Can epoxy resin-based endodontic sealers be softened within 1-2 min? An in vitro study with chloroform and xylene

Aim: During retreatment procedures, the bulk of root canal filling material can easily be removed within 2-3 min using rotary instruments. Nevertheless, a residue consisting of gutta-percha and sealer is often retained, attached to the canal walls. This residue has to be mechanically removed. The aim of the present study was to test the hypothesis that a short, 1-2-min exposure of set epoxy resin-based sealers to chloroform or xylene would soften them to an extent that may facilitate their mechanical removal. Materials and methods: Twenty samples were prepared from either AH 26 (Dentsply-DeTrey, Konstanz, Germany) or AH Plus (Dentsply-DeTrey, Konstanz, Germany) sealers and allowed to fully set. The surfaces of these samples were exposed for 1 or 2 min to either chloroform or xylene, and their surface hardness tested using the Vickers hardness test. The samples were also weighed before and after the exposure to the solvents, to measure their solubility. Analysis of variance with repeated measures was performed with Tukey's post hoc test for analysis of the results. Results: AH 26 and AH Plus did not differ from each other in their initial hardness. Chloroform softened both sealers within 2 min to 9% of their original hardness (P 0.0001). Xylene softened AH Plus to 19% of its original hardness (P 0.0001), whereas AH 26 was almost unaffected by this solvent, maintaining 89% of its original hardness (P > 0.05). Neither of the sealers lost weight during the 2 min exposure to the solvents. Conclusions: No solubility of the sealers was recorded during a 2 min exposure to either chloroform or xylene. Nevertheless, chloroform was found to be an effective and fast softener for both sealers. Xylene was an effective softener for AH Plus, but not for AH 26. Keywords: AH 26, AH Plus, chloroform, re-treatment, xylene