Initial hydration process of calcium silicate-based materials by thermography and ATR-FTIR spectroscopy

To evaluate whether differences in the formulations of calcium silicate-based materials affect the physicochemical properties during the initial stages of hydration process.

Four experimental groups were prepared: (i) Biodentine (BD); (ii) MTA Flow (FW); (iii) MTA Repair HP (HP); and (iv) PD MTA White (PD) (n = 6 samples/group). The chemical composition and molecular interactions were evaluated using an Attenuated Total Reflectance-Fourier Transform Infrared Spectroscopy (ATR-FTIR) with a spectral resolution of 4 cm^-1 obtained in the range of 4000-400 cm^-1. Thermal profiles were assessed by monitoring temperature variation (ΔT) with a thermographic camera, and alkalinization was evaluated by pH measurements of the incubation media. All analyses were conducted over a 48-hour period.

Distinct hydration-related chemical and thermal profiles were observed among the materials. FW exhibited S-O stretching vibrations due to gypsum content, HP and PD showed Al-O bands indicative of tricalcium aluminate, and BD was characterized by carbonate-related features. ATR-FTIR revealed progressive formation of hydration products, including calcium hydroxide (Ca(OH)₂), with differences in intensity. BD exhibited higher Ca(OH)₂ band intensity and alkalinization, whereas HP showed delayed chemical stabilization. Additionally, thermography detected early surface thermal events followed by low-activity regimes consistent with classical hydration stages.

The combined use of thermography, ATR-FTIR, and pH monitoring enabled detailed evaluation of early hydration events, enhancing the understanding of how compositional differences influence the setting behavior and functional properties of calcium silicate-based cements.