Anatomy of the Tooth
The tooth is one of the most individual and complex anatomical as well as histological structures in the body. The tissue composition of a tooth is only found within the oral cavity and is limited to the dental structures. Each tooth is paired within the same jaw and the opposing jaws have teeth that are classified within the same category, however they are not grouped according to structure but function. They are seated within the upper and lower alveolar bone in the maxilla and mandible respectively and this exclusive type of joint is known as gomphosis.
Types of Teeth
The teeth are divided into four quadrants within the mouth, with the division occurring between the upper and lower jaws horizontally and down the midline of the face vertically. This leaves up to eight adult teeth in each quadrant and separates the opposing pairs within the same alveolar bone as well as their counterparts in the opposing jaw. Each quadrant contains a medial and lateral incisor, a canine, two premolars and between two and three molars.
The incisors are used for cutting and biting, the canines are used for gripping, as well as the premolars and the molars are used for grinding.
The main functions of the teeth include chewing food into a bolus that can be easily swallowed for further digestion, giving structure, tissue support and shape to the face and aiding in the pronunciation of sounds during speech.
Structure of the tooth
The tooth is made up of a crown and either single or multiple roots. The anterior teeth in both the upper and the lower jaws, from the right first premolar to the left first premolar, are single rooted teeth. On the upper jaw the maxillary second premolar may have two roots and all of the maxillary molars have two to three roots. On the lower jaw, the mandibular premolar has a single root and the molars have one to two roots.
The articulating surfaces on the most superior part of the crown of the teeth are designed to accommodate the function of the tooth, so the anterior teeth, from the right canine to the left canine, have a single incisive edge that can clamp down upon and tear away at a piece of food, whilst the premolars and molars have cusps, pits and fissures that are able to grind and mash a mouthful of food so that it is edible.
The crown of the tooth is the visible part of the tooth in the mouth, while the root is hidden beneath the gingiva and alveolar bone. It has a pearl white to yellow colour depending on the thickness of the enamel, the age of the patient, their oral hygiene and lifestyle choices. The enamel is the outer layer of the tooth and it is extremely hard and durable. Underneath this tough exterior lies a second softer layer, that is slightly darker in colour and is known as the dentin. This is the capsule that separates the hard outer tissue from the soft and fragile pulp cavity which is the most inner layer of the tooth and contains the blood vessels and nerves of the tooth. The enamel and the dentin must be intact in order for the tooth to stay alive and healthy, for once any bacteria enters the pulp chamber, the damage is irreversible.
The roots of the teeth, whether they are single or multiple in number each have two of the three previously mentioned layers in their makeup. The pulp chamber continues down from the crown into the roots and finishes at the apex of the root where there is an opening which allows the structures of the pulp chamber to exit and enter. This is also surrounded by dentin that finishes just before the apex, where it is surrounded not by enamel, but by cementum. Cementum is histologically different from enamel, but it acts as its equivalent from just below the gingival line and covers the entire root of the tooth. The meeting point between the enamel and the cementum is known as the cementoenamel junction.