Allan Deutsch
 
 
 
 
 
 
 

LASS-REINFORCED fiber posts have been in clinical use for more than ten years, and the failure rate can be as high as 7 to 11 percent of the cases placed. For most clinical products, this is not an acceptable failure rate. However, because the clinical failure does not include tooth fracture, many dentists feel that they might as well “just throw in a post to make it easier to bond everything together and maybe reinforce the restoration.” I am not thrilled with that philosophy of treatment because when the post fails so does the restoration. In some cases, the restoration can require many units and be quite extensive.
    The leading cause of fiber post failure is decementation, mostly due to the lack of full bonding in the canal, especially near the apical end. Many articles in the literature show that complete bonding of any fiber post to the canal wall is almost impossible to achieve. Most of the bonding of the post occurs in the coronal one-half to one-third of the canal. It is also difficult to get full curing of light cured composite cement near the apical end of the canal space. That is why we recommend using self-curing reinforced composite cement. Currently, all fiber posts are passive and bonded into the canal. The second greatest cause of failure is fiber post fracture. Although fiber posts have approximately the same modulus of elasticity as dentin, their cross-sectional area is much smaller than the root; consequently they are not as strong as the root nor do they flex like a root in clinical reality.
    To address these problems, Essential Dental Systems has developed the first threaded non-bonded active fiber posts, the Flexi-Post® Fiber and the Flexi-Flange® Fiber. Retention of the post in the root is dramatically increased due to the active retention of the fiber threads in the root and the anatomical design of the post. The threading of the root is achieved using the non-stress-causing split-shank technology of the Flexi-Post tap. The tap is a specially designed Flexi-Post or Flexi-Flange post machined to a wrench. The split of the tap creates the thread line for the Flexi-Post Fiber and Flexi-Flange fiber in the root in an atraumatic fashion. The split of the tap acts as a stress breaker and allows the legs of the tap to collapse as it threads the root. This design gradually cuts into the dentin and creates the threads without causing stress to the root as shown in 25 years worth of published research.

FIGURE 1: Flexi-Post Fiber and Flexi-Flange Fiber.

FIGURE 2: Flexi-Post Fiber Intro Kit.

FIGURE 3: The split-shank tap is used to create the threadline atraumatically in the root.

FIGURE 4: Primary Reamer.	FIGURE 5: Secondary Drill.

    When the root has been threaded, the posts are cemented in place by etching the walls of the post-hole with EDS 17 percent EDTA in water and then using super-strong titanium reinforced Flexi-Flow Auto composite cement to lute the post in place. The 17 percent EDTA removes the smear layer and opens the dentinal tubules while it also etches the intertubular dentin. This etching creates fingers in the dentin (a hybrid layer) that facilitate composite bonding. Flexi-Flow cement is self-curing, so it fully cures even at the bottom of the post-hole. The combination of etching the dentin using 17 percent EDTA and Flexi-Flow composite cement provides such high retention that additional bonding with a bonding agent is not required.

FIGURE 6: Flush the canal with 17 percent EDTA for one minute.	FIGURE 7: Showing tap insertion while wet with 17 percent EDTA.

FIGURE 8: The second tier of the post must always fully seat in the preparation. If the post is too long for the post-hole you may cut it at the apical end with a diamond disk.	FIGURE 9: Place Flexi-Flow Auto reinforced composite cement in the canal. No bonding agent is required when using 17 percent EDTA. Thread the fiber post in until it is fully seated into the second-tier preparation.

FIGURE 10: Build up the core by bonding Ti-Core to the coronal dentin.

    The posts are made from a specially formulated unidirectional S glass to increase their strength under function. They also retain a modulus of elasticity close to that of natural dentin. The modulus is slightly higher than that of other fiber posts to approach the stiffness of the much larger diameter of the root dentin. The Flexi-Post Fiber and Flexi-Flange Fiber are both tooth-colored for aesthetic restorations.
    The EDS fiber posts are anatomically designed to increase the intimacy of fit between the posts and the root. This helps to maximize retention and strength. The Flexi-Post Fiber and Flexi-Flange Fiber are designed to take full advantage of all the design and functional features that have made the Flexi-Post and Flexi-Flange clinical successes for over 25 years.