Effects of sealer and root canal filling method on root canal sealing ability after high-frequency current conduction

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Hokkaido University
Objective: To assess the root canal sealing efficacy of two sealers and two root canal filling techniques following high-frequency current application. Methods: Simulated root canal models with a diameter of 0.1 mm were prepared from bovine teeth to replicate actual root canal anatomy. A demineralized layer was induced by administrating Plank-Rychlo solution to the simulated root canals for 5 minutes. These models were randomly assigned to 12 experimental groups. Each simulated root canal was irrigated with NaClO, and high-frequency electrical current was applied for 0, 3, or 5 seconds. The simulated root canals in each group were obturated using either Meta Seal Soft Paste (MSSP) or AH-Plus sealer, as well as either sealer alone or in conjunction with vertical condensation. Subsequently, the degree of dye penetration into the simulated root canals was meticulously quantified following immersion in a dye solution. The simulated root canal walls and the root canal wall-sealer interfaces were examined and observed using scanning electron microscopy equipped with an energy-dispersive X-ray spectrometer. Results: No statistically significant difference (P>0.05) was observed in dye leakage for MetaSeal Soft Paste sealer (MSSP) alone among any energization time, but significant leakage was observed when compared to the vertical condensation group. However, MSSP sealer alone resulted in significantly less dye leakage than AH-Plus sealer alone at 0 and 5 seconds of high-frequency energization (p<0.05). Examination of unfilled root canal walls revealed a porous, lava-like layer characterized by low carbon and high calcium and phosphorus content. In contrast, cross-sectional analysis of root canals filled with MSSP alone and subjected to 5 seconds of energization demonstrated a solid interface between dentin and MSSP, devoid of the porous layer. Furthermore, carbon, in addition to calcium and phosphorus, was detected at this interface, and resin tags were observed within dentinal tubules. These findings suggest that MSSP effectively established a monoblock structure encompassing the root canal filling material, the porous lava-like layer, and the dentin wall, resulting in a hermetic seal. Conversely, when root canals were filled with AH-Plus, only a few resin tags were observed in dentinal tubules, indicating a less robust interfacial seal. Conclusion: Irrespective of high-frequency energization, Meta Seal Soft Paste (MSSP) demonstrated significantly lower dye leakage compared to AH Plus when obturating inaccessible root canals. Subsequent to energization, MSSP infiltrated the porous lava-like layer of the root canal wall, exhibiting strong adhesion to dentin and superior sealing efficacy. Notably, vertical condensation compromised sealing performance for both sealers.
Root canal filling, Methacrylic acid ester adhesive sealer, High-frequency current, Porous layer, Inaccessible root canal area