10/7/2016

Regenerative Endodontic Therapy: The Fountain of Youth for aDying Tooth

journal.iabdm.org/regenerative-endodontic-therapy-the-fountain-of-youth-for-a-dying-tooth/

By Valerie Kanter DMD, MS

Vital Pulp Therapy

Vital Pulp Therapy (VPT) can be performed when a young tooth is suffering from trauma or deep decay yet still hassufficient pulpal blood flow to promote healing. The treatment involves removing diseased tooth structure whilemaintaining the health and longevity of the pulpdentin complex. Not only does VPT offer a young permanent tooth achance at survival; it actually creates an opportunity for the tooth to become stronger by continued root formationand wall thickening during the maturation process. VPT has been proven as a successful treatment modality forimmature teeth, especially when performed in the early stages of pulpal inflammation. As bacteria and theirbyproducts infiltrate the dentinal tubules, they induce odontoblasts to recruit cells of the immune system(chemokines), produce inflammation (pro-inflammatory cytokines), and attempt to modulate the inflammatoryresponses (antiinflammatory cytokines). This fine-tuned network facilitates the eradication of invading microbes butmaintains a balance between pro and anti-inflammation, which creates a favorable environment for tissue repair.

Mature permanent teeth may be more limited in their potential for pulpal regeneration due to decreased pulpal bloodflow, and VPT may not always be a viable treatment option. In these deep carious lesions, bacterial byproducts andtoxins diffuse towards the pulp, causing a series of host reactions that take place in order to reduce dentinpermeability. The most common reaction is dental sclerosis that results from the deposition of apatite and whitlockitecrystals within the dentinal tubules. These degenerative changes within the odontoblasts develop beforeinflammatory changes occur within the pulp. However, if the rate of caries progression is faster than the rate of pulp‐dentin reactions, chronic pulpal inflammation is inevitable. According to the strangulation theory by Professor ACBrown, as inflammation continues, edema in the pulp is impossible because it is encapsulated in rigid walls ofdentin and enamel. Instead, pulp tissue pressure rises, causing compression of tooth pulp venules and veins,leading to an increased postcapillary vascular resistance. This vicious cycle continues, causing ischemia, hypoxia,and eventually necrosis or pulp death. To prevent the need for more aggressive endodontic procedures orextraction, timely intervention is needed before the bacteria colonizing the dental pulp progress to more apicalradicular structures.

When treatment planning these cases and managing carious pulp exposures, it is critical to execute VPT in a sterileand precise manner. There are many factors that affect the success of this type of treatment, including patientsymptoms, the age of the patient, and the size of pulpal exposure, although the biggest challenge in VPT ispredictably diagnosing the degree of pulpal inflammation and properly managing the exposed pulpal tissue.

VPT is initiated by removing the areas of contaminated dentin sequentially from the outside of the tooth structurefirst, then moving towards the central and deeper layers of the cavity preparation. This can be performed with aseries of sterile burs, which should be continuously replaced during the procedure as the preparation gets closer tothe roof of the pulp chamber. Alternatively, the access preparation can be performed directly with Erbium lasers(Er:YAG), which allow a conservative access by targeted ablation of infected enamel and dentin. There are benefitsin using a laser to remove the last layer of infected dentin, as you do not have to stop the access preparation tocontinuously discard and replace the bur to attain a sterile cutting edge. All laser wavelengths set at specific powerlevels can effectively destroy bacteria because of their photothermal effect on the cell wall. The initial damage takesplace via alterations in the osmotic gradient leading to swelling and cellular death. It should be noted that Gram-

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negative bacteria are more easily destroyed with less energy and irradiation compared to Gram-positive bacteria.This is due to the structure of the cell wall. Gram-negative bacteria are usually responsible for the primary infection.Some examples of these initial inhabitants are Prevotella and Porphyromonas, which are both black pigmentedGram-negative anaerobic rods. As the access is extended towards the pulp, the laser decontaminates the dentinand removes bacterial debris. Laser technology has proven to be effective in improving the prognosis of pulpcapping procedures on teeth affected by deep caries pathology.

Incremental rinses with a disinfecting solution also help remove debris and contaminants from the walls of the cavitypreparation. Sodium hypochlorite (NaOCl) and Chlorhexidine gluconate (CHX) have been deemed the gotodisinfecting solutions in endodontics. NaOCl is well known for its ability to disinfect canals and dissolve soft tissue intraditional root canal therapy. It is the only solution that has been shown to eliminate biofilms without enhancedirrigation techniques. CHX has the ability to bind to amino acids in dentin and kills bacteria for several hours afterinitial contact. It has broad-spectrum activity and is specifically effective against Gram-positive bacteria likeStreptococcus mutans, but it is not able to completely eliminate biofilms.

Both of these solutions have major biological drawbacks. They have significant cytotoxic potential on vital humanoral cells, such as odontoblasts and fibroblasts. The cytotoxic effects include inhibition of protein synthesis, inhibitionof DNA synthesis, induction of apoptosis, and cell necrosis. Accidental extrusion of NaOCl into periapical tissuescauses severe tissue reactions like swelling, pain, hematomas, paresthesia, and tissue necrosis. NaOCl alsodecreases the bond strength between dentin and resin, making CHX a better option for single visit VPT. While CHXis a safer alternative, it has been linked to reactions such as desquamative gingivitis and dysgeusia. Many questionremain. Do the benefits of these solutions outweigh the risks? Are there safer alternatives that are equally effective?

Ozone is an alternative and more biological antiseptic agent that has shown success in endodontics. Ozone isconsidered one of the best bactericidal, antiviral, and antifungal agents available. With only 20 seconds of exposure,ozone effectively eliminates 99% of microorganisms in primary carious lesions and also has the ability to destroyoral biofilms and their byproducts. This highly unstable form of oxygen acts as a strong and fast oxidizer of thebacterial cell walls and cytoplasmic membranes. Ozone can penetrate several millimeters into infected dentin,making it possible to disinfect deep decay without risking a pulp exposure. Some skilled practitioners avoid pulpexposures by applying direct ozone gas to deep carious lesions, followed by an indirect pulp cap with a glassionomer cement. After a few months, the pulp recovers by forming a new dentin bridge over the pulp chamber. Thedentist can then go back into the cavity preparation and safely remove any remaining infected dentin. More researchis needed to determine if ozone can completely sterilize the inner layers dentin, where over 65,000 dentinal tubulesare present. Ozone gas has many benefits, including the ability to significantly increase bond strength, but it shouldstill be used very carefully due to potential cytotoxicity. While any potential ozone toxicity is neutralized by thepowerful antioxidant system of blood, odontoblasts may still be vulnerable.

Contrary to NaOCl and CHX, aqueous ozone has essentially no level of cytotoxicity on human oral cells, making itthe most biocompatible antibacterial solution available. Ozone, mixed into water or plant extracts, allows dentistsand patients to use an agent that eliminates infections, promotes healthy gum tissue, and accelerates surgicalhealing. The emergence of ozone and ozonated water shows promise for the field of Endodontics and, specifically,VPT. Exact protocols and further studies are needed to show the ability of different concentrations of ozone andaqueous ozone to safely breakdown oral biofilms.

In the classic protocol for VPT using an irrigant such as NaOCl or CHX, the contaminated dentin should becompletely removed, even if that includes the roof of the pulp chamber. Whether a partial or complete pulpotomy isperformed, it is critical that all inflamed pulp tissue is removed in order to get predictable results with VPT. Capping ahealthy pulp gives very high success rates. On the contrary, capping an inflamed pulp gives very low success rates.Fortunately, in an immature tooth, pulpal inflammation is usually superficial and rarely extends past the canalorifices. This allows great healing, continued growth and vitality, even if a complete pulpotomy is necessary. Theunderlying healthy pulp tissue should be disinfected with the irrigation solution of choice, and bleeding must be

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Figure A. DentinPulp Complex: Tubular dentin (D). Predentin (Pd). Odontoblasticlayer (Od). Cell-free zone (horizontal arrow). Cellrich zone (vertical arrows).

Figure B. Severe Inflammatory response 60 days after a deep cavitypreparation in a human premolar treated with total etch, bonding agent, and

composite resin. Note the zone of inner dentin resorption (arrow).

controlled before the site is covered.

Historically, [Ca(OH)2] was deemed the ideal material for VPT because it has the ability to induce a calcific barrierover the exposed pulp tissue. This bridge formed by tertiary dentinogenesis was initially thought to be a completeprotective layer. In more recent years, we have discovered that carious exposures treated with [Ca(OH)2] basedmaterials fail almost 80% of the time within 10 years of the initial treatment. This may be due to tunnel defects thatform in the calcific barrier over the pulp chamber.

Histological studies of the pulp-dentin complex have found that these calcific barriers actually contain tunnel defectsthat can allow bacterial infiltration into the vulnerable pulp tissue. Figure C shows a tunnel defect in the hard tissuebarrier (HB) present in a [Ca(OH)2] pulp cap. The defect is indicated by the horizontal arrow.

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Since its release in 2002, Mineral TrioxideAggregate (MTA) has proven to be a more reliablematerial to use when initiating the formation of acalcified dentin bridge, resulting in higher successrates and less pulpal inflammation. MTA iscomposed of tricalcium silicate, bismuth oxide,dicalcium silicate, tricalcium aluminate, and calciumsulfate dihydrate. MTA recruits dental pulp stemcells (DSPCs) for the formation of reparative hardtissues. It has the ability to scavenge fossilizedbioactive dentin matrix components such astransforming growth factor β1 and upregulatesexpression of other transcription factors involved indentinogenesis. The hard tissue barrier formationhas been classified as dystrophic calcificationrather than formation of new dentin, representing amaterial that is similar to a pulp stone.

From a clinical perspective, MTA has a majordrawback. Its poor handling characteristics anddelayed setting time make it difficult to work with,especially in pediatric patients. We now have a lineof true bioceramic materials available that are mucheasier to use and can set in as little as 20 minutes.Brasseler USA® EndoSequence Root RepairMaterial is a premixed, flowable Calcium Silicatebioceramic. It is created with nanotechnology andcan actually be injected into the operative site with amoldable plastic syringe (0.012 capillary tip). Thesenewer bioceramics are exceedingly biocompatible,antibacterial, non–toxic, do not shrink, and arechemically stable within the biological environment.They can actually form hydroxyapatite and surpassMTA in their ability to recruit DSPCs. When in place,these new materials create a bond with dentin dueto their hydrophilic nature. The calcium silicates inthe powder hydrate to produce a calcium silicate hydrate gel and calcium hydroxide. The calcium hydroxide reacts

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Figure C. This image shows the pulpdentin complex 60 days after applying

[Ca(OH)2] to the surface of the pulp tissue. A hard tissue barrier formation (HB)with cellular inclusions (vertical arrows) is underlined by a novel layer of

odontoblastlike cells. Note the tunnel defect (horizontal arrow).

Figure D. This image shows the pulp-dentin complex 60 days after applying MTAto the surface of the pulp tissue. A defined hard tissue barrier formation

underlined by a new layer of odontoblastlike cells (arrow).

with the phosphate ions to precipitate hydroxyapatite and water. It even utilizes the water inside the dentinal tubulesto drive the hydration reaction of the material,thereby shortening the setting time. It does all thisand also maintains a high pH environment thatbacteria cannot tolerate, creating a sustainablebacteriafree environment.

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All dentists can benefit from this upgrade in technique for VPT procedures. The recommended protocol: Isolate thetooth under a rubber dam and disinfect the exposure site. Apply a small amount of the EndoSequence Root RepairMaterial (ESRRM) from the syringe, or take a small amount of the ESRRM putty from the jar, and place this over theexposure area. Then cover the bioceramic repair material with a glass ionomer restoration. Following the placementof this material, proceed with the final restoration, including etching if required. Now we have the tools tosuccessfully and predictably complete singlevisit VPT.

With the widespread use of dental operating microscopes and recent developments in biomaterials, endodontistsare embracing the idea of maintaining tooth vitality, even in mature permanent teeth. Dr. Jung Lim, a fellow professorat the UCLA School of Dentistry, calls this a Vital Root Canal Procedure: “There is no better obturation material thanthe pulp itself.” Figures E – J represent a case he treated at his practice in southern California. A seven year-old boy,completely asymptomatic, had a deep carious lesion extending into the pulp chamber of tooth #19. Instead ofperforming a root canal treatment or placing a superficial pulp cap, a new approach was taken. After a specificprotocol in caries removal, involving a series of sterile burs and disinfecting rinses with .12% CHX, the coronal pulptissue was removed. The remaining radicular pulp tissue was determined to be stable by successful hemostasis.ESRRM was used to cover and protect the remaining pulp tissue. As shown in the one-year recall image, the rootstructure continued growing. The clinical exam revealed tooth #19 and its supporting tissues were alive and well.

Figure E. Preoperative radiograph of tooth #19.

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Figure F. Tooth #19 under rubber dam isolation with a deep carious lesion present.

Figure G. Access opening after removing caries and all inflamed coronal pulp tissue.

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Figure H. Bioceramic paste has been placed over the pulpal floor after thoroughdisinfection.

Figure I. Post-operative radiograph of tooth #19

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Figure J. One year recall radiograph of tooth #19 with closure of apices.

Pulpal Revascularization

When an immature permanent tooth is injured by deep decay or the blunt force of an accident, its growth can becompletely halted. The pulp in a young person serves a vital role in the tooth’s early development of the multi‐layered dentin needed for a mature root system. Compromising the pulp at this stage of growth can shut down rootdevelopment, leaving an open apex and signs of periapical pathology. Weakening of the tooth, infection, brittleness,and darkening are just a few consequences of this type of early dental trauma.

Pulpal Revascularization translates to complete restoration of pulpal function, literally waking the dormant tissuefrom the dead tooth and revitalizing the necrotic pulpal tissue. The goal of regenerative endodontics is to reinstatenormal pulp function in necrotic and infected teeth that would result in reestablishment of protective functions,including innate pulp immunity, pulp repair through mineralization, and pulp sensibility. In the uniquemicroenvironment of the dental pulp, the triad of tissue engineering would require infection control, biomaterials, andstem cells.

The majority of children and teenagers who have an infected tooth with an open apex will qualify for PulpalRevascularization. Traditionally, the procedure involves a two-step process. The first step thoroughly disinfects theroot canal system by standard endodontic access and canal irrigation without any form of instrumentation.Classically, NaOCl has been used to irrigate these teeth, although extreme care must be taken due to the enlargedapical opening. Calcium hydroxide is avoided because it could weaken the root dentin, and the high pH destroysvital apical cells, including SCAP. Non-toxic, biocompatible solutions such as ozonated water may also be effectiveat eliminating the presence of bacteria and deactivating the necrotic toxins in these teeth. More research in the areaof biological disinfection techniques is certainly warranted. In addition to extensive irrigation, a triple antibiotic pastehas been proven effective for bacterial eradication prior to revascularization procedures. This mix includesmetronidazole, minocycline, and ciprofloxacin. It is left in place for 1 month to completely eliminate the opportunityfor bacterial colonization to continue inside the canal space. Organic ozonated oil or gas may be acceptablealternatives for practitioners who prefer to avoid antibiotics. Future studies are needed in this field of dentistry.

The second visit is when all the amazing biological events take place. After a complete flush withethylenediaminetetracecticacid (EDTA), bleeding is stimulated at the apex and a scaffold is formed at the level of theCEJ. A scaffold, such as a natural blood clot or platelet rich fibrin, provides support for cell organization,proliferation, differentiation, and vascularization. PDLSCs, mesenchymal stem cells which arise from the periodontalligament, have proven to be multipotent and able to differentiate into odontogeniclike cell lines. Growth factors such

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as bone morphogenic protein, transforming growth factorβ, vascular endothelial growth factor, and fibroblasticgrowth factor are all key players in this process. The new odontoblast lineages arise from stem cells in pulp tissueor apical papilla and begin to lay down atubular dentin at the apex and lateral aspects of the root canal.

A material such as MTA or ESRRM is placed over the scaffold. Well known properties of these materials includetheir osteoinductive and osteoconductive abilities, and the potential for hydroxyapatite formation.

In this monumental case presented by endodontic pioneers Dr. Francisco Banchs and Dr. Martin Trope, therecommended antibiotic paste was placed in the canal of an immature, necrotic lower second premolar. After 26days, the patient returned for follow up treatment, which included a specific irrigation protocol, followed by theinitiation of a novel blood clot developing inside the canal. MTA was placed over top, followed by cotton and Cavit. Atwo-week follow-up appointment was made, and the composite was then placed directly over the firmly set MTA.Due to its long setting time, a direct composite cannot be placed over freshly packed MTA. An option to reduce thenumber of office visits involves placing a glass ionomer base or flowable composite directly over the MTA orESRRM. Once a seal is created, the area can be etched, and the permanent composite restoration should bebonded in place of the access opening. Because coronal leakage is a major risk factor for clinical success, animmediate permanent restoration eliminates the risk of contamination between appointments. An 18 month recall forthis case shows complete resolution of the periapical abscess and continued root formation. The clinical examreveals a vital and responsive pulp. Even though this protocol has proven successful for over a decade, it still feelsremarkable every time a tooth is literally brought back to life. This case was featured in the American Association ofEndodontics’ Spring 2013 edition of Colleagues of Excellence.

Figure K. Preoperative radiograph of tooth #29 with an open apex and a largeperiradicular radiolucency.

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Figure L. Radiograph 26 days after the permanent triantibiotic paste was placed.Radiographic signs of healing are evident.

Figure M. Radiograph showing the placement of MTA approximately 3 mm below theCEJ.

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Figure N. 18 month recall radiograph shows complete healing and continued rootdevelopment.

More research in this field is needed to create a completely effective and biological disinfection protocol. The tripleantibiotic paste first recommended by Banchs and Trope has been shown to be cytotoxic to stem cells at currentrecommended concentrations. NaOCl and CHX have been shown to reduce the attachment of stem cells to dentin.Another area for future research is to evaluate the antibacterial and cytotoxic effect of direct ozone gas on a necroticimmature tooth. With current research proving ozone gas is able to eliminate 99.9% bacteria after 20-secondexposure, ozone could be a key player in successful revascularization. Ozone quickly dissipates in water and is astrong oxidizer that disrupts the cell walls and cytoplasmic membranes of bacteria. Currently, theserevascularization cases are time sensitive and success relies heavily on bacterial elimination and patientcompliance. If total disinfection can be safely attained with ozone therapy, the need for a second visit and risk ofinterappointment leakage could be completely eliminated.

Laser Dentistry

Laser dentistry in many forms has been an exciting addition to the field of endodontics. A breakthrough style of laseractivated irrigation, photon induced photoacoustic streaming (PIPS®), was created by Dr. Enrico DiVito at theArizona Center for Laser Dentistry. It has been shown to be superior to traditional needle irrigation and ultrasonic forremoving biofilm from canal walls. A recent in vitro study showed just 1 minute of PIPS laser activated irrigation with5% sodium hypochlorite eliminated Enterococcus faecalis from infected teeth and inhibited bacterial regrowth.Specially engineered tapered and stripped tips are used along with extremely short, digitally controlled low energypulses (20 mJ at 50 microseconds) to create a powerful shockwave in the irrigant solution that is non-thermal. Thisnovel energetic movement of solutions has been shown to more thoroughly clean the complex threedimensional rootcanal system compared with traditional techniques during conventional root canal therapy. While this exactwavelength is very beneficial for irrigation, it may not be as helpful for disinfection during revascularizationprocedures, specifically due to the large open apex in these cases. Further research has shown that PIPS alsoremoves necrotic debris from dentinal tubule structures, thus significantly improving the current proinflammatorypotential seen with conventional methods.

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It would be preferable to avoid the use of chemicals all together in endodontics, especially when dealing withchildren. Traditional pulpotomies in primary teeth have used agents such as formocresol, which can be absorbedand distributed throughout a child’s body within minutes of its application. Various lasers have shown to be effectivein pulpotomy treatments without the use of chemicals. The lasers have the ability to remove inflamed coronal pulptissue and bacteria, while keeping the underlying radicular pulp completely healthy. Er:YAG, Nd:YAG, and diodelaser systems alike have shown clinical success and are proven alternatives for pulpotomy procedures, eliminatingthe need for chemical additives. Laser therapy now has a central role in progressive regenerative endodontics.

Lasers are also capable of phototherapy that involves the application of lowpower, monochromatic, coherent light toinjuries and lesions. The process is now being referred to as Low Power Laser Therapy (LPL), Low Level LaserTherapy (LLLT) or Photobiomodulation (PBM). PBM uses specific frequencies and pulses of energized light topainlessly activate tissue repair and relieve pain. PBM has proven to successfully induce wound healing byincreasing local fibroblast cell numbers, mitotic activity, collagen synthesis and neovascularization. A study byUsumez showed this laser, at a wavelength of 1064nm, produced an increase in expression of growth factors likePDGF and bFGF during wound healing. A research team at Harvard University, in conjunction with the NIH’sNational Institute of Dental and Craniofacial Research, set out to investigate if PBM could induce stem cells toregenerate components of teeth. Their efforts have proven successful. Using animal studies, they discovered thistype of laser therapy induces the production of a protein known as ROS, reactive oxygen species. ROS stimulatesdentin production by activating TGFB, which is an important signaling molecule in promoting dental stem celldifferentiation. Similar results were achieved in the lab with human dental stem cells, which showed the ability toregenerate dentin after PBM.

We still have a lot to learn about PBM in regards to Regenerative Endodontics. These quick and painlessprocedures could have a profound effect on the entire field of dentistry. Our quest to understand the clinicalapplications, scope of safety, and efficacy of these emerging treatments will continue. It is clear that the launchingpad for success has been created. Regenerative endodontic treatments hold promise that a functional pulp dentincomplex can be recreated. In a little more than 10 years of research, there have been significant developments inthe clinical approaches available to heal our patients.

Endodontists strive to offer the absolute best treatment options available for patients who want to retain their teethafter years of wear, tear, and bacterial invasion. Dr. Weston Price himself believed this is an acceptable option forsome people. “I am not ready to draw the line so rigidly as to state that all root filled teeth should be extracted forevery patient or for all patients at any given time, though I do believe there is a limit of safety for all such teeth andfor each and every patient.”

Our profession has a profound obligation to be skeptical about all aspects of patient care. Endodontics is just onearea deserving continued scrutiny. Currently, most evaluations of endodontic success have used macroobservations–freedom from pain, swelling, drainage, and radiographic observations. How valid and comprehensiveare these criteria for “success”? Just like our prior belief in the efficacy of calcium hydroxide “pulp capping,” we nowknow from microscopic evidence that these barriers that looked so effective on radiographs were nothing more thanleaky sponges leading to further pulpal degradation. In addition to confirming the subjective criteria for healing, it isimportant that we attain data on the genetic makeup of potential species associated with each treated tooth and itssurrounding structures. DNA Connexions is a company that offers a Full View Test, which identifies bacteria,viruses, fungi, and parasites in teeth, blood, tissue, and other biological samples. It tests for 88 different pathogens,including tetanus, botulism, diphtheria, HPV 16 and HPV 1, Candida albicans.

It is incumbent upon us to keep looking further into all these biological processes in order to provide our patients thevery best of care. Our obligation is not necessarily to preserve the teeth as much as the entire body. Perhaps withinanother 10 years, stem cell therapies will go as far as regrowing teeth that become compromised by human habitslike sugar consumption and basketball injuries. Despite the controversy that exists among the various dental groupsaround the world, I believe we can all agree on one thing: The natural vital pulp tissue is in fact the best possible

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obturation material of the root canal system.

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About the Author

Dr. Valerie Kanter is a Board Certified Endodontist practicing in Los Angeles, CA. Shegraduated from the University of Florida College of Dentistry with her DMD and MSdegree. She is a third generation dentist, with dental licenses in California and Florida,where she earned numerous awards of excellence. In addition to her studies, she hasgained many mentors from the highest echelons of endodontics because they recognizeher unique skill set and competency. Dr. Kanter teaches post-graduate residents, pre-doctoral DDS and foreign dental students in Advanced Clinical Endodontics at UCLA.She enjoys the opportunity to help students acquire real-life clinical skills beyond thosethat can be taught in a classroom. Dr. Kanter advocates a patient-centered, biologicalapproach to endodontics. She is a trailblazer in the adaption of stem cell and lasertechnologies, as a more natural and chemical free approach to the treatment of root canals. She is at the forefront ofthe very latest research and studies on regenerative endodontics and less invasive laser therapies to providepatients with the best care her specialty affords.

Contact: Beverly Hills Dental Health & Wellness465 N Roxbury Dr., Ste. 911Beverly Hills CA 90210310-275-4180AskDrVal.com

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