Each tooth is a living part of body containing nerves and blood vessels. The part that is visible in the mouth is the crown and the longer portion anchored inside the gum and the bone is the root.
If you see the internal parts of the tooth, the outermost hardest white cover is known as the enamel. The inner relatively less hard is the dentin. It surrounds the pulp containing blood vessels and nerves of the tooth. The pulp tissue is connected to the circulatory and nervous system via a foramen at the apex of the tooth. Surrounding the roots, which are also made up mainly of dentin, there is a thin bone like layer called cementum. The jawbone is connected with cementum through a shock-absorbing membrane, the periodical ligament.
There are four different types of teeth in human beings. They vary in shape and size according to their particular function. They are:

• Incisors: They are front teeth, four in the upper arch and four in the lower arch. They are shaped to bite and cut food into small pieces.
• Canines: They are conical teeth at the corner of the mouth. Their function is to tear or shred food.
• Premolars: These are two on each side of both the jaws just behind the canines. These teeth have two cusps and the function is to hold and crush the food.
• Molars: They are three in number on each side of the jaws and have bigger chewing surfaces for cutting food into smaller particles.

There are two sets of teeth:

• Deciduous - The first to appear are Milk Teeth and are helpful to the child not only in terms of chewing but also in providing guidance to the developing jaw and permanent dentition. The first milk tooth appear at about 6 months of age and then subsequently all 20 teeth erupt upto two and half years. The milk dentition has 2 incisors, one canine and 2 molars on each side of the jaw that makes 5 teeth on each side and a total of 20 teeth in the mouth. The milk teeth are lighter in colour as compared to permanent teeth.
• Permanent - At six years of age, natural shedding of milk teeth and the eruption of permanent teeth begins which continues till the age of 12 years. The first permanent molar erupts at six years just behind the milk teeth on all four sides of the jaw. At this time the milk teeth start falling and permanent teeth start replacing them. Subsequently most of the permanent teeth erupt till 12 years of age. The second molars erupt behind the first molar at about 12-13 years and the third and last molar (wisdom teeth) erupt between 18-25 years. The permanent teeth are larger and darker in colour as compared to milk teeth. There are two incisors, one canine, two pre-molars and three molars making eight teeth in each quadrant and a total of thirty-two in permanent dentition.