• Journal of the korean academy of Pediatric Dentistry
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• v.33 no.2
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• pp.281-289
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• 2006

Topical fluoride application for children is a widely performed procedure in the field of Pediatric Dentistry for its dental caries prevention effects However, it is recently recognized as having some unwanted effects on several esthetic restorative materials, the author immersed glass ionomer cement, compomer and composite resin specimens in APF gel and measured the surface roughness and also, examined the specimens under the scanning eletron microscope. The followings are the results: 1. In the specimens of glass ionomer cement and compomer, APF gel 4 minute immersion group and pH cycling group show statistically significant increased surface roughness than artificial saliva immersion group (p<0.01). 2. There was no statistically significant surface roughness for composite resin in all group (p>0.05). 3. When the specimens were examined under scanning electron microscope, the surface change were in the order of glass ionomer cement, compomer, composite resin and also in the order of pH cycling group, APF gel 4 minutes immersion group, artificial saliva immersion group.

• Journal of Dental Rehabilitation and Applied Science
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• v.29 no.2
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• pp.141-151
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• 2013

The nano-surface modification techniques could be classified; internal modifications which enhance surface roughness and porosity in nano level and external modifications as nano particle coating. Nano-modified implant surface has various morphograpies such as nanotube, nanopit, nanonodule and polymorphic structures. Creating surface depends upon preparation method and material, however, there is no standard preparation technique not yet. The nano-modified surfacet is electrochemically stable comparing with the surface modified in micron level. Nano-modified surface has little cytotoxicity, stimulates osteoblast proliferation and differentiation. Moreover, it decreases soft tissue intervention by interrupting the proliferation of fibroblast. Nanostructure has similar size and shape with cells and proteins, consequently leads to good biocompatibility and enhanced osseointegration. However, the actual effect in vivo is limited, due to the distance of effect. Even if nano-modified surface has antibiotic property due to photocatalysis, short duration time makes clinical application questionable. Further investigations should focus on the optimal nano-modified surface, which has many potentials.

• Journal of the korean academy of Pediatric Dentistry
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• v.29 no.3
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• pp.362-370
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• 2002

During the last two decades, many new filling materials and material groups have been developed. the number of available restoratives has increased dramatically, especially during the last 5 years. Ormocers are a new class of materials which are still under development with regard to dental applications. However, in the chemical literature these materials have been known for a long time and used for producing scratch resistant coatings on plastic spectacle lenses. It is a combination of inorganic and organic materials. 'Ormocer' is an abbreviation for 'Organically Modified Ceramics'. These compounds are also known in the literature as 'Ormosils' (organically modified silicates). Their chemistry is comparable to that of silicones and organic polymers. The purpose of this study was to determine of compressive strength and flexural strength of a ormocer (Admira) and to investigate the effects of water absorption in comparison with three composite resins(Z-100, Tetric Ceram, Surefil) and one compomer(Dyract AP). The following results were obtained ; 1. Admira had the lower compressive strength than Surefil, but no statistically difference with other materials at 1 day(p>0.05). 2. Admira had the lower flexural strength than all other materials at 1 day. From 2 days, Admits showed lower flexural strength than three composite resin(p<0.05). 3. There was not statistically significant difference of compressive and flexural strengths between hybrid composite resin group(Z-100, Tetric Ceram) and Packable resin group(Surefil) for experimental period(30 days)(p>0.05). 4. All five materials showed an increase in compressive and flexural strength till 2 days and showed a decrease from 7 days in water(p<0.05). 5. Each materials had the statistically similar behavior of compressive and flexural strengths over time(p>0.05).

• Maxillofacial Plastic and Reconstructive Surgery
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• v.22 no.3
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• pp.274-287
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• 2000

The use of dental implants has increased tremendously in recent years and is expected to increase even more in the future. The successful outcome of any implant procedure is surely dependent on interrelationship of the various components of an equation that includes biocompatibility of implant material, macroscopic and microscopic nature of the implant surface, the status of implant bed, surgical technique, undisturbed healing phase and subsequent prosthetic design and long-term loading phase. The purpose of this study was to clarify the effects of adrenalectomy on the osseointegration of pure titanium implants. Seventy rats, 11 weeks of age, were divided into two groups : an adrenalectomized group and a control group. Titanium screw implant(diameter, 2.0mm; length, 3.5mm) was placed into left tibia of 70 rats, 35 in control group and 35 in the experimental group. The rats were sacrificed at different time interval (1, 2, 3, 4, 6, 8, and 12 weeks after implantation) for histopathologic observation, histomorphometric analysis and immunohistochemistry with fibronectin and CD44 antibody. The results obtained from this study were as follows: 1. Histopathogically, findings, newly formed bone was seen at 3 weeks control group and became lamellar bone at 12 weeks. At 6 weeks, lipocytes were observed in bone marrow space. Thickness of regenerated trabecular bone increased till 6 weeks after then, that decreased gradually. 2. By histomorphometric analysis, marrow bone density and contact ratio of marrow bone to implant decreased significantly from 8 to 12 weeks in experimental group compared to control group and also total bone to implant contact ratio decreased significantly from 4 to 12 weeks in experimental group compared to control group. 3. Fibronectin immunoreactivity was very strong at 3 and 4 weeks control group. And after that reduced gradually. But it was continuously strong from 1 to 12 weeks experimental group. 4. CD44 immunoreactivity was very strong in the newly formed osteoblasts at 3 and 4 weeks control group. But it reacted minimally later. However, it reacted continuously strong from 3 to 12 weeks experimental group. From these results, bone to implant contact ratio decreased gradually from 4 weeks in adrenalectomized group compared to control group. CD44 and fibronectin immunoreactivities were strong at all times in adrenalectomized rats. Therefore, it could be stated that immature bone remained continuously for a long time and not readily proceeded into mature status.

• Journal of Oral Medicine and Pain
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• v.36 no.3
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• pp.161-167
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• 2011

Sialolith is one of the most common pathologic conditions found in the salivary glands. The mechanisms responsible for the formation of sialoliths have not been elucidated so far. In this article, the chemical composition and micromorphology of a sialolith of a 58-year old female patient suffering from chronic sialoadenitis of the submandibular gland was analyzed using scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX). In a SEM evaluation, the highly mineralized amorphous core surrounded by lamellar and concentric structures was revealed, however no foreign body, organic material, or signs of microorganism were observed in the core of the sialolith. EDX analysis showed the central core was composed of only Ca, O and P, and that a high level of C was detected near the central area as well. These results indicated that the inorganic composition of the sialolith was hydroxyapatite crystals, and that inorganic and organic substances existed around the central cores. This study suggests that the sialolith was composed mainly of hydroxyapatite crystals and the formation of the nucleus of the sialolith in the submandibular gland duct was secondary to sialadenitis, which favors the growth of an inorganic crystalline nucleus.

• The Journal of Korean Academy of Prosthodontics
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• v.37 no.2
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• pp.200-211
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• 1999

For many years permanent soft denture liners has been widely used in dental practice directly or indirectly because of its function in absorbing and distributing the impact force. However, it reveals problems such as lack of permanency and decreased bond strength in long term use. The purpose of this study is to measure the bond strength and failure between denture base resin and several permanent liners. Lucitone 199 was used as denture base resin with soft acrylic liners (Triad, Tokuso Rebase) and silicone elastomers (Tokuyama, Ufi Gel C) bonded to measure the tensile strength before and after thermocycling. The thermocycling was done in 2000 cycles at $5^{\circ}C,\;26^{\circ}C\;and\;55^{\circ}C$ and the measured tensile strength values before and after thermocycling were compared. The mode of failure was investigated in the separated specimens. The results are as follows. 1. As to tensile strength, the strongest material is Tokuso Rebase followed by Triad, Tokuyama, Ufi Gel C in before thermocycling and the order of Triad, Tokuso Rebase, Tokuyama, Ufi Gel C in after thermocycling state. There was significant difference between the values of Triad, Tokuso Rebase and Tokuyama, Ufi Gel C(p<0.05). 2. As to degree of displacement, Ufi Gel C showed most displacement with or without thermo-cycling treatment and also the difference was significant with the other materials(p<0.05). 3. As to comparisons before and after thermocycling, Tokuso Rebase and Tokuyama showed significant difference in bond strength, whereas Triad and Tokuso Rebase showed significant difference in the degree of displacement(p<0.05). 4. In debonded specimens, Triad and Ufi Gel C showed adhesion failure and Tokuyama showed cohesion failure. Both failures were observed in Tokuso Rebase with adhesion failure up to 70%. The results of this study showed that degree of bond strength between permanent soft denture liner and denture base resin were variable. There was a significant difference between soft acrylics and silicone elastomers with regard to bond strength. Further research in improving bond strength of widely used silicone elastomers and in developing the method of measuring bond strength between denture base resin and the lining materials is needed.

• The Journal of Korean Academy of Prosthodontics
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• v.41 no.2
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• pp.148-159
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• 2003

Statement of problem Metal-ceramic restorations have been used extensively by dental clinicians for nearly 40 years. Strength an functional ability of metal-ceramic restorations are proved to be satisfying, However esthetics and biocompatibility of metal alloy which is used in metal-ceramic restoration is not ideal. Using pure gold as an alternative, have advantage of esthetics, biocompatibility over conventional metal alloy. But there had been little article which studied on the color effect of pure gold on fual porcelain color. Purpose The purpose of this study was to spectrophotometrically evaluate the difference between color of metal alloy(Au-Pt, Ni-Cr) and pure gold, during color masking procedure with opaque porcelain and to analyze the differences, Material and Methods Three types of metal - base metal(Ni-Cr), high gold alloy(Au-Pt), pure gold(GES) - specimen were fabricated 1cm in diameter. Four steps were established - after finishing, after pre-coditioning, after application of first opaque porcelain(0.08mm in thickness), after application of second opaque porcelain(0.15mm in thickness)- and tested color with spectrophotometer every each steps and analyzed with $CIEL^*a^*b^*$ color order system. One-Way ANOVA test was used to and out if there were significant differences between groups tested and Shaffe multiple comparison was used to identify where the differences were. Results 1. After finishing and pre-conditioning, pure gold(GES) group showed most high values in $L^*,a^*,b^*$. 2. After application of first opaque porcelain(0.08mm in thickness), after application of second opaque porcelain(0.15mm in thickness), pure gold(GES) group showed the least difference in $L^*,a^*,b^*$ values and the lowest ${\Delta}E$ value(${\Delta}E$=0.63). 3. After application of first opaque porcelain and after application of second opaque porcelain differences that were significant (P<0.05) between groups were found only in $a^*$ values. 4. Base metal alloy group showed the lowest $a^*$ value in test after application of first opaque porcelain and the highest value in test after application of first opaque porcelain Conclusion Pure gold group and high gold group showed higher $a^*$ values than base metal group when tested after 0.08mm thickness of opaque porcelain was applied and pure gold group showed much similar $L^*,a^*,b^*$ values between 0.08mm thickness and 0.15mm thickness of opaque porcelain. This meant that pure gold was more easily masked by opaque porcelain than the other two groups.

• The Journal of Korean Academy of Prosthodontics
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• v.41 no.2
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• pp.207-222
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• 2003

As a material of metal-ceramic prosthesis, nickel as a form of Ni-Cr alloy has been used for many dental prostheses in many cases. However, several problems in use of the alloy have been revealed (ex ; tissue stimulation, skin allergy, hypersensitivity cytotoxicity and carcinogenecity). Little is known about nickel with respect to the relationship between Ni-prosthesis and gaining of Niresistance in oral microorganisms. The present study was undertaken to check whether use of Ni-prosthesis leads to occurrence of Ni-resistant microorganisms. So this study may suggest the possible relationships between the oral microorganisms and nickel-resistance in oral environment. Bacteria were isolated from the gingival crevicular fluid on the patients wearing Ni-Cr prosthesis. The isolated bacteria were tested fir their Ni-resistance in nickel containing media at different concentration from 3mM to 110mM. E. coli HB101 was used as control. The Ni-resistant bacteria were isolated and biochemically identified. The Ni-resistant bacteria were tested several biochemical, molecular-biological tests. Performed tests were : measuring the growth curve, antibiotic test, growth ability test in liquid media, isolation of the chromosome and plasmid, digestion of DNA by restriction enzyme, electrophoresis of chromosome and plasmid DNA, identification of Ni-resistant genes by the DNA hybridization. The results were as follows 1) The bacteria isolated from gingival crevicular fluid on the patients wearing Ni-Cr alloy prosthesis showed nickel-resistance. 2) The isolated microorganisms grew at nickel containing media of high concentrations (60mM-110mM). 3) Based on the biochemical tests, the isolated microorganisms were identified as Enterococcus faecalis(13 cases), Klebsiella pneumoniae(1 case) and Enterobacter gergoviae(1 case). 4) Enterococcus faecalis expressed not only nickel resistance but also the multi-drug resistance to several antibiotics ; chloramphenicol, kanamicin, streptomycin, lincomycin, clindamycin, However, all strain showed the sensitivity against the tetracycline. 5) DNA hybridization result suggests that there is no homology between the previously known gene of nickel resistance in Klebsiella pneumoniae and chromosomal DNA of Enterococcus faecalis.

• Journal of the korean academy of Pediatric Dentistry
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• v.28 no.4
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• pp.700-708
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• 2001

Traumatic injuries in young patients can result in the interruption of the development of the incompletely formed roots. In teeth with incomplete root-end formation and necrotic pulps, the root canals must be completely debrided. Because of a lack of an apical stop and the presence of thin and fragile walls in these teeth, it is imperative to perform apexification to obtain an adequate apical seal. Calcium hydroxide has become the material of choice for apexification. Despite its popularity for the apexification procedure, calcium hydroxide therapy has some inherent disadvantages that include variablility of treatment time, unpredictability of apical closure, difficulty in patient follow-up, and delayed treatment. An alternative treatment to long-term apexification procedure is the use of an artificial apical barrier that allows immediate obturation of the canal. MTA(Mineral Trioxide Aggregate) is a powder consisting of fine hydrophilic particles of tricalcium silicate, tricalcium aluminate, tricalcium oxide and silicate oxide. MTA has a pH of 12.5 after setting, similar to calcium hydroxide. This may impart some antimicrobial properties. MTA has low solubility and a radiopacity slightly eater than that of dentin. Also, MTA leaked significantly less than other materials and induced hard-tissue formation more than other materials.

• The Journal of Korean Academy of Prosthodontics
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• v.44 no.1
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• pp.124-134
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• 2006

Statement of problem: Streptococcus produces energy and forms extracellular polysaccharides by metabolizing sucrose. Insoluble glucan, a kind of extracellular polysaccharide, is the important material of dental plaque. Fructose affects the metabolism of sucrose. Purpose: The purpose of this study was to evaluate the effect of fructose on the metabolism of sucrose in Streptococcus mutans. Materials and methods: To determine the effect of fructose on the formation of artificial plaque by Streptococcus mutans Ingbritt, S. mutans and fructose were placed in beakers containing M17 broth and sucrose. The wires were hung on frameworks inserted into cork stoppers, and then immersed in each of the beakers. After the incubation with gentle shaking, each wire was weighed. To analyze the effect of fructose on the sucrose metabolism by S. mutans or glucosyltransferase, S. mutans and fructose were placed in M17 broth containing sucrose. After the incubation. the remaining sucrose and polymers were analysed by thin layer chromatography. Results: The following results were obtained; 1. When Streptococcus mutans was cultured in the media containing 3% sucrose for 8 hours, the mean weight of formed artificial plaque on the wires was $124.3{\pm}3.0mg$, whereas being reduced to $20.7{\pm}10.2mg$ in the media added with 3% sucrose and 4% fructose(p<0.05) 2. When the control containing glucose was added with sucrose, the optical density of Streptococcus mutans solution cultured for 24 hours was not increased compared with the control, while being increased by adding with fructose. 3. When Streptococcus mutans was incubated in the media added with sucrose and fructose for 8 hours, the number of viable cells was increased compared with the media added with sucrose. 4. The amount of remained sucrose was increased in Streptococcus mutans culture supernatant of media added with sucrose and fructose than with sucrose only. but the amount of produced insoluble glucan was decreased. 5. The amounts of remained sucrose and produced soluble glucan were increased in the culture of glucosyltransferase-contained media added with sucrose and fructose than with sucrose only, but the amount of produced insoluble glucan was decreased . Conclusion: These results indicated that the sucrose metabolism and the production of insoluble glucan were inhibited in Streptococcus mutans by adding fructose in the media containing sucrose.