A new method for determining the vitality of tooth pulp based on photoplethysmography and diffuse transmission spectrophotometry is being developed. Using a narrow-band light source and detector system designed and constructed in our lab, the ability to determine the quantity of hemoglobin in teeth by measuring the ratio of light transmitted at two wavelengths (595nm and 575nm) has been demonstrated in vitro; however, the sensitivity and selectivity of this method are poor because variations in the volume of hemoglobin contained in the dental pulp of normal teeth are large. To obtain an absolute measure of tooth vitality, we are now developing an instrument capable of measuring the amplitude of the pulsatile variations of light transmitted through the tooth at several wavelengths from which the oxygen saturation (ratio of the concentration of oxyhemoglobin to that of total hemoglobin) can be calculated. Both a bench optical system comprised of a lamp, filter wheel and detector and a portable LED-based spectrophotometer have been designed and constructed to carry out basic studies of the optical properties of teeth and to investigate the clinical utility of different vitality assessment techniques. Reliable detection of plethysmographic pulses in vital incisors and molars has been demonstrated.
