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ePaper created 2017-10-05, 09:25:28 | version 1.38.0
laser_research effect after laser irradiation of water-filled root canals with a diode laser (980 nm). Comparison with Nd:YAG laser application The appearance of a smooth, unstructured sur- face with few wide-open or partly occluded tubule orifices after diode laser application and diode laser–fluoride treatment is comparable to the effects of Nd:YAG laser application, which is already known for its ability to close dentinal tubules26 and for its sealing effects on root dentine.23 A direct comparison of these two laser types by irradiating root canal den- tine found morphological changes, such as melting and setting of the dentinal surface, but without any statistically significant differences between both laser types.27 In our study, laser–fluoride application was not found to be statistically significantly superior to laser irradiation alone. However, such a tendency could be seen. In the literature, we can also find no clear results concerning this, but a combined treatment is pre- ferred in most cases.28, 29 A combined in vivo applica- tion of Nd:YAG laser and fluoridation, for example, achieved an improvement of symptoms that corre- lates to the in vitroreduction of open tubule orifices.30 Fig. 4_Overview of the detected morphological effects in SEM examination after experimental setup (2000x, 40°). (a) wide opened tubuli, (b) partly opened tubuli, (c) impressions of tubuli orifices, Effects after additional absorber application (d) unstructured and smooth surface, (e) precipitates, (f) melted surface. Although the application of an absorber prior to laser treatment enhanced the absorption at the sur- 44 3_2017 44 laser face,31 in some cases under SEM examination after laser application isolated side-effects, such as cracks, were detected, and this phenomenon could possibly be traced back to the absorber effect. In their study, Umana et al.19 proved that the additional application of an absorber enhanced the laser effects, resulting in areas of fusion, melting and narrowing of the tubules, when energy settings of 0.8 W and 1 W were used. At higher energy settings (1.6 W and 2 W), not only com- plete occlusion of the tubules, but also cracks, dental ablation, craters and loss of substance could be seen.19 The occurrence of side-effects with the 1 W output power used in our study could probably be ex- plained by the longer exposure time of 60 seconds compared with 10 seconds in Umana et al.’s study. Since we only observed superficial effects, we could not evaluate the penetration depth of the detected cracks. Concerning the histological examination, no cracks were found, so we assumed that they were only located in the very superficial dentinal layer and there- fore of negligible clinical relevance. Concerning safety and clinical effectiveness, the energy setting of 1 W does not exceed the safety level of 3 °C for pulp injury and is harmless for pulp vitality.19 Human in vivo stud- ies have shown that the diode laser can be a useful in- strument in clinical dentine desensitisation.32–36 The clinical effectiveness was approximately 86–88 % with no differences between the different laser parameters used.36 An exposure time of 60 sec- onds, compared with shorter irradiation times, clini- cally results in immediate pain relief.33 No side-ef- fects were observed34 and a persistent clinical reduc- tion of dentine hypersensitivity after laser use was observed during the follow-up period of up to six months.32, 34 Results with and without pH-cycling With the energy settings used in our study, side- effects were neither predictable nor statistically sig- nificant. In general in our study for all treatment groups, no statistically significant improvement was achieved by the additional use of an absorber prior to laser application or with laser–fluoride application, and absorber application did not induce additional detectable morphological effects at the surface in the majority of cases. Under SEM examination, no statistically signifi- cant morphological differences between cycled and non-cycled groups were observed, whereas patterns of different width were detected after pH-cycling of non-etched and acid-etched samples under histolog- ical examination. The acid resistance of tooth surfaces can be detected with pH-cycling. From other studies, it is known that the application of fluorides can en- hance the acid resistance of dental surfaces.37, 38