The effect of repeated loading on the viscoelastic properties of PMMA denture base resins were investigated using a trial creep testing instrument. The materials used were five PMMA polymers obtained by varying the reaction accelerator loadings or the curing temperature. All specimens were prepared using a stainless steel mold and finished to a specimen measuring 3.0×4.0mm on cross section with a part(1mm in thickness)missing from the circular specimen. The repeated loading test was carried out using four loads(1.0, 1.2, 1.5, 1.7kg). The variation in viscoelastic property caused by repeated loading was intermittently investigated in the process of the repeated loadings test. All measurements were performed in air at a temperature of 23±0.5℃. The S _t -logN diagrams of all materials were linear, and the logN value of the material polymerized at lowest temperature was smaller than those of other materials. The creep compliances(J(t))of all materials increased with a increase in the repeated number of loadings. Linear correlation was not estimated between the amount of residual monomer and the creep compliances(J(0)&J(70)or logN of each material.

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Development of bonding pretreatment that simultaneously bonds to both enamel and dentin was aimed. It was hypothesized that calcium hydrogen phosphate dissolved in etchant could improve monomer permeability of wet demineralized dentin. Prepared specimens of bovine dentin and enamel were etched with 3% calcium hydrogen phosphate in 10% phosphoric acid for 10s(experimental group), rinsed, blot-dried and primed three times with 5% 4-META in acetone for 60s each time. Then, 4-META/MMA-TBB resin was applied. Tensile bond strength to dentin was measured on mini-dumbbell specimens. Experimental group demonstrated cohesive failure in resin and bond strength(25.0 MPa)was higher than that in the control group(14.6 MPa, 10% phosphoric acid, p<0.01). The bond strength to enamel measured by the ISO method in both groups was the same(12 MPa, p>0.01). It was difficult to dehydrate the control substrate. The hybridized dentin of experimental specimens could resist NaOCl and this experimental bond was expected good durability.

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We measured both thermal diffusivity and specific thermal capacity of four kinds of crown and bridge resins containing high concentrations of filler(high-filler resins for crown and bridge), Artglass, Estenia, BelleGlass HP and Gradia by TC-2000L, and then thermal conductivity was calculated. The size of each specimen was φ10×1mm and all specimens were prepared according to the respective manufacturer's instructions. Thermal conductivity(Wm ^-1K ^-1)was 0.289〜0.316 for Artglass, 0.544〜0.561 for Estenia, 0.326〜0.373 for BelleGlass HP, 0.337〜0.357 for Gradia. Thermal conductivity of high-filler resins for crown and bridge showed small values of 1/2-4/5 compared with that of human enamel(0.87Wm ^-1K ^-1). While thermal conductivity of Estenia was almost same as IPS Empress(0.644〜0.733Wm ^-1K ^-1), those of Artglass, BelleGlass HP and Gradia were 1/2 smaller than that of IPS Empress. The above results indicated that high-filler resins for crown and bridge had a greater thermal insulation capacity than human enamel.

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In this study, two commercial 12%Au-20%Pd-Ag-Cu alloys, differing in the ratio of copper to silver, 0.28(14.5mass%Cu)and 0.43(20mass%Cu), were adopted, and an experimental 12%Au-20%Pd-Ag-Cu alloy, in which the copper concentration was increased to the eutectic line of the Ag-Pd-Cu ternary phase diagram, implying a Cu/Ag ratio of 0.58, was fabricated. The effects of the Cu/Ag ratio on thermal features of melting, the mechanical properties, especially the relationships among heat treatment and tensile strength, and internal friction, adhesiveness and discoloring were examined in these alloys. The findings were:1)In the age-hardening region the toughness of the alloys rises with the Cu/Ag ratio. 2)A higher Cu/Ag ratio causes a lower liquidus point of the alloys. 3)Increasing the Cu/Ag ratio can enhance the internal friction of atoms during the heat treatment, thereby making atoms move easily. 4)The adhesion strength between the alloys and the resin is improved by increasing the Cu/Ag ratio. 5)Within the present range of the Cu/Ag ratio, discoloring test by Na_2S shows the alloys satisfy the relative standard.

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In this study, we examined the strength and persistence of the antibacterial effect of polycarboxylate cement(PC) combined with Tannin-Fluoride preparation(HY-agent, HY-PC)on oral bacteria(19 strains of 19 species)containing cariogenic and periodontal bacteria. The HY-PC showed the antibacterial effect on all bacteria tested. The effect differed by species. In addition, the HY-PC also inhibited the growth of bacteria in saliva and dental plaque. Although the antibacterial effect of HY-PC was significantly decreased by immersion in saline for 1 day, decrease of the effect was not observed in immersion for 2 to 7 days, implying that the significant effect remained even after immersion for 7 days. These results suggest that HY-PC with wide range of antibacterial spectra is useful for killing bacteria in the oral cavity and would facilitate the control and prevention of caries recurrence.

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The present study attempted to regenerate the periodontal ligament around a titanium dental implant covered with Poly(ethylene-co-vinyl alcohol)(EVA)and collagen. In this paper, the biocompatibility of periodontal ligament(PDL) derived cell culture onto collagen-EVA films was evaluated:1. Cell-attachment and extension of cultured human PDL derived cells on the EVA films coated by collagen were observed by phase contrast microscope. The results showed that there is a good attachment, extension, flattening of cultured PDL derived cells on the EVA films coated with collagen;2. Growth curve showed that there was a satisfactory proliferation on the EVA films coated with collage;, and 3. Immunostaining of anti-human collagen type I proved that collagen type I was synthesized on the EVA films coated with collagen.

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We examined the effect of serum concentration and two growth factors(b-FGF and IGF-1)on cellular proliferation and protein production of osteoblastic cell line MC3T3-E1. Both cell numbers and Neutral Red optical density were linearly proportional to the serum concentration in the medium up to 4 days incubation. After 5 days incubation, cell morphology changed from fibroblastic to epidermal due to confluence, leding to the loss of the linearity described above. Protein production due to extra-cellular matrix(type I collagen)secreted by the cells after 24 days incubation was also proportional to the serum concentration in the medium. Two growth factors did not increase the cells that had been pre-incubated in low serum medium then further incubated in serum-free medium, but maintained and increased the cells that had been pre-incubated in serum-rich medium then further incubated in serum-free medium.

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Bone defect fillers(BDFs) consisting of α-TCP and 50%-deacetylated chitin binders were implanted in bone cavities created in rat femurs. Histopathological observation of new bone and fibrous tissue were made after 2 and 4 weeks. Cavities in one group were filled with BDFs(Exp.1), those in the other group were filled with BDFs then sealed with alginate gel(Exp.2), and cavities in the control group were not filled(Cont.). Two weeks later, some inflammation reactions were observed in Cont. More fibrous tissues were observed in Cont.than in Exp.1 or 2. In Exp.1, some granules were dislodged from the bone cavity. In Exp.2 group, anchorage of BDFs granules at the bone cavity surface was recognized. Four weeks later, new bone ratios in Exp.2 were significantly higher than those in Cont.(p<0.05). New bone ratios in all groups were increased(p<0.05), and the fibrous ratio decreased with time. Sealing the bone cavity with alginate gel was effective in anchorage BDFs, contributing to the increase in new bone ratio.

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