Dental Formula in Humans and Other Mammals

Teeth are a set of hard, bony, mineral-rich enamel-coated structures found in the jaws(mouth) that extends into the buccal cavity of most vertebrates which is used to grasp, bite, and chew food. Most vertebrates, especially humans, have two sets of teeth during their lifespan including temporary and permanent sets of teeth. All humans have teeth of four different types which include incisors, canines, premolar, and molar. But the temporary set does not contain all the four of them.  All the teeth perform several functions like crushing, tearing, cutting, and shredding the food.

Few animals have the ability to replace their teeth which may be lost due to any disease or injury throughout their life.

Introduction to What is a Dental Formula

The conventional way of describing or expressing the total number of teeth in mammals in which the types of teeth are represented by the first letter i.e incisor (i),  canine (c), premolar (pr), and molar (m), and the number of teeth are written in figures with a fraction above the horizontal line showing the number of teeth, type of teeth on one side of the upper jaw and those below the number of the same type of teeth on one side of the lower jaw according to the arrangement is known as Dental formula.

The Dental Formula is Formulated As

(Half of the upper jaw number of each type of teeth)/(Half of the lower jaw number of the same type of teeth)

Note:- In order to represent the total number of teeth in the mouth, the whole formula is multiplied by two as the formula is for one side of the jaw.

The Dental Formula of Man & Child

Dentition pertains to all types of teeth development and their arrangement in the mouth including teeth numbers. Not all animals have the same type, number, and shape of teeth which are specifically based on their adaptation to the environment, eating habits, and the nutrition they prefer. There are a total of 32 teeth present in a normal adult. Temporary or primary and permanent are two kinds of dentition which are composed of 20 and 32 teeth respectively.

The Dental Formula in Child

There are only 20 teeth present in children that are termed deciduous teeth or milk teeth. These teeth begin to evolve before the child's birth. Around the age of 6 years, children's teeth begin to erupt or fall out. There are 10 teeth in each arch (both the top and bottom of the jaw)  and five in each quadrant, including two incisors i.e central and lateral (cutting teeth), one canine (tearing teeth), and two molars (grinding teeth). There is not a single premolar present in milk teeth. Hence, children have zero premolars. Dentists rather called premolars first molars. Adult premolars are replaced by these baby molars. 

The Dental Formula For Deciduous or Milk Teeth found in Children is

\[ i \frac{2}{2} c \frac{1}{1} m \frac{2}{2} = 10 \]

\[ (\frac{2102}{2102})\times 2 = 20 \]

The Dental Formula of Adults

There are a total of 32 teeth except for wisdom teeth in normal adults that are termed permanent teeth. These teeth start to erupt at the age of 13 years. There are 16 teeth in each arch and eight in each quadrant. Incisors are the eight middlemost teeth (4 up, 4 down) both on the upper and lower jaw. Canines are pointed teeth which are another four teeth (2 up, 2 down) just outside the incisors. Canines are also sometimes referred to as bicuspids because their biting surface has pointed cusps. Beyond that are premolars which are a total of eight in number (4 up, 4 down) present between canines and molars. Molars are a total of six (three pairs) which are flat teeth present in the rear of the mouth. The three pairs of molars are denoted as the first, second, and third molars present in the upper and lower jaw. Third molar teeth are also named wisdom teeth. These teeth come up in the 30s of age but are often removed surgically to prevent other teeth displacement. 

The Dental Formula for Permanent Teeth in Adults is

\[ i \frac{2}{2} c \frac{1}{1} pm \frac{2}{2} m \frac{3}{3} =16 \]

\[ (\frac{2123}{2123})\times 2 = 32 \]

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Note:- Both humans and monkeys have the same dental formula and a similar set of teeth.

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The dental formula is an equation that describes the relationship of the teeth within the jaws of a human or an animal. The dental formula gives information about the number and size of teeth as well as the type of tooth.

To form an understanding of dental formulae, it is important to consider the three parts of a human mouth. The top part of the mouth consists of the lips and the roof of the mouth or nasopharynx. Below the lips are the teeth, which are called mandibular dentition, the teeth in the bottom of the mouth. The lower jaw is connected to the skull via the jaw joint, a hinge. The part of the jaw that holds the teeth, the skull, the lower jaw, the teeth, and the gums are all connected and move as a single piece.

Three parts to the Human Mouth

Teeth

The teeth are the small structures, found inside the mouth, consisting of hard tissue that develops from the embryonic period. They also play a role in chewing, which includes the preparation of food into smaller particles so they can be more easily swallowed.

Teeth are categorized into three parts, namely, anterior teeth, which are found at the front of the mouth, posterior teeth, which are found at the back of the mouth, and molars, which are the grinding teeth, which replace the teeth in babies and young children.

The Human Dental Formula is Composed of Two Parts:

1. The Number of Teeth Per Jaw

A human's upper and lower jaw may have between 18 and 28 teeth in total, with most people having 22 teeth. For some animals such as birds, sharks, and reptiles the number of teeth in their jaws may differ. The numbers of teeth in mammals such as cats, dogs, and cows are very similar.

2. The Number and Types of Teeth

All of a human's teeth are made up of the same biological substance: enamel. In the upper and lower jaws, there are 22 teeth in total. These teeth are separated into four categories, namely, the canine teeth (two in the upper jaw and one in the lower jaw), the incisors (four in the upper jaw and four in the lower jaw), the premolars (six in the upper jaw and four in the lower jaw), and the molars (four in the upper jaw and four in the lower jaw).

Teeth and Jaw Growth

Teeth and jaw growth can occur during different stages of human development. Jaw growth occurs when the teeth have a higher density, and tooth growth occurs when the teeth have a higher number. If the number of teeth is low, the amount of dentine may also be below.

During tooth development, the baby's teeth begin to develop before birth and grow throughout the first two years of life. The baby's second set of teeth develops between one and three years of age and the third set of teeth is added between five and seven years of age. During the first two years, the teeth start to appear and develop rapidly. In the second two years, the teeth mature at a slower rate.

The growth of teeth can continue even after teeth have been worn down to the roots. During this stage, tooth growth slows down but continues. As teeth continue to develop after this stage, the adult teeth start to look sharper and more irregular.

Teeth and Jaw Growth: Causes and Effects

Tooth development can be influenced by both genetic and environmental factors. These factors can affect the timing and order of tooth development. The order of tooth development is as follows:

• The first set of teeth

• The second set of teeth

• The third set of teeth

• Tertiary dentition (adult teeth)

Tooth development starts with the formation of the first set of teeth. The two primary teeth (also known as the deciduous teeth) appear at approximately nine months of age. The two lower teeth in the mouth (the canines and the lower premolars) are commonly called "baby teeth".

The two upper baby teeth (the deciduous molars) usually appear around the age of five to six months. The two upper baby teeth (the deciduous incisors) usually appear before the birth of the baby. The lower baby teeth (the deciduous canines and the lower premolars) usually appear before the birth of the baby. The teeth are usually visible during the first few months.

The baby teeth start to fall out by about three to four years of age. The baby's permanent teeth continue to develop until they reach the adult pattern. The permanent first molars (adult teeth) and the first premolars (adult teeth) usually appear around the age of 18 to 19. The second molars (adult teeth) appear around the age of 25.

The two upper permanent teeth (the deciduous canines and the permanent incisors) usually appear before the baby's permanent teeth. The lower permanent teeth (deciduous and permanent molars) appear around the age of 20. The permanent molars usually appear before the age of 30.

The permanent teeth can take more than six years to completely develop. The permanent teeth usually start to change into adult teeth at about the age of 17 to 18.