The extraction method is one approach to the evaluation of the cytotoxicity of dental materials.However, the method of extraction differs with the testing standard.The objective of the present study was to clarify the efficiency of three different methods of obtaining extracts from prosthodontic materials for crown and bridge use.These methods were the static and dynamic extraction methods and extraction by heating.Extracts used were DMEM tissue culture medium alone or DMEM supplemented with either 10V/V% fetal bevine serum or distilled water.Cells used were L-929 cells from mouse subcutaneous tissues or early passage cultured cells derived from human gingiva.Viability of cells was evaluated by neutral red and MTT assays.The experimental process was repeated five times.Static extraction and extraction by heating did not provide consistent data for the materials tested, while dynamic extraction allowed assessment of the cytotoxicity of such materials as Ni-Cr alloy and cold-curing resin.The extract obtained in tissue culture medium supplemented with serum had higher sensitivity than the other two kinds of extracts in expressing the cytotoxicity of materials, in particular those of Ni-Cr alloy and cold-curing resin.Repetition of extraction five times was useful in examining the sequential change of cytotoxicity.Early passage cultured cells derived from human gingiva were less sensitive to the materials tested.There were no differences in cytotoxicity on the basis of either cell type used or assay method used.These findings demonstrate that different cytotoxicity values are obtained under different extraction conditions, and that extraction methods are useful in the evaluation of the cytotoxicity of materials tested.

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The effectiveness of various dentin primers for adhesion of composite resin to dentin was investigated.Dentin primers composed of N-vinylpyrrolidone(NVP), methoxy polyethylene glycol monomethacrylates(M4G, M9G or M23G), or poly-N-vinylpyrrolidones(PNVP1, PNVP2 or PNVP3)were prepared.HEMA was also used as a component of the dentin primer.Fresh bovine dentin was pretreated with neutralized 0.5M EDTA or 40% Phosphoric acid and primed with each primer for 60s.Then Clearfil New Bond ^® and Clearfil FII^® were applied on the treated surface.The tensile bond strengths between composite resin and dentin were measured after 1 day immersion in 37℃ water.For EDTA pretreatment, NVP, 50% M9G and 50% M23G aqueous solution were effective in improving the resin adhesion.For phosphoric acid pretreatment, a 50% M23G, 35% HEMA and poly-N-vinylpyrrolidone aqueous solution were effective.The newly developed dentin primers MTYA・M9G(2% MTYA-50% M9G aqueous solution), MTYA・G・M9G(A:2% MTYA-50% M9G aqueous solution, B:2% glutaraldehyde aqueous solution), and MTYA・G・PNVP(A:1% MTYA-35% PNVP1 aqueous solution, B:2% glutaraldehyde aqueous solution)were effective for the dentin pretreated with EDTA.MTYA・G・PNVP gave the highest bond strength of 11MPa.

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The dynamic shear moduli of 5 types of denture base resins, two acrylic resins(heat-cured resin and fluid resin), polycarbonate resin, polysulfone resin and polyethersulfone resin were measured using a torsion pendulum viscoelastometer at a temperature between 23 and 200℃.For sulfone resins(polysulfone resin and polyethersulfone resin), the shear moduli at 37℃ were nearly 1×10¹⁰dyne/cm², which were lower than those of acrylic resins.In spite of the increasing temperature, the shear moduli were markedly stable.Though peaks in the loss tangent were observed at 80℃ and 160℃, the values for the loss tangent were lower in comparison with those of other materials.This shows that sulfone resins are fairly tough.The slightly lower modulus for the specimen containing water indicates that the presence of water has little effect on the shear modulus of sulfone resins.

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Macro level composite specimens of treated Carbon Fiber(CF)and Kevlar Fiber(KF)cloths sandwiched by PMMA resin, and micro level molecular composites composed of PMMA resin as matrix reinforced with polyaramides as rigid core molecules have been developed to produce denture base polymers with improved physical properties.The interaction between surface treated fiber cloths and the matrix resin in the fiber reinforced composites was investigated using a Dynamic Mechanical Thermal Analyser(DMTA).In conclusion PMMA resins composed of the polyaramide molecule of straight main chain have suitable dental material properties.

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To elucidate the characteristics of elution of base monomer from a composite resin filling including the bonding layer, elution of TEGDMA from the composite resin, the bonding agent and a combination of them were investigated.In addition, the concentration of TEGDMA permeating through the bonding agent layer of Photobond was measured.The concentration of TEGDMA eluted from the combination was greater than that from the bonding agent specimen.Although the bonding agent specimen of Photobond revealed no elution of TEGDMA, some elution of TEGDMA was found from the specimen containing a combination of Photoclearfil Bright and Photobond.TEGDMA proved to permeate through the bonding agent specimen of Photobond an there was no relationship between the thickness of the bonding layer and the permeability of TEGDMA.The new method used in this study was suggested to be useful to investigate the monomer elution from a composite resin filling including the bonding layer.

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To develop a Au-Pd-Ag alloy with a high hardness, elongation and resistance to tarnishing for use as an adhesion bridge, a 35Pd-20Cu-45Ag alloy and gold addition alloys from 10 to 30wt% to the mother alloy were prepared and melted, and the properties of cast and wiredrawing samples of these alloys were examined.The tensile strength was decreased, the toughness was increased to improve elongation, and resistance to tarnishing was improved after hardening heat treatment by gold addition to the Ag-Pd-Cu mother alloy.The 20Au-28Pd-16Cu-36Ag alloy had excellent mechanical properties and potential as a practical material for adhesion bridge with a high palladium and copper content.The mechanical properties of the cast samples were also compared with those of wiredrawing samples with few casting defects.

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Using aqueous N-(2-methacryloyloxyethyl)-2-pyrrolidone(MEP)as a new dentin primer, we examined the adhesion of composite resin to dentin with light curing bonding agents of commercial and experimental origin.The MEP primer improved the tensile bond strength significantly.Adhesive bond strength of 9.4MPa was obtained with Clearfil Photobond and that of 8.2MPa with our experimental bonding agent consisting of triethyleneglycol dimethacrylate(3G)/dl-camphorquinone(CQ)/1, 3, 5-trimethylbarbituric acid(TMB).

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Adhesion between dentin and MMA resin was investigated using initiator systems consisting of barbituric acids/cupric chloride.Without adhesion-promoting monomers, an adhesive strength of 13.9MPa was obtained between dentin treated with 10wt% citric acid-3wt% CuCl₂ solution and MMA resin using a 1, 3, 5-trimethyl-2-thiobarbituric acid/CuCl₂ initiator system, As a model experiment to understand the mechanism of the adhesion, MMA was polymerized in the presence of decalcified dentin sheet treated with various solutions.Curing time, molecular weight of PMMA, and grafting percent of PMMA to dentin sheet were investigated.The findings suggested that cupric ions absorbed onto dentin are involved in promoting the polymerization of MMA and thus affect the bond strength of the MMA resin to dentin.

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Corrosion resistance and mechanical properties of the dental alloy have been improved by the addition of palladium, platinum, indium, and zinc and others, to the basic alloy which consists of gold, silver, and copper.However, use of precious metals raises the price of the alloy and the surface of cast alloy is covered with black or gray black oxide film.We have manufactured trial alloys utilizing elements that contain boron in copper instead of single copper for the study of an alloy which maintains a golden color without blackish oxide film.The mechanical characteristics and color tone of the alloy were determined.The alloy containing boron-copper(B-Cu), an alloy which consists of 40wt% Au, 30wt% Ag, 10wt% Pd, 15wt% In, 2wt% Zn, and 3wt% B-Cu had the strongest tensile strength during softening heat treatment and also hardening heat treatment.An alloy consisting of 30wt% Au, 40wt% Ag, 10wt% Pd, 15wt% In, 2wt% Zn and 3wt% B-Cu had the largest elongation.An alloy consisting of 40wt% Au, 30wt% Ag, 15wt% Pd, 5wt% In, 2wt% Zn and 3wt% B-Cu had the largest hardness value.The surface of a casted alloy consisting of 30wt% Au, 40wt% Ag, 5wt% Pd, 20wt% In, 2wt% Zn and 3wt% B-Cu had a low lightness(L)value and the other trial alloys had a L value above 50.The L value for most of the trial alloys at the polished surface was above 80.The alloy consisting of 40wt% Au, 30wt% Ag, 10wt% Pd, 15wt% In, 2wt% Zn, and 3wt% B-Cu had a color resembling the low carat alloy as judged from chromaticity index a and b value.The surface of the cast alloy and the polished surface of an alloy consisting of 40wt% Au, 40wt% Ag, 5wt% Pd, 20wt% In, 2wt% Zn and 3wt% B-Cu had the largest color difference and the alloy consisting of 40wt% Au, 30wt% Ag, 10wt% Pd, 15wt% In, 2wt% Zn and 3wt% B-Cu had the lowest color difference.Lightness and saturation were compared between the 18-carat gold alloy and the trial alloys.The trial alloys showed a higher L value and lower saturation value than the 18-carat gold alloy at the surface of the cast alloy.Both had the same lightness and the former had a smaller saturation value at the polished surface.Boron acts as a deoxidizer, and the oxide tunic helped prevent the change in color of the alloy when the copper containing the boron was added.

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A new phoshpate binder was developed for dental investments using the setting reaction between aluminium monophosphate, Al(H₂PO₄)₃ and aluminium oxide hydrate, Al₂O₃・nH₂O at an ambient condition.In this experiment, Al(H₂PO₄)₃ commercially available in both powder and liquid forms(50wt%)were used and Al₂O₃・nH₂O was synthesized by controlling the pH of a 10% aluminum sulfate salt solution.According to the X-ray diffraction method, they were amorphous at pH7.0 and were crystal at pH10.0.The powdered Al(H₂PO₄)₃ was mixed with Al₂O₃・nH₂O in the range of 30 and 70wt% an spatulated with water.The liquid Al₂O₃ was directly spatulated with Al₂O₃・nH₂O.In this study, the setting time of the set binders was measured for the evaluation of the reactivity of Al₂O₃・nH₂O.The reaction products were examined by the X-ray diffraction method and SEM.In the case of powdered Al(H₂PO₄)₃, the setting time became shorter with increasing amount of Al₂O₃・nH₂O in both forms.Furthermore, the amorphous Al₂O₃・nH₂O gave a faster setting time than the crystalline one.The mixture of Al₂O₃・nH₂O and powdered Al(H₂PO₄)₃ showed the highest compressive strength(90kgf/cm²)at the molar ratio Al₂O₃/P₂O₅=1(40wt% Al₂O₃・nH_₂O).The reaction products were mostly in amorphous phase except for the set binder containing crystalline Al₂O₃・nH₂O. In the case of liquid Al(H₂PO₄)₃, the setting time was similar to that for the powdered Al(H₂PO₄)₃. Their compressive strength increased with the increase in the molar ratio of Al₂O₃/P₂O₅ ratio.The reaction products were amorphous in all cases.The SEM graphs of the set binder containing amorphous Al₂O₃・nH₂O, revealed hole-like structure instead of dense structure observed in the set binder containing the crystalline Al₂O₃・nH₂O. The binders containing amorphous Al₂O₃・nH₂O(30〜70wt%)showed a setting time of 0.2〜6hours and the compressive strength of 90〜130kgf/cm² which is high enough for use as dental investments.

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A method of machinning the inner shape of the dental crown was reported.The machine was controlled numerically and the data was based on the measured points of the prepared tooth with the 3D-point digitizer.Generally, the inner site of the dental crown has been manufactured with a NC(Numerical Controlled)machine using detailed measured data.However, the expression of the prepared tooth surface was not with the assemblies of the large amounts of measured points but with the interpolation of small amounts of measured points.Similarly, for the tool pathway, offset-surface data was calculated with the aid of the spline function.At first, for the measured points, the offset points had to be calculated, and these offset points were interpolated with the spline function.Thus the offset surface data was obtained.Calculation was easier with fewer original measured points.In this method numerosu calculations were not required to determine the offset points individually.Here, offset points were determined by the vector products of the two tangent vectors at each measured point.The directions of the offset vectors were opposite of those for the outside of the crown, because one surface value expressed both concavity and convexitywith the difference.For this conversion, the Z values of the measured points had to be changed to negative.To prevent the production of a mirror image, the Y values in addition to Z, were also transformed.

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Studies were conducted on the development of the Dental CAD/CAM system and with which the occlusions were simulated.A method of cutting the undercut area of the outer shape of the dental crown with the 3D(three dimensional)modeling machine at controlled X, Y, Z axes was reported.Initially the origin and X, Y coordinates were set in the lower surface of the waxblock and the upper side of the crown was machined.When the modeling wax was turned, the origin was reset on the upper surface of the waxblock.Here, the Z-data of the undercut area with the CAD data base had to be changed to a negative value.With these procedures, the origin of Z did not change when the waxblock was turned and the continuity of the Z-data was sustained.However, in this reversed waxblock, the coordinates of the measured data(=CAD data base)and that of the modeling machine, were in a symmetrical relation with each other, For the prevention of a mirror image, the Y-data, in addition to Z data, was converted to negative.For the adjustment of the X and Y directions, the nature of the cubic waxblock surfaces, that is, each pair of opposite surface was parallel and the other pair perpendicular, was utilized.The tool offset surface was calculated in the same way as for the occlusal face machining, In this undercut area, the simple shape of the dental crown could prevent interference by the tool movements.

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The fracture toughness of four dental filling cement products was examined using a single-edge notched(SEN)specimen.The validity as plane-strain fracture toughness of the obtained fracture toughness and the effect of fracture toughness on storage in distilled water at 37℃ were discussed.Kc- B/(Kc/σt)² curves obtained from fracture toughness tests on specimens with various thicknesses did not reach a constant and the thickness at which the curves leveled off could not be determined, B/(Kc/σt)² having 1.0〜4.0. Many fracture toughness values obtained from a SEN specimen(thickness B=5.0 mm, width W=5.0 mm and crack length a=W/2)were declared invalid as a plane-strain fracture toughness according to ASTM E399. The mean fracture toughness of four products after storage for 30 days in distilled water at 37℃ decreased to about 75% of the fracture toughness for 24 h specimens.

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Our investigations have shown that the bond strength of adhesive resins to dentinal substrates can be altered by the rate of monomer diffusion into demineralized dentin after smear layer removal.The diffusion rate of monomers is a function of the diffusivity of dentinal substrates and diffusibility of the monomer itself.The effectiveness of treating dentin with 2-hydroxyethyl methacrylate(HEMA)prior to application of an adhesive resin was examined.The adhesive resin was 5% 4-methacryloxyethyl trimellitate anhydride(4-META)in methyl methacrylate(MMA)combined with a poly-MMA powder.Polymerization of this resin was initiated by tri-n-butyl borane(TBB).Bovine dentin samples were ground with 600 grid Carbimet paper discs(Buehler, USA), and demineralized with an aqueous solution of 65% phosphoric acid.Bond strength was improved by HEMA treatment of phosphoric etched dentin which could not be given high bond strength before.The adhesive resin impregnated the exposed collagen bundles and became entangled with them to create the"hybrid", essential in attaining high tensile bond strength. Specimens pretreated with phosphoric acid did not readily form"hybrid"layers.However, when the phosphoric acid pretreatment was followed by HEMA application, a"hybrid"was demonstrated on SEM and TEM, and bond strength increased to 16 MPa. This study indicates that HEMA applied to dentinal substrates enhances monomer diffusion and entanglement with demineralized dentin, and facilitates the formation of a"hybrid"layer.

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Restored dental materials undergo repeated severe mechanical and physical stress in the oral cavity.To evaluate the mechanical properties of the dental material, a dynamic testing method is desired instead of a static one.The efficiency and characteristics of the cyclical fatigue testing device which was constructed as a trial to measure the fatigue shear bond strength in water were examined.The maximum load(τmax)of this testing machine ranged from 320 gf to 4, 020 gf, while the minimum(τmin)was from 200 gf to 3, 220 gf. The practical threshold frequency was 6 Hz. Stable and accurate cyclical loadings were obtained even after one million cycles of continuous operation as compared with the initial operation.In conclusion, this fatigue testing machine is durable, accurate and reliable.

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The amount of wear on posterior composite resin was studied using the 3-D measurement milling apparatus(type A-1).An extracted sound premolar was selected and a class I cavity was prepared on the occlusal surface.The cavity was filled with posterior composite resin and finished(base-line).The base-line impression was taken with silicone rubber impression material.Artificial wear was applied by sand-blaster with a glass-bead.Then, the second impression was taken as a post-worn specimen.Both impressions were electroplated by copper and the dental stone was poured into the electroplated impressions to make the measuring dies.Two measuring dies were digitized with A-1 and the data were registered onto the disk.Both data were denoted on the computer CRT display or X-Y plotter, and compared with the scanning electron microscopic photographs.The measuring accuracy of the A-1 system was 5μm in X, Y and Z directions, and it could be increased up to 2μm.The wear could be observed clearly and measured easily in the two-dimensional display.The A-1 system could display the data at any location, any magnification and desired section.One of the remaining problems is the measuring speed.However, this could be solved by a modification of the software program including the vector movement.

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The initiator systems for cold curing resin composed of thiobarbituric acid derivatives, copper acetylacetonate(CuAcAc)and amine hydrochlorides such as dipropylamine hydrochloride(NPA), di-sec-butylamine hydrochloride(SBA)or di(2-ethylhexyl)amine hydrochloride(EHA)were evaluated using triethylene glycol dimethacrylate monomer.1, 3, 5-Trimethyl-2-thiobarbituric acid(135MS)and 5-butylbarbituric acid(5B)were effective as a reducing agent in the initiator systems, but the other derivatives were not so effective.The initiator system consisting of 135MS, EHA and CuAcAc was most useful.Evaluation of the effect of(thio)barbituric acid derivatives on polymerization of MMA initiated by 2, 2'-azobisisobutyronitrile revealed that the induction period varied significantly with the type of derivative and.therefore, suggested that these compounds are deeply involved in the polymerization reaction besides initiation.The effect was considered to be more pronounced in cold curing than visible-light curing.

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