Mild dental findings associated with severe osteogenesis imperfecta due to a point mutation in the alpha 2(I) collagen gene demonstrate different expression of the genetic defect in bone and teeth.

Serial intraoral photographs, radiographs, and ground sections from an extracted upper permanent canine served to characterize dental abnormalities in a 15-year-old girl suffering from severe (type III) osteogenesis imperfecta (OI) due to a point mutation that substituted glycine 688 of the alpha 2(I) chain of collagen I by serine. Dental records showed that all deciduous teeth exhibited clinical and radiographic characteristics of dentinogenesis imperfecta (DI), whereas permanent teeth including the removed canine appeared normal, although pulp chambers contained unusually large denticles. Despite the unconspicuous clinical appearance of the canine, histologic sections revealed small, canal-like, hypomineralized hard tissue patches that lacked a regular tubular structure and occupied a narrow band of the bulk of normal circumpulpal dentin at about the level of the cemento-enamel junction. The finding that a mutation in the gene for the alpha 2(I) collagen chain with serious consequences in bone has only minor effects in teeth would suggest that odontoblasts, unlike osteoblasts, can largely compensate for this particular genetic defect, possibly by excluding the abnormal alpha 2(I) chains and forming alpha 1(I) homotrimeric collagen I. The discrepant consequences in deciduous as opposed to permanent teeth and the specific localization of the dentinal abnormalities in permanent teeth lead us to speculate that the exclusion of defective alpha 2(I) chains could depend on the developmental stage and/or the rate of extracellular matrix formation.