Two sets of teeth grow in a lifetime. The baby, or primary, teeth start to appear a few months after birth (although they have begun forming while the baby is still in the womb) and will usually have reached their full complement of 20 by about two and a half years of age with ten on the top and ten on the bottom jaw. The front cutting teeth are the incisors, and the back grinding teeth are the molars. Dividing these are sharp pointed eye teeth or canines.
At the age of about six, a child develops the permanent six-year-old molars. Sometime after this, the roots of the baby teeth begin gradually to dissolve and the teeth fall out, in order to be replaced by the permanent teeth. This process will usually be completed during the teens, with individual children varying a great deal. The permanent teeth have started forming in the gum from the age of about two. Care and hygiene of baby teeth are no less important because the teeth will eventually be lost. Decay and infection can spread to the developing teeth and the baby teeth are important in guiding the permanent teeth as they grow out through the jaw.
Permanent teeth are larger than baby teeth and total 32. They are accommodated by the increased size of the older child’s jawbone. Starting from the front there are two incisors, one canine tooth, two premolars and three molars (the one furthest back is the wisdom tooth). This pattern is repeated on both sides, and in the top and bottom jaws.
Sometimes the jaw isn’t large enough for the wisdom teeth, which may not appear until the late teens or early twenties. In this case, they may remain embedded in the jaw, and if this causes problems they may have to be removed by dental surgery. However, some people never grow their wisdom teeth and never develop any problems.
The part of the tooth that can see is the crown and is covered with shiny white enamel – the hardest substance in the human body. The lower part of the tooth that fits into a socket in the jaw is the root, and this is covered by a bony material called cementum. The area where the root and crown meet is called the neck. The root is attached to the jaw by a membrane. The bulk of the tooth consists of a bone-like substance called dentine. In the centre of each tooth is the pulp, which contains the living matter such as nerves, blood vessels and connective tissue. This is the part that hurts if the tooth becomes infected or damaged. A fine canal (the root canal) runs from the pulp down either side of the root, and joins up with the body’s main nerve and circulation systems.
The jawbone in which the teeth sit is covered by the gum, technically known as the gingiva, which is attached to the tooth enamel around the neck of the tooth. The sockets in the jaw in which the teeth sit correspond in shape to the teeth although they are slightly larger. The upper and lower teeth themselves are designed to fit perfectly one into the other when the jaw is closed, a feature that gives maximum chewing efficiency.
The lower jaw (mandible) is joined to the base of the skull by the temporomandibular or jaw joints.