Dental pulp testing is a key diagnostic aid in endodontics, the dental speciality concerned with the study and treatment of dental pulp. The most commonly used in clinical practice are pulp sensitivity tests, yet these tests have drawbacks and practical issues. A team of researchers based in Japan is working towards overcoming these limitations by developing a new dental pulp diagnostic method that makes use of transmitted-light plethysmography (TLP). The researchers are focusing their efforts on the paediatric dentistry arena in particular. Dr Satoko Kakino is based at Tokyo Medical and Dental University, Japan, where she performs research surrounding TLP, non-invasive pulpal blood flow, light emitting diodes (LED) and blood oxygen saturation. In her current work, 'Study on new dental pulp diagnosis method by analysis of pulp plethysmography', she and her team are investigating the mechanisms of pulpal blood flow measurement, with a focus on paediatric dentistry. They are collaborating with the Biomedical Optics Lab in the Graduate School of Biomedical Engineering at Tohoku University, and with engineers in J MORITA, MFG, Dental Corp. The researchers applied TLP, which is an optical technique to detect circulatory changes in pulp tissue, to damaged young teeth and found that TLP pulse amplitudes and pulp shape characteristics change gradually during clinical follow up of dental trauma, which led them to hypothesise that the change of the TLP may be influenced by the pathological condition and viability of the teeth. In their multi-wavelength optical plethysmograph work, the team simplified the tooth as the combination of tooth material and pulpal blood. 'As the dental pulp is very small tissue surrounded by the hard tissue, the detection of the blood volume change is much more difficult compared to the finger plethysmography with abundant blood supply,' Kakino says. 'So, we investigate the optical characteristics of pulpal blood and tooth material using multi-wavelength LED using the extracted tooth model to find the suitable wavelength for tooth TLP measurement.' The team's results suggest the LED wavelength could be selected based on the purpose. 'When we want to measure the blood volume changes, we can use the isosbestic wavelength of Oxy-Hb and Deoxy-Hb, which doesn't depend on the SO2 level,' Kakino explains. 'If we want to know the blood SO2 level, we can use the non-isosbestic wavelength, which depends on both SO2 level and Hb content.' The researchers have also determined that the most suitable wavelength for anterior teeth was 525 nm green LED.