The main objective of this study was to determine the change of hardness and acid resistance of enamel surface after various fluoride treatment in combination of Nd-YAG LASER irradiation.
One hundred and fifty sound enamel blocks were obtained from the 80 extracted human premolars and molars. Each enamel block was embedded into a cube (1.0xl.0x0.5 Cm3) of cold curing acrylic resin in such a way that the natural flat enamel surface were exposed. The exposed enamel were flattened by grinding the surface lightly on flat surface of a sandpaper. The margins of enamel surfaces were covered with inlay wax. These specimens were than randomly assigned into 15 groups 12 specimens each.
The exposed enamel surfaces were treated with their respective regimens consisted of a combination of 3 types of fluoride compounds (NaF, SnF2 and APF), two energy levels (2W and 5W) of Nd-YAG- LASER with and without block dyes on the treated surfaces.
The surface hardness of ten treated surfaces from each group were then randomly determined by - using Vicker Hardness Numbers. The remainder of two specimens from each groups were exposed to 1.0% HC1 for 24 hours and their surfaces were characterized under metallurgical microscopy at 200 magnification.
The results obtained from this study were summarized as follows;
1. The LASER irradiation caused a significant increase in surface hardness (P<0.01). The application of black dyes after the experimental fluoride treatment more significantly increased the surface hardness as compared with the surface divided with black dyes(P<0.01). No significant differences in surface hardness were indicated between 2W and 5W LASER irradiation on the treated surfaces (P>0.05).
2. The topical applications of NaF significantly increased the surface hardness as compared with natural surfaces of enamel(P<0.01). The surface hardness of enamel surfaces was further increased when the surfaces were treated with a combination of iontophoresis and NaF application. The Nd-YAG irradiation of the enamel surfaces treated with a combination of iontophoresis and NaF applications caused a significant increase(P<0.01) in surface hardness as compared with either that of natural (no treatment) or that of a combination regimen of iontophoresis and NaF application.
3. The fluoride applications significantly increased the enamel surface hardness as compared with that of control specimens. However, no significant difference among NaF, SnF2 and APF applications with and without additional LASER irradiations.
4. When the order of each regimen in the combination of three factors, (fluoride, iontophoresis and laser irradiation) was compared for the changes of enamel surface hardness, the LASER irradiation before the fluoride application caused significantly higher surface enamel hardness than that of after the fluoride
application(P<0.01).
5. The enamel surfaces which was treated with fluorides in combination of LASER irradiations showed a lesser changes after the specimens were exposed for 24 hours to the 0.1% hydrochloric acid.
Therefore, it can be concluded that the experimental regimens of the combination of fluoride, iontophoresis and Nd-YAG LASER increase the surface hardness and acid resistance.
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