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ePaper created 2016-07-29, 16:53:04 | version 1.38.0
21 2 2016 laser industry | Fig. 3: Correctly prepared access cavity of the upper molar. Figs. 4a & b: Upper molars after reciprocal preparation, irrigation with 5 % NaClO and 17 % EDTA, PUI and thermoplastic obturation. Fig. 5: Surface after laser treatment in dry canal with end firing tip; Er:YAG laser at 75 mJ, 15 Hz, 1.1 W, and 300 micron.57 work steps following the pre-endodontic build-up. Thedirectcorrelationbetweenthecorrectlyprepared endodontic access cavity and the success of end- odontictherapyhasbeenverified(Fig.3).14 Afterhav- ing applied the access cavity and prepared the coro- nal root canals, we measure the length of the root canal and determine the working length. Given the development of electrometric measurement systems in the past years, electrometric length determination is the measure of choice for this purpose.15 Chemomechanical preparation Asalreadymentionedabove,bacterialinfectionsof the root canal system are the main cause of apical periodontitis.16 Solely preparing the root canals me- chanicallydoesnotleadtosufficientreductionofmi- crobialcontamination.Itwasshownthatmajorparts of the canal were not even attended to mechanically by means of mechanical preparation using rotating instruments.17 Thecombinationofmechanicalprepa- ration, activated irrigation by means of antimicrobial andtissue-resolvingagentsaswellastheapplication of antimicrobial medication between the treatment sessions may reduce bacterial contamination of the canal system considerably.18 Mechanical preparation Mechanical root canal preparation, depending on theavailableanatomyofthecanal,maybeperformed with either manual instruments or rotating nickel- titanium instruments. Compared to manual instru- ments, the use of rotating instruments leads to considerably improved results with regard to the preparation geometry and the preservation of the originaltopographyofthecanal.19 Theintroductionof a novel preparation pattern, i.e. reciprocal prepara- tion movements, facilitates an even better mechani- calpreparation.Besidesthereducedriskoffracture20 , better alignment of the files in the canal system and the resulting predictable and repeatable preparation seemstobeoneofthemainadvantagesofreciprocal movements. Another advantage over fully rotating systems is the effective and thus more rapid canal preparation.21 Because of the improved mechanical properties of reciprocal file systems, the preparation can be limited to a few file sizes, depending on the available canal anatomy. This makes handling easier for the attending doctor and his/her team. Chemical preparation— irrigation solutions The irrigation solutions applied to reduce bacterial contamination must fulfill various tasks in the root canal system:22 1. Antibacterial effectiveness against a broad micro- bial spectrum 2. Destruction of biofilm 3. Dissolution of potentially infected tissue 4. Removal of the smear layer Thesmearlayerisdebrisgeneratedbythemechan- ical preparation, consisting of die dentin chips, bac- teria, infected tissue, organic particles etc.23 Espe- ciallywiththerotatingorreciprocalpreparation,this debris is positively pressed into the dentinal tubules and compacted by the rotational movement. The smear layer thus prevents intra-canal antimicrobial agents and drugs from entering into the dentinal tu- bules and sub-canals.24 The combination of sodium hypochlorite (NaClO) and ethylene diamine tetra- acetate (EDTA) is the gold standard for the chemical reduction of intra-canal microorganisms to this day and has been proven in many research studies. The combination of both solutions and the mechanical preparation makes it possible to reduce contamina- tion of root canals by the factor of 100 to 1,000.25 NaClO has an excellent antimicrobial effect against most of the microorganisms that are significant in endodontics.26 With regard to the tissue-resolving effect, NaClO is clearly superior to all other known irrigation solutions.27 This tissue-lytic, effect com- bined with the excellent antimicrobial effectiveness, are key factors to accomplish comprehensive bacte- rial reduction in the root canal system. Concentra- tions between 1 per cent and 5.25 per cent are dis- cussed.Thehighertheconcentration,thequickerthe lysisofthetissue.28 Becauseoftherapidinactivation of NaClO when it contacts organic tissue, a large quantity of irrigation fluid of at least 10 ml per canal is required.29 Heating the NaClO increases the effec- tiveness of the irrigation solution in the canal sys- Fig. 3 Fig. 4a Fig. 4b Fig. 5 22016