Video microscope observations of human premolar eruption.

It is now possible to observe with an accuracy of 1-2 microns the pattern of eruptive movements of a human premolar as it moves from gingival emergence to the occlusal plane. This was accomplished by use of a video microscope to track the position of an optical ruling on the erupting tooth relative to a reference ruling mounted on adjacent teeth that were in occlusion. Net eruptive movements averaging 25-75 microns occurred from one day to the next until the tooth was almost in occlusion; then the eruptive rate slowed. Eruption occurred almost entirely at night. During the day, there was a marked slowing or cessation of eruption and often intrusion, which appeared to be related to masticatory activity.