Advances in disinfection, cements, and imaging have made saving teeth more predictable
Endodontics is the last line of defense in one of the primary missions of dentistry: preserving the natural dentition. The tools and techniques at the disposal of the endodontists and general dentists who practice this discipline continue to evolve as new products are developed and more clinical evidence is compiled. Currently, the most significant developments fall into three categories: disinfection, cements, and imaging. Some of these innovations and revelations are already proving to be impactful to everyday dentistry, and others could be transformative in the future.
The primary cause of pulpal and periapical infection is the presence of bacteria inside the pulp and root cavity.1 The bacterial biofilms that they form are made up of individual cells and microcolonies, which are all embedded in a highly hydrated exopolymer matrix.2
The main objectives of root canal therapy are to eliminate the bioflora and inflamed pulp tissue in the root canal and to prevent apical periodontitis.3,4 Because microorganisms are protected from environmental threats by the structure of their biofilms, to persist once disrupted, infections depend on the ability of microorganisms to adapt their physiology to the new environmental conditions established by the treatment.5,6
The total elimination of bacteria, or the complete sterilization of the root canal system, though likely unattainable, is the gold standard of root canal therapy. In practice, the aim is to reduce the bacterial load to a level compatible for the healing of periradicular tissue.7 With the currently heightened emphasis on minimally invasive dentistry, proper instrumentation is still key; however, disinfection techniques have become focused on reducing overpreparation of the canals while increasing the efficacy of irrigation, particularly for very small or inaccessible branches. Presently, there is no single irrigating solution that fulfils all of the requirements of an "ideal irrigant;" therefore, optimal irrigation may be achieved by the combined use of two or more irrigating solutions, using a proper irrigating technique.8
The irrigation solution traditionally used in endodontic therapy is sodium hypochlorite (NaOCl), which possesses potent, broad-spectrum antimicrobial properties and the ability to dissolve organic tissue.9 Although NaOCl and ethylenediaminetetraacetic acid (EDTA) are still the most commonly used irrigants, studies have found that the biofilm-related tolerance of Candida albicans can permit regrowth and colonization despite combined treatment using both solutions.10 Other research has explored the effectiveness of other natural compounds, but few have demonstrated antimicrobial efficacy comparable to that of NaOCl.
There is a growing interest in nanoparticles not only for their high antibacterial, antifungal, and antiviral properties but also for their tendency to induce less microbial resistance when compared with antibiotics.11 Nanoparticles derived from bioactive materials have the ability to mediate targeted antibacterial efficacy while sparing the mammalian cells.11 A variety of nanoparticles are being developed and tested, including chitosan nanoparticles, bioactive glass nanoparticles, and silver nanoparticles.
Although irrigation solutions are most often delivered using a normal syringe, other available techniques incorporate the use of shaping files, sonic/ultrasonic instruments, and even lasers to increase their efficacy. Factors to consider in selection include reaction rate, shear stress, apical extrusion of the solution, alteration of the root anatomy, and cost.12 During irrigation, the use of photoactivation methods, such as laser-activated irrigation and photon-induced photoacoustic streaming, can increase the reaction rate of the irrigants.13 In addition, warming NaOCl solution (to a maximum of approximately 60°C) has been shown to increase its reaction rate, positively influencing the irrigant's antibacterial action and its ability to dissolve organic residues.14
NaOCl's cleansing action is also increased when it is agitated inside the canal by gently moving a well-fitting gutta-percha master cone or a manual tool, such as a carrier, finger spreader, or K-file,15 which reduces the vapor lock effect and increases surface contact with the canal walls.15 When compared with traditional single syringe irrigation, sonic activation systems were shown to improve the penetration of root canal irrigants, but proved inferior when compared with activation using ultrasonic and reciprocation methods.16
Other advanced irrigation methods are available that rely on the use of acoustic energy, negative pressure, and more. For example, the GentleWave® System (Sonendo) degasses and optimizes the concentration of procedural fluids as they are constantly circulated through the pulp chamber and root canal system using vortical flow and broad-spectrum acoustic energies to debride and disinfect. Another system, The EndoVac™ (Kerr), uses negative apical pressure to pull irrigant down into the root canals and then up and away into the suction unit. This method thoroughly removes the micro-debris at the apical constriction with no risk of the solution being forced out of the apex into the periapical tissue, which can result in severe tissue damage.17 Although, many new solutions and systems are being introduced, more independent research is needed to determine the comparative efficacy of some.
Developments in the science of endodontic materials have significantly contributed to the exponential growth of endodontic treatment. In recent years, advances in bioceramics have changed the face of endodontics. Bioceramic materials, with their biocompatible nature and excellent physico-chemical properties, are now widely used in endodontic applications. They are available as cements, root repair materials, filling materials, and root canal sealers, which offer the advantages of biocompatibility, potentially increase root strength following obturation, and provide enhanced antibacterial properties and sealing ability.18
With the use of bioceramic materials, treatment of the immature apex can be shortened to one to two visits. Bioceramic root canal sealers have changed the entire concept of root canal obturation from one involving the use of inert materials to establish a hermetic seal to one involving biologic bonding and activity. In addition, the introduction of these materials has improved the treatment outcomes and reduced the treatment times associated with obturation, which is particularly beneficial when treating pediatric patients. The chemical bond and antimicrobial properties of bioceramic sealers in conjunction with hydraulic properties is promising, but further research is needed to establish the most optimal clinical protocols.19
Due to the introduction of and subsequent improvements in bioceramic dental materials, the primary treatment methodologies used in endodontics-apexification procedures for immature or resorbed roots and root canal obturation for fully formed roots-have both changed significantly during the past two decades. The ease with which obturation can now be performed has served to democratize root canal therapy, making it predictable enough to become an efficient component of a general dentist's practice.
To aid in the diagnosis and management of complex endodontic issues, the use of cone-beam computed tomography (CBCT) is rapidly increasing among endodontists. The 3D nature of CBCT overcomes some of the limitations inherent in conventional radiography.20 "Relying on the 2D projections of conventional intraoral radiographic procedures is like trying to solve a crime with circumstantial evidence, whereas using CBCT is like having a video of the crime," says Allen Ali Nasseh, DDS, MMSc, a clinical instructor in the department of Restorative Dentistry and Biomaterials Sciences at the Harvard University School of Dental Medicine, the CEO of RealWorldEndo, and a private practitioner in Boston, Massachusetts. Many teeth present with complex root anatomy that can make root canal treatment challenging, particularly molars, which exhibit the most variability in their canals and can be the most difficult to manage if they fail.21 By examining teeth in 3D prior to endodontic procedures, a much clearer picture of the tooth's anatomy can be visualized, and treatment plans can be personalized accordingly. "Much of my practice in pre-CBCT times involved exploratory treatments, where I'd have to drill into a tooth to really know what was happening, sometimes stopping treatment midway in favor of tooth extraction," explains Brooke Blicher, DMD, an assistant clinical professor at the Tufts University School of Dental Medicine, a clinical instructor at the Harvard University School of Dental Medicine, and a private practitioner in White River Junction, Vermont. "But now I can carefully choose the cases that are appropriate for endodontic treatment or extraction using this minimally invasive tool."
Recognizing that diagnostic imaging is the single greatest source of controllable exposure to ionizing radiation, the potential risks of performing CBCT scans should always be considered. To emphasize optimization in medical imaging, at its 50th annual meeting in 2014, the National Council on Radiation Protection and Measurements introduced a modification of the US Nuclear Regulatory Commission's "as low as reasonably achievable" (ALARA) concept, calling for the use of exposures that are "as low as diagnostically acceptable" (ALADA).22 Because the diagnostic imaging doses associated with CBCT are typically much lower than 100 mSv, the American Association of Physicists in Medicine has stated that, when exposures are medically appropriate, the anticipated benefits to patients are highly likely to outweigh any small potential risks. The organization suggests that the lack of scientific consensus about the potential risks from low doses of radiation makes predictions of hypothetical cancer incidence and mortality highly speculative and that this can lead some patients to fear or refuse safe and appropriate imaging to their detriment.23
On the Horizon: Regeneration
Regenerative endodontics, which involves replacing damaged structures and regaining functionality in previously necrotic and infected root canal systems, is groundbreaking. "The more that we study the pulp and the more unique and varying functions that we learn for maintaining it, the greater our chances are of saving a tooth and the surrounding bone," says Blicher, "Although regenerative procedures have mostly focused on single-rooted, immature permanent teeth, novel applications abound in the literature, including its use in multirooted mature teeth, in primary teeth, and in treating conditions like perforating resorption."
In the immediate future, the main challenge of endodontics is biofilm. "The rate-limiting steps for successful outcomes are irrigation and disinfection," emphasizes Nasseh. The ability to reach total disinfection still lags behind the existing state-of-the-art technology for imaging, shaping, and filling. As the field of endodontics approaches the goal of 100% disinfection, regenerative procedures become increasingly predictable, and the need for root canals may eventually be eliminated entirely.
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