MEET YOUR TEETH
How these pearlescent facial features develop and are maintained in a healthy mouth
WORDS JAMES HORTON
Your teeth offer so much more than just a winning smile. Alongside your tongue and saliva, teeth are integral for mastication, which is the process of breaking down food that enters the mouth into a bolus –a chewed ball of food – fit for swallowing. Teeth are also surprisingly complex components. They are formed of many layers, are organised into various functional shapes and erupt from the gumline at structured times during our development.
Teeth are supported in the mouth by the jawbone and gums, which surround and protect the lower features of each tooth. Teeth are not attached directly to the jawbone, but are linked to it via a strip of tissue known as the periodontal ligament. This ligament acts as a shock absorber for the jawbone, helping to ensure comfort when a tooth is exerting pressure on food and other teeth.
The periodontal ligament is connected to a thin layer of cementum, which provides a protective outer layer for the tooth’s root.Encased within this layer, the horseshoe-shaped root sits embedded in the bone, helping to keep the tooth locked in place. As well as this, the root plays host to the pulp canals –a network of blood vessels and nerves that carries nutrients and signals to the rest of the tooth. The pulp canals coalesce into a pulp chamber above the root, but in healthy teeth the pulp chamber remains unseen, as it is covered by a protective sheath.
The immediate barrier surrounding the sensitive pulp is called dentin, which forms the largest bulk of the tooth. Formed of many tiny tubes, dentin is hard, but remains vulnerable to agents of decay. The outermost layer of the tooth, which forms the visible surface known as the crown that we see when looking at a healthy set of teeth, is formed of enamel.Enamel is almost entirely composed of unliving crystals containing calcium and phosphate, and in adult teeth it is the hardest substance of the body.
ERUPTION
Humans, like our ape cousins and many other mammal species, are diphyodonts. This means we have two sets of teeth: an initial ‘baby’, or deciduous set, and an ‘adult’ permanent set that follow. In humans, the phases of growth in our teeth offer many advantages. The delayed eruption of our first teeth allows mothers to nurse more comfortably.And replacing the smaller deciduous teeth with larger, permanent teeth as a child ages accommodates the rapid increase in head and jaw size that occurs as we mature.Most permanent teeth are in place by the age of 13, as these teeth erupt from underneath the deciduous set and dislodge them. However, wisdom teeth – also known as the third set of molars – do not appear until early adulthood, if at all. Wisdom teeth play a modest role in assisting with mastication, and so offer little advantage to the modern human. Due to the lateness of their arrival and the limited space available in the gumline, wisdom teeth can also unsettle the other molars and cause pain and discomfort. As such, many adults have their wisdom teeth removed, and others never get them, leading to the idea that humans may be evolving away from a third set of molars.