Human oral cavity
In human anatomy, the mouth is the first portion of the alimentary canal that receives food and saliva. The oral mucosa is the mucous membrane epithelium lining the inside of the mouth.
The mouth, normally moist, is lined with a mucous membrane, and contains the teeth. The lips mark the transition from mucous membrane to skin, which covers most of the body.
The first space of the mouth is the mouth cavity, bounded laterally and in front by the alveolar process (containing the teeth), posteriorily by the isthmus of the fauces, superiorly or the roof is formed by hard palate and soft palate and inferiorly or the floor of the mouth is formed by the mylohyoid muscles and is occupied mainly by the tongue. The oral cavity is also known as the mouth which swallows food that then goes down the esophagus and into the stomach.
Teeth of humans are small, calcified, hard, whitish structures found in the mouth. They function in mechanically breaking down items of food by cutting and crushing them in preparation for swallowing and digestion. The roots of teeth are embedded in the maxilla (upper jaw) or the mandible (lower jaw) and are covered by gums. Teeth are made of multiple tissues of varying density and hardness.
The teeth are the hardest substances in the human body. Besides being essential for chewing, the teeth play an important role in speech. Parts of the teeth include:
- Enamel: The hardest, white outer part of the tooth. Enamel is mostly made of calcium phosphate, a rock-hard mineral.
- Dentin: A layer underlying the enamel. Dentin is made of living cells, which secrete a hard mineral substance.
- Pulp: The softer, living inner structure of teeth. Blood vessels and nerves run through the pulp of the teeth.
- Cementum: A layer of connective tissue that binds the roots of the teeth firmly to the gums and jawbone.
- Periodontal ligament: Tissue that helps hold the teeth tightly against the jaw.
A normal adult mouth has 32 teeth, which (except for wisdom teeth) have erupted by about age 13:
- Incisors (8 total): The middlemost four teeth on the upper and lower jaws.
- Canines (4 total): The pointed teeth just outside the incisors.
- Premolars (8 total): Teeth between the canines and molars.
- Molars (8 total): Flat teeth in the rear of the mouth, best at grinding food.
- Wisdom teeth or third molars (4 total): These teeth erupt at around age 18, but are often surgically removed to prevent displacement of other teeth.
The crown of each tooth projects into the mouth. The root of each tooth descends below the gum line, into the jaw.