| Summary: | 碩士 === 國立臺灣大學 === 臨床牙醫學研究所 === 90 === After laser was firstly applied in dental research since 1964, scholars have studied the uses of laser in the treatment of dental hypersensitivity for many years. In recent years, a new type of laser was available in the market known as Nd:YAP laser (Lokki Dt, Vienne, France). According to the instructions provided by the manufacturer, Nd:YAP laser can be used for the treatment of dental hypersensitivity. However, there are no related research or studies regarding to its effectiveness in the treatment of hypersensitivity. Therefore, the purpose of the present study was to investigate the morphological changes in human dentine, after being irradiated by Nd:YAP laser, under both light microscope and SEM. Moreover, the thermal effects on human dentine after the irradiation of Nd:YAP laser will also be investigated. It is expected in the present study that an appropriate laser energy and method of irradiation may be found to completely block the dentinal tubules without damaging the normal dentinal structures.
The first part of the study involved the use of laser fiber to slightly contact the dentinal surface, with the tip of the fiber parallel to the direction of irradiation. The second part of the study involved the irradiation with the laser fiber being placed 5 mm away from the dentinal surface treated with black ink. The third part of the study involved measurement of the thermal effects, resulting from the laser irradiation by using the conditions in the previous two parts of the study. All the samples were randomly divided into six groups form A to F. All the groups were treated by Nd:YAP laser set to 5Hz of frequency and unit pulsed energy of 180 mJ, 280 mJ and 360 mJ, and 10 Hz of frequency and unit pulsed energy of 200 mJ, 300 mJ and 400 mJ, respectively. The first two parts of the experiment involved the use of LM and SEM for the observation of dentinal surface, and the final part of the experiment involved the use of electronic thermometer to measure the thermal changes of the laser irradiation with different energy.
The results from first part of the study showed that the dentinal surface in Group A was smoothly melt without any signs of damage. On the contrary, all the other groups revealed the signs of damage on the surfaces such as craters or cracks. The second part of the study showed that the dentinal surface in Group B consisted of some melting blocks without any exposure of the dentinal tubules. In Group A and Group D, there were some yet to be melting dentinal tubules spreading over the dentinal surface with melting blocks. In Groups C, E, and F, some cracks or bubble-like melting projections were evident over the dentinal surfaces with melting blocks. The final part of the study showed that apart from Group A, all the other groups showed a temperature increase of more than 5.5C. In the experiment involving the irradiation of the dentinal surfaces treated with black ink, all the groups treated without black ink showed a temperature elevation of more than 5.5C. However, in Groups A and B which are treated with black ink, the temperature increase was less than 5.5C. The groups treated without black ink showed a greater average temperature increase than those groups treated with black ink. The differences were statistically significant (P<0.05).
In conclusion, when Nd:YAP laser was applied, under the condition of water spray, with 180mJ and 5Hz of energy for 15 seconds, a smooth melting dentinal surface was produced to have part of the dentinal tubules blocked without causing damage to the surface. When treated by black ink, the Nd:YAP laser energy of 280 mJ and 5Hz for 3 seconds produced a dentinal surface with melting blocks, showing obvious closure of the dentinal tubules. Therefore, the use of black ink not only enhances the effects of Nd:YAP laser, but also prevents the potentially damaging thermal effects of laser irradiation.
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