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10 I I special _ laser The need to take advantage of the thermal effect to destroy bacterial cells, however, results in changes at the dentinal and periodontal level. It is important to evaluate the best parameters and explore new techniques that reduce the undesirable thermal effects that lasers have on hard- and soft-tissue structures to a minimum. Morphologicaleffectsonthedentinalsurface Numerousstudieshaveinvestigatedthemorpho- logicaleffectsoflaserradiationontheradicularwalls as collateral effects of root-canal decontamination and cleaning performed with different lasers. When theyareuseddry,boththenearandmediuminfrared lasers produce characteristic thermal effects (Figs. 7 & 8).51 Near infrared lasers cause characteristic mor- phological changes to the dentinal wall: the smear layer is only partially removed and the dentinal tubules are primarily closed as a result of melting of the inorganic dentinal structures. Re-crystallisation bubbles and cracks are evident (Figs. 9–12).52–55 Waterpresentintheirrigationsolutionslimitsthe thermal interaction of the laser beam on the dentinal walland,atthesametime,worksthermallyactivated by a near infrared laser or directly vaporised by a medium infrared laser (target chromophore) with its specific action (disinfecting or chelating). The radiation with the near infrared laser—diode (2.5W, 15Hz) and Nd:YAG (1.5W, 100mJ, 15Hz)—performed after using an irrigating solution, produces a better dentinalpattern,similartothatobtainedwithonlyan irrigant. Radiation with NaClO or chlorhexidine produces a morphology with closed dentinal tubules and presence of a smear layer, but with a reduced area of melting, compared with the carbonisation seen with dry radiation. The best results were obtained when radiationfollowedirrigationwithEDTA,withsurfaces cleanedofthesmearlayer,withopendentinaltubules and less evidence of thermal damage.35–38 In the con- clusion of their studies on the Erbium laser, Yamazaki et al. and Kimura et al. affirmed that water is neces- sary to avoid the undesirable morphological aspects markedly present when radiation with the Erbium lasers is performed dry.56, 57 The Erbium lasers used in this way result in signs of ablation and thermal dam- ageasaresultofthepowerused.Thereisevidenceof ledge cracks, areas of superficial melting and vapori- sation of the smear layer. A typical pattern arises when dentine is irradiated with the Erbium laser in the presence of water. The thermal damage is reduced and the dentinal tubules are open at the top of the peri-tubular more calcified and less ablated areas. The inter-tubular dentine, which is richer in water however, is more ablated. The smear layer is vaporised by radiation with Erbium lasers and is mostly absent.58–64 Shoop et al., investi- gating the variations of temperature on the radicular surface invitro, found that the standardised energies (100mJ, 15Hz, 1.5W) produced a measured thermal increase of only 3.5°C on the periodontal surface. Moritz proposed these parameters as the interna- tional standard of use for the Erbium laser in en- dodontics, claiming it as an efficient means of canal cleaning and decontamination (Figs. 13–16).14,16 Even with Erbium lasers, it is advisable to use irrigating solutions. Alternatively, NaClO and EDTA can be utilised during the terminal phase of laser- assistedendodontictherapywitharesultingdentinal pattern, with fewer thermal effects. This represents a new area of research in laser-assisted endodontics. Various techniques have been proposed, such as laser-activated irrigation (LAI) and photon-initiated photoacoustic streaming (PIPS). Photo-thermal and photomechanical phenomena fortheremovalofsmearlayer George et al. published the first study that exam- ined the ability of lasers to activate the irrigating liquidinsidetherootcanaltoincreaseitsaction.Inthis study, the tips of two laser systems—Er:YAG and Er,Cr:YSGG (400µm diameter, both flat and conical tips) with the external coating chemically removed— were used to increase the lateral diffusion of energy. roots2_2011 Figs. 21–23_SEM images of radiated dentine with radial firing tip, at 20 and 50 mJ, 10 Hz for 20 and 40 seconds, respectively, in a canal irrigated with EDTA, showing notice- able cleaning of debris and smear layer from the dentine and exposure of the collagen structure. (Figures courtesy of Dr Enrico DiVito, USA.) Fig. 21 Fig. 22 Fig. 23