Dental Tissue Changes in Juvenile and Young Adult Mice with Osteogenesis Imperfecta

Osteogenesis imperfecta (OI) encompasses a heterogeneous family of heritable connective tissue disorders characterized by insufficient or malformed type I collagen protein causing bone fragility, skeletal deformity, and significant dental issues. The most prominent oral characteristic of OI patients, dentinogenesis imperfecta (DI), is characterized by dentition with significant discoloration and structural defects. During normal dental development, specialized cells secrete layers of collagen-rich matrix, which are then mineralized to form the two hard tissues of the tooth – the enamel, the protective tissue that forms the crown of the tooth, and the dentin, which sits internal to the enamel and forms the bulk of the tooth. Importantly, the matrix on which dentin forms is primarily composed of type I collagen. In DI, the secretion of malformed type I collagen in the developing dentin matrix disrupts the normal regulation and organization of this process, causing issues such as hypomineralization, disorganized dentin tubule structure, and dentin hypertrophy. These abnormal structural properties result in the disease phenotype of DI, including discoloration, enamel attrition, and spontaneous dental fractures. This practicum aims to investigate the dental effects of OI by comparing mineralized dental tissue volumes of mice with a type I collagen mutation with wild-type mice with littermates at the juvenile and adult life stages. The animal model under study, the oim mouse (B6C3FE a/a-Col1a2OIM/J), produces abnormal type I collagen due to a mutation in the COL1A2 gene. Mice that are homozygous for this mutation demonstrate a severe OI phenotype, while heterozygotes demonstrate a mild OI phenotype. Prior studies demonstrate that adult oim mice have dental issues similar to those of humans with OI, including reduced dentin tubule density and dentin cross-sectional area. However, the effects of these mutations on dental tissues across the juvenile and young adult periods have not yet been characterized.