Untreated enamel and dentin were observed in air, water and acid agents consecutively by atomic force microscopy(AFM).AMF allowed observation in situ of the change in morphology during the etching process.The change before and after etching could be observed for the same spot in the same specimen using the newly designed syringe for exchanging liquids.In 10% citric acid the smear layers of both enamel and dentin disappeared wihin 30 seconds.Then, enamel prisms or dentinal tubles appeared and demineralization progressed with time.

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Aqueous bonding agents were developed to make the adhesion between composite resin and dentin retaining its smear layer without any etchings and primings in order to simplify the clinical operations.The water-soluble photo polymerization initiator, 2-hydroxy-3-(3, 4-dimethyl-9-oxo-9H-thoixanthen-2-yloxy)-N, N, N-trimethyl-1-propanaminium chloride(QTX), was used at a concentration of 2% with 0.3% N-phenylglycine(NPG).The bonding agent was applied onto the polished bovine dentin surface.After drying, the bonding agent was polymerized by photo-irradiation.The low viscosity composite resin was applied as a thin film and then the composite was filled, and was respectively polymerized by photo-irradiation.The tensile bond strength was measured after the immersion in 37℃ water for 24hr.The adhesive durability was determined by measurement of the bond strength after thermal cycling between 4 and 60℃ in a water bath.The bond strength by the scrubbing method was also measured as above mentioned.The NPG agent gave the mean bond strength of about 10MPa after a 60 sec application and 30 sec irradiation.Although the mean bond strength with a 15-sec application was only about 4MPa, the bond strength with a 15-sec scrubbing was about 8MPa.The remaining smear layer and dentinal plug were observed by SEM after the application and scrubbing of NPG agent.The 15 sec scrubbing of NPG agent showed no decrease in the bond strength after 2, 000 thermal cycles.

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The aim of this study was to improve a visible light-cured denture base resin.A monomer was prepared by mixing cyclophosphazene oligomer with various quantities of MMA and its physical properties were examined.The compressive yield strength did not vary with changes in the quantity of oliogomer.When the oligomer was 10〜20wt%, the transverse strength was 120〜123MPa in dry specimens and 117〜119MPa in wet specimens but it decreased by more than 30%.Hardness showed a tendency to increase with a higher proportion of oligomer.Water sorption increased with higher proportions of oligomer, but solubility did not vary.Abrasion ratio showed a tendency to decrease with higher proportions of oligomer.A monomer with good properties was obtained when 10〜20wt% cyclophosphazene oligomer was mixed with MMA.

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Mixing of gypsum products with disinfectant solutions is a handy disinfecting method for stone models to be applied in daily practice.The effect of this method on some properties of stone models was examined.A type 2 plaster, a type 3 stone and a type 4 stone, high-strength were mixed with the solutions containing 0.1 and 0.5% sodium hypochlorite, 1, 000 and 10, 000ppm sodium dichloroisocyanurate(TBS), 0.1% povidone-iodine and 2% alkaline glutaraldehyde.Setting time, setting expansion, tensile and compressive strengths, surface roughness and scratch resistance were measured.The solutions with 10, 000ppm TBS and glutaraldehyde degraded the properties of the stone models.The reverse effect was largely noted on the type 2 plaster.Mixing with the other solutions was clinically acceptable.

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The induction period(IP)and initial rate of polymerization(IRP)of methyl methacrylate(MMA)by BPO(1.0mole%)at 70℃ in the presence of antioxidants and their related compounds were studied by a differential scanning calorimetry.IP at 0.1mole% was as follows, 2, 6-Di-tert-butyl-4-methylphenol>Eugenol>Phenol>Vitamin E>Vitamin A.At the high concentration of 1.0mole%, the IRP of all test compounds decreased markedly, indicating their large interaction with free radicals due to thermal decomposed BPO.Phenolic antioxidants were concluded not to be an inhibitor but a retardant at 1.0mole%.Furthermore, the effects of antioxidants on the IR and IRP by azobisisobutyronitrile(AIBN)and their interaction with diphenyl-p-picrylhydrazyl(DPPH, free radicals)were studied.

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Although many adhesive resins have been developed, the durability of bonding between metals and resin requires further improvement.Stress generated by difference in thermal expansion coefficient of materials involved in the bonding may influence durability.In this study, four types of resin cements, including an experimental one intended for improving durability, were examined for their properties and effect on the change of tensile bond strengths in bonding of titanium and gold/silver/palladium alloy with acrylic resin or stainless steel after thermocycling test.Durability of bonding between the metals and acrylic resin, in which the combination difference in thermal expansion coefficient between the two was relatively large, was far inferior to that between those and stainless steel in all cements.The durability against the thermal stress depended on the type of the resins.A composite resin type cement with high elastic modulus was the least durable.The experimental cement, composed of fluoropolymer/MMA-TBB, with a relatively low elastic modulus and water sorption was most durable.Studies of the experimental resin after curing by DSC and fractionation followed by infrared spectroscopy suggested that it was composed of PMMA and fluoropolymer/PMMA block polymer.The structure and composition of the resin may be related to its improved strength and durability.

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Titanium flow change with time was examined in the case of plate cavities.A very unsteady flow was recognized by means of flow observation of the casting surface and the section.In the thick cavity(1.4mm), a solidification shell was formed of an early stage, and then later inlet fluid was solidified after filling the cavity.As a consequence of that process, large inner defects are liable to generate within the shell.In the thin cavity(0.55mm), the solidification layer which was generated by early inlet flow markedly narrowed the fluid passage, so that the later inlet fluid hardly proceeds the same path because of the large friction, and generated the new passage as a bypass.Large inner defects were rarely generated but outer defects tended to ocurr.In conclusion, unsteady flow strongly affects the generation of casting defects.

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The effects of pr;mers consisting of chelating agents combined with metallic ions on bonding to the tooth were examined in connection with the decalcification abilities of these primers.The shear bond strength of Photo Bond to vobine dentin and enamel treated with an aqueous solution of phytic acid(PYA)salts the pH of which was controlled, 10% PYA(pH0.68), 10% PYA-2Na(pH1.14), 10% PYA-4Na(pH2.08), 10% PYA-6Na(pH3.52), 10% PYA-8Na(pH6.34)and 10% PYA-12Na(pH7.42), and then the 3% solution of tin(II)fluoride(SnF₂)was measured.The effects of these primers were evaluated from bond strength and SEM observations of the treated tooth surface.The bond strength was equally high to dentin and enamel in the treatments with 10% PYA+SnF₂〜10% PYA-6Na+SnF₂.The bond strength to dentin was in the range of 8〜10MPa, and that to enamel was in the range of 14〜18MPa. However, the bond strength decreased significantly in the treatments with 10% PYA-8Na+SnF₂ and 10% PYA-12Na+SnF₂ in which the smear layer was observed on the tooth surface.When the smear layer was removed with these primers, the pH(decalcification abilities)of these primers was not correlated with the bond strength.These findings suggest that the chemical interaction between the functional monomer, MDP, contained in the bonding agent and tin fixed on tooth surface contributes to the bonding.

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The gold content of gold-palladium-silver alloys used for health insurance in Japan is 12%, according to JIS T 6106.The effects of the gold content on the mechanical properties and the tarnishing resistance of Au-Pd-Cu-Ag alloys were examined.Twelve kinds of Au-Pd-Cu-Ag alloys, containing 20 mass% palladium, 12, 16, 20 mass% gold and 5, 10, 15, 20 mass% copper were melted and cast to the specimens using dental precision casting.After softening heat treatment(water quenching after 800℃, 3 min soaking, Q)and hardening heat treatment(furnace cooled 450→250℃/30 min, H), the mechanical properties of the alloys depend on the copper content;in most cases, as the copper content increased, the tensile strength/proof stress/elastic limit and the Vickers hardness number increased, while the elongation decreased.As the gold content increased, the tarnishing resistance slightly increased and in the composition range of 20 mass% gold and less than 12 mass% copper, the brightness L* after tarnishing test, was over 70.The melting points of the alloys were under 1100℃ except 20 Au-5 Cu-20 Pd-55Ag.As the copper content increased, the lattice constant of α solid solution at the quenched condition decreased, and when the gold content of the alloys increased, the α-transition temperature decreased.

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The thermal diffusivity of commercial dental ceramics was determined by a laser flash method.ASTM specification was applied for the tests, that is, thermal diffusivity was determined at room and elevated temperatures up to 700℃ for the specimen which was set in an evacuated electric furnace.The thermal diffusivity of the core porcelain which has a high volume fraction of alumina showed the following temperature dependency;1.9 and 1.0mm²s^-1 at room temperature and 700℃, respectively.However, the thermal diffusivity of the other dental porcelains tested had little temperature dependency and was from 0.5 to 0.8mm²s^-1. For the castable ceramics, low temperature dependency of the thermal diffusivity was detected, being 0.4〜0.8mm²s^-1. Crystallization of the castable ceramics was considered to affect its thermal diffusivity.From the model calculation, the thermal transient stress in the material during heating/cooling was confirmed to be directly proportional to its coefficient of thermal expansion and elastic modulus, and inversely proportional to the thermal diffusivity.These findings suggested that high service stress can be achieved in controlling the thermal diffusivity by a design of constitution and structure of dental ceramics.

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We chemically analyzed the monomer compositions by GC, HPLC and LC-MS and filler compositions by firing, XRD and SEM of four commercial light-cured composite resin veneering materials.1.The monomer analyses revealed that all materials contained CQ as a photo-initiator and urethane monomer as a base monomer.Diluent monomers varied with the materials.2.The filler analyses clarified that all materials contained a micro-filled SiO_2 filler embedded in a pre-polymerized organic substance.

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Titanium and its alloys are gathering much attention as dental alloys because of their good corrosion resistance and biocompatibility.However, their applications are limited as compared to other conventional dental alloys.Especially, studies for clinical application are insufficient.The mechanical properties of dental alloys are estimated as an ultimate tensile strength, proof strength and hardness by the tensile test, the bending test and the hardness measurement.Although, these static data of the materials are useful to determine the properties of the macroscopic materials, considering the actual environment for the alloys, the dynamic properties must be determined by the fatigue test.For development of the application of titanium in the dental field, it is important to clarify its basic fatugue data.In this study, the fatigue test for cast titanium specimens was carried out.The findings ware compared with those of cobalt-chromium alloy.In the fatigue test the specimens ruptured under a small stress below the ultimate tensile strength.The number of stress cycles to rupture was decreased with the in crease of repeated stress.In the case of relatively small stress, the strain of the specimens was small by the work hardening during the test.In the case of large stress, fatigue cracks were initiated in the early stage of the test and a fast propagation was observed.There were different kinds of mechanisms on the crack initiation and propagation between titanium and cobalt-chromium alloy.Many small cracks were initiated on the surface of titanium instead of a few large cracks on the cobalt-chromium alloy propagating to the internal of the specimens.In conclusion from the view point of fatigue strength, the design of cast materials having a stress of 1/5 of the ultimate tensile strength is necessary to be good for ten years for an adult person.This is also the case for the cobalt-chromium alloy.This stress level was below the elastic limit.

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Effect of smear layer on bonding to dentin prepared with either a steel or a diamond bur-was studied.A half of the prepared dentins was pretreated with an aqueous solution of 20% 2-methacryloyloxyethyl phenyl hydrogen phosphate(Phenyl-P)and 30% 2-hydroxyethyl methacrylate(HEMA)for 60s, and then a photocure bonding agent, 5% Phenyl-P in triethyleneglycol dimethacrylate(TEGDMA)was primed.The other half was conditioned with 10-3 for 10s to remove the smear and 4-META/MMA-TBB was bonded to the surface.The tensile bond strength to the smear-retained dentin was lower(5-8MPa)because the tensile strength of the hybrid layer prepared by burs or ground with #180 paper was too weak to reinforce with the impregnated resin.On the other hand, that of the latter to the smear-removed dentin was 14MPa.These conclusions were drawn through SEM examinations of the fractured surface due to tensile load and cross-sections and through TEM examination of the hybrid layer.The dentin cavity prepared with burs must be improved to condition to obtain reliable bonding with an adhesive.

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In this study we evaluated the tensile and shear bond strengths to the tooth structure using one experimental and four commercially available resin cements.In addition, the interfaces between the cements and dehtin, and the failure patterns after debonding were observed under the SEM.The tensile and shear bond strengths of the cements to enamel were significantly higher than those to dentin except for MASA Bond.Comparison of the tensile and shear bond strengths for all cements revealed that the shear bond strengths to enamel, as well as that of MASA Bond to dentin, were significantly higher than the tensile bond strengths.The SEM observations showed that the resin cements employed in this study formed a hybrid layer of different thicknesses.Furthermore, comparison of the tensile and shear specimens often revealed a different failure morphology.

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Recently, titanium is the material of choice for uncoated implants because of its biological acceptance in the bone.SEM observations of commercial implants revealed a different surface micromorphology for their bone contact area which was affected by the preparation procedures used in implant fabrication.In this study, the surface morphology of the titanium plates prepared by wire type electric discharge machining(Wire-EDM)was compared with those prepared by plasma coating and mechanical lathing used in commercial implant fabrication.The surface roughness(Rmax)of the titanium plates with plasma coating and lathing was 30.1 and 2.6μm, respectively.The surface micromorphology of the titanium plates with Wire-EDM varied according to the applied electrical conditions, and higher electrical conditions produced a surface with a higher roughness.The Rmax value of the titanium plates with Wire-EDM was in the range of 7〜22μm.Titanium plates with lathing showed the surface with regular morphology.On the other hand, both the titanium plates with Wire-EDM and plasma coating showed the surface with irregular morphology.The surface with a Wire-EDM was irregular but rather controlled, and that with plasma coating was highly irregular and porous.

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The in vitro early cellular responses of osteoblast-like cells(MC3T3-E1)were studied on titanium surfaces with different micromorphologies.Surfaces with a regular mophology were produced by polishing with 1500-grit, 400-grit or 60-grit emery papers, and those with an irregular morphology were produced by wire type electric discharge maching(Wire-EDM).The surface roughness(Rmax)of the surface with 1, 500-grit, 400-grit, 60-grit, and Wire-EDM was 0.8, 2.6, 8.0 and 20.9μm respectively.Early cellular attachment for the remaining time period of 60 minutes was calculated by measurement of the lactic dehydrogenase(LDH)activities of the attached cells.Significantly higher levels of cellular attachment were found on the irregular surface with Wire-EDM than the regular surface with emery polishing.Among the surfaces with emery polishing, surfaces with a higher surface roughness had a tendency to have higher attachment.Attached cells were observed to already extend flopodia to form a bridge-like anchor between indentations of the irregular surfaces for 60 minutes on the surface with Wire-EDM.These findings suggested that the surface micromorphologies influenced the cellular responses of the osteoblast-like cells and further studies on longer time cellular responses are required.

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Although titanium has been widely used as dental implants and the screws and plates for bone fixation because of excellent corrosion resistance and biocompatibility, the mechanical strengths of commercially pure titanium are not completely sufficient.In this study a plasma activated sintering method(PAS)was applied to fabricate sintered blocks with higher mechanical strengths using commerical pure titanium powder.Furthermore, pure palladium powder(0.063-4.0wt%)was added to improve sintering ability.Approximately 40g titanium powder(#350, #235 and #100)was sintered in a graphite mold with a different sintering current(2800-4000A)in air.The sintering process was completed in a few minutes and sintered blocks with a high density(more than 99% of ideal density)were obtained.Tensile and flextual strengths of sintered blocks were about twice of those from commercial pure titanium plates(JIS H 4600 grade 2)as a control which showed high strength because of oxygen diffusion and solution inside the sintered blocks during a sintering process.On the other hand, the elongation of the sintered blocks was approximately 10% and smaller than that of the control.Addition of palladium powder decreased the sintering period drastically which suggested that the sintering process could be performed with a lower energy.The sintered block with 0.063wt% Pd had a higher elongation than that without Pd.The increase of Pd content increased tensile and flextual strengths but decreased elongation because of the contribution of the increasing alloy phase.It was concluded that PAS could provide high purity titanium blocks with higher density and strength which were expected to be applicable to biomedical products by a secondary fabrication process such as electric discharge machining and milling.

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Titanium plates(TPs)were prepared with either an irregular and rough or a regular and rather smooth surface morphology.TPs with an irregular surface were produced by either wire-type electric discharge machining(Wire-EDM)or plasma coating(Plasma).TPs with a regular surface were produced by polishing with 1, 500-grit emery papers(Emery).The surfaces of TPs were characterized by surface profilometry, scanning electron microscopy(SEM), X-ray photoelectron spectroscopy(XPS)and X-ray diffraction(XRD).Mouse osteoblast-like cells(MC3T3-E1)were exposed to the surfaces of the prepared TPs and cultured for 15 days.Glass plates for tissue culture(TCP)were used as a control.Total DNA of the cultured cells was evaluated as a marker of cell proliferation.Alkaline phosphatase(ALP)enzyme activity was evaluated as a marker of cell expression.The amounts of Ca and P at day 12 and 15 were also measured.The surface roughness(Rmax)of TPs prepared with Wire-EDM, Plasma and Emery was 20.5, 31.4 and 0.80μm respectively.The surfaces with Wire-EDM were irregularly oriented in morphology with many small depressions and indentations, but the height of depression was rather controlled.On the other hand, the surfaces with Plasma were highly irregular and porous.XPS and XRD appeared that the surface oxide layer of the surface of the TPs with Wire-EDM were composed of TiO₂, TiO and Ti₂O and were far thicker than those with Plasma and Emery.The amount of DNA of cultured cells gradually increased on all surfaces, and became significantly higher with Wire-EDM and Plasma than with Emery and TCP after day 9.The phenotypic characteristic of bone cells in vitro are often characterized by relatively high ALP enzyme activities.ALP activities/μg DNA of cultured cells on the titanium surfaces with Wire-EDM and Plasma were significantly higher than those with Emery and TPC after day 9.The Ca/P ratios of the cultured cells on the titanium surfaces with Wire-EDM and Plasma at day 15 were 1.26 and 1.28 respectively.Therefore, the cells prolifierated more abundantly and expressed their phenotypic characteristics earlier on TPs with irregular and rough surfaces than with regular and smooth surfaces.SEM observation of the cultured cells appeared that the body of the cells changed the shape extending the flopodial-like processes connecting irregular edges, which suggested the alterations in cell shape inducing cellular expression.These findings suggest that the micromorphology of the bone contact surface of implants influenced the biological responses and further investigations are reguired to optimize the surface micromorphology of the implants.

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