Tag: structure and functions of living organisms -ii

Humans, like other mammals, are diphyodont, meaning that they develop two sets of teeth. Among deciduous (primary) teeth, ten are found in the maxilla (upper jaw) and ten in the mandible (lower jaw), for a total of 20. The dental formula for primary teeth is 2.1.2/2.1.2.

A diastema is a space or gap between two teeth. It happens when there is an unequal relationship between the size of the teeth and the jaw.

Odontoblast is one of the dentin-forming cells, derived from mesenchyme of neural crest origin, lining pulp cavity of teeth; arranged in a peripheral layer in dental pulp, each with an odontoblastic process extending part way into dentinal tubules.

The four front teeth in each arch are called incisors, and their function is to cut food with their sharp thin edges.

A diastema is an area of extra space between two or more teeth. The two front teeth of the upper jaw area is where diastema is most frequently seen. Many children experience diastema as primary teeth fall out, though in most cases these spaces close when the permanent teeth erupt. Diastemas may also be caused by a tooth size discrepancy, missing teeth or an oversized labial frenum, the tissue that extends from the inside of the lip to the gum tissue where the upper two front teeth are located. Secondary reasons involve oral alignment issues such as a protrusion of the teeth. Thus, option B is correct.

The teeth of a carnivore are long and pointed, for tearing raw flesh. Herbivores have flat teeth and flat back molars to grind their food. Carnivores do not have flat back molars at all.  Some herbivores do have small, what we call “canine” teeth for biting into tough plants like apples but these are nothing compared to the size and shape of a carnivore’s teeth. True omnivores teeth are most similar to carnivore teeth. Thus, option B is correct. 

The four front teeth in each arch are called incisors, and their function is to cut food with their sharp thin edges. On each side of the incisors, at the corners of the mouth, are the canines. These teeth have one cusp, or pointed edge, and are used for holding or grasping food, and are very strong, stable teeth. Behind the canines are the premolars, which are designed for holding food like the canines because they have cusps, but they also function to crush food. Sometimes these teeth are referred to as bicuspids, meaning two cusps, but this is not always accurate because some premolars may have three cusps. Therefore the term premolar is preferred. The teeth farthest back in the mouth are the molars. These teeth have broad chewing surfaces with four or five cusps, and are designed for grinding food. The incisors and canines are called anterior teeth, because they are located in the front of the mouth, while the premolars and molars are called posterior teeth because they are located in the back of the mouth. Thus, option A is correct.

In anatomy, a heterodont is an animal which possesses more than a single tooth morphology. For example, members of the Synapsida generally possess incisors, canine, premolars, and molars. The presence of heterodont dentition is evidence of some degree of feeding/hunting specialization in a species. In contrast, homodont dentition refers to a set of teeth that possess the same tooth morphology. Acrodont is a formation of the teeth whereby the teeth are consolidated with the summit of the alveolar ridge of the jaw without sockets. Pleurodont is a formation of the teeth that are fused by their sides to the inner surface of the jaw bones. Thus, option D is correct.

The permanent molars occupy the most posterior portion of the dental arch. They have the largest occlusal surfaces of any of the teeth and have from three to five major cusps. Lower permanent molars always have two lingual cusps and upper permanent molars always have two buccal cusps. Lower molars have two roots and upper molars have three roots. Molar teeth by definition are cheek teeth that are not preceded by primary teeth. Permanent molars are accessional teeth without primary predecessors. In contrast to the molars, permanent incisors, canines and premolars are succedaneous (successional teeth). Premolar, canine and incisors does not have three roots. Thus, option A is correct.

A wisdom tooth or third molar is one of the three molars per quadrant of the human dentition. It is the most posterior of the three. Wisdom teeth generally erupt between the ages of 17 and 25. Most adults have four wisdom teeth (a third molar in each of the four quadrants), but it is possible to have fewer or more, in which case the extras are called supernumerary teeth. Wisdom teeth commonly affect other teeth as they develop, becoming impacted or "coming in sideways". They are often extracted when this occurs.