Serologic Survey of IgG Against SARS-CoV-2 Among Hospital Visitors Without a History of SARS-CoV-2 Infection in Tokyo, 2020-2021

BACKGROUND

Tokyo, the capital of Japan, is a densely populated city of >13 million people, so the population is at high risk of epidemic severe acute respiratory coronavirus 2 (SARS-CoV-2) infection. A serologic survey of anti-SARS-CoV-2 IgG would provide valuable data for assessing the city's SARS-CoV-2 infection status. Therefore, this cross-sectional study estimated the anti-SARS-CoV-2 IgG seroprevalence in Tokyo.

METHODS

Leftover serum of 23,234 hospital visitors was tested for antibodies against SARS-CoV-2 using an iFlash 3000 chemiluminescence immunoassay analyzer (Shenzhen YHLO Biotech, Shenzhen, China) with an iFlash-SARS-CoV-2 IgG kit (YHLO) and iFlash-SARS-CoV-2 IgG-S1 kit (YHLO). Serum samples with a positive result (≥10 AU/mL) in either of these assays were considered seropositive for anti-SARS-CoV-2 IgG. Participants were randomly selected from patients visiting 14 Tokyo hospitals between September 1, 2020 and March 31, 2021. No participants were diagnosed with coronavirus disease 2019 (COVID-19), and none exhibited COVID-19-related symptoms at the time of blood collection.

RESULTS

The overall anti-SARS-CoV-2 IgG seroprevalence among all participants was 1.83% (95% confidence interval [CI], 1.66-2.01%). The seroprevalence in March 2021, the most recent month of this study, was 2.70% (95% CI, 2.16-3.34%). After adjusting for population age, sex, and region, the estimated seroprevalence in Tokyo was 3.40%, indicating that 470,778 individuals had a history of SARS-CoV-2 infection.

CONCLUSIONS

The estimated number of individuals in Tokyo with a history of SARS-CoV-2 infection was 3.9-fold higher than the number of confirmed cases. Our study enhances understanding of the SARS-CoV-2 epidemic in Tokyo.

Influence of diffuse reflectance measurement accuracy on the scattering coefficient in determination of optical properties with integrating sphere optics (a secondary publication)

An estimation error of the scattering coefficient of hemoglobin in the high absorption wavelength range has been observed in optical property calculations of blood-rich tissues. In this study, the relationship between the accuracy of diffuse reflectance measurement in the integrating sphere and calculated scattering coefficient was evaluated with a system to calculate optical properties combined with an integrating sphere setup and the inverse Monte Carlo simulation. Diffuse reflectance was measured with the integrating sphere using a small incident port diameter and optical properties were calculated. As a result, the estimation error of the scattering coefficient was improved by accurate measurement of diffuse reflectance. In the high absorption wavelength range, the accuracy of diffuse reflectance measurement has an effect on the calculated scattering coefficient.

Genotype of FLOWERING LOCUS T homologue contributes to flowering time differences in wild and cultivated roses

Rose flowers have long delighted humans as ornamental plants. To improve the ornamental value of roses it is necessary to understand the regulatory mechanisms of flowering. We previously found that flowering time is controlled by three minor quantitative trait loci (QTLs) and a major QTL co-localised with RoFT. In this study, we isolated three RoFT alleles encoding completely identical amino acid sequences from the parents of a mapping population. Correlation analysis of the RoFT genotypes and flowering time phenotypes in the mapping population showed that the RoFT_f and RoFT_g alleles contribute to the early-flowering phenotype, while the RoFT_e allele contributes to the late-flowering phenotype. We developed two novel cleaved amplified polymorphic sequence (CAPS) markers based on the genomic sequences of the RoFT alleles and clearly showed that the relationship between RoFT genotype and flowering time was applicable to 12 of 13 cultivated roses grown at the Higashiyama Botanical Gardens, Japan. Allele-specific expression analysis using a reverse transcription CAPS assay suggested that these RoFT alleles are regulated differentially at the transcription level. Furthermore, transgenic Arabidopsis thaliana plants ectopically expressing the RoFT gene showed an early-flowering phenotype. Conversely, in roses, RoFT was continuously expressed after floral bud formation, and RoFT transcript accumulation reached its peak after that of the floral meristem identity gene RoAP1b. These data suggest that RoFT may be essential not only for floral transition but also for normal floral development and flowering in roses.

Anxiety accelerates T-helper 2-tilted immune responses in patients with atopic dermatitis

BACKGROUND

Stress, which mediates anxiety, worsens skin symptoms in patients with atopic dermatitis (AD). The contribution of anxiety to immune dysfunction, which plays a critical role in the pathogenesis of AD, requires clarification.

OBJECTIVES

To examine the relationship between anxiety and atopy-relevant immune function in AD.

METHODS

Eighty-five patients with AD and 58 normal individuals without a history of allergic disorders were enrolled in this study. To assess anxiety, the state-trait anxiety inventory was completed for both groups. In the AD group, measurements were made of SCORAD scores, serum IgE levels, itching (visual analogue scale), blood eosinophil count and T-helper (Th) 1/Th2 ratio in the peripheral blood.

RESULTS

Anxiety was significantly higher among the subjects with AD than the normal subjects, and trait anxiety (TA) was higher than state anxiety (SA) in the AD group. Serum total IgE levels were correlated positively with TA and the TA/SA ratio and inversely with SA, and the Th1/Th2 ratio was correlated inversely with TA and the TA/SA ratio.

CONCLUSIONS

The patients with AD had higher anxiety levels than normal individuals, and those with a stronger perception of TA than SA showed enhanced serum IgE synthesis and Th2 shifting.

Ribostamycin inhibits the chaperone activity of protein disulfide isomerase

In the process of screening of proteins binding to ribostamycin in bovine liver using the affinity column chromatography, we found that ribostamycin inhibited the chaperone activity of protein disulfide isomerase (PDI), but it did not inhibit the isomerase activity. PDI was identified by SDS-PAGE, Western blotting, and N-terminal amino acid sequence analysis. A 100:1 molar ratio of ribostamycin to PDI was almost sufficient to completely inhibit the chaperone activity of PDI. The binding affinity of ribostamycin to purified bovine PDI was determined by the Biacore system, which gave a K(D) value of 3.19 x 10(-4) M. This suggests that ribostamycin binds to region distinct from the CGHC motif of PDI. This is the first report to describe the inhibitor of the chaperone activity of PDI.

Nucleotide sequence of the porcine 60S ribosomal protein L35 cDNA

The cDNA encoding the 60S ribosomal protein L35 was cloned from the porcine liver cDNA library using the N-terminal fragment coding region of human protein disulfide isomerase as the probe.

The dipeptide, gamma-glutamylcysteine, is recognized by the anti-glutathione antibody single chain Fv fragment 20C9

The anti-glutathione antibody scFv 20C9, which we previously isolated from a human synthetic phage antibody scFv library [Hirose, M., Hayano, T., Shirai, H., Nakamura, H., and Kikuchi, M. (1998) Protein Eng. 11, 243-248], was expressed in the E. coli pET system and purified by sequential chromatography on Ni and glutathione-conjugated affinity resins. The purified scFv 20C9 antibody was characterized for its binding affinity for several glutathione derivatives by the BIACORE system. Although GSH, GSSG, and gamma-Glu-Cys could bind to the immobilized antibody, this was not the case for Cys-Gly, l-Glu, l-Cys, l-Gly, or several other glutathione derivatives such as gamma-Glu-Ser-Gly. The results suggest that a gamma-glutamic acid and sulfur atom are important for scFv 20C9 antibody recognition of glutathione. This is the first report to indicate that an scFv antibody can recognize a region as small as a dipeptide.

A case of hemangioma accompanied by inflammatory pseudotumor of the spleen

Both hemangioma and inflammatory pseudotumor (IPT) of the spleen are rare benign mass lesions. Moreover, a splenic hemangioma accompanied by IPT is extremely rare. A 61-year-old woman who suffered from liver cirrhosis had a splenic cavernous hemangioma surrounded by granuloma. The literature on IPT of the spleen has described several possibilities of its causes; however, it is still unknown. This case was accompanied by portal hypertension due to liver cirrhosis, which may cause microrupture of hemangioma resulting in an IPT.

Nuclear cyclin D1 overexpression is a critical event associated with cell proliferation and invasive growth in gallbladder carcinogenesis

Cyclin D1 overexpression is remarkably frequent in several human carcinomas and is believed to be a critical event in oncogenesis. We examined cyclin D1 expression, p53 expression, and the Ki-67 labeling index by immunostaining in human gallbladder mucosa in conditions varying from normal to malignant tissue. We also examined K-ras codon 12 mutations in these tissues with a two-step polymerase chain reaction. Nuclear cyclin D1 overexpression was observed in 48% of carcinomas occurring independently of adenoma, but not in adenomas, carcinomas arising in adenomas, or nonneoplastic lesions. Cytoplasmic cyclin D1 overexpression was observed in about 15% of abnormal specimens, irrespective of the type of epithelial abnormality. Carcinomas showing nuclear cyclin D1 overexpression had significantly higher Ki-67 labeling indexes than those with no overexpression. Moderately to poorly differentiated adenocarcinomas showed a higher incidence of nuclear cyclin D1 overexpression than papillary to well differentiated carcinomas. Specimens with cyclin D1 overexpression showed a high incidence of lymph permeation, venous permeation, and lymph node metastasis. We conclude that nuclear cyclin D1 overexpression is a critical event importantly associated with cell proliferation and invasive growth in gallbladder carcinogenesis, and that cyclin D1 immunostaining may become a useful marker for evaluating gallbladder carcinomas.

[Study of transforming growth factor-alpha expression in duodenal ulcer]

Various growth factors were also reported to promote healing of peptic ulcer. We have used a monoclonal antibody in conjunction with a standard immunohistochemical technique to characterize the expression of transforming growth factor-alpha (TGF-alpha) in duodenal ulcer. TGF-alpha immunoreactivity is found in Brunner's gland, also in immature gland and in duodenal epitheliums, but not in gastric metaplasia of the duodenum. TGF-alpha expression of healing and scar stage was higher than that of active stage. The presence or absence of Helicobacter pylori infection did not affect the expression of TGF-alpha in duodenal ulcer.

K-ras codon 12 and p53 mutations in biopsy specimens and bile from biliary tract cancers

To evaluate whether it is useful for diagnosis to detect K-ras and p53 mutations in biopsy specimens and bile of biliary tract lesions, 12 cholangiocarcinomas (CC), eight cases of cholangitis, seven gallbladder carcinomas (GBC), seven gallbladder cholesterol polyps, four cases of adenomyomatosis of the gallbladder and five cases of cholecystitis were examined. K-ras and p53 mutations in bile were detected by a two-step polymerase chain reaction (PCR) and nested PCR-single-strand conformation polymorphism (SSCP) analysis. In addition, p53 protein expression in biopsy specimens from CC were examined by immunostaining. K-ras mutations at codon 12 were detected in 50% of CC and 57.1% of GBC in both biopsy specimens and bile. The incidence of p53 mutations was 33.3% in CC and 42.9% in GBC. p53 protein overexpression was observed in 60% CC biopsy specimens. In contrast, K-ras and p53 abnormalities were not detected in any non-neoplastic biliary tract lesion. K-ras and p53 mutations in biliary tract cancers showed the same mutation patterns in spite of differences in the collection methods used between bile and biopsy specimens or surgically resected tissue. Genetic analysis of K-ras and p53 mutations in biopsy specimens and bile may be useful for the diagnosis of biliary tract cancers, although it may be effectively limited to patients with advanced disease.

[Waldenström's macroglobulinemia effectively treated with chronic daily oral administration of low-dose etoposide]

A 77-year-old woman with complaints of fever and systemic lymphadenopathy was admitted to our hospital on February 16, 1995. Serum IgM was elevated to 2,097 mg/dl. Lymph node biopsy showed diffuse infiltration with lymphoplasmacytoid cells. Thus, she was diagnosed as having Waldenström's macroglobulinemia. Considering her age and congestive heart failure, she was treated with oral administration of low-dose etoposide (25 mg/day). Splenomegaly and superficial lymphadenopathy disappeared after one course of therapy. Until her death due to pneumonia, complete remission continued for one year without any symptoms and adverse effects except for mild diarrhea. Low-dose etoposide therapy was considered to be well tolerated and useful for elderly patients with Waldenström's macroglobulinemia.

[Plasma cell leukemia associated with monocytosis]

A 51-year-old man was admitted to our hospital in December 1993, because of fatigue. Peripheral blood tests showed a WBC of 49,400/microliter with 36% plasma cells and 35% monocytes, Hb 14.5 g/dl, and Plt 137,000/microliter. Bone marrow aspirate revealed hypercellularity with 48.7% plasma cells and 22.4% monocytes. Plasma cells in blood were positive for CD38 and PCA-1. Serum calcium, IgA and M-CSF levels were elevated to 14.1 mg/dl, 2,337 mg/dl and 2.7 ng/ml, respectively. Immunoelectrophoresis of serum and urine revealed IgA lambda type M protein and lambda type Bence Jones protein, respectively. Rearrangements of immunoglobulin heavy chain and light chain were demonstrated by Southern blotting analysis. Plasma cell leukemia (IgA lambda type) was diagnosed. He was treated with combination chemotherapy and IFN-alpha and achieved complete remission. However, he suffered a meningeal relapse in February 1995, and died in April 1996. It seems likely that the enhanced production of M-CSF by myeloma cells and/ or activated B cells stimulated monocyte production.

Polymeric calcium phosphate cements: analysis of reaction products and properties

Chemical and mechanical properties of water-based polymeric calcium phosphate cements (PCPC) were investigated. These cements were derived from mixing several types of water-soluble polymers, e.g., gelatin, poly(vinyl alcohol) (PVA), and poly(alkenoic acids) such as poly(acrylic acid), with a calcium phosphate cement (CPC) mixture consisting of equimolar amounts of tetracalcium phosphate (TTCP) and anhydrous dicalcium phosphate (DCPA) as well as several other TTCP-containing mixtures. Cement formation was observed with all of the PCPCs. With the gelatin and PVA cements, significant amounts of hydroxyapatite (HA) formation were observed within 24 h. Their setting times and mechanical properties were similar to those of the purely inorganic CPC that is derived from the reaction of TTCP and DCPA in water. Although the mechanical properties of a gelatin-CPC cement were only slightly improved, its handling characteristics were superior to that of CPC. Significantly faster setting and stronger cements were obtained using polycarboxylic acid polymers with CPC. However, only small amounts of HA were observed in these types of polymeric cements even after 1 mon storage in distilled water at 37 degrees C. This research demonstrates the feasibility of preparing several new types of dental cements based on the interaction of water-soluble polymers with a self-setting calcium phosphate powder mixture.

Polymeric calcium phosphate cements: setting reaction modifiers

In this study, the effects of several additives on the setting behavior and mechanical properties of polymeric calcium phosphate cements were investigated. The cements were derived from a polycarboxylic acid (PCA) and a calcium phosphate cement (CPC) powder that consisted of equimolar amounts of tetracalcium phosphate (TTCP) and dicalcium phosphate (DCPA). Retardation of the setting reaction in the PCA-CPC cements was observed by adding tribasic sodium phosphate and fluorides such as stannous fluoride, zirconium(IV) fluoride and titanium(IV) fluoride. It was found that increasing the concentration of these additives decreased the mechanical strength of the cements. However, improvements in both setting and mechanical properties for the PCA-CPC cements were observed by the combined use of 8% (w/w) stannous fluoride and 10% (w/w) tartaric acid. The mechanical properties of the PCA-CPC cement also were improved by adding calcium acetate, calcium methacrylate, zirconium(IV) sulfate and phosphonoacetic acid.

Properties of test metal ceramic titanium alloys

Four test alloys were prepared using a high frequency centrifugal casting machine and a ceramic crucible for the development of titanium bonding alloys that can be cast in the ordinary atmosphere. Of these alloys, 10.06% Ti, 78.79% Ni, 9.02% Pd, 1.77% Sn and 9.91% Ti, 78.56% Ni, 9.07% Pd, 1.86% Sn, 0.65% Ir could be cast by the conventional high frequency centrifugal method; however, 89.18% Ti, 8.75% Ni, 1.03% Pd, 0.28% Sn and 89.81% Ti, 8.15% Ni, 1.01% Pd, 0.18% Sn, 0.67% Ir could be cast only by the argon are melting method. The alloys 10.06% Ti, 78.95% Ni, 9.02% Pd, 1.77% Sn and 9.91% Ti, 78.56% Ni, 9.07% Pd, 1.86% Sn, 0.65% Ir showed excellent physical and mechanical properties and bonding strengths, surpassing those of the commercial alloys TPW and Unimetal. Concerning the elution of component elements, the amounts of titanium eluted from these alloys were far smaller than those from pure titanium or a Ti-6Al-4V alloy, and nickel elution, which has become an issue in relation to metal allergy, was almost nil in contrast to Unimetal (Ni-Cr alloy). The alloy 9.91% Ti, 78.56% Ni, 9.07% Pd, 1.86% Sn, 0.65% Ir showed properties that indicated its favorable use as an alloy for the bonding of dental porcelain.

Liquid gallium alloys for metallic plastic fillings

Ga-In-Sn alloys that are liquid at room temperature have been developed to replace mercury in metal plastic fillings. These liquid alloys were mixed with Ag-Pd-Sn-Cu-Zn to form powder alloys, 'a plasto-metallic body'. Various physical properties of these materials were evaluated. Strength increased markedly immediately after mixing, and polishing was possible on the same day. A good marginal seal could be expected as these materials expand on setting. The technique for filling is simpler and more rapid than is the case with amalgam materials. These materials also seem to be useful in paediatric dentistry for the handicapped, where extensive treatments are frequently performed under general anaesthesia.

Line analysis of interface layer on dentin by means of electron-probe microanalysis

Three types of brominated methacrylates, SBPPM, BPylM, and BNEM, were synthesized. The distribution of Br, Ca, and Fe at the interface between dentin treated with the 10-3 solution and resin containing these monomers was analyzed using an electron-probe microanalyzer (EPMA) in order to predict the composition and thickness of the interface layer on dentin for the corresponding unbrominated methacrylates. There was no significant difference between the brominated and unbrominated methacrylates in either the bond strength to the treated dentin or in the thickness of the interface layer on dentin observed with a scanning electron microscope (SEM). The thickness determined with EPMA was equivalent to that observed with SEM. The concentration of each brominated methacrylate in the interface layer was higher than the original concentration in the resin monomers, and BNEM showed higher concentration than the others. The presence of Fe in the layer was confirmed by EPMA.

[Mechanical properties and curing depth of urethane tetramethacrylate-based composite resins]

Mechanical properties and curing depth of light-cured composite resins based on five types of urethane tetramethacrylate (UTeMA; IP-4 M, XY-4 M, MC-4 M, HM-4 M and TM-4 M) were investigated, and compared them with those of UDMA-based composite resins. Composites based on UTeMA monomers containing an aromatic or cyclohexane ring in their chemical structure (IP-4 M, XY-4 M and MC-4 M) showed a relatively rigid properties than those based on aliphatic UTeMA (HM-4 M and TM-4 M). The composite resins based on XY-4 M monomer showed a curing depth and transmission coefficient superior to the other composite resins. UTeMA-based composites showed a significantly higher rigid properties than UDMA-based composites, while their rigidity did not improve the flexural strength.

Influence of water on bonding of various methacrylates to dentin treated with 10% citric acid-3% ferric chloride solution

The bond strength of resins (MMA-TBB resin system), containing 2-hydroxyethyl methacrylate (2-HEMA), 3-methacryloyloxypropionic acid (3MPA), 2-phenylethyl methacrylate (Py1EM) and 2-(1-naphthyl) ethyl methacrylate (NEM), to dentin treated with a solution of 10% citric acid and 3% ferric chloride was measured after being immersed in water at 37 degree C for a long period of time to investigate the influence of water on bonding, and the relationship between the monomer structure and the decrease in bond strength in water. The bond strength of the resins did not change with the time spent immersed in water up to 6 months, but decreased with any further increase in time. The decrease in bond strength of all the resins tested was caused by either the degeneration and swelling of collagen or a difference in the degradation of the resin inside and outside the acid-proof dentin layer. There was no significant relationship between the decrease in bond strength in water and the monomer structure.

[Electron-probe microanalysis examination of acid-proof dentin layer]

To predict the presence and thickness of the acid-proof dentin layer by the method of combining the halogenated methacrylate and electron-probe microanalyzer (EPMA), 2-methacryloyloxyethyl hydrogen chloromaleate (CIMEM) used as a base monomer for a bonding agent and 2-bromoethyl methacrylate (2 BEM), 2-(4-bromophenyl)ethyl methacrylate (BPy1EM), 2-(4-bromo-1-naphthyl)ethyl methacrylate (BNEM) and 2,4,6-tribromophenoxy methacrylate (TriBr-PM) used as tracers were synthesized. The bond strength to dentin treated with 37% phosphoric acid solution for 30 sec. was not statistically different for the bonding agents with and without tracers. The SEM micrographs revealed that the layers, which may be acid-proof dentin layers, were 3-4 microns thick at the resin-dentin interface for all bonding agents. According to EPMA analysis, cps of C1Ka and BrLa increase at the same points and the acid-proof dentin layer thickness was about 4 microns.

Correlation between air-drying duration and bond strength of composite resins to teeth

Cavity preparations involve both enamel and dentinal walls, but moisture contamination of these surfaces adversely influences the effectiveness of bonding interface. This in vitro study investigated the relationship between air-drying time and the bond strength to bovine enamel and dentin for two types of composite resins and their bonding agents. Comprehensive shear bond tests were performed with a universal testing machine, and mean bond strengths were computed by an analysis of variance and by Scheffé's multiple comparison test. No statistical differences were noted between the bond strength to the unetched and etched enamel and air-drying duration for bondings. The bond strengths to the etched dentin was comparable despite the time of air drying, but the bond strengths to unetched dentin were dependent upon the length of air drying.

[Studies on gallium alloys for dental restorations. 2. Electron probe microanalysis for hardened gallium alloys]

Hardened gallium alloys were analyzed by scanning electron microscopy (SEM) and electron probe microanalysis (EPMA). The cores, matrix and white irregular shape phases were visible with SEM. The round or irregular shape cores contained Ag, Pd, Cu and Zn but did not contain Ga and In. The dark irregular shape matrix, which surrounded the core, consisted of Ga-Ag, Ga-Pd, Ga-Cu and Ga-Sn phases. However, the amount of Ga-Sn phase was very low. The white phase in the matrix was Ag-In phase.

[Mechanical properties and cure depth of UDMA-based composite resins]

Mechanical properties and cure depth of visible light-cured composite resins based on six types of UDMA (IP-HEMA, IP-HPMA, XY-HPMA, MC-HPMA, UEDMA and UPDMA) monomers were investigated. Under wet conditions, the mechanical properties of the composite resins based on aliphatic UDMA (UEDMA and UPDMA) monomers were inferior to those based on the other UDMA monomers containing aromatic or cyclohexane rings in their chemical structures. The cure depth for these UDMA-based composite resins increased with increasing irradiation time. The composite resin based on the XY-HPMA monomer showed a cure depth and transmission coefficient superior to the other composite resins.

A scanning electron microscopic investigation of bonding of methacryloyloxyalkyl hydrogen maleate to etched dentin

Three types of methacryloyloxyalkyl hydrogen maleates--2-(methacryloyloxy)ethyl hydrogen maleate (2MEM), 1-(methacryloyloxy-methyl)ethyl hydrogen maleate (MMEM), and 1-(methacryloyloxymethyl)propyl hydrogen maleate (MMPM)--were prepared for use as bonding agents. The relationships between the thickness of an acid-proof dentin layer and the bond strength and chemical structure of the synthesized monomers were investigated. The bond strengths of 2MEM/composite system to dentin treated with either 37% phosphoric acid solution or 10% citric acid-3% ferric chloride solution (10-3 solution) were superior to those of the others. The acid-proof dentin layer for all bonding agents containing the synthesized monomers at the resin-dentin interface was clearly visible in a scanning electron microscope, regardless of the types of dentin etching agents used. After treatment of the dentin with the phosphoric acid solution, the layers of 2MEM, MMEM, and MMPM were 5-6 micron, 3-4 micron, and 2-3 micron thick, respectively. When the dentin was treated with the 10-3 solution, the layer for each bonding agent was approximately 1 micron thick.

[Relationship among the composition and the physical and chemical properties of photo-cured composites for crown and bridge]

In this study, the relationship among the chemical composition and the physical and chemical properties of four photo-cured composites and one heat curing composite for crown and bridge were investigated. Five composites were composed of the base monomer, UDMA, TriEGDMA, 1, 3-BDMA, 1, 4-BDMA, 1, 10-DDMA, 1, 12-DDDMA or those mixture, and the composite-filler consist of the resin (TMPTMA, UDMA, 1, 10-DDMA or 1, 12-DDDMA) and micro-silica particles. Four photo-curing composites had a high elastic modulus and Vickers hardness and a low thermal expansion coefficient and water sorption compared with the heat-cured composite (Is). The effects of filler contents in the composites examined were positively on the elastic modulus and the hardness, and were inversely on the bending strength and the thermal expansion coefficient of the cured products. While the organic phase in the composite fillers had effect on the abrasive resistance of the composites. But no significant correlation between the abrasive resistance and the filler contents and the physical properties of the materials tested was noted.

Effect of monomer structure on the mechanical properties of light-cured composite resins

The effects of monomer structure on the mechanical properties of visible light-cured composite resins based on the seven types of aromatic dimethacrylates were investigated. The results of this study suggested that the mechanical properties of the composite resins were dependent upon the chemical structure of the dimethacrylate monomers employed. The composites based on dimethacrylates with hydroxy groups showed a relatively significant decrease in flexural strength, elastic modulus, and compressive proportional limit under wet conditions. The segmental mobility of dimethacrylate monomers considerably influenced the nature of cured composites. Bis-GMA-F-based composite showed superior mechanical properties to a conventional Bis-GMA-based material. The SEM observation of fractured surfaces revealed that failure mainly occurred through the resin matrix of the composite resins.

[Effect of filler system on the mechanical properties of light-cured composite resins. I. Effect of various types of silica fillers on the mechanical properties of the composite resins]

To investigate the effect of silica fillers on the mechanical properties of visible light-cured composite resins, Bis-GMA-based composites with four types of silica fillers were prepared. The mechanical properties of the composites with splinter-shaped silica fillers increased with increasing the filler fraction. Although the spherical silica filler could be filled more with resin monomer than the splinter-shaped silica filler, the mechanical properties of spherical silica-filled composite were relatively lower than those of the composite with splinter-shaped silica fillers. The micro particle silica-filled composite showed no obvious increase in the mechanical properties in either the dry or wet conditions. SEM observations of the fractured resin surface revealed that fracture occurred through the resin matrix as well as the resin/filler interface and the mechanical properties of each composite resin were correlated with the nature of crack propagation.

[Effect of filler system on the mechanical properties of light-cured composite resins. II. Mechanical properties of visible light-cured composite resins with binary filler system]

To improve the fracture resistance of the composite resin system under highly stressed conditions, a variable amount of microfiller was incorporated into the light-cured composite resins containing splinter-shaped silica filler. With the increasing the microfiller content (10-30 wt%) in the resin matrix, the elastic modulus, compressive proportional limit and compressive fracture strength of the composite resin were increased. The plastic deformation of the composite resins under compressive stress were decreased with increasing microfiller content. These findings suggested that the combination of a larger silica filler and microfiller would increase the compressive fracture resistance of the composite resin systems.

Polymerization of multifunctional methacrylates and acrylates

The cross-linking reaction of 15 dimethacrylates, one trimethacrylate and five diacrylates was studied by means of differential scanning calorimetry (DSC) and high performance liquid chromatography (HPLC) to investigate the relationship between the polymerization characteristics and the chemical structure of these monomers. The amount of pendant double bonds (Dp) and the efficiency of cross-linking (Ec) were calculated from both the extent of polymerization (Ep) and the amount of residual monomer (Rm) obtained by DSC and HPLC analyses, respectively. The Ep and Ec values of various monomers increased with an increase in the number of chain members between the functional groups, while Rm and Dp values decreased. The dimethacrylates consisting of aliphatic chains polymerized more readily than those containing aromatic units. High Ep was obtained in the aliphatic dimethacrylates and diacrylates with more than eight chain members and the aromatic dimethacrylates with more than 20 chain members among the monomers examined. These results depend presumably on the flexibility of the functional groups in the polymer network. With most dimethacrylates and diacrylates, high Ep was also observed in thermal scanning polymerization compared to isothermal polymerization at 90 degrees C. The diacrylates showed a high rate of polymerization compared to the corresponding dimethacrylates.