| Background:Dental caries is one of the common diseases among human beings. WHO has already taken it, together with cancer and cardiovascular diseases, as the major diseases that should be paid more attention to prevent and cure. Of all the means to resist caries, the fluoride has been generally recognized by different researchers as the effective drug. But while affirming its function on caries resistance, people also find something with which they can't be satisfied. With the development of caries-resisting research, laser has attracted the attention of the reaearchers for its high ability of acid resistance for human enamel in vitro. The pulsed Nd:YAG laser has pliant and tough optic fiber delivering the light beam, red light toghther the road instructions as well as apt to arrive the oral cavity. But the function of the high-energy laser is higher than the low-energy laser, whose thermal effect could damage the dental pulp. So the single use of laser to resist the caries is controversial. In recent years, some researchs have showed that before and after the low-energy laser treatment the adopting of other caries-resisting measures such as fluoride can not only enhance the caries-resisting effect, but reduce the energy of the laser thus increase both the utilization of and the safety of fluoride. Nevertheless, current studys on the caries-resisting effect of the laser, especially the pulsed Nd:YAG laser combined with the fluoride were just done on the teeth in vitro. And the co-action way of the laser and the fluoride as well as the dose of the laser has not been unanimously acknowledged. Further and systematical studys on its safety and clinical applicability are still needed. Objectives: Based on the fixed concentration and the acting time of the sodium fluoride, to explore the efficiency and the safety of the pulsed Nd:YAG laser combined with sodium fluoride to resist caries, to obtain the most effective co-action way of the laser and the fluoride as well as the most suitable parameters of the laser, to research the mechanisms of the caries resistance, and to confirm the applicability and reliability of the laser combined with the fluoride in clinic. Materials and Methods:1. 200 teeth in vitro were routinely made into 100 enamel mass, dentine mass and cementum mass respectively. By demineralization experiment and by using the calcium selective electrode to explore the validity of the enhanced acid-resisting property of the human teeth in vitro by the laser combined with the fluoride, the effective co-action way of the two and the suitable dose parameter of the laser.2. Choosing another 80 teeth and made them into mass by the same means. In line with the experiment condition comfirmed by the experiment before, the validity of the caries resistance of the human teeth in vitro by the laser combined with the fluoride was explored in morphological level by experiment artificially developing the caries, by polarized light microscopy to observe the morphology and the depth of the artificial caries. 3. Selecting the extracted integrantly constant premolar teeth of the adolescents of 12~15 years whose teeth should be treated for orthodontic purposes. The teeth were exposed to the laser whose dose was confirmed by the previous experiment and were extracted according to the different observing timetable: immediate, 3 days and 14 days. The same teeth at the other side were considered as the control. In histological level, the thermal effect of the laser affecting the normal dental pulp tissue was observed dynamically and the safety of this laser dose was evaluated in vivo. 4. 86 samples were treated with both the laser and the fluoride; the laser only, the fluoride only, or no treatment (control). 16 samples, among which 8 samples were caused artificial caries, were prepared regularly to observe the ultrastructure of the teeth surface by Scan Electronic Microscope. The others were cut into halves and the vertical sides were polished so that the distribution of the fluoride was analyzed by... |
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