| Summary: | 碩士 === 高雄醫學院 === 牙醫學研究所 === 87 === According to numerous studies, an enamel surface has the increased resistance to acid following laser treatment which implies that we can use a laser to the prevent caries. Fluoride plays an important role in prevention of caries. The purpose of this study was to attempt to understand the difference between the resistance to acid before and after treatment of the CO2 laser and Nd: YAG laser. We also explored the relationship of resistance to acid with the combined use of acidulated phosphate fluoride (APF) with laser and that of using APF alone. In clinical use this will allow us to prevent the occurrence of the caries.
Forty newly erupted permanent premolars which were extracted for orthodontic treatment. Two surface planes of 2 mm x 4 mm were available for each tooth. Eighty surface planes were available for samples. Eighty samples were classified in 8 groups as follows: (1) control group (2) treated with APF alone (3) treated with the CO2 laser alone (4) treated with the Nd:YAG laser alone (5) treated with fluoride following CO2 laser treatment (6) treated with fluoride prior to CO2 laser treatment (7) treated with fluoride following treatment with the Nd:YAG laser (8) treated with fluoride prior to treatment with the Nd:YAG laser.
The conditions for the laser were as follows: (1) CO2 laser, 1W, 750 pps, light spot 0.3 mm, scanning speed 4mm/sec, energy density 83.33 J/cm2 (2) Nd:YAG laser, 6W, 50 pps, light spot 0.6 mm, scanning speed 12mm/sec, energy density 83.33 J/cm2. Treatment with fluoride was APF for 4 minutes. Each sample was immersed in 5ml of lactic acid buffer solution for 24 hours (pH=4.5, 0.1 M).The area of enamel for acid-etching was confined to 1 mm x 3 mm. Therefore the conditions for all 8 groups in this experiment were different. Ten samples of each group were finally evaluated for tooth resistance to acid according to the following 4 aspects :
(1) Measure the calcium concentration with the atomic absorption spectroscopy
(2) Observe the changes to the surface caused by acid-etching under the scanning electron microscope
(3) Measure the etching depth by polarized light microscope
(4) Qualitative analysis of cross section by polarized light microscope
By measuring the calcium concentration with the atomic absorption spectroscopy, we can observe the following facts :
(1) Combined treatment of CO2 laser/or Nd: YAG laser with fluoride was superior to that of laser/APF alone .
(2) APF treatment followed by laser treatment was more effective than other groups.
(3) When CO2 laser, Nd:YAG laser and fluoride are used alone, CO2 laser was by far superior to the Nd:YAG laser alone and APF alone for resistance to acid. There is no obvious difference between the Nd:YAG laser alone and APF.
(4) Calcium dissolved in the CO2 laser group was less than that of the Nd:YAG laser group, so the etching depth of the CO2 laser group was less than that of the Nd:YAG laser group.
Observation of the cross section from the polarized light microscope, found a dark layer (5 — 20 μm ) over the un-etched area following treatment with the CO2 laser or Nd:YAG laser alone. Following 24-hour etching the etching depth of all groups increased. The depth was obviously less for the group which was treated with APF following laser treatment. The dark area for this group was narrow and smoother (15 — 50 μm). The dark area increased significantly for the group which was treated with APF prior to laser treatment (100 — 200 μm). The surface of the etching area was not smooth. It was relatively smooth for the etching surfaces of the control group and the group treated with APF alone. The dark band was thinner and straighter. Analysis of the etching depth , increases the anti-acid etching ability for enamel when we use APF combined with laser treatment. It is much more effective in anti-acid etching than that of APF or laser alone. The difference is small when we compare the groups of APF before and after laser treatment. This seems to be contradictory to the result of the calcium concentration of the lactic acid solution by atomic absorption spectroscopy. This may be due to the fact that the area for cross section does not represent the whole sample. Observation of the depth change with the naked eye may result in error.
We can get the following results according to the above analyses and observations : combined treatment of CO2 laser/Nd:YAG laser with APF increases enamel resistance to acid, which was much greater than that of treatment by laser alone or APF alone. This increased enamel surface resistance to acid by APF treatment followed by the application of the CO2 laser produced the best results. The CO2 laser alone was by far superior to the Nd: YAG laser alone and APF alone for resistance to acid. The effect of the CO2 laser was superior to that of the Nd:YAG laser.
Summary : We can use laser treatment combined with APF to prevent the occurrence of dental caries. The best results can be expected with topical use of APF following laser treatment.
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