Methods: After root canal treatment, 32 bovine mandibular incisor roots were shaped into uniform configuration simulating human mandibular premolar roots on a lathe. The root canals were enlarged to leave approximately 0.8mm thick of dentin walls.
The roots were divided into four types of restorations: cemented cast post and cores (Castwell M.C. 12% Gold, GC Corp., Tokyo, Japan [M]), built up with dual-cured resin composite (Clearfil DC Core Automix, Kuraray Medical Inc., Tokyo, Japan [CR]), built up with resin composite in combination with prefabricated glass fiber posts (FibreKor Post, Pentron Co, Wallingford, USA [FRC]), and reinforced with a thick layer of dual-cured composite before fabrication of small-diameter tapered cast post and cores [CRM].
All the specimens were embedded in acrylic resin up to 2mm below the cervical line and subjected to a static loading test with a crosshead speed of 10 mm/min at a 45 degrees angle to the long axis of the root until failure occurred. The failure modes were observed after the testing. The data were analyzed using one-way ANOVA and Dunnett's T3 test (a=0.05).
Results: CRM group (719.38±196.73 N) showed significantly high fracture resistance compared to the other groups (M: 429.56±82.43 N, CR: 349.56±66.21 N, FRC: 398.94±112.71 N) (P<0.05). There were no significant differences among M, CR, and FRC groups. In all specimens, fracture lines extending over 2mm below the cervical line were observed.
Conclusion: The CRM restoration showed the better structural properties for structurally compromised roots with no ferrules, though all methods in this study showed non-restorable fracture modes.