The prevention of dental caries and oral sepsis 1924

Front matter

a z :

Pie sPREVENTION OF DENTAL Corie St AND,ORAL SEPSIS

THE PREVENTION OF MeN rAlL, CARIES AND “ORAL SEPSIS

Preface To: First Eve

WHEN this work was commenced nearly six years ago, a “‘ plan of campaign ’”’ was drawn up to which it was decided to adhere, and to continue the work until the whole field had been covered, or at least investigated to some extent. It was further decided to publish nothing until the chain of evidence was more or less complete. This has obvious disadvantages, one of which is the length to which the subject has grown, and another the fact that in several matters the results have been forestalled in publication by others working along similar lines. The work, like all work, is still incomplete, but sufficiently important conclusions have been reached, I think, to justify publication.

The present volume is an amplified form of lectures which have been delivered in this University to Medical Practitioners and to Medical and Dental Students.

be BP.

November, 1911.

Vili

CHAPTER i II. Ti, EV; Vi

Wilt,

WANS VIII.

12,

XVI.

XVII.

XVIII.

XIX,

XxX.

XXI.

HISTORICAL = = = = = = = THE INCIDENCE OF DENTAL CARIES - = = = PATHOLOGY OF DENTAL CARIES = = = 2 THE ,.ANATOMY AND PHYSIOLOGY OF MASTICATION = a FACTORS OTHER THAN DIET INFLUENCING THE DISPOSITION OF

THE TEETH AND LOWERING THEIR RESISTANCE TO CARIES THE ENAMEL SURFACE: ITS PHYSICAL PROPERTIES AND

POWERS OF RESISTANCE S = =; = ms THE ENAMEL SURFACE: THE ODONTOGRAPH - = = THE ENAMEL SURFACE: ORIGIN AND SIGNIFICANCE OF THE

IMBRICATION LINES - 5 = = = =

THE ENAMEL SURFACE: DEPARTURES FROM THE ‘‘ NORMAL ”’

STRUCTURE, AND THEIR PATHOLOGICAL SIGNIFICANCE PHYSICAL PROPERTIES OF THE ENAMEL SURFACE = =

- CHEMICAL COMPOSITION OF ENAMEL - = = S

THE SALIVA = = = = = = = THYROID INSUFFICIENCY AND DENTAL CARIES = = THE REDUCTION OF THE CARBOHYDRATE FACTOR BY PHYSIO-

LOGICAL MEANS - = = = = = THE REDUCTION OF THE BACTERIAL AND CARBOHYDRATE

FACTORS BY ARTIFICIAL MEANS - = = = THE INOCULATION OF THE MOUTH WITH OTHER ORGANISMS ALIMENTARY SECRETIONS CONSIDERED AS A WHOLE - - THE DIET OF RACES RELATIVELY IMMUNE TO CARIES = THE DIETARIES OF MODERN CIVILIZATION: THEIR ERRORS

AND CORRECTION = = = = = = EDUCATIONAL MEASURES = = = = S THE NEED FOR SPECIAL LEGISLATION = = Ga

LIST OF AUTHORITIES - = = = : ~

PAGE

Dey i)

302 315 323

329 339

Introduction

NEARLY one hundred years ago Fox wrote, as regards the prevention of dental caries, that “‘ this delightful secret, although it is pretended to in the advertisement of every quack, we can only expect to acquire when the philosopher’s stone and the grand panacea have been obtained.”’ If this somewhat prophetic utterance is to be fulfilled, there would not seem to be any reasonable hope that the prevention of dental caries can yet be regarded as within the limits of practicability.

There is no doubt, though, that the disease has become much more serious in its proportions since Fox’s time, and the attitude of fatalism towards it is no longer justifiable, and is not consonant with our modern knowledge of pathology and the means of immunity.

The general plan of the present work has been to inquire into past methods of the preventive treatment of dental caries, to compare these with present methods, and to collect data as to the incidence of caries in various nations and in various stages of civilization.

A critical examination of the powers of passive resistance on the part of the teeth has been carried out, together with an investigation of the forces of active natural protection, and a consideration of the means whereby both passive and active resistance might be fortified against the attacks of the oxygenetic or acid-forming forces as constituted in the combination of carbohydrates with organisms, and a further consideration

X1 xii INTRODUCTION of how these latter forces might be weakened or destroyed entirely.

The dietaries of “natural”? and civilized peoples have been examined in detail, and inference from the one and corrections for the other have been made.

Finally, educational and legislative methods of dealing with the problem have been suggested.

Pero e RE VENTION OF DENTAL CARIES AND ORAL SEPSIS

CHAPTER I AIS PORICAL

Tue records of the practice of dentistry chiefly by medical means date back in the case of the Egyptians to somewhere about three thousand years before the Christian era. Even at this early period we have some evidence that methods were in vogue for the prevention of dental disease. For instance, the ““Ebers”’ papyrus, probably compiled gradually from 3000 B.C. to 1550 B.C., contains prescriptions for “ strengthening the teeth,”’ of which the following is an example:

Powder of flint stones mi »s nen Parte Green lead 45 38 as Sn Pale Honey - .. wie = bets Dale aueal,

To be rubbed on the teeth.

This might now be classified as an antiseptic and abrasive tooth-paste.

Records of Chinese medicine written about the same time as the above, and translated by Dabry, give prescriptions for whitening the teeth, and for a powder to prevent the progress of caries, the oe ingredients of which were musk, salt, and “ Tsang-eul-tsee.’

The writings of the early Greeks contain very little reference to dental hygiene, and as far as caries is concerned their attention seems to have been confined to relieving pain and hygiene of the gums; yet how near Aristotle came to the modern conception of the cause of caries may be judged from this sentence taken from his book on ‘‘ Problems ”’

Z DENTAL CARIES AND'ORAL SEPSIS

‘“Why do figs, when they are soft and sweet, produce damage to the teeth? Perhaps because the viscous softness of the fig causes small particles to adhere to the gums and insinuate themselves into the dental interstices, where they very easily become the cause of putrefactive processes. ”’

The only allusion made by Celsus to dental prophylaxis is that, “after rising, if it be not winter, the mouth should be rinsed with a quantity of fresh water.’”’ To be avoided in winter probably because of the teaching of Hippocrates, that * Cold is.:the enemy of the teeth: *

Pliny states that the ashes of the head of a hare are a useful dentifrice, and if spikenard be added it will lessen the bad smell of the mouth. He also recommends burnt eggshells as a good tooth-powder.

Toothpicks of bone and metal seem to have been used commonly by the Romans, And it is stated by T. Wright* that | Saxon women carried toothpicks of ivory in their chatelaines.

Messalina, the wife of the Emperor Claudius, we are told, used a dentifrice composed of calcined stag’s horn, sal-ammontiac, and mastich of Chios. And several writers of this time mention | that old (ammontacal) urine was popularly used to preserve thesteeth:

Paul of Atgina, during the seventh century, gives the following rules for the preservation of the teeth: All tainted food to be avoided, and also all possibility of indigestion and frequent — vomitings; the use of very hard or glutinous food, or of such as may easily leave a residuum between the teeth—for example, — dried figs—and likewise very cold food and such as sets the teeth on edge, should also be avoided.

He advises, too, that hard things should never be broken — with the teeth, and that the latter be carefully cleaned, especially after the last meal of the day.

A representative of Arabian science, Avicenna, pointed out (about A.D. 1000) that very hard powders should be avoided, © as these were likely to damage the teeth, and he recommends the use of burnt hartshorn.

* “ The Celt, the Roman, and the Saxon ’’ (London, 1852).

HISTORICAL 3

During the fifteenth century, Giovanni of Arcoli drew up ten canons of dental hygiene which represented all the accepted teaching on the subject up to that time. The following is a brief summary of each canon:

1. Nothing must be eaten or done which would interfere with digestion.

2. Vomiting.

: icky food.

Sweet and sticky foo (aioe . Hard substances. eet ery . Food which sets the teeth on edge. | ae a ee | avoided.

. Food too hot or cold.

Teeeks.

Teeth to be cleaned with a piece of stick after every meal.

g. The mouth to be washed out afterwards with an aromatic decoction.

10. A dentifrice to be used last thing at night or early in the morning. —

It is with considerable surprise that one learns that so “advanced ’’ a code of oral hygiene was advocated, and we may presume practised, over four hundred years ago, and to the significance of this fact and to the inferences to be drawn therefrom we shall have occasion to refer later on.

A century later (1580) we find Foreest of Leyden condemning the consumption of sweetmeats as harmful to the teeth.

Passing on to the seventeenth century, we have a somewhat different line of preventive treatment advocated by Riviére (1589-1655), who advised that the teeth should be cleaned with a small stick immersed in a mixture of “ spiritus sulphuris aut vitrioli et mel rosatum,”’ or, if the teeth were very dirty, in the acid undiluted. Unfortunately, no records are given of the

OI Ao Eos results obtained by this somewhat heroic treatment.

Anton Nuck, a Dutch surgeon of the end of the seventeenth century, gives a formula for a tooth-powder much used in his time. The ingredients were powdered cuttle-fish, coral-powder, cream of tartar, Armenian bole, and powder of red roses.

During the next century we have Junker, Professor of Medicine at the University of Halle, recommending sage and also

4 DENTAL CARIES AND ORALSSEFPSIS common salt to be rubbed on the teeth to preserve them from caries. ;

From Pierre Fauchard’s book, “Le Chirurgien Dentiste,”’ published in 1728, we learn that tooth-brushes made of horsehair were in use at that time. He himself, however, condemns their use, and advises that the teeth should be cleaned with a fine sponge and tepid water to which has been added a fourth part of aqua vite. Instead of the sponge, the root of the marshmallow or lucerne might be used. He also gives lengthy and complicated prescriptions for mouth-washes, the chief ingredients of which seem to have been aromatics, alcohol, gums, and sweetening agents. The same author makes the following very decided statement: “ Little or no care as to the cleanliness of the teeth 1s the cause of all the maladies that destroy them.”

Bunon in 1748, in an excellent work, pointed out the necessity of attention to cleanliness of the milk-teeth, and correctly stated the influence of disease of the latter over the permanent teeth.

At the end of the eighteenth century two erroneous theories gained ground, and did much to negative the teaching of dental hygiene. The first of these, shared alike by Hunter and Bell, was that caries originated from within, and was influenced little, if at all, by external agencies. The second was that, in order to keep the teeth free from “ tartar,’’ it was desirable that coarse and gritty dentifrices should be used, and the resulting denudation of the enamel of the teeth did not at all matter, since it would be developed afresh (presumably like nails or hair).

This latter theory was, however, strenuously opposed by Thomas Berdmore, dentist to King George III., who performed experiments to show the destructive effect of these toothpowders.

Fox in 1814 stated that “ the principal means of preserving the teeth from decay consists in paying such a degree of attention to them in early hfe, during the period of the second dentition, as to allow the permanent teeth to acquire a. proper regularity; and when these circumstances have been observed, young persons should be urged to keep their teeth very clean, and the daily use of a tooth-brush, with water only, will in

LIS LOR GC Aus 5 most cases be quite sufficient. In addition to cleanliness, the habitual use of all kinds of food at a moderate temperature will most certainly prevent any disease from taking place, unless there be any radical defect in the teeth themselves.”

The methods adopted in America during the middle of the last century are given by Harris (1858) and Goddard (1854). The former, referring to experiments which had been done by Westcott ten years previously on the effect of various acids (including the acids produced by fermentation) on the teeth, states that he believes caries to be due more to acid oral secretions than to either acids introduced as condiments or tonics or formed by fermentation, and is of the opinion that if the functional operations of the body were properly performed, caries of the teeth would never occur. But he further states that it is necessary to artificially keep the teeth absolutely clean to avoid caries, and gives prescriptions for chalk dentifrices.

Goddard lays great stress upon perfect cleanliness and the frequent use of the toothpick and floss silk, and he gives various formule for antacid, detergent, and aromatic dentifrices.

Thus we are brought down to within measurable distance of the present time, and it will be convenient now to briefly summarize the methods we have already considered as having been used for the prevention of caries. We thus find that from the very earliest times—from the dawning of a higher civilization—soft sweet foodstuffs were recognized as a factor in the causation of dental disease (Aristotle); that very hard substances were to be avoided; that carbonate and phosphate of lime (as eggshells or burnt and powdered bones) were constantly prescribed as dentifrices; that alkaliesin the form of ammoniacal salts were also frequently used and prescribed; that acids of all sorts were to be avoided; that “‘ aromatics’’ were usually combined with dentifrices; that mechanical prophylaxis by means of toothpicks and frayed-out wood was in vogue from earliest times.

And all this before Pasteur had discovered the réle of micro- Organisms in the process of fermentation, or Lister had demonstrated the relationship of bacteria to disease and the method of eliminating them from diseased foci, or Miller had shown that caries of the teeth depends upon the formation of acids produced by the action of organisms on carbohydrate foodstuffs.

After these epoch-making discoveries, surely it would be thought that enormous strides would have been made in the preventive treatment of this particular disease; that the rationale of prophylaxis would have undergone a complete change; and that the incidence of caries would have been materially lessened. But has this been so °

On all counts we are bound to answer in the negative. True, for some time after the discovery of antiseptics, such drugs were | largely used in the mouth in order to endeavour to eliminate | the bacterial factor; but it was soon found that it was impossible to sterilize the oral cavity, or even to decrease appreciably the number of organisms present for even an hour, without using drugs in such strength as could not be tolerated, on account of their disagreeable taste and deleterious effect on the oral mucous - membrane. So that the routine use of antiseptics for this particular purpose has largely been given up.

What, then, are the means employed at the present time for the prevention of dental caries ?

Naturally, they are numerous, and it is impossible here to review them in detail; but the two principles generally recognized may be gleaned from at least two widely accepted authorities. The British Dental Association, in its pamphlet on the preservation of the teeth (1905), advocates—

1. The use of a small tooth-brush with stiff bristles, used after the last meal. |

2. The use of alkalies, such as soap, chalk, whiting, and also common salt.

3. The use of hard food.

Dr. Rose of Munich, like Giovanni of old, has drawn up a decalogue for the care of the teeth, in which he advocates—

1. Education of children and guardians in oral hygiene.

2. Mechanical cleansing of the teeth with a suitable brush or toothpick.

3. Avoidance of soft sweet foods.

HIS LORICAL Gi

4. Active mastication.

5. Alkaline and antiseptic dentifrices and mouth-washes.

Can it be possibly claimed that these measures differ in any fundamental principle from those which have been in the main practised ever since decay of the teeth has been treated by civilized man ?

Compare the teaching of the nineteenth and twentieth centuries with that of the fifteenth, and it will be seen to be almost identical, differing only in one respect—the advocacy of “ active mastication.”

In view of the fact that the incidence of dental caries has not decreased, but increased, in geometrical ratio almost, during the last 500 years, and in view of the fact that a similar line of preventive treatment has been systematically carried out for the last five centuries, what inference are we entitled to draw ?

A priovt, it would seem obvious that the treatment was radically wrong; that the judgment of time and experience alike condemned it, or at least some important part of it; and that such measures have proved futile to arrest the progress of what has become the most prevalent disease of civilized communities.

REFERENCES.

DENSHAM: Proceedings of the Royal Society of Medicine: Odontological mection, vol. ii., p..71.

HENDERSON: British Dental Journal, vol. xxix., pp. 350, 392, 497.

Harris: Principles and Practice of Dental Surgery, 1853.

GUERINI: History of Dentistry, 1909.

Fox: Natural History and Diseases of the Human Teeth, 1814.

GODDARD: Anatomy, Physiology, and Pathology, of the Human Teeth 1854.

“ify

GHAPIE Rs

THE INCIDENCE OF DENTAL CARIES

A. Racial.

IT is now universally admitted that dental caries is to a great extent a disease accompanying civilization, and that its numerical incidence is largely proportionate to the state of civilization to which a particular race has attained. Nevertheless, it will be useful here to briefly recapitulate the evidence which has given rise to this opinion.

Magitot,! examining the skulls in the Paris museums, found no caries of the teeth in the following races: Mexicans, Peruvians, Patagonians, aborigines of Australia, Madagascar, New Caledonia, the Malay Peninsula, or Java.

The now classical researches of J. R. Mummery? into this question shed considerable light on the subject. The results of his investigation into the prevalence of caries in existing primitive races may be classified as follows:

Percentage of Race. Skulls showing Carious Teeth.

Esquimaux I°4 Maoris ; 3°O Indians of N., W. ‘American Coast 3°9 Fiji Islanders .. : ey Northern Hindoos ne a ae 3G) North American Indians os Np 9°5 Eastern Polynesians a oe II°4 Southern Hindoos oA a ae 14°0 Zulus ae ca Ae 14°2 Sandwich Islanders os Se ae 19:0 Australians a a Ss RA 20°5 Bushmen zo Be ot 5 20:6 Negroes (slaves) Be Aer sh 20°8

Such statistics as these, although tabulated here in the apparent order of prevalence, cannot be accepted as repre- 8

LHE INCIDENCE OF DENTAL CARIES 9 senting exactly the true state of affairs, since the number of skulls of each race examined varied considerably, and was in no case very large; neither is the proportion of sound to carious teeth given. Also, of course, the ages of the skulls in each race probably varied considerably.

Again, some in each race may have been Paleolithic, some Neolithic, and some from quite recent times.

Nevertheless, in spite. of these possible soures of error, the tables may be taken, I think, as representing roughly the comparative prevalence of caries in the different races.

On comparing the incidence of caries in uncivilized races with that in civilized races of the present time, a vast difference is observed. The Physical Deterioration Committee reported in 1904 that “ there is no doubt that the teeth of the people have become much worse of late years, and in many parts of the country may now be described as very bad.”’ There can be no doubt that these words do not err on the side of exaggeration, as the following statistics will prove:

Percentage Number | of Persons Class of Person examined. of Persons having Investigators. examined. Carious Teeth.

English and Scotch school | 10,500 86:00 British Dental Asboys and girls sociation?

Residents of Baden and \ xt (98°75 -

Hamburg if \96-40 Rose* Halifax children es a 95°00 M.O.H. for Halifax? Leith school-children... 270 98-60 Robertson# Kettering children Sea, Bare 93°00 Layton® Birmingham school- 1,424 94°70 Richards®

children Cambridge Dental Clinic 1,403 96°50 Cunningham? School-children of North- | 19,725 95°00 Schleswig-Holstein

ern Germany Dental Association

These figures show a quite remarkable uniformity.

The British Dental Association’s report is, I believe, less recent than the others; so that this would tend to show that even in quite recent years the number of persons affected with Caries is increasing.

IO DENTAL CARIES AND ORAL SEPSIS.

It is also of interest and some importance to compare the increase in the prevalence of caries which has occurred in individual races. |

Mummery, investigating the number of Ancient British and Anglo-Saxon skulls showing carious teeth, gives the following — figures: Per Cent.

British skulls of the Stone Age showed carious teethin .. 2°9 British skulls of the Bronze Age showed carious teethin .. 21°8 Romano-British skulls showed carious teethin .. Sep 2 0 Anglo-Saxon skulls showed carious teeth in ae ee CSTO

Wright® examined the Driffield Collection of Skulls from the | barrows of the East Riding of Yorkshire. They belonged to the Bronze and Early Iron Ages. The percentage of actual caries was only 1:5. Wright, in the communication referred to, attributed ‘“‘ alveolar abscesses to caries,’ and this, of course, made the percentage much higher; but, from my own experience in the examination of skulls and teeth of uncivilized races, I think that such an inference was probably erroneous, since alveolar abscesses result in such races most commonly through an opening up of the pulp cavity due to excessive attrition, without the slightest trace of caries.

Anexamination of 562 skulls from long barrows gave 8 per cent. of caries, and 47 skulls from round barrows showed 21 per cent.

In an examination of 260 Maori skulls—all from an uncivilized age—I found carious teeth present in only two skulls, or 0-76 per cent.

By taking the average of Mummery’s and my own investigations, the incidence of caries in the Maori is found to be I-2 per cent. in a total of 326 skulls. This is lower even than the Esquimaux, and shows the Maori to have been the most immune race to caries, for which statistics are available.

Comparing these figures with those applicable to the present time, we find that the descendants of the Britons and Anglo- Saxons are afflicted with dental caries to the extent of 86 per cent. to 98 per cent.; and after examining fifty Maori school-children living under European conditions entirely, I found that 95 per cent. of them had decayed teeth.

Pa I NCIDENCE-OF DENTAL CARIES II

It will be of interest now to compare the percentage of carious teeth found in uncivilized races and in the higher civilized races of to-day.

Patrick® has examined all the “ prehistoric crania to be found in the various museums in America.’’ The-results are as follows: | Number Percentage Race. | of Teeth of Carious | examined. Teeth.

Asiatics (including Malays, Chinese, Japanese,

Armenians, Hindoos, and Burmese) a 2,180 2064 | Egyptians and Africans 2 a ce 3,306 3°418 Polynesians and Australians ae ie 2,738 4°309 Central Americans .. ye 930 4:3 72% | North Americans (including Esquimaux) DRO? S093 | South Americans (including Tierra del Fuegians |

and Guanches) .. t 6,759 s-804 | ce

Europeans (including a few modern ‘soldiers ”) BAZ? alee O70

Comparing these low percentages of carious teeth with those obtaining at present, we find that Ottofy,?® after an examination of 14,644 teeth of American school-children, reported that 30 per cent. were carious. Cunningham,’ reporting on the work of the Cambridge Dental Clinic, gives statistics which show that 52:3 per cent. of the teeth of the children examined (1,403) were Carious.

In an examination of two schools of Maori children living under civilized conditions, I found that 15-6 per cent. of the teeth were carious.

Very few statistics of this nature are available, and it is a matter for regret that, when examinations are made, the number of sound, as well as of carious, teeth in each mouth is not tabulated more frequently; for, after all, this is by far the most important and serious aspect of the present prevalence of this disease.

If the incidence of caries per head of the population were Ioo per cent., but if only 5 per cent. of the total number of teeth were affected, there would be but little work for the dental profession and no occasion for the present argument.

Summing up the results of these investigations, we find—

1. That the number of, persons affected with dental caries who live under uncivilized or “natural’’ conditions is comparatively small, varying from I to 20°38 pericene, whilst in civilized modern races the percentage is as high as 98 per cent., theaincrease being at leash 77-4 pen comm

2. That the number of teeth affected with caries in each individual is far less in those leading natural lives than in those leading artificial or highly civilized lives, in the former varying from 2 per cent. to 7 per cent., whilst in the latter it has become as high as from 15 per cent. to 52 per cent., showing a maximum increase of 45 per cent.

3. That in the British race, which has been subject to the influence of civilization for nearly 2,000 years, the increase in the percentage of caries is about 79 per cent. (calculated from the averages of the statistics given above). This corresponds closely to the difference in percentage given above ineNOocL,

4. That in the Maori race, which has been subject to the influences of civilization for only seventy or eighty years at the very most, but has only become “ civilized’ in habits quite recently, the increase is one of 93 per cent. (But against this apparently high figure has to be set the fact that the incidence of caries in each mouth is comparatively low.)

Reviewing now all the above investigations, we are clearly justified in our original statement that there is a distinct relationship between the incidence of caries and the state of civilization. An interesting example ofthis is found in the fact that the prevalence of dental caries apparently fell in England after the invasion by the Anglo-Saxons—a race less civilized than the Romanized Britons whom they displaced.

Civilization, however, fer se, cannot be the cause of so much difference in the incidence of caries. For instance, the Maori was undoubtedly a more “ civilized ’’ and a higher type of savage than the Zulu, the Esquimaux than the Bushmen, and the North American Indians than the Australian aborigines; yet in

Bie NCIDENCE OF DENTAL CARIES 13 each of these cases the race of higher type showed the least incidence of caries.

It must be, then, some particular, though not always essential, accompaniment of civilization which is responsible for the increase. Naturally, one would expect that factor of civilization which particularly affected the function of the teeth to be responsible, and this undoubtedly is so to a very large extent. The function of the teeth is primarily to masticate food, and there can be no doubt that in those races in which this function is most perfectly carried out, and in which the teeth have the most natural work to do, dental caries is correspondingly rare. In fact, it would be more correct to say that the numerical incidence is largely proportionate to the state of “ civilized ’”’ diet to. which a particular race has attained. The physical, chemical, anatomical, and physiological effects of this dietetic evolution on the teeth will be considered in detail subsequently. -

B. Sexual.

The opinion seems to be unanimous that females are slightly more liable to caries than males. Statistics vary on the point. Magitot gives the difference as 25 per cent. in favour of males. Rose gives the percentage of caries in boys as 26, and in girls 26:2. Greve! states that 3 per cent. more girls than’ boys are affected with caries.

Cage:

Since statistics bearing upon the incidence of dental caries are almost entirely based upon the examination of school-children, it is difficult to give any precise data as to the percentage of incidence in later life, but in general terms it may be stated that caries is essentially a disease of adolescence. It is a matter of common observation that the progress of the disease in any particular mouth is much slower, and even may be altogether arrested, after the patient has attained to adult life. Or, expressed otherwise, if a tooth remains free from decay for some years—say eight to ten—after eruption, there is a strong probability that it will remain immune for at least a prolonged period. This is an important fact, and will be referred to later.

The accompanying diagram (Fig. 1), drawn up by Mr. F. W. Richards, illustrates graphically the rapid increase in incidence of caries between the ages of six and thirteen. It illustrates not only the fact that the number of carious teeth increases, but also—more serious—the much increased extent of the disease in each tooth.

Cunningham’s figures show a similar increase, but the incidence of caries is much higher throughout. Thus, at three years

NO OF CHILOREN ! 160

Made Savable rtificially but not Sound all Filled

Fic. I1.—DIAGRAM GRAPHICALLY REPRESENTING THE RELATIVE LIABILITY TO CARIES ACCORDING TO AGE.

(By permission of the “ British Dental Journal.’’)

old the percentage of children having carious teeth is 84. This increases steadily up to the fourteenth year, when the number reaches nearly Ioo per cent.