Premolars and molars Archives

TYPES OF MAMMALIAN TEETH Mammals have four kinds of teeth The incisors are found at the front of the jaw They are sharp-edged and are used for biting The canines are located at the sides of the jaw They are pointed and are used for tearing and piercing The premolars are next to the canines and the molars are at the back of the jaw Both premolars and molars are used for crushing and grinding Teeth are replaced only once in a lifetime The first set is the milk or deciduous teeth These are replaced by the second set or the permanent teeth Dentition refers to the type of teeth, the number and their arrangement in the jaw A dental formula shows the type and number of teeth in each half of the jaw The number of teeth in half of the upper jaw is represented above a line and those on the lower jaw below the line The first letter of each type of teeth is used in the formula i.e i incisors, c canines, pm premolars and m molars The total number is obtained by multiplying by two (for the two halves of each jaw) Adaptation of Teeth to Feeding In general, incisors are for cutting, canines for tearing while premolars and molars are for grinding However, specific modifications are observed in different mammals as an adaptation to the type of food they eat Teeth of Herbivores Incisors are long and flat with a sharp chisel¬like edge for cutting The enamel coating is thicker in front than at the back so that as the tooth wears out, a sharp edge is maintained Canines are reduced or absent If absent, the space left is called the diastema The diastema allows the tongue to hold food and push it to the grinding teeth at the back of the mouth Premolars and molars: These are transversely ridged The ridges on the upper teeth fit into grooves on the lower ones This gives a sideways grinding surface The teeth of herbivores have open roots i.e , wide opening into the pulp cavity This ensures a continued adequate supply of food and oxygen to the tooth In some herbivores, such as rabbits and elephants, the incisors continue to grow throughout life Teeth of Carnivores Incisors are reduced in size and pointed They are well suited for grasping food and holding prey Canines are long, pointed and curved They are used for piercing and tearing flesh as well as for attack and defence Premolars and molars: In general, they are long and longitudinally ridged to increase surface area for crushing Carnassial Teeth: These are the last premolars on the upper jaw and the first molars on the lower one They are enlarged for cutting flesh They act as a pair of shears They also crush bones The teeth of carnivores have closed roots i.e , only a very small opening of the pulp cavity to allow food and oxygen to keep teeth alive Once broken, no re-growth can take place Teeth of Omnivores Incisors have a wide surface for cutting Canines are bluntly pointed for tearing Premolars and molars have cusps for crushing and grinding The premolars have two blunt cusps while the molars have three to four. The tooth consists of two main parts: Crown: The portion above the gum; it is covered by the enamel Root: The portion below the gum; it is covered by the cement The tooth has two roots Neck: Is the region at the same level with the gum It forms the junction between the crown and the root It is covered by enamel Incisors and canines have one root only Premolars have one or two roots while molars have two to three roots each Internally, the bulk of the tooth is made up of dentine which consists of living cells and extends to the root It is composed of calcium salts, collagen and water It is harder than bone but wears out with use This is why it is covered by enamel which is the hardest substance in a mammal's body Pulp Cavity: Contains blood vessels which provide nutrients to the dentine and remove waste products It also contains nerve endings which detect heat, cold and pain Cement: Fixes the tooth firmly to the jaw bone Also See HETEROTROPHISM ENZYMES POLYSACCHARIDES PROCESS OF PHOTOSYNTHESIS NUTRITION IN PLANTS