• Journal of the korean academy of Pediatric Dentistry
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• v.33 no.2
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• pp.192-200
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• 2006

The aim of this study was to assess the microleakage underneath a pit and fissure sealant bonded to occlusal surfaces treated by Er:YAG laser To determine the most effective energy density of laser, fourteen specimens were irradiated from 50mJ to 300mJ at 3Hz. After irradiation, the lased specimens were observed under the scanning electron microscope. Thirty six non-carious extracted premolars were randomly assigned to four groups of nine teeth: group 1, no treatment on the occlusal surface; group 2, acid etching for 15 seconds; group 3, Er:YAG laser irradiation; group 4, acid etching followed by Er:YAG laser irradiation. The pits and fissures were sealed with unfilled sealant(Helioseal F) and the specimen teeth were thermo-cycled, immersed in 2% Rhodamine B solution, longitudinally sectioned and analyzed for microleakage with fluorescent microscope. The results were as follows: 1. Er:YAG lased surfaces with 50mJ, 3Hz showed a similar pattern of irregularity with acid etched enamel surfaces 2. The mean microleakage score increased in the order of group 2, 4, 3 and 1. There was no significant difference among group 1, 3 and 4(p>0.05), however group 2 showed significantly less microleakage compared with group 1 and 3. Conclusively, the laser irradiation seemed not enough to replace the acid etching for proper retention of pit and fissure sealants.

• Journal of the korean academy of Pediatric Dentistry
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• v.35 no.1
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• pp.11-17
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• 2008

The purpose of this study was to investigate early histological changes and calcitonin gene-related peptide (CGRP) expression in the dental pulp of the rat after Er:YAG laser preparation. Occlusal cavities were prepared in the upper first molars using either Er:YAG laser and conventional bur. At 48 hours after cavity preparation, the teeth were processed for hematoxylin-eosin stain and CGRP immunohistochemistry. The results were as follows : 1. The cavity floor by Er:YAG laser preparation was more irregular shape compared with those by bur preparation and there are some cracks in the directions of dentinal tubules. 2. There were more inflammatory cell infiltration and disruption of odontoblast in the dental pulp by Er:YAG laser preparation in comparison with the dental pulp by bur preparation. 3. CGRP expression in the pulp tissue by both Er:YAG laser and bur preparations were increased and higher than in the normal pulp. The expression pattern of CGRP was more strong in the pulp by Er:YAG laser preparation. These results indicate that Er:YAG laser is useful in the operative dentistry such as caries removal and cavity preparation if properly applied.

• The korean journal of orthodontics
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• v.27 no.1
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• pp.141-155
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• 1997

The purpose of this study was to evaluate the effectiveness of the Nd:YAG laser and the Er:YAAG laser on etching enamel for direct bonding of orthodontic bracket. The advantages of laser etching rather than conventional acid etching are to reduce the subsurface demineralization rate, to inhibit the spillage of acid onto uninvolved ""its of enamel, and to save the clinical manipulation time involving drying, trashing and drying again. 189 freshly extracted human premolars were prepared for this research. 165 out of them were divided into 11 groups of 15 teeth. One group was acid etching and the rest groups were irradiated with Nd:YAG laser by four different energy levels(100mj 10pps, 100mj 20pps, 150mj 20pps, 200mj 20pps) and with Er:YAG laser by six different energy levels(60mj 5pps, 60mj 10pps, 100mj 10pps. 200mj 10pps, 200mj l5pps, 400mj 10pps). Shear bond strength was tested with Instron after 24 hours, one week, and three weeks. Twenty-four out of 189 teeth were divided into twelve groups untreated control, acid etching, and ten laser irradiation subgroups. And the ultrastructural enamel surfaces of each group were observed with scanning electron microscope. The results were as follows; 1. The means and the standard deviations of shear bond strength of Nd:YAG and Er:YAU laser irradiation by different energy levels were obtained. 2. Shear bond strengths of Er:YAG laser irradiation groups were higher than those of Nd:YAG laser irradiation groups at the identical energy level. 3. Maximum bond strengths was achieved at the energy of I50mj, 20pps in Nd:YAG laser irradiation groups or 60mj, 10pps in Er:YAG laser irradiation groups. 4. It was acceptible for direct bonding to irradiate lb0mj 20pps with Nd:YAG laser or to irradiate 60mj 10pps with Er:YAG laser considering the results of shear bond strength tests and SEM obsesvation.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.25 no.4
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• pp.166-171
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• 2015

In this study, using solid-state and flux, $Y_3Al_5O_{12}:Er^{3+}\;(YAG:Er^{3+})$ powders were successfully synthesized at low temperatures. To analyze the crystallinity of powders according to the synthesis or non-synthesis of powders and powder calcination temperatures, X-ray diffraction (XRD) was measured. In the case of pure YAG, when YAG was analyzed using the general solid-phase method, it was calcined for 12 hours at $1400^{\circ}C$ and pure YAG phase could be obtained. But when $BaF_2$ was added to YAG, YAG was synthesized at lower temperature (1000^{\circ}C$). It was thus found that the synthesis temperature could be lowered by about $400^{\circ}C$. Also, when BaF2 with an optimal concentration was added to $YAG:Er^{3+}$, the particle shape and size according to synthesis temperatures were surveyed, and corresponding luminous intensity was discussed.

• Journal of the korean academy of Pediatric Dentistry
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• v.30 no.2
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• pp.272-285
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• 2003

This study was conducted to observe the microscopic structures of cavities formed after ablation of primary teeth, permanent teeth, enamel and dentin in using a bur and cavities formed after ablation using laser and the following results were obtained after comparing the effects of ablation. Using a #330 bur and Er:YAG laser irradiated at 150 mJ, 200 mJ, 250 mJ and 300 mJ all at the frequency of 5 Hz, 1 mm enamel and dentin samples were ablated and the ablation time was measured. In order to measure the surfaces ablated, 5 each of primary teeth and permanent teeth were ablated using a #330 bur and Er:YAG laser at 150 mJ, 200 mJ, 250 mJ and 300 mJ for 1 sec and the cross section and vertical section were observed. The following results were obtained : 1. Cutting time of Er:YAG laser was longer than that of conventinal high-speed bur regardless of teeth type. 2. Cutting on enamel, Cutting time of conventional high-speed bur in deciduous teeth was longer than in permanent teeth(P<0.05). But Er:YAG laser was not showed any difference between the deciduous and permanent teeth(P>0.05). 3. Cutting on dentin, Cutting time of conventional high-speed bur in permanent teeth was longer than deciduous teeth. Er:YAG laser of 150 mJ, 5 Hz in permanent teeth was longer than in deciduous teeth(p<0.05). But laser of other power did not showed mean difference. 4. The cavity surface treated with the convetional high-speed bur revealed a relatively flat appearance, almost covered with a debris-like smear layer. Cavity wall showed striped appearance because of blade of bur. 5. The cavity surface treated by the Er:YAG laser system was irregular or rough surface with the absence charring, carbonization, or cracking of the dentin. In addition, there was an absence of a smear layer. Cavity floor was round and relatively smooth. According to these results, cutting time of Er:YAG laser was almostly same in permanent and deciduous teeth, but more effective in dentin than enamel. Cutting the sample, Er:YAG laser was needed more time than conventional bur. But SEM findings suggested that laser device produced favorable surface characteristic(i.e, no smear layer, irregular surface, cracking).

• Journal of the korean academy of Pediatric Dentistry
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• v.33 no.4
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• pp.597-605
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• 2006

It is introduced that pit and fissure sealant is the most universal and effective to prevent occlusal dental caries. In processing of being applied the pit and fissure sealant, the various kinds of methods are developed to remove organic matters, plaque, microflora and debris in the pit and fissure for increasing the rates of maintain the sealant. Recently, the Er:YAG laser has been used as a new enamel surface treatment method. The purpose of this thesis is compared whether that enamel surface treatment method is superior to other methods or not. 1. 100mJ 5Hz Er:YAG lased enamel surface was similar to acid-etched enamel in SEM evaluation. 2, Mechanical preparation showed decreased microleakage when compared with acid-etching only, but no significant differences in both method. 3. After laser and acid-etching method showed decreased microleakage when compared with acid-etching only.

• Journal of the korean academy of Pediatric Dentistry
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• v.30 no.3
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• pp.439-447
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• 2003

This was performed to evaluate the inhibitory effect of laser on the growth of S. mutans. The bacterial pallets containing S. mutans KCTC 3065 were irradiated with Er:YAG laser and Nd :YAG laser by non-contact method at an intensity of 50mJ for 5 sec with the pulse repetition rates of 10Hz and 30Hz, respectively. The following results were obtained on colony count, acid producing ability, and the amount of insoluble extracellular polysaccharide synthesis. 1. The irradiation of Nd:YAG laser after photosensitization with Chinese ink inhibited the proliferation of S. mutans the most, and the irradiation of Er:YAG also inhibited the proliferation. However, the irradiation of Nd:YAG laser alone could not inhibited the proliferation of S. mutans. The pulse repetition rate did not affect significantly on the proliferation of bacteria in overall. 2. The irradiation of Nd:YAG laser after the photosensitization with Chinese ink inhibited the acid production of S. mutans the most for a certain period of time. Er:YAG laser also inhibited acid production. When Nd:YAG laser was used alone, the acid production of S. mutans was not been inhibited. The irradiation of Nd:YAG laser after photosensitization with Chinese ink inhibited the acid production ability of bacteria the most as the pulse repetition rate increased. 3. Laser irradiation did not inhibited the synthesis of insoluble extracellular polysaccharide of S. mutans. From these results, we conclude that the irradiation of Er:YAG laser and Nd:YAG laser after photosensitization with Chinese ink would inhibit the proliferation and acid production by S. mutans, which may prevent dental caries. However, this effect does not last long time so that the laser irradiation should be repeated frequently in order to obtain clinical effect; thus, this laser irradiation would not have a clinical usefulness in preventing dental caries when used solely.

• Journal of the korean academy of Pediatric Dentistry
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• v.28 no.3
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• pp.374-382
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• 2001

The purpose of this study was to investigate the surface morphology and measure shear bond strength of Er : YAG lased enamel. To determine the most effective energy density of laser for improving bonding strength of human enamel, 24 specimen were lased from 30mJ to 150mJ at 1Hz used focused, defocused beam. After irradiation, the lased specimen were observed scanning electron microscope. To determine the resin shear bond strength of Er : YAG lased enamel, the 90 specimen were divided into 3 groups. The Control group was etched with 37% phosphoric acid for 15seconds and rinsed. Group 1 was only laser irradiaton(60mJ, 10Hz), Group 2 was irradiated as Group 1 regimen, followed 37% phosphoric acid etching. The following results were obtained: 1. In both focused and defocused Er : YAG lased enamel surface are similar to acid-etched enamel more than 60mJ in SEM evaluation. 2. The more increased laser energy, the more observed fissuring surface. 3. The highest mean shear bond strength value was observed in control group with the statistical significance(p<0.05) between all the other groups and the shear bond strength in group 1 was the lowest with significant difference among the other groups.

• Journal of the korean academy of Pediatric Dentistry
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• v.30 no.4
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• pp.660-666
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• 2003

The purpose of this study was to investigate the inhibitory effect of Er:YAG laser against the intraoral acid producing bacterium of S. mutans. Bacterial pellet containing S. mutans KCTC 3065 was irradiated by Er:YAG laser having a $650\;{\mu}m$ diameter beam by non-contact mode. Irradiated parameters were 50mJ, 10Hz and exposure time were 1s, 3s, 5s, 7s, 9s respectively. We obtained the following results of relative growth rate and acid-producing ability of S. mutans by culturing for 48hrs. 1. The growth rate of S. mutans was decreased in the group of laser irradiation compared to the control group(P<0.01). 2. The growth rate at laser irradiation group of 7s, 9s irradiation time was decreased significantly compared to the laser irradiation group of 1s, 3s, 5s irradiation time, until 12 hours(P<0.05). After 24 hours, all groups of laser irradiation were not found to be statistically different in each other. 3. The acid-producing ability of S. mutans was inhibited for a certain duration by irradiation of laser. In summary, the growth rate and acid producing ability of S. mutans decreased according to laser irradiation. This effect was directly related to the amount of irradiation time. These results suggested that Er:YAG laser had an growth inhibition effect on S. mutans.

• Journal of the korean academy of Pediatric Dentistry
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• v.23 no.4
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• pp.954-967
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• 1996

Laser application to modify healthy permanent dentin to improve microhardness and caries resistence has been previously reported but the physical modification and ablation thresholds of carious and sclerotic dentin has yet to be identified. This study determined the energy density required by modify (physical modification threshold, PMT) and remove (ablation threshold, AT) infected carious, affected and selerotic dentin compared to healthy permanent dentin. $1{\pm}0.25mm$ thick dentin sections(n=272) from extracted human teeth were used. Smear layer was removed 0.5M EDTA for 2 minutes. Utilizing three pulsed fiberopitc delivered contact lasers with different emission wavelengths($1.06{\mu}m$=Nd : YAG, $2.10{\mu}m$=Ho : YAG and $2.94{\mu}mEr$ : YAG). The energy density($J/cm^2$) was incrementally increased and the resulting tissue interaction classified on a scale from 0-6. A minimum of 5 repetitions/energy density were completed. Light microscopy(10-25X) was used to verify the physical modification(scale=3) and ablation thresholds(scale=4) of the various forms of dentin and the data were analyzed by logistic regression at the 95 % confidence interval. PMT and AT by the laser and the dentin types were: PMT and AT was lower in infected dentin than in sound dentin for all lasers. PMT and AT induced by Nd : YAG>Ho : YAG>Er : YAG for all forms of dentin. Microhardness was increased in sound dentin at PMT. Morphology of crater examined by light microscopy showed Nd : YAG was safe and effective for removing carious dentin and Er: YAG was effective for removing sound dentin. The PMT and AT for YAG lasers are different as a function of dentin type which may be utilized for selective modification and removal of dentin.