Bridging the Canal

Once a root canal has been shaped and cleaned, complete obturation of the root structure is essential. Therein lies the challenge. We explore the latest strategies clinicians can use to up the odds of endodontic success for long-lasting restorations.

When the pulp of a tooth goes nova, it’s usually due to bacterial infiltration into the root canal. A common culprit in this scenario is a filling compromised by marginal leakage. Other causes may stem from an incomplete cleaning or disinfection from a previous canal treatment. Whatever the cause, a root canal treatment (RCT) — or retreatment — often pops up on a patient’s to-do list.

Due to the complexities of canal anatomy, it is widely accepted that canal sterilization is an unobtainable goal. In lieu of sterilization, RCT success relies on proper shaping and cleaning of the canal, followed by thorough obturation, which essentially entombs any remaining bacteria so it can do no harm.

“Obturation is one of the key elements to success as we strive to seal the root canal from further bacterial contamination apically and coronally, and to encourage healing of the periapical tissues at the end of the root,” says James Gutmann, DDS, an endodontist based in Dallas, and widely published author on topics involving RCT. “However,” he adds, “our task is not complete until the tooth is fully restored to function with a leakproof restoration and proper occlusion.”


But “leakproof” is the operative word here, and has long been a bit of a high wire act for clinicians. That’s because gutta percha is the principle core obturation material in use. This natural rubber, derived from the Palaquium gutta tree, is combined with zinc oxide, heavy metal salts, and wax or resin for dental applications.1 And it has a lot of things going for it. Gutta percha is biocompatible, can be softened with heat to facilitate condensation and enhance adaptation in the canal, is radiopaque, and can be easily removed in the event that retreatment becomes necessary.

But there are a couple of significant downsides to gutta percha. It shrinks upon cooling, and it lacks the ability to adhere to tooth structure. As a result, its use carries the potential for leakage.

In the quest to find an ideal obturation material, dental researchers and manufacturers have explored several alternatives. Some studies show promise derived from infusing gutta percha with other properties. For instance, researchers at the University of California at Los Angeles are exploring the possibilities of nanodiamond-embedded gutta percha. So far, they report that due to the faceted surface chemistry offered by nanodiamonds — which are approximately 4 to 6 nanometers in diameter (thousands of times smaller than a human hair) — mechanical properties can be improved, resulting in better handling. Some of these formulations have been combined with broad-spectrum antibiotics to help fight endodontic infections and inhibit bacterial growth.2

Other research has involved embedding nanometric bioactive glass particles in a gutta-percha matrix. This has shown promise in its sealing capabilities when heated.3 Still other studies are centered around regenerative endodontics and the use of stem cells and growth factor to coax pulpal regrowth.

But to date, gutta percha still rules. “Different formulations of gutta percha are available, but nothing has been proven better than the usual formulations that oscillate around 80% zinc oxide and 20% gutta percha with other trace components,” says Eugene Pantera, DDS, clinical associate professor emeritus in endodontics at the University at Buffalo School of Dental Medicine in New York.

So, to get around the leakage problem, sealers are typically used.


Happy couple


Perhaps manufacturers have come up with the key to obtaining the best seal with gutta percha by creating core material that corresponds to instrumentation. Aside from research that seeks to modify the tree sap cocktail of gutta percha, according to James Gutmann, DDS, an endodontist based in Dallas, “The most recent advances include the development by a number of manufacturers of precision master gutta-percha cones that better match the shaping of the root canal.”

Indeed, as Eugene Pantera, DDS, clinical associate professor emeritus in endodontics at the University at Buffalo School of Dental Medicine in New York, observes, “There are many more shapes of gutta-percha cones that match the various rotary file contours, making fitting a master cone more predictable.”

Such cones also correspond with techniques, and, by extension, the instrumentation immediately preceding their placement. That could be a heated plugger, used in down packing, or the size and taper of a rotary nickel-titanium file, used to shape a canal. Such pairings allow the use of one tapered master cone, rather than adding several auxiliary cones, to provide a three-dimensional fill to the desired working length of the canal. This helps to reduce voids that could be vulnerable to bacterial proliferation. But the caveat here is that the cones must precisely match the instrumentation. This is one reason that sealers come in handy.


As long as gutta percha remains the go-to obturation material, sealers will continue to play an important role. Although gutta percha can’t bond with dentin, sealers can bond with both substrates to form a bridge.

Besides enhancing the chances for a leak-proof restoration, sealers also provide lubrication for gutta-percha cones. Some manufacturers even offer cones that are pre-coated with a sealer. Sealers can also infiltrate canal anatomy that may not be reached by the core material. In fact, newer formulations can reportedly penetrate dentinal tubules.1

Sealers may be composed of zinc oxide-eugenol, glass ionomer, bioglass, resins or silicone. Pantera, however, notes, “While several endodontic sealers have been introduced, there is no real evidence regarding clinical outcomes supporting one over the other.”

But Gutmann believes that newer sealers offer better adaptation of the filling to the canal walls, and potential biological healing at the apex, supporting cemental formation. In fact, a recent landmark development in the world of endodontic materials is that of biocompatible and bioactive materials — particularly pertaining to sealers. In Gutmann’s estimation, the development of bioaggregate and bioceramic root canal sealers has been a game changer in the obturation of root canals.

Fred Barnett, DMD, chairman of the Department of Dental Medicine, and chairman and program director in the Division of Endodontics, Albert Einstein Medical Center in Philadelphia, agrees, telling Mentor that bioceramic materials, which have been widely used in orthopedic applications, are proving to be an important advancement for root canal obturation. He explains that these materials demonstrate dimensional stability, and rather than shrinking upon setting, actually slightly expand. “This makes them one of the best sealing materials in dentistry,” says Barnett. “They are not sensitive to moisture and blood contamination, are insoluble in tissue fluids, and, therefore, are not overly technique sensitive.”

Barnett adds that when fully set, bioceramic materials are biocompatible and even bioactive. “When bioceramic materials come in contact with tissue fluids,” he explains, “they release calcium hydroxide, which interacts with phosphates in the tissue fluids to form hydroxyapatite.4–6 This property may explain some of the tissue-inductive properties of these materials. Bioceramics are now the material of choice for pulp capping, pulpotomy, perforation repair, root-end filling, and obturation of immature teeth with open apices, as well as the sealer for root canal filling of mature teeth with closed apices.”5–7

There is, in fact, evidence that bioceramic sealers actually strengthen root canals and increase fracture resistance. They are also said to set at a high pH, which discourages bacterial proliferation.8

Bioceramics comprise a fairly large category of materials, including alumina, zirconia, bioactive glass, glass ceramics, hydroxyapatite and calcium phosphates. In addition, bioaggregates and some calcium-silicates fall under this umbrella. These kinds of sealers are inorganic, biocompatible and bioactive. For instance, calcium silicate-based cements promote precipitation of calcium phosphate, a natural component of tooth enamel, when exposed to moisture. Some have even demonstrated a degree of antibacterial activity. They have also shown excellent sealing capability.9,10

Barnett ticks off a list of bioceramic sealers, including mineral trioxide aggregate and other similar, but proprietary, branded formulations that have become available. One, in particular, he explains, is a premixed and injectable endodontic sealer. “Its nanoparticle size and superior flow allows it to penetrate into canal irregularities and dentinal tubules,” says Barnett. “It is hydrophilic and uses moisture from the dentinal tubules to initiate and complete its setting reaction. In addition, as no shrinkage occurs on setting, a gap-free interface between the gutta percha, sealer, and dentin walls has been shown.”11

Barnett notes that, according to the manufacturer, this formulation can be used by itself to fill canals. Still, he says he would recommend the use of gutta percha. As he sees it, the function of gutta percha is to occupy space and help distribute the sealer throughout the canal system. But, he adds, “As it is the sealer that is responsible for the ‘seal,’ we should look for sealers that are dimensionally stable (do not shrink upon setting), biocompatible, hydrophilic, easy to use, and can flow into the intricacies of the root canal system.”

POINT OF SALE | The Right Stuff

  • Gutta percha, though not perfect, remains the preferred obturation material for root canal treatment.
  • There are scores of sealers used in conjunction with gutta percha to help ensure leakproof seals.
  • New bioceramic sealers are demonstrating excellent sealing capability and bioactive benefits.
  • Many clinicians elect to warm gutta percha prior to or during placement, and various heating devices and systems are available to assist.
  • Core-carrier systems are enjoying popularity among a number of clinicians.


The efficacy of gutta percha can certainly be impacted by how it is delivered and applied. Gutta percha manifests in two crystalline forms. Its room-temperature phase is known as “beta,” but it transitions to its alpha phase once it reaches approximately 115º F. Between 130 and 140º F, it transforms into its amorphous state. But the nagging problem with gutta percha is that when heated, it will shrink to some degree as it returns to its beta phase.1

Delivery systems correspond with obturation techniques, and while some clinicians opt for cold lateral compaction of sealer-coated, beta-phase gutta-percha master cones into canals, others favor techniques that warm the material to its alpha state for vertical compaction or injection. Warming thermoplasticizes the material, allowing it to more easily conform to canal anatomy.

There are a few ways to thermoplasticize gutta percha. Some manufacturers sell small ovens for this purpose. While some heating devices offer heated pluggers to use inside canals to compact gutta percha, others feature cordless extrusion of sealer and thermoplasticized gutta percha. Many allow the clinician to dial in the precise temperature needed. And once the single-patient-use cartridges filled with gutta percha are loaded, the clinician’s got a filling device that supports warm lateral, vertical or continuous-wave condensation. Motor-driven extruder handpieces and pluggers can also ensure a complete fill after syringe application of gutta percha.

Still other systems are designed around core carriers that warm the gutta percha on the obturator prior to insertion into the canal. Core-carrier-based systems are favored by a number of clinicians, who see their advent as significant. These systems consist of an obturator: a master gutta-percha cone on a handle that allows easy transfer between a warming device and the tooth. Silicone stoppers on the handle are set to reflect working length determined by the use of a size verifier and confirmed with a radiograph. Prior to placement, the canal is coated with sealer and the obturator is warmed to thermoplasticize the gutta percha. It is reported that this method helps ensure a three-dimensional fill in less time than it takes to condense material. Further, no difference in quality can be discerned. Depending on the system used, handles can be easily removed before or after seating of the cone.12–14

Gutmann notes that in one manufacturer’s core-carrier systems, the core is made of cross-linked, stable and strong gutta percha. Cross-linking means that the polymer chains of the material are connected with one another to increase strength. “I personally favor the core-carrier technique for approximately 80% of cases because of adaptation of the softened gutta percha that is on the core to the intricacies of the shaped root canal,” Gutmann explains. And Pantera agrees. “Certainly the number, types, and improvements of delivery systems for warmed gutta percha are important. The further development of carrier-based systems using modified gutta percha as the carrier core has been welcomed by many general practitioners,” Pantera says.


Apex: The point of the root.
Bioactive: Interacts with the body.
Bioaggregate: Biocompatible powder composed of bioceramic nanoparticles.
Bioceramic: Ceramic materials designed for medical or dental use.
Biocompatible: Doesn’t harm the body.
Cemental formation: Refers to the cementum, which is the outer calcified layer of the tooth root that covers dentin.
Periapical: Refers to tissues surrounding the apex.
Spreader: Long, tapered hand instrument that is used to compress gutta percha into canal wall anatomy.
Thermoplasticize: Warm to a plastic state.


Overall, key opinion leaders stress that good obturation starts with effective shaping and cleaning of canals. “The requirements for long-term endodontic success are multifactorial,” says Barnett. “The main purposes of root canal obturation are to prevent re-infection/re-contamination from the oral fluids and to seal in any canal irritants (bacteria/biofilm) left behind. However, many cross-sectional, retrospective studies from several countries have all shown that poor-quality root canal obturation is associated with the presence of periapical disease as compared to teeth with higher-quality root fillings.”

Pantera adds, “It is less important what you put in than what you take out of a canal to ensure success. If we could actually sterilize, rather than sanitize canals, obturation would not be necessary. Many practitioners have examples of periapical lesions healing in the absence of obturation. However, since we cannot predictably eliminate bacterial etiology from canals, we seal behind what we have left behind. Thus the practical importance of obturation. The holy grail would be developing a material that actually strengthens the tooth after obturation.”

Until that day comes, clincians will continue to bridge canals. But how well each step in the RCT process is performed will determine whether they are building a bridge over trouble waters or a stairway to heaven.



  1. Himel VT, DiFiore PM. Endodontics: Colleagues for excellence: Obturation of root canal systems. American Association of Endodontists. Available at: Accessed November 21, 2017.
  2. Lee DK, Kim SV, Limansubroto AN. Nanodiamond-gutta percha composite biomaterials for root canal therapy. ACS Nano. 2015;9:11490–11501.
  3. Mohn D, Bruhin C, Luechinger NA, Stark WJ, Imfeld T, Zehnder M. Composites made of flame-sprayed bioactive glass 45S5 and polymers: bioactivity and immediate sealing properties. Int Endod J. 2010;43:1037–1046.
  4. Richardson IG. The calcium silicate hydrates. Cement and Concrete Research. Available at: Accessed November 21, 2017.
  5. Haapasalo M, Parhar M, Huang X, Wei X, Lin J, Shen Y. Clinical use of bioceramic materials. Microsurgery in Endodontics. 2015;32(1):97–117.
  6. Wang Z. Bioceramic materials in endodontics. Microsurgery in Endodontics. 2015;32(1):3-30.
  7. Trope M, Bunes F, Debelian G. Root filling materials and techniques: bioceramics a new hope? Microsurgery in Endodontics. 2015;32(1):86–96.
  8. Koch KA, Brave DG. Bioceramics, Part I: the clinician’s viewpoint. Dentistry Today. Available at: Accessed November 21, 2017.
  9. Kishen A, Peters A, Zehnder M, Diogenes AR, Nair MK. Advances in endodontics: Potential applications in clinical practice. J Conserv Dent. 2016;19:199–206.
  10. Debelian G, Trope M. The use of premixed bioceramic materials in endodontics. Giornale Italiano di Endodonzia. 2016;30(2):70–80.
  11. Hess D, Solomon E, Spears R, He J. Retreatability of a bioceramic root canal sealing material. J Endod. 2011;37:1547–1549.
  12. Clinton K, Van Himel T. Comparison of a warm gutta-percha obturation technique and lateral condensation. J Endod. 2001;27:692–695.
  13. Abdulrazzaq Alhashimi R, Foxton R, Romeed S, Deb Sanjukta. An in vitro assessment of gutta-percha coating of new carrier-based root canal fillings. The Scientific World Journal. Available at: Accessed November 21, 2017.
  14. Li GH, Niu LN, Selem LC, et al. Quality of obturation achieved by an endodontic core-carrier system with crosslinked gutta-percha carrier in single-rooted canals.
    J Dent. 2014;42:1124–1134.


From MENTOR. January 2018;9(1): 22-24, 26, 28.

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