Thermal behavior and viscoelastic properties of gutta-percha used for back-filling the root canal

Abstract

Background/purpose: In clinical operations, qualitative differences in the texture and operational feeling of the regular type and soft type back-filled gutta-percha are readily discernible. This study aimed to investigate and compare the thermal behavior and physical properties of the two gutta-percha materials.

Materials and methods: The chemical compositions of regular and soft type Gutta-Percha Obturator® pellets were examined via energy dispersive X-ray spectroscopy. The thermal behaviors of the pellets during heating and cooling were evaluated using a differential scanning calorimeter. Finally, the viscoelastic properties of the two materials during cooling were assessed using a modular compact rheometer.

Results: The soft type gutta-percha contained a greater atomic percentage of zinc than the regular type material. In addition, the soft type gutta-percha exhibited exothermic peaks during cooling, whereas the regular type gutta-percha did not. The two materials exhibited different viscoelastic behaviors under cooling. In particular, the rate of change of the loss factor for the soft type gutta-percha was more than that of the regular type gutta-percha at temperature lower than 80°C.

Conclusion: The soft type gutta-percha underwent significant crystallization during cooling, and therefore exhibited pronounced volume shrinkage. Furthermore, the soft type gutta-percha underwent a greater rate of change in viscoelasticity under cooling than the regular type gutta-percha, and exhibited poorer physical stability. Consequently, in the back-packing procedure, soft type gutta-percha must be compacted more often over time than regular type gutta-percha to ensure the same quality of root canal obturation.

Keywords: Differential scanning calorimetry; Gutta-percha; Root canal obturation; Viscoelastic substances.

Figure 1

Thermograms of regular-type and soft-type gutta-percha with slow cooling procedure.

Figure 2

Thermograms of regular-type and soft-type gutta-percha with rapid cooling procedure.

Figure 3

Viscoelastic parameters of regular-type and soft-type gutta-percha during slow cooling. (a) Storage modulus G’; (b) loss modulus G’‘; (c) loss factor tan δ; (d) complex viscosity η*.