Objective To investigate the influence of the restoration methods with different post-and-core systems and root rehabilitation on the fracture resistance property of mandibular premolars with flared root canals. Methods Thirty-six human mandibular premolars were divided randomly into four groups（n=9）. Three experimental groups with flared root canals were restored with prefabricated glass fiber posts and composite resin cores（group A）, prefabricated titanium metal posts and composite resin cores（group B） and cast post-and-cores in combination with root rehabilitation using composite resin（group C）, respectively. The control group with normal root canals was restored with cast post-and-cores（group D）. The four groups were restored with metal crowns. A compressive load was applied at a 30° angle to the long axis of the tooth until fracture, at a crosshead speed of 1 mm·min-1. The fracture was categorized into repairable mode and unrepairable mode. The data was statistically analyzed with ANOVA and Fisher′s exact test. Results The mean failure of the four groups were listed as the followings: Group A（1.39±0.56）kN, group B （1.17±0.40）kN, group C （1.21±0.30）kN, group D （1.31±0.56）kN. There were no significant differences among the groups（P>0.05）. The number of unrepairable fracture in group A, B, C, D were 6, 8, 9, 9, respectively. No significant differences were found among the groups（P >0.05）. Conclusion Different post -and -core systems have no influences on the fracture resistance property of mandibular premolars with flared root canals. Composite resin rehabilitation is an effective method to restore flared canal roots.
