The purpose of this study was to compare the fracture resistance, mode
of fracture, and stress distribution of endodontically treated teeth
prepared with three different fiber post lengths and two different
abutment heights, using both experimental and finite element (FE)
approaches. Forty-eight human maxillary premolars with two roots were
selected and endodontically treated. The teeth were randomly distributed
into six equally sized groups (n = 8)
with different combinations of post lengths (7.5, 11, and 15 mm) and
abutment heights (3 and 5 mm). All the teeth restored with glass fiber
post (Rely X Fiber Post, 3M ESPE, USA) and a full zirconia crown. All
the specimens were thermocycled and then loaded to failure at an oblique
angle of 135°. Statistical analysis was performed for the effects of
post length and abutment height on failure loads using ANOVA and Tukey’s
honestly significant difference test. In addition, corresponding FE
models of a premolar restored with a glass fiber post were developed to
examine mechanical responses. The factor of post length (P < 0.01) had a significant effect on failure load. The abutment height (P > 0.05)
did not have a significant effect on failure load. The highest mean
fracture resistance was recorded for the 15 mm post length and 5 mm
abutment height test group, which was significantly more resistant to
fracture than the 7.5 mm post and 5 mm abutment height group (P < 0.05).
The FE analysis showed the peak compression and tension stress values
of 7.5 mm post length were higher than that of 11 and 15 mm post length.
The stress value of remaining tooth decreased as the post length was
increased. Within the limitations of this experimental and FE analysis
study, increasing the post length inside the root of endodontically
treated premolar teeth restored with glass-fiber posts increase the
fracture resistance to non-axial forces. Failure mode is more favorable
with reduced abutment heights.