Mechanistic insights into dentin bridge properties in a vital pulp therapy mimetic murine model

Vital pulp therapy (VPT) is an established approach for preserving pulp vitality following direct exposure. Its success depends on the formation of a dentin bridge that seals the exposure site. This study investigated the localised mechanical properties of dentin bridges formed using different VPT materials and applied a quantitative protocol for their assessment. Dentin bridges induced by calcium hydroxide, mineral trioxide aggregates (MTA), or a bioceramic material were examined in a murine model of direct pulp capping. Nanoindentation load-hold-displacement data were interpreted using a generalized Kelvin-Voigt framework to resolve instantaneous elastic and delayed viscous deformation. Morphology and composition were assessed using scanning electron microscopy with energy-dispersive X-ray spectrometry and Raman spectroscopy, enabling correlation of mechanical parameters with mineral content and collagen-related features. Nanoindentation revealed material-dependent differences in the mechanical response of dentin bridges. The bioceramic-induced bridge exhibited elastic stiffness and viscous damping values most closely approximating those of native dentin under wet conditions. Conversely, bridges formed by calcium hydroxide showed significantly lower values for elastic stiffness. Mineral density was highest in native dentin, whereas Ca/P ratios were higher in the MTA and bioceramic groups, indicating that the elastic modulus was associated with the mineral density and the Ca/P ratio. The quantitative protocol applied in this study revealed that different VPT materials influenced the structure and mechanical properties of the resulting dentin bridges.