Introduction: Calcium hydroxide is widely used as an intracanal medicament in endodontics. Its therapeutic effects depend on the dissociation of calcium hydroxide into calcium and hydroxyl ions, which, in turn, depends on the vehicle used. The purpose of this in vitro study was to evaluate the sustained release of calcium ions and the pH change of calcium hydroxide over a period of 30 days when formulated with propylene glycol, polyethylene glycol 6000, chitosan, and guar gum. Methods: Various formulations were prepared and placed inside the root canals of human teeth and were suspended in glass vials containing distilled water. At specific time intervals, the calcium ion concentration was analyzed using an ultraviolet spectrophotometer. pH changes of the medium were measured at various time intervals up to 30 days. Results: Results revealed that chitosan formulation showed the maximum sustained release of calcium ions compared with the other three formulations. All the formulations exhibited high alkaline pH upto 30 days. Conclusion: From the results of this in vitro study, it can be concluded that chitosan can be used as a promising vehicle for for the sustained release of calcium ions from the calcium hydroxide in the root canal system. © 2010 American Association of Endodontists.