These are hard structures present in the mouth and both the jaws(i.e,. upper and lower jaw). Each tooth is embedded in a socket of jaw bone. A tooth consists of three major parts namely crown(upper part), neck(middle part) and root(lower part). In humans, the number of teeth present is 32 (16 in each jaw). The half teeth of the jaw is towards left while the rest half is towards right. Arrangement of these teeth includes two incisors, one canine, two premolars and three molars(2123).
Each of the tooth is specialised to perform a particular function. The main function of the teeth is to perform physical digestion.
- Incisors are outer mostly forward , flatten and extremely sharp, which helps in biting and cutting the food.
- Canines are sharply pointed which crack and split or tear the food.
- Premolars and molars, crush, grind and chew food smoothly.
Various types of teeth are present in different animal groups which are listed below:
1- Homodont– All the teeth are of same type, e.g., sharks and crocodiles.
2- Acrodont– The teeth are attached to the crest of bone, e.g., snake.
3- Pleurodont– teeth are attached to the median side of the bone, e.g., lizard.
4- Thecodont– Teeth are attached to the bony socket, e.g., alligator.
5- Heterodont– Different types of teeth are present, e.g., humans.
6- Polyphyodont– Appear many times in lifetime, e.g., in most lower vertebrates.
7- Diphyodont– Appear twice in lifetime, e.g., incisors, canines, first and second molar of humans.
8- Monophyodont– Appear once in lifetime, e.g., third molar and all premolars of humans.
DENTAL FORMULA
The number and kinds of teeth in mammals are represented by an equation, called dental formula. Since two halves of each jaw are identical, the teeth of only one side are considered in the equation. Dental formula can be represented as below:
{ ICPmM/ ICPmM }
where, I= Incisors, C= Canines, Pm= Premolars, M= Molars.
Among deciduous(primary) teeth, 10 are found in maxilla(upper jaw) and 10 in the mandible(lower jaw), for a total of 20. The dental formula for primary teeth in humans is 2.1.0.2/2.1.0.2
Among permanent teeth, 16 are found in the maxilla and 16 in the mandible, for a total of 32. The dental formula is 2.1.2.3/2.1.2.3
PARTS OF HUMAN TEETH
1- ENAMEL: It is the hardest and most highly mineralized substance of the body. It has its origin from oral ectoderm. Its primary mineral is hydroxyapatite, which is a crystalline calcium phosphate. The large amount of minerals in enamel accounts not only for its strength but also for its brittleness.
2- DENTIN: It is secreted by the odontoblasts of the dental pulp. The formation of dentin is known as dentinogenesis. It is a mineralized connective tissue with an organic matrix of collagenous proteins.
3- CEMENTUM: It is a specialized bone like substance covering the root of a tooth. The principal role of cementum is to serve as a medium by which the periodontal ligaments can attach to the tooth for the stability.
4- DENTAL PULP: It is the central part of the tooth filled with soft connective tissue. The tissue contains blood vessels and nerves that enter the tooth from a hole at the apex of the root. It is commonly called “the nerve” of the tooth.