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ePaper created 2016-11-22, 09:52:12 | version 1.38.0
role of the microscope industry report | 41 roots 4 2016 Preparation of root canal system The cause of failure of endodontic treatment has been attributed to the presence of microorganisms persistingintheapicalpartoftherootcanal(Siqueira 2001).Muchattentionhasthereforebeenfocusedon preparation and obturation of the apical part of the canaltherebydependingontheapicalsealtoprevent toxins from leaking out into the periradicular tissues. While success rates of endodontically treated teeth withoutperiradicularlesionsisveryhigh,therecanbe a significant reduction in success in both teeth with periradicular periodontitis and in those teeth where endodontictreatmenthasfailed(Ngetal.,2011).This is predominantly due to the failure to remove mi- crobesformtherootcanalsystem.Thequestistofind more effective irrigants and irrigation techniques, as well as rotary files and preparation techniques to overcome these difficulties. An ideal preparation shape with a rotary instru- ment can only be achieved in a canal with a matched crosssection.Manycanalsarevariableinshape.They mayhaveirregularandovalcross-sectionsandwhile muchofthedebrisiscapturedwithintheflutesofthe instruments, some is compacted into those spaces betweentheinstrumentandthecanalwall(Fig.2).The incidenceofisthmusesinbothmaxillaryandmandib- ular first molars is very high (von Arx 2005). They are particularly liable to have an accumulation of com- pacted debris after preparation and the inability to clean these areas effectively has been implicated as a majorcauseoffailureofrootcanaltreatment,partic- ularly in both mandibular and maxillary first molars (Fig. 3) (Hsu & Kim, 1997; Tam & Yu, 2002). The more the debris is compacted, the more dif- ficult it is for chemicals such as sodium hypochlo- rite and calcium hydroxide to penetrate through the interface. Paque et al. (2010) reported that ap- proximately half of the debris that accumulated during rotary instrumentation of the mesial canals of lower molars remained in the canal system after irrigation. Failure of endodontic treatment in maxillary mo- lars has been attributed to the failure to locate and treatthemb2canal(Weine,1969;Wolcottetal.,2005). Various studies have shown the presence of the mb2 canal in up to 90 % of maxillary first molars. A study by Somma et al. (2009) showed that in 58 % of teeth, the mb1 and mb2 merge apically into one canal. In a proportion of these failed cases where the mb1 canal has been located, cleaned, shaped and obtruded well, the question should be asked, “Was the failure due to inadequate treatment of the apical part of the mb1 canal,orbecausethemb2canalandisthmusbetween the two canals had been missed?” Identification and treatment of the mb2 canal with concommitant re-treatmentofthemb1canaloftenleadstohealing. This suggests that the seals are not always good enough to “entomb” the bacteria. Indeed coronal microleakage has been implicated as a major cause of failure of endodontic treatment (Saunders and Saunders, 1990). Undoubtedly tracts of debris run- ning along side root fillings are conduits for bacteria to cause failure by this method. In an invivo study by Nair (2005) the mesial canals ofsixteenlowermolarswithinfectedrootcanalswere root treated by conventional techniques in a single visit and the apical portions removed by flap surgery and evaluated by corrective light and transmission electron microscopy. In the majority of cases residual microbes were located in inaccessible recesses, unin- strumented areas of the main canals, accessory ca- nals and intercanal isthmuses. If the lateral extensions feed into the apical part of the canal, then removing bacteria and nutrients from theseareasreducesthebacterialloadandthishastobe beneficial for the outcome of treatment. A variety of techniqueshavebeenproposedtoovercometheinad- equaciesofmechanicalpreparationinnon-circularca- Fig.2: Oval shaped canal in the apical third of the distal root of a lower molar. Fig.3: Debris accumulated after preparation in the isthmus between the mesial canals of a lower molar. Fig.2 Fig.3 42016