• 대한예방의학회:학술대회논문집
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• 1996.10a
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• pp.403-404
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• 1996

• Composites Research
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• v.28 no.1
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• pp.6-14
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• 2015

Polymerization shrinkage stress analysis of dimethacrylate-based composite (Clearfil AP-X, Kuraray) and silorane-based composite (Filtek P90, 3M ESPE) used for dental composite restorations was performed using strain-gage measurement and FEM analysis. A theoretical equation based on Young's modulus and polymerization shrinkage of the composite resin was proposed to predict the polymerization shrinkage stress. Experimental results showed that the maximum shrinkage stress of Clearfil AP-X was about 2.8 times higher than Filtek P90. FEM analysis agreed with such experimental stress behaviours and showed that the maximum Von-Mises stress appeared near the margin of the filled resin adhered with PMMA ring. The stress concentration at the interface on the specimen surface was higher than that in the interior. The maximum error of shrinkage stress by the theoretical equation was reasonable within 5% in comparison to FEM results under plane stress.

• Composites Research
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• v.32 no.3
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• pp.163-169
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• 2019

In this paper, we constructed a molecular dynamics (MD) polymer model of PMMA with 95% of conversion by using dynamic polymerization algorithm of a thermoplastic polymer based on free radical polymerization. In this algorithm, we introduced a united-atom level coarse-grained force field that combines the non-bonded terms from the TraPPE-UA force field and the bonded terms from the PCFF force field to alleviate the computation efforts. The molecular weight distribution and the average molecular weight of the polymer were calculated by investigating each chain generated from the free radical polymerization simulation. The molecular weight of the polymer was controlled by the number of initiator radicals presented in the initial state and molecular weight effect to the density, the glass transition temperature, and the mechanical properties were studied.

• Journal of Korean Ophthalmic Optics Society
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• v.5 no.2
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• pp.87-90
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• 2000

Poly(HEMA)s have been used as the optometric material for the preparation of soft contact lens. The bulk thermal polymerization of 2-hydroxyethyl methacrylate (HEMA) with various hydrosilanes such as $phSiH_3$, $phMeSiH_2$, and $ph2SiH_2$ were performed to produce poly(HEMA)s containing phenylsilyl end moeity. It was found for thermal polymerization that while the polymerization yield and polymer molcular weights decreased as the relative phenylsilane concentration increases, the TGA residue yields and the relative intensities of SiH IR stretching bands increased as the relative hydrosilane concentration increases over HEMA. The polymerization yield, molecular weight, and TGA residue for the thermal polymerization were higher than those for the photo polymerization. Thus, the hydrosilanes significantly influence on the polymerization as both chain-initiation and chain-transfer agents.

• Restorative Dentistry and Endodontics
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• v.29 no.2
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• pp.177-184
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• 2004

Objectives : This study investigated the hypothesis that increasing light-curing time would leave the oxygen-inhibited layer (OIL) of the adhesive thinner, and in turn, result in lower shear bond strength (SBS) than those obtained by the routine curing procedures. Methods：120 human extracted posterior teeth were randomly divided into three groups for bonding with three adhesives：All Bond 2/sup (R)/, One Step/sup (R)/, and Adper Prompt/sup (R)/. They were subsequently divided into four subgourps with different light-curing time (10, 20, 30 and 60s). The assigned adhesives were applied on superficial occlusal dentin according to the manufacturer's instructions and cured with one of the four curing times. Composite resin cylinder, 2.35㎜ in diameter, were built on the cured adhesive and light-cured for 40s. SBS were measured after 24h from the bonding using a universal testing machine (crosshead speed 1.0 ㎜/min). The relative thickness of the OIL and the degree of conversion (DC) were determined from the adhesive on a slide glass using FT-NIR in an absorbance mode. Data were analysed with One-way ANOVA and Duncan's multiple test (p〈0.05), Results：With increasing cure time, although there were no significant difference in th SBS of One-step and Adper Prompt (p〉0.05), those of All Bond 2 decreased significantly (p〈0.05). The relative thicknesses of the OIL on each adhesive were not affected by the cure time (p〉0.05). Although the DC of All-Bond 2 were statistically not different with increasing cure time (p〉0.05), those of One-Step and Adper Prompt showed an increasing trends with increasing cure time (p〈0.05). Conclusions：Increasing light-curing time did not affect on the relative thickness of the OIL of the adhesives, and in turn, on the SBS to dentin.

• Polymer(Korea)
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• v.30 no.2
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• pp.135-139
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• 2006

To evaluate the dental restorative application of polymer composites filled with hydroxyapatite (HAP) which is an inorganic component of human bone material, dental properties of the polymer composites were investigated. A visible light system was utilized to activate the acrylate resin matrix of the composites. Maximum loading percentage of HAP in composite was 65 wt% and the depth of cure was 6.0 mm which can be applicable for dental restoration. With increasing the HAP content, degree of conversion of polymer composites was slightly decreased, however, polymerization shrinkage value was not varied. Diametral tensile strength value was enhanced with an increase of HAP content, however, there was no strict trend between flexural strength and HAP concentration. Anyhow, polymer composites prepared herein have superior mechanical properties sufficient specifications applicable to dental materials.

• Journal of the Korean Chemical Society
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• v.55 no.1
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• pp.98-103
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• 2011

This study was done for the preparation of macromolecular material with UV-blocking features by adding the benzophenone group that is commonly used as a UV-absorbent and $TiO_2$ which is known to be a very stable material in chemical and physical aspects. Also, we compared the level of UV absorbency of the polymer produced from polymerization with previous materials and measured basic properties such as water content, refractive index and optical transmittance of produced contact lenses. The results of the measurement showed that the refractive index and water content of the contact lens with added UV-absorbent was 1.430~1.440 and 35.0~45.0% respectively, which was similar to that of previous contact lenses. Also, for optical transmittances of each wave length, contact lenses without the UV-absorbent was 89%, 88% and 89% respectively for UV-A, UV-B and visible light, indicating that the UV transmittance is very high though contrary with cases of contact lenses with added 2-hydroxy-4-methoxy-benzophenone and 2,4-dihydroxy-benzophenone which showed transmittances of 0% and 6% respectively for UV-A and UV-B showing a UV-blocking effect. Meanwhile, contact lenses with added $TiO_2$ showed transmittance of 6% and 51% respectively for UV-A and UV-B also showing a UV-blocking effect. The visible transmittance was 77~89% showing that it satisfies the visible transmittance required for ophthalmological materials.

• Restorative Dentistry and Endodontics
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• v.21 no.1
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• pp.360-365
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• 1996

The purpose of this study was to evaluate the changes in the degree of conversion on a composite resin surface following heat treatment and mylar strip finishing. The effects of the time interval between the light-curing and heat-curing process were also evaluated. The composite resin surface which had been covered with a coverglass showed a lower conversion rate than the surface from which a layer of $500{\mu}m$ was ground away. The composite resin surface was definitely affected by oxygen during the heat curing process when it had not been insulated. When the composite resins were heat cured after 3 days of storage following the light curing process, the increased in the degree of conversion through heatcuring was limited.

• Journal of Technologic Dentistry
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• v.38 no.3
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• pp.193-199
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• 2016

Purpose: The purpose of this study was to know of photopolymerization effect of self-etch dual-cured resin cement on different transmittance and thickness of zirconia disks. Methods: The two types of transparent and opaque zirconia speciments were prepared. The five speciments of each groups were seperated with 0.5mm and 1.0mm thickness. Degree of conversion(DC) were studied by FT-IR spectroscopy using ATR method before and after irradidaion for 40 sec. Results: The relative DC was showed the higher results of ZS5 as compared with ZS10 (p < 0.05). And OP5 and OP10 were lower results than ZS10 (p < 0.05). Conclusion: The photopolymerization effect of dual-cured resin cement were affected by the transmittance and thickness of zirconia.

• Restorative Dentistry and Endodontics
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• v.20 no.2
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• pp.827-831
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• 1995

This study was designed to etermine the changes in the degree of conversion for composite resins after heat curing following the methods proposed by Lee & Park(1995). 8-mm diameter hole was made in 1mm teflon plate and one of three types of composites (Charisma, Brilllant, Z100) was placed and light cured for 60seconds. The samples were devided into 3 groups according to the placing composites. After light curing, the samples were separated from the moulds. Using this method, 10 samples were prepared in each group; 5 samples from each group were heat cured according to the methods proposed by manutfactures, These samples were then thinned to 50-$70{\mu}m$ and analysed with a Fourier Transform Infrared Spectrometer. Standard baseline technique was used to calculate the degree of conversion. When the samples were light cured, the degrees of conversion in each groups were 47.1 % (charisma), 53.3% (Z100), and 70.1 % (Brilliant). The degree of conversion after heat curing were; 60.1 % (Charisma), 71.1 % (Z100), and 73.3 % (Brillant). Once the samples were heat cured, there were significant increases in degree of conversion.