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Endodontic gutta-percha undergoes deformation at temperatures above 65°C. The temperature influence of heat carriers on gutta-percha cones was investigated in vitro.Six single-rooted extracted teeth were embedded in resin and fixed. The root canals were prepared (ProFile; Dentsply Maillefer, Ballaiques, Switzerland) to different tapers and bisected. Thermographic images when heating the gutta-percha cones (Roeko, Langenau, Germany) with a heat carrier (ML .12; SybronEndo, Orange, CA) at 1 and 5 mm from the working length were made with an infrared thermal imaging camera (ThermaCam P640; Flir Systems, Täby, Sweden). The device temperature was preset at 200°C. The pixel temperature registered at the contact lines between the heat carriers and gutta-percha cones in the thermographic images was recorded and statistically described.A mean temperature (°C) instability in the heat carrier (324.96 ± 46.10, minimum = 147.35, maximum = 474.13), a temperature drop of the gutta-percha cones (159.52, ±37.57, min 67.64, max 259.04) at the measuring level, and a mean temperature penetration depth (mm) equal or to higher than 65°C (1.05 ± 0.28, minimum = 0.20, maximum = 1.30) were recorded. No correlation between the penetration depth into the gutta-percha cones and applied temperatures, regardless of the size and/or taper, could be established.Temperature discrepancies between the device preset and achieved ones of the heat carriers was observed. Gutta-percha is a poor thermal conductor, transports heat irregularly, and should be heated 1–2 mm from the target area.