Oral Health Group
Feature

Fibre Posts ARE the State-of-the-Art

February 1, 2011
by Len Boksman DDS, BSc, FADI, FICD


Practicing clinicians in advanced countries generally acknowledge and appreciate efforts by authors and editors to publish timely information attempting to summarize the techniques and materials and technologies that constitute the state-of-the-art or standard of care in their field. This is because few practicing dentists have the time available to scour all of the scientific data that could be available to them. In fact, over the last 50 years, these advancements have come at us SO fast that even the most prestigious dental textbooks and handbooks are republished every other year or so, more and more journals, magazines; even some subscription – based newsletters, have emerged to help keep the contemporary dentist informed.

The reprint of a 1999 article, in the November 2010 Oral Health issue about “Current knowledge” in foundation restorations in fixed prosthodontics is, by definition, anything but current. Re-publishing an article about clinical decisions and treatment options that were relevant more than 10 years ago, underscores just how much things have changed. The elements of foundation restoration may have changed as much in the last 11 years as they did in the 300 years covered in the November reprint.

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Let me jump into it where the authors are describing the legacy of the “custom cast post”, as if this was a good thing. Until the 1950s this was all we dentists had to work with, and the double appointment, and double -digit failure rate simply had to be acceptable. The 1999 review article discusses ways of minimizing the damage and the risk of root fractures. The dangers associated with cast posts – and even prefabricated metal posts – have been known by generations of dentists. The endodontic and prosthodontic textbooks published in recent years acknowledge this. As a testament to the progress we have made, a recent survey of US dentists1 indicates that 33% of them use a cast post “10% of the time or less often” and 54% of them NEVER use cast posts. Morgano cites one six-year clinical study (1989), with cast posts demonstrating a 90.6% success rate, and considers this “providing excellent service”. In contrast, I would cite a 4 year clinical study2 comparing 100 cast posts with 100 of the 1st generation fibre posts. At 4 years the cast posts have demonstrated 9% root fractures, and 7% other failures, while the fibre posts had a 95% success rate (3% non-compliance and 2% endodontic complications; NO root fractures. Even in the shorter term (1 year) the differential is still remarkable.3

This is just the beginning of why I am compelled to write to the Editors of Oral Health. At the time Morgano published (1999), fibre reinforced posts (FRP) had been in North America for nearly 7 years (in the USA for 4 years), and there were only a dozen or so in vitro and clinical studies published in the main stream media. Today, I have collected a personal bibliography of over 300 articles from 1996-2010 addressing the use of low modulus “Monobloc” foundation restorations. It is by no means complete, but it is more than 90% favorable to fibre posts, when tested one way or another against metal posts. There are a number of high quality FRPs, composites and resin cements that work well together; some combinations better than others.

I would like to take this opportunity to describe the progress over the past 10 years, since the article was published, rather than invoke Fouchard and GV Black in reminiscing 18th and 19th century dentistry. Here are the conclusions and opinions in reviewing all of this literature and through my own clinical experience, consultation with other clinicians, manufacturers and researchers:

  • Properly placed fibre posts minimize or eliminate the predisposition to root fracture that we have come to anticipate with metallic (especially cast) posts. This difference has been shown in vitro4-7 and clinically.3,8-11
  • Fibre posts tend to be more fatigue-resistant than stainless steel or titanium posts,12,13 but some fibre posts are more fatigue-resistant than others14-16 dependent upon their composition.
  • Fibre posts, translucent and tooth-colored, are esthetically pleasing, do NOT interfere with composite or ceramic shading or optical properties, and do not cause root discoloration.
  • Unlike base metal alloys (cast or machine-milled), fibre posts cannot corrode. This benefit eliminates one more failure modality typical with metal posts.17
  • If fibre posts are exposed to 100% humidity for a long enough period of time, they will lose some flexural strength.18,19 However, if the post is bonded into the tooth, this is virtually impossible.20 Furthermore, more recent research indicates that the degree of weakening effect would not be clinically influential.21
  • Fibre posts are removed in a matter of a few minutes by drilling them out from “their middle”. 22-25 Naturally, the difficulty of clinical removal will vary according to specific access, visibility and working space.
  • Traditional Instron-type tests often show a higher failure / fracture load in endo-treated teeth with metal posts than with fibre posts, but the failure mode with fibre posts is always more favorable, allowing further repair.26-28
  • Clinically, there appears to be no difference in the 2-year29 and 8-year30 result between parallel and tapered fibre posts (unlike the difference with metallic posts), but all dentists empirically know that tapered posts are more anatomically correct, are more conservative by removing less tooth structure and are less invasive.
  • A ferrule (the taller and wider the better) is always the ideal situation. Always preserve tooth structure. But in vitro research indicates that in worst-case-scenarios (de-coronation at the gumline), a fibre post restoration has a better prognosis than the rigid (high modulus) posts.4,31
  • Zirconia (ceramic) posts are esthetic and radiopaque, but are inherently brittle, rigid and nearly impossible to remove.32

Perhaps the most significant and hopeful horizon emerging in the realm of fibre reinforced post-core restoration, covered by full coverage, is what follows. Owing to a mechanical properties, shape, compatibility with the tooth structure, stress dissipation, it appears that some brands of fibre posts from certain manufacturers, actually do appear to reinforce these compromised teeth to the level of uncut or unrestored teeth, or superior to teeth without posts or superior to teeth restored with rigid posts.33-40

The fibre post is but the centerpiece of the 21st century monobloc restoration.

The other components; bonding, cementation, core build-ups and ceramic prostheses have advanced almost as much as fibre posts since Dr Morgano’s 1999 status report.

Morgano talks briefly about “bonding” posts, citing one study from 1992, which used early generation bonding agents with metallic posts. I now have the benefit of reviewing a dozen decent clinical studies published between 1995 and 2010 which demonstrate minimum failure (de-bonding) rates (1-4%) for fibre posts bonded with a variety of 4th and 5th generation adhesive systems.3,8-10,41-45 The 1999 review article assumes and implies a high risk of micro-leakage using bonded fibre posts (compared to conventional methods), however actual comparative testing indicates the opposite: Cast metallic posts are more likely to leak,46 as are prefabricated metal post foundation restorations.47-50

Adhesive bonding agents have become less technique sensitive, while at the same time, less capable of providing the polymeric seal that was typical of the previous 4th and 5th Generations (51). Today, resin cements can provide that seal.

The early Resin Modified (reinforced) Glass Ionomers (RMGIs) did experience some problems underneath crowns, IF the margins leaked. Today some lecturers recommend RMGIs in cases where isolation / moisture control are a challenge to the straightforward bonding procedures. More and more current studies are reporting in-vi
tro results placing posts with self-adhesive / selfetching resin cements equivalent to the total etch cementations.52,53 These cements are simple to mix and apply, provide good working times, achieve polymerization on command, are esthetic, radiopaque and they are virtually insoluble; like regular resin cements. However, there are concerns about hydrolysis with these cements,53a they are working with a smear layer that is different (sealer, gutta percha), and typically have lower bond strengths than total etch in roots. I still prefer the etch-prime-bond, or etch, bond (the so-called 4th and 5th generation bonding agents) -composite resin cement technique, because I have reason to believe that I will get higher and longer term stable bond strength to the interior radicular dentin.54-56

Composite core build-ups are described as more or less “experimental” in the 1999 Morgano status report. Yet they have been successfully documented in the mainstream literature as esthetic, reliably bondable, adequately durable57-60 and clinically stable.3,8-10,41-45,61 (The terrible things that the prosthodontist authors predicted did not come to pass except, perhaps, in cases of sloppy technique.) Now that the formulations of the resin cements and core build-up resins have been optimized, there is a trend towards using the same (dual-cure) resin for BOTH applications, right out of the same dispenser. The only step between the two is the actual insertion of the post. OH

Dr. Leendert (Len) Boksman DDS, BSc, FADI, FICD is a part-time consultant to Clinical Research Dental acting as Director of Clinical Affairs, an Adjunct Clinical Professor at the Schulich School of Medicine and Dentistry and is in private practice in London, Ontario, Canada. He can be reached at lboksman@clinicalresearchdental.com.

Oral Health welcomes this original viewpoint.

References

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17. Drumond

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