Effects of Endodontic Irrigants on Elastic Modulus and Host-Derived Endogenous Enzymatic Activity of Radicular Dentin

Background/Objectives: This study evaluated the effects of endodontic irrigation protocols on the apparent elastic modulus and post-treatment total endogenous matrix metalloproteinase (MMP) activity of mineralized radicular dentin. Methods: Radicular dentin beams obtained from 60 extracted single-rooted teeth were allocated to six groups: distilled water, 2.5% sodium hypochlorite, 17% ethylenediaminetetraacetic acid (EDTA), 7% maleic acid (MA), 1% phytic acid (IP6), and 5% IP6. Apparent elastic modulus was determined before and after immersion using three-point bending, while total MMP activity was quantified using a generic colorimetric assay. Data were analyzed using two-way mixed ANOVA, Welch’s ANOVA with Tamhane’s T2 post hoc test, and Spearman’s correlation (α = 0.05). Results: A significant irrigation protocol × time interaction was observed for apparent elastic modulus (p < 0.001), with the greatest reductions following 7% MA and 5% IP6 treatment. Relative total MMP activity differed significantly among the irrigation protocols [Welch’s F(5, 23.05) = 36.285, p < 0.001] and was highest following 7% MA and 5% IP6 treatment. No statistically significant difference in relative total MMP activity was detected between the 1% IP6 and 17% EDTA protocols (p = 0.086). ΔEM% and relative total MMP activity were negatively correlated in the pooled analysis (rs = −0.679, p < 0.001); however, this association was no longer statistically significant after adjustment for irrigation protocol (partial rs = −0.146, p = 0.288). Conclusions: Protocol-dependent responses were observed. Low-concentration IP6 warrants further investigation as a potential EDTA alternative, although equivalence and clinical substitutability remain unestablished.