Effects of different acidic/chelating solutions on root canal dentin microhardness and mineralization: An in-vitro study

The aim of this in vitro study was to comparatively evaluate the effects of conventional acid/chelating solutions such as 17% ethylenediamine tetraacetic acid (EDTA) and 10% citric acid (SA) as well as 1% phytic acid (FA), 5% boric acid (BA), 0.02% hypochlorous acid (HOCl), 2% peracetic acid (PAA), 25% tannic acid (TA) and 9% etidronic acid (HEBP) solutions on root canal dentin microhardness and mineralization values. For the microhardness test, 45 extracted maxillary incisors were decoronated and sectioned vertically in the buccolingual direction, yielding a total of 90 dentin specimens. These were embedded in acrylic blocks, leaving the dentin surfaces exposed. The Vickers microhardness tester was applied at 100 µm from the pulp-dentin junction, with three measurements per sample averaged. For mineral analysis, 90 extracted mandibular premolars were used. After shaping of the root canals using NaOCl, each test solution was applied into root canals for 5 minutes (1 ml/min). Dentin powder obtained from canals was analyzed using ICP-OES. In the statistical analyses of both microhardness and mineral test data, the distribution of the data was assessed using the Kolmogorov-Smirnov and Shapiro-Wilk tests. One-way ANOVA and Tukey's HSD test were used for normally distributed data, while Kruskal-Wallis test and pairwise comparisons with Bonferroni correction were used for non-normally distributed data (p<0.05). According to the results obtained from the Vickers test, the greatest decrease in microhardness was observed in the FA, PAA, and EDTA groups compared to the control group (p<0.05); no statistically significant difference was found among the three groups (p>0.05). A decrease in microhardness was also observed in the BA, SA, and HOCl groups compared to the control group (p<0.05), and the difference between the groups was also found to be statistically significant (p<0.05). The least decrease in microhardness was observed in the HEBP group (p<0.05); TA was the only solution that showed an increase in microhardness, although not statistically significant (p>0.05). According to the results obtained in the ICP-OES test, there was no statistically significant difference in terms of dentin Ca⁺², Ca/P, Mg⁺² and S⁻² levels between the groups applied with different solutions (p>0.05), but there were significant differences in the levels of other elements (p<0.05). The group with the greatest increase in B⁺³ level was found to be BA (p<0.05). While Cu⁺² level increased in EDTA, FA and PAA groups, it was observed to decrease in HOCl (p<0.05). While Fe⁺² level increased in EDTA and FA, it decreased in HOCl (p<0.05). While all solutions decreased K⁺ level, the greatest decrease was seen in PAA group, and the least in TA group (p<0.05). The increase in Na⁺ was highest in EDTA and lowest in PAA (p<0.05). While EDTA solution caused the greatest decrease in Zn⁺² level, TA was found to be the solution causing the greatest increase (p<0.05). A significant decrease was observed only in the PAA group at the P⁻³ level (p<0.05). Under the current study conditions, HEBP which was observed to have less impact on dentin structure and TA showed the least adverse effects on dentin microhardness, suggesting their potential as alternatives to EDTA and CA. Considering the mineralization assessment results, all irrigation solutions used did not cause changes in the basic structural mineral levels of dentin, such as Ca⁺², Ca/P, Mg⁺², and S, while they did cause changes in other elements at different levels. Consequently, considering these differences in dentin mineral levels, particularly when determining the optimal duration and concentration of solutions for clinical use, will contribute to a better understanding of their contributions and/or limitations to short- and long-term clinical success. Keywords: Root canal dentine, irrigation, chelation, mineralization, microhardness, ICP-OES, Vickers