Microhardness and structural changes in calcium silicate-based sealers after short-term exposure to EDTA and organic...

Calcium silicate-based root canal sealers are widely used because of their bioactivity and favorable properties. However, their resistance to chemical challenge and the role of chelating and acidic solutions in retreatment remain unclear. This study evaluated the effects of short-term EDTA and organic acids exposure on the microhardness and structure of two sealers (CeraSeal and TotalFill BC Sealer) and explored the underlying mechanisms.

A total of 160 disc-shaped samples (80 per sealer) were prepared and incubated at 37 °C and 100% relative humidity. Vickers microhardness was measured weekly. X-ray diffraction (XRD) analyses were performed at weekly intervals using different samples, starting from the first measurable microhardness and continuing during material maturation. The final microhardness was defined as the plateau in value. After the final microhardness was reached, the samples were immersed for 5 min in 17% ethylenediaminetetraacetic acid, 10% citric acid, 10% formic acid, or distilled water to simulate retreatment conditions. Postexposure microhardness, phase changes, and surface morphology were evaluated via Vickers hardness testing, X-ray diffraction (XRD), and scanning electron microscopy (SEM), respectively. Statistical analyses included the Shapiro-Wilk test, t tests or nonparametric equivalents, one-way and Welch's ANOVA, and linear mixed model analysis (p < 0.05).

CeraSeal appeared to reach its final microhardness earlier than TotalFill BC Sealer did, whereas TotalFill BC Sealer tended to exhibit higher ultimate microhardness values. Exposure to the test solutions significantly reduced the microhardness of both sealers (p < 0.001), with the greatest reductions observed in the formic acid (58%) and citric acid (52%) groups. XRD and SEM analyses suggested dissolution of the calcium silicate hydrate and calcium carbonate phases, increased surface porosity, and a possible tetragonal-to-monoclinic zirconia transformation in TotalFill BC Sealer, whereas no clear evidence of zirconia phase transformation was observed in CeraSeal.

Within the limitations of this in vitro study, TotalFill BC Sealer presented higher final microhardness values; however, it was more susceptible to structural degradation following exposure to the test solutions, which was associated with a marked reduction in microhardness values. In contrast, CeraSeal, despite demonstrating a lower final microhardness, exhibited comparatively smaller percentage reductions after solution exposure, suggesting relatively greater resistance to solution-induced degradation.