Editing Human tooth (section)

=== Eruption ===
{{Main|Tooth eruption}}

[[File:ToothLost-2917.jpg|thumb|right|Bottom teeth of a seven-year-old, showing primary teeth ''(left)'', a lost primary tooth ''(middle)'', and a permanent tooth ''(right)'']]
Tooth eruption in humans is a process in tooth development in which the teeth enter the mouth and become visible. Current research indicates that the periodontal ligaments play an important role in tooth eruption. Primary teeth erupt into the mouth from around six months until two years of age. These teeth are the only ones in the mouth until a person is about six years old. At that time, the first permanent tooth erupts. This stage, during which a person has a combination of primary and permanent teeth, is known as the mixed stage. The mixed stage lasts until the last primary tooth is lost and the remaining permanent teeth erupt into the mouth.

There have been many theories about the cause of tooth eruption. One theory proposes that the developing root of a tooth pushes it into the mouth. Another, known as the cushioned hammock theory, resulted from microscopic study of teeth, which was thought to show a [[ligament]] around the root. It was later discovered that the "ligament" was merely an [[Artifact (observational)|artifact]] created in the process of preparing the slide. Currently, the most widely held belief is that the periodontal ligaments provide the main impetus for the process.

The onset of primary tooth loss has been found to correlate strongly with somatic and psychological criteria of school readiness.<ref>Kranich, Ernst-Michael (1990) "Anthropologie", in F. Bohnsack and E-M Kranich (eds.), ''Erziehungswissenschaft und Waldorfpädagogik'', Reihe Pädagogik Beltz, Weinheim, p. 126, citing [[Frances Ilg]] and [[Louise Bates Ames]] (Gesell Institute), ''School Readiness'', p. 236 ff</ref><ref>{{cite journal|quote=...the loss of the first deciduous tooth can serve as a definite indicator of a male child's readiness for reading and schoolwork|title=Second Dentition and School Readiness|journal=New York State Dental Journal |volume=43 |pages=155–8|pmid=264640|year=1977|last1=Silvestro|first1=JR|issue=3}}</ref>{{Clarify|date=January 2012}}