Up to the present the electrochemical method for the determination of mass transfer coefficients between a liquid and a solid has been applied to many geometrical configurations, either with a view to designing electrochemical reactors or in order to solve heat transfer problems through the analogy between mass and heat transfer or for the study of local velocity gradients at walls [1, 2]. An application of this method was made in small size cells simulating the root canal and the associated secondary canals of a tooth (Fig. la). These secondary canals appear as ramifications of the main canal, and doubt exists concerning their irrigation, and thus their disinfection, by the disinfecting solution introduced by the dentist in the main canal during treatment. At the present time, the vibration of a file introduced in the main canal is used, together with a flowthrough irrigation of this canal, to debride, clean and disinfect the root canal system. Depending on the type of the commercial equipment used, the vibrations of the file (which is mounted at the extremity of a suitable insert in which the vibrations are produced) are sonic or ultrasonic, while the irrigating solution flows, under pressure, into the root main canal along the file (see Fig. 1 b and 2). The use of ultrasonic vibrations is discussed in [3]. The idea of the research described here was to simulate the root canals as in Fig. lb: the main canal is a straight cylindrical hole the ramifications of which are the secondary canals and the apical canal or apex. The secondary canals may be inclined or not as shown in Fig. lb. The electrochemical method was applied in order to ascertain the value of the mass transfer coefficient between the liquid introduced into the main canal and electrodes located within the secondary canals; the values of the mass transfer coefficient,/~a, are representative of the intensity of the convection within the secondary canals. In initial exploratory experiments made in our laboratory [4], the lateral canals were simulated by short nickel capillaries (500#m inner diameter) but the resulting analog cell model was then considered too complex for further work.