Last Friday, after another busy week, a colleague came over to discuss a challenging endodontic case. We started to discuss workflows, treatment philosophy and how important it is to have systems in place to streamline treatments. We reminisced about what we were taught in dental school and, while the biological concepts are broadly the same, the technical execution of treatment has evolved significantly.
A periapical radiograph is the standard endodontic view of choice prior to treatment. However, it has limitations of being a two-dimensional picture, can have anatomical noise and may have geometrical distortion. A CBCT scan, for me, is essential in all endodontic surgical cases and in cases where the diagnosis or cause of failure is not clear. In multi-rooted teeth, we can see exactly which root is associated with pathology before we start. We can visualise how many canals are present and the location of the canals prior to designing an access cavity. The curvature in both the mesio-distal and buccolingual planes can be deciphered and then finally a shaping strategy can be designed to minimise tooth structure loss. An idealised access cavity and shaping protocol can be formulated while respecting the endodontic treatment objectives. Cutting sound dentine is an irreversible event and no matter how good our restorative protocols have become we need to consider minimising our footprint in endodontic treatment (Figure 1). There has been a growing realisation that the trend of large taper endodontic shapes that make the technical process of endodontic treatment easier may be adversely reducing the long-term survival of the tooth by removing excessive dentine in the pericervical region. This is the dentine located 4mm above the crestal bone and 6mm below this level. Pure endodontic failure in well executed root canal treatment is rare. The vast majority of cases fail due to restorability issues, periodontal disease or root fracture. These traditional shapes have morphed from the limitations of older generation nickel titanium instruments and obturation requirements of introducing a heat plugger deep into the root canal anatomy. The relative stiffness of these systems required straight-line access, which in many cases necessitated
significant removal of healthy dentine in a critical area for the long-term survival of the tooth. Now, with the advent of super flexible control memory files, we can be much more conservative in access cavity design and canal shaping procedures. This means the files can be pre-bent similar to a stainless steel file (Figures 6 and 7) and has extreme flexibility. This makes it an excellent choice for curved canals. Using larger taper files for treatment of the UL7 with acute apical periodontitis (Figure 2) would risk causing a strip perforation or procedural errors such as ledging or instrument separation. The case illustrated in Figures 2 to 5 provides reasons for using heat-treated files. In this case, the UL7 had a triple curve in the mesial and distal root. This is a technically challenging case even for a specialist endodontist. The risk of fracture of a traditional rotary instrument or a procedural error around the second and third curves is very high. Heat-treated files A heat-treated file with controlled memory means that it has a very low restoring force and therefore is less likely to deviate from the glide path when negotiating curves. When used with the correct technique, a 13 04 VS Slexi file is a very safe file and can be used immediately after a loose size 10 file has reached a specific length. In my experience of running endo courses over the last 13 years, the most common procedural errors start with the jump from size 10 file to 15/20 stainless steel files. This is due to the stiffness of these files as they increase in diameter. The efficiency and safely of treatment in complex cases increases significantly when a protocol using a size 10 stainless steel file followed by 13 04, 17 04 and 20 04 files are used. A decision can then be based on the anatomy of the tooth and biological condition as to what the final apical size will be. Should a larger apical size be required, I would recommend considering using a regressive taper file that will only cut in the apical 3mm and not remove additional sound dentine coronally due to the preexisting shape of the file. The VS Flexi Blue system is an example of a regressive taper file system recently introduced in the UK.
Consider the case illustrated in Figures 8 to 12, which was referred for acute irreversible pulpitis in the UR7. There are long, 27mm length roots and narrow root shapes. The carious and unsupported tooth structure needs to be removed. We then need to consider how much sound tooth structure is removed to satisfy the objectives of our endodontic treatment. The more tooth structure that is removed, the easier the treatment becomes but to the detriment of the strength of the tooth.
It is tempting not to consider any of these factors and just use a single file system that will predetermine the amount of tooth structure that is removed due to its size and taper. The cutting shaft is 16mm, meaning the widest diameter of the instrument will extend deep into the roots in this case, as the roots are 27mm long. However, if you wish to progress your skills and achieve excellent technical endodontic results, it may be worth making the effort to become familiar with super flexible nickel titanium systems such as VS Flexi Blue files or similar systems
The traditional concept of straight-line access to canals is no longer required due to the flexibility and performance of these files. Saving additional tooth structure may be the single most important factor that is within our control in endodontic treatment. In this case, the canals can be prepped to 25 06 in the apical 3mm but the regressive taper means that we conserve the critical tooth structure coronally. Using an endo motor with a super mini contra-angled head means we can comfortably use 25mm files to reach working length. While these shapes have a narrow taper, irrigants can still be delivered to apical zone with ultrathin needles – for example, the Irriflex irrigation tips. Obturation can be seamlessly carried out using custom adjusted gutta percha points and a bioceramic cement such as One-Fil bioceramic cements. The advantages of bioceramic cements have been discussed in the literature and summarised by Raghavendra et al (2017): ‘Excellent biocompatibility properties due to their similarity with biological hydroxyapatite. Intrinsic osteoinductive capacity because of their ability to absorb osteoinductive substances if there is a bone healing process nearby. Function as a regenerative scaffold of resorbable lattices which provide a framework that is eventually dissolved as the body rebuilds tissue. Ability to achieve excellent hermetic seal, form a chemical bond with the tooth structure and have good radiopacity. Antibacterial properties as a result of precipitation in situ after setting, a phenomenon that leads to bacterial sequestration. ‘Bioceramics form porous powders containing nanocrystals with diameters of 1-3nm, which prevent bacterial adhesion. Sometimes, fluoride ions are constituents of apatite crystals, and the resulted nanomaterial has antibacterial properties.’ With these cements we can confidently use a single cone obturation technique, as the material doesn’t shrink like traditional sealers and has favourable biological properties. Taking a step back It may be worth taking a step back and considering why we do what we do in our instrumentation phase of endodontics. How much is predetermined by using a protocol set by manufacturers rather than examining the specific requirements of the case in front of us and then deciding on an optimal shaping protocol that conserves as much pericervical tooth structure as possible but yet achieves the goals of our endodontic treatment? Personally, I have found our restorative colleagues are very excited with this approach as they have always protested against the straight-line access and large coronal shapes that in the past often removed health dentine critical for longevity of their coronal restorations.