Dentin remineralization induced by experimental composites containing calcium orthophosphate particles

Objectives: This study aimed to verify if composites containing dicalcium phosphate dihydrate particles (DCPD) are able to induce dentin remineralization in vitro. Additionally, the mechanical properties of the materials were tested.

Methods: Four composites with 50 vol% inorganic content and 1 BisGMA: 1 TEGDMA (mols) were prepared, with different DCPD:glass ratios (50:0, 40:10, 30:20 and 0:50). Ca^{2 +} release in water was monitored for 8 weeks using inductively coupled plasma optical emission spectrometry (n = 3). Composites were applied to artificial lesions (180 μm in depth) prepared in dentin discs and the specimens were kept in simulated body fluid for 8 weeks (n = 8-10). Dentin elastic modulus (EM) and hardness (H) across the lesion were determined by nanoindentation (5 mN, 5 s). Mineral density was determined by microCT. Composite degree of conversion (DC) was determined by near-FTIR spectroscopy (n = 3). Fracture strength and elastic modulus were determined using biaxial flexural test (n = 10). Data were analysed by ANOVA/Tukey test, except for mineral density (Kruskal-Wallis, alpha:0.05).

Results: Ca²⁺ release increase linearly with DCPD fraction in the composite (p < 0.001). Lesions kept in contact with composites containing 40 % and 50 % DCPD presented significant increases in EM and H in the outer region (0-90 μm) and in EM in the inner region (90-180 μm) compared to the negative control. MicroCT was not able to differentiate among treatments. DCPD-containing composites presented DC higher than the control (p < 0.01). Flexural strength and modulus were inversely related to DCPD content (p < 0.001).

Significance: The composite containing 40 vol% DCPD presented the best compromise between mechanical properties and remineralization potential.