Yield Strengths of FRC Posts with Coronal Shank or Head

Objectives: High bending forces are transmitted onto the coronal part of root posts. Posts with coronal head might strengthen the cervical area. Titanium posts (TI) might be too rigid, therefore glass fiber reinforced composite posts (FRC) are favored due to their flexural properties. This study compared yield strengths of FRC and TI posts each with or without coronal retention for core build-up.

Methods: Tapered posts (ER post-restoring system, Brasseler) of four sizes in diameter (ISO 50, 70, 90, 110), two materials (FRC, TI) and two head designs: shank (SH) without retention with post of 12mm length as well as head with horizontal retention (RET) with posts of 9 and 12mm lengths were investigated forming 24 groups (n=9). Conventional titanium posts (TI-SH, TI-RET) served as control. The 0.2% yield strengths (R0.2) of all specimens were tested on a universal testing machine. Three-way and one-way ANOVA with Bonferroni-Dunns multiple comparison tests were performed for statistical analysis (a=0.05).

Results: The results of TI-RET were significantly higher (p<0.05) compared to the respective FRC-RET posts for ISO 110/ 9mm (82.9+-12.7N TI, 66.1+-3.2N FRC) and for ISO70 (50.0+-6.4N TI, 35.5+-6.5N FRC) and 110 with 12mm (71.8+-7.9N TI, 60.2+-5.6N FRC), whereas in all other groups TI-RET and FRC-RET showed no significant differences. FRC-SH groups (11.9+-1.7N ISO 50, 33.8+-2.1N ISO 70, 42.3+-4.7N ISO 90, 66.6+-7.7N ISO 110) did not differ from the respective FRC-RET groups of 12mm length (22.9+-3.1N ISO 50, 47.4+-10.9N ISO 90). TI-SH showed significantly lower yield strength for ISO 70 (29.7+-4.0N) compared to TI-RET of 12mm length, but significantly higher values for ISO90 (85.3+-6.0N SH, 56.5+-3.7N RET) and 110 (110.9+-14.7N)(p<0.05).

Conclusion: Head design of the tested FRC posts does not improve the yield strengths compared to FRC posts with shank design. Diameter and material of the posts had a significant effect on the yield strengths.