New gutta percha composite with high thermal conductivity and low shear viscosity contributed by the bridging fillers containing ZnO and CNTs

Gutta percha (GP) point is typically used as the filling material during the root canal therapy, as its malleable, inert, and biocompatible properties. However, due to its low thermal conductivity (TC) and high shear viscosity, the vimineous GP point is difficult to melt and to flow into the root canal. In this study, a new GP composite with high TC and low shear viscosity is prepared by mixing a large amount of zinc oxide (ZnO) fillers bridged by a small quantity of carbon nanotubes (CNTs) (GP/ZnO@CNTs). Compared with the GP composite filled by ZnO alone (450phr), the TC of GP composite increases by 75.6% with 400phr ZnO and 50phr CNTs. Moreover, the TC and shear viscosity of GP composite containing 400phr ZnO and 20phr CNTs are 9.3% more and 4.5% less than those of a common commercial GP point (Bio-gutta percha (BP) point), respectively. The in vitro experiments confirm that the GP/ZnO@CNTs possesses the large filling depth of lateral canal, which is 9.0% longer than that of BP point at position WL-3. The cytotoxicity of the new GP composite extracts is grade 0–1, indicating that the material is qualified to prepare the GP point.