Dental health 229 Since both caries and periodontal disease have destructive components which loom large in their natural history, the only logical approach to management is prevention. To achieve this a working understanding of their natural history is essential. The common factor in both diseases is dental plaque. Plaque is a dense microbial deposit which adheres firmly to the surfaces of the teeth and gingivae. It tends to accumu- late in stagnation areas between and around the necks of the teeth and in the gingival crevice. Plaque is not readily recognised but when a disclosing agent is used its presence and distribution are vividly identified. Structurally plaque comprises micro-organisms of many kinds which colonise on the surface of teeth and gums and are bound together in a matrix of polysaccharides which give it the sticky and slimy character. The bacterial composition of plaque varies from individual to individual but generally it is true to say that young plaque is made up predominantly of gram positive, aerobic cocci, whereas older plaque comprises gram negative, anaerobic rod-shaped forms. The micro-organisms undergo metabolic activity, the nature of which depends upon the substrate provided by the dietary intake. Periodontal disease is mainly brought about by the adsorption into the tissues of toxic metabolic end products - endotoxins - which cause irritation and inflammation of the tissues surrounding the tooth. The toxins enter the tissues through the mucosa especially that of the crevice causing the chronic in- flammatory response which leads to destruction of the more specialised tissues and their replacement by granulation tissue. Such specialised tissues include the periodontal membrane and the alveolar bone. This leads to pocket formation around the teeth and, with loss of the supporting bone and attachment, the tooth sooner or later becomes loosened and eventually is exfoliated. Sugars, of which sucrose is the most important, play a major role in the onset of decay. Plaque bacterial enzyme systems metabolise sucrose in two ways. First, the sucrose is broken down anaerobically to form lactic acid which is capable of lowering the pH at the plaque-tooth interface to levels at which dissolution of enamel occurs. Second, sucrose units can be polymerised to form polysaccharides, mainly of the stable glucan type. These polysaccharides provide substrate for the micro-organisms between food intake and cause the plaque to thicken. Plaque is relatively impermeable to salivary buffers but it is even less so the thicker it becomes. It is for this reason that salivary buffer systems are unable to neutralise the acid at the plaque-tooth interface. Decay begins as a sub-surface demineralisation and it is only when the lesion is quite extensive that the surface collapses and cavitation actually occurs. It is clear therefore that plaque is the common feature of both periodontal disease and decay and it is reasonable to suppose that if it can be eliminated totally, then neither disease would occur. This is far easier said than done! There are chemotherapeutic drugs which will have a profound effect on plaque organisms, either killing them or preventing reproduction but for very good reasons, plaque control by this means is to be condemned. There are a number of mechanical methods of removing plaque but of these the toothbrush is by far the most efficient and popular. The brush is only effective on acces- sible surfaces the mesial and distal aspects of the teeth in a complete dentition are not reached by the bristles. In recent years the use of dental floss has become increasingly advised by practitioners. However, it is only recently that actual evidence of the value of sustained immaculate oral hygiene has become available. A study carried out in Sweden on school children, the test groups of which- and their parents- were subjected to a continuous programme of oral hygiene instruction supported by regular two-weekly

230 M. N. Naylor sessions with a hygienist. The results after 3 years showed major reductions in gingivitis, decay and plaque when the test groups were compared with the controls. Returning to periodontal disease, there is overwhelming evidence that the basis of all treatment is plaque control. All the complex and sophisticated surgical procedures which are available today are doomed to failure unless supported by regular and effective re- moval of microbial deposits. An important advance in the provision of dental care is the widespread introduction of Dental Hygienists, first trained by and employed in the dental branch of the Royal Air Force during World War II. After the war hygienists were employed within the Hospital Service only, but in 1957, following the passing of the 1956 Dentists Act, they were allowed to work in general practice. The number of training school for hygienists has increased and the number of girls applying for the 1-year course far exceeds the number of places available. At Guy's Hospital, the School of Dental Hygienists started in 1963 with five trainees per year. We now have 20 per year and have no difficulty selecting high quality trainees from the many applicants. Many colleagues in general practice, the community service and in hospitals regard these girls as an indispensible feature of the service they provide to their patients. Not only do they carry out scaling and plaque control instruction, but they play a vital role in the provision of dental health education in its widest sense. To contemplate a preventive and periodontally orientated form of practice without hygienists' support would be rather like contemplating Heaven without Angels. As indicated previously, the composition of the diet is extremely important in determining decay experience. Sugars, especially sucrose, have long been regarded as being heavily implicated in the initiation and progressing of decay but it was not until the mid-1950's that it was appreciated that the relationship between intake and disease was not a simple one. A human study carried out at the Vipeholm Hospital at Lund in Sweden demonstrated that both the form of the sugar food and its pattern of consump- tion were of crucial importance. Sucrose consumed at mealtimes only, in whatever form, caused little or no new decay, but continuous between-meal consumption of sticky toffees profoundly increased decay experience. Subsequent animal studies and human dietary investigations have confirmed these findings. It must be clear therefore that dietary regulation is an important aspect of any pre- ventive programme. Dental health education which emphasises the differences between right and wrong patterns of sugar consumption, is much more likely to be successful than trying to banish dietary sugar which anyway is an important and relatively cheap form of calories. Perhaps the one and only truly community measure to prevent decay is fluoridation. The inverse relationship between the decay experience in a community and the fluoride ion content of the drinking water supplies has been known since the early 1930s. In 1937 Trendley Dean carried out a survey of the decay levels of children living in 21 U.S. cities with different levels of fluoride in the drinking water. The results clearly demonstrate that when the fluoride ion level of the water supply was 1 ppm (i.e. 1 mg/litre) the decay experience was considerably reduced. Studies in other parts of the world including the U.K. have confirmed these findings. In 1945 the first programme to adjust the fluoride level to 1 ppm was initiated at Grand Rapids, Michigan. After 10 years the reductions were entirely similar to natural fluoride areas. Thus began the water fluoridation story. Many areas have been fluoridated in countries throughout the world, amongst which are Canada and the U.S., S. Ireland and Hong Kong and, to a disappointing extent, the U.K.