Comparative Effect of Hydrochloric, Carbonic, and Acetic Acids on the Microhardness of MTA Putty and Root Dentin: An in Vitro Study

Background: This study evaluated the effects of 7.5% hydrochloric acid, 2% carbonic acid, and 2% acetic acid on the microhardness of mineral trioxide aggregate (MTA) putty and root dentin after 24 hours and 21 days of MTA maturation. Methods: Seventy-two extracted single-rooted permanent teeth were prepared as standardized 4-mm mid-root sections and filled with MTA putty. Specimens were allocated to four groups: 7.5% hydrochloric acid, 2% carbonic acid, 2% acetic acid, and normal saline (control). After 24 hours or 21 days of MTA maturation, specimens were exposed to the respective solutions for 10 minutes. Microhardness was assessed using a computerized Vickers microhardness tester. Data were analyzed using one-way analysis of variance (ANOVA) followed by Bonferroni post hoc testing. Results: Hydrochloric acid produced the greatest reduction in microhardness of both MTA putty and root dentin at both evaluation periods. Compared with saline, MTA microhardness decreased by 17.1%, 9.5%, and 4.3% at 24 hours and by 24.3%, 13.8%, and 8.7% at 21 days following exposure to hydrochloric, acetic, and carbonic acids, respectively. Corresponding reductions in root dentin microhardness were 9.4%, 3.6%, and 1.7% at 24 hours and 14.3%, 4.6%, and 2.6% at 21 days. Intergroup differences were statistically significant for both substrates at both time points (p < 0.001). Conclusion: Hydrochloric acid produced the greatest reduction in MTA putty microhardness but also caused the greatest reduction in root dentin microhardness. Carbonic and acetic acids produced comparatively smaller reductions in dentin microhardness. These findings support further investigation of acidic solvents as adjuncts for MTA retrieval, with consideration of their effects on dentin integrity.