El recurso internacional para la evidencia científica en la investigación con animales

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Diet and dental disease

Delivered 3rd June 1930
by Mrs Edward Mellanby
 
We are to-day living in the Golden Age of medical science, and, indeed, of biological science in general. Why is this? The answer, I think, is simple: we are realising more and more the value of the animal experimental method. And, as regards medicine in particular, we have learned to adapt animal experiments to human as well as to animal needs, thus involving a new branch of investigation, which is perhaps best described as experimental medicine. No longer are we content merely to examine and observe the sick, classify and docket their symptoms, and attempt to alleviate these symptoms by various empirical forms of treatment.

We now observe animals suffering from the same or similar diseases. We can then put Nature into the witness-box, and cross-examine her step by step until, after eliminating all the secondary and complicating details, we can track down the essential and fundamental cause of the trouble. It is true that occasionally an important discovery has followed observations made directly on the sick. Two such recent discoveries are the malarial treatment of general paralysis of the insane, and the effect of ultra-violet rays on rickets.

Such discoveries are, however, not only rare, but are often accidental and their true significance is usually missed unless they are developed by the animal experimental method. For instance, Jaswegg's work on G.P.I, has remained undeveloped since it was first done. Again, what significance would Huldschinsky's observations on the effects of light on rickets have had had it not been for the other observation made by my husband a few years previously? He showed that bone calcification is controlled by a fat-soluble vitamin, a discovery entirely due to experiments on animals. For these experiments it was necessary to use dogs, which are known often to suffer from rickets. Attempts to produce rickets in small animals, such as rats, failed, until experiments on dogs showed the way. Since that time many details have been elucidated by hundreds of investigators all over the world, using rats as their experimental animals. In this way the two apparently unrelated facts have been correlated.

The only way I can possibly hope to interest you is to show you lantern slides illustrating the results of some experiments made by my husband, Edward Mellanby, and myself, animal experiments which I hope you will think have helped towards the elucidation of the causes, and so towards the prevention of some of the commonest diseases of man and animals. These experiments merely entailed the feeding of animals on diets such as are commonly fed  to children to-day, especially to children of the poorer classes. And yet, as I have already mentioned, they are included among the so-called vivisection experiments. In reality, they are far less cruel than is the treatment often meted out to our pet dogs, and also than that involved  in the feeding of untold numbers of children who develop badly-formed teeth and other defects of malnutrition.

There will not be time to give you more than a few of the main facts, and these I will put before you in the order in which they came to light. For that part of the work which deals with children, I believe, would not and could not have been done had it not been for the previous experimental work on animals. My work was begun, as previously mentioned, as an offshoot of my husband's experimental work on rickets; moreover, without his continued help and encouragement I could have made little, if any, progress.

Let me say, at this point, that the teeth are really living organs, not so many pieces of ivory stuck in the jaws, as dentists used to think ; they can only be looked upon in this latter way when the pulp of the teeth is killed and they cease to live.

I will begin by showing you lantern slides illustrating some variations in the superficial structure and in the arrangement of the dog's teeth.

The first is a photograph of the jaws of two dogs. There is no need to tell you which is the well-formed set of teeth. The top one has white shiny teeth which are regularly arranged in a well developed jaw, whereas the lower one has teeth that are badly calcified, rough and pigmented.

The first problem is to determine what are the dietetic conditions, if any, responsible for the formation of the perfect and imperfect teeth I have just shown you. The only way to test each possible factor in turn is to keep all conditions, except the one being tested, the same. I do not  want to go into the details of the methods used in these experiments, except to say that the animals were kept in large cages, which were cleaned out every day, and each animal had its own bed lined with shavings. In attempting to test the effect of any one condition, animals of the same litter were used, and the diets were started and the animals were killed at the same time.

The next slide shows the effect of eating different kinds of fat or foods containing fat. There are photographs of the jaws of four puppies of the same litter. The experiments were started when the puppies were six weeks old, and at that time they had their milk teeth erupted, but their permanent teeth were still in the jaw; they had, in fact, only just begun to calcify. The diet for all of the puppies consisted of white flour, separated milk, lean meat, a little orange juice and a little yeast. This diet alone results in badly formed permanent teeth, which are developing during the experimental period. The only differences in diet were that the first puppy had salad oil, the second had butter, the third had egg yolk, and the fourth had codliver oil. It is evident that there is a great difference in the structure of the teeth. Salad oil results in very badly formed teeth which are rough and discoloured ; butter results in good teeth, but cod-liver oil and egg yolk give the best results of all, the teeth being white and shiny and regularly  arranged in well developed jaws.

Now I will show you photomicrographs of sections cut through the jaws and teeth of two dogs. The only difference in the diets of these two animals was that cod-liver oil was given to the first and linseed oil to the second. The dog having cod-liver oil has thick enamel, thick dentine (or ivory) which is well calcified, and a well formed jaw bone, while the dog having linseed oil has thin enamel, thin dentine which is poorly calcified, and a badly formed and spongy jaw bone. Moreover, the tooth, instead of being in its normal position, appears to be displaced.

Other slides illustrate the comparative effect of suet, lard and bacon fat.

The main differences in the diets so far mentioned consist of the presence or absence of a fat-soluble vitamin, the anti-rachitic vitamin, or, as we usually call it now, vitamin D. It is present in cod-liver oil, but absent from linseed oil. It is present in egg yolk and in butter, but is not present in salad oil. Suet usually has more vitamin D than lard, which again usually contains more than bacon fat which is very deficient in this respect. Vitamin D can be produced by the action of certain of the sun's rays or by the direct action of ultra-violet light on the skin of an animal or on the food material it eats.

The next slide illustrates the calcification of the teeth of three animals fed on a basal diet deficient in vitamin D and containing olive oil. The first puppy was untreated, the second had its skin exposed to ultra-violet rays, and the third was given olive oil only after it had been exposed in thin layers to ultra-violet rays.

PLATE 1,

Photographs of the lower jaws of four puppies of the same litter.

The only variants in the diets were:

1 had oatmeal and cod-liver oil.
2 oatmeal and olive oil.
3 white flour and olive oil.
4 White four plus wheat germ and olive oil.

The teeth of the untreated animal were very badly formed; the second animal, which was irradiated (exposed to ultra-violet light), had fairly good teeth which might have been better calcified had the time of exposure been increased; the third animal, having irradiated olive oil,  had very well calcified teeth.

That is all I have time to say about the calcification of teeth in relation to vitamin D. It is unfortunate that vitamin D is present in general only in the more expensive foods, for instance, in yolk of egg, suet, and fat fish, including the livers of some fish such as the cod. It is present in butter and milk, but not to a very great extent; a puppy must drink a large quantity of milk to get sufficient vitamin D under most conditions. The actual amount of vitamin D required depends on the other factors in the diet. It is therefore not possible to state the minimal amount required without knowing many other conditions. Just as vitamin D helps in calcification, so there is something in the cereals which antagonises vitamin D and tends to prevent good calcification. This factor in cereals is present to a greater extent in oatmeal than in white flour.

Three puppies of the same litter were fed on the same basal diet, with the following additions:

The first puppy had oatmeal and little vitamin D, the second had white flour and little vitamin D, the third had oatmeal and a liberal supply of vitamin D. This slide (Plate I) shows that, all other conditions being the same, when vitamin D is deficient oatmeal results in worse teeth than white flour, but that when sufficient vitamin D is given good teeth may result even when oatmeal is eaten, for the first puppy has very bad teeth, the second has better teeth, the third (eating oatmeal and cod-liver oil) has perfect teeth.

I hope you will feel convinced that there are two very important dietetic factors in the development of teeth, namely, vitamin D which helps the dental tissues to lay down good teeth, and a substance in cereals, called by my husband "toxamin," which tends to prevent the teeth being calcified.

Now we must consider the structure of the teeth of man. It has usually been said that the teeth  of children, and especially the milk teeth, are well calcified. As a result of the animal experiments, some of which I have just described, it appeared that this could not be quite true since the diet of children was so often deficient in vitamin D and contained much cereal. I knew little when I started the work about children's teeth, but I began to investigate the matter, and as the result of examining large numbers of children's teeth, both with the naked eye and through the microscope, I am convinced that the majority of such teeth, especially the milk teeth, of the children of the British Isles are poorly calcified : in other words, their structure is bad.

This slide (Plate 2) shows the variations seen in the surface enamel of human teeth. The photographs were taken with a strong side light, thus emphasising the defects. The first picture shows a white shiny surface, while the other three are rough to varying degrees. There are only 2 per cent, of the gross defects usually recognised, whereas there are over 80 per cent, of more general defects found in children's milk teeth.

The following slide is a photomicrograph of a section of a child's tooth. Near the enamel there is a little normal dentine, formed before birth, during which time the child evidently received the necessary vitamins from its mother. Later, however, it apparently was given a diet very deficient in vitamin D, for the enamel and dentine are poorly calcified.

The diets of the children whose teeth have been shown were not known, but from analogy with the pictures of dogs' teeth (also taken with a strong side light) which you see on the screen for comparison (Plate 2), there seems to be little doubt that the structure of children's teeth is largely dependent on the amount of vitamin D in the diet, especially in relation to the amount of cereals.

PLATE - Enlarged photographs taken with an oblique light to show surface irregularities of teeth.

Figs 1 & 2 Human milk molars showing smooth and rough surfaces.

Figs 3 & 4 Dogs’ "carassial" teeth. Liberal amounts of vitamins A and D included in diet. Surface of the teeth smooth.

Of 1,500 children's milk teeth examined, 71 per cent, of the front teeth were nearly perfect in structure, 29 per cent, defective. Of the back teeth, 14 per cent, were well calcified, 86 per cent, badly calcified. That is to say, the front teeth are very much better calcified, as a rule, than are the back teeth.

The next question we have to ask ourselves is whether there is any relation between the structure of teeth and the presence of decay? I have no doubt that there is a definite relationship between the two. Out of the 1,500 teeth examined to ascertain the amount of decay and the type of structure, 29 per cent, of the front teeth were defective in structure and 30 per cent, were badly decayed. Of the back teeth, 86 per cent, were defective, 82 per cent, decayed.

Having satisfied ourselves that the worse the structure of a tooth the greater its liability to decay, we ask ourselves whether the initiation and spread of decay in children's teeth can be influenced by diet when the teeth, whatever their structure, are fully formed and erupted. What I say of children's teeth should also apply to the teeth of adults, but I have so far only investigated children's teeth.

Animal experiments of another nature, which there is not time to describe here, indicated that diets after the development of teeth should influence the spread of decay. A suitable diet may not always stop decay, especially when the teeth are poor in structure, but it certainly influences the spread of decay, and does quite often actually stop its progress. This fact is illustrated in an investigation, the details of which I have not time to enter into now, undertaken by Dr. Lee Pattison and myself. We examined very carefully the teeth of 130 children in a hospital and then divided them into four groups. The basal diet was the ordinary hospital diet, but one group of children had, in addition, extra vitamin D alone ; the diet of the second group included extra vitamin D in the form of cod-liver oil, eggs, etc.; a third group had a little extra fat-soluble vitamins, and the fourth had comparatively little vitamin D and much oatmeal. The results of these slight variations in diet are shown in Table I.

Table I.—The Effect of Certain Diets on the Spread and Healing of Caries in Children.

(Average age under 6 years.)

The next few slides show a series of photomicrographs of teeth shed or extracted at various times. The child from whom the teeth were obtained was under treatment at the hospital for many years for bone tubercle. The series shows that as time went on the decay of the teeth became less and less, and finally stopped. I have also been investigating the subject of periodontal disease (pyorrhoea alveolaris) by feeding experiments on dogs similar in nature to those described above. Dogs, and especially pet dogs, suffer greatly from gum trouble and  "pyorrhoea." It is necessary, in order to allow the development of advanced general periodontal disease in dogs, to continue the feeding period for several years. The results of one experiment are shown in Table II and of another somewhat similar experiment in Table III.

Table II.—The Effect of Diet on " Pyorrhoea:' Condition of mouths of two dogs after an experiment of over 7 years.

Both animals were fed on same basal diet from age of 6 weeks to 7 years (still alive).

Table III.—The Effect of Diet on " Pyorrhoea"

Condition of mouths of two dogs after an experiment of over 6 years.

Both animals had the same basal diet (which included oatmeal) from the age of 2 months to 6 1/4 years.

The main facts deduced from such experiments as these are as follows:—

It is possible to initiate and prevent periodontal disease (pyorrhoea alveolaris) in dogs by feeding them on different diets.

Absence or deficiency of vitamin A in the diet in the growing animal produces abnormality Animal 1 had fat containing no vitamins A and D.

Animal 2 had fat containing vitamins A and D.

Much general absorption of the soft tissues surrounding the gums just as a deficiency of vitamin D results in abnormal bony sockets and defective calcification of the teeth.

When once these tissues arc abnormally developed it is a matter of great difficulty to prevent the subsequent onset of pyorrhoea even when vitamins A and D are added to the diet. On the contrary, if the diet in the early stages of life brings about perfect development of both soft and hard dental tissues, then in later life these tissues are very resistant to disease even when vitamins A and D are removed from the diet.

It will be noticed that, as in the case of the teeth so in the case of the gums, it is of the greatest  importance that the diet should be perfect in composition during the early stages of life when the tissues are developing. Whereas, however, in the teeth vitamin D is allimportant, the perfect development of the gums requires also an abundant supply of vitamin A.

animal experiments have elucidated the results of some of the defects of modern diet. In other words, we now know some of the dietetic requirements which bring about the development of good teeth and jaws. There is no need for me to emphasise the fact that very many people suffer from dental trouble. In England to-day, in spite of all the extra care which is now being taken of the teeth of old and young—old if there are any teeth left—there is still as much as, or even more than, there was of dental decay. Last year I examined the mouths of 1,300 unselected London school children, all of about five years of age, and of these only about 5 % were free from dental decay. 63 % had badly-decayed teeth, or had had many teeth extracted, and this in spite of the valuable and very necessary work of the school dentists; for, although we all hope that prevention will be the ride, rather than cure, and that in the future very few dental surgeons will be required, we must all admit that today their services are a real necessity. Dental disease is rampant, not only in this country but all over the world. Even uncivilized natives taken away from their natural surroundings and brought nearer to civilization are becoming more and more liable to suffer from dental decay and from  affections of the gums. Instead of white shiny teeth, regularly arranged in wellformed jaws, there are seen to-day, in some native races, discoloured teeth in ill-formed jaws, and susceptible to decay and disease of the gums.

Why is it there is so much dental disease in civilized countries? And why is it that until recently we had not discovered the cause of such disease. My answer is that until recently we had not the means, or we had not realised the cans, by which we could discover the cause. Until we do know the cause it is not easy to find a remedy. The only suitable method available as a basis for such discovery is, I believe, the animal experimental method, which is being used in the elucidation of some dental problems.

You will notice that in the work I have briefly described, experiments on animals and investigations on man have been intermingled. The animal experiments have supplied all the fundamental facts on which the hypotheses are based, and some of these have been examined in their human aspects. Only the beneficial influences can be tested on man. In the case of the teeth themselves, this is of little significance, for the average human being in this country is fed, especially during childhood, on just those diets which produce defective teeth and disease of related tissues in animals, namely, large amounts of cereals, with little whole milk, egg yolk and other foods containing fat-soluble vitamins. We know some of the worst errors in feeding, and especially in feeding children, and so long as we persist in these errors, so long, I believe, will the teeth of civilised man remain in their present deplorable state. If the people of the British Isles decide to remedy this defect by encouraging the use of the right kind of food, and so bring into existence a race with white, shiny teeth, evenly arranged in well-formed jaws, they ought to realise that this has only been made possible by animal experiments, which would not have been performed if a small section of the community had had its way. That this and a large number of other researches have been possible is, to no small extent, due to the hard work of Stephen Paget.

NOTE.—Unfortunately it is impossible to reproduce all the photographs used by Mrs. Mellanby to illustrate her lecture, but the Plates I and II clearly demonstrate the main facts brought to light by her researches.


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