Teeth, Structure of the Tooth, Dentition and Dental Care

The Teeth

Teeth are bone-like structures embedded in the gums of many vertebrates, and are modified for biting, tearing, grinding and chewing. In this regard, the teeth is defined as a set of hard, enamel-coated structures in the jaws of most animals with with backbone (vertebrates), used for cutting, tearing and grinding.

Below are the types of teeth in humans:

• Incisors: These are four flat front teeth used for cutting food.

• Canines: These are four pointed (sharp) teeth suitated just after the incisors, and before the premolars. They are used for tearing flesh.

• Premolars: These are eight flat teeth used for crushing food. They are suitated just after the canines and before the molars. Together with the molars, they are called the cheek teeth.

• Molars: These are the last large twelve teeth with broad surfaces used for grinding food. They are suitated just after the premolars. Included in the molars are 4 wisdom teeth. The wisdom teeth are the third molars which erupts typically between ages 17 and 25. It may be extracted from the mouth due to crowding.

Note: Humans have two sets of teeth. These are 20 milk teeth present in children and 32 permanent teeth in adults.

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Structure of the Tooth

A tooth has two main structural regions. These are: the crown (which is visible), and the root. The crown is the top part of the tooth which we see above our gums. It is used to bite and chew food. The root is the hidden structure under the gum that holds the tooth in place.

The image below show the various structures of the tooth:

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The various layers and tissues of the tooth comprises the following parts:

• Enamel: This is the hard, white and shiny covering of the crown of the teeth. The enamel is the toughest tissue in the human body, and it functions to protect the tooth.

• Dentine (or Dentin): This is a hard layer just under the enamel. The dentin is the largest part of the tooth. It assists in cushioning chewing pressure, consequently protecting the inner nerves.

• Pulp Cavity. This is the soft hollow central part of the tooth containing the sensory nerves and blood vessels. Its blood supply and innervation keeps the tooth alive.

• Cement. This is is the structure which fixes the tooth to its socket, glueing it to the jawbone. It is therefore a hard connective tissue covering the outer root. It is also called the cementum.

• Periodontal Ligament: These are tiny fibers that hold the root tightly against the jaw bone.

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Dentition

Dentition is defined as the development, number number and arrangement of the different kinds of teeth in the mouth of an organism. We have two types of dentition in animals. These are:

1. Homodont Dentition: The teeth in an organism's mouth have the same shape, size and structure. Examples are seen in mammalian vertebrates like reptiles (e.g, lizard and alligators), amphibians (e.g, frogs, toads and salamanders), and fishes (e.g, the great white shark and barracuda).

2. Heterodont Dentition: The teeth in an organism's mouth are differentiated into various sizes, numbers, shapes, forms; and are used for distinct purposes. For example, humans have heterodont dentition in which the teeth are differentiated into incissors (for cutting), canines (for tearing), premolars (for crushing), and molars (for grinding).

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Below are the characteristics of the various types of teeth in heterodont dentition.

1. Incisors: They show the following characteristics:

• They are chisel-shaped and are usually situated in front of the mouth.

• Each incisor has one root.

• They have broad flat and sharp cutting edge.

• They are used for biting and cutting off pieces of food.

• They develop from four lobes (three on the labial/facial side and one lingual lobe forming the cingulum).

2. Canines: They show the following characteristics: 

• Canines are conical and have sharp-point at the tips, as seen in carnivorous animals like dogs, lions, wolves, etc.

• They are located just after the incisors, and before the premolars.

• They possess the longest and strongest single roots, making them deeply and firmly anchored in the jawbone.

• The upper canine (located in the maxilla) are larger and sharper than the lower canine (located in the mandible), which are slightly narrower and longer-crowned.

• They are used for tearing flesh, and are consequently absent in herbivores like ruminants.

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3. Premolars: They show the following characteristics:

• They have broad and flat surfaces with pointed sides.

• Most premolars have a single root. However, the maxillary first premolar is an exception, since it commonly features two roots.

• They act as a bridge to crush, shear, and grind food before it reaches the back molars.

4. Molars: They show the following characteristics:

• They are the largest, strongest, and most posterior teeth in the human mouth.

• Molars have broader surfaces than the premolars.

• They possess between 4 and 5 distinct chewing bumps (cusps) on the occlusal surface.

• They are used for crushing and grinding food. For this reason, they are absent in infants.

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Dental Formula

A dental formula is a formula which shows the actual number and arrangement of the different kinds of teeth in the upper and lower jaws in one half of the mouth. In this regard, the dental formua lists teeth for one side (half) of the upper and lower jaws.

Dental formula is represented as a fraction (or ratio) multiplied by two (so as to calculate its value for both sides of the jaw).

The numerator in this fraction are the teeth in the upper jaw in one half of the mouth, and the denominator represents those of the lower jaw.

Note: You can think of dental formula as a shorthand method typically used to express the number and types of teeth in a mammal.

When reading a dental formula, "I" stands for incissors, "C" for canine, "PM" for premolars, and "M" for molars. Dental formula use capital letters for permanent teeth and small (lowercase) letters for baby or deciduous teeth.

Below are the dental formula of some animals:

• Man: I 2/2, C 1/1, PM 2/2, M 3/3 = (16 × 2) = 32

• Dog: I 3/3, C 1/1, PM 4/4, M 2/3 = (21 × 2) = 42

• Rabbit: I 2/1, C 0/0, PM 3/2, M 3/3 = (14 × 2) = 28

• Cow: I 0/4, C 0/0 or 0/1, PM 3/3, M 3/3 = (16 × 2) = 32

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Dental Care

Dental care is the maintenance of a healthy mouth, including the teeth, gums, and tongue.  The decaying of teeth is caused by bacteria which breaks down and ferment sugars into acids within the teeth, causing pains, weakening, and consequent decay or removal of the tooth if not treated.

You can read on tooth structure and care of the teeth here.

Tooth decay can be prevented by adequately caring for the teeth. The teeth can be cared for through the following ways:

• Proper brushing of the teeth twice daily with a good toothbrush and toothpaste.

• Avoidance of sugary food since bacteria feed on sugars, converting it into acids that attack the teeth.

• Periodic washing of the mouth with hydrogen peroxide to remove kola and tobacco stains.

• Regular eating of vegetables, fresh fruits and balanced diet.

• Avoid misuse of the teeth through opening of bottle corks with it.

• Daily use of dental floss to reach plaque and food pieces stuck between the innermost part of the teeth where the toothbrush cannot fit.

• Drinking of adequate water to help wash away food particles. This also keeps the mouth hydrated.

• Visit the dentist at least once a year.

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