# Evaluation of pH and Optical Properties of Dual Ringe HEDP Irrigating Solution
## 4 Discussion
Previously, the low pH of citric acid was shown to yield more active chelating properties in this solution [37]. On the contrary, most EDTA solutions used in endodontics have pH values from neutral (pH = 7.5) to more alkaline (pH = 9.0) [38]. The 17% EDTA solution tested in our study showed alkalinity with a pH of 9.99, which is known to have a milder chelating effect compared to more neutral pH levels [38]. In our investigation, Dual Rinse HEDP revealed an alkaline pH, consistent with findings by other authors [20]. This alignment with the observed alkalinity of EDTA suggests a shared capacity for effective chelation [39]. However, the most important factor to note is the effect of combining HEDP and NaOCl on the pH of this mixture. In the continuous chelation concept, NaOCl should maintain its pH and available hypochlorite with an additional decalcifying effect during the approximate course of an endodontic treatment. When EDTA is mixed with NaOCl, it usually results in a rapid and dramatic decrease in free available chlorine, significantly reducing the ability of NaOCl to dissolve organic tissue [40]. Recently, more alkaline solutions of EDTA (tetrasodium salt EDTA) were introduced for continuous chelation with NaOCl. This combination resulted in the longer maintenance of both free available chlorine and desirable pH conditions [41]. It has been previously shown that HEDP in aqueous solution, when freshly mixed with NaOCl, impedes neither the antimicrobial properties of the NaOCl [15; 42] nor its ability to dissolve necrotic tissue [43]. This is reflected in our study, where mixing Dual Rinse HEDP with NaOCl did not produce a significant change in the pH value of this mixture. However, we did not explore the effects of mixing these solutions on chemical aspects such as available chlorine and stability. This limitation underscores the need for future research in these areas. Spectral analysis offers insights into how these solutions interact with light across different wavelengths, providing valuable information for applications such as laser-activated irrigation. LAI in endodontic involves the use of lasers with specific wavelengths that are well suited for interactions with water, a key component of irrigating solutions. The effect of LAI is based on cavitation, a physical phenomenon that induces the formation and implosion of vapor bubbles at the fiber tip, causing very rapid fluid movement in the canal [25; 26]. LAI has been shown to have a greater efficacy in the removal of canal debris and greater antibacterial effect than other activation techniques [44; 45; 46]. For LAI to be effective, the high absorption of laser energy into the irrigating liquid is necessary. In a root canal setting, it has to be taken into account that the radiation that is not absorbed by irrigants can potentially cause unwanted side effects such as damage to the canal wall or to the periradicular tissues. As [PERSON] et al. [31] proposed, LAI is safe to use if the absorption coefficient of the irrigants is not below 10 cm\({}^{-1}\). In the present study, we employed UV-Visible-NIR spectrophotometry to explore the transmission values of different irrigating solutions across a broad wavelength range, from ultraviolet (UV) to visible light (VL) and near-infrared (NIR), and to compare them to the well-established spectral properties of water. The transmission and absorption data for water align with previously published optical absorption data on DW available in the literature [47]. In our research, DW exhibited consistently low absorption coefficients in the UV range of the spectrum, which is consistent with previous reports [31]. On the contrary, endodontic irrigants presented high variations in absorption values. In the UVC region, all irrigating solutions presented high absorption values over 30 cm\({}^{-1}\). This can be attributed to electronic transitions occurring within the molecular structures of the irrigants.