• Journal of the Korean Society for Precision Engineering
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• v.21 no.3
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• pp.171-179
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• 2004

Micro-stereolithography technology has made it possible to fabricate a freeform 3D microslructure. This technology is based on conventional stereolithography, in which a UV laser beam irradiates the open surface of a UV-curable liquid photopolymer, causing it to solidify. In micro-stereolithography, a laser beam of a few $\mu m$ diameter is used to solidify a very small area of the photopolymer. This is one of the key technological elements, and can be achieved by using a focusing lens. Thus, the solidification phenomena of the liquid photopolymer must be carefully investigated. In this study, the photopolymer solidification phenomena in response to variations in the scanning pitch of a focused laser beam was investigated experimentally. The effect of layer thickness on the solidification width and depth was also examined. These studies were conducted under the conditions of relatively lower laser power and relatively higher scanning speed. Moreover, the photopolymer solidification phenomena for the relatively higher laser power and lower scanning speed was investigated, too. In this case, comparing to the case of lower laser power and higher scanning speed, the photopolymer absorbed large amount of irradiation energy of the laser beam. These results were compared with those obtained from a photopolymer solidification model. From these results, a new laser-scanning scheme was proposed according to the shape of the 3D model. Samples by each method were fabricated successfully.

• Proceedings of the Korean Society of Laser Processing Conference
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• 1998.11a
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• pp.39-42
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• 1998

• Journal of the korean academy of Pediatric Dentistry
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• v.26 no.2
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• pp.377-398
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• 1999

Calcium fluoride, created by topical fluoride application, is the reservoir for fluoride ion regulated by pH in the oral environment. Therefore, the amount and the maintenance of calcium fluoride have an important role in preventing dental caries. The aim of this study is to evaluate the effect of Nd:YAG laser irradiation on the generation of calcium fluoride and the acid resistance of tooth enamel. The bovine anterior permanent teeth were prepared (n=276), and divided into following groups : no treatment (control) fluoride application alone, laser irradiation alone, laser irradiation after fluoride application, and fluoride application after laser irradiation. And each group was subdivided based on the application time of 1.23% acidulated phosphate fluoride (APF) (5 min and 30 min) and the irradiation energy of Nd:YAG laser ($20J/cm^2\;and\;40J/cm^2$). In case of fluoride application, each group was divided according to KOH treatment. Twenty three treatment conditions were made for this experiment and twelve specimens were assigned to each treatment condition. In each treatment condition, ten specimens were used for chemical analysis and two specimens were observed under SEM. In groups without treating KOH, fluoride content and the depth of enamel dissolved were measured using enamel biopsy technique. In groups with treating KOH, the amount of calcium fluoride was measured by the treatment with 1 M KOH for 24 hours and enamel biopsy was performed after KOH treatment. The results were analyzed by the fluoride content and the depth of enamel dissolved by enamel biopsy, amount and thickness of calcium fluoride, and the surface structures of enamel. The results are as follows: 1. In groups without treating KOH, the fluoride content of removed enamel showed a positive relationship with the energy density of laser when the laser irradiated before fluoride application 2. In groups without treating KOH, the depth of enamel dissolved decreased more with the combined laser and fluoride treatment than with laser or fluoride treatment, except for the case of $20J/cm^2$ laser irradiation after 5 minute fluoride application (p<0.05). 3. The amount of calcium fluoride did not increased by laser treatment with no statistical significance(p>0.05). 4. The particle size of calcium fluoride increased in case of fluoride treatment after laser irradiation, compared with fluoride application alone. In case of laser treatment after fluoride application, the particle size of calcium fluoride increased and some of the particles fused as well. 5. There were no significant differences in the fluoride content of dissolved enamel between groups without treating KOH and control group, except for the case of laser irradiation after treatment of APF for 30 minutes (p>0.05). 6. In groups with treating KOH, depth of removed enamel in the groups of combined treatment with laser and fluoride was shallower than that in fluoride application groups (p<0.05). 7. In groups without treating KOH, the relationship between fluoride content and the depth of enamel dissolved showed more negative (Spearman correlation coefficient: -0.6281) than in groups with treating KOH (Spearman correlation coefficient: -0.3792). The greater amount of calcium fluoride could be found in case where there was a significant differences of the depth of enamel dissolved between groups with and without treating KOH. From these results, it can be concluded that laser seems to be a little effects on the amount of calcium fluoride formation, but has some effect on the lowering the solubility of calcium fluoride. As the combined treatment of laser and fluoride application showed more effective acid-resistant property, more extended recall period for fluoride application can be achieved with this combined treatment in the clinic.

• Journal of Periodontal and Implant Science
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• v.40 no.3
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• pp.105-110
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• 2010

Purpose: It has been reported that low-level semiconductor diode lasers could enhance the wound healing process. The periodontal ligament is crucial for maintaining the tooth and surrounding tissues in periodontal wound healing. While low-level semiconductor diode lasers have been used in low-level laser therapy, there have been few reports on their effects on periodontal ligament fibroblasts (PDLFs). We performed this study to investigate the biological effects of semiconductor diode lasers on human PDLFs. Methods: Human PDLFs were cultured and irradiated with a gallium-aluminum-arsenate (GaAlAs) semiconductor diode laser of which the wavelength was 810 nm. The power output was fixed at 500 mW in the continuous wave mode with various energy fluencies, which were 1.97, 3.94, and 5.91 $J/cm^2$. A culture of PDLFs without laser irradiation was regarded as a control. Then, cells were additionally incubated in 72 hours for MTS assay and an alkaline phosphatase (ALPase) activity test. At 48 hours post-laser irradiation, western blot analysis was performed to determine extracellular signal-regulated kinase (ERK) activity. ANOVA was used to assess the significance level of the differences among groups (P<0.05). Results: At all energy fluencies of laser irradiation, PDLFs proliferation gradually increased for 72 hours without any significant differences compared with the control over the entire period taken together. However, an increment of cell proliferation significantly greater than in the control occurred between 24 and 48 hours at laser irradiation settings of 1.97 and 3.94 $J/cm^2$ (P<0.05). The highest ALPase activity was found at 48 and 72 hours post-laser irradiation with 3.94 $J/cm^2$ energy fluency (P<0.05). The phosphorylated ERK level was more prominent at 3.94 $J/cm^2$ energy fluency than in the control. Conclusions: The present study demonstrated that the GaAlAs semiconductor diode laser promoted proliferation and differentiation of human PDLFs.

• Journal of Periodontal and Implant Science
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• v.27 no.4
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• pp.829-844
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• 1997

Dentin hypersensitivity must be one of the most frequent postoperative complaints in periodontal patients. Obliterating the open dentinal tubules or decreasing the diameter of their orifices would, therefore, be an objective of treatment for hypersensitive teeth. The purpose of this study was to evaluate the effect of a pulsed Nd:YAG laser irradiation on obliteration of dentinal tubules and to determine any difference according to irradiation methods. The 45 posterior teeth that had been extracted due to periodontal disease were initially treated with tetracycline HCI(100 mg/ml, 4 min.) to remove the smear layer after root planing. The root surfaces were then irradiated by a pulsed Nd:YAG laser(EL.EN.EN060, Italy) by different laser beam spot size and different exposure condition: ${\cdot}$ group 1: irradiated group by small spot(beam diameter=1mm, lW, 2 sec) ${\cdot}$ group 2: irradiated group by large spot(beam diameter=10mm, 1W, 200 sec) ${\cdot}$ group 3: irradiated group by gradual increase of watt (from 0.3W to 1.0W), beam diameter=4mm ${\cdot}$ group 4: irradiated group by fixed watt(1.0 W), beam diameter=4mm ${\cdot}$ control group: no irradiation but root planing and tetracycline HCI conditioning only. Additionally, the specimens were retreated with tetracycline HCI(100mg/ml, 4min.) to evaluate the stability of obliteration effect by Nd:YAG laser. Specimens were examined under the scanning electron microscope(JEOL, JSM-840A, Japan). Photomicrographs were taken at ${\times}4,000$ magnification and were analyzed statistically. The results were as follows: l. Scanning electron micrographs of root surface treated by tetracycline HCI alone(control group) showed widened, funnel-shaped dentinal tubules, while those of the root surface irradiated by various methods showed partially or completely obliterated dentinal tubules and various surface alterations, eg, flat, multiple pitted, melted and resolidified surface at the same energy density. 2. There was no significant difference in the obliteration effect of dentinal tubules between group 1 and group 2, and between group 3 and group 4(p>0.05). 3. The obliteration effect of dentinal tubules by a Nd:YAG laser irradiation was relatively stable to tetracycline HCI. The results demonstrate that a pulsed Nd:YAG laser irradiation within 1.0W, regardless of irradiation methods, can obliterate dentinal tubules effectively.

• The Journal of Korean Medicine
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• v.17 no.2 s.32
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• pp.237-244
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• 1996

The purpose of this study was to investigate the effect of ILIB(Intravascular Laser Irradiation of blood) on Hyperfibrinogenemia. 20 patients with fibrinogen level of over $400mg／d{\ell}$ were treated with IUB. After !0 times' treatment, changes of fibrinogen level and clinical symptom were observed. The results were as follows: 1. Fibrinogen level was decreased in all of cases. 2. Most cases were suffered from neural symptoms(headache, palpitation, etc), circulatory symptoms (dizziness, numbness, deficiency of sensation, etc), musculo-skeletal symptoms(L.B.P, neck stiffness, arthralgia, etc.), fatigue, pollakiuria, constipation. After treatment, neural and circulatory symptoms were improved considerably.

• The Korean Journal of Pain
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• v.5 no.1
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• pp.44-51
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• 1992

This study examined the microscopic changes following irradiation of infrared low dose laser on injured sciatic nerves of rats. In these days, many clinicians use the low dose laser therapy in pain clinicians use the low dose laser therapy in pain clinic on various fields and dieases. But the basic mechanism and indications were not known completely. Low-dose IR(infrared) laser irradiation applied to a crushed injured sciatic nerve of rats in the right leg in bilaterally inflicted crush injury. The results were as follows 1) There are a little histological differences between laser treated group and nontreated group. 2) Low power IR-laser irradiation, when applied to the injured sciatic nerve, increased vascularization and relatively well conserved tissue organization. 3) There are little histological difference in distal muscle biopsy, but atrophic muscle fibers were seen partially. 4) We found out that more hypertrophic epineurium was present in laser-treated group.

• Journal of Welding and Joining
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• v.20 no.1
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• pp.34-40
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• 2002

The laser strengthening of $35kgf/\textrm{mm}^2$ grade steel sheet is investigated by using $CO_2$ laser beam irradiation. The increase of tensile strength is dominated by the number of fully penetrated melting lines. Also, the optimal laser irradiation pattern is obtained by 3-point bending test. Local laser strengthening clay be effective for the weight reduction of automobile components where the tailored welded blank can not be applied.

• Laser Solutions
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• v.14 no.4
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• pp.21-27
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• 2011

In this work, we have studied on time-resolved transient reflective image of single crystalline Si surface after single-shot fs-laser irradiation with varying the laser fluence under two different laser spot sizes. The temporal profiles of transient reflectivity changes as well as its maximum values at the early delay time were found to be strongly dependent on both the laser beam spot size and laser fluence. We have interpreted the dependence of transient reflectivity changes on the laser spot size in terms of a relaxation of the generated free carriers to the bulk silicon, which should be interacted with the plasma.

• Journal of Periodontal and Implant Science
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• v.26 no.4
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• pp.989-1002
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• 1996

The purpose of this study was to determine the effect of a pulsed Nd:YAG laser irradiation on human gingival tissues. The patients, who were planned to be treated by clinical crown lengthening procedure and gingivectomy, were selected. All the patients received oral hygiene instruction, scaling and root planing at preoperation. The crest of gingival tissue on upper and lower anterior teeth was irradiated by a pulsed Nd:YAG laser(El. EN. EN060, Italy) with a fiber optic of 300 m in contact mode for 20 seconds. Gingival tissues were divided into 4 groups according to the laser power of 1.0W(10Hz, 100mJ), 2.0W(20Hz, 100mJ), 3.0W(30Hz, 100mJ) and 4.0W(40Hz, 100mJ). Immediately after the laser irradiation, the specimens were excised, fixed 10% neutral formalin, sectioned $4-6{\mu}m$ thick, stained by Hematoxylin-Eosin and Periodic Acid Schiff stain and observed under light microscope. The removed tissue depth and the coagulated layer depth due to a laser irradiation by a laser irradiation were measured on the microphotographs. The difference of measurements according to the different laser power was statistical1y analyzed by Kruskal Wallis Test with SAS program. The results were as follows : 1. In histologic findings of irradiated gingival tissues; a. In the irradiated gingival specimen with 1.0W laser power, some vesicles were observed in limited superficial layer of gingival epithelium. b. In the irradiated gingival specimen with 2.0W and 3.0W laser power, the epithelium was almost removed except for the traces of viable basal cell remnants at ret peg, and coagulation necrosis related with the thermal effect of laser was noted. c. In the irradiated gingival specimen with 4.0W laser power, complete removal of epithelium, partial removal of underlying connective tissue, and the coagulation necrosis of subjacent gingival tissue were shown. 2. The removed tissue depth was deeper in the irradiated specimens with higher power. There was a statistical significance in the difference of removed tissue depth between 1.0W group ($44.54{\pm}6.99um$) and 3.0W group ($99.75{\pm}6.64{\mu}m$), and between 1.0W group($44.54{\pm}6.99{\mu}m$) and 4.0W group($111.36{\pm}4.50{\mu}m$), and between 2.0W group($98.01{\pm}4.53{\mu}m$) and 4.0W group($111.36{\pm}4.50{\mu}m$)(P<0.05). 3. The coagulated layer depth was deeper in the irradiated specimens with higher power. There was a statistical significance in the difference of coagulated layer depth between 1.0W group($31.82{\pm}8.99{\mu}m$) and 3.0W group($55.99{\pm}20.94{\mu}m$), and between 1.0W group($31.82{\pm}8.99{\mu}m$) and 4.0W group($83.68{\pm}10.34{\mu}m$)(P<0.05). From this study, the results demonstrated that the effects of a pulsed Nd:YAG laser irradiation on gingival tissues seemed to depend on the laser power and that the irradiation with high power could be harmful to adjacent healthy tissue.