Chapter 20 An update on endodontic issues
Although the basics of endodontics have not changed fundamentally since the early days of the specialty, the discipline has seen changes in recent years that have enabled practitioners to provide more comprehensive treatment and in some cases speedier outcomes than in the past. The introduction of rotary nickel titanium instrumentation has been a great asset in making the delivery of quality endodontic treatment easier for the general dental practitioner. Similarly, the improved use of lighting and magnification, especially the operating microscope, has meant that cases previously considered untreatable can be managed with confidence. In this article we revisit some of the fundamentals of endodontics and also discuss two of the current issues prompted by recent research; the debate between root canal treatment and implants, and the diagnosis of the joint periodontal-endodontic lesion. Access cavity While every stage of root canal treatment needs to be completed to the highest standard, creating a successful access cavity is the first crucial step. The subsequent preparation of the canal or canals can be made more difficult or severely comprised if this is not well executed. Inadequate access can lead to canals being left untreated, poorly disinfected, difficult to shape and obturate and may ultimately lead to the failure of the treatment. Good access design and preparation will result in a situation which will facilitate cleaning, shaping and obturation of the root canal system in order to maximise success. Although diagrams or pictures are often published of an ‘ideal’ access cavity in relation to particular teeth, because of biological individual variation it is unlikely that many cavities will exactly match this ideal. The vast majority are in fact created in teeth where a significant amount of dentine and enamel has been replaced by restorative materials. It is therefore important that it is the anatomy of the pulp chamber that is being treated, and not a preconceived notion which attempts to dictate the outline form of the access cavity. The aims of the access cavity can be considered as:
• Removal of the entire roof of the pulp chamber in order to inspect the pulp
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• Creation of tapered cavity walls
• Creation of a smooth unimpeded pathway for instruments to canal orifices
• Preservation of natural tooth substance consistent with the above.
The technical aspects of root canal preparation can then be continued in three further phases:
• Pulp chamber penetration and enlargement
• Canal identification
• Cavity finishing.
Mechanical preparation The use of mechanical instrumentation is accepted as being one of the most important steps in root canal treatment. It is also recognised as being one of the more difficult practical challenges in operative dentistry. The main objectives of canal preparation include:
• The removal of vital and necrotic pulpal tissue from the root canal space
• The removal of microorganisms and their products from the canal space
• The removal of infected dentine
• To create a space that can be both irrigated and medicated
• Allow predictable placement of a root canal filling material
• Maintain sound root and coronal tissue to allow effective restoration and
function of the tooth.
There are basically two groups of design differences in rotary NiTi systems with regard to cross sectional shape: files with radial landed features and non-landed types. As a generalisation ‘landed’ files allow a slower, but slightly more predictable preparation because of their ability to stay centred in a canal. ‘Nonlanded’ instruments have a more effective cutting action, and usually allow a more rapid preparation technique although these require a higher level of operator care and experience in order to avoid preparation errors, especially in relation to working length determination. Measuring working length This is a question that has been a matter of debate for many years. Most practitioners will aim to prepare to the apical constriction of the canal, the point at which the pulpal tissues become peri-apical tissues. However, locating this position can be difficult as it cannot be identified radiographically, it is highly variable in relation
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to the radiographic apex of a root, and disease processes may have altered or destroyed it. In practice a combination of measurement techniques, including radiography, electronic apex location, tactile awareness, and the use of paper point measuring techniques often allows a more consistent method of measurement than a single technique alone. Modern electronic apex locators are now so consistently accurate that they form an invaluable aid to endodontic treatment. Limitations of rotary NiTi instrumentation If correct procedure is followed, many root canals can be effectively shaped using rotary NiTi files. A ‘golden rule’ is to explore the canal system using small, flexible hand files, usually sizes 8, 10 and 15, before inserting a rotary file to the same length. This ‘scouting’ of the canal can provide valuable tactile information on the safety of the preparation case. Specifically, canals that exhibit sharp curvatures and recurvatures, division, or convergence with abrupt change of direction, can provide challenging environments for rotating NiTi files due to increases in torsional and flexural stresses. In these situations it is often prudent to complete preparation using pre-curved fine stainless steel hand files. The ‘single file’ concept Many rotary NiTi systems require several files to achieve their preferred preparation shape. Along with concerns over file separation, decontamination and cost issues have driven manufacturers to try and reduce the number of NiTi instruments necessary to create an ideal shape. Some rotary NiTi systems are now available that have a greatly reduced number of files for example, Twisted Files® (Sybron Endo, Orange, CA), and others that utilise a single rotary instrument (One Shape®, Micro Mega®, Bescanson, France). Both these systems retain a full 3600 rotational motion, and TF files utilise an altered state NiTi alloy that is reported to be more resistant to distortion and fracture. More recently the use of NiTi files in a reciprocating motion have been commercially developed that claim to allow canal shaping using only a single file (Wave OneTM, Dentsply Maillefer, Ballaigues, Switzerland, and Reciproc®, VDW®, Munich, Germany). This concept was first reported by Yared where a Protaper F2 finishing file was driven in a reciprocating fashion rather than through a conventional 3600 rotation. The clockwise (1440) and anti-clockwise (720) motions were controlled via an electronic motor, and the root canal was only pre-negotiated by an ISO 0.02 taper size 8 file. Such an approach was claimed to be effective at shaping and maintaining canal curvature. Additionally there are advantages in reducing potential instrument cross contamination and associated cost reductions. These types of instruments have now been launched commercially, with a small number of preparation files to simplify the clinician’s choice between small, medium
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and large canal sizes. Both these reciprocating systems are made from a modified NiTi alloy (M-wire) and claim to be able to prepare adequate canal shape with a minimised risk of file fracture due to the reciprocating nature of the file movement. Reciproc® is recommended for use without the need to create a ‘glide-path’ before its introduction into the canal, a claim that appears to have some experimental merit in roots with little or moderate canal curvature. Another study compared the shaping and cleaning potential of these new designs compared to ‘conventional’ rotary NiTi systems. Both reciprocating systems maintained root canal curvature and were considered safe. The shaping time for the reciprocating files was naturally shorter due to the reduced number of files used, but it was noted that irrigation time of the canal should not be compromised by this reduced mechanical preparation time. There is no doubt that the introduction of reciprocating files has generated a high level of interest, especially in the general dental practitioner population. Their use in selected situations can produce consistently good results and the reduced number of files needed to prepare adequate shapes has obvious financial and time saving potential. The need to purchase a specialised motor capable of driving the reciprocating file correctly does initially offset some of these cost savings, but many of these dedicated units also allow the use of more conventional rotary systems, allowing the clinician to apply hybrid approaches to canal preparation using a combination of instruments. Implants and endo Recent debate has centred around the relative merits of conducting root canal treatments on compromised and infected teeth compared with the extraction of these teeth and their replacement with implant retained restorations. The evidence of outcome studies into both therapies suggest that they are both valid and that preference depends on particular clinical considerations and the opinion of the clinician. There are indications for both but the usual generalised summary is that a saveable tooth should not be extracted and replaced by an implant if reasonably possible. In essence, decision-making should be based upon proper treatment planning in each individual case. A systematic review found that both treatments had a high success, which was better in the long-term than fixed partial dentures. Direct comparisons among studies were difficult because success criteria were very different. Interestingly, extraction of teeth without replacement was shown to produce poorer psychological outcomes in a direct comparison between a cohort of patients that had received root canal treatment and another that received implants. The success rate was the same for both treatments after an average of 36 months but
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implants required more post-operative treatments than root canal treated teeth (12.4% versus 1.3%). In another study based over an eight-year period found that outcomes for the two treatments was essentially the same. In summary the decision to undertake root canal treatment or implant therapy cannot be based on outcome alone because both treatments are based on differing biological and diagnostic principles, failure patterns and patient preferences. The diagnosis of periodontal-endodontic lesions (PEL) The diagnosis of pulpal/periapical or periodontal disease as distinct entities is based on a thorough clinical examination utilising pulp sensibility tests, percussion, transillumination, test cavities, probing pocket depths, an assessment of mobility, and identification of bleeding and, or suppurating pockets. Occasionally, a localised problem such as an extensive periapical lesion that tracks coronally through an otherwise healthy periodontal ligament may present as a narrow sinus tract and mimic periodontal disease. This might be classified as a primary endodontic lesion with secondary periodontal involvement although this would not be included in the definition of a concurrent PEL suggested earlier in this paper. Consequently, the management would simply involve root canal therapy of the affected tooth. Concurrent PELs will usually affect a single tooth although multiple affected teeth may present in a patient where there has been widespread dental neglect. The teeth involved may have extensive carious lesions and large restorations and will consequently fail to respond to sensibility tests. There will be increased, widebased probing depths with bleeding or suppuration from the pockets and the tooth may be tender to percussion in the presence of an acute apical or periodontal abscess (or both). Panoramic oral radiographs will reveal the extent, morphology and the severity of the periodontal bone loss and supplementary, conventional or digital periapical films may be exposed for those teeth which, on the basis of clinical findings and the panoramic film, appear to have apical pathology. A periapical film will provide the required definition to ascertain the apical extent of the periodontal lesion (the point at which the periodontal membrane space assumes normal width) and the coronal margin of a periapical lesion and thus help in identifying whether or not the separate periodontal and pulpal inflammatory lesions communicate. Periodontal-endodontic lesions may be associated with teeth having previously been root filled and the limitations of conventional (two-dimensional) periapical radiographs must be recognised as they may not correlate with the three-
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dimensional quality of a root filling. An apparently well-condensed and well-adapted root filling associated with a PEL may need to be retreated if the long-term outcome for the tooth is to be assured. Furthermore, when conventional, plain films fail to provide sufficient diagnostic information limited-volume, high-resolution cone beam computed tomography may be justifiable for assessing and treatment planning periodontal-endodontic lesions. Further reading Heasman PA. An endodontic conundrum: the association between pulpal infection and periodontal disease. Br Dent J 2014; 216: 275-279. Waplington M, McRobert AS, Shaping the root canal system. Br Dent J 2014; 216: 293297. Saunders WP. Treatment planning the endodontic-implant interface. Br Dent J 2014; 216: 325-330. Adams N, Tomson PL. Access cavity preparation. Br Dent J 2014; 216: 333-339.
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