The mammalian teeth
What is dentition?
Dentition refers to the number, arrangement and conformation of teeth in an organism.
TYPES OF DENTITION
There are two major types of dentition. They are
1. Homodont dentition and
2. Heterodont dentition
i. Homodont dentition: in this type of dentition, the organism possesses or have the same types or sets of teeth. In this types of dentition, there are no specialized set of teeth for a particular type of function. All the teeth of a typical homodont dentition are of the same sizes, shape and functions. Typical examples of homodont dentition is found in the reptiles, amphibians and fishes
ii. Heterodont dentition: in this type of dentition, the organism has teeth different sizes, shapes and functions. Examples organisms having the heterodont dentition are mammals like rabbits, man, dogs, lions, cattle and pigs.
Mammals generally has four types or set of teeth. These are
iii. Premolars and
The type of teeth possessed by an animal depends on the types food it eats.
Mammals have two sets of teeth, they are milk teeth and permanent teeth.
this the set of teeth possessed by young ones that in the case of humans, the children. It is made up of incisors, canines and premolars and the molars are absent. It is common in children and infants and numbers around 20. It will later fall off to be replaced by the permanent teeth.
this is the sets of teeth possessed by adults and are usually four groups consisting of the incisors, canines, premolars and molars. The permanent teeth stays till old age and may number up to 32 for a full grown adult human
TYPES OF TEETH
There are four types of teeth in mammals. These are incisors, canines, premolars and molars.
i. Incisors: these are located in the front of the jaw. They are flat, chisel shaped and sharp edge used in cutting and holding on the prey so that they cannot escape.
ii. Canines: these set of teeth are found next to the incisors. They are sharp and pointed at the tips. Canines are used for tearing flesh and bones in the case of carnivores
iii. Premolars: premolars are located at the back of the jaw following the canines. They have flat ridged surfaces or cusps used for grinding and chewing of foods
iv. Molars: molars are located at the extreme back of the jaws. They are closely packed with ridged surfaces. They are used for chewing and grinding of food
The structure of a tooth
A typical tooth such as the canine or incisor is made up of three parts or regions which are the crown, the neck and the root
1. The Crown: the crown is the parts of the tooth which above the gum
2. The Root: the root is the part of the tooth that is embedded in the socket of the gum
3. The Neck: this is the narrow junction between the crown and the root
Incisors and canines have one root each while the premolars and molars have two or three roots each
Starting with the external parts, then tooth consists of enamel which is manufactured by special cells of the gum. Enamel is a very hard, non-living substance containing calcium salts. The enamel protects the dentine and pulp cavity and form an efficient hard biting surface.
Below the enamel, the dentine is located. The dentine is a bony-like material which contains the pulp cells thereby making it alive.
At the centre of the tooth is pulp cavity which is made of connective tissues, sensory nerves and blood capillaries.
The blood capillaries of the pulp are important in the transportation of oxygen and digested food substances. Due to the presence of sensory nerves endings, the tooth is able to respond to heat, cold and pain.
At the root region, the tooth is not covered by enamel but by a bone-like material called cement.
The tooth is embedded in the jaw bone of maxilla (upper jaw) and the mandible (lower jaw). A fibrous tissue called periodontal membrane fixes the tooth into the jaw bone.
Meaning of dental formula
What is the dental formula?
The dental formula refers to the numbers and types of teeth present in the mouth of an animal. The number and type of teeth present in the mouth of a mammal or animal is a reflection of special adaptation of mammalian teeth for feeding.
The adaptation of mammalian teeth for feeding
– The four front teeth in both the upper and lower jaws are called incisors. Their primary function is to cut food. The two incisors on either side of the midline are known as central incisors. The two adjacent teeth to the central incisors are known as the lateral incisors. Incisors have a single root and a sharp incised edge.
– There are four canines in the oral cavity. Two in the maxillary arch and two in the mandibular area. They are behind and adjacent to the lateral incisors. Their main function is to tear food. They have a single, pointed cusp and a single root. They have the longest root of any tooth. They also serve to form the corners of the mouth.
– These teeth are located behind and adjacent to the canines and are designed to crush food. There are eight premolars in the oral cavity. There are two in each quadrant of the mouth. The one closest to the midline is the first premolar and the one farthest from the midline is the second premolar. These teeth can have 3-4 cusps. The maxillary first premolar has two roots, and the remaining premolars have a single root. There are no premolars in the primary dentition.
– The most posterior teeth in the mouth are the molars. They have broader and flatter surfaces with 4-5 cusps. They are designed to grind food. Molars typically have two roots, although the maxillary first molar (behind the second premolar) has three roots. There are 12 molars in the permanent dentition with three in each quadrant of the mouth. They are named starting with closest to the midline as first molars, second molars and third molars. Although, some people do not fully develop the third molars. Third molars are often referred to as wisdom teeth. The primary dentition only contains eight molars.
The human teeth
The dental formula of man is as follows
I= ,c= ,p= ,m= total=32
Man is an omnivore, i.e. it feeds on both flesh and vegetables and the total number of teeth in the mouth is 32, which is also adapted to its type of diet.
i. Incisors: incisors are broad and sharp for cutting food
ii. Canines: canines are bluntly pointed and are used for gripping and tearing food
iii. Premolars: premolars and molars have strong cusps for chewing and grinding of food
The teeth of dogs
I= ,c= ,p= ,m= total=42
Dog is a carnivorous animal, which means it feeds on flesh hence it has 42 in number and are adapted to the kind of food its eat. So here is the arrangement of the teeth in the mouth of a dog
i. INCISORS: the incisors of carnivores are very small and pointed. They are mainly used for cutting and tearing off flesh from bones.
ii. Canines: the canines of a typical carnivore are long, a little curved, large and pointed. The canine is used for attack and defense as well as for seizing prey, and tearing off flesh from the bones
iii. Premolars: premolars and molars are broad and thick. The last premolar in the upper jaw and the first molar ion the lower jaw are large and modified to form CARNASSIAL TEETH. The possess sharp cutting edges which are used to cut up meat and tear it away from bones. They are also used for cracking bones. Premolars and molars are cusped, blunt with flat surfaces used mainly for cutting and grinding
The teeth of Rabbit
The dental formula of rabbit is
I= ,c= ,p= ,m= total=28
The rabbit is a herbivorous animal, that is to say it feeds on vegetables mainly hence its teeth is 28 in number, and is adapted for the kind of food it eats.
i. The incisors of a rabbit are flat with sharp cutting edges for cutting vegetables or grasses.
ii. The canines are practically absent in rabbit. So the space created by the absence of canines in rabbit is called DIASTEMA. The DIASTEMA allows the manipulation of grasses in the mouth.
iii. The premolars and molars of the rabbit are large, closely packed and have large ridge surface area cutting and grinding of food
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