- Open Access
Apical termination of root canal procedures—ambiguity or disambiguation?
© The Author(s) 2016
- Received: 11 June 2016
- Accepted: 14 June 2016
- Published: 22 July 2016
The issues of working length determination, its apical extent, and the position of the final root canal filling have been controversial, as differing points of view have existed between the biologically based and clinically based endodontic gurus regarding this concept for decades. Coupled with the following issues, it has become somewhat of an empirical bastion for clinicians, especially those in the limelight or who use social media to augment their clinical prowess: (1) the variable anatomy of the root apex; (2) where to terminate canal enlarging and shaping apically; (3) status of the accessory communications apically; (4) size of the apical preparation; (5) ability to debride the apical extent of the root canal and remove both bacteria and biofilm; (6) response of the periapical tissues, when both vital and necrotic, to the intracanal filling materials and techniques that may impinge on these tissues; and (7) long-term outcomes and assessments of the procedures rendered. For purposes of succinctness, the concept of working length, the apical position of instrument termination, and the position of the final filling will be addressed simultaneously in this paper.
- Root Canal
- Dental Pulp
- Root Apex
- Pulp Tissue
- Root Canal Filling
Cravens JE. Immediate root filling. Trans Ill State Dent Soc—29th Annual Meeting, The Dental Review Co., HD Justi & Son 1893;45–59.
One could consider using a systematic review to try and answer the controversial challenges cited in the abstract; however, this approach would not work historically, and from a contemporary standpoint, so very few, if any, published studies qualify to fit into the higher levels of the hierarchy of scientific evidence that the essential issues would not be addressed (Gutmann & Solomon 2009). Therefore, a somewhat unorthodox approach to this concept has been chosen, one in which historical reflection and contemporary assessment will be used to compare and contrast philosophies that address the issues of concern. The starting point will be the First International Endodontic Conference that occurred in Philadelphia, PA, USA, in 1953.
Codification of the principles of root canal procedures
While not a recognized specialty of dentistry globally at that time, endodontics and the provision of root canal procedures had been advocated routinely in some, very limited, and visionary areas of dentistry, even with the name of endodontia being proposed by Dr. H. B. Johnston and accepted by the community at large, including the American Association of Endodontists (Gutmann 2008). However, this first world conference established some significant guidelines for clinical procedures based on historical documentation and treatment philosophy up to that point, both clinical and biological. It is here that this manuscript will begin to explore the issue of working length in an attempt to clarify all aspects of the challenges involved in apical biology in relation to a preferred termination point for root canal procedures.
What were the important outcomes of this first conference?
Traumatic injury to the surrounding (periapical) soft tissue should be avoided at all times. To this end, instrument stops should be used and instruments should be confined entirely within the root canal (Grossman 1953).
“…the canal filling should seal the apical foramen, and that if the apical millimeter or so of the canal is filled with healthy living tissue, the root canal filling should terminate at this level rather than at the apical foramen” (Grossman 1953).
Historically, what contributed to the thinking that helped to solidify these principles?
What was it about the biology of the periapical tissues and the clinical techniques at that time that led to this definitive position?
Was this approach to managing the apical portion of the root canal and root apex to be the same in teeth with viable apical tissues or necrotic apical tissues with or without the obvious presence of an apical rarefaction?
Was the best evidence available to the individuals in this conference? What role did apical resorption play in these guidelines, if any?
What was known about the root apex in 1953 that was not known in 1911 or before?
What was known about treatment outcomes in 1953 relative to current practices at that time and previous practices that may have impacted on tooth retention or successful outcomes?
It should be borne in mind, that at the point where the vessels and nerves in question enter the root, the passage is much smaller that it is immediately within. This strait (constriction) will be easily recognized when reached, by the touch, the instrument appearing to be arrested by an obstacle, and not by being wedged in a narrow passage. Care should be taken, I think, that the instrument is not allowed to pass through the strait, either by being too small or by being revolved there till it cuts its way through. For, by wounding the parts without the tooth, and forcing particles of bone (dentin) out upon the parts external to the roots, the danger of an unfavorable result would be greatly increased. (Harris 1855)
…the treatment of pulps was not seriously undertaken by the profession previous to 1865, and that after 1870 the attempts to save teeth with exposed living pulps, or with dead pulps, became quite common practice, the method generally employed being the removal of the contents of the canal and placing of from one to many treatments of creosote on cotton, most operators leaving such a treatment as a root filling. (Noyes 1922)
It is our practice at this time to amputate large pulps somewhere in the apical third of the root. With small canals, as in the buccal roots of upper molars and the mesial roots of lower molars, we have been excising at the floor of the chamber… (Davis 1923);
…where we cannot (reach the apical foramen), as in contracted or tortuous root canals, we force tannic acid solution into the inaccessible pulp tissues…we used the tannic acid solution because when brought into contact with any remaining pulp tissues in the root canal, it forms an albuminate of tannin; a compound which is insoluble in any of the fluids of the surrounding tissues, and consequently no disintegration can take place to cause any after trouble. (Mills 1897)
Simple ramifications or branches and lateral canals within the radicular dentin
Intercommunicating canal system
Islands of hard tissue within the canal
These differentiations were named as bifurcations and ramifications, which created a complex system of apical morphology. With his method, Fisher established the accurate morphologic variations of a developing tooth, either in physiological or pathological conditions. He described very accurately the neoformation of dentin and pulpstones within the root canals. Furthermore, by associating macroscopic and microscopic observations, he showed how the root canal morphology is very complex due to the ramifications present, calling them lateral canals (Seitenkanal), and also apical ramifications called regio ramificatoria, which is referred to presently as an apical delta. The complexity and inability to predict the canal morphology brought him to name the whole system as the radicular canal system (Kanalsystem).
Subsequently, there began a true appreciation for the nature of the tissue at the end of the root, as histological studies were able to demonstrate that the pulp tissue ended at the dentinal-cemental junction and that there were few if any incidences of pulp tissue going all the way to the end of the root or to the extent of the major foraminal opening (Grove 1916; Noyes 1921). The issue now was the clinical management of these tissues.
Key investigators, such as Noyes (Noyes 1922; Noyes 1921), Grieves (Grieves 1915; Grieves 1919), Blayney (Blayney 1927; Blayney 1922; Blayney 1926; Blayney 1940; Blayney 1932; Blayney 1936; Blayney 1929a; Blayney 1929b), Skillen (Skillen 1922), Hatton (Hatton 1922), Coolidge (Coolidge 1921; Coolidge 1922), Groves (Grove 1921; Grove 1931), and Davis (Davis 1922a; Davis 1922b), recognized these anatomical challenges, including that of cemental permeability, especially in light of the focal infection theory and still approached teeth with compromised or necrotic pulps with the same focus, “Shall we, or shall we not, attempt to retain the pulpless tooth? In the presence of the irrefutable dictum that the natural organ is better than any substitute, the answer is ‘We shall.’ Noyes said it succinctly; ‘…let us rather make it a practice to extract only such teeth as diligent, conscientious and persistent effort have proven conclusively to be beyond our present ability to put in wholesome, safe condition.’” (Noyes 1921).
The dental pulp may be removed without causing irreparable damage to the periapical tissues, provided the following definite plan of operation is carried out: a) surgically clean technic ; b) use of only mild antiseptics, all caustics being eliminated; c) avoidance of injury to soft tissue in the apical foramina; d) removal of all true pulp tissue; (and) e) filling of the canal with a bland, non-irritating, non-absorbable filling material to near the site of amputation.
Following the operation, there is begun, in the apical region, a process of resorption that enlarges the apical foramen, or a new channel may be cut that more successfully meets the conditions within the canal.
These resorptions may heal, with the formation of calcified material resembling cementum.
Many of the apical foramina may be reduced in size by repair calcification. But this reduction seldom obliterates the canal. as sufficient space usually remains for an efficient circulatory apparatus.
The filling material, when in contact with soft tissues, excites a foreign-body reaction. Better results are obtained in the cases that are slightly underfilled.” (Blayney 1929b).
There is one more thing I want to say in regard to these fillings that do not reach the ends of the canal. It is my belief that we should in every case, wherever we can possibly do so, get our filling to the end of the PULP CANAL (Author’s Emphasis). In every one of those cases in which I did not get there, you may depend I spent an hour or more, may two or three, in trying to get there. But the point I want to make particularly is that we may ignore absolutely the foramen through cementum if we can fill the pulp canal to the end of the dentin. While you cannot fill a minute foramen, which is as fine as a hair in some cases, in my judgment a tooth is three or four or ten times as safe if you fill the root to the end of the pulp canal, leaving the fine foramen through the cementum of the root without meddling with it, as it would be if you drilled through the foramen and carried the filling to the end of the root and put a cape over the end of it, as Dr. Rhein advocates. (Fig. 8) (Author’s note: Dr. Rhein advocated filling beyond the end of the root so the filling material would encapsulate the apical 2–3 mm, thereby sealing off all the accessory communications. He referred to this as “mortarization” of the root end.) (Fig. 9)
The question of root-canal therapy is one that embraces a very particular point, and that is, there is no question that I know of, as a medical man, outside of brain surgery, (and I would even include a large amount of brain surgery) that requires the same amount of skill, patience and time…When I show hundreds of roentgenograms - some of them dating back to work done almost 30 years ago (Author’s note: which would be in the late 1890s), showing absolutely, so far as a roentgenogram can show, normal tissue (with) thorough encapsulation of gutta percha on the apices of the roots - I definitely refute the essential point of criticism of the essayist’s paper. (Rhein 1920) (Author’s note: that root canals should only be filled to the end of the dentinal canal and not impinge on the cementum).
Where I have found re-infection in my own cases and have had to extract teeth, I have also found invariably extra foramina at some point that had not been encapsulated, and which were the cause of the recurrence of infection. (Rhein 1920)
The issue of necrotic remnants being left in apical accessory canals and treatment failure still reverberates in today’s clinical practice and provides the impetus for the promotion of filling to the root apex, using a technique in which these canals may be filled. However, this achievement may be flawed with regard to histologically identified outcomes (Ricucci & Siqueira 2010).
There is some evidence for believing that remaining vessels and apical pulp-shreds, lying in touch with surrounding vascularity, either become organized into fibrous tissue or foramina are closed by deposits of cementum or osteo-dentin. This can occur only in a vital apex, not infected, nor saturated with chemicals, nor PERFORATED AND OVER FILLED (Authors’ Emphasis); and only in one to which the periodontium is physically attached. However, he goes on to say, in his extensive treatise, “The vital apex is, thus, the crux of all canal operations. Its maintenance is worth any amount of time and effort. It cannot be encapsulated (Author’s note: as per Dr. Rhein) because periodontal fibers are everywhere attached to it. There is, therefore, no denudation or hypoplasia in which encapsulations may lie, unless they traumatically protrude into the membrane, granulomata, or cysts. Quite the reverse: the denuded apex, necrotic by whatever means, is not worth a moment’s effort, no matter how medicated nor how well filled (Author’s note: this reflects the impact of focal infection). One of the gravest mistakes of dentistry is the stubborn belief that correct root-canal filling will cure apical disease.” (Author’s note: this same concept is present today when clinicians say they are treating periapical lesions or apical periodontitis) The most perfect canal operation is never curative, but only a preventive procedure. (Grieves 1920)
There be dentists who conscientiously believe that a pulpless tooth is a dead tooth; that every dead tooth is doomed to infection; and that all infected teeth are a menace to the health of the individual. to such practitioners this communication is not addressed. There be others who believe that a pulpless tooth may be so treated that it will not only be tolerated by the human body, but may be made to serve its function of mastication, and aid in the initial step of digestion, thus becoming an important factor in metabolism and an ultimate contributor to the health of the subject. From such as subscribe to these tenets I crave attention, trusting that I may deliver to them a message which may in some small degree render their efforts to minister to suffering humanity more certain and more effacious. (Ricucci & Siqueira 2010)
Any radiographic evidence of gutta percha beyond the apex of the root, is a protrusion of the filling material…
The protusion of gutta percha beyond the apex demands space for its occupation.
…any appearance of gutta-percha beyond the apex of a healthy root is an evidence of a fault in the technique.
In the presence of infected apical areas…and the gutta percha has been forced beyond the apex…whether such infection, both of the area and of the protruding foreign body can be overcome, will be determined solely by the vital responses of the patient in each instance. Sometimes a cure will be accomplished in spite of the gutta percha. It is inconceivable, however, that the protruded material can act as a curative factor.” (Ottolengui 1922)
Transitions in thought and reaffirmation of clinical directives
…in the case of extraction of the pulp it was or importance to establish, how any given method would operate when the pulp canal was in direct connection with the periapical connective tissue. In the case of the dog, on account of its ramifications the pulp tissue is without exception separated from the connective tissue, so that no connection is established with the periapical connective tissue throughout the manipulation in the canal. We now had to drill through the tooth to this area, and at once it was evident that we must use a much more pretentious method, if we are to come in direct contact the periapical tissue and if we were to care for injuries to the connective tissue. This change made in the procedure of the experiment by this drilling was necessitated by the fact that in the human mouth it was not at all uncommon to come in contact with the periapical connective tissue during pulp extraction. (Gottlieb 1938)
The claims that we had to satisfy in the treatment of a periapical focus of infection took an a much more complicated form, and aspects developed that we could in nowise anticipate. We could form no clear picture of what happened to the necrotic root surfaces, nor could we imagine what might be expected from branchings of the root canals that harboured dead tissue. It was demonstrated that soon after sterilizing and freeing these dead tissue of germs, the neighbouring inflamed connective tissue regained health, and almost at once deposited cementum upon the necrotic surfaces of the tooth. This cementum may also close up the apical foramen, and thus produce a complete surface consisting of living cementum, which removes completely every doubt concerning retention of such a tooth. (Gottlieb 1938)
Once a piece of foreign material has penetrated through the foramen, no favorable condition of any kind can induce the closure of the entrance by the formation of a hard wall. (Gottlieb et al. 1950)
…first, it must be resorbable, and second, it must stimulate the connective tissue to form new additional hard tissue which will replace it. (Gottlieb et al. 1928)
Enter empiricism as the endodontist’s mantra
…the closure of the root end with cementum, while both possible and desirable, is demonstrable much more readily in animal experimentation that in human patients, and is unnecessary for the health and function of the apical periodontium. (Schilder 1974)
The enormous success which has followed filling root canals to their radiographic apices or beyond has led some to theorize that healing of large periapical radiolucencies may be stimulated by root canal filling material outside the confines of the canal. While this may be possible, it is more likely that, as in the case of filling to the cementodentinal junction, continued success results from the thoroughness of the three-dimensional filling along the major extent of the root canal and not on the fractional overextension or underextension of the filling. The wise old suggestion to slightly underextend root canal fillings in case of vital extirpation and to fill to the radiographic apex or slightly beyond in cases of pulpal necrosis and gangrene is probably more meaningful in terms of patient comfort that in terms of the ultimate result. (Schilder 1974)
In many respects, these empirical comments cast a dark shadow on many years of histopathological research and in-depth investigations by the few biologically motivated clinicians who fought the fight against both focal infection and the inadequacies that permeated clinical practice. In doing so, this ushered in the “look or thrill of the fill” on the two-dimensional radiographic, and as long as the filling material was positioned at the extent of the root, and one or more accessory or lateral canals evidenced some type of filling with puffs or buttons of sealer or gutta-percha along the root surface, success was considered inevitable and the focus of treatment was on new instruments and new techniques.
…it will be understood that the instruments are, in most cases, slightly beyond the confines of the root canal in the adjacent periodontal ligament space. This position will be reached from time to time with appropriate caution, to ensure both a complete debridement of tissue debris and to maintain the patency of the canal. Deliberate instrumentation short of this point without occasional probing of the apical opening predisposes to dentin mud accumulation at the apex, thereby increasing the risk of inadvertent blockage of the primary canal. This major source of frustration for inexperienced operators can be avoided by probing to or near the radiographic apex sufficiently often to keep dentin mud from accumulating there. (Schilder 1967)
This was the first indication that “patency filing” was being advocated over attempting to retain instruments within the “pulp canal,” while other authors who recognized the possibility of packing debris and dentin mud advocated apical clearing without going beyond the confines of the pulp canal (Walton & Torabinejad 1989).
In the late 1980s, due to the plethora of advances in enlarging and shaping techniques and enhanced instruments and the focus on a more thorough cleaning of the root canal system, patency filing was advocated as a routine clinical procedure (Buchanan 1989), albeit empirical, which gained acceptance, especially in many of the dental schools in the USA (Cailleteau & Mullaney 1997). Claims were made that the removal of accumulated debris in the apical portion of the canal was essential for both cleaning the apical foramen and ensuring success through a more thorough canal obturation. Since then, while there have been numerous publications that have addressed the value of this procedure, it has been accepted globally by many with the exception of the some areas in Northern Europe and Scandinavia (Goldberg & Massone 2002; Cemal-Tinaz et al. 2005; Araújo Souza 2006; Gonzalez Sanchez et al. 2010). In a recent randomized controlled trial that addressed the effect of maintaining apical patency on post-treatment pain in posterior teeth with necrotic pulps and the presence of apical periodontitis, no significant differences were noted between patency filing and no patency filing (Arora et al. 2016).
Contemporarily, four philosophies tend to permeate the clinical world of endodontics regarding where to terminate enlarging, shaping, and obturation: (1) those based strictly on the anatomical studies; (2) those based strictly on prognostic studies and outcomes of treatment; and (3) those based on empirical directives… “it works for me.” Using one of these first three positions as arguments, it is conceivable that every endodontist or dentist who performs root canal procedures can use all three for a given case or a selective, whichever was convenient, to exercise cognitive dissonance (Seltzer & Bender 1965). According to Simon and associates, “…differences represent conflicting opinions concerning the apical limit of preparation and overall differences in concepts.” (Simon et al. 2009). Possibly the most influentional concepts within this dilemma of where to terminate both the enlarging and shaping and obturation lie in the status of the dental pulp at the time of the procedure. However, even this can create consternation due to the inability of the clinician to determine without question the viability of the dental pulp and/or the mere presence of bacterial species or bacteria and their associated biofilms, along with the location of such. Finally, (4) those based on the status of the dental pulp and periapical tissues may be the determining criteria for many clinicians, but the exactness of such is severely wanting.
One of the more interesting publications (two parts) that addressed the focus of this paper appeared in 1998, before the availability of micro-CT (Ricucci 1998; Ricucci & Langeland 1998). Part 1, which was a literature review, confirmed what the previous prognostic studies had indicated, that the practice of staying short of the apex with a homogeneous root canal filling yielded the highest success rate (90–94 %), when done by or under the supervision of a specialist. However, results in the general population resulted in a greater failure rate (>50 %) (Martins et al. 2014). Furthermore, the author indicated that it was impossible to instrument accessory canal ramifications and that, when these ramifications appeared filled on the radiograph, it was only due to the forcing of root canal sealer into the tissues located in these ramifications, which was verified in a later study (Ricucci & Siqueira 2010)… an outcome that was frowned up decades earlier (Grieves 1914a; Grieves 1914b).
When the sealer and/or gutta-percha was extruded into the periapical tissues, the lateral canals and the apical ramifications, there was always a severe inflammatory reaction including a foreign body reaction despite the absence of pain. (Ricucci & Langeland 1998)
In a unique study that addressed tooth anatomy risk factors that influenced root canal working length accessibility, Tang et al. (Tang et al. 2011) found that tooth type, root canal curvature, canal calcification, and retreatment were primary risk factors in an independent factor analysis. However, using a multiple-factor regression model, root curvature and canal calcification were found to most significantly influence working length accessibility and ultimate treatment success. In particular, as the extent of the canal calcification increased, the difficulty in reaching the root canal constriction increased sevenfold, whereas an increase in canal curvature only increased the difficulty twofold.
Prognostic studies and treatment outcomes
“The optimal result was to end the root filling one to two mm inside the radiographic apex - exactly the same recommendation that emerged from the anatomical studies (in the early 1900s). If the root filling is shorter than that, the success rate will drop; but overfills will yield an even poorer results. (Hasselgren 1994)
Most prognostic studies could only relate to radiographic findings identified at the time of filling and subsequent control or recall appointments. Therefore, the issue of where the measurement was taken, to what level the canal was “carefully instrumented” and the ultimate obturation, both vertically and laterally may be issues that could never be resolved in the historical studies. Furthermore, outcomes with teeth having vital, inflamed pulps that had obturations that go beyond the confines of the canal may have been worse than teeth with necrotic pulps that had obturations within the canal confines and vice versa depending the degree of canal cleaning and disinfection in each situation. The scenario just addressed brings to the forefront another important issue in these studies, with that being there may be insufficient evidence to support the clinical achievement of bacterial eradication prior to obturation at whatever level the filling is placed. Studies do support better outcomes regardless of the position of enlargement, shaping, and obturation if the root canal is bacteria free. However, two issues come to mind in that regard: (1) that the presence or absence of bacteria at the time of obturation cannot be reliably determined at this point and (2) not every root that contains bacteria at the time of obturation will result in failure, again regardless of the position of the root canal procedures that had been performed (Sjögren et al. 1997). Moreover, and possibly most important, virtually all the studies only used two-dimensional radiographic assessments, which by today’s standards may be woefully substandard, as there is substantial disagreements between periapical and CBCT radiographs for assessing the periapical status of molar teeth, especially for the maxillary arch (Cheung et al. 2013). These findings have serious implications in periapical diagnosis and for evaluation of the outcomes of root canal procedures (Cheung et al. 2013).
After vital pulpectomy, the best success rate has been reported when the procedures terminated 2 to 3 mm short of the radiographic apex. With pulpal necrosis, bacteria and their byproducts, as well as infected dentinal debris may remain in the most apical portion of the canal; these irritants may jeopardize apical healing. In these cases, better success was achieved when the procedures terminated at or within 2 mm of the radiographic apex (0 to 2 mm). When the therapeutic procedures were shorter than 2 mm from or past the radiographic apex, the success rate for infected canals was approximately 20% lower than that when the procedures terminated at 0 to 2 mm. Clinical determination of apical canal anatomy is difficult. An apical constriction is often absent. Based on biologic and clinical principles, instrumentation and obturation should not extend beyond the apical foramen. (Wu et al. 2000)
When the technical quality of the root-filling was related to treatment outcome, the studies demonstrated success rates of 70-100 %, if the quality was assessed to be optimal. If the root-fillings were short of the apex, a lower success rate of 57 %-95 % was found, If extrusion of root-filling material in periapical tissues were found, the success rate was ever lower at 50 %-90 %. (Kirkevang & Bindslev 2002)
…vital tissue in the accessory communications was not removed during canal shaping and cleaning and although lateral canals appeared radiographically filled they were actually not obturated, and the remaining tissue in the ramification was inflamed and enmeshed with the filling material. (Ricucci & Siqueira 2010)
This finding supports the dictates of our forefathers, discussed previously, who encouraged the preservation of the tissues in these ramifications to allow normal healing to occur.
In a 10-year clinical follow-up study, a group of investigators from Croatia identified success in comparison to length of root canal instrumentation and obturation in 163 patients (Tamarut et al. 2006). In this study, they used controlled over-instrumentation (1.62 mm ± 0.92 mm) in all pulpal diagnostic states and obturation to the physiological foramen or apical constriction and found that it was not harmful to healing. Furthermore, slight overfilling did not impair success. Keep in mind, radiographic evaluations were done with traditional two-dimensional assessments
In another 10-year follow-up study of 15 single-rooted teeth following root canal procedures from a population of patients aged 25–40, the teeth were extracted due to caries, resorption, or trauma. In order to obtain surrounding apical bone for histological analysis, an apical block dissection was performed (Khayat 2005). While limited in sample size, the teeth had root fillings that were extruded beyond the apex (47 %) or flush with the radiographic apex (53 %). Radiographs showed that 8 of the 15 had overfilling of gutta-percha and sealer, while 7 of the cases had gutta-percha and sealer to the root apex. Healing activity was observed in all cases; however, active macrophage with phagocytic activity was seen even in a case that was 10 years old, which would imply some degree of persistent inflammation. However, many studies of this nature show “healing” in some areas of the periapical tissues, while chronic inflammation can be present in other areas; additionally, healing does not equate with healed (Glossary of Endodontic Terminology 2012).
Most recently, Azim and associates reviewed radiographically 422 roots from 291 root-treated teeth that met an inclusion criteria of a mean follow-up period of 2 years (Azim et al. 2016). Roots instrumented apically within 0.5 mm from the radiographic apex had a significantly more favorable outcome (88 %). Those >2 mm short from the radiographic apex had the least favorable outcome (33 %). Teeth with overextended root fillings showed delayed healing by almost 14 months.
While it is true that the foramen is not always at the extreme apex…there may be more than one foramen to the root, the one method to be presented will meet this condition with precision…an electrical method of extreme delicacy and accuracy…The electrical method is based upon the difference in the electrical conductivity of a dry pulp canal or one filled with a non-conducting liquid, and the conductivity of the tissues just beyond the apical foramen. (Custer 1918)
While popular in its application for working length determination, the EALs have not resolved issues as to the apical limit for canal instrumentation and obturation (Mohammed et al. 2015), as survey results of UK-trained or qualified respondents indicated that the majority preferred to go to the same apical limit with all apical procedures. This is in deference to empirical directives that may indicate that the status of the pulp and periapical tissues may require variations in apical terminations. As a confirmation of the former choice of relying on the EALs for the working length in all cases, being the same position for all procedures, Tsesis et al. (Tsesis et al. 2015) found the use of the EALs was not influenced by the status of the pulp tissue, although the precision of the length determination was based on the particular device and the type of canal irrigant. In contrast to this issue, Martens and associates, in a systematic review of the literature on the clinical efficacy of the EALs, noted that in addition to using the EALs, and due to the fact that the available scientific evidence base for efficacy is minimal and at risk for bias, at least one radiograph control should be used to detect possible errors in the application and interpretation of data from these devices (Martins et al. 2014).
There are no guidelines that can be identified with this directive as they are all clinician-based and are determined on a case-by-case basis; however, even this would not be an accurate assessment, as many clinicians manage their apical root canal procedures in the same way for all teeth, that is instrumenting and obturating to the same apical limit (Mohammed et al. 2015), claiming complete success, as long as the patient is comfortable. In this regard, most will follow the dictates of a professor where they received their education or grasp on to the directive given to them in their most recent continuing educational pursuit from those claiming to have the magic way to achieve success. The hallmark of this approach usually is characterized by the presence of root canal sealer puffs and the extrusions of filling materials beyond the root end, with claims of having achieved a perfect seal of the canal system (using only two-dimensional radiographic evaluations).
Status of the dental pulp and periapical tissues
The wide range of anatomical variables and technical interpretations regarding the apical location for determining the working length and the position of the final obturation have been identified. Furthermore, because the actual location of this variable terminal position has resulted in significant number of clinical opinions, along with variable applications and advocacies, at least two camps of polarized thought, along with a vast array of outliers, have evolved. Advocates have been driven by passion, concern for radiographic appearance, staunch adherence to the use of EALs, strong advocacy for patency filing, and the incorporation of cognitive dissonance into their decision-making and proffering (Seltzer & Bender 1965). One major philosophy is to retain all procedures within the confines of the root, while the other philosophy espouses the determination of working length, enlarging, shaping, cleaning, and obturation to the anatomical root apex or root length. In most teeth, while overlap or agreement may occur in some cases, these two philosophies are not compatible. However, in light of this controversy, there seems to be a middle-of-the-road position that most clinicians can travel comfortably and that will yield success. While the choices can vary, it would seem to be dependent on the status of the dental pulp, access to the end of the root, and the clinician’s skill and expertise, in addition to experience that demonstrates that particular choices provide positive outcomes in the majority of cases. However, evidence-based data at the highest level to verify this approach are not available, and therefore, it is empirically driven.
If the dental pulp is vital (inflamed; irreversible pulpitis), then the working length is established clinically as close to the constriction as possible and attempts are made to retain all procedures within the root canal. While this position has been advocated as approximately 0.5–1.0 mm from the radiographic apex, this dictate is flawed (Ricucci 1998). In essence, the thought behind this approach is that the tissue that invaginates into the canal from the periodontal ligament, and which is periodontal in nature, is not disturbed by the subsequent manipulations that are performed within these confines (see Fig. 7) (Gutmann & Reagan 1998; Gutmann 2005). This recommendation is based on sound wound-healing principles in that severance of the tissue at its narrowest point will create the smallest wound possible for healing (Ricucci 1998; Ricucci & Langeland 1998). It also encourages the potential for tissue regeneration with the formation of cementum as opposed to just fibrous connective tissue repair or persistent chronic inflammation (Gutmann 2005).
Ironically, both of these philosophical and clinically practiced positions provide no evidenced-based data to support them as the ideal working-length technique for instrumentation and obturation, and it is only when the teeth are obturated can one conjecture where the exact working length was terminated during the procedures. Therefore, data to support either position contemporarily are elusive and unfounded, except for information gleaned from outcome studies that take into account all phases of the root canal procedures. For example, according to Gesi and Bergenholtz (Gesi & Bergenholtz 2003), when no infection is present, it is hard to rationalize, as it is sometimes advocated that the apical foramen be pierced and root canals be overfilled with so called puffs. It would seem that overfills of this nature actually reflect the inexactness of the obturation technique, whereas the clinician is hoping that the canal is truly filled and sealed. Furthermore, an inadvertent overfilling may not necessarily be harmful or cause a periapical lesion to form but may actually reflect a unfavorable apical shaping and alteration of the normal anatomy, which may put the apical tissues at risk for delayed healing or lack thereof (Bergenholtz et al. 1979). Many of these studies that address these issues are retrospective in nature, have questionable bearing on contemporary practices, and are based on two-dimensional radiographic assessment.
The author would like to thank the following individuals for their invaluable professional assistance and guidance in procuring the necessary documentation in support of the figures/photos in this manuscript.
Andrea Matlak, Archivist, American Dental Association, Library and Archives
Arlene Shaner, Historical Collections Librarian, The New York Academy of Medicine
Dawn McInnes, Rare Book Librarian, Clendening History of Medicine Library, University of Kansas Medical Center
Helen Jameson, Assistant Executive Director, American Association of Endodontists
Joanna Goldberg, Information Services Librarian, The New York Academy of Medicine
Nicola Perrini, Fondazione Castagnola, Milano
Tim Horning, University Archives, University of Pennsylvania
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