The type and number of teeth in the human dentition is expressed using a formula called human dental formula. In the dental formula, the alphabet and numbers are used to designate the type and number of teeth present in the dentition. The same method of expressing the type and number of teeth is also used to describe the dental formula of species (sheep, horse, cat, and dog) other than humans.
The humans have two sets of dentition deciduous dentition and permanent dentition with different numbers and types of teeth. Therefore, dental formulae are different for children and adults.
The dental formula of the child
The dental formula of a child is
The type of teeth is designated by the alphabet and the quantity in each side of the upper and lower jaw is designated by a number.
I= Incisors both central and lateral in the maxillary and the mandibular arches and 2= quantity of teeth in the maxillary and mandibular right quadrants
C= Canine teeth both in the maxillary and mandibular arch and 1= quantity of maxillary canine in maxillary and mandibular right quadrants
M= deciduous first and second maxillary and mandibular molars and 2= number of teeth each in the maxillary and mandibular right quadrants. There are no premolars in the deciduous dentition.
If this dental formula is multiplied by two it gives the total number of teeth in the entire deciduous dentition that is twenty teeth.
The following picture also describes how the dental formula is written.
The dental formula of complete deciduous dentition
Adult dental formula
The adult dental formula is
Like the deciduous dental formula, the type of teeth is designated by an alphabet and the quantity in each side of the upper and lower jaw is designated by a number.
I= Incisors both central and lateral in the maxillary and the mandibular arches. 2= quantity of teeth in the maxillary and mandibular right quadrants.
C= Canine teeth both in the maxillary and mandibular arch and 1= quantity of maxillary canine in maxillary and mandibular right quadrants only.
PM= Premolars both in the maxillary and mandibular dental arches and 2= quantity of premolars in maxillary and mandibular right quadrants only.
M= Molars maxillary and mandibular (first, second, and third molars) 3= quantity of molars in maxillary and mandibular right quadrants only.
The dental formula is multiplied by two it gives the total number of teeth that are present in the entire permanent dentition that is 32 teeth.
The following picture also describes how the adult dental formula is written.
The dental formula of adult complete permanent dentition
The dental formula (Dental formula of child and adult dental formula) indicates that humans are omnivores (eat a variety of diet both of plant and animal origin). The canines are poorly developed as compared to pure carnivore animals such as cats and dogs. The dental formula also indicates that humans have a heterodont dentition (teeth in the dental arches are of different shapes or types).
It should be kept into consideration that animals other than humans may have different dental formulae. In a few cases, humans have the same dental formula as some of the ancient species of monkeys and apes but the human teeth are much smaller in size as compared to these species.