Introduction - Materials and methods.
T. Attin, W. Buchalla, C. Zirkel & A. LussiDepartment 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.Introduction.
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.