New Post Designs and Applications

Barry L. Musikant, D.M.D., F.A.C.D., Brett I. Cohen Ph.D., Allan S. Deutsch D.M.D., F.A.C.D.
New Post Designs and Applications

Barry Musikant

Allan Deutsch

uch has been written about new post designs that bend like the tooth structure and, through the use of bonding agents, have very high retention values. One study has stated that the new composite posts create no stress under function because they bend like the tooth. Other “passive” post systems are ceramic, look like tooth structure, are bonded into place with high retention and are, consequently, said to be superior.
    From a review of literature, and from our own clinical experience, we hope to clarify the situation.
    First of all. There is no thing as a “passive” post. They still distribute functional stresses to the walls of the root. They may have the advantage of not inducing insertional stresses, but if not designed properly still have the potential of distributing functional stresses in a concentrated fashion. In fact, the only passive post is the one in the box!
    Another point to remember is that to date, no combination of etchants, microabrasion, bonding agents, or cements has proven to be as resilient or as strong as dentin. A threaded post with even a weak cement still offers more tensile resistance than any passive post because the thread is locked into the dentin. The resistance that dentin offers is far greater than any cement developed to date. More importantly, the fatique charachteristics far exceed that of any composite cement.
    Research has made it abundantly clear that threaded posts have the potential of creating high levels of insertional stresses. We could not agree more! The concept of the split flange, a characteristic of the Flexi family of posts, was developed to mitigate the stressful effects of the thread while maintaining its retentive advantages.
    Many independent studies confirm the combination of high retention with minimal insertional stresses and the even distribution of functional stresses associated with the split-shank concept.
    One relevant clinical question is when to use the Flexi-Post versus the Flexi-Flange. First, it is important to know that the Flexi-Flange exists. It is the third tier that was designed to give the post greater stability when no coronal tooth structure exists.
    The flange creates a broader metal-to-dentin surface. Under function, all posts put tensile stress on the cement interfaces between the shank of the post and the walls of the root. A large flange offers vertical resistance to the post’s lateral movement, consequently preserving the cement interface along the post shank. Added reinforcement is not necessary when adequate coronal tooth structure exists, but is a necessity when it doesn’t.
    To take advantage of the multi-tiered design, the post may be fully seated. If the flange is not seated, it is the same as not being there! Depending on the amount of dentin remaining, either a Flexi-Post or a Flexi-Flange is our choice when it has been determined that a post is necessary.
    During our courses on Simplified Endodontic Techniques, we practice instrumentation on plastic blocks. If you wish to practice placing Flexi-Post or Flexi-Flange in these blocks, let us know, and we will accommodate you.

11/02/1999

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