Diamond film thermistors for dental vitality assessment

Abstract

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.