Our previous findings have demonstrated that the rat autosomal-recessive mutation, whitish
chalk-like teeth (wct), induces enamel defects resembling those of human
amelogenesis imperfecta (AI) in continuously growing incisor teeth. The present study clarifies the effect of the wct mutation on the morphogenesis and calcification of rat molar teeth.
Formalin-fixed maxillae obtained from animals aged 4-30 days were examined by electron probe micro-analysis (EPMA) and by immunocytochemistry for
amelogenin, ameloblastin, and
enamelin. There were no distinct differences in the
calcium and phosphorous contents and the amount of enamel between homozygous mutant and wild-type teeth during postnatal days 4-11. Although the
mineral density in the enamel matrix considerably increased in the wild-type teeth until day 15, no changes occurred in mutant teeth during days 11-30. The immunoreactivity for enamel
proteins in the secretory-stage ameloblasts in mutant teeth was similar to that in the wild-type teeth, and subsequently mutant maturation-stage ameloblasts became detached from the enamel surface, resulting in
odontogenic cyst formation between the enamel organ and matrix until day 7 and the expansion of the
cyst around the whole tooth crown on day 15. On day 30, the erupted mutant teeth presented morphological changes such as enamel destruction and tertiary dentin formation in addition to low
mineral density in the enamel. Thus, the wct mutation prevents
mineral transport without disturbing the synthesis of enamel
proteins in molar teeth because of the absence of maturation-stage ameloblasts, in addition to the occurrence of
odontogenic cysts.