Twelve aliphatic methacrylates with a carboxylic group[succinate(2MES, 5MPeS and 10MDS), methylsuccinate(2MEMS, 5MPeMS and 10MDMS), maleate(2MEM, 5MPeM and 10MDM)and citraconate(2MEC, 5MPeC and 10MDC)]were synthesized by the addition of four dicarboxylic acid anhydrides to each of three different alkylene chain length hydroxy methacrylates to investigate the relationship between the methacrylate structure and its bonding to tooth.The bond strenght of methacrylates to polished tooth surface decreased with increasing alkylene chain lengths under dry conditions, but water immersion reduced this change.The bond strength of succinate and maleate to polished tooth surface was higher than that of methylsuccinate and citraconate under dry conditions.All methacrylates showed high bond strength to etched enamel, with maleate showing the highest bond strength.On the other hand, the bond strength of 2MEM and 5MPeM to etched dentin was markedly high, and about 5μm thick resin reinforced dentin at the interface between etched dentin and resin(2MEM or 5MPeM)was observed by SEM and EPMA analysis.

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Dissolution of eight silver-based alloys for small casting was investigated under dynamic conditions that accelerated abrasive particle wear.The extract was separated into filtrate and sediment with a 0.22μm cellulose acetate filter and added to cell culture to study cytotoxicity.Dissolution of silver exhibited the highest dissolution into the extract in the alloys tested.Tin was eluted from six alloys, and indium from five alloys.Following filtration with a 0.22μm filter, silver, tin and indium were not detected in the filtrate.Zinc was also eluted from all of the alloys, ranging from 5.073ppm to 29.52ppm.The amount of zinc in the filtrate was one fifth to tenth of that of the extract.Copper was eluted from two alloys.The amounts of copper in the filtrate and extract were similar.The extract was most cytotoxic, while the filtrate was also cytotoxic except for after one day extraction.The present results demonstrate that extraction under dynamic conditions appears to be useful for investigation of metal corrosion and cytotoxicity in vitro.

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The quantities of in vitro accumulated plaque(S.mutans), cultured in 5% sucrose BHI broth, to the surface of PMMA, Co-Cr alloy, porcelain, PTFE, PCTFE, Composite PCTFE, and detachment time as an indicator of plaque retaining capacity, were measured.The former increased with the increase in surface roughness on all materials, except for the Co-Cr alloy, and with contact angles, which suggests that hydrophobic interaction may play an important role for formation of plaque on materials.By contrast, the quantities of accumulated plaque, cultured in 5% sucrose BHI broth containing synthetic saliva constituents, to the surface of various materials, also increased with the increase in surface roughness, but decreased with values of contact angles, which suggest that the effect of hydrophobic interaction on forming plaque to materials seems to be weakened by constituents of synthetic saliva.

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Studies were done to improve the physical properties, especially degree of conversion of visible-light cured resin(VLCR), and accordingly to lower its water sorption and solubility in water.Trial products of VLCR were prepared using various kinds of amine, reducing agent, and the photoinitiator to be mixed with cyclophosphazene monomer, 4PN-(TF)_1-(EMA)_7.As amines ethyl-p-dimethylaminobenzoate(DMAB), methacryloxyethyl-p-dimethylaminobenzoate(DMAB-EMA)and methacryloxyglycidyl-p-dimethylaminobenzoate(DMAB-GMA)were used.Of their set products immersed in water and MeOH, their water sorption, solubility in water, MeOH sorption and solubility in MeOH were examined.The resin with DMAB-EMA used was preferable, showing comparatively small solubility.Next, VLCR, with various amounts of DMAB-EMA mixed, 0.5〜5.0 in mol ratio to photosensitizer(CQ+DB), and of their set products water sorption, solubility in water, MeOH sorption, solubility in MeOH, THF sorption and their mechanical properties after immersion in water were examined.Immersion of the resin products in water and MeOHfor 30 days, lowered the Solubility in water and MeOH to a minimum at the mixing ratio of 3.0 in mol ratio.solubility in MeOH(HPLC)became minimum at 2.0 in mol ratio, and at less than 2.0, the photosensitizer and monomer were dissolved, while at more than 2, 0, the photosensitizer and DMAB-EMA were dissolved.THF sorption decreased in accordance with the increase in the mixed amount of DMAB-EMA, became almost constant at more than 3.0 in mol ratio.The compressive strength of set product after immersion in water for 7 days increased in accordance with the increase of the mixed amount of DMAB-EMA, while the transverse strength also increased up to 2.0 in mol ratio.The optimum reducing agent to be mixed with VLCR was DMAB-EMA, and the mixing ratio should be 2.0〜3.0 in mol ratio to photosensitizer.

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The fatal demerit of resin materials which causes a marginal sealing defect or marginal fracture is hard to eliminate.A series of studies seeking for dental resin for restoration having no polymerization shrinkage, applying polyester resin used as base resin.This study was conducted to promote the improvement of composite resin, in which the author examined the composition with catalyst, accelerator and subaccelerator having preferable working time, setting time and peak temperature which is not clear, so as to obtain the fundamental data.In accordance with the increase in the amount of catalyst, accelerator and subaccelerator added, peak temperature showed a tendency to increase.Contrarily, working time and setting time showed a tendency to decrease.The composition showing preferable working time, setting time and peak temperature, is as follows:to the base resin, polyester with 38wt% of shrinkage inhibitor mixed, catalyst by 1.0wt%, accelerator by 0.50wt% and subaccelerator by 0.02wt% were added.The trial product of composite resin a 70wt% of surface-treated glass beads added showed a working time of 2.3 minutes, setting time of 9 minutes and peak temperature of 57.0℃, approximately the same values as of commercial composite resin.

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A graft polymerization of MMA onto silk was carried out under several conditions and the relationship between the grafting and the bond strength to dentin was compared in the case of a MMA-TBB resin.Phosphoric acid, EDTA5-0 and EDTA3-2 pretreatments to silk decreased the degree of grafting.On the other hand, 10-3 pretreatment increased it.The canformation of silk peptides was changed by the pretreatments and it was responsible for the diffusion of MMA and sites of grafting.Ferric ion absorbed on the silk enhanced the graft polymerization of MMA.Pretreatment which gave higher grafting onto silk did not always promote the bond strength to the dentin pretreated by the same pretreatments.We concluded that the graft polymerization of MMA on collagen was not necessary for the adhesion of resin to dentin.

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The fracture toughness (K_IC) of human enamel was examined by means of Indentation Microfracture Method(IM method).The IM method was a simple, efficient and economical means to obtain K_IC of human enamel.Judging from the relationship betweet load and crack size, a median crack occurred in the range of 2.45〜5.88N, and _IC was hardly affected by the difference of surface roughness.K_IC of a 58-year-old man's teeth was 0.61MPam^1/2 in |1 and 0.77MPam^1/2 in |7 and the difference was ignificant(P<0.01).K_IC differed much from the direction of the sindenter pressed to enamel rods and the K_IC of the direction of enamel rods axis I was markedly higher than that of others.In the 58-year-old man's |1, K_IC was 0.61MPam^1/2 in the direction of enamel rods axis V, 0.66MPam^1/2 in the direction of H and 0.84MPam^1/2 in the direction of I, and the difference was significant(P<0.01).The values for a 10-year-old man's permanent teeth was slightly higher but showed a similar inclination to the 58-yer-old man's teeth.

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The possibility of dental application of Ti-Ni shape memory alloys was examined.To determine whether this material which is difficult to be machined could be processed by the electric discharge machining method(E.D.M.), the E.D.M.characterisbics of this material were investigated.Trial straight-slit type posts were made by this material under an appropriate electric condition.The term of yield strength, retention force after cementing, and pressure of post when into a root canal filled unset cement were investigated.Ti-Ni shape memory alloy could be processed without a loss of shape memory effect by E.D.M.Hardenning layer in the machined surface was observed by both Ram-type and Wire-type E.D.M., but a thinner hardening layer was observed by the latter method.The retention force after cementing of the trial straight-slit type post were the same or stronger than those of posts on the market.Especially, the dependence for the post's length on this strength was not strong in the trial posts.The pressure produced by inserting the trial post into the root canal filled with unset cement was very low compared with those of posts on the market.The trial straight-slit type posts made of Ti-Ni shape memory alloy may be useful for dental application.

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The purpose of this study is to clarify a cause of disintegration of composite resins by long-term immersion in distilled water.Three kinds of visible light-cured composite resins(Heliosit, Plurafil Super and Visio Dispers)and one conventional composite resin(Clearfil F II)were prepared as the specimens with a 20mm diameter and 1mm thickness.These specimens were immersed in distilled water at 37±1℃ for 3 years.These specimens were analysed and observed by a comprehensive multi analyzer and scanning electron microscope.The other hand residues in distilled water were analysed by infrared(IR)and nuclear magnetic resonance(NMR)spectrometers.The surface layer of all four composite resins showed signs of disintegration.The composite resins with abundant dissolved substances had disintegrated markedly, and such disintegration occurred deep inside the specimens.In IR and 1H-NMR spectra of dissolved substances, two visible light-cured composite resins(Heliosit and Plurafil Super)could be detected unreacted monomers, but one visible light-cured composite resin(Visio Dispers)and one conventional composite resin(Clearfil F II)could not be detected them.In 1H-NMR spectra of dissolved substances of all four composite resins, new signals not composed originally were observed.The progress of disintegration were demonstrated clearly.The dissolved substances were shown as the disintegrated substance between resin matrixs and silane coupling agents.It is suggested that the disintegration of composite resins by long-term water immersion is derived from hydrolysis.

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As a model experiment to understand the mechanism of adhesion of the MMA/TBBO resin to dentin, polymerization of MMA/TBBO was investigated in the presence of a collagen sheet treated with the aqueous citric acid(CA)solutions of copper fluoride(CF), ferric fluoride(FF), or ferric chloride(FC), which is usually used as a treating agent in bonding of the resin to dentin.The curing time of MMA/TBBO resin was considerably reduced in the presence of collagen treated with CF-CA or FF-CA solutions when compared to that with FC-CA solution.Molecular weight of PMMA depended on the site of polymerization;PMMA polymerized inside the collagen sheet was the highest and that polymerized outside was the lowest.Bond strength to dentin treated with CF-CA, FF-CA solutions was as strong as that treated with FC-CA solution.Treatment of dentin with CF-CA or FF-CA was as effective as that with FC-CA in bonding the MMA/TBBO resin.These results suggested that ferric compounds adsorbed to collagen are involved in polymerization of MMA and thus influence bond strength of the MMA/TBBO resin to dentin.

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A preform compression molding method to make a polysulfone denture has been reported.Retentive strength of artificial teeth to the denture base was examined to select artificial teeth for the compression molding method.Ceramic teeth with metal pins and polysulfone teeth heated at above 140℃ were retained to the denture base by useful retentive strength.Acrylic teeth on which the adhesive was used were also retained by useful strength.Each of the teeth, acrylic teeth, ceramic teeth and polysulfone teeth, could be used in the compression molding method.

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Vibrant load is known to be effective to thin the film thickness of various luting cements.In this study, a vibrator which can change various conditions such as frequency, form of wave were made, and the changes of viscosity, film thickness and bond strength were tested statistically.Furthermore, the most effective condition for the slurry of some luting cements(i.e.domestic two zinc phospate cements, one polycarboxylate cement and one glass ionomer cement)were investigated.The results obtained were as follows.1)When vibrant load was applied to the slurry of cement in the setting process, the rise in viscosity was apt to be slower than the same case of static load.2)The effect of vibration appears in the early sixty seconds especially, and the effect varied with the kind of cement, frequency or form of wave.3)Vibration was also effective for the increase of compressive strength and of bond strength.

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Distribution of diamond grain size of seven fine finishing diamond points was measured by a digital image analyzer.Also influence of diamond grain size of fine finishing diamond points on finished surface of two types of visible light cured composite resins(semihybrid type and submicron filler type)were investigated.Diamond grain size was almost from 10 to 100μm² in area.Diamond grain size was closely related to the surface roughness of semihybrid type composite resin, although it was not related to that of submicron filler type composite resin.Surface roughness of a submicron filler type composite resin finished at a low speed was less than that at a high speed.Grain size of diamond point and revolution speed may play an important role in surface texture of composite resin.

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Several problems associated with mateirals and clinical techniques are pointed out for posterior composite resin restoration.One of the solutions to these problems is the application of the indirect composite resin inlays.Three kinds of products for composite resin inlay are being marketed at present.We examined the mechanical properties, surface roughness and rediopacity for each product.Inlay/Onlay(Ivoclar), Brilliant D.I.(Coltene)and CR Inlay(Kuraray)were used in this study, and composite resin inlays were fabricated in accordance with the manufacturers' instructions.The highest values of mechanical properties after immersion in water for 24 hours are shown below:-Compressive strength:Inlay/Onlay……4350kg/cm²-Tensile strength:CR Inlay……668kg/cm²-Transverse strength:CR Inlay……1589kg/cm²-Hardness(K.H.N.):CR Inlay……104.4 The mechanical properties of the composite resin inlay, subjected to thermal cycling at 4℃ and 60℃ for 3 minutes each for 5,000 cycles, tended to decrease in comparison with those immersed in water for 24 hours.Inlay/Onlay showed the smallest surface roughness(Ra), i.e.the best smoothness value below:-Surface finished with white point……0.11μm-Surface finished with SUPER-SNAP……0.08μm The rediopacity was highest for Inlay/Onlay with Brilliant D.I.and CR Inlay being successively lower.

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EDTA3-2(Fe・NH₄), EDTA3-2(Co・NH₄) and EDTA3-2(Cu・NH₄) at pH7.4 were investigated to determine effective pretreatment to promote strong adhesion of 4-META/MMA-TBB resin to enamel with minimum demineralization.EDTA5-0(NH₄) solution which does not contain a metal salt was also investigated as a control.The amount of Ca²⁺ demineralized during the pretreatment and the tensile bond strength to enamel were measured.The pretreated enamel surface and the resin surface of the adhesion junction were observed with SEM.When the enamel surface was pretreated with EDTA3-2(Fe・NH₄) for 60 seconds, the tensile bond strength of the resin to enamel was 7.1MPa after the thermal cycling test.No direct correlation was observed between the amount of Ca²⁺ demineralized and the tensile bond strength.The stable and strong bonding to enamel was taken place without strong mechanical retention.

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