Objective: To evaluate the long-term mineralizing effects of an experimental ion-releasing, short fiber-reinforced flowable composite (SFC-active) applied to human teeth with molar-incisor hypomineralization (MIH).

Methods: A total of 16 first permanent molars, extracted due to MIH, received two occlusal restorations each. All cavities were acid-etched for 15 seconds before applying the restorative materials. One of the cavities in each tooth was restored with a commercial conventional particulate-filled composite (PFC; G-aenial Universal Injectable) after placement of the SFC-active liner. The other cavities were restored without the liner, using PFC alone (n = 8) or resin-modified glass ionomer cement (RMGIC; Fuji II LC) alone (n = 8). The teeth were stored in simulated body fluid at 37°C for 30 months. The mineralization effect was assessed at three regions (coronal, middle, and apical) under the restorations using micro-computed tomography (CT) (dentin density), micro-indentation (dentin hardness) and scanning electron microscopy/energy-dispersive spectroscopy (microstructure and calcium-to-phosphorus [Ca/P] ratio) analyses.

Results: Micro-CT analyses revealed no statistically significant differences (p > 0.05) in dentin mineral density between the restorative materials at any of the three regions beneath the restorations. At the coronal region of interface, dentin hardness was higher with SFC-active than with PFC, but lower than with RMGIC (p < 0.05). The Ca/P ratios of dentin varied beneath the different restorations, ranging from 1.49 to 1.60, with the highest ratios observed at the coronal region of the interface with SFC-active. Strontium and fluorine were detected in the dentin adjacent to the RMGIC restorations.

Conclusion: SFC-active demonstrated a positive mineralizing effect on dentin, reflected by higher hardness and Ca/P ratios at the coronal region of the interface. These findings indicate that SFC-active is a promising restorative material for the management of MIH-affected teeth.