High conversion self-curing sealer based on a novel injectable polyurethane system for root canal filling

• A new root canal sealer based on self-curing injectable polyurethane was provided.
• More than 90% NCO group reacted after 4h, and only about 5% remained after 24 h.
• By culturing with L929 murine fibroblasts, the PU sealer showed perfect cytocompatibility.
• Volumetric dilatancy after curing will make the sealer achieve a tight seal.

Low monomer–polymer conversion is the key factor leading to cytotoxicity for resin-containing restorative materials. This paper provides a new root canal filling system based on self-curing injectable polyurethane which can achieve high conversion in a short time. Traced FTIR spectra show more than 90% NCO group participated in the curing reaction after 4 h, and only about 5% remained after 24 h. The calculated data also testified the curing process supports a third-order reaction, and this efficient and sufficient reaction is postulated to weaken the toxic stimulation. By culturing with L929 murine fibroblasts, the PU sealer is shown to be favorable for cell attachment and proliferation. Then physicochemical properties of the injectable PU-based sealer were evaluated according to the Standard [ISO 6876:2001 (E)] for clinical application. A series of physicochemical properties of PU sealer have been tested comparing with AH Plus and Apexit Plus. And the results present that the self-curing PU sealer could not only match the clinic requirements, but even has better properties than the other two commercial sealers. We expect the high conversion PU sealer has a tremendous potential in the field of root canal filling after further biological evaluation.