Family Doctor Books


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Family Doctor Books
Preview of Understanding your Teeth and Mouth

To understand what the various parts of the mouth do, we need to consider each of them in turn:
  • Gums (gingivae) and teeth, which are embedded in the upper and lower jaws.
  • The tongue, the palate and the cheeks, which are covered by the soft lining of the mouth.
  • The salivary glands.
Our teeth are designed for eating and each tooth plays a particular role.

Teeth and gums

Teeth are designed for eating: the incisors (the four front teeth) for biting, the canines (the eye teeth) for tearing, and the molars and premolars (back teeth) for chewing. The furthest back teeth (the third molars) are commonly known as the wisdom teeth and these do not usually appear in the mouth until the age of 17 to 21 years. These different teeth have evolved functions from both meat eaters such as tigers and lions, and grinders such as horses and cattle because we, and our teeth, are designed to eat both meat and vegetables. In other words, we are omnivorous.

Each tooth has a pulp in the core which consists of nerves and blood vessels and this is surrounded by dentine, a hard bone-like substance which is itself covered with enamel over the crown. Enamel is the hardest tissue in the body and has no feeling in it. It is made of calcium crystals (hydroxyapatite), whereas the underlying dentine, which is in contact with the central nerves, is sensitive, and can be painful if exposed to hot or cold or to some foodstuffs like sugar.

The teeth are held in the bones of the jaws by ligaments called the periodontium and the bones and the necks of the teeth are covered by gum tissue (the gingivae). When they are healthy the ligaments are constantly tightening to keep the teeth together and to let you know how hard you need to bite when you’re chewing food. The jaw bones are called the maxilla (the top jaw) and the mandible (the bottom jaw). The mandible is a horseshoe shape and joins on to the base of the skull at the temporomandibular joints (TM joints), which lie directly in front of the ears. The TM joints have a cartilage like the knee joint and can occasionally click when you open and close your mouth but, although this may be annoying, it is harmless.

Teeth vary in shape and size but have an identical structure.

Lining of the mouth

The soft lining of the mouth (mucosa) covers the tongue, palate and cheeks and the floor of the mouth. The top of the tongue looks pink and furry and has small dots or papillae on it. There are larger papillae at the back which are full of tastebuds. The hard palate forms the roof of the mouth which is ridged and joins to the soft movable palate and the uvula which hangs down at the back of the mouth. The tonsils are behind the mouth in the throat, and form part of the immune system, but we can do without them if necessary. There are also tonsillar tissues at the root of the tongue on both sides and these sometimes cause concern because they can be mistaken for some types of cancer. Confirming that these structures are normal is, in fact, easily done. The swellings occur on both sides in the same place and, if they were cancerous, only one side of the tongue, not both, would be affected – cancer is not bilateral and symmetrical. The floor of the mouth under the tongue is also bumpy and there are often prominent dark veins running under the tongue.

The mouth is one of the most sensitive areas of the body, made up of many different elements all of which have important functions.

Saliva

The lining of the mouth is kept moist by saliva which comes from the major salivary glands lying directly in front of the ears (the parotid glands) and under the chin (the submandibular glands). There are also small mucous glands in the lips which help keep the mucosa that lines the inside of the mouth moist and lubricated. When we eat or drink, we produce large quantities of watery saliva to help us swallow and digest food. The rest of the time, saliva, which is mildly antiseptic, helps to prevent infection in the mouth and helps protect the teeth from decay by neutralising acid and killing bacteria.

Baby and second teeth

Usually when a child is born, he or she has no visible teeth, although the primary (baby or milk) and some of the permanent (second) teeth have already started to form in the bones of the jaws. Babies get their first teeth at around six to eight months of age, usually starting with the lower two front teeth, although sometimes they can erupt much later than this. The baby teeth come in at regular intervals (see box), and usually all 20 teeth have erupted by around the age of two and a half.

Parents of babies and toddlers often associate teething with problems such as drooling or a raised temperature and think that their children are more inclined to be fractious during this phase.

Like adult teeth, primary teeth are important for both eating and appearance, but they also act as a stimulus for the jaws and face to grow and maintain spaces for the second teeth to erupt from underneath. Early loss of baby teeth as a result of accidents or tooth decay often, therefore, leads to crowding of the permanent teeth. Any child who has lots of decay in their baby teeth is likely to have the same problem with their permanent teeth unless something – particularly their diet – changes drastically in the meantime.

The permanent teeth start to erupt around the age of six to eight and, again, the front teeth (incisors) on the lower jaw are usually the first to appear, along with the first permanent molars which appear behind all the baby teeth. The front teeth are followed by the premolars (aged around 9.5 to 12) and again the canines (9 to 12) before the second molars appear (11 to 13). The wisdom teeth (the third molars) do not appear usually until 17 to 21 years of age and can occasionally be impacted (see page 15). To allow these permanent teeth to erupt, the roots of the baby teeth are dissolved by the eruption of the permanent teeth so that the baby teeth then become loose and fall out.

ERUPTION OF TEETH
Incisors Canines Premolars First molar Second molar Third molar
First (primary) teeth
Upper
8–13 16–22 13–19 25–33  
months months months months
Lower
6–12 17–23 14–18 23–31  
months months months months
Permanent teeth
Upper
6.5–8.5 10–12 9.5–11.5 6–7 11.5–12.5 17–21
years years years years years years
Lower
6–8 9–11 9.5–12 6–7 11–13 17–21
years years years years years years

 

Development of the teeth from birth to adulthood. Primary (baby or milk) teeth shown as blue, permanent (second) teeth as white.

KEY POINTS

  • Teeth have evolved different functions – incisors for biting, canines for tearing, molars and premolars for chewing
  • Each tooth has a core of pulp, surrounded by dentine, which is covered with enamel over the crown (exposed surface of the tooth)
  • Saliva functions to assist us to swallow food, prevent infection in the mouth and protect teeth from decay by neutralising acid
  • Humans have two sets of teeth: first the primary (baby or milk teeth) and then the permanent (second or adult teeth)