A. Nanci et al., Morphological and immunocytochemical analyses on the effects of diet-induced hypocalcemia on enamel maturation in the rat incisor, J HIST CYTO, 48(8), 2000, pp. 1043-1057
During the maturation stage of amelogenesis, the loss of matrix proteins co
mbined with an accentuated but regulated influx of calcium and phosphate io
ns into the enamel layer results in the "hardest" tissue of the body. The a
im of the present investigation was to examine the effects of chronic hypoc
alcemia on the maturation of enamel. Twenty-one-day old male Wistar rats we
re given a calcium-free diet and deionized water for 28 days, while control
animals received a normal chow. The rats were perfused with aldehyde and t
he mandibular incisors were processed for histochemical and ultrastructural
analyses and for postembedding colloidal gold immunolabeling with antibodi
es to amelogenin, ameloblastin, and albumin. The maturation stage enamel or
gan in hypocalcemic rats exhibited areas with an apparent increase in cell
number and the presence of cyst-like structures. In both cases the cells ex
pressed signals for ameloblastin and amelogenin. The content of the cysts w
as periodic acid-Schiff- and periodic acid-silver nitrate-methanamine-posit
ive and immunolabeled for amelogenin, ameloblastin, and albumin. Masses of
a similar material were also found at the enamel surface in depressions of
the ameloblast layer. In addition, there were accumulations of glycoprotein
aceous matrix at the interface between ameloblasts and enamel. In decalcifi
ed specimens, the superficial portion of the enamel matrix sometimes exhibi
ted the presence of tubular crystal "ghosts." The basal lamina, normally se
parating ameloblasts and enamel during the maturation stage, was missing in
some areas. Enamel crystals extended within membrane invaginations at the
apical surface of ameloblasts in these areas. Immunolabeling for amelogenin
, ameloblastin, and albumin over enamel was variable and showed a heterogen
eous distribution. In contrast, enamel in control rats exhibited a homogene
ous labeling for amelogenin, a concentration of ameloblastin at the surface
, and weak reactivity for albumin. These results suggest that diet-induced
chronic hypocalcemia interferes with both cellular and extracellular events
during enamel maturation.