Teeth

Our teeth fulfil a number of functions, namely for chewing, to enhance our appearance and for making certain sounds in speech in which the tongue contacts the teeth. In earlier times our teeth were important for attacking and defending, but nowadays, apart from an occasional show of aggression in children, we seldom see them being used in this way. The mouth is a gateway into the body. Being dark, warm and moist it is an ideal place for cultivating bacteria. Given the correct type of sugary diet and left on their own to multiply, these bacteria, their waste products and particles of food – which we call dental plaque – will begin to attack the teeth (dental decay and caries) and cause gum diseases. These, in turn, can cause pain, bad breath (halitosis) and digestive problems because food is not chewed properly. Both of these conditions can easily be prevented; yet dental disease is the most common health problem in many countries of the world.

Parts of a tooth

The crown is the part of the tooth located above the gum and is covered by enamel, the hardest structure in the body. It protects the dentine and pulp underneath from biting forces and other irritants such as hot, cold or sweet foods. Densely-packed, calcified crystals arranged in prisms make up the enamel. The dentine forms the bulk of a tooth. It is the product of special cells called odontoblasts, which are derived from the tooth pulp. The dentine is composed of masses of microscopic hollow tubes resembling a bundle of curved straws, containing fluid and projections of odontoblasts. When these pass irritant substances to the pulp, when you may feel pain. Dentine is more elastic than the rigid enamel and acts as a shock-absorbing layer.

Cementum covers the dentine of the root, and acts like fibrous glue to support the tooth in its bony socket.

Pulp is the soft tissue inside the dentine of the crown and root. It consists of nerves, blood vessels and cells. Around the edge of this pulp chamber lie the odontoblasts which continually form dentine tubules, and dentine is formed continually throughout life as a defence mechanism. With increasing age the pulp cavity gets smaller. Surrounding the teeth is the gum or gingiva. In health it is pale pink and slightly stippled like orange peel, and is in close contact with the tooth, encircling its neck. There is a shallow gingival crevice separating the free gum from the tooth; this is where the disorder periodontitis begins with the breakdown of the cementum. Gradually the supporting tissues and bone are removed so that the tooth is loosened in its socket and eventually lost.

Types of teeth

The incisors are the eight front teeth, four in the upper jaw and four in the lower jaw, whose main function is to cut food. The flat crown resembles a curved spade except for the bulge near the gum on the tongue side which is called the cingulum. Each incisor has a single root. The central incisors are located on each side of the midline of the jaws and next to these are the four canines (two in the upper jaw and two in the lower jaw), the main function of which is to tear and hold food. The tip or cusp tends to be pointed but flattens gradually with wear. Each canine possesses a single root, which is the longest and most powerful root of all teeth and gives rise to the name of’eye tooth’ in the upper jaw because the root points towards the eye. The eight premolars (bicuspids), which are located between the canines and the molars with two on each side of the upper and lower jaws, help the molars to chew and grind. Each premolar has two cusps, one on the cheek side (bucally) and one on the tongue side (lingually). Maxillary premolars have cusps that are nearly equal in height but in the mandibular (lower-jaw) premolars the buccal cusps are larger than the lingual cusps. Except for the upper first premolar, which tends to have two roots, premolars usually have only one root.

The molars are the most posterior teeth on each side of the jaw; they function to grind and masticate food. Each molar has four or five cusps separated by fissures; lower molars have two roots and upper molars have three roots. The third molars (wisdom teeth) are last to erupt, and in some people they never do so.

Insufficient room may cause them to be impacted (jammed against other teeth), which may give rise to problems.

Milk teeth

Each of us has two sets of teeth. The first set is given a variety of names: milk teeth, baby teeth, primary teeth or deciduous dentition. Perhaps it is better to think of them as foundation teeth. Their development begins just six weeks after conception. After about six months of foetal life, the foundation teeth, while still in the jawbone and covered by gums, start to harden by the process of calcification. The crown, the part of the tooth that will appear above the gum, is fully calcified when the tooth erupts (grows out of the gum) but the roots are not hardened completely until just over a year later.There are 20 milk teeth: two incisors, one canine and two molars in each half of each jaw. They tend to be smaller and whiter than their permanent successors. Their crowns are more bulbous, with thinner and softer enamel. Close to the surface of the crown is the pulp chamber, a cavity filled with blood vessels and nerves. Their roots are delicate and those of the milk molars splay out to accommodate the permanent teeth developing underneath. About six months before a permanent tooth is ready to appear above the gums, the milk tooth falls out.

Permanent teeth

Calcification of the permanent teeth begins about six years before they erupt, with the canines beginning calcification four months after birth. This hardening is sometimes disturbed by illness or poor nutrition. The roots usually harden about three years after the tooth appears in the mouth. Variation in age of eruption is wide: girls’ teeth tend to erupt before boys’ teeth, and mandibular (lower-jaw) teeth before maxillary (upper-jaw) ones. There are 32 permanent teeth; two incisors, one canine, two premolars and three molars in each half of each jaw.

Dental anomalies

Occasionally a congenital condition may be inherited in which no teeth are formed (anodontia) or there are aberrations in number with either some teeth missing (hypodontia) or extra teeth forming (supernumaries). Sometimes the calcification or shape of teeth can be affected, known as dental hypocalcification or dental hypoplasia respectively. These are conditions over which there is little preventive control, as yet. On the other hand, we have excellent control over preventing the two major dental diseases – tooth decay and gum disease, preventable by good oral hygiene for which the message is simple: . keep to a healthy diet without sugary snacks . brush teeth twice a day to remove plaque. . Regular (six-monthly) dental checks to monitor your personal prevention programme.