Teeth

• Each tooth has three parts, namely crown, neck and root. Crown remains capped with hard enamel ,formed principally of calcium phosphate:,it forms the chewing surface of the tooth. Both crown and root are composed of dentine, secreted by odontoblast cells( mesodermal in origin), inside which a central pulp cavity is present in which there is nerve and blood supply. 
• Elephant tusks are modified incisor. 
• Walrus tusks are modified canine. 
• Teeth of sloth and armadillos have no enamel. 
• Teeth are absent in birds,spiny anteater, scaly anteater, some whales. 
• Majority of mammals including human beings, have two sets of teeth during their life., i.e.one temporary set and one permanent set. Aset of temporary milk or deciduous teeth replaced by a set of permanent or adult teeth. Such type of dentition is called diphyodont. 
• Each tooth is embedded in a socket of jaw bone. This type of teeth attachment is called thecodont. 
• An adult has 32 permanent teeth which are of four diff. types, namely incisors(I) , canine(C) ,premolars(PM) , molars(M). Such type of dentition is called Heterodont.
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• The arrangement of teeth in each half of the upper and lower jaw is in the order I, C, PM, M is represented by a dental formula. 
• The dental formula of adult human beings is 2123*2=8*2=16=32
•     2123      8       16
• The hard chewing surface covering is made up of enamel which helps in the mastication of food. The enamel is hardest substance of the human body, secreted by ameloblast cell ( ectodermal in origin).