Dentition refers to the number, arrangement and conformation of teeth in an organism.
Types of Dentition
There are two main types of dentition. These are:
Homodont dentition: In this type of dentition, the organisms have the same type of teeth. No set of teeth is specialised for any function. All the teeth are of the same shape, size and functions. Examples of homodont dentition are found in fishes, amphibians and reptiles.
Heterodont dentition: In this type of dentition, the organisms possess teeth of different shapes, sizes and functions.
Examples of organisms having heterodont dentition are mammals, e.g. rabbits, man, dog, cattle, etc. The mammals generally have four different types of teeth. These are incisors, canines, premolars and molars. The type of teeth possessed by an animal is closely related to the type of food it eats.
Mammals again have two sets of teeth. These are milk teeth and permanent teeth.
1) Milk Teeth: This is the set of teeth possessed by the young ones (i.e. children in the case of human) and it is made up of the incisor, canine and premolar teeth (i.e. without the molar). It is common among the young ones and may number up to twenty (20) and later fall off to be replaced by the permanent teeth.
2) Permanent Teeth: This is the set of teeth possessed by adult mammals and are usually four types. These are incisor, canine, premolar and molar teeth. They remain till old age and may number up to 32 in man.
Types of Teeth
There are four types of teeth in mammals. These are incisors, canines, premolars and molars.
- Incisors: These are located in the front of the jaw. They are flat, chisel-shaped with a sharp edge used for cutting and holding on to the prey so that they do not escape.
- Canines: They are found next to incisors. They are sharp and pointed at the tips. Canines are used for tearing flesh and for catching the prey.
- Premolars: Premolars are located at the back of the jaw following the canines. They have large, ridged flat surfaces or cusps used for grinding and chewing of food.
- 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.
Structure of a Tooth
A typical tooth such as the canine or incisor is made up of three regions which are the crown, the neck and the root.
- The crown is the part of the tooth that is above the gum.
- The root is the part of the tooth that is embedded in the socket of the gum.
- The neck is the narrow junction between the crown and the root.
Incisors and canine have one root each while premolars and molars may have two or three roots each.
Starting with the external part, the tooth consists of enamel which is manufactured by special cells of the gum. Enamel is a very hard, non-living substance containing calcium salts. It protects the dentine and pulp cavity and form an efficient hard biting surface. Below the enamel is the dentine. It 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 up of connective tissue, 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 nerve 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 mandible (lower jaw). A fibrous tissue called peridontal membrane fixes the tooth into the jaw bone.
The dental formula refers to the numbers and types of teeth present in the mouth of an animal. The numbers and types of teeth present in the jaw of an animal is a reflection of special adaptation of mammalian teeth for feeding.
Adaptation of Mammalian Teeth for Feeding
The Teeth of Man
Man is an omnivore, i.e ., he feeds on both flesh and vegetables and the teeth, 32 in number is adapted to the kind of diet it feeds on.
- Incisors are sharp and broad for cutting food.
- Canines are bluntly pointed and are used for gripping and tearing of food.
- Premolars and molars have strong cusps for chewing and grinding of food.
The Teeth of Dog
Dog is a carnivorous animal, i.e. it feeds on flesh hence its teeth, 42 in number are adapted to the kind of food it eats.
- Incisors which are small and pointed are used for cutting small pieces of meat from bones.
- Canines are long, curved, large and pointed. They are used for attack, defence as well as allowing the animal to seize its prey and tear off flesh from bones.
- Premolars and molars are broad and thick. The last premolar in the upper jaw and the first molar in the lower jaw are large and modified to form carnassial teeth. They possess sharp cutting edges which are used to cut up meat and tear it away from bones. They are used also for cracking bones. Premolars and molars are cusped, blunt with flat surfaces used mainly for cutting and grinding.
The Teeth of Rabbit
The rabbit is a herbivorous animal, i.e ., it feeds mainly on vegetables hence its teeth, 28 in number, is adapted to the kind of food it eats.
- Its incisors are flat with sharp cutting edges for the cutting of vegetables or grasses.
- The canines are absent. The space created by their absence is called the diastema. The diastema allows the manipulation of grasses in the mouth.
- Premolars and molars are large, closely packed and have large ridged surface area for cutting and grinding.
The decaying of teeth by bacteria and other fermentation of starch within the teeth can be prevented by adequately caring for the teeth. The teeth can therefore be cared for in the following ways:
- The teeth should be cleaned with brush or chewing stick and tooth paste twice a day especially after meal and before going to bed.
- Stains due to eating kola or tobacco smoking should be removed by using hydrogen peroxide to wash the mouth.
- Vitamins and mineral containing food such as green vegetables, fresh fruits, butter, cheese, milk and eggs should be taken regularly.
- Sugary foods and drinks like sweet, ice cream, soft drinks etc should be avoided because bacteria feed on sugar and in the process turn them into acid which attack the teeth.
- The dentist should be visited for regular check-up at least twice a year.
- Artificial teeth should always be removed and washed with germicide solution after each meal.
- Food particles or meat should be removed after meal.
- Misuse of teeth such as opening bottle cork or cracking large bones that may cause damage to the enamel should be avoided.