Fluid-tight obturation of the root canal space is an important requirement forsuccessful root canal treatment. Gutta percha, used as a core material in combinationwith different sealers, is the most commonly used root filling material and is consideredthe gold standard. However, it does not possess all the properties of the ideal obturationmaterial. Mineral trioxide aggregate (MTA) is a cement material based on calciumsilicates (CSC). It sets by hydration, provides excellent sealing ability, is biocompatible/bioactive and has performed successfully in different clinical applications. The use ofMTA as an orthograde obturation material has been proposed. However, MTA is difficultto handle and very little is known about the most appropriate technique to ensure goodcompaction within the shaped root canal.This research aims to investigate the performance of MTA when used as an orthogradeobturation material. The effect of different times of ultrasonic activation of unsetmaterial on the incidence of voids in root canals was investigated. Manual compactionof MTA using hand pluggers without ultrasonic activation resulted in minimal voidformation. Ultrasonic activation resulted in significantly higher incidence of voids.The removal of the smear layer prior to obturation with MTA resulted in asignificantly reduced push-out bond strength between the MTA and radicular dentine.The apical sealing ability of MTA orthograde filling was assessed in comparison withgutta percha and sealer using a dye leakage model. It was concluded that MTAprovides a better apical seal against dye penetration over a 30-day observation period.The ability of MTA to reinforce the remaining root structure in comparison with guttapercha and sealer was investigated. MTA significantly increased the resistance tovertical root fracture after one month of storage in synthetic tissue fluid.The radiopacity of MTA together with new calcium silicate cements was assessed andit was concluded that MTA was more radiopaque than gutta percha but lessradiopaque than AH-plus sealer.The use of MTA as an orthograde obturation material has shown some potential ofenhanced clinical performance in comparison with gutta percha and sealer in terms ofsealing ability and bioactivity. However, there are certain disadvantages for obturationwith this category of materials in its present form. It is important to point out thatMTA is still in its early stages of development. With further improvements to itsphysical properties, MTA can present a valuable option for obturation of the root canalspace.