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
NUTRITION IN PLANTS