Teeth

The teeth (Latin: dentes) are small structures containing solid bone-like tissue on the outside and soft connective tissue on the inside. The teeth belong to the digestive system, and they lie in the dental alveoli of the maxilla and mandible. They are mainly responsible for mechanical food procession in the digestion process.

Types of teeth 

Humans have two types of dentition during their lifetime. The first set appearing is the primary dentition or milk teeth, also called the deciduous teeth. During childhood, they slowly get replaced by the secondary dentition or permanent teeth

Primary teeth are smaller with smaller roots but relatively bigger pulp chambers compared to the secondary dentition. Children have 20 milk teeth starting to appear at the age of six to eight monthsAround the age of 6 to 7 years starts the replacement of milk teeth. It usually continues till 12 to 14 years. The dentures of the permanent teeth lie down between the milk teeth’ roots until the time of replacement. The last permanent teeth to appear are the last molar teeth, also known as the wisdom teeth. It usually happens between the age of 17- 24 years.

The permanent teeth divide into two groups. One contains teeth that replace the milk teeth, but the other group - teeth that don’t have ancestors from the milk dentition. The first group includes the incisor, canine, and premolar teeth. The second group is formed by the molar teeth and increases the teeth number from 20 to 32 as each side of the upper and lower jaw contains three molar teeth. Children’s molar teeth are the premolar teeth in adults.

Teeth eruption times

The first teeth that appear from primary dentition are the medial incisors around 6-8 months. Not so long after, the lateral incisors appear. The first molar tooth of the primary dentition can be visible around 12 to 15 months, the canine teeth emerge around 16 to 20 months, but the next premolar tooth can be visible only at 20 to 24 months of age.

The first molar tooth of the secondary dentition appears around the age of 6-7 years. Medial incisors replace milk teeth around eight years, lateral incisors - 9 yearsfirst premolar tooth around ten yearscanine around 11 to 13 years, while the second molar tooth appears only around 13 to 16 years. Wisdom tooth or the last molar tooth can emerge anytime between 17 to 30 years or even later, but usually, it happens till 24 years.

Teeth anatomy

Each tooth has three parts - the crown, the neck, and the root. 

The visible part of the teeth is the crown, elevated above the gingiva. It has white or yellowish-white color depending on several factors such as the person’s age or nutrition. The roots of the teeth are located in the dental alveoli of the alveolar arches of the mandible and maxilla, while the neck of a tooth connects both parts (the crown and the root) located in the middle between them. The neck of the tooth has a connection with the marginal gingiva, and the height of it varies between 1 up to 1,5 mm (0.039 to 0.059 inches).

The root of the tooth is fixated by a gomphosis. It is a continuous bone connection or synarthrosis type called fibrous joint type. It binds the teeth to dental alveoli. The movement in gomphosis is minimal, although it can increase by changes caused by aging, various disorders, and pressure changes. 

Each tooth is also fixated in its place by the periodontium, which is formed by specialized fibrous tissue between the root of the tooth and the bone. Between the periodontium and tooth’s root collagen fibers stretch that also help in fixation.

Teeth surfaces

Every tooth has several surfaces. 

The surface that faces lips and the oral cavity opening is the labial surface. It only has incisors and canine teeth, while the one facing the cheeks is the buccal surface, and premolars and molar teeth have it. The labial and buccal surface together form the facial one

Part of the lower teeth facing the tongue is the lingual, while for upper teeth, it is the palatal surface as they face the palate. 

The teeth’ mesial surface is the side of the teeth closest to the midline of the jaws. The distal surface is the other side of the teeth that is farthest from the midline. 

The occlusal or biting surface has only premolars and molar teeth, and it is the top surface with several cusps and grooves. The sharp and pointed top part of the incisors and canine teeth is the incisal surface.

All surfaces of each tooth have a design for their functions. As the canine and incisor teeth help in the food cutting process, they have a single sharp top surface. Still, premolars and molar teeth have larger and flatter occlusal surfaces with several cusps, grooves, fissures, and pits designed for food grinding and chewing.

Teeth microanatomy

The primary mass of the tooth is formed by dentinDentin in the crown part of the tooth from the outside is covered by enamel, while the outside of the root part’s dentin is covered by cement. The transition between cement and enamel is the neck part, where cement thinly layers on the enamel, and this junction is known as the cementoenamel junction

Cement and dentin make the so-called bone tissue, while enamel is special mineralized epithelial cell secretion. Although teeth look like bone, they have different histology apart from the bones. 

The enamel of a newly erupted tooth is covered by a delicate membrane called Nasmyth’s membrane, also known as the primary enamel cuticle. It gets removed by the mastication process, but usually remains intact on the crown’s sides close to the gingiva. It has a protective role, and it is acid-resistant.

Enamel is the hardest substance in the human body. It forms a durable protective layer that protects the tooth from various harmful factors. The thickness of the enamel is not the same everywhere. The hardest part is the top part of the enamel. Closer to dentin, the hardness gradually decreases. A tooth can’t heal by itself, except the enamel part.

Every tooth in the middle of the crown and the neck part has a pulp cavity or chamber containing blood vessels and nerves. It converts into pulp or root canal in the root part of the tooth. Every root canal ends with a small opening called root end opening or apical foramen, the place through which nerves and blood vessels pass through the root canals to the pulp chamber.

Teeth classification

Adult teeth can be classified into four groups according to their functions, the number of the roots they have, and the shape of their crowns

There are four main groups: incisors, canine, premolar, and molar teeth. As mentioned before, adults have 32 teeth. The upper teeth are the maxillary teeth, 16 in total. The other 16 teeth are the mandibular teeth located in the lower jaw. Upper and lower teeth from the same group are similar to each other, but still, they are not identical. 

The jaws divide into quadrants, and there are four quadrants in the oral cavity. Each alveolar arch divides into two parts in the midline of it. According to this, every quadrant has eight teeth: medial or central incisor, lateral incisor, a canine tooth, two premolar teeth, and three molar teeth.

Incisor teeth

In total, there are eight incisors, and four are located in the middle of each jaw. Every jaw has two central (medial) incisors and two lateral incisors

Incisors help to cut, pluck, and bite the food during chewing; they also help to hold food. Incisors have only one but long conical root. Its crown has a chisel-shaped form.

Canine teeth

Canine teeth are also known as eyeteeth or cuspids. All humans have four canine teeth. Every jaw has two canines, 1 in each quadrant located between lateral incisors and first premolars. 

This type of teeth has a single but very long and deep root that is flattened and grooved on the sides. It is longer than other teeth roots. The crown has a sharpened conical shape with spear-like cutting edges. This type functions for food gripping, cutting, and tearing.

Premolars

Premolar teeth or premolars are also known as bicuspids. There are 4 maxillary premolars and 4 mandibular premolar teeth, 8 in total

They lie between the canine and first molar teeth, and this type provides food crushing and grinding during chewing

Premolars have one, usually bifurcated root. The crown has a cuboid formThe biting area of a premolar tooth has two elevations or cusps, helping to break food into particles.

Molar teeth

Every human has a set of 12 molars, six on each jaw and three on each quadrant. They are located in the back of each jaw, and they are the last teeth

The molars have a crown with a cuboid-shape. The occlusal surface of each molar tooth is square with four or five cusps. 

Usually, the upper molar teeth have five cusps on the surface, while the lower have 4The upper molars have three roots, but the lower ones - only two

Molar teeth provide food grinding and crushing. The last molar teeth or the third molar teeth on every side of the upper and lower jaw are called wisdom teeth. These are the last teeth to erupt. For some individuals, it doesn’t happen during their lifetime.

Dental notation systems

Dentists use several systems to make descriptions and write down the information about patients’ teeth

The most commonly internationally used are three systems - the ISO system, universal numbering system, and the Palmer notation system. From all three mentioned, the most widely used is the ISO system, while the universal numbering system mainly operates in the USA, while the Palmer system - in the UK.

ISO dental notation system

It is the international standard numbering system that has been defined by the World Health Organization.

Each tooth has two numbersThe first number is related to the quadrant in which the tooth is locatedwhile the second one is the tooth sequence number in the quadrant.

ISO System for secondary or permanent dentition

Upper right quadrant (maxillary) -1

Upper left quadrant (maxillary) - 2

Lower left quadrant (mandibular) - 3

Lower right quadrant (mandibular) - 4

 

Medial/central incisors - 1

Lateral incisors - 2

Canine - 3

First premolar - 4

Second premolar - 5

First molar - 6

Second molar - 7

Third molar (wisdom tooth) - 8

 

For example, the canine tooth in the left upper quadrant has a numbering of 23, as 2 - left upper quadrant, but 3 refers to canine.

ISO system for primary dentition

Upper right quadrant (maxillary) -5

Upper left quadrant (maxillary) - 6

Lower left quadrant (mandibular) - 7

Lower right quadrant (mandibular) - 8

 

Medial/ central incisors - 1

Lateral incisors - 2

Canine - 3

First molar - 4

Second molar - 5

 

For example, the canine tooth in the left upper quadrant has a numbering of 63 (6 refers to the upper left quadrant, while 3 - to canine).

Palmer notation system

It is also known as the Zsigmondy system. The Palmer system uses symbols for quadrants and numbers for permanent teeth but letters for primary teeth.

Palmer system for secondary or permanent dentition

Upper right quadrant (maxillary) - ┘

Upper left quadrant (maxillary) - └

Lower left quadrant (mandibular) - ┌

Lower right quadrant (mandibular) - ┐

 

Medial/ central incisors - 1

Lateral incisors - 2

Canine - 3

First premolar - 4

Second premolar - 5

First molar - 6

Second molar - 7

Third molar (wisdom tooth) - 8

 

For example, the canine tooth in the left upper quadrant has a numbering of  3└.

└ - left upper quadrant, 3 - canine.

Palmer system for primary dentition

Upper right quadrant (maxillary) - ┘

Upper left quadrant (maxillary) - └

Lower left quadrant (mandibular) - ┌

Lower right quadrant (mandibular) - ┐

 

Medial/ central incisors - A

Lateral incisors - B

Canine - C

First molar - D

Second molar - E

 

Therefore, the canine tooth in the left upper quadrant is described with  C└.

└ - upper left quadrant, but C refers to canine.

Universal numbering system

This system is also known as the American system. As mentioned before, it is mainly used in the United States of America. 

This system uses only numbers for secondary dentition, while letters for primary. The counting starts from the upper right quadrant, continuous to the left side, and then goes down to the lower left quadrant going next to the right side.

Universal system for primary dentition

Upper right

Upper left

A

B

C

D

E

F

G

H

I

J

Lower right

Lower left

T

S

R

Q

P

O

N

M

L

K

Incisors

Canine

Molars

Universal system for secondary dentition

Upper right

Upper left

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

Lower right

Lower left

32

31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

Incisors

Canine

Premolars

Molars

Teeth functions

The primary function of teeth is the support during mastication process as teeth help to form the bolus by cutting, bitting, gripping, and grinding food into smaller pieces and particles

However, teeth also take part in the articulation process and speech formation. They help shape the face and support tissue, also giving a visual and personal appearance to the oral cavity.

Neurovascular supply of the teeth

Arterial blood supply

The arterial blood supply for the teeth is provided by the maxillary artery, a terminal branch of the external carotid artery. 

The anterior and middle parts of the upper teeth are supplied by the anterior superior alveolar arteries originating from the infraorbital artery. 

The posterior part of the upper teeth are provided with the arterial blood by the posterior superior alveolar arteries

In contrast, the lower teeth are supplied by the inferior alveolar arteries.

Venous drainage

Venous drainage is provided by veins with similar names as arteries mentioned above. 

The upper teeth are drained by the anterior and posterior superior alveolar veins, while the lower teeth are drained by the inferior alveolar veins

All veins drain into the pterygoid plexus or the facial vein.

Lymphatic drainage

Lymphatic drainage of upper and lower teeth occurs via submandibular and deep lymph nodes, except the mandibular incisors, as they are usually drained to the submental nodes.

Innervation

The teeth are innervated by the maxillary and mandibular branches of the trigeminal nerve.

The upper teeth are innervated by branches arising from the maxillary nerve. To be more precise - the superior alveolar nerves from the infraorbital nerveThe incisor and canine teeth are innervated by the anterior superior alveolar nervesPremolar teeth get innervation from the middle superior alveolar nerves, while molar teeth - the posterior superior alveolar nerves.

The lower teeth are supplied by the branches from mandibular nerves - the inferior alveolar nerves and the incisive nerve.

Teeth cavities

One of the most common disorders that affect the teeth is teeth cavities, also known as teeth decay and caries, characterized by holes or the damaged area on the teeth surfaces that can get bigger and deeper, affecting the soft tissue of the teeth. 

Untreated cavities can lead not only to tooth extraction but also to life-threatening conditions and severe infections. 

Cavities can form in the root part or present as a smooth surface or pit, and fissure cavities.

Risk factors

The most common risk factor for caries development is poor dental hygiene and unhealthy nutrition with large consumption of sweets and sugary drinks or starch-containing products. Also, frequent snacking is a risk factor. Some food types are not easy to wash down by drinks and saliva. They stick to teeth and start the destruction process. Some of these foods are chips, cereal, and hard candies. Persons of younger age and children or older people are at higher risk. Individuals who have mouth dryness also are at higher risk. It can be caused by several conditions and certain medications. People with old dental fillings also are at higher risk as the filling can weaken during time. Eating disorders such as bulimia or gastroesophageal reflux disease can also cause cavities because of stomach acid.

Most often, tooth cavities happen in the molar and premolar teeth because of the cusps and fissures they naturally have on their surfaces. It promotes the food to stick between them. 

Cavity formation process

The human mouth contains a massive amount of various bacteria forming dental plaques covering the teeth. When a person eats sugary or starch-containing products, some bacteria use the carbohydrates from those products and start to produce the acid. The acid begins to erode the enamel slowly. When the cavity in enamel is present, it is much easier for the acid and plaque to go deeper as dentin is not as hard as the enamel. The process goes further. Without suitable protection and prevention, the bacteria can quickly enter into the pulp part

The best teeth protection is regular teeth brushing shortly after eating and mouth rinsing, teeth flossing, and regular dental visits.

Symptoms

Small cavities usually don’t have any symptoms, while they affect only the enamel. It is the reason why regular dental visits are essential to recognize the hole in a tooth while it is still minimal

The most common symptoms include toothaches that worsen in the evening and during the nighttime and tooth sensitivity. It signifies that the cavity has formed in the dentin or even pulp part when the pain appears. The tooth can react to sweet, hot, and cold drinks or food. Pain can be very sharp, or it can be continuous when starting. Visible holes and staining also is a sign of caries, as well as bad breath.

Summary on the teeth

What are the four groups of teeth?

The four groups of the teeth are incisors, canines, premolars, and molars.

What are the names of the teeth?

The first teeth next to the midline are the medial or central incisors, next to them are the lateral incisor and canine teeth, then first and second premolar teeth, and finally the last ones are the first, second, and third molar teeth. The third molar teeth are also known as the wisdom teeth.

What are the two front teeth called?

Two front teeth are known as the central or medial incisors.

Are teeth bones?

No, they are not. Although teeth look similar to bones, they have different histology than bones.

What are teeth?

The teeth are small solid bone-like structures from the outside containing soft connective tissue on the inside.

At what age teeth stop growing?

The last molar or wisdom tooth can emerge anytime between 17 to 30 years or even later, but usually, it happens till 24 years.

How do I identify my teeth?

To identify teeth, divide the upper and lower jaw in the midline. The first teeth next to the midline are the medial or central incisors, next to them are the lateral incisor and canine teeth, then first and second premolar teeth, and, finally, the last ones are the first, second, and third molar teeth. The third molar teeth are also known as the wisdom teeth.

What type of teeth do humans have?

Humans have two dentition during the lifetime. The first set appearing is the primary dentition or milk teeth, also called the deciduous teeth. During childhood, they slowly get replaced by the secondary dentition or permanent teeth.

How many teeth do humans have?

Children have 20 deciduous teeth, while adults have 32 permanent teeth.

What tooth is number 11?

Number 11 is the canine tooth in the upper left quadrant.

What are chewing teeth called?

Two groups help in chewing - the molar and premolar teeth.

Are the teeth naturally yellow?

They have white or yellowish-white color depending on several factors such as the person’s age or nutrition.

What color of teeth is healthy?

Healthy teeth have white or yellowish-white color depending on several factors such as the person’s age or nutrition.

What are the four quadrants of teeth?

The upper and lower jaw can be divided in the midline, creating four quadrants - two in the lower jaw and two in the upper jaw. To sum up, the four quadrants are the upper left and right and the lower left and right quadrants.

What is the function of teeth?

The primary function is the support of the mastication process as teeth help to form the bolus by cutting, biting, gripping, and grinding the food into smaller pieces and particles. But teeth also take part in the articulation process and speech formation. They help to shape the face and support tissue, and also give a visual and personal appearance to the oral cavity.

Does everyone has 32 teeth?

Yes, everyone has 32 teeth, although some don’t have visible wisdom teeth because they have not erupted yet.

Does everyone get wisdom teeth?

Yes, everyone does have wisdom teeth.

Is 32 a wisdom tooth?

32 refers to the wisdom tooth that is located in the lower right quadrant.

Do you feel your teeth?

Yes, teeth can be felt because the pulp contains nerves.

Can a tooth heal itself?

No, a tooth cannot heal by itself, except the enamel part.

Where are the teeth located?

Teeth are a part of the digestive system located in the oral cavity on the alveolar arches of the maxilla and mandible.

At what age do you get wisdom teeth?

The last molar or wisdom tooth can emerge anytime between 17 to 30 years or even later, but usually, it happens till 24 years.

Does everyone get four wisdom teeth?

Everyone does have four wisdom teeth, but not all four erupt in everyone during their lifetime.

Can teeth grow back?

No, teeth can’t grow back. However, during childhood you have a primary dentition or milk teeth, and when they fall out secondary dentition or primary teeth replace them

How are the teeth numbered in your mouth?

Dentists use several systems to make descriptions and write down the information about patients’ teeth. ISO system divide teeth into quadrants. Each quadrant has a number as well as each tooth in the quadrant also has a number. So each tooth has two numbers - one for the quadrant and another for the teeth. The American system uses only numbers for secondary dentition. The counting starts from the upper right quadrant, continuous to the left side, and then goes down to the lower left quadrant going next to the right side.

What are the next teeth to your front teeth called?

The next teeth to the front teeth are the canine teeth.

Which tooth has the longest root?

The longest root belongs to the canine teeth.

What are the teeth cavities?

The teeth cavities, also known as teeth decay and caries, are characterized by a damaged area on the teeth surface that can get bigger and deeper, affecting the soft tissue of the teeth. 

How can I prevent teeth cavities?

The best teeth protection is regular teeth brushing shortly after eating, as well as mouth rinsing, teeth flossing, and regular dental visits.