Variables affecting ion release from resin-based materials containing calcium orthophosphate particles

To investigate the influence of experimental variables on Ca²⁺ release from experimental resin-based materials containing dicalcium phosphate dihydrate (DCPD) particles.

Experimental materials were prepared, both with BisGMA and TEGDMA and either 25 % or 50 % DCPD (by volume). Ca²⁺ release in deionized water (DW) was quantified using induced coupled plasma-optical emission spectrometry (ICP-OES, n = 3) according to the variables (1) frequency of DW renewal (weekly, biweekly, monthly or no renewal in 8 weeks), (2) volume of DW (5 mL, 10 mL or 50 mL) and (3) specimen dimensions (in mm, 9×2, 10x1, 5×4 or 5×1). Release kinetics was described using the semi-empirical Peppas-Sahlin model. Data were analyzed by two-way ANOVA/Tukey test (alpha: 5 %).

Weekly and/or biweekly DW renewal increased Ca²⁺ release compared to monthly and no renewal (p < 0.001). Ca²⁺ release was higher in 50 mL compared to 10 mL (50 % DCPD) and 5 mL (25 % DCPD) (p < 0.001). The specimen with the highest area-to-volume ratio (5×1 mm) presented the highest release expressed in μg/cm² or as fractional (i.e., % of the total Ca in the specimen, p < 0.001). At early stages and high DW volumes, diffusion was the main release mechanism, particularly for the 25 % DCPD material. Polymer relaxation becomes more important than diffusion over time, most noticeably for the 50 % DCPD material.

Researchers and clinicians must be aware of the fact that ion release is influenced by a large number of experimental variables, including (but not limited to) immersion medium renewal frequency, volume of immersion medium and specimen dimensions.