Effect of different core to fiber post length ratios and luting cement types on failure resistance of endodontically treated teeth

The objective of this study was to evaluate the effect of different core to fiber post length ratios on failure resistance of endodontically treated teeth. Forty-eight mandibular first premolar were randomly divided into six groups (n=8 for each group) which were restored with three different core length to fiber post length (2:3, 1:1 and 3:2) and two different post luting cement; Panavia F 2.0 (Kuraray) and RelyX Unicem (3M ESPE). All teeth were removed the crown and endodontically treated with step-back technique. The group 1, 2 and 3 were restored with different three core to fiber post length ratios; 2:3 (6mm:9mm), 1:1 (7.5mm:7.5mm) and 3:2 (9mm:6mm) respectively. The specimens were cemented fiber post (DT light post No.1, Bisco) with Panavia F 2.0. The cores were built up with resin composite (Tetric ceram, Ivoclar) and full metal crowns (Ni-Cr) were fabricated and cemented on all specimens with Panavia 2.0. For group 4, 5 and 6, specimens were prepared the same as the group 1, 2 and 3 respectively but using RelyX Unicem for luting fiber posts. All teeth were embedded in acrylic resin blocks with periodontal ligament simulation. Failure resistances were determined using universal testing machine at 45 degrees angle to tooth long axis with cross head speed 1.0 mm/min until failure occurred. The result found that the failure resistance of group 1, 2, 3, 4, 5 and 6 were 454.3 ±22.4 N, 423.1 ±27.9 N, 295.7 ±24.8 N, 556.2 ±16.9 N, 541.1 ±20.2 N and 413.0±13.4 N, respectively. The data were analyzed with one way ANOVA showed that in groups using Panavia F 2.0, group 1 and group 2 were significantly higher than group 3 (p<0.05). In groups using RelyX Unicem, group 4 and group 5 were significantly higher than group 6 (p<0.05). The t-test showed that the groups using RelyX Unicem were significantly higher failure resistance than the groups using Panavia F 2.0 in each ratio (p<0.05). Within the limitations of this study, teeth restored with core:post ratio at 2:3 and 1:1 indicated significantly higher failure resistance than restored with ratio 3:2. RelyX Unicem used for luting fiber post exhibited significantly higher failure resistance than Panavia F 2.0 in each ratio.