Yield strength of fiber-reinforced composite posts with coronal retention

Currently, glass fiber-reinforced composite (FRC) posts with shank heads are only recommended for moderate coronal defects. Restoring endodontically treated teeth with large coronal defects remains a challenge, requiring posts with coronal retention and high bending resistance.

The purpose of this in vitro study was to investigate the yield strengths of FRC posts and titanium posts (TI) with coronal retention for core foundations compared to FRC and TI posts without coronal retention.

Tapered posts (ER root post system) of 4 diameters (ISO 50, 70, 90, 110), 2 lengths (tapered part: 9 and 12 mm) of identical shape, 2 materials (FRC, titanium), and 2 head designs (shank without retention (SH) and post head with horizontal retention (RET)) were evaluated (n=9). Titanium posts (TI-SH, TI-RET) served as the control. The 0.2% yield strengths (R(0.2)) of all specimens were tested in a universal testing machine. Three-way and 1-way ANOVAs with Bonferroni-Dunn's multiple comparison tests were performed (alpha=.05).

The yield strengths of the control groups TI-RET were significantly higher for ISO 110 with a 9-mm length and for ISO 70 and 110 with a 12-mm length, compared to the respective FRC-RET posts (P<.001), whereas in all other groups, TI-RET and FRC-RET showed no significant differences. FRC-SH groups did not differ from FRC-RET groups. TI-SH showed significantly lower yield strength for ISO 70 compared to TI-RET, but significantly higher values for ISO 90 and 110 (P<.001).

Head design of the tested FRC posts does not improve the yield strength, compared to FRC posts with a shank design. The diameter of the posts had a significant effect on the yield strengths of RET as well as SH groups.