The Pattern and Control of Human Premolar Eruption
Dr. Bill Proffit

Within the last few years, high-precision optical measurement devices have been adapted for study of human premolars during the pre-functional stage of post-emergent eruption. Video microscope observations provide a resolution of 2 microns and can give a continuous record of tooth position for periods of up to 12 hours. Tracking interference fringes and taking advantage of Moire magnification allows a resolution of better than 0.05 microns, enough to see a tooth bounce with each arterial pulse. It is known now that eruptive movements follow a diurnal cycle, with all eruption occurring during the early evening. Current experiments indicate that intermittent force applications to an erupting tooth (like those during function) have little effect on eruption and do not seem to be a part of the control mechanism. Alterations in blood flow to the apical area, in contrast, immediately affect eruption. Hormonally-induced changes in blood flow are the likely explanation for the eruption rhythm.

Key Points:
-What is the mechanism of pre-emergent eruption?
  1. not the proliferation of cells at the root apex
  2. not the shortening of collagen fibers in the PDL
  3. almost surely, a result of pressure from blood flow in PDL
-What is the mechanism of resorption to clear the eruption path? The activity of crest cells formed within the follicular epithelium

-Pre-emergent eruption is controlled by resorption of tissues in the eruption path not the development of force to move the teeth

-Primary failure of eruption – eruption path is clear and tooth doesn’t follow

-During post-emergent eruption the fastest the tooth moves during the eruption phase is during the “pre-functional” phase.

-What force is necessary to stop eruption? As for other “equilibrium” effects, force duration not magnitude, appears to be the controlling factor

-using new optical instrumentation, during the pre-functional stage most eruption occurs in early evening as with skeletal growth (6PM through 12 midnight), which follows the cycle of HgH.