Objective: The aim of the present study was to characterize the excess hard tissue on the mandible of the microphthalmic mouse having a mutation at the mitf locus.
Design: Homozygous mutant (mi/mi) and wild-type (+/+) mice were obtained by mating a breeding pair (strain name, B6C3Fe a/a-Mitf(mi)/J). We used mi/mi and +/+ mice at ages 6, 7, 8, 9, 28, and 49 days for micro-computed tomographic and histologic analyses.
Results: Excess hard tissue was found on the mesio-buccal surface of the mandibular first molar in all 11mi/mi mice, but none was found in the 8mi/+ or 14 +/+ mice. The excess hard tissue was located in the mental foramen connected to the mandibular canal. The mandibular canal passed near the basal part of the incisor and the root of the mandibular first molar due to aberrant development of the teeth and mandible. The excess hard tissue contained predentine immunostained for dentine sialoprotein, a marker for early stages of dentinogenesis, which was first observed at about 7 days of age. Dentine, predentine, pulp, and root-like structures were observed in the excess hard tissue, but neither enamel nor enamel organ was observed.
Conclusion: Odontogenic cells in the basal part of the incisor and/or the mandibular first molar with the ability to develop into odontoblasts and pulp cells appeared to migrate through the mandibular canal to the mental foramen, where they developed into odontoblasts and pulp-like cells, and then formed dentine and predentine-like structures.