Evaluation of tooth-specific optical properties for the development of a non-invasive pulp diagnostic system using Transmitted-light plethysmography: An in vitro study.

OBJECTIVES: Transmitted-light plethysmography (TLP) is an objective and non-invasive pulp diagnosis method that has already been validated for applications for incisors. However, there is a demand for TLP use in the molars, it has not yet been established for this application. This study investigated the optimal light source wavelengths for TLP in premolars, to establish a pulp diagnosis system based on measuring pulpal blood flow. DESIGN: One extracted incisor and one extracted premolar, which were fully developed and healthy, were prepared. The optical properties of model teeth filled with 0-30 % hematocrit contents in the pulp chamber were analyzed at 525, 590, and 625 nm wavelengths. The incident and transmitted light intensity of model teeth were measured to determine the optical density (O.D.) using a prototype plethysmograph (J.Morita) and a spectrometer. The significant differences in O.D. at each wavelength were analyzed using the Kruskal-Wallis test followed by the Steel-Dwass test as a post-hoc test. Light propagation through the teeth was also observed under a microscope. RESULTS: A statistically significant differences in O.D. were observed among the three wavelengths at all hematocrit concentrations (p < 0.05). The observation of light absorption and scattering in the whole teeth supported the optical measurement results. CONCLUSION: The results indicated that the most appropriate wavelengths are 525 nm for incisors and 590 nm for premolars, as it balanced the light transmission through the tooth structure and the sensitivity for detecting changes in blood concentration. Further research is expected to expand the range of applications of TLP in premolars.