| Objective: This research was performed to observe the influence of GaAlAs semi -conductor laser irradiation time towards dental pulp and dentin through animal experiment and experiment in vitra ,in order to investigate the maximum amount of semiconductor laser irradiation time in curing tooth hypersensitivity. This will provide worthy experiment basis for exalting the clinical curative effects.Methods:Experiment one:animal experimentIn the experiment four China healthy mongrel adult dogs were selected, included two females and two males, and the weight of each dog was about 12to15kg. There were 70teeth selected ,included canine, premolar and molar, and 17to18teeth were selected from each one. When the dogs were under sarcous anesthesia, these tooth were prepared for dentin hypersensitivity models . All the teeth were randomly divided into 7groups of 10 teeth each. One group wasn't irradiated with laser, anothers were irradiated with laser.All dogs were fed routinely for one week. SUNDOM- 300I type semiconductor laser therapeutic machine was used in the experiment, which was continuous adjustable, wave-lengh was 810nm, and laser medium was GaAlAs.Laser parameter was: 300mW300s, 300mW 330s, 300mW 360s, 500mW180s, 500mW 210s, 500mW 240s. After three days of laser irradiation, all the animals were put to death,then extracted the experimental teeth immediately. All the teeth were put into the paraformal- dehyde, and kept in refrigerator which temperature was fixed at 4℃. 48 hours later, the teeth were taken out and put into decalcification fluid.The histological specimens were taken out 4 weeks later , paraffin embedded, made paraffin section, and then made HE staining.All the stained sections were studied under the light microscopy and analysis. All the data were statistically analyzed.Experiment two:experiment in vitraTen molars were selected, which were extracted integrallty and coronals weren't carious. All the teeth were made into dentinal specimens, which were randomly divided into 5 groups. One group wasn't irradiated with laser, anothers were irradiated with laser.With the same laser therapeutic machine, laser parameter was:300mW300s,300mW330,500mW180s,500mW 210s. All the specimens were studied under the scanning electron microscopy.Results:Results of HE staining after pulsed GaAlAs semiconductor laser irradiation of first experiment : the change of dental pulp tissue was slightly with 300mW300 to 330s and 500mW180 to 210s, but it was seriously with 300mW 360s and 500mW 240s. The results of 300mW groups were statistically analyzed with one-way ANOVE. There were statistical difference.Those were statistically analyzed with LSD, then it was found there were statistical difference between 300s group and 360s group, 330s group and 360s group.But there wasn't statistical difference between 300s group and 330s group. So laser parameter should be 300mW 300 to330s. With the same way analyzing 500mWgroup, laser parameter should be 500mW180 to 210s.With t-test analyzing there wasn't statistical difference between 300mW 330s group and 500mW 210s group.Experiment two: The dentin surface of the group without being irradiated with laser is normal.To the groups with being irradiated with laser, detinal tubules were blocked out, but there were not crackles. The close effects of 300mW300s group and 500mW180s group weren't enough.Conclusion:Through the animal experiment and the experiment in vitra the conclusion of this studyit with semiconductor laser irradiating is:1,Used the laser parameter of 300mW 330s ,there are not devastating damnify to the dental pulp .Also detinal tubules were blocked out, and there were not crackles.2,Used the laser parameter of 500mW 210s ,there are not devastating damnify to the dental pulp .Also detinal tubules were blocked out, and there were not crackles.
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