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ePaper created 2015-03-10, 11:16:47 | version 1.33.01
issue 1/2015 — 73Laser Dentistry Article Although most micro-organisms are de- stroyed at pH of 9.5, afew can survive a pH of 11 or higher, such as E. faecalis and Can- dida.21Becauseoftheresistanceofsomemi- cro-organisms to conventional treatment protocols—andthedirectrelationbetween the presence of viable bacteria in the canal system and the reduced rate of treatment success—additional effort has to be made to control canal system infection. Lasers in endodontics Lasers were introduced to endodontics as acomplementarytherapytoconventional antibacterial treatment. The antibacterial action of Nd:YAG, diodes, Er:YAG and photo-activated disinfection (PAD) have been explored by a number of investiga- tors. In the following section, each laser is evaluated with the aim of selecting an ad- equate protocol with a high probability of success in teeth with apical periodontitis. Nd:YAG laser TheNd:YAGlaserwasoneofthefirstlasers testedinendodontics.Itisasolid-statelaser. The active medium is usually yttrium alu- minium garnet (Y3A15O12), where some Y3+ ionsarereplacedbyNd3+ ions.Itisafour-level energy system operating in a continuous wave or pulsed mode. It emits a 1,064nm infra-redwavelength.Thus,thislaserneeds aguidelightforclinicalapplication.Flexible fibers with a diameter between 200 and 400μm are used as delivery systems. The lasercan be used on intra-canal surfaces, in contact mode (Figs. 4a and b). Fig.1 Fig.2 Fig. 1 Success in endodontic treatment: apical radiolucency repair. Fig. 2 rimary infection: black pigmented strains and G-rods. Fig. 3 Persistent infection. Thetypicalmorphologyofroot-canalwalls treated with the Nd:YAG laser shows melted dentine with a globular and glassy appearance, and few areas are covered by a smear layer. Some areas show dentinal tubulessealedbyfusionofthedentineand deposits of mineral components.31, 34This morphological modification reduces den- tine permeability significantly.35, 36How- ever, because the emission of the laser beam from the optical fibre is directed along the root canal, not laterally, not all root-canalwallsareirradiated,whichgives more effective action at the apical areas of the root.37 Undesirable morphological changes,suchascarbonizationandcracks, are seen only when high energy parame- ters are used. Fig.3