What is it?

Mouth and oral structures

The gums

The gums consist of mucous membranes connected by thick fibrous tissue to the membrane surrounding the bones of the jaw. Around the base of the crown (exposed portion) of each tooth the gum membrane rises to form a little collar. The gum tissues are rich in blood vessels, receiving branches from the alveolar arteries; these vessels, called alveolar from their relationship to the alveoli dentales, or tooth sockets, also supply the teeth and the spongy bone of the upper and lower jaws, in which the teeth are lodged. The veins and lymphatic of the gums correspond essentially to the arteries.

The teeth

The teeth are hard white structures found in the mouth of humans and many other animals and usually are used for mastication (chewing). Humans, who are omnivores (eaters of plants and animal tissue), have teeth that belong, functionally and structurally, somewhere between the extremes of specialization attained by the teeth of carnivores and herbivores. The members of one class of vertebrates, the birds, have no true teeth.
 

Tooth Growth & Development

What's the difference between "baby" teeth and permanent teeth?

At between six and ten months of age, most infants begin to get their "baby" teeth. The central incisors (front middle teeth) usually come in first, and then teeth begin appearing on either side and work their way back to the second molars. By the time a child has reached three years old, most of the "baby" teeth should be present. The process begins to repeat itself when the child is about seven years old. The central Incisors fall out first and are replaced by permanent teeth. By the age of 21, most people have all of their permanent teeth.

"Baby" teeth are important because they hold the place for permanent teeth and help guide them into correct position. "baby" teeth play an important role in the development of speech and chewing.

Are there different types of teeth? What do they do?

Adult humans typically have 32 teeth—16 in the upper jaw and 16 in the lower jaw—that fit together and work in concert to chew food. Teeth on the right side of each jaw are usually identical to the teeth on the left side and matching teeth on opposite sides are referred to as sets, or pairs. Humans are heterodonts—that is, they have teeth of different sizes and shapes that serve different functions, such as tearing and grinding. In contrast, the homodont teeth found in many animals are all the same size and shape, and perform the same function.

Humans have four types of teeth, each with a specific size, shape, and function. Adult humans have eight incisors, located at the front of the mouth—four in the upper jaw and four in the lower jaw. Incisors have a sharp edge that is used to cut food. On either side of the incisors are the canines, named for their resemblance to the pointy fangs of dogs. The upper canines are sometimes called eyeteeth. There are two canines in each jaw, and their primary role is to tear food. Behind the canines are the bicuspids, or premolars, flat teeth with pronounced cusps that grind and mash food. There are two sets, or four bicuspids, in each jaw. Behind the bicuspids are the molars, where the most vigorous chewing occurs. There are twelve molars—three sets in each jaw—referred to as the first, second, and third molars. Third molars are often called wisdom teeth; they developed thousands of years ago when human diets consisted of mostly raw and unprocessed foods that required the extra chewing and grinding power of a third set of molars. Today wisdom teeth are not needed for chewing and, because they can crowd other teeth, are often removed.

What are the parts of a tooth?

Enamel, the clear outer layer of the tooth above the gum line, is the hardest substance in the human body. In human teeth, the enamel layer is about 0.16 cm (about 0.06 in) thick and protects the inner layers of the teeth from harmful bacteria and changes in temperature from hot or cold food. Directly beneath the enamel is dentin, a hard, mineral material that is similar to human bone, only stronger. Dentin surrounds and protects the pulp, or core of the tooth. Pulp contains blood vessels, which carry oxygen and nutrients to the tooth, and nerves, which transmit pain and temperature sensations to the brain. The outer layer of the tooth that lies below the gum line is cementum, a bonelike substance that anchors the tooth to the jawbone.

The visible portion of the tooth is called the crown. Projections on the top of each crown, used primarily for chewing and grinding, are called cusps. The portion of the tooth that lies beneath the gum line is the root. The periodontal ligament anchors the tooth in place with small elastic fibers that connect the cementum in the root to a special socket in the jawbone called the alveolus.

Each tooth consists of a crown and one or more roots. The crown is the functional part that is visible above the gum. The root is the unseen portion that supports and fastens the tooth in the jawbone. The shapes of the crowns and the roots vary in the different parts of the mouth and from one animal to another. Humans normally have two sets of teeth during their lifetime. The first set is acquired gradually between the ages of six months and two years. As the jaws grow and expand, these teeth are replaced one by one by the teeth of the secondary set. The first set is known as the milk, deciduous, or primary dentition. The teeth on one side of the jaw are essentially a mirror image of those located on the opposite side. The upper teeth differ from the lower and are complementary to them. There are five deciduous teeth and eight permanent teeth in each quarter of the mouth, making a total of 32 permanent teeth to succeed the 20 deciduous ones.

After a child's milk tooth becomes loose and falls out, the permanent tooth begins to emerge, a process that can be seen in this seven-year-old's mouth.

Teeth are formed from the skin, the enamel originating from the outer layer or epidermis and the inside of the tooth from the dermis. The milk (baby) teeth begin to form in the fetus at around seven weeks post-conception. Ten weeks later they are fully developed in the jaw, and the buds of the permanent teeth have started to form behind them. The buds for the permanent teeth lie dormant until they start to grow in the sixth week.

What About Protecting My Teeth with Fluoridation?

You may have been told that fluoridation can help prevent tooth decay. You'll be very surprised that this is NOT true.

• Water fluoridation and fluoride in your food can harm you.
• Why fluoride doesn't reduce dental caries (cavities).

Taking Care of Your Teeth

“Most parents do assume that cavities are caused by candy,” says pediatric dentist Jeanne Hibler, DDS. “But it’s not just candy: it’s any food that has any kind of sugar or carbohydrates that can be broken down by the bacteria in your mouth.” Read the entire article here.
 

Disorders of Human Teeth

The three main diseases of human teeth are tooth decay, also called dental caries; gum disease, or periodontal disease; and problems with tooth alignment, called malocclusions. Human teeth problems are treated or prevented by dentists, professionals who are specially trained to practice dentistry.

Tooth decay affects approximately 90 percent of all children by the time they are 14 years old. Tooth decay begins when bacteria are passed from mothers or caregivers to children between their first and second birthdays. When these bacteria are exposed to sugars commonly found in foods, the bacteria produce harmful acids that attack tooth enamel. Left unchecked, the acid eats holes in the enamel and forms cavities of tooth decay. Most tooth decay forms in the deep grooves on the chewing surfaces of the molars, called pits and fissures. Daily tooth brushing and proper dental care help prevent and reduce tooth decay. Dentists use preventive treatments to reduce the risk of tooth decay; clear plastic coatings painted on the teeth, called dental sealants, and applications of the mineral fluoride, which fortifies tooth enamel, are two such treatments. Fluoride is also added to public water supplies in a process called fluoridation, which benefits more than 150 million Americans.

Gum disease, or periodontal disease, is a progressive condition that worsens with age. Gum disease occurs when bacteria eat away at gum tissue, causing it to pull away from the teeth. This space between the tooth and gum, called a periodontal pocket, traps even more bacteria. Gum disease develops in two stages. Gingivitis, the early stage, causes red, swollen gums that bleed easily. Gingivitis can be eliminated through good oral hygiene and dental care. If not treated, gingivitis can progress to periodontitis, when bacteria attack the bone supporting the teeth. To treat periodontitis, dentists may have to surgically cut out the infected portion of the gum so the bacteria can be removed.

Malocclusions—teeth that are crowded, crooked, or out of alignment—make it more difficult to clean teeth, which can lead to other oral health problems such as tooth decay and gum disease. Many of these disorders start to appear between the ages of 6 and 12, when permanent teeth begin to erupt. Generally, malocclusions result when the jaw is too small to hold all of the teeth. Malocclusions are often genetic, tending to run in families. In other cases, dental injury or chronic thumb sucking may lead to poorly aligned teeth. Malocclusions are treated by dentists specially trained to correct them, called orthodontists.

To view the various conditions involving the digestive tract go to the Condition Center.

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