Improving endodontic success through coronal leakage prevention — part 1

Dr. Gregori M. Kurtzman discusses a major determinant of endodontic success or failure

Introduction

Coronal leakage within the canal system following obturation has been associated with endodontic failure. The literature suggests this is more likely a determinant of clinical success or failure then apical leakage.^1-3 Recent advances in obturation materials have shown to provide superior sealing of the canal system. But without addressing the coronal aspect of the tooth following endodontic treatment, endodontic failure still may occur. Studies confirm that a sound coronal seal is of paramount importance to the overall success of root canal treatment.^4-7 Regardless of which obturation method or materials used, the best rule is, a properly cleaned, shaped, and obturated tooth should be permanently restored as soon as possible.⁸

No matter what our intentions are following obturation of the canal system, patients may delay restoration of the tooth that has been endodontically treated. Time and financial constraints often influence when the final restoration may be completed. Additionally, between appointments, an adhesive material will prevent leakage and subsequent contamination of the canal system.

Coronal leakage

The literature indicates coronal leakage as the major determinant of endodontic success or failure. No matter what is placed into the canals, if the coronal portion of the tooth is not sealed with materials that are adhesive to tooth structure and are resistant to dissolution by oral fluids, over time, endodontic failure may be inevitable.

It is common to have a patient present with marginal decay of a crown that the underlying tooth had prior endodontic treatment. Because the tooth was treated endodontically, sensitivity that may indicate a problem under the crown will not alert the patient to the need to seek dental treatment on that particular tooth. Coronal leakage may quickly lead to apical migration of bacteria even when of short duration, related to what materials are present obturating the canal system and in the coronal aspect of the tooth. When the patient does present, coronal leakage may have been ongoing for an extended period of time, complicating treatment or rendering the tooth non-restorable necessitating extraction.

Significant coronal dye and bacterial leakage following exposure of sealed canal system to artificial and natural saliva leading to complete bacterial leakage may occur within 2 days.^9,10 Dye leakage can occur in as little as 3 days as reported in an in vitro study.^11-13 It has been suggested that gutta percha does not offer an effective barrier to crown-down leakage when exposed to the oral environment.^14-16 Additional studies using gutta percha and various sealers indicate that gutta percha will allow bacterial leakage. Yet, the use of an adhesive sealer may significantly slow or stop coronal-apical bacterial migration related to adhesion of the sealer to the gutta percha cone(s) in the obturation.¹⁷

The predominant bacteria found in endodontically treated teeth undergoing coronal leakage with persistent apical periodontitis is Staphylococcus, a gram-positive facultative anaerobe. This is followed by Streptococcus and Enterococcus, all normal salivary flora.^18,19 Thus, coronal leakage provides a constant source of microorganisms and nutrients that can initiate and maintain periradicular inflammation and may well be the largest cause of failure in endodontic therapy.²⁰

Endodontic obturation materials do not prevent coronal microleakage for an indefinite period of time.²¹ One study reported on a sample of 937 obturated teeth, which had not received restorative treatment during the previous year. The data reported that the technical standard of both coronal restoration and root filling were essential to periapical health.²² It is not uncommon following root canal treatment for coronal leakage as a result of the presence of a deficient composite resin fillings and secondary caries under restorations to occur.²³

Yet the endodontic materials utilized over the past 50 years when challenged have shown that they do not prevent coronal leakage. Another study reported on 45 teeth that were cleaned, shaped, and then obturated using a lateral condensation technique with gutta percha and a root canal sealer. The coronal portions of the obturation materials were placed in contact with Staphylococcus epidermidis and Proteus vulgaris. The number of days required for these bacteria to penetrate the entire root canals was determined, with over 50% of the root canals becoming completely contaminated after a 19-day exposure to S. epidermidis. Fifty percent of the root canals were also totally contaminated when the coronal surfaces of their fillings were exposed to P. vulgaris for 42 days.²⁴ AH-26^® and other commonly used sealers when compared after 45 days exposure to the oral cavity, none of the sealers was capable of preventing leakage and coronal dye penetration.²⁵ So we can see that the quality of both the coronal restoration and obturation material are essential to periapical health as none of the present-day root canal sealers may hermetically seal “the root canal wall — gutta-percha obturation interface.” The importance of perfectly sealing coronal restorations (both temporary and permanent) needs to be emphasized and considered during and following treatment.²⁶

Pre-endodontic therapy buildups (canal projection)

Coronal leakage is a major contributor to endodontic failure.^27,28 When significant coronal breakdown is present or replaced by a previously placed non-adhesively bonded direct restoration, a bonded core placed prior to instrumentation/disinfection and obturation of the canal system can greatly diminish the leakage potential both during and after endodontic therapy.

Isolation of the pulp chamber can be a challenging task when minimal coronal structure remains, and endodontic treatment is required as part of the oral rehabilitation (Figure 1). Coronal reinforcement has traditionally been addressed following the endodontic phase.²⁹ Yet a coronal bonded buildup can simplify the endodontic phase, strengthening the remaining tooth structure. This can decrease the possibility of further damage to the tooth due to dam-clamp placement or functioning on the tooth before a full coverage restoration can be placed. The Canal Projector core allows isolation of the individual canals by adhesively surrounding them with a resin buildup. Sealing the pulpal floor to the outer periphery of the tooth and surrounding the canal orifices will decrease coronal leakage potential during and following endodontic treatment.

Following identification of the canal orifices and caries removal prior to instrumentation of the canals, a Canal Projector cone (CJM Engineering, Santa Barbara, California; www.cjmengineering.com) is placed on a hand file and inserted into each canal. (Figure 2) The Canal Projector cone is pressed into intimate contact with the coronal aspect of the canal orifice with cotton pliers pressed apically on the cone sitting on the file in the canal. A dentin adhesive is placed on all exposed surfaces with a microbrush and light-cured. Addition of a dual-cure activator that matches the dentin bonding agent can be added (following manufacturer’s instructions) should the practitioner chose to ensure complete curing of the adhesive on the deeper aspects of the coronal portion of the endodontic access preparation. Next, a dual-cure buildup material is injected around the projector cones, backfilling from the pulpal floor coronally. The placed buildup material is light-cured and then allowed to complete self-cure in the deeper aspects for 3-4 minutes. When the buildup material setting has been completed, the hand files and projectors can be removed leaving straight-line access into each individual canal (Figure 3). Visualization of the orifice is elevated to the occlusal plane instead of deep within the tooth, and a bonded seal coronally around each orifice is achieved. When endodontic treatment cannot be completed at the initial visit, following calcium hydroxide (CaOH) placement as a medicament into each canal, the projectors are shortened at the coronal aspect of the cone by 2 mm and are reinserted into the projected canal (Figure 4). A provisional temporary material is then placed over the shortened cone to seal each projected orifice (Figure 5). At the subsequent appointment, the temporary filling material is removed from atop the projector cone, and the cone is removed by threading a hand file into it and tugging it out. When restoring the tooth, if the practitioner wishes to place posts into the tooth, post space preparation is simplified, and misdirection of the post preparation is minimized.

Conclusion

Coronal leakage prevention needs to be implemented when endodontic treatment is initiated to maximize the long-term results and prevent reinfection of the canal system after obturation. Frequently, patients may delay restoration of the endodontically treated tooth due to financial reasons, and the old saying “out of pain, out of mind” rings true. Once the pain in the tooth is alleviated, patients are not well motivated to get the tooth restored in some cases.  This may lead to coronal leakage at the restorative material placed to temporarily seal the access over the canal system obturation. So, with that in mind, engineering the tooth prior to and during the endodontic phase of treatment can aid in coronal leakage prevention until a definitive final restoration can be placed.

Part 2 will appear in the Spring 2021 issue.