Page 40 - Journal of Laser Dentistry 1

investigate (SEM) the ultrastructural morphological changes of the root canal surface of endodonticaly treated human teeth after irradiation with 810-nm diode laser energy at different parameters.

Material and Methods

Twentyfive, freshly extracted single-root human teeth, stored in 10% formalin solution were used for this study. Root canals were cleaned and shaped by a conventional step back technique, by means of k-files up to a 20 k-file size at working length and subsequently shaped by Ni-Ti root-canal crown down rotary instrumentation up to 30/06 (Hero 642, Micromega, Besancon, France) and irrigated with 5% sodium hypochlorite solution (Niclor 5, Ogna, Milano, Italy) each step. The samples were divided in two groups:

G1: 10 samples were irradiated with 810-nm laser (Creation, White Star, Verona,Italy), via 200-microns optic fiber at 2.5 W power in pulsed mode (10 msec on and 10 msec off) for 5 sec, for three times in 17% ethylenediaminetetracetic acid (EDTA) wet canal.

G2: 10 samples were irradiated with the same equiped 810-nm laser at 1,5W power in continuous mode in 5% sodium hypochlorite solution, always three times per 5 sec. In both the groups, the 200 micron fiber was placed up to 1mm to the apex and then moved coronally with 5 sec of duration spiral movement.

2 teeth were irradiated in continuos wave three times for 5 sec (at 1,5W) in dry canal as laser control group; other 3 teeth (non laser control group) were left unlased.

A Philips 515 (Eindhoven, The Netherlands) field emission electron microscope was used to examine the specimens. The prepared samples were sectioned longitudinally, dried, sputter coated and examined apically with

over 100 photographs taken at varying magnifications ranging from 22X to 6500X.

Results

The SEM images revealed debris and smear layer on the root canal surface obscuring the dentin tubules of the control specimens.

When the root canal walls were irradiated with Diode laser only (laser control group), the surfaces showed morphologic changes, varying from fusion and resolidification of the dentin surface to partial removal of debris and smear layer; also some open dentinal tubules, craters and cracks were present on the root surface.

The G1 specimens irradiated with Diode laser in EDTA wet canal in gated mode (at 2,5W), showed more cleaned surfaces with opened tubles and less smear layer.

G2 specimens, irradiated with Diode laser in continous wave (at 1,5W) in sodium hypoclorite wet canal, show intermediated results, with areas of cleaned and smear layer free surfaces and areas with signs of thermal damage (fusion and superficial melting).

Discussion

The removal of organic and inorganic debris, thus the bacterial biofilm, and smear layer, is necessary to ensure the maximum decontamination of the canal before the final filling. Lasers have been widely used in endodontics and beside its bactericidal effect, their use have been proposed for smear layer and byofilm removal.

The bacteria and the smear layer in the laser treated root canals are evaporated and removed by the thermal effect of the near infrared laser. A study from Wang et al (2005) (9) reported as the smear layer removal in diode laser irradiated root canals was significantly superior to the control non