Diamond film thermistors for dental vitality assessment

In this study, we have demonstrated, for the first time, the use of diamond film thermistors for dental vitality assessment. Thermally sensitive boron-doped diamond films were grown by hot-filament CVD on Si₃N₄ ceramic substrates, and their thermal sensitivity (β) in the 30–50 °C range was optimized using the Taguchi methodology. This analysis facilitated a comprehensive investigation into the effects of argon flow, gas pressure, CH₄/H₂ ratio, and the distance between the sample and heated filaments on the films' microstructure, growth-rate (GR), crystalline quality, and β. Additionally, we introduced an empirical parameter (Y), defined as the ratio of β to electrical resistance.

Using optimized CVD parameters, we fabricated a fully functional diamond thermistor with a thermal sensitivity of 1435 K, which was then used in dental vitality assessment tests. These tests were conducted on a specialized stand featuring two closed water circuits, allowing the tooth to be cooled to temperatures as low as 10 °C and heated up to 40 °C. The heating response times of our diamond thermistor (DT) and a standard, metal-oxide-based commercial thermistor (CT) were comparable, but the diamond sensor exhibited a broader temperature detection range. Specifically, the DT was able to detect tooth temperatures within the range of 18 °C to 35 °C, whereas the CT was limited to a narrower range of 22 °C to 32 °C. Additionally, the cooling response time for the DT was significantly shorter (190 s) compared to the 260 s required for the CT. These findings highlight the potential of planar diamond thermistors for applications in endodontic medicine, enabling more accurate assessments of dental vitality.