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Jaw From Wikipedia, the free encyclopedia This article is about the anatomical part. For other uses of the term, see Jaws. For the village in Bahrain, see Jaww.

Human jaw left view The jaw is either of the two opposable structures forming, or near the entrance to the mouth. The term jaws is also broadly applied to the whole of the structures constituting the vault of the mouth and serving to open and close it and is part of the body plan of most animals.

Tooth From Wikipedia, the free encyclopedia

"Teeth" redirects here. For the film, see Teeth (film). Teeth

An adult human's teeth.

CGI posterior view of teeth taken from inside mouth Dorlands/Elsevier	Tooth Teeth (singular, Tooth) are small whitish structures found in the jaws (or mouths) of many vertebrates that are used to tear, scrape, milk and chew food. Some animals, particularly carnivores, also use teeth for hunting or defense. The roots of teeth are covered by gums. Teeth are not made of bone, but rather of tissues of varying density and hardness. Teeth are among the most distinctive (and long-lasting) features of mammal species. Paleontologists use teeth to identify fossil species and determine their relationships. The shape of the animal's teeth are related to its diet. For example, plant matter is hard to digest, so herbivores have many molars for chewing. Carnivores, on the other hand, need canines to kill and tear meat. Mammals are diphyodont, meaning that they develop two sets of teeth. In humans, the first set (the "baby," "milk," "primary" or "deciduous" set) normally starts to appear at about six months of age, although some babies are born with one or more visible teeth, known as neonatal teeth. Normal tooth eruption at about six months is known as teething and can be painful. Some animals develop only one set of teeth (monophyodont) while others develop many sets (polyphyodont). Sharks, for example, grow a new set of teeth every two weeks to replace worn teeth. Rodent incisors grow and wear away continually through gnawing, maintaining relatively constant length. Many rodents, such as the sibling vole and the guinea pig[verification needed], have continuously growing molars in addition to incisors.[1][2]

Anatomy

A third molar. Main article: Dental anatomy The bottom teeth are used more for the grinding of food and the top front teeth are mainly used for biting. Dental anatomy is a field of anatomy dedicated to the study of tooth structures. The development, appearance, and classification of teeth fall within its field of study, though dental occlusion, or contact among teeth, does not. Dental anatomy is also a taxonomical science as it is concerned with the naming of teeth and their structures. This information serves a practical purpose for dentists, enabling them to easily identify teeth and structures during treatment. The anatomic crown of a tooth is the area covered in enamel above the cementoenamel junction (CEJ).[3] The majority of the crown is composed of dentin with the pulp chamber in the center.[4] The crown is within bone before eruption.[5] After eruption, it is almost always visible. The anatomic root is found below the cementoenamel junction and is covered with cementum. As with the crown, dentin composes most of the root, which normally have pulp canals. A tooth may have multiple roots or just one root. Canines and most premolars, except for maxillary (upper) first premolars, usually have one root. Maxillary first premolars and mandibular molars usually have two roots. Maxillary molars usually have three roots. Additional roots are referred to as supernumerary roots.

Models of human teeth as they exist within the alveolar bone. Humans usually have 20 primary teeth (also called deciduous, baby, or milk teeth) and 32 permanent teeth. Among primary teeth, 10 are found in the (upper) maxilla and the other 10 in the (lower) mandible. Teeth are classified as incisors, canines, and molars. In the primary set of teeth, there are two types of incisors, centrals and laterals, and two types of molars, first and second. All primary teeth are replaced with permanent counterparts except for molars, which are replaced by permanent premolars. Among permanent teeth, 16 are found in the maxilla with the other 16 in the mandible. The maxillary teeth are the maxillary central incisor, maxillary lateral incisor, maxillary canine, maxillary first premolar, maxillary second premolar, maxillary first molar, maxillary second molar, and maxillary third molar. The mandibular teeth are the mandibular central incisor, mandibular lateral incisor, mandibular canine, mandibular first premolar, mandibular second premolar, mandibular first molar, mandibular second molar, and mandibular third molar. Third molars are commonly called "wisdom teeth" and may never erupt into the mouth or form at all. If any additional teeth form, for example, fourth and fifth molars, which are rare, they are referred to as supernumerary teeth.[6] Most teeth have identifiable features that distinguish them from others. There are several different notation systems to