Measurement of the thermal diffusivity of dental filling materials using modified Ångström's method

Summary 

Objectives

A new measuring technique for the determination of thermal diffusivity is proposed. Using this technique, the thermal properties of a few different dental filling materials were measured.

Methods

The proposed method for measurement of thermal diffusivity is based on the classical Ångström's method. The method exploits the propagation of a plane thermal wave generated by a Peltier's device in a cylindrical sample along its axis. The thermal diffusivity of the sample is calculated from the phase difference between harmonic components of temperatures measured at sample surfaces, perpendicular to the direction of thermal wave propagation. The estimated accuracy of measurement is typically about 10% for samples with low thermal diffusivity. The proposed method was used for the determination of thermal diffusivities of Achatit Bichromatic, Charisma and Dentimet dental filling materials.

Results

The measured thermal diffusivities were: 0.295(0.020)×10⁻⁶m²s⁻¹ for Achatit Bichromatic, 0.321(0.015)×10⁻⁶m²s⁻¹ for Charisma and 1.70(0.12)×10⁻⁶m²s⁻¹ for Dentimet. The thermal conductivities of these materials were also estimated. The results were compared with values obtained from independent constant flux measurements with marble as a reference material.

Significance

There are no standard techniques for the determination of the thermal properties of dental filling materials. Moreover, it is difficult to find the thermal diffusivity and the thermal conductivity of many of them. The method proposed in this paper allows the simple and accurate measurement of thermal diffusivity. Thermal parameters of dental filling materials should be compatible with the parameters of human teeth. Lack of thermal compatibility can cause not only patient discomfort but also mechanical stresses leading to microcracks.

Keywords: Dental filling materials, Thermal properties, Thermal diffusivity, Thermal conductivity, Measuring techniques, Dynamic thermal measurements, Thermal waves