Teeth

HumanTeeth

The teeth  are the  hardest  part of the body.  The jaws  bear  teeth  which are used  to  chew  or masticate food  into  smaller  pieces. The arrangement  and number  of teeth  is  called  its dentition. Humans  have  two  successive  sets  of teeth.  The  deciduous  or  milk teeth  appears first,  and  are progressively  replaced by  the  permanent teeth.  The  teeth  have  different shapes  and size  and possess  uneven  biting  surface.  This  is  called  heterodont  dentition. Milk dentition  appear  at  the age of  about 6 month  and  lasts  until  the age  of  5-6. There  are 20 milk  teeth.  Human  possess up to  32 permanent  teeth.  Each half  of the  jaw  bears  2 incisors,  1 canine,  2 premolars  and  3 molars.  The  basic structure  and  function  of each type  of teeth  is  as follows  

i.  Incisor:  Incisor  situated  at the  front  of the  buccal  cavity.  They  have  flat  sharp  edge.

Incisors  (total  8)  are  used  for  cutting  and biting  food.

ii.  Canine: They  are pointed  teeth.  Canines (total  4) are  used  for  grasping.

iii.  Premolar:  They  possess  one  or two  roots  and  two cusps  (projections  on the  surface  of this  tooth  is  called  cusp).  They  (total  8) are specialized for  crushing  and grinding. They  many  also  be used to tear  food.

iv.  Molar: They  possess  more  than  one  root, upper  molars  have  3 roots,  lower  molars 2. Each  has 4 or 5 cusps.  They (total  12)  are used  for  crushing  and  grinding  the  food.

Generalized  structure of a tooth:  The tooth  is  typically  consists  of 3 parts:

i.  Crown: The visible  part  above  the  gum.

ii.  Root: The  part  hidden  below the gum.

iii. Neck: The tooth  between  crown and  root.

The crown  is  covered  witir  enarnel.  Enamel is  the  hardest part  of the  body.  The neck of the tooth  is  surrounded  by gum.  Beneath  the  enamel  is  the bone  like  material,  dentine which forms the  bulk  of the  tooth.  It  is  tough  but  not  so hard  as enamel  or as resistant  to decay.  It  contains numerous  small  canals  (canaliculi)  containing  cytopiasmic  extensionsof the  odontoblast,  the dentine  producing  cell. Dentine surounds  a  pulp  cavity  with  blood vessels, odontoblasts  and nerves  running  through  it.  The  blood  supply  nourishes  the living  bone  with food  molecules and oxygen,  and  also  removes  waste  products.  The nerves  allow to sense pressure  and  touch,  and, if the  nerve  is  exposed  by damage,  we experience  intense  pains. The root  of the  tooth  is  covered with cement,  a substance  similar  to  bon:.  Numerous fibres,  connected  to the  cement  at one  end and  the  jaw  bone at  the  other,  anchor  the  tooth firmly  in  place.  However,  it  is  still able to move slightly  and  this  reduce the  chances  of it being  sheared  off during  chewing.