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In
Lesson 2, students add to their awareness of the mouth as an environment.
First, students use their fingers to "take a trek" in their mouths. They explore
the overall environment of the mouth and the various structures inside. Next,
students explore the different types, shapes, and functions of the teeth and
estimate and confirm the number of teeth in their mouths. Then, students create
records and graphs to illustrate the number of teeth among the students in
the class. As an extension, students recognize the importance of teeth, lips,
and tongue to the formation of speech as they try to say "funny" ABCs. Students
also practice recognizing the structures of the mouth while they play a matching
game.
In this lesson, students will
After completing this activity, students will
The
mouth, or oral cavity, is a gateway to the entire body. It allows us to talk,
smile, eat and drink, digest food, and helps protect us from disease. The
mouth can reveal signs of diseases (vitamin deficiencies, immune diseases)
and provide physical clues to illness (a fever). The tissues of the mouth
can serve as an early warning system. For example, the mouth can show the
effects of tobacco use, providing perhaps the only visible evidence of its
harmful effects. These relationships between the mouth and the rest of the
body reinforce the importance of maintaining good oral health. Currently,
researchers are exploring whether or not there is a link between chronic oral
infections and other diseases such as heart disease, stroke, diabetes, and
premature births.1
The mouth is an amazing environment made up of many physical structures. We can see and feel some of the structures, such as the crowns of the teeth, tongue, gums, lips, cheeks, and roof of the mouth. Other structures are invisible to the naked eye because they are covered by bone or skin tissue, such as the roots of the teeth, salivary glands, and the developing permanent teeth in young children.
Did you know that the outer layer of our teeth, the enamel, is the hardest substance in the body? Although some children, and even some adults, may think that teeth are merely hard, rocklike structures, teeth are composed of living tissue. Each tooth has a crown, the visible portion of the tooth, and a root (or roots) embedded in the bone. The enamel consists of many tiny, long, thin rods made of minerals. Directly under the enamel is dentin, a mineral material somewhat like bone but stronger. The innermost part of the tooth, the pulp, is a chamber containing nerves and blood vessels that carry nutrients and oxygen to the tooth.2 The root is covered and protected by a thin layer of cementum, a bonelike tissue that helps attach the tooth to its bony socket via elastic fibers (a ligament).
Humans have two sets of teeth: primary and permanent teeth. The two sets of teeth are similar in structure, although primary teeth have thinner enamel and larger pulp chambers. Humans have 20 primary, or deciduous, teeth that begin to emerge at around six months of age but develop well before birth.3 Expectant mothers need to eat a nutritious diet containing adequate calcium to ensure the proper development of their baby's teeth. Primary teeth play a key role in the development of children by:
Keeping primary teeth healthy is just as important as keeping permanent teeth healthy. Children who develop tooth decay in their primary teeth are more prone to decay in their permanent teeth. Also, if a primary tooth is lost prematurely, the adjacent teeth may drift into the open space, leaving insufficient room for the permanent teeth that follow.4 This tooth movement may result in crowded or misaligned permanent teeth (dental malocclusion). These types of malocclusions may not necessarily affect oral health or function but can compromise aesthetics and self-image.
 Primary teeth are shaded in this drawing. Unshaded areas indicate permanent teeth. Reprinted with permission from Stephen J. Moss, Growing Up Cavity Free: A Parent’s Guide to Prevention, Chicago, 1993, Quintessence Publishing Co. |
The loss of a child's first primary tooth is a noticeable and memorable event, a rite of passage that typically starts at about five or six years of age. Much less celebrated but extremely important is the appearance of a child's permanent molars. The initial permanent molars to erupt are the first (or 6-year) molars followed by the second (or 12-year) molars. The permanent molars erupt in the space behind the primary molars. Because a primary tooth is not lost before these molars appear in the mouth, the growth of the molars is often unnoticed. Care of these new molars is crucial, however. The biting surfaces of molars have many grooves and pits that make them prone to decay. Fortunately, good dental care and dental sealants can keep them healthy. (See Lessons 4 and 5 for more information on the causes and prevention of decay.)
When the permanent teeth are ready to erupt, the bone around them pushes them into the mouth through the gums. Have you ever noticed that brand new permanent incisors have small projections or bumps on their edges? These projections, called mamelons, help the tooth rise through the tissues and into the mouth; they usually wear out with normal chewing and biting to leave a smooth edge. When all their permanent teeth have emerged, humans have 32 teeth—16 in each jaw. For most people, 28 permanent teeth have emerged by age 14, while the last four third molars, the wisdom teeth, erupt only if the jaw allows space for them.3
All teeth have similar structure, with a crown and root(s), but they have different shapes to help them perform unique functions. For instance, the incisors are chisel-shaped to cut or incise food, while the canines have stronger, deeper roots and single-pointed cusps for tearing and ripping food apart. The premolars (or bicuspids) and molars are shaped to crush and finally grind food for easier digestion.3
| Did You Know? Grown dogs have 42 permanent teeth. Adult humans have 32 permanent teeth. (Puppies have 28 primary teeth while children have 20 primary teeth.) The front teeth of beavers can grow up to 4 feet per year. When they chip or wear their teeth down, the teeth continue to grow. Human teeth do not keep growing; if we wear or chip our teeth, the damage is permanent. |
Humans, similar to other mammals, including cats and dogs, have a primary set and a permanent set of teeth. Others, like most rodents, sharks, and other fish, have only one set of teeth that keeps growing throughout their lifetime. Animals eat different types of foods, so they have teeth that are specialized to help break down the food in their diet so that they can swallow it. For example, meat-eating animals have well-formed, pointed canines for holding and tearing food while plant-eating animals, such as cows and horses, have well-formed incisors for cutting grassy food and flat molars for grinding it.2
The gingiva, commonly known as gums, is a dense, soft tissue that surrounds the teeth. It covers the bone that surrounds the roots of the teeth and anchors them in place. If plaque is allowed to build up along and under the gum line, through lack of oral hygiene, oral bacteria release harmful enzymes and toxins that cause the gums to become red, swollen, and tender and to bleed easily during tooth brushing or flossing. This inflammatory process is called gingivitis. If the bacterial infection reaches the bone and supporting tissues around a tooth, it may lead to loss of support of the tooth and, in some cases, tooth loss. The vast majority of gum disease can be prevented by careful daily plaque removal with a toothbrush and floss and through regular dental office visits.
The tongue is a strong and flexible muscle in the mouth. It extends from the back of the mouth and is attached to the floor of the mouth. The great range of movement of the tongue helps it move food around the mouth so that a person can chew and swallow.2 The tongue is a sensory organ, allowing humans to taste using the taste buds that are scattered on its surface and sides. The human tongue twists and turns, allowing us to form specific sounds and words that make up speech.
Another visible structure in the oral cavity is the palate, or roof of the mouth. Humans have a hard palate made of bone covered by a tissue called a mucous membrane. Behind the hard palate is the soft palate, which is a movable fold of mucous membrane that encloses muscle tissue. The soft palate prevents food or drinks from going into the nasal passages by pressing against the back of the throat during swallowing. If, during fetal development, the two sides of the palate do not fuse, a cleft palate occurs, leaving an opening in the roof of the mouth. This developmental defect occurs very early in pregnancy due to a combination of genetic and environmental factors.2
Saliva, the fluid produced by salivary glands, makes the oral environment moist. The major salivary glands are the parotid, submandibular, and sublingual glands. Humans have two parotid salivary glands, located in the cheeks, in front of and just below each ear. The two submandibular glands and the two sublingual glands are located on the floor of the mouth, beneath the tongue. 5 In addition to these major glands, the human mouth contains hundreds of tiny glands, called minor salivary glands, located on the inner side of the lips, on the inner cheek area, and in other linings of the mouth and throat. Salivary glands may be affected by viral infection. Mumps, the most common salivary gland infection, occurs when the parotid glands become infected. Salivary glands also can be affected by bacterial infection, small stones that cause obstruction in the salivary ducts, or cancer. These salivary gland diseases and disorders can be treated either medically or surgically.5
 Major salivary glands. |
Saliva plays a major role in the health of the oral cavity and the entire body. Saliva is made up primarily of water but also contains digestive enzymes, such as amylase, and minerals. The flow of saliva helps to wash off microorganisms from the teeth and soft tissues of the mouth that cause bacterial, viral, and yeast infections. Saliva does more than simply cleanse materials from the teeth. Saliva contains molecules that can kill or inhibit microorganisms; it is the body's own antibiotic. Saliva also helps preserve the teeth by bathing them with protective minerals, such as calcium, phosphate, and fluoride, that make the enamel on the surface of the tooth stronger. These minerals can aid in the early repair of tooth decay through the process of remineralization.3 (See Lesson 5 for more information about remineralization.)
Saliva also contributes to digestion by breaking down food chemically as the teeth break down the food physically. Together, saliva and teeth initiate the digestive process by breaking down food into smaller particles that pass to the back of the mouth where they are swallowed. Saliva helps clear the mouth by turning starches that we eat into sugars, which then dissolve and leave the mouth. It also enhances the taste of food by allowing the food to interact with the taste buds. The salivary glands also help indicate if the body is hydrated; a dry mouth gives us the signal to take fluids.
Another special quality of saliva is its ability to neutralize acids. Acids are produced in the mouth when certain oral bacteria break down food particles. (See Lesson 4 for more information about the actions of oral bacteria.) These acids, when held onto the tooth surface, destroy enamel and cause tooth decay. However, saliva neutralizes the acids produced by plaque bacteria. Thus, saliva protects the teeth from demineralization and tooth decay.4, 6
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| Activity Number | Web Version |
| Activity 1 | no |
| Activity 2 | yes |
| Take-home Activity | no |
| Activity 3 | yes |
| Extension Activity 1 | no |
| Extension Activity 2 | optional |
| Photocopies | ||
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| Activity Number | Master Number | Number of Copies |
| Activity 1 | Master 2.1, The Parts of the Mouth | 1 transparency (optional) |
| Activity 2 | none | none |
| Take-home Activity | Master 2.3, Take-home Activity 1: My Tooth Record | 1 copy for each student |
| Activity 3 | none | none |
| Extension Activity 1 | none | none |
| Extension Activity 2 | Master 2.4, The Parts of My Mouth | at least 3 sets* for the class (optional) |
| *A set consists of game cards mounted or copied onto thick paper or card stock. | ||
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