Various types of teeth and structural anatomy of human tooth


The human body includes different types of teeth in the jaws of the mouth. This article gives an account of the different types of teeth present in the human body, their functions, and also their arrangement. This resource also gives a detailed account of the structure of the human tooth and important dental diseases. Some frequently asked interesting questions also appear at the end of this topic.

Introduction

The teeth are the hardest parts of the human body meant for biting and chewing food. The teeth of the human body are said to be thecodont type as they are enclosed in the sockets of bones. Human teeth are also known as heterodont type as they have more than one type of teeth, differing in size, shape, and function. Human teeth are said to be the diphyodont type because two types of teeth exist in one's lifetime. The two types of teeth are deciduous teeth (milk teeth) and permanent teeth.

Deciduous teeth

These teeth are also known as primary teeth or milk teeth. These teeth start developing when the fetus is 2.5 months old. They start appearing externally when the baby 6-8 months old. As each teeth grows, it pushes out of the gums, and that what we call it teething. By two years of age, the complete set of 20 milk teeth appear in the child.

There are twenty deciduous teeth, arranged ten in each jaw. They consist of three kinds of teeth, namely four incisors, two canines, and four molars. The deciduous teeth make way for the permanent teeth to erupt in their normal position. Between the ages of three to twelve, the roots of deciduous teeth dissolve, and the permanent teeth start erupting from below. As it happens, the deciduous teeth get loosen and fall out.

Permanent teeth

In humans, between six and twelve years of age, all milk teeth are replaced by permanent teeth. Four different kinds of permanent teeth are present throughout their life in adults. They are incisors, canines, premolars, and molars.

Incisors

These teeth are located on the front side of each jaw meant for biting and cutting the food. There are four incisors present in each jaw, two each in two halves of each jaw. These teeth are characterized by sharp chiseled cutting edge and the teeth have a single root canal. The central incisors of the lower jaw are considered to be the smallest permanent teeth in our mouth.

Canines

There are two canine teeth in each jaw, one on each half of the jaw located next to incisor teeth. They are long, conical, sharp ant pointed teeth meant tear fleshy food. These teeth also have only one root. These are usually absent in herbivorous animals as they do not eat the flesh like a rat but well developed like in dogs.

Premolars

They are four in number in each jaw and are present next to canines on each half. These teeth are provided with a large broad, humping surface. The small surface humps of the teeth are known as cusps. As premolars include two cusps on their teeth, the premolars are popularly known as bicuspid teeth. The premolar teeth are provided with one or two roots for them. They help in mashing, crushing, and grinding the food.

Molars

There are six molars present in each jaw and 3 on each half of the jaw. Molars are larger than the premolars and are usually have 3-5 cusps. The last molar on each side of the jaw is known as wisdom teeth. These teeth develop only in adult age usually around 25 years. Molars usually appear in adults in their early twenties. Like premolars, molars also help in crushing and grinding food.

Dentition and dental formula

The development of teeth and their arrangement in the mouth is known as dentition. The dentition of an individual species of the organism depends upon the diet and feeding habits of the organism.

Dental formula

A dental formula express the arrangement of the teeth by expressing the kind of teeth and the number in one half of the upper jaw and the denominator, the teeth in one half of the lower jaw. The whole formula is multiplied by two to get the total number of teeth.

I: C: Pm: M
------------ x2
I: C: Pm: M
Here in the above dental formula, I represent Incisors, C for Canines, Pm for Premolars, and M for Molars.

Dental formula in a human adult

{ i 2/2 c 1/1 pm 2/2 m 3/3}

The formula can be briefly written as 2 1 2 3/ 2 1 2 3

Number of teeth on one side of the jaw = 2+1+2+3 = 8
Number of teeth on both sides of the jaw = 2x8 = 16
Total number of teeth in both jaws = 2x16 = 32.

Dental formula in a human child

{ i 2/2 c 1/1 pm 2/2 m 0/0 } and Total = 20

The formula can be briefly written as 2 1 2 0/ 2 1 2 0.

Dental formula in a young human

{i 2/2 c 1/1 pm 2/2 m 2/2} and Total=28.

The formula can be briefly written as 2 1 2 2 / 2 1 2 2

Typical structure of human tooth

Human has a fixed upper jaw and movable lower jaw. Teeth are embedded inside the bony sockets or alveolus of the jaw. Each tooth consists of three parts namely, Crown, Neck, and Root.

Anatomy of human Molar Tooth
Anatomy of Human Molar Tooth (Diagram by the Author)

Crown

The visible part of the tooth that is exposed beyond the gum is known as the crown. It is covered with the hardest substance of the body called enamel. Calcium, phosphorus, and small amounts of water are the constituent parts of enamel. The enamel helps the tooth to withstand very high pressure while the tooth is cutting, biting, and grinding the food. The enamel is white in colour and may get wear out with age. As it wears out the tooth appears to be yellow in color as the dentin below the enamel gets exposed.

Below the enamel, a hard yellowish bone-like tissue made up of minerals, living cells, and water present is known as dentin. Dentin is also hard but not as hard as enamel and can decay.

Neck

It is the narrow portion present between crown and root is known as the neck. The neck is also known as the dental cervix situated between crown and root. The cementum that covers the root will meet here the enamel of the crown.

Root

The basal part of the tooth that is embedded in the jaw bone and that holds the tooth firmly in its place. Dentine forms the bulk portion of the tooth. There lies a pulp cavity in the dentine that encloses sensory cells, nerve fibers, and blood vessels. The pulp cavity can be divisible into the pulp cavity located in the crown and the root canal in the root.

The dentine in the root region is covered over by a hard material called cement or cementum. It is mainly composed of minerals and water. This layer of hard material meets the enamel layer of the crown in the neck region. Cement material help to hold the tooth in the socket firmly in its position.

Periodontal ligaments are very short fibers that extend through cement into the bony socket and helps to anchor the tooth. It also absorbs shocks while chewing.

Dental health

The loss of our permanent teeth is mainly due to dental decay and gum disease.

Dental decay (dental caries)

Decay of teeth occurs when small cavities form in the enamel. The bacteria present on the surface of our teeth are the cause for the formation of these cavities. The acids produced by the bacteria on the tooth surface will dissolve the calcium salts in the enamel layer causing cavities. The acids produced by bacteria will reach the pulp cavity through cavities and irritate the nerve endings that cause tooth pain. The only way to get over this problem is to remove the affected tooth. One best way to avoid tooth decay is to avoid eating sugars more frequently and thoroughly washing your mouth after eating.

Gum disease (periodontal disease)

Usually our teeth are covered by a layer of saliva and mucous. The bacteria present in this layer by its activities builds up a coating over the teeth called plaque. The plaque layer becomes still hard due to the deposition of mineral salts of calcium and magnesium. If this bacterial plaque is not removed periodically, it spreads into the gaps between gum and enamel causing inflammation called gingivitis. This disease causes redness, bleeding of gums, and bad breath. If gingivitis is not treated in time, the fibers holding the tooth in the jaw get destroyed, and the tooth become loosened and falls out is the final result. This diseased condition is known as periodontitis.
A deficiency of vitamin D is associated with enamel defects and an increased risk of dental caries

Most frquently asked questions;-


  1. What is the hard outer covering of tooth?
    Ans. Enamel

  2. What is the number of molar teeth in an adult?
    Ans. 12

  3. where do you find nerve fibers and blood vessels in the internal structure of the tooth?
    Ans. Pulp cavity

  4. What is the hard substance present around the root of the tooth that holds the tooth in the socket?
    Ans. Cement

  5. What do you mean by diphyodont type of teeth?
    Ans. If two successive sets of teeth present in man's life are said to be the diphyodont type of teeth

  6. Name the teeth helpful for tearing food.
    Ans. Canines

  7. Name the teeth which are shed and replaced in human life?
    Ans. Deciduous teeth (Milk teeth)

  8. State symptoms of gingivitis dental disease.
    Ans. Bleeding of gums and bad odor from mouth

  9. What is a wisdom tooth?
    Ans. The last molar in each jaw is known as a wisdom tooth

  10. Where do you find the dentine layer in a tooth?
    Ans. Next to enamel layer


Here is a video on the structure of the human teeth:-


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