Teeth and Malocclusion

by Robert Tallitsch, PhD | November 15, 2023

Video explaining Teeth and Malocclusion with a patient example!

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Teeth are part of the digestive tract. They perform a variety of functions during the mastication (chewing) of food, including cutting, tearing, grasping, crushing, and grinding. Teeth also play other roles, including assisting in the formation of words during speech, and in the formation and maintenance of the shape of your face.

The proper positioning of teeth should result in a small overlap of the teeth of the maxillae with the teeth of the mandible. This allows the ridges of the upper molars to fit into the grooves of the lower molars. This proper alignment prevents you from biting your cheeks and lips and protects your tongue during mastication and talking.

In this Brain Builder we will talk about the general anatomy of a tooth, and the two sets of teeth — deciduous (baby) teeth and adult, permanent teeth. Then we will discuss what a malocclusion is, how it develops, and some of the most common forms of treatment for malocclusion.

Structure of a Tooth

A tooth is composed of the following three subdivisions:

Crown, which is the portion of the tooth that lies above the gum line.
Root, which is the portion of the tooth that is embedded in bony sockets of the mandible or maxillae. These bony sockets are termed the root sockets, or root alveoli.
Neck, which marks the boundary between the crown and root of the tooth.

The layers, from deep to superficial, of a fully formed tooth are the

Dentine (or dentin), which makes up the bulk of the tooth. This layer of the tooth is composed of a mineralized matrix that is similar to bone. However, unlike bone, the dentine does not contain living cells. The living cells of the tooth are found in the hollow pulp cavity of the tooth. These cells send cytoplasmic processes superficially into the dentine and serve to maintain the dentine of the tooth.
- A layer of cement covers the dentine of the root of the tooth. The cement protects the dentine of the root and also firmly anchors the root of the tooth into the socket of the mandible or maxillae.
Enamel, which is the hardest substance made in the human body, covers the dentine of the crown of the tooth.

Two Sets of Teeth

Two sets of teeth appear at different times as you mature. Although the times may vary from individual to individual, the first set, termed deciduous teeth (also termed primary or baby teeth), typically start to appear at six months of age and are completely present by the end of the second year. There are typically twenty deciduous teeth: four molars, two canines, and four incisors in the mandible, and an equal number in the maxillae. Deciduous teeth of the mandible typically erupt before the corresponding teeth of the maxillae. The approximate times of eruption are

Central incisors: six to eight months
Lateral incisors: eight to ten months
First molars: one year
Canines: eighteen months
Second molars: two years

At approximately six years of age the deciduous teeth begin to be replaced with permanent teeth. There are thirty-two permanent teeth, sixteen in the mandible and sixteen in the maxilla. Their approximate times of eruption are:

First molars: six years
Central incisors: seven years
Lateral incisors: eight years
First premolars: nine years
Second premolars: ten years
Canines: eleven years
Second molars: twelve years
Third molars (also termed the wisdom teeth): seventeen to thirty years

As with the deciduous teeth, permanent teeth of the mandible typically erupt before the corresponding teeth of the maxillae.

Malocclusion

A malocclusion, also termed a “bad bite”, is when an individual’s upper and lower teeth don’t align properly when the mouth is closed. There are numerous causes for malocclusions. In most individuals, malocclusions occur when the teeth are too large for the mouth. This causes crowding of the teeth, which affects the alignment of the mandible and maxillae.

Other possible causes for malocclusions include

Premature loss of a tooth, which results in the shifting of some of the remaining teeth to fill in the gap.
Sucking of the thumb as a child, which caused a shifting of the position of one or more developing or adult teeth.
Although rare, there are some more severe inherited conditions cause the malalignment of the mandible and maxillae, resulting in a malocclusion.

There are three classes of malocclusion:

In a class-one malocclusion the bite is normal, but the upper teeth overlap the lower teeth slightly more than normal.
A class-two malocclusion, also termed retrognathism (or overbite), occurs when the teeth of the maxillae severely overlap the teeth of the mandible.
In a class-three malocclusion, also termed a prognathism (or underbite), the lower jaw protrudes, or juts forward such that the mandible and lower teeth overlap the maxillae and associated teeth.

If the malocclusion is not corrected, or is not corrected properly, the individual may develop one or more of the following: a temporomandibular joint disorder (also termed TMJ), a speech impediment, such as a lisp, or experience severe discomfort when biting or chewing.

The treatment of a malocclusion is typically accomplished by braces. Braces cause the teeth to be pulled into a normal alignment over a prolonged period of time. As the teeth are pulled into their new positions the bone of the maxillae and/or mandible will be remodeled. This remodeling causes the tooth socket to change shape, allowing the teeth to be held in their proper, new position.

In some circumstance oral surgery may be required to either remove one or more permanent teeth, thereby eliminating the overcrowding of the teeth. Such a procedure is typically followed up with braces, which causes the remaining teeth to be realigned into a better position, thereby eliminating the malocclusion of the teeth of the maxillae or mandible.

In rare circumstances, such as the correction of an inherited malocclusion, bone may be added to or removed from the mandible, thereby allowing the teeth of the mandible and maxillae to align properly.

Left untreated, a malocclusion will affect one’s oral health, in that the presence of a malocclusion increases the chances of cavities and gum disease. In severe cases an untreated, severe malocclusion may affect the patient’s self-esteem and/or mental health.

The proper treatment of a malocclusion takes both time and patience on the part of the patient, and the skill of a trained orthodontist or oral surgeon.

Key Terms

Class-one malocclusion - The bite of the individual is normal, but the upper teeth overlap the lower teeth slightly more than normal.

Neck of the tooth - The portion of the tooth between the crown of the tooth, which is superior to the gum line, and the root of the tooth, which is embedded within the socket of the tooth.

Maxilla (plural is maxillae) - One of two bones that forms the upper jaw of an individual.

Malocclusion - Also termed a “bad bite”, is when an individual’s upper and lower teeth don’t align properly when the mouth is closed.

Deciduous teeth - Also termed “baby teeth”, these teeth typically start to appear at or around age two. Deciduous teeth are replaced by permanent teeth starting at or around age six.

Enamel - The hardest substance made in the human body, which covers the dentine of the crown of the tooth.

Mandible - The bone that forms the lower jaw of an individual.

Mastication - The process of chewing food by the teeth of the mandible and maxillae.

Tooth socket (also termed the tooth alveolus) - Bony sockets within the mandible and maxillae that surrounds and embeds the root of the tooth, thereby holding it in place.

Root of the tooth - The portion of the tooth that is embedded in bony sockets of the mandible or maxillae.

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