Human teeth and its structure

• Human teeth are thecodont, diphyodont and heterodont.
• They are borne by the premaxillae of upper jaw and mandibles of lower jaw.
• They are found embedded in jaw sockets which we call thecodont.
• Human have two sets of teeth.
• The milk teeth also known as deciduous dentitions appear first and are progressively replaced by the permanent teeth which cannot be replaced.
• This is known as diphyodont.
• At birth, the teeth of both dentitions are present in immature form in the mandible and maxillae.
• The temporary teeth are 20 in number, 10 in each jaw.
• They begin to erupt when the child is about 6 months old, and should all be present by the end of 24 months.
• The permanent teeth begin to replace the deciduous teeth in the 6^th year of age and this condition is completed by the 24^th year with 32 teeth.
• Teeth are of different shapes and sizes and possess uneven biting surfaces.
• Human possesses up-to 32 permanent teeth, consisting of 8 incisors (i), 4 canines (c), 8 premolars (pm) and up-to 12 molars (m).
• The arrangement of teeth is expressed in the form of a dental formula which is given as:

• Third molar appears only when one will cross the age of 20 years. So, they are called wisdom teeth.
• They may not appear in the case of certain person sometimes.
• The number, size and shape of teeth are directly affected by diet.
• On the basis of structure and function of each type of tooth, four different types of teeth (heterodont) are as follows:

a) Incisors

• They are situated at the frontal region of buccal cavity.
• They have got flat and sharp edges. They are used for cutting and biting food.

b) Canines

• They are pointed dagger-shaped teeth.
• They are poorly developed in humans, but highly developed in carnivores used for piercing and tearing flesh.

c) Premolars

• They are broad and strong having one or two roots and two cusps (projections on the surface of tooth).
• They are used for crushing and grinding food, although in human they may also be used to tear food.

d) Molars

• They have more than one root; upper molars have three roots, lower molars have two.
• Each has four to five cusps.
• They are used to crush and grind food.

Structure of a tooth

• A typical tooth consists of three parts. They are:

i) Crown

• It is the exposed part of tooth.
• It is covered with the hardest substances called enamel.
• It is relatively resistant to decay.
• Internally, it has the hard substance called dentine.
• Inside the dentine is a cavity called pulp cavity which is lined by a layer of odontoblast cells.
• The pulp cavity contains connective tissues, blood vessels and nerve endings.
• Chemically the dentine is bone-like and contains many fine canaliculi.

ii) Neck

• It is a short part embedded in gums.

iii) Root

• This part is embedded in bony jaw that holds the tooth.
• Blood vessels and nerves pass to the tooth through a small foramen present at the apex of each root.
• The number of root vary in different teeth.

References: 

i) https://www.tandaradental.com.au/what-are-the-4-types-of-teeth-and-why-do-we-have-them/

ii) https://www.medicinenet.com/teeth_types/article.htm

Human teeth and its structure