Your mouth: The basics
Date Posted: April 1, 2007
In-Depth Report
Your mouth: The basics
Your mouth plays a vital role in a variety of processes — from breaking food into small particles so it can be swallowed and digested to enabling verbal communication to serving as a first line of defense for the body by preventing microbes and other harmful agents from entering your system. Learning a little about the structure of your mouth will help you maintain the best possible oral health.
Your teeth
Your first teeth — called primary, deciduous, temporary, or baby teeth — form in the gums before birth and begin erupting at about six months. The complete set of 20 temporary teeth is usually in place by age two or three. These teeth serve several important functions. First, they allow an infant to begin eating solid foods and to develop speech. They also act as placeholders, enabling the permanent teeth to align correctly as they grow in.
Beginning at about age 6 and continuing until age 12 or 13, the baby teeth fall out and are replaced by their permanent counterparts, plus an additional eight teeth. Four more teeth, often called the wisdom teeth, usually emerge between ages 17 and 21, completing the adult set of 32 teeth.
You have several different types of teeth, including incisors, canines, bicuspids, and molars (see Figure 1). The variety in tooth shapes reflects the range of foods in the human diet. The set of teeth supported by your lower jaw is called the inferior dental arch, while the set of teeth supported by the upper jaw is the superior dental arch.
Your teeth are surprisingly strong. The incisors can exert 30–50 pounds of pressure, and the molars can bear down with more than 200 pounds of force.
Figure 1: Your teeth and their functions
The adult mouth has three types of teeth. Incisors: eight teeth in the middle front of the jaw (four upper and four lower) that have straight sharp edges shaped for cutting food. Canines: four larger teeth, also called cuspids or eyeteeth, with sharp points designed for ripping or tearing. Bicuspids and molars: the remaining teeth — 8 bicuspids (sometimes called premolars) and 8–12 molars, which have broad, flat surfaces with small mounds for grinding food. |
Anatomy of a tooth
The part of the tooth visible above the gum line, known as the crown, is covered with a hard, whitish material called enamel. Enamel is a nonliving substance composed of calcium and phosphorous. It's the hardest substance in the body, so it's ideal for biting, chewing, and resisting decay.
The enamel ends at the tooth neck (also called the cervix), where the root (the largest portion of the tooth) begins (see Figure 2). A tooth has one to three roots, depending on its size and the amount of chewing pressure it has to endure. The root of the tooth is covered with a thin layer of pale yellow bonelike material called cementum. Because cementum is softer than enamel, it's more vulnerable to decay if the gum line recedes enough to expose it.
Figure 2: A look inside your teeth
When you look at one of your teeth, the portion that you see is the crown. The root lies below the gum line and is embedded in bone. The crown is covered in enamel, a hard and strong whitish material. The root is covered with cementum, a bonelike material that is more vulnerable than enamel. Dentin is found inside the tooth. It protects the pulp, the soft core of the tooth that houses blood vessels and nerves. |
Inside the tooth are two other types of dental tissue: dentin and pulp. Dentin is harder than cementum but softer than enamel. It constitutes the largest portion of the tooth.
At the core of the tooth is a chamber extending from the crown into the root. Inside this chamber is the pulp, the only part of the tooth not hardened with calcium deposits. It consists of loose connective tissue laced with blood vessels that bring nourishment to the dentin. A network of nerves that runs through the pulp communicates pain when the pulp is damaged or infected. The nerves also respond to heat, cold, electricity, and some chemicals.
The teeth are secured by the periodontal ligaments, bands of fibrous tissue that connect the cementum to the bone.
Beyond your teeth
Several other important oral structures enable the teeth to do their job.
Oral mucosa. This is the soft pinkish-to-purplish tissue covering the inside of the mouth. Its primary function is to prevent irritants and infectious agents from entering the body. A fibrous protein called keratin makes most of the surfaces of the oral mucosa more resistant to injury.
Gums. Gum tissue (gingiva), a specialized portion of the oral mucosa, connects to each tooth at the neck and extends over the root and supporting bone. In a healthy mouth, the root remains entirely out of sight below the gum line. The gum tissue attaches securely to the underlying structures except at the upper edge, where it forms a tiny flap about 1.5 millimeters wide, at the margin of the tooth and gum. The V-shaped hollow under this flap is called the sulcus. It's easy for food and bacteria to get trapped in this pocket. This can lead to inflammation and eventually to periodontal disease, also called gum disease. Because gum tissue contains no keratin, it's particularly vulnerable to infection from bacteria that collect in the sulcus.
Bones and jaw. The five bones that make up the mouth include the powerful, horseshoe-shaped lower jaw (the mandible); the two bones of the upper jaw (the maxilla); and the two bones that form the roof of the mouth (the palate). The way in which your upper and lower teeth come together when you close your mouth is called your bite, or occlusion. For you to chew effectively, your teeth must mesh correctly.
Tongue. This muscular structure manipulates food in your mouth, bringing it into contact with the teeth and moving it into the throat. Your tongue is also essential for clear speech. Taste buds on the tongue enhance the pleasure of eating.
Salivary glands. Three pairs of glands release saliva into the mouth. There are two types of saliva: a watery substance that clears food and dead cells from the lining of the mouth, and a thicker secretion that binds chewed food into a ball so it can be swallowed. Saliva serves many purposes. It helps cleanse food and bacteria from the teeth, protects the mucosa from irritants and toxins that enter the mouth, and prevents the membranes from drying out. Saliva forms a protective film on the teeth, and its slightly alkaline pH helps neutralize acids (from food, drink, bacteria, or the digestive process) that could erode tooth enamel. It also contains compounds that destroy or prevent the growth of certain microbes, especially fungi. In addition, it contains calcium and phosphorous, which help regenerate tooth enamel that's been damaged by decay. Adding fluoride to the saliva, by way of toothpaste, drinking water, or mouth rinses, amplifies these healing effects. An insufficient flow of saliva — which can be caused by medications, irradiation, or certain diseases — greatly increases your risk for tooth decay.
Review Date: 2007-04-01
Harvard Medical School does not endorse products or services.
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