Structural Porosity and Low Mineral Density in Enamel Rods Drive Molar Incisor Hypomineralisation

Abstract Enamel – the hardest material in the human body – protects against wear during mastication and resists chemical degradation. In the condition termed molar incisor hypomineralisation (MIH), impaired enamel quality leads to rapid tooth decay, hypersensitivity, and frequent need for early tooth extraction. MIH is highly prevalent in children, affecting ≈14.2% of the global population, yet the mechanisms underlying the accelerated decay and structural breakdown of the enamel crown remain unclear. In this study, comprehensive multiscale material characterization is applied to focal MIH‐affected regions and adjacent non‐MIH enamel. MIH lesions display reduced mineral content, increased organic content, and micron‐scale widening of prism sheaths accompanied by elevated carbon levels. Interrod regions exhibit altered mineral organization compared with enamel rods, resulting in distinct local material properties. These spatially heterogeneous changes appear to facilitate acid penetration and diminish several extrinsic toughening mechanisms that normally enhance enamel resilience. The findings highlight that MIH involves coordinated compositional and microstructural alterations across multiple length scales, underscoring the need for scale‐dependent assessment to guide the development of effective preventive and therapeutic strategies.