• Composites Research
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• v.36 no.2
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• pp.126-131
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• 2023

Growing environmental concerns regarding pollution caused by conventional plastics have increased interest in biodegradable polymers as alternative materials. The purpose of this study is to develop a 100% biodegradable nanocomposite material by introducing organic nucleating agents into the biodegradable and thermoplastic resin, poly(lactic acid), to improve its properties. Accordingly, cellulose nanofibers, an eco-friendly material, were adopted as a substitute for inorganic nucleating agents. To achieve a uniform dispersion of cellulose nanofibers (CNFs) within PLA, the aqueous solution of nanofibers was lyophilized to maintain their fibrous shape. Then, they were subjected to primary mixing using a twin-screw extruder. Test specimens with double mixing were then produced by injection molding. Differential scanning calorimetry was employed to confirm the reinforced physical properties, and it was found that the addition of 1 wt% CNFs acted as a reinforcing material and nucleating agent, reducing the cold crystallization temperature by approximately 14℃ and increasing the degree of crystallization. This study provides an environmentally friendly alternative for developing plastic materials with enhanced properties, which can contribute to a sustainable future without consuming inorganic nucleating agents. It serves as a basis for developing 100% biodegradable green nanocomposites.

• Journal of the korean academy of Pediatric Dentistry
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• v.28 no.3
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• pp.464-470
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• 2001

The purpose of this study was to evaluate the tensile strength of light-cured restorative posterior resin-based composites. Five commercially available light-cured composites(Denfil : DF, P60 : PS, Unifil S : US, Z100 : ZH, Z250 : ZT) were used. Rectangular tension test specimens were fabricated in a teflon mold giving 5mm in gauge length and 2mm in thickness. Specimens were subjected to the 5,000 thermal cycles between $5^{\circ}C$ and $55^{\circ}C$ and the immersion time in each bath was 15 second per cycle. Tensile testing was carried out with Instron at a crosshead speed of 0.5mm/min and fractured surface were observed with scanning electron microscope. The obtained results were summarized as follows; 1. The tensile strength of PS was highest. PS was significantly higher than DF, US and ZH(p<0.05) but in the case of ZT was similar to PS(p>0.05). 2. The tensile strength DF was lowest. DF was significantly lower than PS, US, ZH and ZT(p<0.05). 3. The tensile strength of US and ZH were significantly lower than PS and ZT(p<0.05). but were significantly higher than DF(p<0.05). The tensile strength of US and ZH were similar(p>0.05).

• Journal of Dental Rehabilitation and Applied Science
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• v.27 no.1
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• pp.1-13
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• 2011

The aim of this study was to evaluate shear bond strength of pressed reinforced composite resin ($TESCERA^{TM}$ ATL) veneering to zirconia with various surface treatments. Forty sintered zirconia specimens and forty pockmarked zirconia specimens were fabricated. All the materials were categorized as Group 1 (Control : porcelain veneering on zirconia surface), Group 2 ( $TESCERA^{TM}$ ATL dentine veneering after bonding agent application on zirconia surface), Group 3 ($TESCERA^{TM}$ ATL dentine veneering on pockmarked zirconia surface), Group 4 ($TESCERA^{TM}$ ATL dentine veneering after bonding agent application on pockmarked zirconia surface), Group 5 (Thermocycling on Group 1), Group 6 (Thermocycling on Group 2), Group 7 (Thermocycling on Group 3), and Group 8 (Thermocycling on Group 4). SBS(Shear bond strength) of 8 groups was determined with an Instron Universal Testing Machine. Also fractured surface of specimens were observed with a scanning electron microscope. There were no significant differences in the initial SBS between Group 1(control group), Group 3, and Group 4. (p>0.05) Group 2 presented the lowest SBS values. There was a no significant difference between just as 24hour water storage and simulated aging on pockmarked zirconia groups. (p>0.05) A formation of pockmarked irregularities on zirconia surface as mechanically pitted surface was reliable method for establishing a stronger bond between $TESCERA^{TM}$ ATL and zirconia-based material.

• Restorative Dentistry and Endodontics
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• v.34 no.2
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• pp.130-136
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• 2009

The aim of this study was to develop a method for measuring the slumping resistance of flowable resin composites and to evaluate the efficacy using rheological methodology. Five commercial flowable composites (Aelitefil flow:AF, Filtek flow:FF, DenFil flow:DF, Tetric flow:TF and Revolution:RV) were used. Same volume of composites in a syringe was extruded on a glass slide using a custom-made loading device. The resin composites were allowed to slump for 10 seconds at $25^{\circ}C$ and light cured. The aspect ratio (height/diameter) of cone or dome shaped specimen was measured for estimating the slumping tendency of composites. The complex viscosity of each composite was measured by a dynamic oscillatory shear test as a function of angular frequency using a rheometer. To compare the slumping tendency of composites, one way-ANOVA and Turkey's post hoc test was performed for the aspect ratio at 95% confidence level. Regression analysis was performed to investigate the relationship between the complex viscosity and the aspect ratio. The results were as follows. 1. Slumping tendency based on the aspect ratio varied among the five materials (AF

• Journal of the korean academy of Pediatric Dentistry
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• v.38 no.3
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• pp.244-249
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• 2011

This in vitro study compared the remineralization of incipient interproximal caries in the presence of three glass ionomer cements(highly-filled glass ionomer cement, resin-modified glass ionomer cement, compomer) and a resin composite(control). Thirty-two extracted premolars were selected based upon the lack of any visible demineralization. The teeth were coated in a transparent acid resistant nail varnish leaving $3{\times}3$ mm square. The teeth were subjected to the demineralizing buffer for 3 days and quantitative light-induced fluorescence(QLF) images of the subjects were taken. Proximal restoration was simulated by placing tooth specimens and the various glass ionomer cements in closed containers with artificial saliva at $37^{\circ}C$ and pH 7.0 with constant circulation. Further QLF images were subsequently taken at 30, 60, and 90 days. The changes of mineral loss(${\Delta}Q$) were evaluated by QLF and the change of ${\Delta}Q$(${\Delta}{\Delta}Q$) were compared between groups in order to evaluate the effects of remineralization. All data were analyzed using ANOVA and the post-HOC Dunnett C multiple comparison test at p<0.05. While ${\Delta}Q$(changes of mineral loss) increased for all treatments, the increases for three glass ionomer groups were significantly higher than that for the resin group at first month period. As time went on, the amount of ${\Delta}{\Delta}Q$ decreased.

• Journal of the Korean Wood Science and Technology
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• v.35 no.6
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• pp.100-107
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• 2007

People have spent lots of time inside building about 90% of these day. Industry has been developed rapidly after I960. Construction materials had changed from natural materials to chemical materials and confidentiality of building has been more higher than before by policy of saving energy. These have caused sick-building syndrome (SBS) for us. So people want environmental construction materials for their house. We designed a environmental loess (yellow soil) finishing material which was composed of loess, water, water-soluble resin, hardener and filler. The purposes of this study were that making an environmental loess finishing material with optimum ratio, evaluating the usability of loess finishing material for wall. Furthermore it was suitable for wall to evaluate mechanical properties that are impact test, cracking test, abrasion test and de-bonding test, environmental properties that were emission of VOCs, formaldehyde and far infrared radiation.

• The Journal of Korea Assosiation for Disability and Oral Health
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• v.12 no.2
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• pp.82-86
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• 2016

Lowe syndrome is X-linked gene disorder, characterized by cataracts, renal dysfunction and brain abnormalities. Oral healthcare of young patients with Lowe syndrome could be easily neglected due to the uncooperative behavior or other systemic condition of the child. We are presenting a case of successful treatment under general anesthesia with uncooperative child with Lowe syndrome. A 3-year old boy with Lowe syndrome visited Seoul National University Dental Hospital for multiple caries. He had been suffering from congenital cataract, medullary nephrocalcinosis and hypotonia. Multiple caries were observed from clinical and radiographic examination. Concerning behavior management problem and possibility of aspiration due to hypotonia, dental treatment under general anesthesia was planned. Left upper primary first molar was extracted to prevent further infection. Other teeth were treated with Stainless steel crown or composite resin restoration based upon the extent and the severity of dental caries. Under general anesthesia, dental procedure was carried out successfully and safely. Considering uncooperative behavior and other medical conditions of the patient, general anesthesia could be effective. Home oral care and periodic visit to dental clinic should be emphasized to the caregiver of patient with Lowe syndrome, considering the susceptibility of dental caries and other oral manifestation.

• The Journal of Korean Academy of Prosthodontics
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• v.54 no.1
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• pp.49-56
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• 2016

Excessive occlusal wear can result in unacceptable damage to the residual teeth structure, anterior guidance and masticatory function. An 86-year-old man presented with worn dentition and anterior deep bite due to loss of the posterior support. Two implants covered by Korean national health insurance, fixed partial denture and direct composite resin were used to restore the dentition, instead of removable prosthesis. The occlusal vertical dimension was increased by 2 mm in the premolar area and shortened dental arch concept was applied. This treatment was a less expensive alternative to full-mouth rehabilitation with positive esthetic and functional outcomes after 7 months of follow-up.

• The Journal of Korean Academy of Prosthodontics
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• v.53 no.4
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• pp.295-300
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• 2015

Purpose: The aim of this study was to evaluate the shear bond strength between Ni-Cr alloy and composite resin using universal adhesive systems coMPared to conventional method using metal primers. Materials and methods: For this study, a total of 120 cast commercial Ni-Cr alloy (Vera Bond 2V) disks were embedded in acrylic resin, and their surfaces were smoothed with silicon carbide papers and airborne-particle abrasion. Specimens of each metal were divided into 6 groups based on the combination of metal primers (Metal primer II, Alloy primer, Metal & Zirconia primer, MKZ primer) and universal adhesive systems (Single Bond Universal, All Bond Universal). All specimens were stored in distilled water at $37^{\circ}C$ for 24 hours. Shear bond strength testing was performed with a universal testing machine at a cross head speed of 1 m/min. Data (MPa) were analyzed using one-way ANOVA and the post hoc Tukey's multiple comparison test (${\alpha}$=.05). Results: There were significant differences between Single Bond Universal, All Bond Universal, Metal Primer II and Alloy Primer, MKZ Primer, Metal & Zirconia Primer (P<.001). Conclusion: Universal Adhesive system groups indicated high shear bond strength value bonded to Ni-Cr alloy than that of conventional system groups using primers except Metal Primer II. Within the limitations of this study, improvement of universal adhesive systems which can be applied to all types of restorations is recommended especially non-precious metal alloy. More research is needed to evaluate the effect of silane inclusion or exclusion in universal adhesive systems.

• Journal of the korean academy of Pediatric Dentistry
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• v.33 no.1
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• pp.25-34
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• 2006

Fluoride released from dental restorative materials effectively declines the incidence and activity of dental caries and inhibits tooth demineralization. This study investigated the fluoride release and uptake characteristics of one composite resin $(Z-250^{TM})$ three glass ionomer-based restorative material ($Dyract^{(R)}$ AP, Fuji II $LC^{(R)}$, Fuji IX GP $Fast^{(R)}$) Forty discs(6mm diameter and 1mm height) were prepared for each material. Each disc was immersed in 5ml of distilled water within polyethylene vial and stored at $37^{\circ}C$. The distilled water was changed every 24 hours and the release of fluoride was measured for 31 days. At the end of this period, each specimen was subjected to one of four treatments : (A) no fluoride treatment (control), (B) application of a fluoride dentifrice (500ppm) for three minutes three times; (C) application of the 1.23% acidulated phosphate fluoride(APF) foam for one minute once, (D) the same regimen as (B), plus application of the APF foam for one minute once. Then, all samples were reassessed for an additional 7 days. For all samples, the greatest fluoride release was observed after the first day of the study but diminished with time. On the 7th day of the study, fluoride release level was stabilized. Fuji II $LC^{(R)}$ and Fuji IX GP $Fast^{(R)}$ released higher amount of fluoride than other materials ; however, no statistically significant difference was found from Fuji II $LC^{(R)}$ and Fuji IX GP $Fast^{(R)}$. The amount of fluoride of $Dyract^{(R)}$ AP, Fuji II $LC^{(R)}$ and Fuji IX GP $Fast^{(R)}$ was increased after fluoride treatment, and diminished with time.