To reline the metal denture base by a silicone resilient liner, some methods of producing a durable adhesion between silicone rubber and denture metal(Co-Cr alloy, Ni-Cr alloy or Ti)as an extension of the adhesion between silicone rubber and acrylic resin were tested.The monomer with a-SiH group, γ-MPTDMS, was synthesized and copolymerized with MMA.When the copoly(MMA/γ-MPTDMS)solution in tetrahydrofuran, named a g-MPTDMS adhesive, was used after the copoly(MMA/4-MET)was applied as a primer, the Co-Cr alloy specimen yielded a tensile bond strength of 49kgf/cm²under dry conditions, though it did not show any stability in water after thermal cycling(4℃-60℃, 60s).When the mixture solution of copoly(MMA/4-MET)and copoly(MMA/γ-MPTDMS)was used as an adhesive, the tensile bond strength of the specimens tended to increase with the increasein the concentration of copoly(MMA/γ-MPTDMS)in the adhesive.The net copoly(MMA/γ-MPTDMS)solution, i.e., γ-MPTDMS adhesive, had the highest tensile bond strength.Thus the adhesive developed for bonding silicone rubber to acrylic resin was also effective for bonding silicone rubber to denture metals.When the γ-MPTDMS adhesive was used to bond the Co-Cr alloy, Ni-Cr alloy, or Ti to silicone rubber, thetensile bond strength was 48, 44 or 41kgf/cm², respectively, under dry conditions, and the stability in water was enhanced by the sandblast treatment.

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Prosthetic materials become brittle by repeated heat shock such as sudden heating and cooling.Especially, porcelain is brittle under heat shock.Heat resistance of porcelain was tested by the thermal cycle method and the effect on the mechanical properties of porcelain such as bending strength, deformation and surface stress value was examined.The thermal shock of porcelain-fused-to metal with increase the number of thermal cycles got weak in the bending strength and the bending elasticity coefficient became small and the toughness became gradually small.The surface stress of porcelain-fused-to metal became small by the effect of the thermal cycles and the deformation get to be shaped like an ellipse shape by being free from stress.The thermal shock resistance of chemically strengthened porcelain is stronger than that nontreatment.

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Casting shrinkage is compensated for by the stting expansion and thermal expansion of the investment material;the setting expansion may be obstructed by the wax pattern, thereby rendering the compensation inadegueate.The exothermic heat coincident with the setting may increase the flow of the wax, thus permitting sufficient setting expansion for proper compensation.We accordingly investigated the relationship between the time of kneading of four types of investment material, their volume, and the resulting increase in the mold temperature accompanying setting.The setting time decreased with an increase in the mixing time for all four materials.The mold temperature increased with the increase in mixing time for all four materials.For Dentivest only, the setting expansion decreased with a longer mixing time.Changes in the mixing time had no effect on thermal expansion.For Dentivest only, a longer mixing time improved the casting accuracy.For Cerami gold only, castings were overfit.Mold temperature and casting accuracy both increased with larger volumes of investment material for Ceravest G.

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Tissue response in rat subcutaneous tissue to gallium alloy and amalgams was histopathologically examined to observe the biocompatibility.Immediately after trituration of gallium alloy and amalgams, they were put into the stainless steel mold of inner size of 1×1×5mm shape.The specimens were aged for 20 hours at room temperature after trituration, and polished metallugically to a mirror surface.At 24 hours after trituration, the specimens were implanted into a dorsal site of rat subcutaneous tissue using a hypodermic needle.Rats were killed at 3, 7, 30 days, and the tissue was fixed with 10% neutral formalin and the specimens were carefully removed from the implant site after the tissue was fixed.The tissue was dehydrated and embedded in paraffin, sectioned longitudinally to the specimen, and stained with hematoxyline and eosin.The gallium alloy was disintegrated into pieces in the tissue, and the tissue around the gallium alloy consisted of granular tissue containing small fragments of gallium alloy with moderate inflammatory cell infiltration.There were no differences in the degree of inflammation with or without zinc containing high copper amalgam.Tissue was formed around the amalgam showing capsular formation with moderate or virtually no inflammatory cell infiltration.The properties of the gallium alloy should be improved to obtain as good a tissue response as with the amalgams.

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The histological effects of solubility behaviour and shape on the soft tissue stability of hydroxyapatite granules for grafting four categories of hydroxyapatite granules into the abdominal hypoderm of rats were examined.Three kinds of granules were on the market and another was newly developed.The granule, which showed a large repose angle, an irregular surface shape, and lower solubility stabilized quickly and also showed smaller deformation of implant-connective tissue complex.The inflammation of the implanted area healed in four weeks after implantation, although the stabilization of the implant-connective tissue complex of the granule which showed high solubility behaviour was recovered after three months.The compact surface, open pores ranging from 50 to 200μm in diameter, and also multi-nucleated shape of the newly developed granule promoted the osteoconduction of the granule applied to the region where the bone and soft tissue co-exist.

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The surface roughness of dental stone models in combination with alginate impression materials was measured by using a non-contact photogenic surface roughness analyzing system.This system was made by way of trial to evaluate the surface roughness simply.A correlation was found between the measured value and Ra.From the SEM observation, the surface roughness of dental stone models showed a tendency to be influenced by its crystal structure.In conclusion, this analyzing system can be used to evaluate the surface roughness of dental stone models in combination with alginate impression materials.

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Twelve kinds of Au-Ag-Pd-Cu alloys, containing 10wt% Au, 22.5, 27.0, 31.5, 36.0wt% Pd and 13.5, 18.0, 22.5wt% Cu were melted and cast using dental precision casting.Heat treatment at 800℃, water quenching(softening heat treatment), and subsequently, 450→250℃ oven cooling(hardening heat treatment)were applied to the alloys and their mechanical properties and tarnishing resistance were measured.After softening heat treatment, the tensile strength of the experimental alloys, ranged from 45 to 57kgf/mm² the elongation ranged from 11 to 22%, and the Vickers hardness number(VHN)ranged from 143 to 202, while after hardening heat treatment, the tensile strength and VHN increased to 80〜99kgf/mm², 223〜405, respectively, and the elongation decreased to 1〜15%.After hardening heat treatment, the estimated composition showing the maximum tensile strength was about 10Au-44Ag-27Pd-19Cu and the estimated strength was 100kgf/mm² however, the elongation was less than 1%, and the brightness(L^*)of the specimens immersed in 0.1% sodium sulfide solution at 37℃ for 3 days was 62.After hardening heat treatment, the composition having a high strength and over 69 L^* was 10Au-36Ag-36Pd-18Cu.The tensile strength and the elongation of this alloy were 80kgf/mm²and 4%, respectively, and they satisfied ANSI/ADA Spec.No.5(for dental casting gold alloys)type IV.After softening heat treatment, the brightness(L^*)of the specimens after the tarnishing test, ranged from 62〜67, and those after the hardening heat treatment 65〜69.

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The surface of titanium specimens was treated by anodic oxidation and immersion in aqueous solutions containing phosphate ions and calcium ions, in order to obtain a more biocompatible surface of titanium.The surfaces treated by the above methods were characterized using scanning electron microscopy, x-ray photoelectron spectroscopy, and Fourier transformed infrared absorption spectroscopy with reflection absorption spectroscopy.In addition, the specimens treated were immersed in Hanks' solution at 37℃ for 30 days and then the surfaces were analyzed using the above methods.The results indicated that the treatments accelerated the formation of calcium phosphate during immersion in Hanks' solution.Some treatments produced a calcium phosphate surface resembling apatite on the titanium in Hanks' solution.

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Sixteen kinds of Ni base alloys, adding 0〜12mass% Mo and 0〜6mass% Si to 80Ni-20Cr alloy were prepared and cast.The mechanical properties and tarnising resistance of these alloys were measured.The tensile strength decreased to below 35kgf/mm² in the composition range including from about 1 to 3% Si and from 0 to about 6% Mo.The elongation was decreased to 3% containing over 2.5% Si and the elastic limit increased with increasing Mo and Si contents.The tarnishing resistance hardly changed in this alloy series, and the brightness L^*represented by CIE system was 71±1, but improved slightly in the composition with a Si content of about 3%.

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Acoustic emission(AE)activity was measured during heating and cooling of dental porcelain-fused-to-metal(PFM)laminated substrates.Transient and residual stresses in the PFM strips were calculated by computer simulation using viscoelastic stress analysis.The detected AE event was discussed with the relative roles of the simulated incompatible stresses.High AE activity was detected near 600℃ where the incompatible stress faded away from the PFM strip for heating.Elastic energy was suggested to have been released with the relaxation of the stress by viscoelastic deformation of porcelain and could be detected by the AE method.For the cooling of the PFM strip, high AE activities were detected from 700 to 500℃(first peak)and temperature lower than 300℃(second peak).Compared with the simulated transient stresses, the AE source of the first peak was considered to be related to the viscous flow of the porcelain.However, the AE source of the second peak could not be specified.The AE activity was low when a thick alloy was used for the PFM strip.This is consistent with the computed result of its low shear viscous flow.These findings suggest that the AE method is helpful to understand the mechanism of the generation and relaxation of residual stress during cooling and heating of PFM strips, dynamically.

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Using a centrifugal casting machine for titanium, the effect of gas conversion, in air or in argon, on the titanium flow was investigated in the case of a mesh pattern.This factor exerted a profound influence on the shape of filled area rather than the castability.In argon, the early inflow reached the farthest portion of the mesh cavity, which was not observed in air.The flow observation indicated that the titanium flow in the cavity was laminar in argon or turbulent in air.In the case of laminar flow, the character of the centrifugal casting appeared more clearly where the driving force of flow was its velocity even in such a complicated pattern.

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With the advance in the dental casting of titanium, much attention has been directed to the surface layer produced by the reaction with mold materials.To investigate the influence of the reaction layer on the mechanical properties of titanium castings, a silica base investment and a magnesia base investment were used as mold materials and tensile test, hardness test and microstructure observation were performed.In the tensile test, the specimens cast with the silica base investment showed not only a higher strength and less elongation but also larger scattering in stress-strain curves than those with the magnesia base investment.The hardness test and microstructure observation, revealed that the surface reaction layers in the castings with the silica base investment had a clearly multiple structure, and were thicker than those with the magnesia base investment.The instability of reaction layer production and the irregularity of cracking in the layer was considered to have caused the larger scattering in the mechanical properties of the castings with silica base investment.

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It is important for dentists to know the inclination angle of their dental handpieces while they are cutting teeth, to set crowns and bridges after preparation and to minimize axial reduction of the teeth.A new measurement device for the inclination angle of the dental handpiece was developed.The device was designed to measure the two inclination angles of a handpiece in a non-contacting way by using four magnetic coils and three magnetic sensors.The sensor unit was attached to a goniostage and the device was calibrated within a 10cm×10cm area.The influence of the sensor unit position to measured angles was less than 2°, and the device was linear enough in a ±20° range.These findings lead to the conclusion that it is possible to measure the inclination angles of a handpiece magnetically.

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To improve the transmittance of light-cured composite resins, some composite resins with adjusted refractive indices of the matrix monomer and filler, were prepared.They were 6 light-cured composite resins(experimental group)which were prepared with a 30wt% of monomer mixed with one of 6 newly synthesized fluorinated aromatic dimethacrylates or diacrylates with a low refractive index and TEGDMA at the ratio of 30:70mol%, and 70wt% of SiO_2 filler.As a control, a composite in which 100mol% of the TEGDMA was used as the matrix monomer was also prepared.The depth of cure, compressive strength, flexural strength, elastic modulus, amount of toothbrush abrasion and water absorption of these composites were measured and the effects of the matrix monomer composition on the transmittance and physical properties of composites were examined.The depths of cure of 6 experimental group composites were in the range of 6.5〜7.2mm when they were irradiated in a metal mold for 20 sec with Translux CL^®.The mechanical properties of these composites were comparable to those of the control composite.However, the composites based on monomers with a short chain between double bonds were slightly brittle.The composites based on diacrylates had slightly higher mechanical properties than those based on dimethacrylates.The amount of water absorption in the 6 experimental group composites was about 35% of that of the control composite.In conclusion, the 6 experimental monomer formulations were useful as matrix monomers of light-cured composite resins.

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The bond strength of light-cured composite resin with a bonding agent, which contained 2-methacryloxyethyl hydrogen maleate to dentin treated with 37% phosphoric acid solution(PA solution)and 10% citric acid-3% ferric chloride solution(10-3 solution)was measured after being immersed in water for 1 day, 1 month, 3 months, 6 months and 1year to investigate the influence of water on bonding.The bond strength to dentin treated with a PA solution did not change with the time spent immersed in water up to 6 months, but significantly decreased with any further increases in time.For 10-3 solution, the bond strength did not change with time.The bonding agent created an acid-proof dentin layer with different thickness on the treated dentin surfaces as observed by SEM.The layer thickness was about 5μm for PA solution and about 2μm for the 10-3 solution.When treatment with PA solution was used, the SEM of 1-day-old specimens after the bond test revealed resin-dentin interface failure and superficial dentin cohesive fracture.The 1-year-old specimens had resin cohesive fracture, dentin cohesive fracture and resin-dentin interface failure.When the treatment with 10-3 solution was used, the SEM of 1-day-old specimens revealed resin-dentin interface failure and superficial dentin cohesive fracture.The 1-year-old specimens showed resin cohesive fracture, superficial dentin cohesive fracture and resin-dentin interface failure.

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In this study, the CAD process of the CAD/CAM system for laminate veneer restorations was developed.Since laminate veneer restorations are used for discolored teeth, diastema and microdont, three different CAD systems were developed because their indications have a different shape of prostheses.In the case of discolored teeth, the labial surface of natural teeth should be used as the labial surface of laminate veneers.Two models before and after preparation were measured on a specially designed jig and their data were combined by a CAD program.In the other cases of diastema and microdont, the design of the labial surface was made by interpolation of several CAD points.The CAD points used measured data of abutment teeth on the CRT monitor and were input manually with a P/C mouse.S-spline interpolation was used since the function could pass the CAD points and modify the shape of the labial surface locally.In conclusion, the labial surface of various laminate veneer restorations could be made and CAM process data were obtained.

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Porosity is usually regarded as an undesirable property of dental restorative materials.Its presence will affect the curing shrinkage of materials and the marginal seal to the cavity performed in the human teeth.The porosity was determined for the restorative composite materials and the effects of the air bubbles on the curing shrinkage and the microleakage using extracted human teeth were examined.When the viscosity of the composite material paste increased, air bubbles easily formed within the material during the manipulation.Furthermore, the presence of air bubbles within the composite resin paste increased the apparent amount of curing shrinkage and impaired the marginal seal to the cavity.

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Adhesion of MMA-TBB resins to ivory instead of to dentin was studied to identify the bonding mechanism of resins to dentin. Tensile bond strength of MMA-TBB resin to ground ivory was 14 MPa but that to ground dentin was lower than 5 MPa. The width of the hybrid layer created by diffusion of MMA into ground ivory and by the polymerization was 50 μm, but the methacrylate could not diffuse into dentin. These findings suggested thet the permeability of ivory was much higher than that of dentin. Therefore, 4-META which was effective in promoting the diffusion of MMA was not necessary for the adhesion to ivory. On the other hand, it was required for the bonding to dentin. It was concluded that diffusion of monomers into teeth, which is changed by either the permeability of substrates, diffusion capability of monomers or both, is essential to bond resins to teeth.

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