Different viewpoints on methacrylate endo cements

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Different viewpoints on methacrylate endo cements

Postby BarryMusikant on Mon Jun 07, 2010 10:57 am

In an article titled, Bonded Obturation: a detailed overview authored by Richard Mounce and Houda Naayem, published in Endodontic Practice, they state the advantage of Real Seal (Epiphany/Resilon) over that of gutta percha, listing the short comings of gutta percha. That advantage is stated to be a reduction in the migration of bacteria compared to gutta percha. They further state that clinical studies show that RS is equal to or better in clinical success than GP, but certainly no worse.

The authors’ article is certainly one that is supportive of Resilon/Epiphany also knows as RealSeal. For dentists to have a better chance of balancing these claims, an article titled Critical Review on Methacrylate Resin-based Root Canal Sealers authored by Young Kyung Kim et al and published in the March 2010 issue of the JOE is worth looking at.

In the abstract the authors conclude that “on the basis of the in vitro and in vivo data available to date, there appears to be no clear benefit with the use of methacrylate resin-based sealers in conjunction with adhesive root filling materials at this point in their development.

The body of the article is organized to address the claims made by the advocates of methacrylate sealers, a general term that includes Resilon/Epiphany, Realseal, EndoRez, Fiber Fil R.C.S., Meta SEAL.

Reality Check on Contemporary Methacylate Resin-based Sealers
“The predominant adhesive mechanism of methacrylate resin-based sealers to radicular dentin is micromechanical retention of resins that infiltrated the partially demineralized collagen matrix. Thus, effective bonding in the root canal environment remains a challenge. This is due to the limited vision and access even with the use of an operating microscope, the preponderance of sclerotic dentin along the apical part of the root canal, differences in regional bond strengths, debris on the canal wall, and high cavityh configuration factor (C-factor) inside long narrow canals. Under these circumstances, the sealing performance of thin films of low viscosity resin selars might be severely jeopardized. Therefore, a number of issues are raised in this review to highlight the problems that might be expected in application of methacrylate resin-based sealers.”

Can Methacrylate Resin-based Sealers create Adequate Retention in Radicular Dentin to Prevent Disruption of Sealing Integrity During Polymerization?
“Recent studies regarding the limited aggressiveness of contemporary self-etch and self-adhesive resin composites raised similar concerns on the true self-etching potential of self-etching and self-adhesive sealers to hybridize intact radicular dentin. Mechanically prepared canals contain areas that are inaccessible by currently used endodontic instruments. Moreover, canal irrigants might not reach all parts of the canal space. This results in retention of debris and smear layers along the apical third of the canal walls and isthmi.” The authors are simply stating that bonding is compromised.

“…Contrary to the manufacturers’ claims, neither the second nor the fourth generation sealers are likely to bond well to radicular dentin if EDAT is not used to remove the smear layer and smear plugs, or when EDTA does not reach the apical third of the canal walls. In adequate dentin hybridization might also occur in the calcospherite-containing noninstrumented dentin for those clinicians who elect to use NaOCl as the only active root canal irrigant.” The use of NaOCl poses a dilemma for dentists. On the one hand, it is the single most effectice irrigant available to digest organic debris and kill bacteria. On the other hand, the oxygen released from NaOCl inhibits the setting of the methacrylate cements.

How Strong Is Resin Adhesion Inside Root Canals?
“A major problem associated with bonding inside root canals is the challenge to relieve the shrinkage created on the canal walls of these long narrow “cavities” during polymerization of resin sealers. Polymerization shrinkage which is more severe in sparsely filled, low viscosity root canal sealers, can disrupt the close initial contact between the sealer and the surrounding dentin and create shrinkage gaps where microorganisms can penetrate and multiply. In view of the high probability for imperfect dentin bonding in root canals and the high volumetric shrinkage, slow polymerization of the dual-curable sealers would improve the chances for the relief of shrinkage stress via resin flow…However, in vitro studies comparing the push-out strengths of various root filling materials to radicular dentin invariably showed that roots obturated with bondable root rilling material/methacrylate resin-based sealer combinations had surprisingly, significantly lower push-out strengths than gutta-percha/conventional nonbonding sealer combinations. Resion/Epiphany (RealSeal)-filled canals also contained significantly more voids and gaps than those filled with gutta-percha and conventional sealers. More importantly, when filled canals were subject to occlusal loading that simulated the behavior of the sealer-dentin interface under cyclic functional stresses, Resilon/RealSeal obturated canals exhibitied significantly greater interface disruption when compared with unloaded controls.”

Do Methacrylate Resin-based Sealers Prevent Leakage?
“Resilon/Epiphany system was not better than gutta-percha/conventional sealers in preventing coronal leakage. It is known that polymers degrade over time through physical and chemical processes. As the bond degrades, interfacial leakage increases which resembles in vivo aging. In addition, Resilon is susceptible to alkaline and enzymatic hydrolysis. Therefore, biodegradation of Resilon by bacterial/salivary enzymes and endodontically relevant bacteria might occur in the event of apical or coronal leakage, further compromising the seal achieved after root canal treatment. Bacterial degradation of gutta-percha also occurs with the bacteria using poly (trans1,4-isoprene) as the sole carbon and energy source for growth. However, such a process is seen only in the genus Nocardia, which is found mostly in soil and is not a recognized endodontic pathogen. Gutta-percha can be decomoposed by the heat generated with the use of warm vertical compaction techniques. However, decomposition of gutta-percha components had only been detected by using chemoanalytical methods. The decomposition of gutta-percha is a slow oxidative process that has been detected chemically from gutta percha retrieved 5-to 15-year old retreatment cases. Apart from chemical detection of bredakdown products, there was no radiographic documentation of the disappearance of gutta-percha from filled canals.”

Does Adhesion Exist between Core Materials and Sealers to Create a Monoblock?
“…Taken together, the data sugest that the chemical coupling between comtemporary methacrylate resin-based sealers to root filling materials is generally weak or insufficiently optimized. In view of the extremely high C-factor encountered in long narrow root canals, it is doubtful whether the core material-sealer bond is capable of resisting polymerization shrinkage stresses that develop during the setting of the resin sealer to permit the realization of the goal of creating a monoblock in the root canl system.

Do methacrylate Resin-based Sealers Strengthen Roots?

Collectively, currently available methacrylate resin-based sealers and their recommended adhesive procedures are not able to influence the mechanical properties of root canal dentin. This conclusion might be due to the following factors: (1) polymerization that occurred along the sealer-dentin interface in the coronal part of the root is possibly affected by oxygen inhibition; (2) creeping of incompletely polymerized resinous sealers, which results in failure along the sealer-dentin interface; (3) presence of residual monomers in the root canals; and most importantly. (4) the low cohesive, tensile. Compressive strengths and modulus of elasticity of the currently available root filling materials when compared to dentin, with the former behaving as elastomers that dissipate instead of transmitting stresses. In addition, the extremely unfavorable cavity geometry of root canals causes gaps along the dentin/sealer interface during polymerization of the methacrylate resin-based sealers.

       Are Methacrylate Resin-based Sealers Biocompatible?
       “…The cytotoxicity profile of Metal SEAL revealed that it remained severely
        cytotoxic during the first week, whereas an epoxy-resin-based sealer became only
         moderately cytotoxic fater the same period. Both sealers eventually became non-
         cytotoxic. The same finding was also observed in the Epiphany sealer. Generally,
         the freslhly mixed condition might be more relevant to clinical use because unset
         sealers are placed into the canals.

        Other studies that evaluated the cytotoxicity of Epiphany and RealSEAL produced
        highly variable results. Sousa et al observed bone formation and only minor
       inflammatory reactions in guinea pigs. However, Epiphany in both freshly mixed and
       set conditions showed a severe to moderate cyctotoxic effect and its cytotoxicity
       actually increased with time, posing significant cytotoxic risks. The cytotoxicity of
       Epiphany might be explained by the presence of unpolymerized hydrophilic
       monomers (such as HEMA) that can easily diffuse into the cell-culture medium and
       elicit significant toxicity. Epiphany requires body temperature and total elimination
       of air contact to polymerize. It polymerized within 30 minutes in an anerobic
       environment, but in the presence of air, material setting took up to 7 days. Forty
       percent of the sealer remained unpolymerized despitea post-curing time of as long as
       2 weeks in vitro. Consequently, extrusion of a methacrylate resin-based sealer
       through the periapical foramen would create an uncured surface layer for extended
       time periods. This might alter the toxicity profile of resin-based sealers because more
       incompletely polymerized toxic monomers are present in the exposed
       sealer….Therefore, these results support the need to continue to develop better
       endodontic sealers that combine optimal sealing and bonding properties of resin with
       acceptable biologic properties for endodontic applications.


Future Research and Concluding Remarks
Are bondable methacrylate resin-based sealers better alternative for root canal obturation than their nonbonding counterparts? This statement does not appear to be openhandedly supported by the plethora of ex vivo studies. Moreover, very few of the currently limited clinical outcome studies have included a control group to support the advantages of these new materials over conventional nonbonding materials. Indeed, the paucity of evidence-based clinical information available on some of these aggressively promoted materials might serve as food for thoughts for clinicians to think twice about adopting these approaches to root canal obturation….Under the conditions of well-executed cleaning and shaping and the provision of adequate coronal restorations, it is dubious whether the merits of adhesive methacrylate resin-based sealers might be revealed in future prospective randomized controlled clinical trials, particularly when more stringent criteria for evaluating success are used.

I am not a fan of methacrylate resins as endodontic cements. I believe this paper helps in broadening ones knowledge of which cement to use and is a good counterweight to a paper that imo clearly was used as a marketing tool.

Regards, Barry
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Re: Different viewpoints on methacrylate endo cements

Postby william on Sat Jun 12, 2010 11:08 am

Barry, thanks for posting the other studies on Methacrylate endo cements
with scientific studies to back you up.

I remember a problem I had many years ago when I posted some concerns about restorative dentin bonding on the other dental board.
The guy from a big resin company came out of nowhere and spewed all sorts of studies at me about the "science" supporting dentin bonding
and all I could site were a few seminars and personal experience with
my own patients.  I had at the time questioned the durability of dentin
bonding under large resin restorations and also dentin bonding
for pulpal blushes and exposures.

My personal experience indicates that your observations are correct and
I would not trust dentin bonding, esp down a canal.
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Re: Different viewpoints on methacrylate endo cements

Postby BarryMusikant on Sun Jun 13, 2010 7:47 am

William,

I had a similar experience when I used to participate on a couple of other message boards. I had no problem with those differing with me. In fact, we would often bring up different studies to support our different viewpoints. It got to the point where I used to call them "dueling abstracts'. I thought this was all well and good. However, over time, on too many occasions it degenerated into personal attack that had nothing to do with the issues. It was simply a goal to attack those who didn't ascribe to the conventional wisdom of the day, that wisdom being formed via ubiquitous advertising and well known (and well paid?) advocates.

Once again, that is the main purpose of this message board. Even though I started it, I have no right to control the viewpoints that are stated here. I'm sure going to have my opinions, but it is the freely stated and open opinions of others that legitimize this site which is more important than any opinion I might have. In short, it should be a site for unbiased learning. So far so good.

Regards, Barry
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