Ključne riječi liječenje korijenskog kanala; rubno prijanjanje materijala za punjenje; tehnika kolčića i nadogradnje; vlaknima ojačani polimeri www.ascro.hr Prilagodba dvaju različitih sustava intrakanalnih kolčića Muttlib i sur. 330within the root canal, making the tooth more susceptible to fracture (10,11). This increases the stress within the root and increases the chances of failure. A poorly adapted post will create a marginal gap in which the presence of insufficient cementation can lead to microleakage (12). The prolonged leakage will cause the separation of the post from the root canal and eventually lead to common failures of the post-core systems. Oral fluids, bacterial toxins and all kinds of ions that penetrate through the interfacial space between the restoration and the tooth may lead to marginal discoloration (13), secondary caries and marginal fracture (14)(15)(16).A post's passive retention is improved when it adapts properly into the prepared post space and if the luting agent is thin and even (17,18). A thin layer of cement instead of the different amount of luting agents surrounding the customized post helps to limit stress concentration in the root canal. A study by Kremeier et al. (18) demonstrated that thicker layers of luting agent increase the risk of shrinkage strain, resulting in reduced bond strength by creating more stress during polymerization. Thicker cement found between the post and the canal could lead to displacement of the post (11,19). The cement-dentine interface is the site at which decementation generally occurs due to the bubbles and pores that form due to curing stress (20,21). Therefore, a well-adapted post that fits the root canal shape can reduce the risk of debonding which is subsequently leading to failure of the post (19).When a post does not adapt well, a gap or space will be created in the canal which will become a harboring place for bacterial infection. Despite having a good apical seal from the remaining gutta-percha, bacteria from the coronal portion can spread through it. It may take only a few days for bacteria to pass the apical 3-5mm of apical root canal filling (22). Little is known about the intra-canal adaptation of the fiber reinforced composite (FRC) post systems. Therefore, the aim of this study was to investigate the adaptation of cast post-and-core (CPC) and FRC post system inside the root canal. In addition, the CPC's adaptation quality will be compared with the FRC's adaptation quality. Materials and methodsThis was an experimental study based on in-vitro procedures. It was performed in the Craniofacial Laboratory of School of Dental Sciences, Health Campus, Universiti Sains Malaysia.PS software (Dupont and Plummer, 1997) was used to calculate the sample size with standard deviation (σ) which is assumed to be 7.4 (23) of the mean gamma count with 80% power and alpha 0.05. Fifteen samples were needed for this study. Having anticipated possible problems with 10% of samples during the procedure, total samples of 17 were prepared for this study.Sev...