## 4 Discussion
Harvard MTA also contains bismuth oxide. It has, nevertheless, demonstrated a low porosity percentage. It was suggested that **merwinite** (calcium magnesium orthosilicate) may be responsible for its advantageous characteristics due to its excellent biological and physicochemical properties [9]. Magnesium-containing silicate ceramics and nanocomposites that have been researched for biomedical applications have recently gained serious scientific interest due to their proven bioactivity and ability to form an apatite-like layer. One of the fundamental minerals utilized for producing those types of biomaterials is merwinite [9; 36; 37]. It generally demonstrated low to partial solubility in a variety of test conditions [38; 39]. The ceramics containing this mineral have exhibited high reactivity in SBFs. Their dissolving behavior in these media is quite intriguing, as they simulate clinical conditions [36; 37]. [PERSON] et al. evaluated the apatite layer produced on the surface of such ceramics using the Energy Dispersive Spectroscopy (EDS) technique. They discovered in it the presence of a large amount of Ca (15.05 at%) and P (7.43 at%), while the quantities of Si (2.92 at%) and Mg (0.91 at%) were substantially lower. In parallel, Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES) was used to assess the content of SBF solutions, following the in vitro test. The results showed that Ca\({}^{2+}\) ions were predominantly present and that their concentration increased gradually until day fourteen of the experiment. Their quantity significantly exceeded the Ca and Mg values, indicating a low partial solubility of these ions [37]. Of particular interest is the Mg and Si ion release profile on SBF, found in the aforementioned investigation. The concentrations of Mg\({}^{2+}\) and Si\({}^{4+}\) increased slightly after 7 days of soaking in SBF, but after 14 days, their amounts were reduced, as the ceramics nearly completely eliminated the Mg\({}^{2+}\) ions from the solution. The authors suggested that the ceramic material released Ca and Si ions and removed P ions from SBF [37]. It was speculated that the lower solubility of merwinite may be a result of the significantly lower dissolution of magnesium ions compared to calcium ions, especially at an alkaline pH [9; 36]. However, there are probably more complex causes behind this. Merrwinite is composed of Mg\({}^{2+}\), Ca\({}^{2+}\), and SiO\({}_{4}^{4+}\) ions; its crystal structure is [MgO\({}_{6}\)] octahedral, linked at every corner by [SiO\({}_{4}\)] tetrahedra [40]. Overall, it exhibits greater stability than the mineral-crystal structure of certain other minerals, such as such as dacicium silicate and hedigite [38], and probably hurturite (which consists of Ca\({}^{2+}\) ions and SiO\({}_{5}\) polyhedra). According to [PERSON] et al., ProRoot MTA showed higher solubility compared to Harvard MTA [9]. Considering hurtite is the main ingredient in the ProRoot MTA composition, one can assume that its presence is the cause of this. However, there is sufficient scientific evidence to support the low solubility of this first MTA brand, which falls within the limits of the relevant ISO standard [41; 42]. Low porosity and solubility for rearative endodontic cements are desirable to ensure a long-lasting seal and avoid microleakage [29]. These two properties of CSCs may be associated since a higher amount of porosity may occur after immersion in tissue fluids or in various experimental media as a function of the material solubility [35]. This can be a possible explanation for the low porosity of Harvard MTA found by us. The inconsistency in the results obtained from our investigation and those of other researchers should also be attributed to the different testing conditions and methodologies applied. Generally, this disparity may be due to the lack of standard assessment methods. In a research series, [PERSON] et al.