Comparative assessment of hardening of demineralized dentin under lining materials using an ultramicroindentation system.

The aim of the current in vitro study was to evaluate the influence of three lining materials with a reported mineralizing capacity on hardness and elasticity of demineralized dentin. Four standardized microcavities were prepared in exposed dentin surfaces of 16 extracted human molars each. Dentin was demineralized in 0.5M EDTA for 2 h. One microcavity was left empty. The others were filled with a resin-modified glass ionomer cement (RMGIC), a bioactive glass S53P4 suspension, and a prototype Ca-PO(4) cement. Teeth were then immersed in deionized water or simulated oral fluid. After 3 weeks, hardness and composite elastic modulus of the dentin subjacent to the microcavities were assessed under wet conditions using the ultramicroindentation system (UMIS). After immersion in deionized water, there was no significant improvement of the mechanical properties of dentin irrespective of the material applied beforehand, indicating a lack of direct material effects. Exposure to simulated oral fluid resulted in significantly (p < 0.05) higher hardness and composite elastic modulus values of the dentin subjacent to empty microcavities and counterparts lined with bioactive glass compared to corresponding dentin under the RMGIC. UMIS profiles showed little variance.