human tooth , tooth decay
Teeth of humans are small, calcified, whitish structures found in the mouth that are used to break down food. The roots of teeth are embedded in the maxilla (upper jaw) or the mandible (lower jaw) and are covered by gums. Teeth are made of multiple tissues of varying density and hardness.
Teeth are among the most distinctive (and long-lasting) features of mammal species. Humans, like other mammals, are diphyodont, meaning that they develop two sets of teeth. The first set (also called the "baby", "milk", "primary", and "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.
Structure of Human Tooth
The teeth are the hardest substances in the human body. Besides being essential for chewing, the teeth play an important role in speech. Parts of the teeth include:
• Enamel: The hardest, white outer part of the tooth. Enamel is mostly made of calcium phosphate, a rock-hard mineral. • Dentin: A layer underlying the enamel. Dentin is made of living cells, which secrete a hard mineral substance. • Pulp: The softer, living inner structure of teeth. Blood vessels and nerves run through the pulp of the teeth. • Cementum: A layer of connective tissue that binds the roots of the teeth firmly to the gums and jawbone. • Periodontal ligament: Tissue that helps hold the teeth tightly against the jaw.
• Crown : Exposed part of tooth
• Root : Part embedded in jaw
• Jaw Bone : Sockets for teeth
• Gum : Protects jaw bones and roots of teeth
Because mammalian teeth are specialized for different functions, many mammal groups have lost teeth not needed in their adaptation. Tooth form has also undergone evolutionary modification as a result of natural selection for specialized feeding or other adaptations. Over time, different mammal groups have evolved distinct dental features, both in the number and type of teeth, and in the shape and size of the chewing surface.
The number of teeth of each type is written as a dental formula for one side of the mouth, or quadrant, with the upper and lower teeth shown on separate rows. The number of teeth in a mouth is twice that listed as there are two sides. In each set, incisors (I) are indicated first, canines (C) second, premolars (P) third, and finally molars (M), giving I:C:P:M. So for example, the formula 22.214.171.124 for upper teeth indicates 2 incisors, 1 canine, 2 premolars, and 3 molars on one side of the upper mouth.
Different types of teeth
In the human mouth there are 4 different types of teeth, each specialised for different functions. There are also 2 sets of teeth: the first - also called milk or deciduous teeth - usually "erupt" over a period from the age of about 6 months to 3 years.
From the age of about 5 to 14 these are gradually replaced from below by the permanent set, with the final "wisdom" teeth appearing in the late teens or early twenties. [pic]
Dental caries, also known as tooth decay or a cavity, is an infection, usually bacterial in origin, that causes demineralization of the hard tissues (enamel, dentin and cementum) and destruction of the organic matter of the tooth, usually by production of acid by hydrolysis of the food debris accumulated on the tooth surface . If demineralization exceeds saliva and other remineralization factors such as from calcium and fluoridated toothpastes, these tissues progressively break down, producing dental caries (cavities, holes in the teeth). The two bacteria most commonly responsible for dental cavities are Streptococcus mutans and Lactobacillus. If left untreated, the disease can lead to pain, tooth...
Please join StudyMode to read the full document