On Extrusion of Irrigants and Debris

Through the Apical Foramen

Concerning the extrusion of debris through the foramen during cleaning and shaping procedures, differences in the experimental design between published ex vivo studies as well as differences with what would be in vivo clinical situations make it difficult to extrapolate the results of extrusion from ex vivo studies to clinical reality.

Two studies have shown that even without the use of a patency file, extrusion of debris/irrigants occurs frequently in vitro. Lambrianidis et al. [19] used thirty-three human maxillary incisors in their study in which debris and irrigant were measured after being extruded into a glass vial. All root canals were instrumented to the apical constriction with the step-back technique, but a patency file was not used. The total volume of irrigant used per canal was 10 ml. After this procedure, the apical constriction was further enlarged and the measurement was done again. They found more extrusion when the constriction remained intact and concluded that with more instrumentation, the formation of an apical plug could have helped prevent the extrusion of the irrigant, just as it was shown in a previous study assessing extrusion [20].

Another study used a colour-changing reagent in acrylic receptacles in contact with the root tips of maxillary molars [9]. The authors assessed the extrusion of the irrigant without any instrumentation technique used to flare the canals. In phase one of the study, irrigation was done with 3 ml of NaOCl, placing the needle at the entrance of the canal and injecting without pressure after establishing apical patency. In phase two, size 10 and 15 K-Flexofile were used as patency files; then the canals were irrigated again. The study reported extrusion in 9/17 specimens after the use of the 10 K file for patency from phase one and in all specimens from phase two.

These are examples of how variable the results can be when determining this sensitive issue, because the kind of extrusion reported ex vivo would lead to postoperative pain and flare-ups in the vast majority of cases in vivo. By contrast, clinically postoperative pain after root canal ther-

apy occurs with very low incidence. In addition, not blocking the foramen when using ex vivo specimens would not mimic the in vivo situation, allowing for a larger amount of debris and irrigants to be extruded through the foramen. In vivo, the vapour lock effect present in a closed system would result in different intra-canal hydrodynamics [39].

Conclusions From these results we could conclude that using a small patency file should not alter the anatomy of the apical root canal in a way that could affect clinical results. Further comparative studies with strictly controlled variables should address the influence of a patency file on debris extrusion through the foramen. It is not clear if the use of a patency file would lead to more debris/irrigants being extruded through the apical foramen. Clinically, the use of a patency file helps to maintain working length and to avoid packing debris in the apical third of the complex root canal anatomy.

Role of the Patency File on Irrigant Penetration into the Apical Third of Root Canals

Irrigants should be able to reach the apical third with enough concentration and contact time so that they can dissolve organic tissue, kill planktonic bacteria, and disturb or eliminate biofilms attached to the dentin in the very complex apical anatomy. Salzgeber and Brilliant showed [29] that irrigants (Hypaque) could not reach the apical third of human root canals that contained vital tissue in vivo. They also showed that if the canals were flared to small apical sizes, the irrigant was detected at the apex and, in some instances, in the periapical lesions in nonvital teeth. Instrumentation techniques used at that time would probably push a larger amount of NaOCl and debris through the foramen because of the “pumping” action of hand files. However, comparative studies in vivo have not been carried out to prove such a statement.

In a recent in vivo study using a radiopaque solution Claritrast 300 (ioversol 678 mg/mL)

mixed with 5.25 % NaOCl, which was approximated in density and viscosity to that of NaOCl alone, 40 human root canals considered small (buccal roots of maxillary molars, mesial roots of mandibular molars, and both roots of maxillary first premolars) were irrigated with the solution to within 2 ml from the working length (WL) after the use of every rotary instrument. Then, passive ultrasonic irrigation (PUI) was used in both groups for 1 min at the end of the procedure. In group one, apical patency was maintained during the shaping and cleaning procedure with a 10 K file, but not in group two. A blinded calibrated reader determined the presence or absence of the radiopaque irrigating solution in the apical 2 mm of the treated roots. Statistical analysis showed that there was significantly more irrigant after the use of PUI when a patency file had been used throughout the cleaning and shaping procedure compared to the group where it was not [42] (Fig. 7.4).

In a different study where the same methodology was used [45], penetration of irrigants into

the apical 2 mm of 43 large root canals (palatal roots of maxillary molars, distal roots of mandibular molars with one canal, and anterior teeth measuring between 19 and 21 mm) was measured. A 27-G side-vented needle was inserted to 2 ml from the WL with gentle in and out movements and maintaining apical patency, demonstrated a higher incidence of the mixture of NaOCl/radiopaque solution in the apical 2 mm of the root canals compared to those teeth where apical patency was not maintained throughout the cleaning and shaping procedure. It was concluded that the low flow rate used was not very efficient in delivering the irrigant into the apical 2 mm when a patency file was not used.

In both of these studies, the lack of penetration of the irrigant deep into the apical 2 mm could have been caused by the presence of the remaining pulp tissue in the apical anatomy that was not removed adequately by the combination of the cleaning and shaping technique and the dissolving action of NaOCl or the presence of an apical gas bubble or vapour lock effect as proven in

some in vitro studies [39]. Furthermore, the gas bubble could grow larger in size because of the reaction of the irrigant with organic tissue [14]. However, other authors have doubted the presence of a vapour lock if a high enough flow is used while irrigating and by also using an open-ended needle that should be positioned closer to the WL [6]. The advantages and risks involved in irrigating in such a way will be discussed in another chapter of this book.

Besides the role of the patency file in the penetration of irrigants into the difficult-to-reach apical anatomy in human root canals, its influence on the presence of large gas bubbles in the middle and cervical third of human root canals in vivo was evaluated in another study [43]. Apical patency was maintained with a 10 K file in two groups (small and big canals), but not in the other two groups also consisting of both small and large canals. Irrigation was also done using a mixture of 5.25 % NaOCl and the radiopaque solution Claritrast 300, which had been tested in pilot studies to dissolve pulp tissue efficiently. Then, a calibrated reader evaluated the presence of gas bubbles in radiographs that were taken during every step of the cleaning and shaping procedure. It was surprising to note that, when present, these gas bubbles could move in the root canal, but they were not easy to break. Furthermore, when a patency file was not used, the gas bubbles in the middle/cervical third appeared in 40 % of the cases, compared to only in 25 % when the 10 K file was used to maintain patency. Even though the importance of such bubbles may not be much concerning the penetration of the irrigants into the apical third, the consistent presence of these bubbles in the middle and cervical thirds would limit the contact of NaOCl with organic tissue and microorganisms attached to the dentin and hiding in isthmuses and areas where there would be more gas than irrigant during the cleaning and shaping procedure. Some other articles have described this vapour lock effect in closed-ended canals/tubes, preventing irrigating solutions from reaching their apex [10]. However, some studies have mentioned the possibility that the change in composition of the irrigant by mixing NaOCl with a

radiopaque solution could also vary the density, and especially its viscosity and surface contact angle, when compared to NaOCl by itself, thus favouring the apical vapour lock effect [6].

Conclusions Using a patency file appears to help irrigants penetrate into the apical 2 mm of the complex anatomy of human root canals both in large and small canals and to prevent gas accumulation in them, at least under the conditions of the aforementioned studies. Whether this in vivo penetration really improves the “cleaning” of the root canal is still not demonstrated and will be discussed further in the following section of this chapter.

The Use and Effect of the Patency File in Cleaning of the Root Canals in Teeth with Vital Pulps

Concerning cleaning and shaping of the apical third, some studies have tested the importance of apical patency during the preparation of the root canal. Some authors have recommended the proper working length to be determined 1–2 mm short of the radiographic apex and avoiding patency [17, 25, 26] (Fig. 7.5).

Fig. 7.5 A small K file used short of the foramen. No patency (Courtesy of Fernando Durán-Sindreu)

These authors question and criticize the need for a patency file in cases with vital pulp and actually state that it is contraindicated in cases where there is a clean wound in the apical pulp tissue. A photomicrograph depicting this situation is shown Fig. 7.6, of the buccal root of a maxillary first premolar to be extracted for nonrestorability. The pulp was vital and the canals were instrumented before extraction. Rotary NiTi files were employed, 1 % NaOCl was used as the irrigating solution, and the working length was established 1.5 mm short of the radiographic apex. The section shows an apical delta with undisturbed vital tissue. The use of a patency file in such situations could destroy the connective tissue, impairing or delaying wound healing.

In light of this terminology, it is important to differentiate that the maintenance of apical patency will prevent the blockage of one of the foramens with dentin chips, and not necessarily all of them, because of the complex anatomy of

the region (Fig. 7.7). One disadvantage of not using a patency file in noninfected teeth is the possibility of being blocked out or losing working length during instrumentation of the root canal. However, experience and proper use of endodontic instruments should still prevent this accidental procedure. Furthermore, it has been shown clearly that the use of an electronic apex or foramen locator helps determine the ideal position in space for the determination of the optimal working length. The vast majority of studies, as well as indications for the use of different brands of apex locators, recommend advancing the file until the “long” signal is displayed on the screen and then withdrawing it until the display shows “at the foramen” or “slightly short” of the foramen [37]. Therefore, to properly use a device, which is important in modern root canal therapy, a patency file should be used at least once per root canal. The injury that this procedure could potentially inflict on the periapical tissues and the possibility that further use of the patency file two or three more times throughout the shaping and cleaning procedure could increase that injury in a clinically significant manner remain unknown. Interesting discussions on the matter remain academic and possibly without sufficient scientific background to support or avoid the use of this procedure.

Conclusion The use of a patency file in teeth with noninfected root canals has not proven histologically to aid in cleaning and shaping procedures.

Fig. 7.6 Buccal root of a maxillary first premolar. The pulp was vital and the root canals were instrumented before extraction with NiTi rotary instruments and NaOCl used as the irrigant. WL was established 1.5 mm short of the radiographic apex. Note the apical deltas with undisturbed vital tissue (Courtesy of Domenico Ricucci)

Fig. 7.7 Distal and mesial roots of a mandibular molar showing multiple foramens (Courtesy of Ronald Ordinola-Zapata)

Whether the use of a patency file in such teeth affects healing of the periradicular tissues remains a speculative issue that warrants further histological research. This would be a difficult task since such histology studies could not be performed in humans and animal studies would probably indicate differences from the immunologicalinflammatory responses in humans. Nevertheless, achieving patency with a small file is necessary to ensure the proper use of apex locators.

The Use and Effect of the Patency File in Cleaning of the Root Canals in Teeth with Necrotic Pulps

and Apical Periodontitis

Some questions have arisen concerning the ability of the patency file to truly clean the foramen. For that, it would have to be instrumented; therefore apical patency and apical cleaning are two procedures that are accomplished differently [36].

The presence of bacteria in the cementum canal [4] is of concern for some authors when attempting to finish the instrumentation technique “short” of the foramen. However, whether the use of a patency file is by itself capable of cleaning these difficult areas has not been demonstrated [44]. In this study, after treating human teeth in vivo and with the use of a patency file in all specimens, masses of amorphous material that included dentin shavings and infected necrotic masses were observed to be packed into the dentin root canal walls and projected in the filling material in all segments of the root canal. Because of the large amount of apical ramifications that remained infected, or contained remnants of organic tissue, as shown in the mentioned study, maintaining one foramen open with the use of the patency file may not help in the cleaning of accessory canals and other foramens present in the same root (Fig. 7.7). Furthermore, in the study by Vera et al., debris and/or bacteria were present in the main foramina in 8 of 13 cases. This clearly shows that in vivo, proper elimination of the bacterial bio-burden and tissue may not depend on the use or lack of use of the patency file. Since there were no teeth that were instrumented with-

out the use of patency, however, proper comparisons could not be made.

In another recent case report in which apical patency was maintained throughout the procedures, with the use of 5 % NaOCl, smear layer removal, and ultrasonic agitation of chlorhexidine, a bacterial biofilm was demonstrated in a network of apical ramifications. This case presents evidence against the concept that patency files are expected to be able to disrupt apical biofilms in vivo; or, at least, these in vivo observations have not been able to demonstrate such a concept [3]. Therefore, some authors have recommended that when pulp necrosis is present, patency should be used only to help maintain proper working length and to avoid packing debris in the apical foramen but that cleaning of the apical foramen be achieved with bigger size files [36]. Other authors have even recommended cleaning the divergent cementum canal with files bigger than the file used to clean the root canal in its apical portion [35]. Whether performing this procedure really helps clean the canal in such a way remains to be demonstrated in histological studies.

Conclusions The use of a patency file has not been proven to aid in the cleaning of accessory canals/ foraminas when evaluated histologically. Remnants of tissue and biofilm remain in these “hard to reach areas” despite the use of the patency file. However, it is important to note that the histological information that has been mentioned was obtained either from single cases or from a study where no comparison could be made to cases treated in a similar way but where a patency file had not been used.

The Influence of the Use

of a Patency File on Postoperative Pain and Flare-Ups

Controversial results have been presented concerning the possible role of the patency file in causing damage to the periapical tissues [25, 26], in part caused by the file extruding a larger amount of contaminated debris, irrigants, and dentinal chips [19], and, therefore, increasing the incidence of postoperative pain [32].

The use of a patency file is considered by some clinicians as being a non-harmful biologic event because of the great capabilities of the immune and inflammatory system in the periradicular tissues [28]. Some studies or articles have also shown how well these tissues tolerate the use of the file throughout the cleaning and shaping procedures. In fact, one study has shown that contaminated patency files could be disinfected with the NaOCl present in the root canal after irrigation, thus showing that the use of patency would not contaminate or inoculate microorganisms into the periapical tissues [18].

Siqueira et al. [33] evaluated the incidence of postoperative pain. They collected and examined data from 627 teeth that needed to be retreated endodontically or that had necrotic pulps. Only undergraduate students were used as operators, and patients were asked about the occurrence of postoperative pain and its severity. Apical preparation was performed 1 mm short of the root apex with master apical files ranging from #35 to #60. Then, apical patency was confirmed to the radiographic root end with a small file after each larger file. The cleaning and shaping procedures were carried out with 2.5 % NaOCl as the irrigant. The incidence of postoperative pain was calculated for each variable involved in the study, and statistical analysis was applied. Maintaining apical patency did not influence the occurrence of postoperative pain or flare-ups. Torabinejad et al. [40], in a retrospective study, collected and analysed information from 2,000 patients who had undergone root canal therapy and who had been diagnosed as having teeth with necrotic pulps. All 17 operators were endodontists with at least 5 years of practice limited to endodontics. Half of the patients that were treated had reported having had inter-appointment pain or swelling. The other half of the analysed patients reported no pain or complications after the cleaning and shaping procedure. In this study, penetration through the foramen with small instruments during working length determination (in many cases being accidental) had no influence on the incidence of postoperative pain or swelling.

A prospective study on the influence of the patency file on post-endodontic pain was per-

formed by Arias et al. [2]. The incidence, degree, and length of postoperative pain were compared between two groups. In one group of 150 teeth, apical patency was maintained throughout the cleaning and shaping procedures with a size 10 K file, but not in the other group that consisted of 150 teeth in which special care was taken to avoid using any instrument longer than the determined working length. Some other diagnostic factors, including the presence or absence of vitality, preoperative pain, and the location of the tooth in the maxillary or mandibular arch, were taken into consideration. The shaping procedures were performed with the use of Gates-Glidden drills (Dentsply Maillefer) and K-Flexofile instruments (Dentsply Maillefer), and the master apical files used varied from #20 to #30 for small canals and to sizes 25–40 in bigger or wider canals. The working length was confirmed carefully with the use of apex locators. NaOCl was used as the irrigant between all instruments, and all teeth were filled in one appointment. Patients were asked to record the presence or absence of postendodontic pain and its duration. They were also asked to rate the discomfort as mild, moderate, or severe, using criteria as to whether the discomfort did not require any treatment (mild), the pain was relieved with analgesics (moderate), or the pain did not subside with analgesics (severe). After the patients responded to the questionnaires, 121 teeth were designated as the patency group and 115 as the no patency group. The results were analysed statistically and showed no differences in pain between the patency and the no patency groups. However, some interesting findings were obtained when analysing different variables. For example, when there was preoperative pain present, the number of days in which pain persisted was more in the patency group (up to 3 days more). There was also more postoperative pain in the lower teeth when patency was maintained, and in nonvital teeth the cases where patency was maintained showed less postoperative pain when compared to the nonpatency cases.

Conclusions The use of a patency file appears not to increase the incidence of pain or flare-ups when used even in teeth with necrotic pulps or in cases of re-treatment.