The mouth and the teeth

Front matter

SSI

THE

Teeth

Contents

CHAPTER

I. Introductory 9

II. The Mouth !3

Chapter I. Introductory

HE mouth is not only the most expressive and

1 characteristic, but it is also the most important, of all the features. No other portion of the human organism is of such complex structure, and no other has such diversified functions to perform.

The preservation of the health of the mouth is essential to the general well-being. Disease of the body involves an unhealthy condition of the mouth, and is manifested by perceptible changes in the tongue, gums, lips, and mucous membrane. On the other hand, it is reasonable to conclude that an unhealthy condition of the mouth will act prejudicially to the general health of the organism. The breath, if made offensive by a diseased state of the mouth or teeth, cannot be wholesome when inhaled into the lungs and brought into contact with those delicate structures, the air-cells ; nor can it exercise the best

IO THE MOUTH AND THE TEETH.

influence upon the blood, which depends in great measure for its quality upon the purity of the air supplied to the lungs. Moreover, it is very undesirable to transmit offensive matters into the stomach, as vitiated saliva or food polluted by noxious secretions.

The value of a good set of teeth — a complete and perfect "denture" — is not to be computed, if only the service of dividing and masticating the food be considered ; mastication being the first step in a series of processes by which the food is transformed into nourishment adapted to the needs of the system. When to this consideration we add their importance in assisting vocalization — distinctness of utterance in speech and song — and the necessity for their preservation in order to maintain the natural symmetry of the features, it would appear to be a positive duty that every one should study to avoid the causes which tend to the premature destruction of the teeth.

There is abundant reason for an effort to awaken a general interest in the prevention and arrest of the process of decay in human teeth. That there has been a progressive deterioration in the quality of the dental outfit of mankind through successive generations, is claimed by many observing practitioners of dentistry. There can be no doubt that dental caries is on the increase — is well-nigh universal; while recession of the gums and absorption of the support-

I I ing alveolar processes are fearfully prevalent, even in the mouths of the young. If these tendencies are to be successfully combated, it must be not alone nor chiefly through the manipulative skill of dental operators, but through a better appreciation by the people of the causes of the deterioration and of the means by which it may be counteracted. The importance of a wide diffusion of information in regard to these matters has been recognized by every intelligent dentist. It is high time that more attention be given to the subject.

Matters of much less importance to personal appearance, of vastly less account to individual comfort, and beyond all question of smaller moment to health and life, are made the subjects of constant study and care ; while the amount of information possessed by the public in this direction is lamentably small, and much of that is erroneous. Many otherwise intelligent people are sadly deficient in a proper comprehension of this subject. There are no other organs of the body which are not more appreciated than the teeth, and yet there are none the neglect of which entails more serious results.

It is estimated that twenty millions of teeth are annually sacrificed in the United States. The criminal neglect thus exhibited involves not only this waste of teeth, but is the fruitful cause of abscesses, facial deformities, neuralgias, dyspepsias, headaches,

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eye and ear troubles, and other morbid conditions. Protracted derangements of sight, of hearing, and of the general health not infrequently have their unsuspected origin in the mouth.

For these reasons, the facts relating to the formation, structure, development, eruption, character, functions, and diseases of the teeth, and to the preservation of their health and that of the associated parts, should be better and more generally understood.

In the hope of awakening interest and stimulating thought with reference to the intelligent care of the mouth this monograph has been prepared.

Chapter II. The Mouth

THE mouth is the organ of taste, of speech, of song, of mastication, and of insalivation ; the avenue for the entrance of the food and drink essential to life, and the channel through which passes much of the air which is inhaled, as well as that which is expired. The same membrane which lines its cavity is continued throughout the nose, the throat, the stomach, and the intestinal canal; throughout the larynx, the windpipe, the bronchial tubes, and the lungs. It is thus closely related to the functions of digestion and respiration, while by open passages direct communication is maintained with the eyes, ears, and nose,, and by the nerves, with which it is abundantly supplied, with every part of the body.

The mouth is made up of the lips, cheeks, upper and lower jaws, with their alveolar processes ; the hard and the soft palate, the tongue, salivary and mucous glands, mucous membrane, gums, and teeth. It is a wonderful combination of bones, muscles, arteries, veins, nerves, glands, membranes, and a cu- 2 13 rious structure of hard and soft tissues constituting the teeth. These, like all other parts of the body, depend upon the general system for their development and nourishment.

The lips, which are fleshy folds surrounding the orifice of the mouth, and the cheeks, with which they are continuous, forming the sides of the face and the boundaries of the mouth, are composed of true skin externally and mucous membrane internally, between which are the muscles which produce their movements ; also, blood-vessels, nerves, and small bodies called mucous glands, having ducts or tubes opening by minute orifices upon the inner or mucous surfaces. These glands secrete a fluid which helps to lubricate the mouth. (By the terms ' ' secrete ' ' and ' ' secretion, ' ' as here used, is meant a process by which various matters derived from the blood are collected and discharged at particular points in order afterwards to be employed for special purposes in the economy.)

The palate or roof of the mouth, well shown in the Frontispiece, consists of two portions — the hard palate in front, and the soft palate (called the velum) behind it, terminating in a central pendulous structure — the uvula, commonly but erroneously called the palate. The hard palate, which is a bony plate, is covered by a dense tissue called the periosteum {around a bone). The soft palate is a soft, movable fold or curtain of mucous membrane, inclosing muscular fibres. It serves important purposes in the mechanism of the mouth, assisting materially in the articulation of sound, in the act of swallowing, and, conjointly with certain muscles connected with it and with the tongue and pharynx, preventing the passage of food into the nose, which opens into the upper part of the throat above the soft palate.

The tongue is a muscular body lying on the floor of the mouth within the lower dental arch. It is covered by mucous membrane, beneath which are mucous glands having orifices opening upon its surface. It is the organ of the special sense of taste, and presides over the processes of mastication and swallowing. The exquisite sensibilities of touch and taste residing in the tongue are important aids in mastication. Its sense of taste informs us of the qualities of the food, and its sense of touch recognizes its physical condition — consistency, size, form, and when it has been sufficiently masticated. By its muscular structure it collects and moves the food from one side of the mouth to the other, and, with the aid of the lips and cheeks, keeps it between the masticating surfaces of the teeth. When the food is in a sufficiently softened condition, the tongue collects it upon its upper surface and passes it backward into the pharynx — a funnel-shaped canal situated on the middle line in front of the spinal column, between the base of the skull and the esophagus or gullet — which serves as a common origin for the digestive and respiratory tracts, giving passage to the air during respiration and to the food at the time of deglutition or swallowing. By virtue of its complicated muscular structure the tongue is also capable of the great variety of movements essential to suction and to speech. At the base of the tongue is a cartilaginous oval or triangular flap called the epiglottis, its apex attached, the other and larger part free. Its special use seems to be to cover the glottis (an aperture in the larynx or the apparatus of voice, situated at the top of the trachea or windpipe), and thus prevent the passage of food into the air-tubes. The tongue sympathizes with all derangements of the general system — especially with those of the alimentary canal. As an index of the state of the general system, it affords, doubtless, more varied information than any other single means of judgment. Its bulk, color, dryness or moisture ; the character of its surface, of its coatings, and of its movements show to the skilled observer the degree, progress, and stage of systemic derangement. The tongue is liable to a variety of local diseases and injuries. Among the latter, ulcers, sometimes very serious, are caused by the persistent irritation of the jagged edge of a broken or carious tooth or a projecting root. Similar effects from like causes are also produced upon the cheeks. Whenever such sources

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of irritation are recognized, they should be promptly corrected.

Opening upon the mucous surfaces of the mouth are the excretory, or discharging ducts or tubes of three pairs of salivary glands — the parotid, the submaxillary, and the sub-lingual. The parotid glands (so named from two Greek words signifying "ear" and "near" — near the ear) are the largest of the three pairs, weighing from a half ounce to an ounce each. They are situated upon the sides of the face immediately below and in front of the external ear. Their ducts lead to outlets, which can usually be readily seen, upon the inner surfaces of the cheeks opposite the second molar teeth of the upper jaw. The glands called submaxillary {beneath the jaw) are situated below the lower jaw, and have their outlets on either side of the middle line beneath the tongue. The glands called sublingual {beneath the tongue) are situated beneath the mucous membrane of the floor of the mouth, their ducts — from eight to twenty in number — opening under the tongue.

The secretions or products of the mucous and salivary glands differ in character as do those of the latter from one another. They differ also in the quantity of fluid which they discharge, and as to the causes which excite their action. The parotids are called the masticatory glands, because they are not found generally except in animals which are furnished with 2* B iS THE MOUTH AND THE TEETH.

grinding or masticating teeth. A larger quantity of secretion takes place from them than from either of the other salivary glands, especially during the movements of the jaw in eating, and particularly on that side of the mouth on which the chewing is being done. When thus stimulated to action they pour out an abundant secretion, which becomes incorporated with the food during mastication, uniting dry particles into a coherent mass. These glands are also active during the movements of the jaw caused by continuous speaking. The parotid gland is the seat of the inflammation in the disease called mumps. The submaxillary glands are more immediately concerned in the sense of taste. They are found only in those animals which subsist on food which appeals to that sense, being almost entirely absent in the grain-eating birds. They are excited to special activity by the introduction into the mouth of sapid (tasteful) substances. The sublingual glands are particularly stimulated by the act of swallowing.

The secretion from the parotid glands is a clear and limpid fluid ; that from the submaxillary glands is clear, but thick and viscid; that from the sublingual is thick, glutinous, and ropy. All are slightly alkaline.

The function of the parotid glands is supposed to be to moisten the food, and thus, by the aid of mastication, to give it the requisite consistency and

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convert it into a homogeneous mass; that of the submaxillary, to promote the solution of soluble substances, in order that they may make an impression upon the nerves of taste ; that of the sublingual, to lubricate the food, and thus facilitate its passage into the pharynx.

The secretion of the mucous glands of the lips, cheeks, gums, tongue, floor and roof of the mouth, is a more or less viscid, transparent, or somewhat turbid fluid, generally slightly acid.

These different and distinct secretions all unite to form the fluid ordinarily termed saliva. This mixed fluid is in health inodorous, insipid, slightly viscid, and generally alkaline, but so slightly as to be detected only by chemical tests; it is composed of water holding animal and various earthy matters in solution. It is this mixed fluid by which the cavity of the mouth is kept constantly moistened — a necessity, if for nothing else, that the parts may be in proper condition for the purposes of speech. Another important office of the saliva is its dissolving effect upon soluble substances introduced into the mouth, thus bringing them into contact with the nerves of taste, which is essential to the enjoyment of food. It also lubricates the surfaces of the mouth and teeth, and thus prevents the adhesion of food to them. In consequence of its glutinous and frothy character, it imprisons innumerable globules of air along with the

THE MOUTH AND THE TEETH.

food with which it becomes mixed, thus tending greatly to favor the subsequent solution of the latter by the fluids of the stomach. It also coats the masses of food when ready for swallowing, thus favoring their easy transmission to the stomach. To these varied offices must be added another — a certain chemical effect upon the food (changing starch and cane or crystallizable sugar into grape or uncrystallizable sugar), which is the first step in the series of chemical processes (digestion) by which the food is prepared for the uses of the economy. That the action of the saliva upon starchy foods is of great importance becomes apparent when it is understood that starch as such is insoluble, and would therefore be not only valueless as nutriment, but a positive burden in the alimentary tract, while the sugar into which it is converted by the saliva is readily soluble and nutritious. Still another, and a curious as well as important, result of the slight but constant discharge from the mucous and salivary glands, is its direct influence upon the sense of hearing. Its presence, even when unnoticed and during sleep, causes the act of swallowing at short intervals, which effects the opening of the Eustachian tube (a passage leading from the ear to the throat) and permits the renewal of air in the cavity of the middle ear — a condition essential to the maintenance of perfect hearing. A most interesting provision is shown in the fact that a nerve (the chorda tympani),

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whose function it is to excite the secretion of saliva, passes through the middle ear, and thus establishes a direct relation between the sense of hearing and the salivary glands, so that certain discordant sounds cause an abundant secretion of saliva, the swallowing of which serves by the constant renewal of air to protect the ear from irritation, as before explained. As a result of other curious nervous connections, the salivary secretion, so essential, as has been shown, to the functions of speech and of hearing, is also stimulated by the sight, smell, or even the thought "of savory food. The quantity of saliva discharged into the mouth varies with the condition of the food introduced, being abundant in proportion to the dryness of the food. Its secretion varies, also, with the varying health of the body. It is much diminished and sometimes almost suspended by fear, anxiety, or other depressing emotions. In diseased conditions of the general system its character is variously modified, becoming acid or excessively alkaline ; acting upon the soft tissues of the mouth, causing ulcerations of the mucous membrane and recession of the gums ; acting upon the hard tissues, causing their disintegration.

Diseased conditions, therefore, of the general system influence unfavorably the health of the mouth, and notably of the dental organism. In febrile conditions there is more or less suppression of

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the secretions of the salivary glands, and often a greatly increased and vitiated secretion from the mucous glands, which because of its viscidity collects and thickens about the teeth, entangling with it various extraneous matters and ddbris found in the mouth, its accumulation being favored by the fact that during illness the usual cleansing of the mouth and teeth by thorough rinsing and the brush is neglected ; and, as ordinarily at such times there is but slight demand for food, and especially for food requiring mastication, the deposit is left undisturbed and soon undergoes fermentation, becoming strongly acid. Thus it often happens that during a severe illness very serious inroads are made upon the integrity of the structures of the teeth, which are attributed frequently and erroneously to the medicine taken. It follows, therefore, that during sickness these untoward influences should be combated with more than ordinary care. Such care is suggested not only by the rapidly destructive effects of the vitiated salivary and mucous secretions upon the teeth, but by the vicious circle thus established ; the products of the deranged action of these glands not only creating local mischief, but causing an irritation of the mucous membrane of the alimentary tract, and by this means, as well as by their presence, resulting in an impairment of the digestive fluids. The exhalations from a diseased mouth may also produce an injurious effect upon the bron-

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chial tubes and lungs, and through them upon the blood.

Sometimes, and owing to various causes, such as wounds, burns, abscesses, or dead and ulcerated roots remaining in the mouth, the continuity of the ducts or tubes of the salivary glands is destroyed, and false openings upon the cheek, chin, or throat result. In such cases the secretion is discharged through the false opening, and poured over the external parts. Sometimes also, from similar or other causes, these ducts become obstructed, in which case the secretion, continuing and finding no means of escape, distends the tissues, and forms a soft tumor called a "ranula," generally upon the lip, or upon the floor of the mouth beneath the tongue. Such conditions require, of course, surgical interference for their cure.

The gum is a thin, compact, tough, elastic, fibrous tissue enveloping the alveolar processes, and surrounding the teeth at their necks. It is continuous with the mucous membrane which lines the inside of the lips and cheeks and the floor and roof of the mouth, and at the necks of the teeth with the membrane (called the pericementum ) which lines their sockets and also invests their roots. In a healthy condition the gum has comparatively little sensibility, bearing without irritation the friction to which it is subjected in mastication. This insensibility is also evidenced by the immunity from pain when the gums are used

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in chewing, by the child before the eruption of teeth and by those who have suffered the loss of their teeth. Fig. I. shows one-half of the upper jaw. The called the antrum (a cave) ; the floor of which is sometimes perforated by the roots of the teeth if they are unusually long. The upper jaw is tightly wedged in by the outer bones of the face, and has no power of motion — the teeth of the upper jaw presenting a fixed surface, against which those of the lower are brought to bear in mastication. That part of the upper jaw which carries the incisor teeth has a separate centre of development, and in early intra-uterine life in man is a separate bone called the "incisive" or "intermaxillary" bone. It remains a separate bone in most adult mammals, but is generally closed

Fig. I.

upper jaw — called the superior maxilla — is formed by two bones united in the central, or median, line of the face. Each of these bones contributes to the formation of three cavities — the roof of the mouth, the outer wall and floor of the nose, and the floor of the socket (the orbit) of the eye.

Each upper jawbone has a triangular - shaped cavity

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in man. Occasionally the fissure between this bone and the upper jaw is not closed on one side or both. This deformity is called "cleft-palate." When the fissure is in the lip only, it is called " hare-lip," from its resemblance to the grooved lip of the hare. The anatomical development explains why this is never in the middle line, but always on one side, or in case of "double hare-lip" on both- Hare-lip often exists alone, but where the palate is cleft the lip is apt to be so too, though this is not always the case.

The lower jaw — called the inferior maxilla, or mandible (shown in Fig. II.) — is the largest and strongest bone of the face. It consists of a curved horizontal portion (the body), and two upright portions called the rami (singular, ramus — a branch).

In infancy these upright portions form an obtuse angle with the horizontal portion ; in the adult, almost a right angle, the angle becoming again obtuse in old age. It is these modifications in the lower jaw which to a large degree give the characteristic forms to the face in infancy, in maturity, and in old age. Fig. III. shows the 3

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relative forms of the lower jaw at these three periods of life. A canal of considerable size runs through the body of the lower jaw, giving space for the passage of

blood-vessels and nerves for the supply of the teeth.

These pass out through openings beneath the bicuspid teeth on either side (shown in Fig.

III.), and are distributed to the chin, flower lip, and gum W of the lower jaw.

The closure of the jaws is effected by four pairs of strong muscles — two attached to the outer and two to the inner side of the rami of the lower jaw. The peculiar articulation or jointing of the lower jaw in man allows of a great variety of movements, in keeping with the diversified character of his food, as well as with other and varied uses.

The alveolar processes consist of two plates of bone, an outer and an inner, forming borders to the jaws

III. The Mouth

and supports to the gums. These are connected by transverse plates, dividing the space into numerous cavities which form the sockets of the teeth. An upper jaw from which the teeth have been recently extracted is illustrated in Fig.

IV. The edges of the alveolar processes dip down between the teeth, so that their margin presents a festooned appearance. At the boit om of each socket there is an opening to admit the passage of the blood-vessels and nerves of the teeth. After the loss of the teeth the alveolar processes are absorbed and disappear ; so that the roof of the mouth generally loses its arched appearance and becomes nearly flat, and the' lower jaw assumes the peculiar form characteristic of old age. When the processes are carious or have been absorbed, the teeth become loose and have to be removed.

The pericementum is a tough, fibrous tissue which invests the roots of the teeth and lines their sockets. The cementum or outer layer of the roots receives its nourishment through it. It is owing to this fact

Fig. IV.

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that after the death of its pulp a tooth still possesses a certain amount of vitality, and is therefore retained in its socket, — frequently for years, — which would not be the case if it did not hold a vital relation to the jaw. The pericementum, moreover, while attaching the teeth firmly to their sockets, serves as an elastic pad or cushion, preventing to a considerable extent the damaging effects upon the teeth which would otherwise be experienced from accidental blows or other violence, as well as from the thoughtless and unnecessary voluntary injury by efforts to crack nuts, untie knots, and other like foolish procedures.

The movements of the masticatory apparatus of the human being are more complex and more varied than of any other animal, resembling those of both the flesh-eating and grazing species, showing, as does also the comparative anatomy of the teeth, that the human race is adapted to live on a mixed diet. The process of mastication, which is one of very great importance, consists in dividing and comminuting the food by the teeth, reducing it to a state of complete disintegration, which is a necessary condition for its insalivation — the mixture of the food with the fluids of the mouth — and subsequently for the action of the digestive fluids of the intestinal tract. Food is more or less easily digested in proportion as it has undergone thorough mastication. To appreciate this fact, it must be remembered that stomach digestion

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is chiefly chemical. It will, therefore, be readily understood that the more finely the food is divided before it is brought into contact with the digestive fluids, the larger will be the surface exposed to their action, and consequently the more easily will it beattacked and the more speedily will it be dissolved, just as any solid is more readily dissolved if first ground to a powder. It is not easy to overrate the importance to the digestive process of a thorough preliminary mastication. Masses of food introduced into the stomach may remain for a long time — days, even weeks — undissolved, disturbing its functions and undergoing fermentative and putrefactive changes, caused by warmth and moisture, creating gases and acids, and, if not expelled by vomiting, becoming a source of irritation and disturbance in its course throughout the whole length of the intestinal tract. In fact, if mastication is not properly performed, the subsequent process of digestion is likely to be d'eranged. There is no more common cause of indigestion or dyspepsia than imperfect mastication ; no more fruitful source of headache, neuralgia, nausea, heartburn, flatulence, cramp, diarrhea, dysentery, and various other disorders. Indigestion, largely induced by imperfect mastication, is the prevailing malady of civilized life — probably the occasion of more disorders than can be traced to any other one cause. The result is, of course, the same, whether the fault 3* lies in the haste with which the food is swallowed without proper mastication, or whether the masticatory apparatus be defective. There is no question that in many cases an increase of longevity is fairly attributable to the improved facilities for mastication secured by proper attention to the natural teeth, or in case of their loss by the use of artificial teeth. It should be remembered that when, owing to imperfect mastication, the food is passed into the stomach in a crude state, and therefore unfit for digestion, the teeth themselves suffer by reason of the resulting vitiation of the digestive fluids, which by regurgitation exercise an injurious influence upon tooth structure. Another argument in favor of thorough mastication is to be found in its directly beneficial effects upon the teeth ; for, although these organs serve the purposes of vocalization, ornamentation, etc., there can be no doubt that their chief office is the mastication of food. Neither can there be any doubt that the neglect to exercise this special function impairs their vitality, as the disuse of any organ, sense, or structure of the body results in its degeneration and gradual loss of power. A tooth having lost its antagonist — that is, the tooth which opposed it in mastication — will generally elongate or rise beyond the line of its fellows, as though in search of an opposing force ; from which it appears that the pressure exerted upon the teeth during use in mastication is essential to their retention

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in a healthy condition in the jaws. The teeth are strengthened in their attachments and in their vital relations to the jaws by exercise. There is, therefore, in the case of teeth not properly exercised, a lessened nutritive supply, both through the pulp and through the membrane which gives vitality to the roots. Nor can the use of the brush and powder compensate for the important service which the habitual, thorough mastication of food accomplishes in securing cleanliness of the surfaces of the teeth ; the trituration of food effecting that which one is utterly unable to do with the brush. In addition to the offices of the teeth in ornamentation, in their mechanical functions, in their relation to the articulation and modulation of sound, they serve another and important purpose as conservators of the lungs and the organs of voice, preventing the breath in the act of speaking from being exhausted too rapidly. Persons who have lost their teeth find continued speaking, as in conversation, difficult, because each utterance empties the mouth of air, and more rapid breathing is required to keep up the supply. This effort soon becomes fatiguing ; causes a feeling of weakness and distress, and is apt to produce an irritation of the larynx and a chronic cough. The cough in turn increases the irritation, and thus a vicious circle is established which may involve the bronchial tubes and the lungs, and result in serious discomfort and even in dangerous complications.