From collagen denaturation caused by a COL1A2 variant to mineral disorganization and tubular occlusion in primary dentin with dentinogenesis imperfecta.

Dentinogenesis Imperfecta (DI) is a rare genetic disorder that disrupts the structure and mechanical integrity of dentin, often through alterations to the collagen matrix. In cases associated with Osteogenesis Imperfecta, DI arises from COL1A1 or COL1A2 variants (DI type I). The multiscale mechanisms linking alterations of the collagenic scaffold to dentin microstructural defects remain poorly understood. In this proof-of-concept study, we employed a multimodal 3D characterization framework combining biochemical assays and advanced imaging techniques to investigate the relationship between collagen integrity, mineral organization, and microstructural defects in four (n=4) primary teeth from a DI patient carrying a COL1A2 variant (c.982G>A (p.Gly328Ser)) and eight (n=8) primary teeth from healthy donors. A threefold increase in molecular-level collagen uncoiling (i.e., denaturation) was found in DI dentin compared to healthy dentin using trypsin-hydroxyproline assays. A reduction in the second harmonic generation signal combined with increased spatial variability were observed, indicating pronounced heterogeneities in the collagen scaffold. These heterogeneities were spatially associated with disorganization of the mineral phase, the emergence of hypermineralized regions, and a 30% higher mean mineral density, as measured by high-resolution micro-computed tomography. Severe disruption and partial occlusion of the tubular network were further identified using confocal microscopy, resulting in reduced porosity. These results support a multiscale association between collagen alterations, mineral heterogeneity, and pore network disruption, consistent with a model in which compromised collagen integrity alters the mineral organization and the tubular network of dentin. Although requiring confirmation on larger cohorts, these findings provide a preliminary mechanistic framework for understanding how disruptions of the hierarchical structure of DI dentin, impairing its toughness, may originate from molecular collagen denaturation. Statement of significance: Dentinogenesis Imperfecta (DI) is a rare genetic disorder that weakens teeth, leading to fractures and enamel loss. However, how molecular defects translate into fragile dental tissue remains poorly understood. In this proof-of-concept study, we show that a COL1A2 mutation induces collagen denaturation at the molecular scale, which is associated with major disruptions in dentin structure and mineralization at larger scales. Such structural changes are known to reduce tissue toughness. Our findings provide early but compelling evidence for a direct link between molecular-scale collagen defects and macroscopic fragility in dentin. This work introduces a multiscale framework contributing to the understanding of structure-property relationships in mineralized biological tissues.