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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