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ePaper created 2016-10-12, 10:31:46 | version 1.38.0
| research 08 laser 3 2016 The biophysical effects of blue laser radiation thereforefavourtheeffectiveablationoftissuefrom the beginning. Transmission properties and thermo- graphic investigations confirm these observations: Transmission through agar layers of 3 mm thickness is approximately 80 % at 445 nm, independent of the laser power from 100 mW to 1 W for irradiation peri- ods between 5 and 20 seconds. The increase in tem- perature in this layer cannot be measured when the laser power is 100 mW, with a laser power of 1 W, a temperature increase of T = 2 °C could be observed. In contrary, in blood agar, high absorption (> 98 %) andtemperaturesweremeasured.Thecomparisonof the biophysical properties of laser radiation between diode lasers with wavelengths of 445 nm and 810–980 nm shows that in both cases photothermal effects are responsible for the laser-tissue interac- tion.Onthebasisofthelasersettingsthataretechni- cally possible, no non-linear effects, for example the formation of plasma, are assumed. The different ab- sorption constants, however, support the vaporisa- tion of oral soft tissue at 445 nm in comparison with IR lasers at 810 nm and 980 nm. In vitro investigations using a 445 nm diode lasers Preparations from pig jawbones are particularly suitableasamodelsystemfortheinvestigationofthe effects after laser irradiation under in vitro condi- tions. The macroscopic structure, the dimensions and the histological structure are very similar to human tissue so that valid statements can be made.17-22 Gin- giva preparations obtained from the vestibular man- dibles of freshly slaughtered pigs were used for the investigation of the cutting effectiveness and histo- logicallyanalysisofsideeffectsduringtissueprepara- tion.Theyconsistedofarectangularsegmentofbone covered with gingival tissue (Fig. 3a). These samples were stored in physiological saline solution and were fixed to an optical bench immediately after removal (Fig.3b).Thisbenchwasequippedwithalinearmicro- Fig. 4 Fig. 6 Fig. 5 Fig. 4: Ex vivo sample from pig gingiva after 445 nm laser incision (2 W, cw). The high resolution photo collage shows that, starting from the surface, the morphology of the tissue has been preserved with a thin carbonisation film. No vacuolar structures and bleed- ing into the connecting tissue were detected. The incision edge is covered by a very small carbonisation layer. – Fig. 5: Detailed images of the subepithelial connective tissue after incision with 445 nm/2 W, cw. An undermined blistering (tissue destruction) in the area of the lamina propria as is known with the 980 nm is only very slightly pronounced. The micromorphology of the tissue is preserved underneath the cutting level despite increased staining; no tissue haemorrhage was detected. – Fig. 6: Histological thin section after irradiation of a pig jawbone specimen using a 980 nm diode laser (2 W, cw, left) and using a 445 nm diode laser (2 W, cw, right), undecalcified thin section, staining: toluidine blue. With 980 nm, wide carbonisation zone with surrounding necrosis; with 445 nm, narrow carbonisation and necrosis zones. 32016