Why doesn't your permanent teeth grow back?

[briangumble]

I'm not a dentist, and I don't really know that much about how the human body works and whatnot, but why doesn't your permanent teeth grow back? I mean what makes your teeth grow the 2nd time, but not again if you lose them? And are there any advances in science/medicine that gets around this problem? I was just wondering this.

[witchdr420]

You had the bad luck to be born human instead of a shark.

[qwerty1234]

A significant amount of research has focused on determining the processes that initiate tooth development. It is widely accepted that there is a factor within the tissues of the first branchial arch that is necessary for the development of teeth.[11] The tooth bud (sometimes called the tooth germ) is an aggregation of cells that eventually forms a tooth and is organized into three parts: the enamel organ, the dental papilla and the dental follicle.[12]

The enamel organ is composed of the outer enamel epithelium, inner enamel epithelium, stellate reticulum and stratum intermedium.[12] These cells give rise to ameloblasts, which produce enamel and the reduced enamel epithelium. The growth of cervical loop cells into the deeper tissues forms Hertwig's Epithelial Root Sheath, which determines the root shape of the tooth. The dental papilla contains cells that develop into odontoblasts, which are dentin-forming cells.[12] Additionally, the junction between the dental papilla and inner enamel epithelium determines the crown shape of a tooth.[13] The dental follicle gives rise to three important entities: cementoblasts, osteoblasts, and fibroblasts. Cementoblasts form the cementum of a tooth. Osteoblasts give rise to the alveolar bone around the roots of teeth. Fibroblasts develop the periodontal ligaments which connect teeth to the alveolar bone through cementum.[14]

Tooth development is commonly divided into the following stages: the bud stage, the cap, the bell, and finally maturation. The staging of tooth development is an attempt to categorize changes that take place along a continuum; frequently it is difficult to decide what stage should be assigned to a particular developing tooth.[11] This determination is further complicated by the varying appearance of different histologic sections of the same developing tooth, which can appear to be different stages.

[Plastic Jesus]

Humans are diphyodont, meaning that they develop two sets of teeth throughout life. 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 eruption of teeth starting at about six months is known as teething and can be quite painful for an infant.
Some animals develop only one set of teeth (monophyodont) or develop many (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 the animal's gnawing, maintaining approximately constant length. Some rodent species such as the sibling vole<SUP class=reference id=_ref-0>[1]</SUP> and the guinea pig<SUP class=reference id=_ref-1>[2]</SUP> have also continuously growing molars.

Wikipeded...