Teeth, or dentes, are Accessory Digestive Organs located in sockets of alveolar processes of the Mandible and Maxillae jaw bone.
• Upper jaw is immovable made of maxillae bone, whereas lower jawbone mandible is movable.
• The alveolar processes are covered by the gingivae, or gums.
• Sockets are lined by the Periodontal Ligament/membrane, which anchors the teeth to the socket walls and acts as a shock absorber during chewing.
• Tooth has three major external regions: Crown, Root, and Neck.


Structure Of Typical Tooth

Crown is the visible portion above the level of the gums. Embedded in the socket are one to three roots. Neck is the constricted junction of the crown and root near the gum line.
• Tooth is made up of Dentin which consists of a calcified connective tissue that gives the tooth its basic shape and rigidity. It is harder than bone because of its higher content of hydroxyapatite.
• The dentin of the crown is covered by enamel. Enamel consists primarily of Calcium Phosphate and Calcium Carbonate. It is also harder than bone because of its even higher content of calcium salts (about 95% of dry weight).
Enamel is the hardest substance in the body. It serves to protect the tooth from the wear and tear of chewing. It also protects against acids that can easily dissolve dentin. The dentin of the root is covered by cementum, another bonelike substance, which attaches the root to the periodontal membrane.
• The dentin of a tooth encloses a space called as Pulp Cavity, which lies within the crown and is filled with pulp. Pulp contains connective tissue containing blood vessels, nerves, and lymphatic vessels. Narrow extensions of the pulp cavity, called Root Canals, run through the root of the tooth. Each root canal has an opening at its base, the Apical Foramen, through which blood vessels, lymphatic vessels, and nerves enter a tooth.

Human teeth are Thecodont, Diphyodont and Heterodont.

Thecodont: When each tooth is embedded in a socket of jaw bone. This type of attachement is called thecodont
Diphyodont : Forms two sets of teeth during the life ,i.e, temporary milk or deciduous teeth or primary teeth, or baby teeth which are replaced by a set of permanent or adult teeth or secondary teeth. This type of dentition is called diphyodont.
Heterodont: Adult human has 32 permanent teeth which are of four different types. These are Incisors (I), Canine (C), Premolars (PM) and Molars(M).

• Arrangement of teeth in each half of the upper and lower jaw in the order
I-2/2, C- 1/1, PM-2/2, M-3/3 is represented by a dental formula which in human is (2123) / (2123).

Incisors are chisel-shaped and adapted for cutting and bitting into food. They are situated at the front of buccal cavity. Total 8 in no. (4 in upper jaw & 4 in lower jaw).
• Next to the incisors, moving posteriorly, are the Canines, which have a pointed surface called a cusp. Canines are used to tear and shred food. Total 4 in no. (2 in upper jaw & 2 in lower jaw).
• Posterior to the canines lie Premolars. Premolars are broad and strong. They are bicuspids. Used to crush and grind the food to prepare it for swallowing. Total 8 in no. (4 in upper jaw & 4 in lower jaw).
• Lastly after premolars lie Molars. They have four cusps. Also used to crush and grind the food to prepare it for swallowing. Total 12 in no. (6 in upper jaw & 6 in lower jaw).
• Total comes to 32 (8+4+8+12)
There are 20 teeth in a complete deciduous set and 32 teeth in a complete permanent set.
• In case of Deciduous or Temporary teeth set or Primary Dentition, dental formula is I-2/2, C-1/1, PM- 0/0, M-2/2.
• In case of deciduous teeth set, posterior to the canines lie the first and second deciduous molars. Premolars are absent in primary dentition. The deciduous molars are replaced by the first and second premolars when all of the deciduous teeth are lost, between ages 6 and 12 years.
• Third molar appears only after the age of 20 years. So, they are called Wisdom teeth.


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