Magister Scientiae Dentium - MSc(Dent) / The treatment objectives in the restoration of an endodontically treated tooth are maximum retention of post and core and to create a design in which the tooth is preserved when the restoration fails. The ferrule effect in root treated teeth requiring cast post and core has been studied extensively and has been shown to greatly improve fracture resistance (Gluskin et al 1995, Libman & Nicholls, 1995. Hemmings et al, 1991. Barkhordar et al, 1989. Rosen & Partida-Rivera, 1986). Studies have also shown that in the case of cast post and core, the longer the ferrule, the greater the fracture resistance (Libman and Nicholls, 1995). The use of the new bonding agents, composite resin cements and core materials, have led to a more conservative approach to post and core restorations. However few studies have considered the effect of different ferrule designs on prefabricated post and composite core systems (Volwiler et al 1989, Al Hazaimeh and Gutteridge 2001). There is little information as to whether the ferrule is of additional value in providing reinforcement in these restorations. This study investigated the effects of different ferrule designs on the fracture resistance of teeth incorporating prefabricated posts and composite cores. In addition teeth restored with a composite core but with no prefabricated post were included in the study to assess the necessity of a post in the restoration of endodonticallytreated teeth. Sixty extracted maxillary incisors (centrals and laterals) and carunes were randomly assigned into three groups and restored. Two groups had a prefabricated post and composite core with varying ferrule designs. A third group had a core with composite packed into the root canal but no post. All teeth were restored with cast crowns to simulate the clinical situation. A Zwick universal testing machine was used to apply compressive loads progressively on the restored teeth until failure occurred as a result of either root, tooth or post fracture. Failure loads, modes of fracture, post and core systems and tooth preparation were recorded and statistically analysed. The results showed no significant difference in the amount of force needed to break the teeth in the different groups irrespective of whether the teeth had a ferrule or not. They also showed no significant difference in the amount of force needed to break the teeth in the different groups irrespective of whether the teeth had a post or not.