228 M. N. Naylor It is an unfortunate fact that the public generally does not place good dental health high on the list of priorities. This is not surprising since most people remain entirely unconcerned about their general state of health - until of course, they become seriously ill. Testimony of this are peoples' smoking habits, the prevalence of obesity and the scant regard paid to even the simplest forms of exercise. Small wonder that dental health is ignored when people are prepared to set themselves onto a head-on collision course towards coronary heart disease, malignant neoplasia and other equally devastating conditions resulting from personal abuse. At all levels of society dental diseases are accepted as inevitable. Dental treatment, whether it be based upon regular routine visits to a practitioner or when driven to seek extractions because of pain, is likewise regarded as an unpleasant inevitability. There are still people who regard a full clearance of all natural teeth and the provision of full upper and lower dentures as the sole criterion for good dental health. Not so long ago a girl's marriage prospects were regarded as being greatly enhanced when she became the proud possessor of full dentures! Despite the fact that both decay and periodontal disease can be prevented, most people accept as normal, bleeding and inflamed gums, and the inevitable bad breath, decaying teeth and the various types of pain which accompany the different phases of the disease. Compared with some of the 'killer' diseases with which our medical colleagues have to deal, dental diseases may seem but minor considerations. Nevertheless, dental diseases have such a high prevalence that the cost of NHS treatment is running at over t 140,000,000 per annum a conservative estimate of the working days lost due to dental disease has been put at 0'6 million. Finally, despite its relatively minor nature, dental diseases do have a mortality rate and it has been estimated that about 12 people per year die either from dental disease, the consequences of the disease or treatment. Some of these are anaesthetic deaths and others are associated with sub acute bacterial endocar- ditis of dental origin. It is quite impossible of course, to quantify the pain and distress which people suffer from dental diseases. Periodontal disease, when it has reached a certain stage in its natural history, and dental decay., are both irreversible conditions. When the periodontal disease is confined to the gingival margins and not involving the deeper periodontal structures, the situation can be reversed and normal health restored. However, when the deeper structures are involved, namely the periodontal membrane and the alveolar bone, the condition cannot be reversed and the best that treatment can do is bring the inflammation under control and prevent further destruction of tissue. If the destructive processes proceed inexorably, eventually the teeth become loose and finally are exfoliated. The onset of destruction and indeed the rate of destruc- tion varies considerably from patient to patient. Unfortunately, the reasons for this variance are not clear. Caries, certainly when an established lesion is present, is irreversible and the only treatment available is surgery which takes either the form of extraction of the tooth or excision of the diseased tooth substance and its replacement by means of one of several filling materials. There is evidence that very early lesions which have not involved a breach of the surface continuity of the tooth can be reversed or arrested. Examples of this are, reversal by sodium fluoride rinses of experimentally induced very early lesions, and the common clinical experience of an early lesion becoming arrested when stagnation is eliminated by extraction of the neighbouring tooth.

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