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The effect of the elastic modulus of endodontic posts on static load failure.

AIM
To compare posts of different flexibility using static load testing. Hypotheses tested were (1) the flexural modulus of endodontic posts does not show a linear relationship with failure load and (2) the flexural modulus of endodontic posts does not show an association with failure mode.


METHODOLOGY
Thirty 2 mm diameter rods of a glass fibre material Aesthetiplus (A), a carbon fibre Composipost (C) and stainless steel (S) were cemented into 90 roots of extracted human teeth using resin cement. Composite resin cores were added and the roots embedded in self-curing acrylic resin. Samples were loaded at 90° in a universal testing machine until failure. Failure loads and fracture levels were compared using one-way anova and post-hoc Scheffé tests. Proportions of different failure modes were compared with Chi square tests (α = 0.05).


RESULTS
Mean failure loads - MPa (SD) were A - 278.69 (85.79), C - 258.86 (82.05), S - 347.37 (74.50). There was no significant difference in the mean failure load of roots containing the FRC posts (P = 0.639), but it was significantly greater for steel post samples (P < 0.01). The mean level of fracture among the groups was not significantly different (P = 0.879). No root fractures were 'favourable'. Significantly more root fractures and fewer core fractures occurred for group A than for groups C or S (P < 0.01).


CONCLUSION
The elastic modulus of an endodontic post does not appear to be a principal factor influencing load at failure or mode of failure of post-restored teeth.