Discussion
dislocation
Bioceramic cement applied to the repaired area is often exposed to periodontal tissue that contains pH regulatory systems controlling regional pH [Microhardness is a crucial parameter for assessing the setting process and overall strength of a material [The current study assessed the microhardness values of multiple test materials under varying experimental conditions. The study revealed that the microhardness values of the test materials, in descending order, were Biodentine, WMTA, ERRM Putty, iRoot FS, and IRM. Consistent with previous studies [This study investigated changes in the microhardness and elastic modulus of HCSCs and CPSCs in various environments over time. The findings indicated that all the tested cements showed an increase in microhardness when stored in PBS over time. However, when exposed to an acidic environment, the microhardness values of these cements decreased over time, except for iRoot FS, which exhibited a less pronounced reduction in microhardness. Similar trends were observed for the elastic modulus of the cements. The setting process of iRoot FS appeared to be less affected by butyric acid compared to the other cements, possibly due to differences in their constituents and hydration processes. Although iRoot FS and ERRM Putty are both CPSCs, their hydration processes differ, as confirmed by isothermal calorimeter measurements [Furthermore, the present study showed that the microhardness values were significantly higher when the cements were exposed to PBS (pH 7.4) than when exposed to butyric acid (pH 5.4) at the same setting time. This finding is consistent with previous studies that have reported that acid can lower the microhardness of materials [The results of SEM analysis in this study suggested that the acidic environment had an adverse impact on the internal microstructure of both tested HCSCs and CPSCs. Samples stored in acid had more or larger pores than those stored in PBS, consistent with previous studies [The main components of HCSCs are tricalcium silicate and dicalcium silicate, while in CPSCs, phosphate salts are added based on hydraulic calcium silicates. The hydration behaviors of these substances are expected to vary theoretically, and interpreting the chemical phase transitions in the current testing scenario still poses a challenge. XRD analysis confirmed that calcium phosphate was only detected in CPSCs (iRoot FS and ERRM Putty) rather than HCSCs (WMTA and Biodentine), regardless of the cement setting conditions, even in the samples stored in PBS. This is possibly due to the trace amount of by-product calcium phosphate in hydrated HCSCs, which sets in PBS. Calcium silicate hydrates (CSH) and portlandite (crystalline CH) are the main hydration products of HCSCs [In hydrated cements, CSH is not identifiable by XRD due to its poor crystalline structure, while only hydration byproduct CH crystals can be identified [The present in vitro experiment was limited in its ability to fully replicate the clinical local acidic situation, as the realistic inflammatory environment does not maintain a constant level of acidity and the duration of each acidic scenario is uncertain. What’s more, the effect of blood on cements was not considered. Further studies could be performed in the same acidity-basicity experimental settings using extracted human teeth root end filling model to test the material dislocation resistance, sealing ability, bioactivity and so on, in order to provide more laboratory evidence for the selection of root canal repair materials in clinical inflammatory environments.