Facts about Human Teeth

5 min


beautiful smile with child teeth

Humans are peculiar vertebrates with two sets of teeth. One set contains 20 teeth which we call it Milk teeth or primary teeth. The other set contains 32 teeth which we call it permanent teeth.

PRIMARY DENTITION:

This dentition comprises of 20 teeth. The upper jaw/ maxillary arch has 10 teeth. The lower jaw/ mandibular arch has 10 teeth. Each quadrant has 5 teeth namely incisor 2, canine 1 & molar 2.  

The dental formula for one side of the mouth is I 2/2, C 1/1, M 2/2=10, where I represent Incisors, C represents Canine, M represents Molars. These teeth fall out due to the natural process of shedding for the eruption of their successors.

SECONDARY DENTITION:

The process of succession follows the falling of the milk teeth hence the secondary dentition/ Permanent teeth is also called succedaneous teeth. They start erupting at the age of 6 years preceded by the shedding of milk teeth. This dentition comprises of 32 teeth. The upper jaw/ maxillary arch and lower jaw/ mandibular arch have 16 teeth respectively. Each quadrant has 8 teeth namely Incisor 2, Canine 1, Premolar 2 & Molar 3.

The dental formula for one side of the mouth is I 2/2, C 1/1, PM 2/2, M 3/3=16.

The permanent dentition is grouped into the anterior (incisor & canine) & the posterior teeth (premolars & molars). These teeth do not shed they are permanent.

ANATOMY OF TOOTH STRUCTURE:

A tooth comprises enamel, dentin, cementum, and pulp.

  • Enamel is highly mineralized part in the body, consisting mainly of the mineral hydroxyapatite. It’s translucent in nature.
  • Cementum is a calcified structure covering the root of the tooth.
  • Dentin is the next layer constituting a major portion of the teeth, which is hard, porous & yellowish tissue beneath enamel and cementum.
  • The pulp is the innermost & unmineralized layer of the teeth composed of soft connective tissue, vascular tissue, lymphatic and nervous components. They supply nutrients to the teeth.

ERUPTION OF TOOTH:

Tooth eruption starts with the first primary tooth which erupts at the age of 6-10 months the teeth that come out at this age are the lower central incisor and the last tooth to erupt is upper second molar at the age of 25-33 months.

At the age of six, the permanent teeth erupt after the initiation of shedding. The first permanent tooth to erupt is the lower central incisor and first molar. The last permanent tooth to erupt is the third molars at the age of 17-21 years.

FUNCTIONS OF TEETH:

Incisor- used to cut the food.

Canine – used to tear the food.

Premolars – used to crush the food.

Molars – used to grind the food.

TO IDENTIFY THE TOOTH THE FOLLOWING SYSTEMS ARE USED:

  1. The universal system ( Adopted by ADA in 1975)
  2. The palmer notation system
  3. The international numbering system/ FDI system.

THE UNIVERSAL SYSTEM:

  • The primary teeth are assigned alphabets.

 A to J starting from upper right second molar to upper left second molar. K to T from lower left second molar to lower right second molar.

  • The permanent teeth are assigned numbers.

1 to 16 from the upper right third molar to the left upper third molar. 17 to 32 from lower left third molar to lower right third molar.

PALMER NOTATIONS:

Teeth are given numbers from 1 to 8 in each quadrant:

  • 1-central incisor
  • 2-lateral incisor
  • 3-canine
  • 4-First premolar
  • 5-Second premolar
  • 6-First molar
  • 7-Second molar
  • 8-Third molar

The tooth differentiated by using brackets which resemble each quadrant

THE INTERNATIONAL NUMBERING SYSTEM:

It is a recognized and commonly used system. In this system, each quadrant is assigned a designated number in both primary and permanent dentition. Each tooth is given a designated number as follows:

QUADRANTS FOR Milk Teeth

  • 5- Upper right quadrant
  • 6-upper left quadrant
  • 7- Lower left quadrant
  • 8- Lower right quadrant

QUADRANTS FOR PERMANENT TEETH

  • 1- Upper right quadrant
  • 2-upper left quadrant
  • 3- Lower left quadrant
  • 4- Lower right quadrant

TEETH NO FOR PERMANENT TEETH

  1. Central Incisor
  2. Lateral Incisor
  3. Canine
  4. First Premolar
  5. Second Premolar
  6. First molar
  7. Second molar
  8. Third molar

Example Teeth number 35 means lower left second premolar.

TEETH NUMBERS FOR MILK TEETH

  1. Central Incisor
  2. Lateral Incisor
  3. Canine
  4. First molar
  5. Second molar

Example Teeth number 64 means upper left first molar of milk teeth

Let us see about some anomalies in the formation of the teeth

Developmental deformities of the teeth are defined as the deviation in the following physical aspects of teeth like shape, size, number, and degree of development.

The reason behind them can be either due to local or systemic disturbances.

These disturbances can occur before birth or after birth affecting primary dentition or secondary dentition. In some cases, both the dentition is affected.

Frequently noted are Hyperdontia, dilacerated root, Taurodontism, Microdontia (peg-shaped teeth) and Hypodontia.

DEVELOPMENTAL DEFORMITY OF TEETH – NUMBER:

Hyperdontia: Supernumerary teeth or the existence of more number of teeth.

Hypodontia: Physiological absence of a tooth mostly with permanent canines.

Oligodontia: It is the absence of 6 or more teeth without taking 3rd molars into count.

DEVELOPMENTAL DEFORMITY OF TEETH – SHAPE:

Dens invaginatus (DI): It is inward development of the surface of the crown of a tooth or tooth root lined with enamel and dentin.

Dens Evaginatus: It is the outward development of the surface of the crown of a tooth resembling an enlarged accessory cusp of the tooth.

Talon’s cusp: It is an outward projection of the lingual cusp (the elevated portion present on the inner surface of the teeth) of the front teeth. It is referred to as an eagle’s beak.

Fusion: As the word implies it is the fusion of the two adjacent teeth.

Gemination: It is the development of two teeth from on tooth bud. It has a single root and often confused with fusion.

Concrescence: It is the union of the two adjacent teeth only at their roots. It is commonly explained as the fusion of cementum (outer enamel like a layer of a tooth root) of the two adjacent teeth.

Dilacerations: It is a curvy or bent form of the tooth root along its length. The bend or curve can happen anywhere along the length of the root.

DEVELOPMENTAL DEFORMITY OF TEETH – SIZE:

Microdontia: The size of the teeth appears to be smaller than that of the normal size. They have a small pulp cavity with narrow root canals.

Macrodontia: The size of the teeth appears to be greater than the normal size. They appear bulkier in size.

Taurodontism: It’s a common deformity found in the molars presenting a bigger tooth crown with shorter root. The point of division of the root (bifurcation) is close to the apex of the root. It is often referred to as bull-like teeth due to its appearance in radiographs.

DEVELOPMENTAL DEFORMITY AFFECTING DEGREE OF DEVELOPMENT OF TEETH:

The development of the teeth happens prenatally for primary teeth and after birth for permanent teeth.

Thus if a child is exposed to any bacterial or viral infection the eruption and the form of the teeth are compromised. Other reasons include:

  • Use of medications like tetracycline by pregnant mothers causing discolored teeth of the child.
  • The mother exposed to syphilis affects the form of the infant’s permanent teeth.
  • Iron, calcium and other essential nutrients deficiency affect the development of the infant’s teeth.

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Dr Arun

Dr. Arun is a practicing dentist with more than 11 years of experience. Loves to blog and in constant search of new knowledge in dentistry and health niche.

One Comment

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  1. I haven’t checked in here for a while since I thought it was getting boring, but the last several posts are good quality so I guess I will add you back to my daily blog list. You deserve it, my friend 🙂

    This is a great article about human teeth!