ムコ多糖症I型におけるエナメル質および象牙質の機械的特性と鉱化作用のマルチスケール効果：COL1A2バリアントを有する一次象牙質のパイロットスタディ

Dentinogenesis Imperfecta (DI) is a rare genetic disorder characterized by dentin hypomineralisation. While DI is known to impair dentin's mechanical properties of the tissue and cause multiple tooth fractures, the microstructural origins of dentin fragility remain poorly understood. To address this gap,we conducted a pilot study comparing primary healthy dentin (n=4 - four incisors) and dentin affected by DI associated with a COL1A2 variant (DI type I, n=4 - two canines and two molars) using thermogravimetry and backscattered electron scanning microscopy to quantify mineralization at macroscale and microscale. We further assessed mechanical properties using nanoindentation to evaluate the effect of mineralization changes. Unlike prior studies, we found that our DI group exhibits 8% higher mineralization of the bulk of the tissue; however shows a 34% reduction in effective nanohardness. At the microscale, the DI group displays profound mineralization heterogeneities with hypermineralized zones exhibiting twice the nanohardness of hypomineralized zones. Our findings show that cracks predominantly propagate in these hypermineralized zones in DI samples, particularly beneath the dentin-enamel junction, where cracks can cause enamel detachment. These findings suggest that, for the DI group with the COL1A2 variant studied, mineralization heterogeneities, rather than bulk mineral content, is the key determinant of fragility. They provide preliminary results to investigate the mechanistic origins of crack propagation of this DI phenotype, that could be further supported by broadening the sample size and ensuring tooth-type consistency.