DENTAL CARIES

1.INTRODUCTION

Dental caries is an ecological disease in which the diet, the host and the microbial flora
interact over a period of time in such a way as to encourage demineralisation of the
tooth enamel with resultant caries formation. Dental caries is still one of the most
common diseases in the world today. Until recently almost everyone had experienced
tooth decay in their lifetime. However, today many people are caries free and there has
been a 40-60 % reduction in the incidence of tooth decay around the Western world.
Most developed countries and many non-industrialised countries are now well below the
World Health Organisation goal of less than 3 decayed, missing or filled teeth per 12
year old child.

2.THE HOST

Teeth are composed of a thin layer (1-2mm) of dental enamel which forms the hardprotective coating over the tooth. This consists mainly of calcium, phosphate and otherions in a structure known as "hydroxyapatite". Dental enamel is porous and issusceptible to acid dissolution during the process of demineralisation. Thisdemineralisation process is offset by the repair process known as remineralisation.

Tooth susceptibility varies among individuals. The reasons are not fully known, butinfluences include:

* Shape, size and order of the teeth which affect the "washing" effects of saliva. Thisis largely determined by hereditary factors.

* Salivary components which can be critical in controlling dental caries since theyaffect bacteria, immune status, plaque formation, and enamel structure and canneutralise acids. Saliva has a vital role in the balance between demineralisation andremineralisation. These salivary factors will be outlined in greater detail below.

* Enamel structure can be altered by a selection of mineral ions and fluoride, as wellas by acid. The balance between demineralisation and remineralisation of theenamel determines whether caries occurs. Availability of fluoride favoursremineralisation.

3. SALIVA

Saliva is the body's natural protective mechanism against decay. It contains salivaryproteins which adsorb strongly onto the teeth, protecting enamel against aciddissolution. This adsorbed protective layer is referred to as the pellicle. Salivary proteinsalso act as antibacterial agents.

Saliva is the primary resource of calcium, phosphate and fluoride, the materials used to remineralise the enamel.

Saliva also acts quickly to clear away food debris from the mouth and to buffer theorganic acids that are produced by the bacteria.Saliva is therefore a very vital and complex material in the prevention of dental caries.Thus, salivary dysfunction can lead to rapid deterioration of dental enamel. Salivarydysfunction can occur whenever certain medications are taken or medical treatmentssuch as radiotherapy are undergone.

4. THE BACTERIA

Dental caries will not occur if the oral cavity is free of bacteria. These bacteria areorganised into a material known as dental plaque which is yellowish coloured film on thesurface of the teeth. Of the many types of bacteria in the mouth, the most caries activeappear to be Streptococcus mutans, Lactobacillus spp., Veillonella spp. andActinomyces spp. These bacteria can be transferred from mother to child and arepresent at varying levels in all human mouths. A variety of carbohydrates providesubstrates for these organisms to grow on and the waste products of their metabolism -acids - initiate the tooth decay process by dissolving tooth enamel.Most research on the bacteriology of dental caries has focused on the ubiquitous

S. mutans and its ability to ferment sucrose. This organism preferentially fermentssucrose to produce significant amounts of acid and extracellular polysaccharide(plaque). However, most researchers now agree that other organisms present in themouth are capable of plaque formation and acid production from a variety offermentable carbohydrate substrates besides sucrose which are present in the normalmixed diet.

5. THE ROLE OF THE DIET

The dietary components that contribute most to the caries process are fermentablecarbohydrates. These need to be retained in the mouth long enough to be metabolisedby oral bacteria (principally Streptococcus mutans, but others can be involved) toproduce acid. The acid attacks the tooth enamel and gradually dissolves it(demineralisation). This demineralisation process is offset by the repair process knownas remineralisation. The balance between remineralisation and demineralisationdetermines whether caries occurs.Extensive data now exists to show that any foodstuff or drink containing fermentablecarbohydrate (sugars or cooked starches) has the potential to cause significant acid production, followed by demineralisation of the enamel.

Biochemical Studies: Studies of plaque pH both in vivo and in vitro have shown that allfermentable carbohydrates whether cooked starches, added or naturally occurringsugars - have the potential to cause acid production in the mouth.The amount of carbohydrate is not important.

Animal Tests: The cariogenic potential of foods has been assessed using laboratoryrats. Again, these tests demonstrate that all fermentable carbohydrate foods - whethercooked starches or sugars - have the potential to cause decay. Again the amount ofcarbohydrate is not important.

Food retention: The ability of a food to be retained in the mouth will alter its potentialcariogenicity. Tests to determine food retention indicate that high sugar foods, oftenperceived to be sticky, are not necessarily retained in the mouth for a longer time. Inpractice starchy foods are retained longer in the oral cavity than some of the fastclearance sugary foods.

6. FREQUENCY OF CARBOHYDRATE INTAKE

It is now widely recognised that it is not what one eats but how often carbohydrate isingested that is the most significant dietary factor in the aetiology of dental caries. Insubjects with normal salivary function an acid challenge occurs within 10 - 15 minutesafter ingesting fermentable carbohydrate foods or drinks, and it lasts for between 30-60minutes. Greater time between such acid attacks allows greater time for the repairprocess - remineralisation - to occur.

Although there is now a consensus that frequent eating of carbohydrate foods anddrinks is the main dietary factor in the development of dental caries, no one has yetdetermined precisely how many occasions per day are safe for all individuals. It is,however, generally agreed that three meals plus three to four snacks per day isacceptable. Research is needed to further establish the dynamic interactions betweenfrequency of eating/drinking and oral hygiene and the use of fluoride. There is howeveran increasingly recognised view that, provided that oral hygiene is adequate and the useof fluoride optimal, the frequency of eating diminishes in importance. This has beendemonstrated in human studies in New Zealand, UK, USA, Spain, Sweden, Norway andNetherlands.

7. SENSIBLE SNACKING

It had been common practice among many in the dental profession to recommend that'three meals a day' is safe for teeth, and 'snacking' is unacceptable. This advice is nolonger given as such. Some reasons why the dental profession has modified theirmessage are as follows:

1. It has been well documented that eating and drinking frequency has been increasingin most industrialised countries over the last few years, and that the 'three meals aday' pattern of eating has long been abandoned by most sectors of the population.

This change in frequency has occurred over a period when the incidence of dentaldecay has declined. Sugar consumption has also remained static or increased.This would suggest that another factor - which most believe to be fluoride (especiallyin dentifrices) has counterbalanced and overridden the effect of increased frequency.

This is well documented in Sweden, Norway, UK and Switzerland.

2. An experimental caries model has been developed in the US and the Netherlandswhich stimulates what happens in the human mouth, by alternating periods ofdemineralisation and remineralisation. The model has been used to mimic humaneating experiences over a 24 hour period, and it demonstrated the power of fluorideto 'neutralise' the effect of frequent snacking. Where fluoride was used twice daily,there was less mineral loss following 10 challenges, than there was following 3 in theabsence of fluoride.

8. HOW IMPORTANT IS DIET ?

In most industrialised countries, the percentage of the population that is caries free hasbeen steadily increasing. It is generally accepted that the major factor has been the useof fluoride in water, toothpastes, mouth rinses, and tablets. This decline in caries hasnot been associated with any significant reduction in sugars ingestion or in snacking. Infact as noted above, while frequency of eating has generally increased, sugarsconsumption is either stable or increasing.

Additionally, recent epidemiological studies (UK, USA, Spain, New Zealand) haveshown that in both children and adults, the total of all dietary factors examined(carbohydrate amount, type and frequency) accounted for only a very small increase incaries incidence. Dietary factors, although statistically significant were clinicallyinsignificant as they were overridden by the effects of fluoride and oral hygieneprogrammes.

This contrasts markedly with the older studies of the pre-fluoride era where diet andparticularly sugars intake was directly related to caries experience in most countries andin most population groups. Availability of fluoride, especially used topically intoothpastes, has brought about a dramatic change in the aetiology of the disease.

9. CARING FOR TEETH

Dental caries is primarily a disease of children and teenagers. Its causes are complex,but there are some quite simple methods for preventing it. This advice aslo applies tothe adults who are increasingly suffering from decay because of the greater number ofnatural teeth that they maintain into adult and older life.

1. Sensible eating:

Eat a well balanced diet which includes a variety of foods. 'Nibbling' or drinkingconstantly throughout the day should be avoided because it provides moreopportunities for demineralisation and less time for remineralisation.Sensible snacking, that is six to seven eating occasions a day, is acceptable, but'grazing' is not.

2. Cleaning teeth:

Teeth should be cleaned thoroughly at least twice a day using a fluoridetoothpaste. Brushing helps to remove the plaque and food particles from the toothsurface and flossing helps to remove the plaque and food particles from the areasbetween the teeth. Regular brushing, also keeps gums healthy. Fluoride in thetoothpaste retards demineralisation and favours the remineralisation process andthus prevents caries.

3. Visiting the dentist:

Visit the dentist for regular checkups and professional plaque removal.