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I 11 special _ laser I roots2_2011 The study was designed to irradiate the root canals thatwerepreparedinternallywithadensesmearlayer grown experimentally. Comparing the results of the groups that were laser radiated with the groups that werenot,thestudyconcludedthatthelaseractivation of irrigants (EDTAC, in particular) brought about better cleaning and removal of the smear layer from the dentinal surfaces.65 In a later study, the authors reported that this procedure, using power of 1 and 0.75W, produces an increase in temperature of only 2.5°C without causing damage to the periodontal structures.66 Blanken and De Moor also studied the effects of laser activation of irrigants comparing it with conventional irrigation (CI) and passive ultra- sound irrigation (PUI). In this study, 2.5% NaClO and the Er,Cr:YSGG laser were used four times for five seconds at 75mJ, 20Hz, 1.5W, with an endodontic tip (200µmdiameter,withflattip)heldsteady5mmfrom the apex. Theremovalofthesmearlayerwiththisprocedure led to significantly better results with respect to the other two methods.67 The photomicrographic study of the experiment suggests that the laser generates amovementoffluidsathighspeedthroughacavita- tion effect. The expansion and successive implosion ofirrigants(bythermaleffect)generatesasecondary cavitation effect on the intra-canal fluids. It was not necessarytomovethefibreupanddowninthecanal, but sufficient to keep it steady in the middle third, 5mm from the apex.68 This concept greatly simplifies the laser technique, without the need to reach the apex and negotiate radicular curves (Fig. 17a). De Moor et al. compared the LAI technique with PUI and they concluded that the laser technique, using lower irrigation times (four times for five seconds), gives results comparable to the ultrasound technique that uses longer irrigation times (three timesfor20seconds).69 DeGrootetal.alsoconfirmed the efficacy of the LAI technique and the improved results obtained in comparison with the PUI. The authors underlined the concept of streaming due to the collapse of the molecules of water in the irrigat- ing solutions used.70 Hmud et al. investigated the possibility of using near infrared lasers (940 and 980 nm) with 200µm fibre to activate the irrigants at powers of 4W and 10Hz, and 2.5W and 25Hz, respectively. Considering the lack of affinity between these wavelengths and water,higherpowerswereneededwhich,viathermal effectandcavitation,producedmovementoffluidsin the root canal, leading to an increased ability to remove debris and the smear layer.71 In a later study, the authors also verified the safety of using these higher powers, which caused a rise in temperature of 30°C in the intra-canal irrigant solution but of only 4°C on the external radicular surface. The study con- cluded that irrigation activated by near infrared lasers is highly effective in minimising the thermal effects on the dentine and the radicular cement.72 In arecentstudy,Macedoetal.referredtothemainrole of activation as a strong modulator of the reaction rateofNaOCl.Duringarestintervalofthreeminutes, the consumption of available chlorine increased significantly after LAI compared with PUI or CI.73 Photon-initiatedphotoacousticstreaming The PIPS technique presupposes the use of the Erbium laser (Powerlase AT/HT and LightWalker AT, both Fotona) and its interaction with irrigating solutions (EDTA or distilled water).13 The technique usesadifferentmechanismfromtheprecedingLAI.It Fig. 24_SEM images of radicular dentine covered with bacterial biofilm of E. faecalis before laser radiation. Figs. 25 & 26_SEM images of radicular dentine covered with bacterial biofilm of E. faecalis after radiation with Er:YAG laser (20 mJ, 15 Hz, PIPS tip) with irrigation (EDTA), showing destruction and detachment of bacterial biofilm and its complete vaporisation from the principal root canal and from lateral tubules. (Figures 25–29d courtesy of Drs Enrico DiVito and David Jaramillo, USA.) Figs. 27a–d_Confocal microscope images of the dentine of the root canal covered with biofilm (a). View in fluorescent light of bacterial biofilm (in green; b). Dentine auto- fluorescence (in red; c). 3-D view superimposed (d). Fig. 24 Fig. 25 Fig. 26 Fig. 27a Fig. 27b Fig. 27c Fig. 27d