In vitro studies and modeling of a controlled-release device for root canal therapy

Endodontic disease is caused primarily by bacteria that interact with perir adicular host tissues. Therefore, treatment of endodontic disease aims at t he exclusion of bacteria from the root canal system. This work focused on i n vitro studies and modeling of a controlled-release device for delivering antimicrobial agents in root canals. A cylindrical, needle-shaped device wa s prepared consisting of a matrix core and a polymer coating, loaded with 3 0-45% chlorhexidine (CHX). The composition of the core, a blend of water-pe rmeable polymers, and the thickness of the coating were tailored to impart various release rates. A relatively steady release rate for over 40 days af ter an initial burst was achieved using a formulation for long-term release , which is desirable for establishing and maintaining the necessary therape utic levels. Mathematical models were developed for both in vitro and in vi vo drug release into a liquid of limited volume, taking into account a movi ng boundary of the dispersed drug and a time-dependent boundary condition. A concentration-dependent effective diffusion coefficient was used to count increased porosity as the solid drug had dissolved. The finite element met hod and computer programs were applied to solve the differential equations and predict the in vitro and in vivo release kinetics. The model prediction agreed well with the in vitro experimental data and provided guidance for designing the device for in vivo release in root canals. The result of in v itro antimicrobial tests, performed using a bovine tooth model, suggested t hat the device was effective in reducing growth of microbes. (C) 2000 Elsev ier Science B.V. Ail rights reserved.