JOHN J. STROPKO , GLEN E. DOYON
This is a sample concept of blended learning. The technical discussion for a specific area of treatment planning introduced as a component of the critical thinking and comprehensive reasoning that goes into a foundational treatment plan. What is missing is the clinical cases to provide examples. They are easy enough to obtain; however, the goal remains to encourage Canadian dentists and others to share and care their work product and develop a truly interactive educational platform using this blog as a seminal launch pad……chat the request up among your peers…….one case starts the ball rolling. As always, double click the image.
Review of the literature over the last decade supports the following common indications for resection of the apical portion of the root during periradicular surgery:
• Removal of pathologic processes– Some examples include symptomatic fractured root apices, suspected contaminated apices (retained microorganisms and biofilms), root apices with tenaciously attached pathologic tissue, and removal of foreign material in the apical portion of the canal.
• Removal of anatomic variations– The anatomic variations most commonly encountered are apical deltas, accessory canals, apical canal bifurcations, severe curves, lateral canals, and calcifications.
• Removal of operator errors in non-surgical treatment– These include,complications such as ledges, blockages, zips, perforations, and separated, instruments
• Enhanced removal of the soft tissue lesion– Root resection is often necessary to gain access to deeply placed soft tissue around the root in order to secure an adequate biopsy.
• Access to the canal system– In cases where the major canal systems are blocked with, for example, a post-core restoration, and the apical portion of the canal has not been properly cleaned, shaped, or obturated, root-end resection (RER) may be necessary to manage the untreated portion of the root canal system.
• Evaluation of the apical seal– This can occur in conjunction with the previous indication, when the canal obturation is questionable, yet access to the entire root system with non-surgical retreatment is impractical or impossible.
• Creation of an apical seal– This is one of the most common indications for RER. In cases where the root canal treatment has already been performed non-surgically, RER may be necessary to create an environment for access and vision so that an adequate apical seal can be achieved.
• Reduction of fenestrated root apices– This situation is most common in maxillary teeth, but can occur anywhere in the dentition. Possible contributing factors include age, anatomical anomalies, orthodontics, and trauma
• Evaluation for aberrant canals and root fractures– In some cases, the root canal obturation is judged to be satisfactory and the etiology of failure is not clinically or radiographically evident. RER will potentially expose these aberrant canal communications, complete, or incomplete vertical fractures, which can be detected on a stained root-end bevel (REB). (See following section on staining.
Root End Resection – the bevel Long bevel vs. short bevel
When the apical end of a root is removed, the remaining surface of the root is described as having been ‘bevelled.’ The amount and degree of the resected bevel are of utmost importance. The overall crown/root ratio, presence of posts or other obstacles, root anatomy, remaining crestal bone, and the periodontal status of the tooth must be considered. If the bevel is made in the traditional manner at a 20–45° bucco-lingual incline, more of the palatal or lingual aspect of the root will be left untreated. This situation occurs when the surgeon is trying to be conservative in order to maintain a more favorable crown/root ratio. Because 98% of apical canal anomalies and 93% of lateral canals system ramifications occur in the apical 3 mm, it is essential that at least 3 mm of the root end is removed. Long bevels require the removal of an excessive amount of root structure to include the lingual, or palatal 3 mm of the root apex. If the bevel is closer to 0°, more root structure can be conserved, improving the crown/root ratio while meeting the objective of removing the vast majority of apical ramifications. The long bevel creates a spatial disorientation that is often difficult to overcome regarding the true long axis of the canal system. As it is difficult to visualize the long axis of the tooth, the subsequent root-end preparation (REP) will usually not be within the long axis of the canal. Failure to comprehend this concept is the primary reason that perforations to the lingual, or palatal, occur (9 <file://localhost/javascript/popRef(‘b9’)>) (Fig. 5 <file://localhost/javascript/popRef(‘f5’)>). Another consideration for the 0° bevel is that the cavo-surface marginal dimensions of the preparation will be considerably decreased, therefore allowing an easier and more predictable seal. A good axiom to consider is this: whatever the angle of the bevel, it is almost always greater than it appears to be.
Knowledge of root anatomy is especially important when there are more than two canals in one root. This anatomical complexity was identified and delineated over 100 years ago and its implications in surgical endodontics were highlighted 70 years ago This occurs most commonly in maxillary premolars and in the mesial roots of nearly all molars; however, multiple canals can occur in any root. Ideally, the short bevel (0°) is as perpendicular to the long axis of the tooth as possible in order to predictably achieve several important criteria:
• Conservation of root length– When a long bevel (20–45°) is made, more tooth structure has to be removed in order to expose the anatomical apex of the tooth. With a long bevel, an inordinate amount of root structure would have to be removed in order to include the entire apical 3 mm.
• Less chance of missing lingual anatomy– The short bevel allows inclusion of lingual anatomy with less reduction. With the long bevel, there is a decreased probability of encroachment on the lingual root surface
• A shorter cavo-surface margin– If multiple canals are present, the distance between them will increase as the angle of the bevel increases. As it is recommended that the isthmus also be prepared, a shorter bevel allows for a shorter cavo-surface margin length in the completed REP
• Less chance of an incomplete resection– The shorter bevel makes it easier for the operator to resect the root end completely and not leave a ‘lingual cusp,’ or incomplete resection .
• Easier to detect multiple or aberrant canals– When the short bevel is prepared, more lingual anatomy can be accessed
• Less exposed dentinal tubules– As the dentinal tubules are more perpendicular oriented to the long axis of the tooth, the short bevel will expose fewer tubules. The long bevel opens more tubules to be exposed to the environment, which can allow more micro-leakage over a period of time.
• Easier to maintain REP within the long axis– Instrumentation of the REP should be kept within the long axis of the tooth to avoid unnecessary or excess removal of radicular dentin. The longer the bevel, the more difficult it is to envision and maintain the REP within the long axis of the tooth.
• Easier to include the isthmus in the REP if multiple canals are present in a single root– The cleaning and preparation of the isthmus that usually exists between the canals whether or not it is visible after the REB is very important. When there are multiple canals in a root, isthmus tissue is present 100% of the time at the 4 mm level. The short bevel facilitates the isthmus preparation by allowing a better ‘mental picture’ of the long axis of the tooth
Ideally, the root-end bevel (REB) is kept as short, or as perpendicular to the long axis of the root as practical, to facilitate complete resection and to expose the entire apical canal system. However, after positive identification of the features on the surface of the bevel has been made, it may be necessary to increase the angle of bevel slightly, to achieve better access for instruments, for improved vision, and/or to enhance ergonomics for the patient and clinician.
Instrumentation and technique Methylene blue staining. After complete hemostasis is achieved, the bevelled surface is ready for close inspection to be certain that the REB has been properly completed. The resected root end is rinsed and dried with an irrigator. The dried surface is then stained with 1% methylene blue (MBS) which is allowed to remain undisturbed on the resected surface for 10–15 s before once again gently flushing with a sterile solution and drying with an irrigator. As the MBS only discolors organic material, it readily defines the anatomy within, or around, the resected root end with a deep blue color. If there are any fractures, tissue remnants in the isthmus, or accessory canals present, the staining process will greatly enhance the operator’s ability to see them. When used properly, the MBS will delineate the periodontal ligament and the operator can be sure the apex has been completely resected.
To obtain the maximum benefits of MBS, and to inspect the bevelled surface thoroughly:
• the surface must be clean and dry before applying the MBS;
• the MBS must be applied for 10–15 s to saturate the surface and periodontal ligament;
• the surface must then be rinsed and dried thoroughly; and
• the REB should be examined using varying powers of the SOM to see whether the RER is complete and to insure that no abnormalities are present.
If after MBS there is an accessory canal present, the easiest way to manage this anatomical entity is to bevel past it and re-stain the surface to be sure that the defect is completely eliminated. Alternately, the accessory canal can be simply ‘troughed out,’ leaving the bevel as it is. If a white background such as Telfa pads, CollaCote, or calcium sulfate has been used to aid in hemostasis, or vision enhancement, it should be replaced after staining so that more light is reflected and vision renewed.
Ultrasonic REP – Prior to ultrasonic instrumentation, various types of rotary handpieces and ‘mini-burs’ were used. Because of the necessity of using a ‘straight-in approach,’ it was not possible to maintain the REP within the confines of the long axis of the tooth and perforation of the lingual surface could easily occur. With the advent of ultrasonic instrumentation, and the array of angled tips currently available to the operator, it is now possible to prepare a REP that will adequately and predictably accept several different root-end filling (REF) materials.
The requirements for an REP include:
• the apical 3 mm of the canal system is thoroughly cleaned and shaped;
• the preparation is parallel to, and centered within, the anatomic outline of the pulpal space;
• there is adequate retention form for the ref material used,
• all isthmus tissue is removed; and
• the remaining dentinal walls are not weakened.
If too little water is used, the necessary amount of cooling and rinsing of the debris will not occur. This can cause overheating of the REP. Micro-cracks and decreased vision may be the undesired result. Numerous studies have shown that when ultrasonic instrumentation is used properly, micro-cracks are uncommon and should be of no concern to the clinician (29–31 <file://localhost/javascript/popRef(‘b29%2520b30%2520b31’)>). Morgan, 1999 – A scanning electron microscopic study of in vivo ultrasonic root-end preparations. Lin 1999 – Root deformation during root-end preparation. Beling, Baumgardner 1997 – Evaluation for cracks associated with ultrasonic root-end preparation of gutta-percha filled canals.
In addition, use of ultrasonic instrumentation for REP, in place of the traditional, or miniature, hand piece results in cleaner preps and fewer perforations (30, 32 <file://localhost/javascript/popRef(‘b30%2520b32’)>). 1999 – Root deformation during root-end preparation. And Lin 1998 – The quality of ultrasonic root-end preparation: a quantitative study.
With the advent of ultrasonic techniques for the preparation of the root end, the use of a rotary hand piece is not advocated for root-end cavity preparation in apical surgery. Of particular interest in the development of the apical preparation is the buccal aspect of the internal wall of the prep. Often, this area is not cleaned adequately because of the angulations of the ultrasonic tip within the canal system. If there is some gutta-percha ‘streaming up’ the side of the wall, it is usually very time consuming, or futile, to remove this gutta-percha with an ultrasonic tip. The most effective way to finish the REP is to use a small plugger and fold the gutta-percha coronally, so the wall is clean once more. A clean and dry apical root-end cavity preparation is essential for good visibility when using the SOM. Throughout the process, and after completion of the REP, the cavity should be rinsed and dried with a small irrigator/aspiration tip if possible. If a 25- or 27- gauge-irrigating needle has been ‘pre-bent’ to a similar shape as the ultrasonic tip used for the REP, the ergonomics of using the irrigator will be more efficient. Subsequently, the cavity is inspected using various levels of magnification and sizes of micro-mirrors to confirm that the preparation is within the long axis of the canal system and all debris has been removed.. As an alternative, some surgeons choose to use small segments of paper points to dry the cavity; however, this may leave particles of paper in the preparation or may fail to provide a thorough drying in all dimensions. The smear layer consists of organic and inorganic substances, including fragments of odontoblastic processes, microorganisms, and necrotic. The presence of a smear layer prevents penetration of intracanal medication into the irregularities of the root canal system and the dentinal tubules and also prevents complete adaptation of obturation materials to the prepared root canal surface. If the surgeon is satisfied that all other requirements for the REP have been met, the smear layer can be effectively removed by etching with 17% EDTA (After etching, the REP is again thoroughly rinsed, dried, and re-examined under varying powers of magnification. The underlying reason for endodontic failures is almost invariably because of persistent infection of the root canal.
In the majority of cases requiring non-surgical retreatment, Enterococcus faecalis is the main and persistent microbial species (40–44 <file://localhost/javascript/popRef(‘b40%2520b41%2520b42%2520b43%2520b44’)>). If the vast majority of teeth requiring endodontic surgery do not responding favorably to previous non-surgical endodontic treatment, it is imperative that treatment be directed at eradicating bacterial infection including E. faecalis from within the REP.
Two percent chlorhexidine (CHX) gluconate is an effective antimicrobial irrigating agent for this purpose, and is available as a liquid or gel. Once the REP has been cleaned, dried, thoroughly inspected, and the smear layeres removed, it should be irrigated with 2% CHX liquid for 15 s or 2% CHX gel for 1 min (47 <file://localhost/javascript/popRef(‘b47’)>), Vianna, 2004 – In vitro evaluation of the antimicrobial activity of chlorhexidine and sodium hypochlorite, then once again, thoroughly rinsed and dried.
