- 03 Jul 2017
There is an interrelation between the form of teeth arid nature of food. These may be omnivorous, carnivorous, insectivorous herbivorous and rodents or gnawing. In Mammals dentition is complete in the first three types. Often incomplete in herbivores where the canines are absent. The absence of canines forms a gap between incisors and premolar. This is called diastema Rabbit). The canines are small or absent and the cheek teeth have broad grinding surfaces with transverse ridges - lophodont molars. In omnivorous mammals the incisors are suited for cutting the canines for tearing and cheek teeth with prominent crowns raised into rounded tubercles are adapted for crushing bunodont molars. In the carnivorous mammals, the incisors are either poorly developed or reduced and few in number and the canines are long and sharp suited for tearing and piercing the flesh But the molars with knife-like edges are modified for scratching the flesh from the bones. In the insectivores, the incisors of the upper and lower jaws become closely united to secure small active prey and the molars have sharp pointed crowns.
Depending upon the shape, size and number of cusps, the teeth are differentiated into:
- Monocuspici teeth - Teeth with one cusp or tubercie
- Bicuspid teeth - Teeth with two cusps.
- Tricuspid teeth - Teeth with three cusps and all the cusps are arranged in one plane by forming a triangle.
- Bunodont teeth - Teeth with a number of distinct blunt pointed cusps - Man and Monkey.
- Lophodont teeth - The cusps are fused in the form of ridges- Horse & Elephant.
- Selenodont teeth - Here the cusps are wear away, exposing the under lying dentineythich-getnuii by crescent -Shaped bands raf -
- Secodont teeth - The cusps are having sharp cuffing surfaces - carnivorous mammals. Carnassial teeth are present.
- Hypsodont teeth - The teeth are having long crown and deeply placed neck. - Horse
- Brachyodont teeth - Teeth with short crow, and neck at the surface gum. - Dog.
In sirenia (sea - Cow and Manatee), the teeth are devoid of enamel.
- 02 Jul 2017
Teeth are the dermal derivatives of integument They are developed as a result of calcification in the mucous membrane of the 1 cavity. Along with the ridge of the two jaws, the teeth are arranged in a row. The teeth are present in almost all the mammals except in a few mammals In whale, the teeth are fused into plates and lost in the adult stage of Ant eaters. But in Echidna (spiny ant eater) the teeth are absent even in the embryo.
Structure of tooth: Each typical mammalian tooth is placed in the socket over the jaw bone. It is distinguished into three main pads.
- Root: It is the basal part embedded in the bony socket.
- Neck: it is the part above the root enclosed by the gum
- Crown It is the upper part beyond the surface of the gum.
The toot is separated from the socket by a vascular pridontal membrane. The vertical section tooth consists of the following parts.
- Pulp cavity: The entire tooth encloses a central pulp cavity surrounded by a layer of odontoblast cells filled with soft pulp. It is made up of connective tissue, blood vessels and nerve fibers.
- Dentin: A substance chemically similar to bone- dentine forms the major part of the tooth. But the dentine is permeated by numerous thin canaliculi.
- Enamel: It is present over the de in the crown and neck regions of the tooth. It is hardest and contains only traces of living matter.
- Cement: It surrounds the denting of the root portion of the tooth. It is bony in nature.
- 02 Jul 2017
The mammalian teeth are placed in the muscular sockets in the jaw bones. This type of dentition is called Thecodont. The teeth are ‘diphyodont’. Two sets of teeth develop during life lime. The first set of teeth develop in the young and known as ‘milk or deciduous teeth’, after certain age these are replaced by the second set of permanent teeth. But in bats ‘and, guinea pigs the milk teeth are shed before birth. In platypus, toothed whales, sloths and sirenians the monophyodont dentition’ is present. Milk dentition is reduced by the replacement of the third premolar in marsupials.
All the teeth are not alike in all mammals. Mostly mammals exhibit ‘heterodont dention’. The teeth are modified in the form and function. But in Dolphins and porpoises it is homodont (all teeth are alike). There are four types of mammalian teeth.
1) Incisors: These are present on the premaxillae bones of the upper jaw and dentary bones of the lower jaw. They have only one ro and sharp cutting edges. So this type of teeth is used in sizing and cuffing.
2) Canine: These are present between the incisors and premolar. There is a single such troth in each half of each Jaw. These are long, conical teeth with a single root and simple, sharp-pointed crown.
3) Premolars : These follow the canines. They have double root and compressed crown with one or two cusps. These possess grinding and crushing surfaces. Premolars are replaced once in life time.
4) Molars: These are next to the premolars. They have more than two roots and cusps. These do not have predessors and always develop in the permanent set. Molars are used for crushing and mastica lion.
Both prermolars and molars are collectively knows, as cheek teeth and are borne on maxillae and dentaries. These have broad crushing and grinding surfaces or cusps.