Endodontic retreatment of failed root canal therapy is primarily a specialist procedure. This fact notwithstanding, the clinical strategies used in retreatment have crossover value to the general practitioner in non-surgical orthograde root canal therapy. In addition, retreatment is one of the primary means for resolution of failed root canal procedures along with apical surgery. All strategies, concepts and materials that optimize retreatment, improve the probabilities for healing of failed cases and have an effect on decision making in the extraction/implant versus tooth retention/endodontic continuum. Many of these strategies and concepts will be discussed here.
Recently, a patient was referred to me with a clinical case that had a number of features of interest to the general practitioner in removal of warm carrier based devices (WCBD), subsequent achievement and maintenance of apical patency, inter appointment medication, obturation technique as well as placement of the post endodontic coronal seal. The case is detailed in a step-by-step manner and includes a comprehensive description of the RealSeal* bonded obturation material utilized.
Subjective and Objective Findings
Tooth #16 had been growing more sensitive to chewing and was becoming spontaneously painful over a period of weeks by the time the patient was referred to RM (Figs. 1 & 2). The pain was characterized by a dull ache and was localized to #16. When it became acute enough, the patient sought treatment from their general dentist. Other than years ago, the patient could not remember how long it had been since the root canal was done. There was nothing untoward reported to the patient at that time of the original treatment. The tooth was crowned without delay at that time. No recent restorative treatment had been rendered in the area.
No obvious coronal leakage or defects in the crown margins were visually or radiographically evident. There was neither swelling nor thermal sensitivity. Clinically, tests for percussion, palpation, mobility, and probings were normal for all of teeth in the quadrant except #16. Percussion sensitivity was noted on #16. Palpation sensitivity was also present on #16, albeit mildly. Mobility and probings on #16 were within normal limits. An examination of the periodontal tissues around #16 was within normal limits, no fistula, drainage or other abnormalities were found.
Radiographic Findings and Interpretation
Radiographically, a lesion of endodontic origin was noted at the apex of the palatal and mesial buccal (MB) root. The relative lack of taper to the preparations and uniformity of the obturation had all the hallmarks of a WCBD. This factor influenced the techniques needed to clear the canals to make them ready for cleansing and shaping.
In all three canals, the coronal preparation was excessive. The taper narrowed rapidly and mid root and was not continuous. The minimal taper and the relatively small apical preparations virtually assured that the irrigation performed at the time of treatment was inadequate. Relatively small taper and apical preparations do not promote optimal exchange of irrigants in the apical third.
Length control in the initial treatment was inaccurate. It is unlikely that any of the roots had been cleansed, shaped and obturated to their minor constriction (MC) initially. While they could have resorbed, there were no sealer puffs evident, an obvious sign of previous apical patency. No apical delta canals appear to have been filled. All of the termination points of obturation appear approximately 3mm from the radiographic apex. While the MC can be up to 3mm away from the anatomic apex, the chances that all three MC’s were simultaneously this distance is very low. The apical obturation of all canals also appears blunted. Obturation does not to come to a tapered point as expected. This blunted apical obturation appears wholly devoid of curvature, a finding that would be very atypical clinically. If the canals had been instrumented and filled to the MC, some degree of apical curvature would have been expected. For all the above reasons, it was assumed that the apex was blocked with debris in each of the canals. Methods to gain patency are described below.
Radiographically, it was not conclusive whether an MB2 canal had been treated previously, but it did not appear so. The endodontic literature is quite clear that approximately 95% of upper first molar MB roots have two canals. It was reasonably expected that a fourth as yet untreated canal would be found during retreatment.
A diagnosis of failed root canal was made, the patient was informed of the recommended procedure, told of the alternatives and risks, all questions were answered and treatment commenced. The patient was told that treatment would likely be carried out in two visits to allow for the placement of calcium hydroxide for its antimicrobial benefits.
The steps taken to treat the tooth are detailed below:
1) After anesthesia, the rubber dam was applied.
2) The surgical operating microscope (SOM, Global Surgical, St. Louis, MO, USA) was used for all treatment phases. The SOM improves the accuracy and efficiency of the entire procedure, especially MB2 canal location and management. In my operatory, the SOM light source is used to illuminate the tooth without a separate overhead light.
Access preparation under the SOM, does not require that the occlusal outline of the preparation be larger than it otherwise would. If anything, the SOM conserves tooth structure through smaller occlusal preparations. SOM lighting, magnification and visualization show the clinician where tooth structure must be removed and alternatively where it can be left in place, facilitating a conservative access (Fig. 3).
3) Access was made through a porcelain crown. Efforts were made to resist porcelain fracture upon widening the access by using copious water spray and ultrafine diamonds. Water spray was used until all of the orifices were clearly identified and ready for carrier removal. Despite the lack of radiographic evidence of coronal leakage, overt leakage was observed after access.
4) As expected, once the orifices were reached, the plastic carrier of a WCBD was clearly visualized in each of the canals.
Ultrasonics (the Elements Ultrasonic Unit*, and Red Star* tips) were available for uncovering the MB2 canal. While available, in this clinical case, they were not needed, MB2 canal location was immediately obvious once the correct dimensions of the access cavity were prepared. Often, but not in this clinical case, a flat ultrasonic tip like the Red Star 2 (RS2) is needed to remove dentin and act as a “sander” to fully expose the isthmus and guide the clinician to the MB2 canal. In cases where MB2 canal location is not straightforward, it may be necessary to place a drop of sodium hypochlorite over the isthmus. The resulting bubbles from the digestion of pulp tissue can direct the clinician to the exact location of the MB2 canal. This method can also of course be employed in any calcified canal location. Use of caries indicators or methylene blue dye also can be helpful in this regard.
5) The WCBDs present were an obstacle to achieving patency of the canal and subsequent optimal cleaning and shaping. Nontraumatic and complete removal of WCBDs is a vital step towards revising the previous treatment and doing so without exacerbating a potential iatrogenic event. Less than ideal removal of WCBDs can remove excessive tooth structure making the tooth susceptible to subsequent vertical fracture, perforation, and canal transportation of all types amongst a host of potential problems. Smaller and less tapered WCBDs are often found cliniFigures cally in long and curved roots. Smaller devices placed into underprepared canals, have the potential to become tightly wedged with frictional retention making removal problematic, especially w
ith the methods available previously.
Emphasis was placed on removal of the existing WCBDs and achieving patency first, then negotiation of the MB2 canal. Carrier removal was achieved using the Twisted File (TF)* and solvent in the form of chloroform that had been predawn into syringes (Fig. 4). TF is manufactured by the utilization of R (Rhombohedral) crystalline phase technology. R phase is the intermediate nickel titanium (NT) crystalline phase configuration between austenite and martensite that allows twisting of NT. Austenite is the non-stressed crystalline phase configuration that is present when NT files are at rest and no stress is applied to them (i. e. when they are in the pack before use). Martensite is the crystalline phase configuration of NT that is present when NT deforms in response to the placement of a stress upon it. Grinding NT leaves microcracks, areas of metal roll over and other irregularities on the surface of the metal after manufacture. As a result, when stresses are placed upon the metal in function, it is at these microcracks that the RNT files preferentially fracture when exposed to excessive torsion and cyclic fatigue forces. Since TF is never ground against the grain structure of the metal and has no perpendicular microcracks, it possesses flexibility, fracture resistance and cutting efficiency far surpassing ground NT files.
The existing orifice preparation in all canals appeared to have been made with a Gates Glidden drill. The over enlargement of the orifices made attainment of a continuous taper impossible after re-treatment. This over enlargement also increased the risk of perforation dramatically during removal of the WCBDs, especially in the MB and DB canals. As a result, the coronal third did not need enlargement beyond that already present and efforts were made to prevent creating a perforation in the removal of the WCBD.
With the correct rotational speed and pressure (described below) TF can grind through the plastic of WCBDs efficiently and with little risk of breakage. The initial TF tapers entered into the MB and DB canals were conservative, .08 tapered TF instead of .10 TF. The .08 TF was rotated at much higher rpms than TF technique for orthograde first time treatment, 1,200 rpm versus 500 rpm. Taking the .10 TF into the MB and DB canals, especially to mid root, could have caused perforation. The palatal canal required a .10 and .08 TF. If a larger TF does not make apical progress during WCBD removal, the next smaller TF should be used. For example, in removal of the palatal WCBD, the .10 TF would not make apical progress without force, but a .08 TF advanced rapidly.
For an average device, removal might take 4-6 insertions as was the case detailed as each of the carriers was removed in approximately five insertions. Insertion of TF into the WCBD during removal was gentle and passive. When undue resistance was encountered, the file was removed. Using the speeds above, TF literally shreds the WCBD providing access to the apical anatomy which in this clinical case was untouched.
After the TF reached the apex and the bulk of the WCBD was removed, a drop of chloroform was placed into each canal and the remaining shards of the carrier and gutta percha were lifted coronally with Hedstrom files and wicked out of the canal, respectively.
6) Once the carriers were removed from the canals, attention was given to negotiation of the MB2 canal and achievement of patency in the other three canals. As mentioned, it was assumed that the apex of all of the ca nals were blocked with debris and that significant effort would be needed to regain patency. Copious numbers of small hand K files (6-10) were available in the effort to achieve patency. These hand K files were entered into canals precurved with EndoBender pliers* with the goal of matching the bend of the hand K file with the expected curvature of the root.
7) Negotiation of the other canals (MB, DB, Palatal) to assure patency was carried out gently and passively (after carrier removal) in a similar manner. After precurving the hand K files, each was inserted to resistance and if apical advancement was possible the file was taken further until the tactile perception of a “pop” was obtained at the apex or an electronic apex locator clearly registered the MC. If a hand K file was pulled from the canal and showed excessive distortion it was either cut to create a slightly shorter hand file or a new hand file was selected, precurved, and reinserted to make apical progression. Patency was achieved easily in the MB, DB and Palatal roots as the canal beyond the WCBDs in all roots had not been touched in the previous treatment.
8) Once patency was achieved, cleansing and shaping progressed as it would have in any clinical non-surgical orthograde case. A glide path was created in all roots so that before TF enlargement, the canal had a minimum #15 hand K file diameter before preparation. TF was used crown down in all roots from the orifice to the apex. The .08 TF was used in a single file technique in the MB and DB canals. The palatal canal was instrumented with two TF files (.10 and .08) used successively and alternatively until the apex was reached. Each TF insertion was passive taking approximately 2-3 seconds. The TF was inserted to resistance and removed. After each insertion, the canal was irrigated and recapitulated followed by the next apical TF insertion.
In this clinical case, .08 TF was used as a single file strategy for canal enlargement because the MB and DB canals accepted them passively moving toward the apex. In the palatal canal, more than one TF taper was utilized because the .10 TF met undue resistance.
In the most general terms, larger and less complex roots allow the use of larger TF tapers (.10) and smaller more complex roots will require smaller TF tapers (.08 and .06). In clinical terms, the palatal root of an upper molar or the distal root of a lower molar will usually accept a .10 TF taper. The mesial root of a lower molar, which is more complex, generally allows insertion of a .08-tapered instrument. With TF experience, doctors will find that they can prepare roots with fewer instruments and using fewer insertions than they thought previously possible. Clinically, this means that what was previously a 2 file TF case can become a 1 file TF case and what might have taken five insertions might, with experience, take three or four. An initial estimate of the TWL was taken before the case started (giving an estimated working length). In each canal, once the first hand file achieved patency and reached the estimated working length, an apex locator was put onto the hand K file and the first determination of TWL was made. TWL was verified when the first TF reached the TWL and again electronically, after the last TF was employed.
9) Bactericidal irrigation was accomplished with chlorhexidine 2.0%. The chlorhexidine was heated and activated. Activation took place ultrasonically with the aforementioned Elements Obturation Unit*, the Ultrasonic file adapter* and a #20 ultrasonic file blank (EMS, Dallas, TX, USA). At the end of the second visit, each canal was ultrasonically activated for approximately 30 seconds after the preparation with both the chlorhexidine and a final rinse of liquid EDTA, SmearClear* designed to remove the smear layer to allow a bonded obturation (Figs. 5-6). Chlorhexidine was chosen because of its effectiveness against E. faecalis, the predominant bacteria found in cases of endodontic failure.
10) As planned, the treatment was performed in two visits with an inter appointment dressing of calcium hydroxide in the form of UltraCal (Ultradent, South Jordan, UT, USA) and delivered with the Navi tip. Figure 7.
11) The authors use the RealSeal bonded obturation system. We believe that this is a necessary switch away from gutta percha. In addition to the rationale below, virtually every access, in our collective experience in many thousands of endodontic retreatment cases has shown overt evidence of co
ronal microleakage under the SOM in the form of combinations of wet cotton pellets left in the access, unset restoratives, caries, open margins, moisture which emerges from gutta percha during re-treatment, discolored gutta percha etc.
RealSeal was chosen instead of gutta percha. An ideal obturation material should be able to bond to dentin and sealer. Gutta percha does not bond to dentin. Gutta percha does not bond to sealer. Gutta percha has no inherent ability to seal canals. Gutta percha is dependent on a coronal seal to make it impervious to coronal leakage. In addition, in the study C. Maniglia-Ferreira, et al. “Degradation of trans-polyisoprene…” IEJ 40 P. 25-30, 2007 the authors stated that in gutta percha harvested from failed root canals (teeth with poor coronal restoration were not included) found that gutta percha degrades in the root canal system. Amongst other conclusions, they noted that:
a) “Polyisoprene degrades inside root canals… periapical lesions… associated with a more rapid onset of degradation.”
b) “… with periapical lesions, the number of years for significant degradation was reduced to 5 (P=0.0009).”
c) Degradation begins immediately after gutta percha is placed inside the root canal. They stated “15 years after RCT, the composition of gutta percha can be modified substantially with a resultant loss in the mass of the root canal filling material that may result in empty spaces inside the root canal system that could permit bacterial recolonization.” d)”The weight loss of the gutta percha polymer could make the material more porous and reduce its root canal sealing property.”
The above limitations argue strongly for a new and more functional obturation material. RealSeal has been shown in the endodontic literature, to a statistically significant degree relative to gutta percha, to stop the movement of bacteria that might migrate down the canal from coronal leakage both in vivo and in vitro.
To emphasize the ability of RealSeal (referenced as Resilon and Epiphany — the original trade names mentioned below) to achieve this goal, a clinically relevant study performed by Leonardo MR, et al. J Endod. 2007 Nov; 33 (11): 1299-303 is detailed here. In this study, “sixty root canals with vital pulps in three dogs were instrumented and obturated in a single session… root canals filled with Epiphany/ Resilon, with coronal restoration, had significantly less periradicular inflammation than root canals filled with gutta percha and Sealapex, with coronal restoration (p = 0.021). No significant difference was observed in the intensity of inf lammation between roots canals filled with Epiphany/Resilon with no restoration and roots filled with gutta percha and Sealapex with restoration (p = 0.269).” In essence, RealSeal, without a coronal restoration was, within the limits of this study, as effective in diminishing leakage as gutta percha that was protected with a coronal seal. The clinical significance of this finding cannot be overstated.
A discussion of how RealSeal performs this function, its chemical components and bonding mechanism are instructive and provided here for reference (see sidebar on page 52):
“RealSeal is a thermoplastic synthetic resin material based on the polymers of polyester and contains a difunctional methacrylate resin, bioactive glass and radio opaque fillers. RealSeal sealer contains UDMA, PEGDMA, EBPADMA and BisGMA resins, silane treated barium borosilicate glasses, barium sulfate, silica, calcium hydroxide, bismuth oxychloride with amines, peroxide, photo initiator, stabilizers and pigment… RealSeal is non-toxic, FDA approved and non mutagenic. With its radio opaque fillers, RealSeal is a highly radio opaque material. The sealer is resorbable. Aside from its capacity to be thermoplasticized, RealSeal can be dissolved with chloroform and retreated.” (Bonded Endodontic Obturation, Another Quantum Leap Forward for Endodontics Mounce Glassman Oral Heath Canada, July 2004).
Obturation with RealSeal One Bo nded Obturators
As a result, at the second visit, RealSeal One Bonded obturators (RS1) were used to obturate the MB, DB and palatal canals (Fig. 8). RealSeal is also available in a variety of master cone based tip sizes and tapers. The MB2 canal was obturated with SystemB and the Elements Obturation Unit.* The decision to use the RS1 form of the material in three canals and the master cone variety in the fourth was a matter of personal preference. The palatal canal was obturated with a #35 RS1, the MB and DB with #30 RS1 obturators.
RS1 obturators are present in a taper of .04 and come in tip sizes of 20-90. The obturators are heated in an oven, much like other WCBDs and placed to length within six seconds of the proper heating time. RealSeal self-etching sealer was applied to the canals with the Skini syringe and Navi tips (Ultradent, South Jordan, UT, USA). Before sealer placement, a size verifier was used to determine which RS1 was appropriate. The size verifier that is placed to length that fits passively is selected as the correct RS1 size.
RS1 obturators can be retreated as needed with TF in exactly the same manner as other WCBDs. Aside from TF removal, the polysulphone carrier of the RS1 is fully dissolvable in chloroform, a feature not shared by all other plastic WCBDs.
12) Early and adequate coronal seal is directly correlated in the endodontic literature with long-term clinical success. After obturation with RS1, the access was immediately restored with Maxcem, (Kerr, Orange, CA, USA) a new self-etching, self-adhesive composite (Figs. 9-11).
The clinical retreatment of a failed root canal has been described. Emphasis has been placed on a passive removal technique of the warm carrier based devices as well as achievement and maintenance of apical patency. Shaping technique has been detailed with description of the taper choice and the means used to prevent iatrogenic events. A detailed chemical description of RealSeal bonded obturation technique has been provided as well as a recommendation for occlusal restoration with a new self-etching self-adhesive composite. The authors welcome your questions and feedback.
*SybronEndo, Orange, CA, USA
Dr. Mounce offers intensive customized endodontic single day training programs in his office for groups of 1-2 doctors. For information, contact Dennis at 360-891-9111 or writeRichardMounce@MounceEndo.com.Dr. Mounce is in private practice in Endodontics in Vancouver, WA, USA.
Dr. Glassman is on staff at the University of Toronto, Faculty of Dentistry in the graduate department of endodontics. He is Fellow and endodontic examiner for the Royal College of Dentists of Canada, Fellow of the Academy of Dentistry International, Fellow of the Pierre Fauchard Academy, and Fellow of the Academy of Dental-Facial Aesthetics. He is the endodontic editor for Oral Health Journal. He maintains a private practice, Endodontic Specialists in Toronto, Ontario. He can be reached through his websitewww.rootcanals.ca.
Oral Health welcomes this original article.
Sidebar
The chemical mechanism for RealSeal to RealSeal self etching sealer bonding as well as RealSeal to obturator bonding which provides the clinical benefits seen are detailed here (personal communication from Weitao Jia, B. D. S., PhD VP Research & Development, Pentron Clinical Technologies):
“The main components of Epiphany™ SE Sealer are:
• Methacrylate monomers, partially containing carboxylic acid groups
• Fillers of calcium phosphate, Ca-Al-F-silicate, silanated barium boro-silicate glass and BiOCl radiopaque fillers
• Chemical initiator system
• Light initiator system
The acidic methacrylate monomer’s molecule contains carboxylic acid groups and reactive carbon double bonds that are connected with each other via a carbon backbone.
Next to the sealer material is the c
anal dentin and Resilon obturation materials as illustrated below.
Upon contact the sealer with the Resilon obturating material surface, the resin monomers in the sealer diffuse into the bulk of the Resilon material, integrate with the resin components within the Resilon material and co-polymerized to unite. In addition, chemical entanglement also occurs by the diffusion of one polymer into another and forms the polymer interpenetrating networks. As a result, a bonded and sealed gap-free Sealer/Resilon interface is formed.
On the root canal wall, i. e. the dentin side, after mixing, the Epiphany™ SE Sealer is slightly acidic (low pH-value) and hydrophilic (water binding). Upon contact with the canal surface the negatively charged carboxylic acid groups of the methacrylate monomers bond to Ca2+-ions in the dentin structure. Thus, the carboxylic acid groups are neutralized (i. e. pH rises) and anchored at the dentin surface. The sealer resin penetration into the dentin tubules further enhances the dentin bonding and sealing ability.
Simultaneously, setting of the sealer takes place through the radical polymerization reaction of the methacrylate monomers. The methacrylate monomers are chemically cross-linked with each other through the interaction of reactive carbon double bonds.
The initiator system generates the necessary starter radicals through light-induced or chemical activation. The methacrylate monomers and fillers are firmly linked and permanently embedded in the three-dimensional network of the sealer matrix. Thus, successively a highly cross-linked three-dimensional network is formed consisting of methacrylate molecules and fillers.
The calcium phosphate filler in the sealer can supply some calcium and phosphate ions, which adds the benefit of possibility of mineralization at the bonding interfaces in the event that the sealer happens to contact with the body fluid.
The bonding between polysulphone (PSU) core and the RealSeal is descried below:
The adhesion between the PSU core/carrier and Resilon coating is largely a combination of mechanical and chemical adhesion mechanism.
Mechanical: Because the Resilon material is injection molded onto the PSU core/carrier, the Resilon material is literally diffused and/or absorbed onto the PSU core surface, just like a “hot melt glue” bonding things together.
Chemical: the ester in the Resilon material and the ether and -SO2-groups in the polysulfone material are polar groups. They do have intermolecular interactions when the Resilon and PSU core polymers come together. Therefore, one may call them as polar attractions (under van der Waals forces) between the two polymers.”
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