45 Degree Failure Strength and Stress of Fiber Posts

Objective:

To determine if the 45º failure strength of a fiber post can be predicted from theory alone.  The null hypothesis is that all fiber posts fail at the same bending stress.

Methods: 

The 5 fiber post systems used in this in-vitro study were ICEPost, ParaPost Fiber, FibreKor, Flexi-Post Fiber, and Flexi-Flange Fiber.  Extracted human anterior teeth (14 per group) were instrumented and posts were placed according to their manufacturer's instructions. Failure strength was determined by mounting the teeth in a special 45º jig and applying a load with a universal testing machine until the post failed.  Bending stress at failure was calculated using post size measurements obtained with digital calipers. The results for each method were compared using non-factorial 2-way ANOVA without interactions.  Significant results (P<0.05) were further analyzed using the Student-Newman-Keuls test.

Results: 

The measured 45 degree failure strengths (N) was:

Post Brand	Approximate Reamer Diameter (mm)
	0.9	1.2	1.4
Flexi-Flange Fiber	109±17	102±9	88±18
Flexi-Post Fiber	115±14	90±21	93±14
FibreKor		43±10	61±6
ParaPost Fiber		41±8	61±10
ICEPost		31±5	41±3

The calculated bending stresses at failure (GPa) was:

Post Brand	Approximate Reamer Diameter (mm)
	0.9	1.2	1.4
Flexi-Flange Fiber	0.93±0.14	1.09±0.10	0.95±0.18
Flexi-Post Fiber	0.91±0.11	0.95±0.22	1.22±0.18
FibreKor		1.08±0.24	1.01±0.09
ParaPost Fiber		1.15±0.21	1.03±0.16
ICEPost		1.10±0.16	1.01±0.08

There was no significant difference in the bending stress between different brands of post (P=0.7).  There was a significant difference between different post sizes (P=0.004); posts using a 0.9 mm reamer had a significantly low bending stress at failure (P<0.05).

Conclusions:

Although some differences in the bending stress at failure were statistically significant, they are much smaller than the differences in the failure strength.  The superior failure strength of the Fiber Flexi-Flange and Fiber Flexi-Post is largely due to the unique shape of the post rather than the strength of the material.