[Effect of thermal conductivity on apical sealing ability of 4 dental gutta-percha cones]

To investigate the effect of thermal conductivity on the apical sealing ability of different dental gutta-percha cones during the warm vertical condensation obturation.

Four kinds of dental gutta-percha cones were used in this study: Bio-GP points (BP, B&L, Korea), large-tapered gutta-percha (DP, DENTSPLY, America), PROTAPER Universal gutta-percha points (DPP, DENTSPLY, America) and mtwo gutta-percha points (VP, VDW, Germany). Volume differences method was used to determine the main components and the thermal conductivity determinator was used to measure the thermal conductivity of these dental gutta-percha cones. Furthermore, 20 cones randomly selected from each kind of dental gutta-percha cones. And 10 cones of each dental gutta-percha cones, which were cut out the part of 4 mm in length from the apical end, were heated (200 °C) from the upper end without compression, and the temperature of the gutta perchacones surface was monitored in time by the infrared thermal imager during the whole heating process. In addition, the rest of the 10 cones of each dental gutta-percha cones were used to obturate the root canal in the transparent root canal resin model using warm vertical condensation technique. The cross-sectional surface was observed by stereomicroscope (× 40) at 1 mm and 3 mm from the working length and the gutta-percha obturation area proportion was measured and analyzed. The data were analyzed by one-way ANOVA.

The proportion of inorganic fillers (80.90%±1.14 %) (P<0.05) and the thermal conductivity (2.247±0.002) of DP was significantly higher than BP (79.28%±3.88%, 1.179±0.003), DPP (68.46%±5.09%, 0.604±0.001), VP (78.86%±1.87%, 1.150±0.001) (P<0.05). During the thermal obturation without compression at the setting temperature (200 °C), DP could achieve 65 °C beyond 1 mm from the heating point, and BP, DPP and VP only reached 65 °C within 1 mm. After warm vertical condensation obturation, all the groups showed increased gutta-percha obturation area proportion. At the position of WL-3, DP (96.89%±0.03%) showed significantly higher proportion of gutta-percha obturation area than BP (95.47%±0.06%), DPP (95.21%±0.03%) and VP (95.15%±0.03%) (P<0.05).

DP contains more inorganic fillers, possesses higher thermal conductivity, and leads a better apical sealing ability than BP,DPP and VP at the position of WL-3 during warm vertical condensation obturation.