Cyclic Induction and Rapid Movement of Sequential Waves of New Smooth-ended Ameloblast Modulation Bands in Rat Incisors as Visualized By Polychrome Fluorescent Labeling and Gbhastaining of Maturing Enamel

¹ Departments of Anatomy and Oral Biology, McGill University, 3640 University Street, Montreal, Quebec, Canada H3A 2B2
² Departments of Anatomy, McGill University, 3640 University Street, Montreal, Quebec, Canada H3A 2B2
³ Departements de stomatologie et d'anatomie, Universite de Montreal, Faculte de medecine dentaire, C. P. 6128, succursale A, Montreal, Quebec, Canada H3C 3J7

The movement of smooth-ended ameloblast modulation bands was studied in continuously erupting incisors of male Wistar rats, with fluorochromes such as calcein (green), xylenol orange (red), tetracycline (yellow), and calcein blue ( turquoise) used to label maturing enamel intensely at sites delimiting the location of smooth-ended ameloblasts at the time of injection. Hence, a fluorescent label of one color was injected to establish a reference position at time " 0" followed by one or more fluorescent labels of different colors, or by in vitro enamel staining with glyoxal bis(2-hydroxyanil)( GBHA), at various times after the initial injection. For example, rats injected with calcein followed by xylenol orange at 10 min or two, four, six, or 12 hr later showed zero, 367, 888,1259, and 2833 fxm incisal movement, respectively, of the red bands relative to companion green fluorescent bands in the mandibular incisors. If one takes into account the eruption rate for these teeth (27.1 jim per hr), these data were indicative of a coordinated, wave-like movement of smooth-ended ameloblast modulation bands incisally along the length of the tooth at a mean rate of 243 | xm per hr. Measurements and graphic plots of the distribution of smooth-ended ameloblast bands in histological sections and in GBHA-stained teeth revealed not only that such bands were positioned at all possible locations along the length of the maturation zone within a group of different teeth, but also that the average interband distance equaled about 2100 | xm in the apical part of the maturation zone. Hence, new modulation waves appear to arise near the region of post-secretory transition and travel along the ameloblast layer toward the gingival margin about once every 8.5 hours. This suggests that a given cohort of ameloblasts may modulate as frequently as three times a day and complete a minimum of 45 modulation cycles by the end of enamel maturation.

Note:

We thank Margo Oeltzschner for her assistance with the graphic illustrations; and Tony Graham, both for his invaluable help in photographing the teeth from rats injected with fluorochromes under ultraviolet light and for doing copy work.

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