# Dental Formula

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## What is a Dental Formula?

The process of ingestion of food starts from the mouth and the oral cavity wherein the teeth carry out an essential function of tearing the food particles, grinding and chewing them, making it easier to swallow and for the rest of the digestive processes. In all vertebrates, the pairing of the teeth, the working of the teeth in tandem with the oral cavity is vital for survival and it evolved in coherence with the adaptation required by the organism over the years of evolution. Thus, the patterning of teeth has become an important aspect not only in day to day life but for the study of extinct animals, and evolutionary studies of fossils, and determining the type of environment that a particular animal lives in. This patterning of teeth is best represented by a dental formula.

The human dental formula is also a representation of the human environment, adaptation, the features of the food that we consume, and our digestive system. The human teeth formula or the dental formula for any animal provides information on the different types of teeth that are present in the specialized sockets of their jawbones. All the types of teeth have specialized functions and hence, are developed largely based upon eating habits. A clear idea of the dental formula and the details provided by it are given below.

### Dentition

Dentition is referred to as the development of the teeth and their arrangement in the oral cavity. It showcases the peculiar pattern of arrangement, the kind of teeth present, and the number of a particular tooth in the mouth, at a given age. The dental formula constitutes the number of teeth in their respective position as they are present in the jaws. It is truly the representation of the dentition of an organism. Thus, the human dental formula or the human teeth formula will provide the information regarding the 32 teeth that are most commonly found in all humans and will also exhibit their internal arrangement.

### Different Types of Teeth

Usually, in most of the vertebrates which include, reptiles, amphibian, and fish, even though the dentition is diversified, they still have the same kind of teeth present in varying numbers for a particular organism, i.e., a particular fish will have the same kind of teeth in its oral cavity, even though it would be different from other fishes. A simple example is of a shark where it has sharp pointed teeth that can be diversified with respect to other fishes, but in its own oral cavity, it invariably has the same kind of teeth. Such animals are called homodonts. Thus, the dental formula will largely provide the facts of the number of teeth present without any variation.

Unlike those homodonts, mammals have up to four distinct varieties of teeth with exceptions such as the monotremes, the xenarthrans, the pangolins, and the cetaceans. Hence, most mammals are known as heterodonts. Consequently, the human dental formula is representative of the fact that each individual will have 32 numbers of teeth which are inclusive of four different types of teeth that are known and classified. Interestingly, a fun fact is that a dental formula can be unique for an entire species.

## The Four Different Types of Teeth are Mentioned as:

### 1. Incisors (I):

These are the front row teeth and their purpose is the cutting and slicing of the food into pieces that fit into the mouth. They are present in both the jaws of most mammals. They are flat and have a chisel-like shape.

### 2. Canines (C):

Following the incisors are the canines. Most commonly known as dog teeth, these sets of teeth are well known for their ability to hold and tear apart food, especially in the case of carnivores because of their pointed structure and their projection above the level of other sets of teeth. In the case of herbivores, these are helpful to break open and split hard surfaces of certain fruits like the nuts. In humans, though they provide an additional advantage of aiding in articulation.

### 3. Premolars (P):

Premolars are the transitional teeth between canines and molars. They are structured in such a way as to provide a smooth surface continuance which further assists in occlusion i.e. the entire process of cutting, chewing, and grinding of the food into a rapidly digestible form.

### 4. Molars (M):

These are the last set of teeth found in the mammals at the posterior end of the oral cavity. Their primary objective is the grinding of the food. In humans, they are 12 molars present as a set of three in each half of the oral cavity and in both the upper and lower jaws. Inquisitively, the molars present in the extreme anterior end of the cavity have lost their functions in modern-day human beings and hence are vestigial organs.

In mammals, the teeth in both jaws have evolved in a tight close-fitting relationship that allows them to work together as a unit. The dental formula provides the information of the number of these types of teeth represented by I, C, P, and M. They are mentioned in the manner of their actual arrangement in the mouth as I:C:P:M.

### Dental Formula

The dental formula denotes the number of teeth arranged in a particular manner on one side of the mouth. Also, the dental formula is written in such a way that it represents the arrangement of teeth in both the lower and upper jaws. Thus, it is written as follows: $\frac{I.C.P.M}{I.C.P.M}$ or I.C.P.M. / I.C.P.M. The upper portion signifies the half side of the upper jaw whereas the lower portion signifies the lower jaw. Doubling the total number of the upper and lower part in the dental formula will give the total number of teeth.

An important thing to remember is that there are different numbers of teeth at different ages. This may not be the case with all mammals. Animals having only one set of teeth throughout their life i.e. no change in the dentition of a child and an adult is called monophyodont, while the ones having continuous discarding and replacing of the dentition is called polyphyodont. For humans, there is a succession of dentition at the child and adult stage and hence have two dental formulas representing the dentition at the child stage and adult stage. So, when it is asked to give the dental formula for human beings rather than in general, the adult dental formula is mentioned rather than the dental formula in child. This happens so because the adult teeth in humans are permanent whereas the teeth in a child are temporary. The teeth in the child are more commonly called deciduous teeth, primary teeth, baby teeth, or milk teeth.

## The Difference Between the Dental Formula of the Deciduous Teeth and Permanent Teeth is Given as Follows:

1. Deciduous Teeth:

The deciduous teeth types are given as di:dc:dp:dm. The dental formula of human child is denoted as - (di2 - dc1 - dm2)/(di2 - dc1 - dm2). Else the dental formula in a child can be represented as $\frac{2.1.2.2-3}{2.1.2.2-3}$ . This indicates that there are two incisors, one canine, and two molars in a child. Here, in this case, the premolars are missing. The dash ‘-’ does not have mathematical significance rather it implies spacers or ‘to’.  If it is mentioned that the given dental formula is deciduous then it can be represented as $\frac{2.1.0.2}{2.1.0.2}$ , since the formula mentions the molars as 0, which is true in the case of a growing infant.

### 2. Permanent Teeth:

The permanent teeth types are given as I:C:P:M. The human dental formula is usually provided in the adult form which is given as (I2 - C1 - P2 - M3) / (I2 - C1 - P2 - M3) or $\frac{2.1.2.3}{2.1.2.3}$ . Since, humans have the same set of teeth in the upper and lower jaw than the dental formula can be written as (2.1.2.3). Given below is the picture showing the dentition as given by the human teeth formula:

Another example of a dental formula for a mammal with quite diversified dentition is that of a kangaroo. The dental formula of a kangaroo is given as: (I3 - C1 - P2 - M4) / (I1 - C0 - P2 - M4), which indicates that there are three incisors, one canine, two premolars and 4 molars in the upper jaw while there is only one incisor, no canines, two premolars and four molars in an adult kangaroo.

As is clear from the above explanation that the dental formula is the representation of the types and the number of teeth of a particular species, it can be easily observed that in what manner it can give an idea about the environment, dietary practices, and living conditions of a particular organism. Hence, many archaeologists and paleontologists as well as scientists who study evolutionary biology take into consideration the study of relatability amongst organisms.

Students while studying the digestive system will understand how crucial the development of the mechanism of the working of the teeth as a single entity leads to the absorption of nutrients in an efficient manner. And the characteristics of the dentition are best presented by the dental formula.