Journal of Endodontics Research -
Clinical evaluation of the cleansing properties of the noninstrumental technique for cleaning root canals
By JofER editor
Published on 11/11/2008
T. Attin, W. Buchalla, C. Zirkel & A. Lussi
Department of Operative Dentistry, Preventive Dentistry and Periodontology, Georg August University Gottingen, Gottingen, Germany.
Department of Operative, Preventive and Pediatric Dentistry, School of Dental Medicine, University of Berne, Berne, Switzerland.

The purpose of the present study was to evaluate noninstrumentation technology (NIT) for root-canal cleansing in vivo.

The results of the present investigation showed that further modifications of the NIT for cleaning root canals are necessary to achieve sufficient cleanliness of root canals in vivo and to be as effective as previously demonstrated under in vitro conditions.

Introduction - Materials and methods.
T. Attin, W. Buchalla, C. Zirkel & A. Lussi
Department of Operative Dentistry, Preventive Dentistry and Periodontology, Georg August University Gottingen, Gottingen, Germany.
Department of Operative, Preventive and Pediatric Dentistry, School of Dental Medicine, University of Berne, Berne, Switzerland.

Optimal cleansing and obturation of the complete root canal system is essential for the long-term success of a root-canal treatment. It has been demonstrated that a thorough and complete debridement of the root-canal system with all its ramifications and anatomical irregularities is nearly impossible with current methods of mechanically driven or hand instrumentation (Kochiset al. 1998, Park et al. 1998, Peters et al. 1998, Versumeret al. 2002).
A novel noninstrumental hydrodynamic technique (NIT) for cleansing of root canals was described in a number of studies and showed an equal or even better cleanliness in all root sections compared to hand instrumentation (Lussi et al. 1993; 1995 a,b; 1999). The noninstrumental technique is based on a system that rinses the root canals with sodium hypochlorite solution (NaOCl) below the ambient pressure. The system, consisting of a vacuum pump and an electrically driven piston, generates alternating pressure and bubbles in the solution, inside the root-canal system. These hydrodynamic turbulences support the ability of NaOCl to dissolve organic pulpal tissue.
To date, the efficacy of the noninstrumental technique for cleansing root-canal systems has been validated only in vitro. In these studies, the system was effectively connected to the crowns of extracted teeth whose roots were embedded in impression compounds. By sealing the roots in impression material, a closed system resulted, which was essential for the development of hydrodynamic turbulences created with aid of a vacuum pump and piston. However, in the in vivo situation, it is conceivable that problems may arise that impair the ability of the system to clean the root-canal system. For example, it was not known whether the hydrodynamic turbulences of the NaOCl solution would irritate the periapical tissue. Furthermore, blood flow from the periradicular tissues into the root canal or diffusion of NaOCl in to the periodontium would change the mechanics of the otherwise closed system described above. Under those circumstances, hydrodynamic turbulences might not be generated, resulting in poor cleansing of the root canal system.
The aim of the present study was to investigate the ability of the NIT to clean the root canals of teeth under in vivo conditions.

Materials and methods.
Prior to the start of the study, the protocol was approved by the Ethics Committee of the University of Freiburg (Number 27/96) where the clinical procedures of the study were conducted. After informed consent was obtained, 18 patients were included in this study. A total of 22 teeth that were to be extracted were treated with NIT for cleansing root canals. The device for NIT and the mode of function have been described in detail previously (Lussi et al. 1993; 1999). The 22 teeth comprised one single rooted tooth and 21multirooted teeth.Extractionof15teethwas necessary due to periodontal disease. The remaining teeth comprised wisdom teeth with severe coronal destruction because of caries or with signs of chronic pericoronitis.
In all cases, radiographs demonstrated that none of the teeth had apical pathosis or were in contact with the maxillary sinus. Periodontal probing depths of the teeth did not exceed 8 mm to confirm that no connection existed between the apex of the respective tooth and the oral cavity. One tooth was nonvital, the remaining teeth were vital and showed no signs of pulpal inflammation when assessed by the response to thermal sensitivity tests. The nonvital tooth was the only single rooted one. Prior to the treatment, local anaesthesia was obtained in all cases with approximately 2 mL of Ultracain (Hoechst Marion Russel, Frankfurt, Germany) containing0.04 g mL articaine and 0.006 mg mL adrenaline-HCl.
After excavation of caries, an adhesive filling was placed using the compomer Dyract (Dentsply DeTrey, Konstanz, Germany) and the corresponding adhesive Prime&Bond 2.1 (Dentsply DeTrey, Konstanz, Germany). The adhesive was applied using the total etching technique. Conditioning of enamel and dentine was performed with 37% phosphoric acid gel (Dentsply DeTrey) before application of the adhesive. After completion of the filling, access to the pulp chamber was created with a pear-shaped diamond bur (ISO 806 314234534 012, Komet, Lemgo, Germany). All dentinal overhangs of the pulp chamber were removed and bleeding of the pulpal tissue was controlled using ferric sulphate solution (Astringedent, Ultradent, Salt Lake City, USA). The coronal pulpal tissue was removed with hand excavators. After etching of the tooth surface with 35% phosphoric acid, a nozzle was tightly polymerized into the access cavity with Dyract. An additional seal of the junction between the enamel/nozzle and material/nozzle was achieved by application of the bonding material Heliobond (Vivadent, Schaan, Liechtenstein).Then, the adaptor of the piston pump, described in detail previously (Lussi et al.1999),was inserted into the nozzle. The piston pump was connected to a reservoir vial filled with3.0%NaOCl and a waste reservoir. A vacuum pump (Biovision, Freiburg, Germany) was connected to the piston pump and the waste reservoir. Reduced pressure of0.2 _104 Pa (20 mbar) below ambient pressure was maintained by the constant hydrodynamic pressure between the reservoir vial and the vacuum pump, resulting in a flow rate of the irrigant of about 7.0 mL min. Alternating pressure fields were generated by the piston pump working at 230 Hz within the reduced pressure environment. When the pressure decreased, bubbles were formed and pressure rising close to ambient pressure caused bubbles in the solution to collapse, there by creating hydrodynamic turbulences. Treatment time was set at 30 min. Prior to extraction, the teeth were irrigated with the system for 2 min using 0.9% NaCl.
After extraction and cleansing of the root surfaces, the root canals were exposed longitudinally by grinding the external root surface with discs and burs under 2.5x magnification until only a thin layer of dentine remained over the root canal. Finally, the remaining dentine was removed with an explorer. Remaining tissue was then coloured with Rhodamin B and photographed. The residual organic debris in the apical (0-2 mm), middle (2-4 mm) and coronal (4-7 mm) section of the canals were assessed as the percentage of the total length examined; the total length of residual pulpal tissue was divided by the total examined length of the corresponding section of the canal. The magnifications used were13_ for the assessment of the organic debris in the coronal parts of the curvatures and 33_ for the apical and middle sections of the root canals.
Percentage of residual debris was categorized as follows: D 1,0 %; D 2,1-50% and D 3,51-100%. Comparisons between the percentages of roots with remaining debris of grade D1-D3 were analyzed with chi-square tests. Comparison with respect to the cleanliness in the different root sections was performed with a Kruskal-Wallis analysis of variance followed by a Mann-Whitney U test.

In two cases, patients complained of severe pain during the treatment with the NIT so that the application had to be stopped. These teeth (one maxillary and one mandibular molar) were not included in the histological assessment. Macroscopic evaluation of their apices did not show signs of resorption or an widely open apex. In14 of the remaining teeth, some blood was discernible in the adaptor after removing the piston pump.
According to the amount of remaining debris in the respective root section, the roots were allotted to one of the three gradings of remaining debris (D1-D3).The percentages of roots with the respective grading of remaining debris in the apical, middle or coronal part of the roots are presented in Table 1. Statistical analysis proved a significant difference between the various root sections (P < 0.001). In the coronal part, the majority of the roots (55%) were totally clean and free of residual debris (D1).In this root section, however, 33% showed the highest degree of remaining debris (D3).With increasing depth of the canal towards the middle and apical parts of the roots, the percentage of roots with D3 drastically increased, whereas the percentage of completely cleansed canals (D1) decreased.
In the only nonvital tooth, which was the only single rooted tooth as well, residual debris was discernible only in the most apical part of the root canal (Fig. 1). The remaining parts of this root canal were totally free of debris. For the multirooted teeth, no distinct differences were seen amongst the different roots (Fig. 2).This means that in the multirooted teeth the efficacy of cleaning was very similar for the different roots of the same tooth.
The mean values of remaining debris in the respective root sections are illustrated in Fig. 3. It is obvious that the amount of residual debris significantly increased from the coronal to the apical sections of the roots. The statistical analysis revealed significant differences between the three root sections. The P-values of the respective comparisons are delineated in Fig. 3.

Figure 1. Root of a single rooted tooth with some pulpal tissue remnants (arrow) in the most apical part of the root.

Root of a single rooted tooth with some pulpal tissue remnants (arrow) in the most apical part of the root

Figure 2. Multirooted tooth showing similar amounts of residual pulpal tissue in the two roots.

Multirooted tooth showing similar amounts of residual pulpal tissue in the two roots

Table 1. Percentage of roots with remaining debris of gradeD1-D3 in the apical, middle and coronal parts of the roots.

Percentage of roots with remaining debris of gradeD1-D3 in the apical, middle and coronal parts of the roots

Figure 3. Mean percentage and SEM (standard error of means) of remaining debris in the coronal, middle and apical root sections with the P-values of the statistical comparisons.

RMean percentage and SEM of remaining debris in the coronal, middle and apical root sections with the P-values of the statistical comparisons

Discussion - References.
The teeth selected for treatment with the noninstrumental technique in the present study were either wisdom teeth or teeth suffering from periodontal disease. Owing to ethical reasons, the study was limited to teeth that were to be extracted.
Despite application of local anaesthesia, two patients complained of severe pain during the treatment with the NIT. As mentioned above, these teeth did not show any unusual macroscopic findings. Many reasons are described for the failure of local anaesthetic in endodontics, such as anatomical variations or various inhibiting effects of inflammation on the action of local anaesthetics (Hargreaves & Keiser 2002). The teeth selected for treatment in the present study did not show signs of pulpal inflammation, therefore, mainly anatomical factors accounted for the pain observed in our two cases. Contact of the apex with the mucous membrane of the maxillary sinus could be regarded as a possible reason for the severe pain observed in the maxillary molar. However, inspection of the extraction sockets did not reveal visible signs of NaOCl leakage into the tissues. For the mandibular molar, accessory innervation could account for the anaesthetic failure despite the inferior alveolar nerve block. However, further investigations must clarify whether application of the NIT results in a higher prevalence of anaesthetic failures compared to conventional endodontic procedures.
In the present study, the cleaning procedure and the arrangement and adjustments of the noninstrumental device were the same as described by Lussi et al. (1999). However, the present study is the first description of the in vivo use of the noninstrumental technique for cleaning root canals. Therefore, the results can only be compared with the outcomes of previous in vitro studies of NIT (Lussi et al.1993;1995a). In these studies, cleaning of the root canals was better compared to control groups where hand instrumentation had been applied. The cleaning efficacy resulting from the use of the noninstrumental technique in these studies was distinctly better than in the present investigation. The application of the NIT in the present study resulted in an unacceptable amount of remaining debris as compared to recent studies using engine-driven rotary nickel-titanium files (Hulsmann et al. 2001, Versumer et al. 2002). This observation leads to the hypothesis that the clinical situation in the present study had a negative impact on the efficacy of the noninstrumental cleaning technique. It is conceivable that the hydrodynamic irrigation provoked irritation in the pulpal and/or periapical tissue resulting in bleeding into the root canal as observed in most of the teeth treated in the present study. The use of NaOCl as a root-canal irrigant may have supported this effect. It is reported that the inadvertent injection of NaOCl in to the periapical tissue may lead to tissue irritation or even destruction with concomitant intraoral bleed in through the root canal (Sabala & Powell 1989, Becking1991).The property of NaOCl to dissolve organic material is dependent on the concentration of the solution (Yesilsoy et al.1995). This effect on organic tissue seems to be important for the success of the NIT, as shown by Lussiet al. (1999) who found superior cleanliness in roots treated with 3% NaOCl compared to 1 and 2% solutions. If bleeding into the canals persists during treatment, it may reduce the concentration of NaOCl at the interface with the pulpal tissue. This reduced concentration of NaOCl may be an important factor responsible for the reduced cleansing ability observed in the present study.
Prior to extraction, the teeth were rinsed with 0.9%NaCl in order to wash out remaining NaOCl from the root canals. This was done to avoid the further effect of NaOCl used in the study on the pulpal tissue until histological assessment of the teeth was conducted. This post-treatment irrigation did not have an effect on the out come of the study because of its low concentration.
Lussi et al. (1999) had demonstrated in vitro that no NaOCl was extruded beyond the apex using noninstrumental hydrodynamic turbulences. Nevertheless, it is conceivable that in vivo, the open apex and the surrounding tissue does not guarantee the maintenance of a closed system which is important to achieve the hydrodynamic turbulence necessary to clean the root canals. The absence of such a closed system may explain the in sufficient cleaning of the root canals observed in this study. Establishment of a closed system could be achieved by formation of an apical barrier which prevents extrusion of the irrigant into the periapical tissue. A dentine plug, blocking the apical foramen could be created with special hand or motor-driven root-canal instruments transporting and condensing dentine in to the apical constriction. This approach would rely on instrumentation of the root canals prior to connection of the noninstrumental device to the tooth. In this case, however, the advantage of the noninstrumental system would be lost. Another approach for reducing periapical irritation might be to change the vacuum pressure which was set at 0.2 _104 Pa below the ambient pressure in the present study. However, prior to further in vivo experiments modifications of the system should be tested under laboratory conditions.


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