The effects of the addition of hydrochloric acid to a silane solution on the adsorption behavior of silane onto the silica surface and the hydrolytic stability of the silane at the interface between silica and the polymeric resin were investigated as a function of the silane concentration.The adsorption aspect of silane under a non-acidic condition differed from that under an acidic condition, because the molecular species of the chemisorbed and physisorbed silanes onto silica under a non-acidic condition were different from those under an acidic condition.The hydrolytic stability of the silane-layer at the interface was strongly dependenet on the aspect of the adsorption of silane onto the silica.Thus, silane forms a more stable multi-layer on the silica surface under a non-acidic condition than under the acidic condition in water.

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The effectiveness of various dentin primers on the adhesion between the composite resin and polished dentin without pretreatment was investigated.As the main components of dentin primers, methacryloyl tyrosine amide(MTYA)and glyceryl methacrylate(GM)were used.Fresh bovine dentin was prepared by grinding with #800 and #1000 stones under running water and then treated with each kind of dentin priner for 60s.Then Clearfil New bond^® and Clearfil F II^® were applied onto the primed surface.The tensile bond strength between the composite resin and dentin was measured after one day immersion in 37℃ water.The dentin primer MTYA・GM(3% MTYA+35% GM aqueous solution)treatment gave the mean bond strength of 8MPa, and MTYA・G・GM(A:6% MTYA+70% GM aqueous solution, B:2% glutaraldehyde aqueous solution)treatment that of 11MPa.When succinic acid was added to the B part of MTYA・GM and MTYA・G・GM at the concentration of 3%, a high bond strength was obtained by a 10-min application and 5-to 10-min application to the dentin, respectively.The dentin primer MTYA・G・GM・S3(A:6% MTYA+70% GM aqueous solution, B:3% succinic acid+2% glutaraldehyde aqueous solution), gave a mean bond strength of 13MPa by a 30s scrubbing.

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A polymerizable thiobarbituric acid, 5-(4-vinylbenzyl)-2-thiobarbituric acid(5VS), was synthesized to evaluate its application to dental materials.The polymerization behavior of triethyleneglycol dimethacrylate(3G)was studied using a dl-camphorquinone(CQ)-5VS visible-light initiator system.Visible-light polymerization of the experimental resin was carried out in DSC at 37℃ for 5min.Time at maximum exothermic peak, maximum exothermic rate and rate of insufficiently polymerized layer were determined.The utility of the CQ-5VS initiator system in visible-light polymerization was evaluated from these determinations and the measurement of the depth of cure after the irradiation for 1 or 2min.Determination of the adhesive strength of MMA-PMMA/TBBO resin to noble metal alloys treated with 5VS revealed that 5VS was a useful monomer for surface treatment.MMA was, further polymerized with AIBN at 70℃ in the presence of 5VS to elucidate the effect of 5VS on the polymerization reaction.Time at maximum exothermic peak and maximum exothermic rate were determined from DSC thermograms.The induction period and initial rate of polymerization were derived from the time-conversion curve.The influence of 5VS was discussed.

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The effects of the temperature to sinter the microfiller and the sintered filler on the physical properties of the restorative resin prepared with the sintered filler were examined.The comparison was made with a restorative resin produced using an unsintered microfiller.The experiment was begun by mixing four types of fillers into urethane dimethacrylate used as the base monomer.The four types of fillers were one unsintered and three sintered at 1000, 1100 and 1200℃.Then, to examine the physical properties of the restorative resin, the restorative resin pastes with different types of fillers mixed into them were polymerized by heat-curing and the compressive strength, compressive yield strength, transverse strength, transverse elastic modulus, hardness, water sorption and brush abrasion ratio, of the resultant polymers were measured.The restorative resin prepared using the filler sintered at 1100℃, had enhanced compressive yield strength and hardness, and reduced water sorption, compared to that prepared unsintered filler.

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The early tensile bond strength of dual cured resin luting cements for composite inlays to bovine enamel and dentin was evaluated.The bond strength was high for all materials tested on enamel, but extremely low on dentin.To increase the bond strength to dentin, bonding systems used for direct fillings were tested prior to the application of the resin cement.A considerable increase in the bond strength was found.The bond strength of CR Inlay resin cement was greatly increased when a new bonding system, Liner Bond, was used to"protect"the dentin surface prior to"luting"with the resin cement for the bond test.

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To study the effect and the water-resistance of silane coupling agents having various organofunctional and hydrolyzable groups, the tensile bond strength of acrylic resin to glass plate treated with the silanes was measured.The silanes used were 3-methacryloxypropyl-trialkoxysilane(3-MPS), -triisocyanatosilane(3-MPSN), -trichlorosilane(3-MPSC₃), -methyldichlorosilane(3-MPSC₂), -dimethylchlorosilane(3-MPSC₁), Vinyl-trialkoxysilane(VS), -triisocyanatosilane(VSN), and-trichlorosilane(VSC).Treatment of 3-MPSC₃, 3-MPSN, VSC and VSN, which have three active hydrolyzable groups, showed a good effect and water-resistance.The tensile bond strength of the resin to glass plates treated with 3-MPS, 3-MPSC₁ and 3-MPSC₂ were similar to that of 3-MPSC₃ after immersion in water at 37℃ for 60 days, but decreased after 2000 thermal cycles between a 4℃ and 60℃ water bath for 1 minute at each temperature.VS showed no effect.In spite of the difference of the organofunctional groups, the silanes having three active hydrolyzable groups showed better water-resistant adhesion, and the substitution of the hydrolyzable group to hydrophobic group on silicon decreased the effect of the treatment and the water-resistance.

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To study the thermal properties of tooth adhesive resin cement, we used two currently available resin cements(Super Bond C & B:SPB and Panavia EX:PAN), both of which are often used for clinical trials.The experiments were made following a xenon flash thermal constant measuring device and performed under the condition of P/L ratio of 0.8, 1.0 and 1.2(P/L=1.0:manufacturer's instruction).The rate of thermal diffusivity(×10^-2cm²s^-1)of SPB was between 0.092 and 0.103 and the rate of PAN was between 0.393 and 0.474.The specific thermal capacity(Jg^-1K^-1)of SPB was between 1.787 and 2.059 and that of PAN was 0.786-0.830.The thermal conductivity(Wm^-1K^-1)of SPB was 0.213-0.221 and that of PAN was 0.657 and 0.799.The thermal conductivity of SPB was not affected by the P/L ratio.While, the thermal conductivity of the PAN decreased with a decrease of P/L ratio.The thermal conductivity of SPB was lower and that of PAN was higher than that of human dentin.

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About 70% of the restorations are made to replace previous restorations.Secondary caries was the main reason for replacement of amalgam fillings, and poor marginal adaptation(ditching/leakage)and isthmus fracture(bulk fracture)were another reason.Poor marginal adaptation was considered to be the cause of secondary caries.The mechanism of marginal fracture of amalgam fillings has been studied by many workers.In this study, the axi-symmetric elastic creep finite element method was applied to simulate the development of the marginal gap and ditch at the interface of the amalgam and tooth.Here, the occlusal force was assumed loaded on the amalgam fillings with creep and vertical direction to the axis of the tooth.The gap and ditch were developed proportionally with the creep value of the amalgam(American Dental Association specification no.1)and proportionally square of the occlusal force.From the estimation of the service life of the restoration, it was concluded that the poor adaptation at the margin can be seen in 4-to-10-year old amalgam fillings when the amalgam with a high creep value was used or high chewing force was loaded on the fillings.This is consistent with the clinical findings reported.

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Machinability of high-strength glass-ceramics containing a large amount of fine calcium mica crystals was evaluated using conventional dental tools for dental prosthetic application in our CAD/CAM system.The glass-ceramics have excellent mechanical properties, i.e., high bending strength(～300MPa)and good hardness equivalent to a natural tooth enamel.These glass-ceramics were easy to machine using dental tools, such as diamond, carbide, and carborandom bars.In terms of chipping and ease of machining, the rotation speed shoud be<2, 500rpm under a machining condition in air, while, in flowing water, a speed of less than 20, 000rpm could be used.The machinability reveals that the glass-ceramics are appropriate material for the dental CAD/CAM system.

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Sulfide-containing monomer, 10-(methylthio)decyl methacrylate(MTD), was utilized for the chemical treatment of various metals to improve the adhesion of resin to them.Three agents for chemical treatments were prepared by dissolving 1mole% of MTD in either MMA, ethanol or 1, 4-dioxane.Various treatments such as(1)polishing and cleaning, (2)MTD treatment, and(3)immersion in water at 60℃ were given to the metals.The tensile adhesive strength between the treated metal and MMA-PMMA/TBBO resin was measured after 2000 times of thermal cycling in water.The contact angle of water on the metal surface was also determined after various treatments.The tensile test revealed that the chemical treatment with MTD improved adhesive strength of resin to noble metal alloys.The contact angle on the metal surface treated with MTD increased by the subsequent treatment(3)except for the Ag alloy, which indicated the desorption of MTD and the lack of long-term stability of adhesion.The adhesive strength was highly correlated to the extent of cohesive failure, but did not depend on the thickness of adhesive resin.These findings suggest that the chemical treatment with MTD is applicable to noble metal alloys to enhance adhesive strength, but that the treatment should be further modified for the long-term durability against water penetration.

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New experimental resins for denture liner were prepared and evaluated.The materials composed of methyl methacrylate(MMA)and vinylidene fluoride/hexafluoropropylene copolymer(2-6F), or vinylidene fluoride/tetrafluoroethylene/hexafluoropropylene copolymer(2-4-6F)were polymerized by visible light curing and cold curing and compared with 3commercial materials by water and oil sorption tests, thermomechanical analysis(TMA)and cytotoxity test.Water sorption and solubility were smaller in the materials containing 2-6F than in those 2-4-6F, and smaller in the light-cured materials containing 2-6F than in the cold-cured materials.The light-cured materials from 2-6F showed less water sorption and lower solubility than the commercial lining materials studied, and very little oil sorption.TMA showed that the glass transition temperature(T_g)of the new materials was slightly lower and that their stiffness was approximately the same when compared with the commercial materials.Cell growth was not inhibited by the materials which implied their low toxic nature.Overall, the new experimental light-cured materials containing 2-6F seem to have suitable properties for a denture liner, and would be worth applying to practical use.

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Photocure bonding resins to smear layer retained dentin were studied.The most effective photocure bonding resin among those studied was composed of 0.5% camphorquinone, 0.5% N-phenylglycine, 5.0% 2-methacryloyloxyethyl phenyl hydrogen phosphate(Phenyl-P)in triethyleneglycol dimethacrylate.Tensile bond strength after immersion in 37℃ water for 1 day was 6MPa, but that after water immersion for 1 year, decreased to 3MPa, because a sufficient amount of monomers could not diffuse into the intact dentin through the smear layer.Suitable pretreatments were considered to improve permeability of smear layer retained dentin.Experimental pretreatments were composed of aqueous mixtures of phosphoric acid or phosphoric methacrylates in 30% 2-hydroxyethyl methacrylate(HEMA).Phosphoric methacrylates were 2-methacryloyloxyethyl dihydrogen phosphate(Phosmer-M), 10-methacryloyloxydecyl dihydrogen phosphate(MDP)and Phenyl-P.Bovine dentin samples were ground with 600 grid Carbimet paper discs(Buehler, USA)and subjected to one of the experimental pretreatments.Pretreated with an aqueous mixture of 5 or 10% Phenyl-P in 30% HEMA, hybrid layer was demonstrated, but bond strength did not increase.Because the hybrid layer was thinner than 1μm and monomers could not diffuse into intact dentin.On the other hand, the bond strength was increased to 10MPa and hybrid layer was demonstrated on SEM and TEM by an aqueous mixture of 20, 30 or 40% Phenyl-P in 30% HEMA pretreatment.The hybrid layer improving tensile bond strength was thicker than 2μm from the adhesive interface.These findings indicate that 1μm hybrid layer was created with a smear layer and the 2μm was created with both smear layer and intact dentin.The smear layer hybrid is not so strong as the intact dentin one at the same resin concentration.

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Dental handpieces, which are vital cutting devices in dentistry of today, are manually controlled by dentists and cutting accuracy depend on their preparation technique.To improve the cutting accuracy of prepared teeth, I have examined a new computer-assisted dental cutting system using automatic control technology.The system is composed of a special dental handpiece equipped with movable head and actuators, a noncontacting parallelometer, and a computer which controls the whole system.Unlike the conventional paralleling instruments, the handpiece is not fastened mechanically but the tilt of cutting tool is automatically controlled by the computer so that it will stay parallel to the fixed axis.The step response of the experimental system was tested to determine the proper gain for automatic control.An error of 5° in tilt of tool will be corrected in about a second.Then the system was applied to cut the dental model by four operators and axial taper angles of prepared teeth were measured.The mean value of the taper angles attained by the system was reduced 3〜4° compared to that of the manual control and the parallelism of prepared teeth was improved.These findings lead to the conclusion that computer-assisted dental cutting is an effective approach to improve cutting accuracy.

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The influence of the specimen length and the filler shape in composite resin and their affect on linear shrinkage was investigated.The amount of linear shrinkage that occurred during the hardening process linearly increased by increasing the length of the specimen.The percent of linear shrinkage was very large when the length of the specimen was less than 5mm.However, the shrinkage became constant with values of approximately 0.8% to 1.2%, when the length of the specimen was more than 5mm.Because the shrinkage in both the width and depth directions was restricted by the block, in the case of a short specimen, the composite resin adhered to the aluminum block.However, when the length was more than 5mm, the shrinkage occurred equally in all directions.This was because the restriction on the shrinkage decreased.Further more, these findings were in agreement with those obtained from the finite element analysis.

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A composite resin produced by way of trial, with various ratios of microfiller(MF)and, irregular, spherical, polimerized spherical, and glass particle macro filler, was measured the shrinking stress during hardening after filling in the open type cavity.The shrinking stress was increased with higher mixing filler ratio.For the effects of various filler, the irregular particle filler contained resin with a higher filler ratio showed the maximum shrinking stress.Depressions were observed at the central area of all specimens the surface profile after hardening.The shrinkage increased with decreasing filler ratios, which was in proportion to the volumetric ratio of monomer, and no difference was seen among these sorts of fillers.The shrinking stress as well as volumetric and linear shrinkage for the enamel bond should be examined clinically, because the shrinking stress was in inverse proportion to the volumetric shrinkage.

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As a part of study on primer used for dentin adhesion, seven kinds of methacrylate monomers shown in Fig.1, having a pyrrolidone ring or acetamide group as a hydrophilic moiety, were prepared and studied for their hydrophilicity by measuring the partition coefficient in octhanol/water, their cytotoxicity by the cell culture method and their effect on adhesion between the MMA/PMMA-TBBO resin and dentin.The partition coefficient of the monomers was 2.6〜20.5, which was similar to the value corresponding to 2-hydroxyethyl methacrylate(HEMA)and MMA.The cytotoxicity of the monomers increased in the following order:(MMA)<MEP<MPP, (HEMA)<MMEA<MBP<MEMP<MPeP<MMPP<MEA.MEP was less cytotoxic than HEMA.Some monomers, when used as a primer, were considerably effective in improving the bond strength between dentin and the resin.Maximum bond strength of 18.2MPa was obtained in an aqueous MPP primer in comparison with control value of 9.4MPa.There was some correlation between the bond strength and partition coefficient of the monomer used for pimer and that monomer with a partition coefficient of 5〜9 was suitable for the adhesion.

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The previous reports showed the superiority of pure Ti and Ti-6Al-4V alloy as the prefabricated post materials by mechanical and 24-hour cytotoxicity tests.In this study, further long-term L-cell growth inhibition test was preformed on these posts and conventional prefabricated Ni-Cr and 18-8 stainless steel posts.The cells were cultured with MEM solution in which the post had been immersed for some specified periods up to 1 month.With Ag alloy core being cast onto the post, the cell growth was markedly inhibited by the significantly accelerated dissolution of the constituent elements from Ni-Cr alloy and stainless steel through the 1-month immersion.However, pure Ti and Ti-6Al-4V alloy showed no inhibition of the cell growth themselves even when Ag alloy core was cast onto them.

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The relaxation modulus in shear{Gγ(10)}of set six soft lining materials was measured in the temperature range from -150℃ to 150℃, using a stress relaxation apparatus and the dependence of the relaxatuin modulus in shear on the temperature was investigated.In addition, the glaas transition temperature(Tg)of each material was determined, and the viscoelastic properties in the temperature range of 4℃ to 60℃ were discussed.The glass transition temperature of all set materials was observed in the temperature range, -55℃〜-18℃.The relaxation modulus in shear of all materials except silicone materials, decreased from 9.3% to 39.5% between 23℃ and 37℃.In the case of silicone materials, the decrease of the relaxation modulus in shear was not quite seen.The highest value of the relaxation modulus in shear at 37℃ was obtained in olefine materials and its value decreased in the order of silicone, fluoro and acrylic materials.

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A new flexible pressure sensor with a pressure sensitive rubber has been developed to fit and measure closely the three-dimensionally complicated structure.By application of the fine coil shaped leading wires, we gave the sensor the characteristics of flexibility.The sensor has a hysteresis phenomena produced from the pressure sensitive rubber;the calibration curves of the pressure increasing and the pressure decreasing do not fit each other.Since each curve showed good reproducibility, the sensor was considered to have a high reliance.To confirm the usefulness of the pressure sensor, we applied it to the temporomandibular-joint model to measure the pressure distribution on the condyle head during clenching.

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Effects of diluted phosphoric acid etching on the adhesion of 4-META/MMA-TBB resin to enamel were investigated.The thermal cycling test was used for the evaluation of adhesive stability.After 30 sec etching with 3wt% phosphoric acid and 5wt% phosphoric acid, the adhesion of the resin to enamel was tested by application of 200 thermal cycles.The tensile bond strength in each diluted phosphoric acid solution was 8.1MPa and 9.3MPa, respectively.These tensile bond strength values were found to be the same as that of 65wt% phosphoric acid etching.Moreover, resin tags were found and no crack in the interface area by SEM, in the case of use of more than 1wt% phosphoric acid.Etching with diluted phosphoric acid was effective in adhesion of 4-META/MMA-TBB resin to enamel.

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Effectiveness of BPDM dissolved in MMA-TBB resin to develop an adhesive bond to bovine dentin pretreated with 10-3 was studied.BPDM is a methacrylate with aromatic carboxylic acid as does 4-META which is a good monomer to improve the bonding.The highest bond strength, 14MPa, was attained with 2% BPDM/MMA-TBB resin among studied.It promoted diffusion of monomers into demineralized dentin and a hybrid layer was created in the subsurface of dentin in the presence of BPDM.The hybird layer prepared by 2% BPDM/MMA-TBB resin showed the highest resistance against degradation with NaOCl immersion.The thickness of the hybrid layer and the resin content were decreased by increasing the concentration above 2% as rate of polymerization which was measured with DSC was increased as it is a dimethacrylate like TEGDMA.TEM examination revealed that the bonding durability of BPDM/MMA-TBB resin might be inferior to that of the 4-META adhesive because collagen in the hybrid layer was more stainable.

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The bond strength of resin to dentin and the stability are influenced by diffusion rate of monomers into dentin, and their polymerization in situ.The diffusion rate of monomers is changed with the permeability of dentin and diffusibility of monomers.Dimethyl sulfoxide can improve the permeability of skin.Polymerizable dialkyl sulfoxide, 2-methacryloyloxyethyl methyl sulfoxide(MEMSO)was effective in improving the permeability of demineralized dentin whose collagen had been shrunk during the removal of the smear layer by pre-treatment with 10% citric acid and air blow.Then monomers could diffuse into dentin.The scanning electron microscopic examination demonstrated the formation of a"hybrid"layer by addition of MEMSO treatment.This"hybrid"layer was essential for higher tensile bond strength to be attained.

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