RO0211

I 15 special _ laser I roots2_2011 laserenergytothemostcriticalpartoftherootcanal, the apical third. The erbium, chromium-doped yttrium, scandium, galliumandgarnet(Er,Cr:YSGG)laseremitsatawave- length of 2,780nm and is highly absorbed by water. The lower the penetration depth in water or tissue (or the higher the absorption), the greater the ability of the laser to cut or ablate tissue (Fig. 1). Since this wavelength is very similar to the absorption maxi- mum of water in hydroxyapatite, photo-ablation occurs where water evaporates instantaneously, therebyablatingthesurroundingtissue.Gordonetal. found that it was possible to achieve expansion and collapse of intratubular water as deep as 1,000µm or more.2 This micro-pulse-induced absorption was capable of producing acoustic waves sufficiently strong to disrupt and kill intratubular bacteria. These findings are significant, as bacteria have beenidentifiedatdepthsof1,000µm,withE.faecalis at depths of 800µm.3,4 Irrigants such as sodium hypochlorite have a limited effect on these bacteria with penetration depths of only 100µm.5 Increasing concentration, exposure time and temperature was recently found to improve NaOCl penetration.6 Promising bacterial kill rates using the Er,Cr:YSGG laser with radial-firing tips have been reported in extracted teeth. A disinfection reduction of 99.7% was obtained for E.faecalis at depths of 200µm into dentine and 94.1% (1 log) at depths of 1,000µm.2, 7 The development of the radial-firing laser tip (Biolase Technology, Inc.) with a tip shape that emits the laser energy as a broad cone allows better coverage of the root-canal walls than end-firing tips (Fig. 2). This facilitates entry of the emitted laser energy into the dentinal tubules reaching bacteria that have penetrated deep into the dentine. _Treatment protocol Current techniques incorporating hand and/or rotary instrumentation, positive pressure irrigation, with or without sonic and ultrasonic agitation, fall shortoftotalcanaldisinfection.Thetreatmentproto- col presented in this article incorporates three main components: management of the working width of therootcanal,negativepressureapicalirrigationand intra-canal laser therapy. Workingwidthmanagement The working width (WW) of a root canal is the diameter of the canal immediately before its apical constriction. Allen found that 97% of canals not cleanedtotheirWWhadresidualdebrisinthecritical apical region, while 100% of those cleaned to their WW were free of debris 1mm from the apical con- striction.8 Studieshavedemonstratedthatweneedto clean to larger sizes to remove bacteria and debris.9,10 Conventional tapered files cannot accomplish this without transporting the canal, creating strip perfo- rations, weakening the tooth or separating instru- Fig. 6_Laser removal of smear layer in apical third of canal (Biolase Technology; unpublished data). Fig. 7_Single dentinal tubule after laser ablation (Biolase Technology; unpublished data). Fig. 8_Accessory canal after laser ablation (Biolase Technology; unpublished data). Fig. 4 Fig. 5 Fig. 6 Fig. 7 Fig. 8 Fig. 4_Master delivery tip delivers irrigant to the pulp chamber and evacuates any overflow. Fig. 5_True negative pressure apical irrigation and evacuation provided by macro- and micro-cannulas.