of particular teeth, dark or soft areas in the enamel,—all these and more are often transmitted as family peculiarities.
But the peculiarities of form or defects of the teeth are transmitted with exact regard to the laws of heredity and variation. Thus, a child's teeth will likely most resemble the teeth of the parent of the opposite sex, or that parent's ancestors, with their peculiar forms or defects. Or, again, its teeth will bear the marks of atavism and resemble a remote ancestor. This will sometimes account for the appearance of a good denture in a family whose individuals have very defective teeth, or vice versa. Sometimes there is a blending of the types of two or more ancestors, the front teeth presenting the good organization of one parent, and the molars the bad structure or diseased organization of another. But this is not so usual as for the entire denture to partake of the structural integrity of the dominant hereditary influence. When this is diseased, as when syphilitic, phthisical, gouty, strumous, etc., the teeth are prone to partake of the taint, subject of course to the occurrences of exacerbation and latent periods of the disease during formation. Through their susceptibility the teeth are unfortunately recipients of a legacy of disease in most of its varied forms; and it does not seem that in them it tends to lessen by the natural powers of elimination which most tissues possess; so that in time hereditary disease will exhaust itself and run out. But with the teeth the opposite rule obtains, that the tendency is toward augmentation by transmission, and the disease exhausts itself only when the organs are destroyed. Natural elimination occurs in the individual, of course, but while the disease is in the system the teeth have no power of resistance to its interference with structural integrity.
But the suppressive effects of disuse, as affecting development of the teeth through heredity and variation, are also to be noticed. In no class of organs are the inherited effects of variation due to the influence of changed conditions so marked as in the teeth of man Being thus susceptible to the effects of active employment or of neglect, they have, by the protracted operation of disuse weighing upon them and retarding their production for generations, become, as one of its effects, so defective and incomplete as to approach the condition of rudimentary organs. The active employment of an organ makes demands upon the nutritive powers for its growth and strength which is responded to by increased nutrition and added strength by those powers, and use gives an impetus to transmission which causes that organ to be well and strongly developed in the next generation. But disuse furnishes no stimulus to either nutrition or transmission, and the organ so affected is produced as a tradition due to the stimulus of past generations, when it was in active employment; but, owing to its disuse in recent generations, it is weak and illformed; it has not the necessary stimulus either for development or strength. Not only that, but an organ that has fallen into disuse and neglect becomes deleterious and injurious, and is, by a natural process of economy of growth, deprived of nutrition, that it may be suppressed and aborted. The remains of many such organs linger in the organization of man as rudiments of former organs which served a useful purpose under different modes of life; but the conditions of life being changed by new environments, these organs became useless, then injurious, and were gradually suppressed by the law of economy of growth.
Such organs the teeth in man are rapidly becoming. Indeed the wisdom teeth have already arrived at that stage in their career of suppression when they are little more than rudiments. They are never well organized, are often rudimentary in form, and often totally absent, either through failure to erupt or to develop. The wisdom tooth in the race is departing, and we are the cotemporary witnesses of the act of its abolition as a useless organ. Will the second molar follow it in time, and then the other teeth in more or less regular succession? We do not know. We only speak of what we observe. But we do know that all the teeth are defective in form and deficient in structure in most of the individuals of the luxurious races of man; that they require the constant care of a skillful and costly corps of professional men to preserve them at all, and that the diseases which are causing their destruction result from the effects, more or less direct, of defectiveness of organization due to disuse. But this branch of the subject is too vast to enter upon at this time.
The effects of disuse are rated as One of many pernicious influences which cause defective formation through inheritance. When so much dental defectiveness prevails it becomes us to estimate all forces likely to contribute to it, and the greatest of these we believe to be the malign power that, through heredity, presides over formation. If heredity is strong for normal structure; if physiological perfection is exactness of detail in the copying of the type, then, indeed* must heredity be strong in its influences where there is present any evil power which detracts from or interferes with normal development. If it transmits evil as readily as good,—and there is no question of this,—then must we charge it with the responsibility of being the medium through which much dental defectiveness is brought down to us. If it would transmit only the good, disease would soon be eliminated in the species, but unfortunately health, unlike some diseases, is not always transmitted and is never contagious.
A PA0T0E IN T00TH-PKESEKVATI0N.
BY C. N. PEIRCE, D.D.S., PHILADELPHIA, PA.
[An Address before the New Jersey State Dental Society, July 16, 1885.]
Mr. President and Gentlemen of the New Jersey State Dental Society: I fear that I am trespassing a little upon your good nature in coming before you without a written essay, but my time has been so limited in preparing for this occasion that the very best I could do was to arrange some thoughts and give them to you as well as practicable under the circumstances. In answer to an inquiry from my friend, Dr. Palmer, as to the title of my subject, I wrote him that it would be "A Factor in Dental Caries," but I subsequently changed it to the more intelligable one announced by your president to-day, "A Factor in Tooth-Preservation;" and I am under obligations to my friend, Dr. Atkinson, for opening the way for me last last evening, by his opportune remarks on the prophylactic influence of function, because that has been really the subject of my thoughts for the last three months, and was the point I endeavored to make in my remarks a month ago on the comparative anatomy of the teeth before the New England and Connecticut Valley Dental Associations at Worcester, Mass. What I shall endeavor to do now is simply to elaborate the remarks of Dr. Atkinson last evening, and confirm them with some illustrations of development of the teeth of the lower animals, hoping with these to leave an impression upon your minds which will not soon be erased.
First, a word or two upon dental caries. If you ask the numerous teachers in this country to formulate an answer to the inquiry, What is dental caries ? they will probably tell you that it is molecular death and disintegration of the tooth-tissue. We will not stop now to discuss the correctness of this answer. It is one that has been almost universally given to classes in dental schools, as well as in the meetings of dental societies. Molecular disintegration we have, but that this is preceded by death is doubtful indeed, and this one point in this pathological phenomenon is well worthy of consideration by any dental society. Many theories have been advanced by thoughtful men regarding the cause of this pathological condition designated dental caries. First, it was held that it was wholly due to chemical action; and there are men to-day who take the ground that that is the only cause. They claim that there is some solvent (an acid) in the mouth which comes in contact with the tissues of the teeth, breaking up the continuity of the structures and dissolving out the lime-salts or inorganic portion. Then, there are others who take the other extreme, and assert that dental caries is the result of vital action; that through some deficiency in nutrition and other abnormal systemic conditions there is a loss of continuity between the hard or inorganic and the soft or organic structures, and in consequence of that loss of continuity the dissolution of the teeth naturally follows. Another theory is that the cause of decay is chemico-vital; that perverted or imperfect nutrition during the calcification of the hard tissues results in abnormality, both as to quantity and quality, this being a predisposing cause of caries, the teeth then becoming an easy prey of some solvent in the mouth, which is assumed to be an acid. We have, also, within the last few years, had advanced by our friends abroad as well as at home what is termed the parasitic theory,—that decay is produced by certain low forms of vegetable or animal organisms in the mouth, some of which, by their roots or mycelium, burrow into the tissues of the teeth and leave them in a condition to readily break down, and that other organisms, by virtue of their contact with the oxygen of the atmosphere, eliminate an acid, and in that way we have a solvent produced by these which disintegrates the tooth-structure.- These latter theories entirely overlook the fact that many of these organisms are merely messmates; that they live in the mouth by virtue of the pabulum on which we also live, and are not parasites at all,—living on the remains of our food, on dead and refuse material, and not interfering with the live tissues in any way. Then we have still another theory, that advanced by Dr. Bridgman in England, called the electrical theory; that it is by reason of a want of correspondence in the electrical conditions of the organic and the inorganic structures that the teeth are broken down.
The fault I find with all of these theories is, not that they, or most of them, have not some grain of truth in them sufficient to warrant their advancement as elements in the problem of decay, but that it is claimed by their several and special advocates that they are the element. In attributing dental caries to any one of these supposed causes, we seem to entirely ignore the laws governing the development and nutrition of structures.
When a tooth is developed, it is in accordance or in correspondence with law, like other tissues. Its morphology, its structural arrangement, its density, its size, its location, ail are subservient to its function and nutrition. If function is delegated to some other part or organ, nutrition is likewise diverted. Health and normality in any and every respect must be preceded by normal or natural exercise of function. The arrangement of the tissues, the size, shape, and density of the teeth are not matters of whim or accident, but are due to the natural result of the mechanical forces that have been brought to bear upon them; they are the result of the degree and direction of force that has been exerted upon them by the food habit through many successive generations; they are in exact correspondence with the amount and direction of force that has been and is exercised in the preparation of the food, or in the exact ratio of the amount of resistance offered by the trituration of the food upon which the animal lives. This brings tooth-formation down to the single point of food habit, and in my estimation tooth-formation and nutrition are the result of food habit.
In the treatment of the mouths of many children we see unmistakable evidence of this absence of function. We risk nothing in saying to the mother or guardian of many of these patients that