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RO0211

08 I I special _ laser Allthewavelengthshaveahighbactericidalpower because of their thermal effect, which, at different powers and with differing ability to penetrate the dentinalwalls,generatesimportantstructuralmodifi- cationsinbacteriacells.Theinitialdamagetakesplace in the cell wall, causing an alteration of the osmotic gradient, leading to swelling and cellular death.16, 34 Decontaminationwithnearinfraredlaser Laser-assisted canal decontamination performed with the near infrared laser requires the canals to be prepared in the traditional way (apical preparation with ISO 25/30), as this wavelength has no affinity and therefore no ablative effect on hard tissue. The radiation is performed at the end of the traditional endodontic preparation as a final means of deconta- minating the endodontic system before obturation. An optical fibre of 200µm diameter is placed 1mm fromtheapexandretractedwithahelicalmovement, moving coronally (in five to ten seconds according to the different procedures). Today, it is advisable to perform this procedure in a canal filled with endodontic irrigant (preferably, EDTA or citric acid; alternatively, NaClO) to reduce the undesirable thermal morphological effects.9, 35–38 Using an experimental model, Schoop et al. demonstrated the manner in which lasers spread their energy and penetrate into the dentinal wall, showing them to be physically more efficient than traditional chemical irrigating systems in decontam- inating the dentinal walls.8 The Neodymium:YAG (Nd:YAG; 1,064nm) laser demonstrated a bacterial reduction of 85% at 1mm, compared with the diode laser (810nm) with 63% at 750µm or less. This markeddifferenceinpenetrationisduetothelowand varying affinity of these wavelengths for hard tissue. The diffusion capacity, which is not uniform, allows thelighttoreachanddestroybacteriabypenetration via the thermal effects (Fig. 5). Many other microbiological studies have con- firmedthestrongbactericidalactionofthediodeand Nd:YAG lasers, with up to 100% decontamination of thebacterialloadintheprincipalcanal.39–43 Aninvitro study by Benedicenti et al. reported that the use of the diode 810nm laser in combination with chemical chelating irrigants, such as citric acid and EDTA, brought about a more or less absolute reduction of the bacterial load (99.9%) of E. faecalis in the endo- dontic system.9 Decontaminationwithmediuminfraredlaser Considering its low efficacy in canal preparation and shaping, using the Erbium laser for decontami- nation in endodontics requires the use of traditional techniques in canal preparation, with the canals preparedattheapexwithISO25/30instruments.The final passage with the laser is possible thanks to the use of long, thin tips (200 and 320µm), available with various Erbium instruments, allowing for easier reach to the working length (1mm from apex). In this roots2_2011 Fig. 13 Fig. 14 Fig. 15 Fig. 16 Figs. 13 & 14_SEM images of irradiated dentine with Er,Cr:YSGG laser (1.0 W, 20 Hz, 1 mm to the apex), spray off and canal irrigated with physiological solution, showing evidence of smear layer and thermal damage. Figs. 15 & 16_SEM images of irradiated dentine with Er,Cr:YSGG laser (1.5W, 20 Hz) with air/water spray of 45/35 %, showing open dentinal tubules without evidence of a smear layer. Note the typical pattern of laser ablation, both on the organic and inorganic dentine.