Dental decay is the result of bacteria which produce acids which attack and erode the tooth surface. Following a meal or snack containing sugar the acidity in the mouth is raised. If this is high enough and remains for long enough, the enamel surface begins to demi-neralize and soften to form a minute cavity – the beginnings of tooth decay. Sites prone to decay are pits and fissures on the tooth surface, and between the teeth. If the enamel layer is breached by decay, further acid and plaque soften the underlying dentine and continue to destroy the tooth structure. If there is only a very small amount of decay then diet control, improved oral hygiene and fluoride applications may be prescribed to try to halt or reverse the process. If the decay is deeper then it must be removed to prevent it from reaching and inflaming the pulp. This may cause pain and treatment of such decay often requires a local anaesthetic. The site of injection is often close to the tooth involved. The anaesthetic contains an active anaesthetising ingredient, lidocaine (a weak derivative of cocaine), sometimes combined with adrenaline, a substance to localize it. Alternative localizing agents can be used for patients with heart complaints.
The anaesthetised area usually remains numb for between one and three hours. It is important during this period that the affected part is not accidentally bitten or chewed; this can cause ulceration.
Active decay which has progressed through to the dentine, the layer of tissue beneath the enamel, must be removed. To obtain clear access a high-speed air-turbine drill is used to cut through the enamel layer. The soft, decaying dentine is removed with a slowly-rotating burr drill or hand instruments. If the decay is close to the pulp chamber in the centre of the tooth the cavity can be isolated and sealed, to prevent exposure of the sensitive pulp. A lining material is placed in the deepest part of the cavity to protect the pulp from thermal and chemical irritation. The tooth is then restored with a filling material. Amalgam, a rapid-setting silvertin alloy, is commonly used to restore the molar teeth for which hardness and strength are of prime importance. A disadvantage of this material is its metallic colour. The alloy is mixed and firmly packed into the cavity; when semi-set it can be carved and trimmed to the tooth contour and bite adjustments made so that the tooth fits snugly with its opposing neighbour in the other jaw. The standard amalgam reaches 50 per cent strength in about an hour, during which time eating should be avoided. Composite or white filling materials are manufactured from resins plus particle fillers such as quartz, to mimic natural tooth appearance. They set rapidly upon mixing. Light-cured composites set when the dentist shines a bright light on the material. In this way the tooth’s shape and contour can be built up or added to more easily before hardening under the light. Final trimming is carried out using polishing discs or stones.
Temporary filling materials based on zinc oxide and eugenol (oil of cloves) are used when a lot of decay has been removed. This material has sedative properties and allows the pulp of the tooth to recover; it is removed at a later date and a permanent filling material is installed.
Dental decay that proceeds unchecked causes irritation, and later inflammation of the pulp of the tooth. This is commonly experienced as pain, often with hot, cold and sweet food or drink. At first it lasts only a few minutes but later it becomes more persistent, often coming on without warning, especially at night. Once the pulp has died the throbbing toothache ceases, but the dead pulp acts as a centre of infection and an abscess may form and spread into the jawbone. This dental abscess may develop in several ways. First, an abscess may not always be spotted until the patient is given an X-ray. Second, it may cause pain on chewing. Thirdly, and much worse, the teeth, provided of course the wearer observes scrupulous oral hygiene.