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CLINICAL MEETING: Clinical challenges and current trends in access cavity design and working length determination
The 2018 ESE Clinical Meeting will provide participants with an update on current concepts of access cavity design and preparation as well as how to assess working length during root canal treatment. The key aims are:
- To describe the most recent progress in term of technology and clinical approaches to both access cavity design/preparation and working length determination;
- To discuss gaps in knowledge and deficiencies in the available technology for access cavity preparation and working length determination;
- To consider the establishment of multi-centred clinical studies to evaluate the impact of access cavity design and methods of determining working length;
- To consider whether the proposed topics are worthy of an ESE Position statement;
- To develop discussion and eventually consensus on the proposed topics to inform the new ESE quality guidelines.
Overview – Part 1
The morning session had two presentations focused on the principles of access cavity design and recent innovations. This has always been a clinically relevant topic, which has recently become more controversial because minimally invasive concepts have been suggested in order to save tooth structure, and thus potentially increase the long-term prognosis of the root filled tooth. Moreover, the clinical approach is also evolving due to new digital endodontic techniques, mainly focused in providing a better access and easier localization of canals in complex cases, i.e. calcified pulp chambers and canals. After the two presentations, a debate was held, with the two speakers answering questions from the audience and discussing related topics arising from the audience.
Gabriel Krastl - Basic principles of access cavity design. Locating canals. Management of calcified canal systems. The use of CBCT for guided access cavities.
The presentation focused on access to the endodontic system and reviewed the current strategies for the treatment of teeth with calcified canal systems. An adequately prepared access cavity is crucial for all steps which follow during the endodontic therapy: for locating the root canals, for effective instrumentation, for irrigation, and root filling. Furthermore, an ideal endodontic access cavity should be a balance between the demands for an adequate endodontic treatment and an optimized structural strength of the tooth. In teeth with severe calcifications of the endodontic system and apical pathosis, the access to obliterated root canals is challenging and it is prone to technical failures, including alterations of root canal geometry, and loss of hard substance, which may result in a considerable weakening of the tooth or in root perforation. Even with the use of a dental microscope, the preparation of an adequate access cavity may lead to excessive substance loss that impairs stability and thereby reduces the long-term prognosis of the tooth.
To overcome these complications, guided endodontics, a novel approach for the preparation of apically extended access cavities was introduced. For this purpose, preoperative surface scans and cone-beam computed tomography scans are matched. After planning the position of the drill for root canal location, a virtual template is designed, and the data is exported as an STL file and sent to a 3D printer for template fabrication. The template is positioned on the teeth. A specific drill is used to penetrate through the obliterated part of the root canal so as to obtain minimally invasive access to the root canal. After miniaturization of the instruments, the technique was made accessible even for teeth with narrow roots such as mandibular incisors.
A recent study demonstrated that the (micro)guided endodontic access leads to a faster and more predictable location of calcified root canals with significantly less substance loss compared to the traditional endodontic access using the OPM. Furthermore, in contrast to the traditional access, the success of the guided approach is not influenced by the experience of the operator. Even though clinical studies are missing, several case reports demonstrate the successful clinical implementation of this technique particularly for anterior teeth, but also in the posterior region.
Apart from static guidance, dynamic navigation may be a new approach for the negotiation of calcified root canals. A stereo vision computer triangulation setup can be used to guide the bur during preparation of the access cavity. While the initial data is available on the accuracy of the method in the field of Implantology, future research has to demonstrate whether its implementation in Endodontics is feasible.
Antonis Chianotis - A rational approach to access cavity designs
Traditional access cavity designs are geometrically predesigned shapes dictated by the underlying anatomy and guided by the endodontic disease. Access cavity designs remained unchanged for many decades because of the inherent advantages they offered. Convenience form, extension for prevention and complete unroofing of the pulp chamber usually resulted in great visibility, ease and safety during all stages of root canal treatment procedures.
However, recently, the traditional access cavity designs have been questioned, modified and regarded as legacy concepts. The reason for this is linked to the development of minimal invasive dentistry concepts in Endodontology. These concepts recognise that an artificial material is of less biological value than the original tissue and they suggest that minimum access cavity designs and limited canal instrumentation sizes in order to preserve dentine. The ultimate objective is an increase on the mechanical stability and fracture resistance of the tooth.
Although technological advancements have enabled dentine conservation procedures, problems do exist and can complicate treatment to unacceptable levels. Moreover, the evidence for an increase in fracture resistance remains limited and controversial. More research is needed to clarify the benefits and possible risks of minimal access cavity designs and the effect they may have on the outcome of root canal treatment.
Overview – Part 2
The afternoon session had two presentations focused on the determination of working length during root canal treatment. The apical limit of root canal treatment has always been a challenge in clinical endodontics due to the limitations of 2D periapical radiographs, the variability of the apical constriction, the problems related to apex locators and the changes of canal length related to different access cavity design and shaping procedures. The two speakers provided an update of the most current research and trends on the topic, aiming to provide useful clinical hints to solve most of the common practical issues related to this procedure. After the two presentations, a debate occurred, with the two speakers answering questions from participants and discussing related topics arising from the audience.
Ashraf ElAyouti - The anatomy of the root apex. Where is the canal terminus? The use of electronic apex locators. Tips and tricks to determine the end-point of canal preparation and filling
A meta-analysis of outcome studies has so far showed a clear consensus and concordance of evidence regarding the end-point of root canal treatment. The scientific consensus is that long root canal fillings do not result in a better outcomes, in fact short fillings have a better outcome than long fillings. Micro-CT analysis and extensive serial measurements of canal cross-sections have revealed the existence of the apical constriction (the smallest canal cross sectional area) in each canal. In contrast, the apical constriction was barely detected when longitudinal sections of the root canal were used, and in addition, canal topography varied greatly according to the position of the longitudinal section. This may explain why the apical constriction remained undetected in many studies using longitudinal sections of root canals. The apical position of the constriction is very close to the foramen; within <¼ mm in most of the root canals examined. At the apical constriction, root canals were rounder, smaller in size and had non-divergent dentinal walls. At the major foramen, root canals were larger in size, oval in shape and the dentinal walls diverged towards the foramen. Moreover, at the foramen, root canals ended oblique to root surface so that a thin dentinal wall was present in most canals. Therefore, in order to keep the area of the wound at the periapical tissues as small as possible and to avoid over-fillings and apical laceration, it is recommended to shape root canals to the apical extent of the constriction and only disinfect to the foramen. Modern apex locators operating on the basis of relative impedance measurements have been shown to be accurate. Using micro-CT images to superimpose the location of the constriction and foramen to the display of apex locators revealed that nearly all apex locators were accurate within +/- ¼ mm. In the process of working length determination, the main source of measurement error was the operator and the procedure itself. Mainly, due to adjusting and reading the length of measuring files as well as adaptation and movement of rubber stoppers. The repeatability and reproducibility of the operators were a further source of measurement error.
Vittorio Franco - The limits of endodontic procedure. Management of the apex and the apical third.
The presentation focused on the management of the apical third of the root canal and in particular of the foramina. Endodontic treatments are currently based on changes in the shape and contents of what is known as the endodontic space: it is difficult to distinguish the point, or, better, the so-called passage between ‘‘in’’ and ‘’out’’. The first part of the presentation is the description of the landmarks and the difficulties when identifying them clinically. Limitations of periapical radiographs and electronic apex locators were briefly described: a systematic review on the use of CBCT for the establishment of working length confirms the possibility of using this device to identify the position of the foramen and its distance from a coronal reference point.
In the second part, several points to consider were presented on the shaping procedure and its relationship with working length: the action of the files on tissues and the modifications of the WL after the pre-flaring were the main points discussed as well as the role of apical enlargement.
The third part was a brief description of the principles of root filling and its relationship with the surrounding tissues.
In the last part before the conclusions. irrigation protocols were described focusing on the apical part of the root canal. The most popular activation systems were briefly described and pros and cons in term od apical debridement and disinfection were evaluated.
Conclusions: all the stages of a root canal treatment have to address the working length issue. The shaping WL could be different, depending on the kind of treatment, e.g. pulpotomy, pulpectomy and revascularization have a totally different approach to the management of the apical foramina. Since all endodontic procedures can cause a microsurgical wound and an inflammation of the involved tissue, in this perspective establishing and using the correct working length could contribute to a better outcome.