Identification of the cell type origin of odontoma‐like cell masses in microphthalmic (mi/mi) mice byin situhybridization

Abstract

Tooth abnormalities occur in microphthalmic (mi/mi) mice. The elongated odontogenic epithelium is interrupted by unresorbed bone at the basal end of the mi/mi incisor, with the epithelium gathered into cell clusters. These clusters develop to odontoma-like masses. To identify the origin of the cell types of these odontoma-like masses, the localization of osteonectin (Osn), osteocalcin (Osc), osteopontin (Osp), matrix Gla protein (MGP) and amelogenin (Am) mRNA in the process of tooth development in mi/mi and +/+ mice was investigated by means of in situ hybridization. Decalcified mandibles of neonatal, 5-, 10-, 14-day-old mice were examined. Osn and Osc mRNA, which localized in osteoblasts and odontoblasts, were also detected in the cells of odontoma-like masses in mi/mi mice. The cells expressing these mRNA were short, columnar and odontoblast-like. Am mRNA was detected in ameloblasts. In mi/mi mice, Am mRNA was also detected in ameloblastic cell clusters, which were formed by the tall columnar cells in the odontoma-like masses. No apparent Osp mRNA expression was detected in the masses. These results indicated that even in odontogenic abnormal cells resulting from physical obstruction in mi/mi mice, the genes that are involved in normal tooth development were still expressed.

Disturbed tooth eruption in osteopetrotic (op/op) mice: histopathogenesis of tooth malformation and odontomas

“…Similar odontoma‐like structures at the apical end of incisor germs have been described previously in other osteopetrotic animals, such as mi/mi mice (13), ia/ia rats (15,16), and op/op rats (18). These authors commonly understood that these malformations were not generated by excessive proliferation of odontogenic tissues but rather by crowding of those tissues which were produced as a result of the lack of resorption in bone.…”

“…As to the oral aspect of osteopetrosis, the disturbed eruption of teeth and formation of odontoma‐like masses around the posterior end of the incisor have been reported in mi/mi mice (11–13), gl mice (14), ia rats (15, 16), tl rats (17) and op/op rats (18, 19). As far as op/op mice are concerned, there have been few reports in which the mechanism of disturbed tooth eruption and odontoma formation occurs (20, 21).…”

Odontoma-like Tumours of Squirrel Elodont Incisors—Elodontomas

“…This has been postulated to be the result of reduced bone resorption (Schour et al, 1949) and a disordered extracellular matrix remodelling capacity in such tissue (Ida-Yonemochi et al, 2002). According to these and other similar postulates, the formation of these tumours is the result of crowding of the odontogenic tissue rather than excessive proliferation thereof (Schour et al, 1949;Philippart et al, 1994;Nakajima et al, 1996;Ida-Yonemochi et al, 2002). Due to the reduced resorption ability of bone, osteopetrotic mice with odontoma-like periapical masses have bone trabeculae invading the tooth germs in early odontogenesis, leading to a further postulate to account for the lesions (Ida-Yonemochi et al, 2004 andIda-Yonemochi et al, 2002).…”

Osteoclasts in the Dental Microenvironment: A Delicate Balance Controls Dental Histogenesis

“…This phenotype was moderate here in Msx2-/-mice where the third molar was principally affected. In a more variable pattern, alterations to odontogenesis have been described; the defects include a complete lack of root formation, as observed in several mouse mutants [Lu et al, 2009], and/or, as shown in Msx2-/-mice in the present study, late growth of odontogenic tumor-like structures [Nakajima et al, 1996;Tiffee et al, 1999], the occurrence of which is frequently reported. It may involve continuously erupting incisors and/or limited growth of molars.…”