Editing Human tooth (section)

====Alteration of eruption====
Tooth eruption may be altered by some environmental factors. When eruption is prematurely stopped, the tooth is said to be [[Wisdom teeth#Impaction|impacted]]. The most common cause of tooth impaction is lack of space in the mouth for the tooth.<ref name="neville66">{{harvnb|Neville|2002|page=66}}</ref> Other causes may be [[tumor]]s, [[cyst]]s, trauma, and thickened bone or soft tissue. [[Tooth ankylosis]] occurs when the tooth has already erupted into the mouth but the cementum or dentin has fused with the alveolar bone. This may cause a person to retain their primary tooth instead of having it replaced by a permanent one.

A technique for altering the natural progression of eruption is employed by [[orthodontist]]s who wish to delay or speed up the eruption of certain teeth for reasons of space maintenance or otherwise preventing crowding and/or spacing. If a primary tooth is extracted before its succeeding permanent tooth's root reaches {{frac|1|3}} of its total growth, the eruption of the permanent tooth will be delayed. Conversely, if the roots of the permanent tooth are more than {{frac|2|3}} complete, the eruption of the permanent tooth will be accelerated. Between {{frac|1|3}} and {{frac|2|3}}, it is unknown exactly what will occur to the speed of eruption.