This study was carried out to determine the adequate range of strain in compression of alginate impression materials for improving the cast reproducibility. Experimental alginate impression materials, at 5grades of the strain in compression for about 10 to 21%, were obtained primarily by adjusting the ratios of the components. Casts of hard stone were prepared by taking the impressions of 3 types of epoxy molds(straigth, taper and undercut). The dimensional accuracy and deformation of the casts were evaluated by the use of a three-dimensional measuring system. No effect of the amount of strain in compression were noted in the straight type and taper type casts. In the undercut type casts, the lower portion of the undercat tended to widen, but the deformation decreased with increasing the strain in compression of the alginate impression materials. The range of strain in compression appropriate for improving the cast reproducibility was indicated to be 15-17%.

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Various new polymeric materials have been applied to the dental field, and better high functional polymers are requested. Recently several polymeric materials have been reported to have shape memory function. However, these polymeric materials have not been adapted to the dental field at present, notwithstanding they have such merits as easy formation, free coloring, non-rust and cheapness compared with the shape memory alloy. First, it is necessary to know the various properties of the polymer which affect shape memory in order to apply it to the dental field. A writer selected the styrene-butadiene copolymer SB system hybrid polymer, from plastics which contain many polymers and examined its mechanical property, thermal property and the effect of shape memory: This polymer has a hydrophobicity hardly absorbing water, and with excellent durability. This polymer has high viscosity and softness, namely a flexible resin of low rigidity. The shape recovery rate of the resin is under 70℃ and becomes larger with the increase in temperature, with recovery to almost the original shape occurring at above 80℃. The force of traction becomes larger in proportion to the extension value. Application of heat eliminates the residual stress by the injection molding. The deformation increases with the increase in the frequency of load at all temperatures. The thermal expansion rate is large even at a low temperature, it shows a maximum value at about 68℃ with, the largest thermal expansion rate being, 0.42%. The resin melts at above 95℃.The endothermic peak is shown at about 44℃ caused by the melting transition when it is measured by the differential thermal analysis (DTA) and coincides with the phase transition point measured by the differential scanning calorimetry (DSC) . The phase transition point of the resin exists at about 44℃. The resin has a characteristic resembling polystyrene more closely than polybutadiene from the result of the fourier transform infrared spectrophotometer analysis (FT-IR) . This resin with its, peculiar shape memory function may be applicable to the dental field after improvement of the molecular structure of the resin is for dental use.

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The mechanism of the initial-stage sintering of the hydroxyapatite(HAP)containing Li₃PO₄ was investigated by using the constant-rate heating technique. For the HAP without additives, the rate-controlling mechanism below 800℃ was the grain -boundary diffusion characterized by the apparent activation energy of 104kcal/mol. For the HAP containing Li₃PO₄, the grain-boundary diffusion controlled the rate of the densification below 750℃.However, above 750℃, the sintering parameter N decreased from 1.9 to 0.6. This suggested that above 750℃ densification occurred by the rearrangement process with the liquid-phase. The calculation of the apparent activation energy value for the liquid sintering was 252kcal/mol.

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Bio-glass is often combined with titanium to off-set the inherent brittlensess of bio-glass. However, due to the diffusion of oxygen from the titanium surface, titanium will also become brittle when bio-gass is baked to its surface. To prevent this phenomenon, we plasma-spray coated the titanium surface with either Mo or Al, or a mixture of the two. Both of these metals have a higher affinity for oxygen than titanium. We then investigated the effects of the metal coating on oxygen diffusion into the titanium. We also measured the effects of the diffusion of the metals or oxygen into the titanium on the hardness, bending strength, and yield strength of titanium. Titaniumu became brittle when heated. This was most evident at 1000℃. When the titanium was spray coated with Al, oxygen diffusion into the titanium was prevented at 900℃. The Al coated layer became porous when heated. When the titanium was spray-coated with a Mo-Al mixture, the titanium became brittle when heated. The higher the rate of Al in the mixture, the more brittle the titanium became when heated. The Mo spray-coated layer actually improved the toughness and other qualities of the heated titanium. Titanium to diffused into tho metal-coated layers.

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The degree of conversion of visible light-cured resins was examined. The optimum composite photoinitiator composition, and the degree of conversion after polymerization, of visible light-cured resins, were determined. As a monomer, triethyleneglycoldimethacrylate (3G) was prepared for the visible light-cured resins by changing the kind of photoinitiator. As photosensitizers, camphorquinone (CQ) , benzanthron (BA) , dibenzoyl (DB) , thioxanten-9-one (T9) , 8-quinolinesulfonyl chloride (QC) and 3-phenyl-5-isoxazolone (PIO) were used.As a reducing agent, methacryloxyethyl-p-dimethylaminobenzoate (DMAB-EMA) was used. As an inhibitor, 2, 6-di-tert-butyl-p-cresol (BHT) was used, The basic photoinitiator composition (here in after NON) was CQ 0.30wt%, DMAB-EMA 1.40wt% and BHT 0.01wt%. The composite photointiators were made of NON and one-three photosensitizers. Trial resins were examined by FT-IR using the liquid film method. The infrared absorbance measurement were made before irradiation and chronologically repeated after the resins had been polymerized by irradiation for 90sec. The quantity of the remaining double bond (RDB) of all trial resins, except BA-PIO system resins, decreased linearly with the logarithmic time after the start of irradiation. The BA-PIO system resins showed an induction period. When the photosensitizer was added to NON, the order of the conversion at 5min after the start of irradiation was:QC>DB>T9>NON>BA. The most appropriate photosensitizer to be mixed with NON was QC, and the optimum mixing ratio was 0.30wt% to monomer.

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To establish the proper polishing technique for the glass polyalkenoate cement restorations, the set cements of three brands were finished and polished with various silicone-rubber points, and different time intervals after setting, and the surface roughness of these finished and polished surfaces was determined with a surface recorder. Also the Knoop hardness of set cement surface was measured in accordance with each finishing and polishing time interval. The positive replicas of polished cement surfaces were observed under the SEM. The glass polyalkenoate cement restorations should be polished one week after mixing. Serial use of Silicone Point Hard Red and Silicone Point Blue under a wet condition produced the smoothest cement surface. A significant negative correlation was obtained the surface roughness of polished cement surface and the Knoop hardness of set cement.

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The polished surfaces of three kinds of set restorative glass polyalkenoate cements were observed using a cryo-SEM at a specimen temperature of-150℃ to prevent damage of the cement specimens and the specimens were analyzed by EDX. Furthermore, the SEM composition images of the polished cement surface were transferred to an image analyzer to obtain the core/matrix area ratio of the set cements.The polished surface of the set cement could be clearly observed by using a cryo-SEM without damaging the cement specimens. The core/matrix area ratios of the Fuji Ionomer Type II-F, HY Bond Glas Ionomer-F, and Ketac-Fil cements obtained by the image analysis were approximately 3:7, 3.6:6.4, and 4.3:5.7, respectively. The elements detected in the Fuji Ionomer Type II-F and Ketac-Fil cements were Al, Si and Ca, and those detected in the HY Bond Glas Ionomer-F were Al, Si, Sr, and Ca.

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Temperature dependence of thermal coefficient of expansion was measured for six commercial body and opaque dental porcelains. The dependence of coefficient of thermal expansion on temperature in the glass transition range was over ten times higher than that of the glassy solid state of the porcelain during the heating process. The onset of the glass transition range and the temperature where the apparent coefficient of expansion reached the maximum value(determined from thermal deformation)were almost equal to the strain and the annealing points (defined by viscosity) . The surface compressive residual stress for the 2mm thick porcelain slabs was simulated to be 16〜25 and 63〜92MPa, respectively, for the porcelain-cooled in air at ambient temperature and for that cooled with forced convection of compressed air from a temperature higher than the porcelain sag point. These findings suggested that the coefficient of thermal expansion in the glass transition range and viscoelastic behaviour of the porcelain are the major factors determining the residual stress in the porcelain-fused-to-metal (PEM) restorations, because the difference of the coefficient of thermal expansion between porcelain and alloy at the temperature where incompatible stress builds up was calculated to be much higher than 10×10^-6/℃.

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To study the binding of free calcium ions in aqueous solutions using poly (acrylic acid) with various molecular weights, potentiometric titration of their polyelectrolytes was carried out, and a calcium ion electrode was used to measure the free calcium ion in the solution. The precipitation reaction occurred, when the concentration of the polyelectrolytes had a mean molecular weight of about 100×10⁴ was 4×10^-3N and the concentration of calciam ion ([Ca]) in the solution was 8mM and when that of the polyelectrolyte had a mean molecular weight of about 35×10⁴ was 8×10^-3 and[Ca]was 16mM. Their precipitates contained the unreacted carboxyl groups with calcium. On the other hand, the binding molar ratio between the carboxyl group and calcium ion was about 2:1 for the polyelectrolytes(35×10⁴ molecular weight, 4×10^-3), and about 3:1 for the concentration of 8×10^-3N.The reaction of the poly(acrylic acid)s with calcium ions was affected by the molecular weight and concentration of the polyelectrolytes.The tensile bond strength of the polycarboxylate cements using poly (acrylic acid) with various mean molecular weights to stainless steel became maximum at a mean molecular weight of about 15×10⁴. The reduction in the strength of cements using a higher mean molecular weight polyelectrolyte may be due to the existence of unreacted carboxyl group in the cements.

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The sprue condition for dental casting is indispensable for casting and affects not only the castability but also the quality of the dental technician's work. The effects of the sprue condition on the castability of titanium casting were examined. Five different sprue diameters (0.88, 1.06, 1.26, 1.48 and 2.10mm) , two different sprue lengths (5 and 10mm) and two different patterns (mesh and plate) were used in this study. The castabilities of each sprue condition were measured by two different evaluation methods.With the mesh pattern, good casting was obtained when the sprue diameter was 2.10mm or greater. With the laminar pattern, good casting was obtained when the sprue diameter was 1.48mm or greater. With the mesh pattern and laminar pattern, the sprue diameter had a marked effect on the casting rate of titanium, but the effect of the sprue length varied widely. The use of two different castability evaluation methods enabled us to screen for more reliable casting methods with higher casting rates.

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We measured change in pH and in infrared spectra of reactants in dilute solution of PCA/CPC(polycalboxylic acid/calcium phosphate cement)cement in presence and absenced tartaric acid and/or stannous fluoride (0.25-0.5g/10-20mlH₂O) to investigate its setting reaction. Stannous fluoride inhibited the hardening of PCA/CPC cement and markedly delayed pH increase. Addition of tartaric acid induced no effect on pH curves. However, comparison of PCA/CPC cement containing tartaric acid and stannous fluoride with that containing only stannous fluoride revealed little evidence of presence of unreacted carboxyl groups in the hardened cement. The increase in the pH curve observed during the first stage was related to the reaction between the tartaric acid and calcium ions in CPC. At pH values over 4, the production of the calcium salt of polyacrylic acid was confirmed. A correlation was observed between the absorbance change due to carboxylate formation and increase in pH.

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The fundamental relationship between the hydrophilicity of rubber impression materials and the setting expansion of dental stones set in contact with the impression materials was examined using α -calcium sulfate hemihydrate, a commercial dental stone and twenty-two commercial rubber impression materials including condensation silicone, hydrophobic addition silicone, hydrophilic addition silicone, polysulfide, and polyether families. The contact angle of water on the sample of the impression material, the weight change of the sample of the impression material after immersion in water, and the dimensional change of the sample of the impression material in water were measured. Moreover, the setting expansion of the dental stone set on the sample of the impression material was recorded, and compared with the measured values. A very significant negative correlation was found between the contact angles and the setting expansions. On the other hand, neither the weight changes nor the dimensional changes correlated with the setting expansions significantly. The relationship between the hydrophilicity of rubber impression materials and the setting expansion of dental stones were examined in detail based on the obtained multiple-linear-regression equations and other results.

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Several experiments were carried out under small casting forces to study the relationship between the entrance velocity of molten titanium and the flow pattern in the mold cavity. When the spring of the centrifugal casting machine was wound up to 20 (the manufacture's instruction is 38) , the flow was turbulent and its pattern was analogous to that of 38winds, and when it was wound up to 10, a laminar flow was observed.When the pressure casting machine was operated with the pressure adjusted to 0.6kg/cm²(the manufacture's instruction, 1.1kg/cm²), the flow patterns were altered appreciably and pressure dependence of interanal defects varied with the position of the sprue. In addition, the influence of various conditions on the entrance velocity, such as casting force, was theoretically considered.

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As a method of determining the compatibility of the alginate impression material and the dental stone, the details of reproduced detail lines were examined, by supplementing the ISO 1563 determination standards. The reproduction of details was examined on the dental stone casts, which were produced by a combination of 4 kinds of commercial alginate impression materials and 9 kinds of commercial dental stones. The effectiveness of these new determination standards, along with the SEM image of the dental stone were studied. A more detailed evaluation was possible by the devised determination standards. Using different combinations of alginate impression material and dental stone, a desirable cast capable of reproducing detail lines of 20μm as well as a cast reproducing detail lines of 50μm partially could be obtained. The devised test for reproduction of details using a test block, which meets the requirements specified in ISO 1563, is appropriate as a method of determining the compatibility of the alginate impression material with the dental stone. An even more detailed study was found possible through determinations made using the devised evaluation standards.

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The purpose of this experiment was to examine trend of F, Zn, Sr and tannic acid on subsurface and the state of the surface of galss ionomer cement (GIC) containing 10% HY-agent (HY10) after immersion in distilled water for three months. To determine the amount of each element at the layers of the subsurface of GIC, using a Microkator, the layers of known thickness were serially removed by abrasion with a lapping film. Electron microprobe elemental analysis (EPMA) of F, Zn and Sr were also made in the X-ray concentration map. Furthermore, the surface of GIC discs was examined by scanning electron photomicrography(SEM). The F content decreased more and at a deeper region than those of Zn, Sr and tannic acid in the analysis of these elements on the subsurface of GIC discs. The analysis by EPMA showed the same tendency as that of their contents, and F and Sr accumulated together. In SEM the surface of the samples after immersion became rough with some deposit .On the other hand, the surface of the samples before immersion was smooth.Furthermore, the condition of roughness on the surface of HY10 was more severe than that of HY0 (control) . These findings suggested that F was released more easily from a deeper portion of the GIC discs than the others.

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Hardened PCA/CPC cement with and without tartaric acid and/or stannous fluoride was subjected to X-ray analysis after storage in three kinds of solutions (artificial saliva-like solution, phosphate buffer solution, and distilled water) , and amount of calcium, phosphate and fluoride ions released into the storage solution was measured. In distilled water, calcium and phosphate ions were continuously released from not only the PCA/CPC cement with tartaric acid and stannous fluoride but also from the cement without these additives. However, in artificial saliva and phosphate buffer solutions, release ceased after about one month and uptake of both ions was detected. X-ray analysis revealed the formation of fluoroapatite and hydroxyapatite in the hardened cement containing tartaric acid and stannous fluoride when it had been stored in artificial saliva or distilled water.Conversely, in the cement without these additives, only minor amount of apatite formation was observed, even when it was stored in distilled water for 6months.In addition, it was observed that fluoride ions were continuously released from the cement containing stannous fluoride for 6months.

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An experimental resin composite loaded with newly designed spherical silica filler particles approximately 1.0μm and 0.1μm in diameter categorlized into duo-spherical type was developed. Several properties of the resin composite as mechanical properties, linear contraction, chemical degradation in an alkakine solution, color change during irradiation, SEM observation of filler particles and set resin, and polishability were examined.In addition, a clinical trial with the resin was performed. As a result, the experimental resin composite exhibited superior properties to the resin composites on the market and the esthetic characteristic was favorable in the clinical use with a good polishability.

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Dentin primers containing N-methylolacrylamide (MEAA) or N-methylolmethacrylamide (MEMA) , which were soluble in water and were readily photopolymerized in the presence of inorganic salts such as ferric chloride, were prepared to improve the bond strength of lightcured composite resin to dentin etched with a 10-3 solution. The bond strength was significantly increased by using all dentin primers except for the dentin primer containing 10wt% MEMA. The dentin primers containing 50wt% MEAA and 30wt% MEMA gave a higher bond strength than the dentin primer containing 35wt% HEMA.Also, when treatment was with dentin primer containing 50wt% MEAA or 30wt% MEMA, the bond strength to dentin etched with 10-3 solution was comparable to that to dentin etched with 10wt% citric acid solution. The acid-proof dentin layers were about 1μm thick at the interface between all resins and dentin as observed by SEM. The SEM revealed that the specimens after shear bond tests had an acid-proof dentin layer cohesive fracture, resin cohesive fracture and dentin cohesive fracture.

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To investigate fluidity and hydrodynamic behavior of investment slurry, a fluidity testing apparatus was machined and constructed.The apparatus was consisted with the reservoir for investment slurry, 4 nozzles (0.60, 0.85, 1.05 and 1.20cm diameter with 4.00cm length) and the receptacle withen two electrodes for detecting the volume flow rate of the slurry. The flow rate of the slurry of the cristobalite investment were measured every 20ml to 100ml using 4 nozzles on each W/P ratio (0.33, 0.31, 0.29) . The average velocity was calculated from an average flow rate between 0 to 60ml. Flow rate measurement revealed the relatonship between the average velocity(v)of the slurry and diameter (d) of the nozzle used approximately by the Poiseuille equation in each W/P tested.This means that the flow of the investment slurry behave likely the Newtonian. The value of 32・l・v/d²(l=length of nozzle)indicated the fluidity of the investment slurry.Therefore, the fluidity of some investments can be evaluated by comparison with calculated values of 32・l・v/d² from obtained average velocity, diameters and length of nozzles used.

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The effect of immersion period in water on mechanical properties of photocured TEGDMA was studied to explain the relative lack of long-term adhesive durability of photocured TEGDMA bonding liner to dentin. The specimens, made of TEGDMA with NPG or EDMABA as a reducing agent, were immersed in water at 37℃ for 1 day to 1 year. Alteration of compressive strength and diametral tensile strength, and amount of water sorption, residual monomer and pendant double bond were measured. Compressive strength and diametral tensile strength decreased with increased immersion time due to water sorption.

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Twelve kinds of Ag-Pd-Cu ternary alloys, containing 25, 30, 35, 40wt% Pd and 15, 25, 30wt% Cu were melted and cast using dental precision casting. After solution 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 hear treatment, the tensile strength of the experimental alloys, ranged from 39〜57kgf/mm² and the elongation ranget from 14〜28%, while after herdening heat treatment, they ranged from 66〜107kgf/mm², 1〜7%, respectively.After hardening heat treatment, the estimated composition showing the maximum tensile strength was about 34〜35Pd-20Cu-45〜46Ag and the estimated strength was 104±3kgf/mm². After softening heat treatment, the Vickers hardness number(VHN)was 141〜200, and after herdening heat treatment VHN was 241〜431. VHN increased with increasing Pd and Cu contents. The brightness(L^*)of the specimens immersed in 0.1% sodium sulfide solution at 37℃ for 3 days, was 60〜67 and their tarnishing resistance was improved with increasing Pd content and decreasing Cu content.

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We report the development of an air turbine handpiece, using the plastic turbine blade for the realization of disposable dental handpieces. Their rotational properties were investigated to examine their clinical usefulness. The speed achieved with the handpiece using a plastic turbine blade was about 90% of that using an aluminum turbine blade and stopping torque was by no means inferior to the aluminum blade. Moreover, the rotational response time of the handpiece using a plastic turbine blade was shorter than that using an alminum turbine blade. Thus the plastic turbine blade was considered applicable to dental handpieces.

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Copolymers of butyl methacrylate (BMA) and ethyl methacrylate (EMA) having different molecular weights were synthesized by suspension polymerization. These polymer powders and a liquid of butyl phthalyl butyl glycolate were used. The storage modulus G', dynamic viscosity η' and loss tangent tan δ of a mixture of powder and liquid were determined over the frequency range of 0.05 to 70Hz at different temperatures. The master curves of G', η' and tanδ were constructed from the data obtained at different temperatures. Marked effects of the molecular weight of polymer on G' and tanδ were observed at the low frequency range.G' of a material containing PBMA was smaller than that of a conventional material using PEMA, because the long side chain in PBMA acts as an internal plasticizer. The tanδ of PBMA was smaller than that of PEMA in the high frequency range, but was raversed in the low frequency range. These properties are an advantage, because new materials are soft and flexible compared with conventional materials which become hard and stiff with time.More desirable properties for tissue conditioners should be attainable by controlling the composition of BMA and EMA, and molecular weight of the copolymers.

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The effect of filler particle size (average particle size:0.04, 0.3, 0.5, 1.0, 1, 6, 3.9 and 5.7μm) on the cure depth of the experimental BisGMA-based light-cured composites filled with different types of silica fillers was investigated. The cure depth of these composites increased with increasing light exposure time. The composites filled with 0.3, 0.5 and 1.0μm fillers showed lower cure depth than those filled with other fillers. For splinter-shaped fillers (1.6, 3.9 and 5.7μm) , cure depth increased with filler particle size.

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A micro-particle filler of cross-linked polymer was prepared, to make a one-paste type crown-bridge resin. It is difficult to make the micor particle filler using suspension polymerization, because of the high viscosity of dimethacrylate. When benzoylperoxide and N, N-dimethyl-p-toluidine were added to the ethanol solution involviong dimethacrylate, solution polymerization occurred at room temperature and the micro-particles were precipitated. The effect of amount of dimethacrylate in ethanol solution on the time to start the precipitation of polymer was investigated. The inverse number of the time increased in proportion to amount of monomer. A trial resin was prepared using a mixing filler between the cross-linked polymer particle the diameter of which was 0.5μm and the micro silica particle and the abrasion test was done. The abrasion loss was low when the mixing filler was applied as a filler.

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A novel organic composite filler was prepared by the redox polymerization (BPO-amine system) of dimethacrylates in an ethanol-water solution in the presence of a colloidal silica filler (MF) , and the mechanical properties of the composite resin which contained the novel filler were examined. The homogeneous polymerization solution became heterogeneous up on the addition of water, and the monomers formed particles the surface of which was covered with MF particles and then polymerization occurred. The obtained particles were micorcapsule particles (MCP) containing 15-90wt% MF and having a diameter of 0.6-13μm.Composite resins containing the MCP or the mixed filler of MF and MCP were prepared, and their mechanical propertieswere investigated. The transverse strength of the composite resin containing 55wt% of MCP (MF content:15-80wt%) was about 100MPa. The transverse strength was lower than 100MPa, when the content of MCP (MF content:80wt%) was over 50vol%. The composite resin containing the mixed filler of MF and MCP, showed the maximum mechanical properties when it contained 70wt% mixed filler the MF content of which was 40-75vol%. Thus, the transverse strength was above 120MPa, the maximum bending attained the maximum value, the elastic modulus was around 7000MPa, and Rockwell hardness(30W)was above 60.

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