The present Study examined the properties of synthesized monomers, with respect to the relationships between hydrophobic group and their mechanical properties and water sorption. The material for synthesis was P₄N₄Cl₈[(4PNC)octachlorocyclotetraphosphazene] having-P=N-hetero atomic bond in its skelton, whose 8 Cls were substituted by hydrophobic group and polymerization group to prepare 12 kinds of monomers. Three kinds of hydrophobic groups, that is, phenoxy group (Ph), 2, 2, 2-trifluoroethoxy group (TF) and 2, 2, 3, 3, 4, 4, 5, 5-octafluoropentoxy group (OF), and as polymerization group, methacryloxyethoxy group (EMA), were used as substituents. Synthesizing reaction was performed in 2 steps; first of all, 1〜6.2 of 8 Cls of 4PNC were substituted by 3 kinds of hydrophobic groups, and then the remaining Cls with polymerization groups, P₄N₄(Ph)_x(EMA)_yCl_8-x-y(PNC-Ph-EMA), P₄N₄(TF)_x(EMA)_yCl_8-x-y(PNC-TF-EMA)and P₄N₄(OF)_x(EMA)_yCl_8-x-y(PNC-OF-EMA). The number of the residual Cl atoms of all the 12 synthesized monomers was 0.04〜0.17. When the temperature of the 2nd step of synthesis was increased from 50℃ to 60℃, the reaction time decreased from 100 to 50hours. The specific gravity of PNC-TF-EMA and PNC-OF-EMA increased with the number of the hydrophobic substituent, but the refractive index decreased.In contrast, the specific gravity of PNC-Ph-EMA decreased with the increase of the number of the hydrophobic substituent, and the refractive index increased. Compressive strength, transverse strength and hardness decreased with the number of the hydrophobic substituent. When bulk polymers were immersed in the water at 37℃, their compressive strength, transverse strength and knoop hardness decreased as compared with those of the dry ones, but their rate of decrease was smaller than that of those having no hydrophobic substituent. Thermal expansion coefficient of bulk polymers increased with the number of the hydrophobic substituent. When the number of the substituent was the same, the order of the thermal expansion coefficients was : PNC-TF-EMA<PNC-Ph-EMA<PNC-OF-EMA. Polymerization shrinkage of the 12 kinds of bulk polymers was 3.09〜9.08vol%. The contact angle between bulk polymers and water increase with the number of the hydrophobic substituent. The refractive index of the bulk polymers, when the hydrophobic group was Ph, increased almost linearly, with the number of the substituent, but in the TF and OF, it decreased. Water sorption of bulk polymers, in any case of hydrophobic substituent, increased with time. However it decreased with the increase of the number of the hydrophobic substituent, and when the number of substituent was the same, the order was : PNC-OF-EMA<PNC-Ph-EMA≦PNC-TF-EMA. Solubility of the 12 kinds of bulk polymers was;0.025〜0.676wt% in 7 days. Among the 12 kinds of bulk polymers, the monomer that showed preferable mechanical properties, such as little decrease in mechanical properties when immersed in water, and smal water sorption, solubility and thermal expansion coefficient, was PNC-TF-EMA 4034. Its polymerization shrinkage was 6.42vol%, compressive and transverse strength were respectively 3905 and 480kg/cm², and knoop hardness was 19.9. Thermal expansion coefficient was 79.0×10^-6/℃, while the contact angle with water was 63.6°. After immersion in water at 37℃ for 1 week, compressive and transverse strength were respectively 3114 and 435kg/cm², and knoop hardness was 19.5.

View full abstract

To clarify the structure-activity relationships and the mechanism of hemolysis, the hemolytic activity of Bis-GMA analogs (Bis-GMA, Iso-Bis-GMA, Bis-MEPP and Bis-MPP) was studied. The activity of Bis-GMA and Iso-Bis-GMA with an OH group was higher than that of Bis-MEPP and Bis-MPP without an OH group. The hemolysis caused by methyl methacrylate (MMA) containing a small amount of Bis-MEPP or Bis-MPP was lower than that by MMA without any compounds. The changes in phase transition properties (phase transition temperature T, enthalpy ΔH, ΔT_1/2 and H/HHW) of dipalmitoyl phosphatidylcholine (DPPC) liposomes induced by Bis-GMA analogs were studied by differential scanning calorimetry (DSC). A shift of T to a lower temperature and increase in ΔT_1/2 (a reduced H/HHW) were larger than those of MMA. Bis-MEPP and Bis-MPP showed a broad DSC peak, which was similar to that caused by DPPC liposomes containing cholesterol. It is suggested that Bis-GMA and Iso-Bis-GMA act on the membranes of erythrocyte as surface active agents, and that Bis-MEPP and Bis-MPP act as membrane stabilizing agents.

View full abstract

Three types of hydroxyapatites with various fluoride contents were synthesized at 60°C and pH7.4 under the presence of gelatin as denatured collagen. The crystallinity of the apatites decreased on the whole with the increase of gelatin concentrations, especially in the a-axis direction indicating a high fluoride content. However, no significant difference in chemical compositions, a-axis dimensions, DTA, IR or apparent solubility of each fluoridated apatite was observed. These results suggest that gelatin may only act as an inhibitor of apatite crystal growth.

View full abstract

Experimental visible light curing resins were prepared by combining MMA-PMMA liquidpowder resin with a photosensitizer, dl-camphorquinone, and a reducing agent, N, N-dimethyl-aminoethyl methacrylate. The depths of cure of the experimental resins depended on the factors such as duration of irradiation, time of standing between mixing and irradiation, and ratio of powder to liquid. The depths of cure increased with the increase in these factors, and exceeded 36mm under the conditions of a powder/liquid ratio of 2/1, 80 min of standing, and 2 min of irradiation. The molecular weights of polymer in cured resin tended to be lower at the surface than in the inner portion. Molecular weights of polymer inside of cured resins increased in the order of cold cured resin < visible light cured resin < heat cured resin. The amount of residual monomer showed a typical U shape, where the amount increased in both the surface and bottom portion. The amounts in the fully cured parts of resins decreased in the order of cold cured resin ≈ visible light cured resin > heat cured resin. Based on the above results, the experimental resin was found to be applicable as a new visible light curing resin.

View full abstract

The testing method for bonding strength of dental adhesive materials such as composite resins and resin cements were investigated. Two types of test specimens were examined, namely butt joints and single lap joints. Circular and square cross-sectional adherends for butt joints specimens were utilized. For lap joints specimens, the tension-shear test and the compression-shear test for the evaluations of bonding strength were conducted. It is found that the cross-sectional shape of adherends did not affect significantly the bonding strength in butt joints specimens. For lap joints specimens, the compression-shear test gave higher and less scattered bonding strength compared with the tension-shear test.

View full abstract

Monomer contents in 12 commercially available composite resins and migration of monomers from the hardened resin plate (10×20mm, 0.15mm thick) to 5ml of various solvents (saline, 20% and 40% aqueous ethanol, and methanol) were determined by high performance liquid chromatography. The monomer contents were as follows: 2, 2-bis[4-(methacryloxy-2-hydroxypropoxy)-phenyl]propane(Bis-GMA), in 11 samples at 3.1〜18.8%; triethyleneglycol dimethacrylate (Tri-EDMA), in 9 samples at 3.4〜11.3%; urethane dimethacrylate (UDMA), in 3 samples at 6.8〜8.1%, respectively. Migration of Bis-GMA to the solvent decreased in the order of methanol, 40% ethanol, and 20% ethanol, but no migration to saline was observed. On the other hand, no significant decrease of migration of Tri-EDMA was found by varying the type of solvent. These findings were thought to reflect the hydrophobic or hydrophilic nature of the monomers. The degree of migration of Bis-GMA and Tri-EDMA was correlated with the monomer contents of the resins.

View full abstract

Three kinds of commercially available composite resins were used.On a slice of cattle anterior tooth was placed a plastic ring (inner diameter 5mm, height 2mm), which was then filled with one of the composite resins. After 1 and 7 days, the plastic ring was removed, and amount of methacrylate monomer in the slice and the hardened resin block was determined by high performance liquid chromatography. The residual amount of monomer in the hardened block increased with the monomer content in the unhardened resin. In repeated experiments with the same resin, amount of Bis-GMA was positive correlated with the amount of Tri-EDMA in the same specimen. However, the amounts of the monomers migrating to the specimen were not correlated with the residual amounts of the monomers in the hardened block. In addition, The migration of Bis-GMA to dentin increased with time, whereas no increase of Tri-EDMA was observed.

View full abstract

To make the casting of titanium with a calcia investment practical for dental use, the improvement of mold treatments and the dimensional fitness of castings were investigated. Lapping the mold with cooking film immediately after investing caused a high strength of mold and resulted in ringless casting. Because of small setting and thermal expansion of the original calcia investment, the dimensional fitness of casting was achieved by utilizing the oxidizing expansion of Zr metal powder mixed in a calcia investment. The calcia investment improved in the study produced a titanium casting with a shiny surface without reaction with the mold, with a good dimensional fitness, and with fewer casting defects inside.

View full abstract

This study investigated the dimensional accuracy of the artificial stone dies made with combinations of various elastic impression materials and dental stones of class I or class II using ceramic original models of cylindrical type. The diameters of the original and resultant stone dies were measured and compared at various heights by the optical ball feeler technique. In addition, the effects of the thickness of impressions and the height of original models on the dimensional accuracy of stone models were investigated. By the use of hydrocal and densite type stones with low setting expansion, the resultant stone dies made from an addition type silicone rubber impression showed similar dimensional changes. Dimensional changes of the stone dies made from various impressions demonstrated the varieties at various heights. Accordingly, these changes resulted in characteristic 3-dimensional die patterns. Decrease in thickness of impression materials in the tray and increase in height of original models caused great distortion of stone dies. The dimensional changes of the stone dies seemed to be markedly affected by the strain caused by tensile force at impression removal or the mechanical strength and elasticity of hardened impression materials themselves.

View full abstract

The present study is concerned with the improvement of heat-cured denture base resin. As a cyclophosphazene monomer, P₄N₄[CH₂=C(CH₃)COO(CH₂)₂O]₈:[4PN-(EMA)₈]having 8 polymerization groups in its molecule and P₄N₄(CF₃CH₂O)₁[CH₂=C(CH₃)COO(CH₂)₂O]₇:[4PN-(TF)₁(EMA)₇]having a hydrophobic group and 7 polymerization groups to be mixed with the monomer at 30 and 40%(wt), and L-resin as a polymer were used. It was found that in any composition transverse strength and hardness showed large values, compared with those of denture base resin on the market, but transverse deflection was small. With 4PN-(TF)₁(EMA)₇ monomer having hydrophobic group, water sorption tended to decrease, compared with 4PN-(EMA)₈ monomer, though solubility and degree of acetone swelling was slightly increased with 4PN-(TF)₁(EMA)₇ monomer. With the present composition, water sorption, solubility and degree of acetone swelling were approximately the same or lower than with those of denture base resin on the market.

View full abstract

The mutagenicity of Bis GMA and Tri EDMA was tested by the Salmonella reversion assay. The mutagenic activity of the test compounds was determined using Salmonella typhimurium TA1535, TA1537, TA98 and TA100. Bis GMA and Tri EDMA did not show any mutagenic potential in the absence of S-9mix in any of the strains tested. Bis GMA preincubated with S-9mix showed a 2-fold increase in the number of revertants compared to the solvent treatedcontrol value in TA1537 and 1.5-fold increase in TA98. Tri EDMA preincubated with S-9mix showed a concentration related increase in the number of revertants above the spontaneous mutation rate that reached 1.7 times in TA1537 and 1.6 times in TA98. These results indicated that Bis GMA is mutagenic and Tri EDMA is possibly mutagenic only in the presence of the metabolic activation system.

View full abstract

Chemically cured composite resins were evaluated by a compression test to detect the difference between dry and wet specimens after storage in deionized water at 37℃. Compressive strength for dry and wet specimens of Adaptic AP, Concise, Clearfil Posterior and P-10 increased during storage in deionized water at 37℃, but showed lower compressive strength than their dry specimens.their wet specimens after storage in deionized water at 37℃. Compressive strength for dry and wet specimens of microfilled composite resin such as Microrest AP, Micro Jar, Silar and Superlux generally increased during storage in deionized water at 37℃ and their wet specimens after storage in deionized water at 37℃ showed slightly higher compressive strength than their dry specimens. Fracture mode for Adaptic AP, Concise and Clearfil Posterior was classified as shear fracture type, for Microrest AP, Micro Jar and Superlux as longitudinal splitting fracture type and for P-10 and Silar as shear and longitudinal splitting fracture-mixed type.

View full abstract

To obtain, implant materials with high adhesiveness to bone, the surface of Ti-Ni shape memory alloy and Ti was coated with Ti by means of plasma thermal spray under argon gas atmosphere. After spray coating, a pure Ti layer was formed, but crevice with 5 to 10μm was observed at the boundary between coated layer and matrix metal. By anodic polarization measurement in 1% NaCl solution, a large current density was detected, suggesting the dissolution of the coated layer. However, after vacuum annealing at 950℃ for 1 to 1.5hr, the crevice between coated layer and matrix disappeared, and instead, a bonded layer with composition corresponding to Ti₂Ni was formed on Ti-Ni matrix. On the other hand, on Ti matrix, mutual diffusion took place and close adhesion occurred between coated layer and matrix. By anodic polarization measurement, appreciable improvement in corrosion resistance was also noted after heat treatment. The current density decreased considerably, being 1/10 to 1/1000 times that of the coated specimens. With Ti-Ni alloy, the coated layer peeled by a large strain upon shape memory effect. Thinner coating layer or application of Ti₂Ni alloy phase is under consideration.

View full abstract

To study the effects of coupling agents of isocyanato-and alkoxy-silanes and zircoaluminates on silica surface, the compressive and diametral tensile strength of the treated silica/acrylic resin composites and adhesive tensile strength of the resin to glass plate were measured after immersion in water at 37°C. The silica fillers and the glass plates were treated with coupling agents, such as 3-methacryloxypropylsilyltriisocyanate, vinylsilyltriisocyanate, 2-trimethoxysilyl-1, 3-butadien, 3-methacryloxypropyltrimethoxysilane (3-MPS), a mixture of 3-MPS and phenyltriethoxysilane (PS), a siloxane oligomer that hydrolyzed the mixture of 3-MPS and PS, zircoaluminate and isopropyldimethacrylisostearoyltitanate. These silane coupling agents, except for butadiene type silane, improved the mechanical properties of the composites and adhesive strength of the resin to glass plate. Especially, the isocyanatosilanes were more effective than 3-MPS, but the butadiene type silane was not, because the olefinic double bonds of the silane were not incorporated into the propagating chain of the matrix resin. Titanate and zircoalminates coupling agents were not effective under the conditions in this study.

View full abstract

Formulation of photocurable bonding liners for denitin was studied. They consisted of four components, 4-methacryloxyethyl trimellitate anhydride (4-META) as an adhesion promoting monomer, mixtures of several methacrylates as a bese monomer, d, l-camphor quinone (CQ) as a photosensitizer and N, N-dimethylaminoethyl methacrylate (DMAEMA) as a reducing agent. The tensile bond strength of the liner on dentin treated with 0.5M EDTA at pH7.4 for 60 sec to a photocurable composite resin was measured. The strength and SEM observation data suggested that 4-META promoted interpenetration of monomers into etched dentin. The best bonding liner was a mixture of 2wt% 4-META, 0.5wt% CQ, 0.5wt% DMAEMA in TEGDMA and the value of the tensile bond strength was 3MPa.

View full abstract

Photocurable bonding liners containing 2-methacryloxyethyl p-methoxyphenyl phosphoric acid(CH₃O〜OH)were studied. They consisted of CH₃O〜OH as an adhesion promoting monomer, TEGDMA as a base monomer, d, l-camphor quinone (CQ) as a photosensitizer and N, N-dimethyl aminoethyl methacrylate (DMAEMA) as a reducing agent. Tensi′e bond test and SEM observation suggested that CH₃O〜OH promoted interpenetration of monomers into etched dentin. The best value was 6.4MPa in the case of 2wt% CH₃O〜OH, 0.5wt% CQ, 0.5wt% DMAEMA in TEGDMA.

View full abstract

Polymerization of the MMA/TBBO resin system was investigated in the presence of collagen powder treated with 3wt% ferric chloride-10wt% citric acid solution (FC-CA), and the curing time, amount of unpolymerized monomer and molecular weight were measured. The curing time of MMA/TBBO resins was markedly reduced in the presence of FC-CA treated collagen, whereas it was increased by either FC-CA or collagen alone. The presence of FC-CA treated collagen resulted in reduction of the amount of unpolymerized monomer. Acceleration of curing and reduction of the amount of unpolymerized MMA were especially significant with MMA/TBBO resins containing 5wt% of 4-META. The number-average molecular weight of MMA/BTTO resin cured in the presence of FC-CA treated collagen increased to 10.0×10⁴, while the value for MMA/TBBO resin cured alone was 5.7×10⁴. The findings suggested that FC-CA contributes to improved bonding of the resins to dentin by promoting polymerization of MMA.

View full abstract

In the course of the studies on functional monomers containing sulfur, 6-(4-vinylbenzyl-n-propyl) amino-1, 3, 5-triazine-2, 4-dithione (VBATDT) was synthesized and applied to adhesion of dental precious alloys. Surface of precious metals were treated with VBATDT and then, they were adhered to each other by MMA-PMMA/TBBO resin. The durability of adhesive strength was compared after 2000 times of thermal cycling. The adhesive strengths to dental alloys without the surface treatment were too poor for practical use, and the strengths to elemental precious metals were zero. However, the strengths to dental precious alloys treated with VBATDT were found to be durable, 46〜54MPa, even after 2000 times of thermal cycling. The values of adhesive strength were much higher than those of MPMA (23〜29MPa), 4-META (7〜35), or 4-MET (0〜11MPa).

View full abstract

To improve the mechanical properties of light cured dental resins, we prepared ethyleneglycol acrylate-methacrylate (EAMA), and the polymerizability was compared with ethyleneglycol dimethacrylate (EDMA). Copolymers of mixture of EAMA and EDMA with UDMA were cured by visible light irradiation. Hardness and compressive strength were improved by increasing the content of EAMA but the amount of water sorption was increased. Light cured composite resins, compounded of these monomers with TMPT filler, were prepared. The mechanical properties such as hardness, compressive strength and abrasion resistance were improved by increasing the composition of EAMA. Especially, hardness of the surface and the bottom was approximately constant with higher compositions of EAMA. These results suggested that EAMA was suitable for light curable dental resins.

View full abstract

Bonding between filler particles and matrix resin is essential to improve the mechanical properties of composite type hard crown and bridge resins, which contain inorganic fillers. A mixture of 2.6E and UDMA (1:1wt) was cured with several inorganic fillers with or without γ-methacryloxypropyl trimethoxy silane treatment and TMPT filler by heat processing, and their physical properties were measured. The silane treatment of inorgnic fillers had a clear effect on their properties. Brinell hardness, amounts of water sorption and abrasion loss were improved by the use of silane-treated inorgnic fillers. Resin surfaces brushed with tooth paste were observed with SEM. TMPT and microfiller resins showed smooth surface after the abrasion, but roughened surfaces were observed in resin containing fillers larger than 10μm. Silane treatment of inorganic filler improved the bonding of the filler to the resin matrix. The difference in resistance against abrasion between matrix resin and filler particles influenced the appearance of brushed surface.

View full abstract

Bond strength to bovine tooth substrates with MMA-TBB resins containing new functional monomers, which have substituent groups at p-position of 2-methacryloxyethyl phenyl phosphoric acid (Phenyl-P) or 2-methacryloxyethyl phenyl phosphoryl chloride (Phenyl-P Cl), was measured. SEM observation of the fractured surface after the tensile bond strength test was also carried out. High bond strength was obtained with Phenyl-P, Cl or CH₃O substituted Phenyl-P, and also with Phenyl-P Cl, CH₃O or NO₂ substituted Phenyl-P Cl. SEM image of fracture surface with CH₃O p-substituent of Phenyl-P showed that tensile failure occurred between resin reinfocred demineralized dentin and intact dentin, even higher bond strength was obtained with this methacrylate. These phenomena differed from those with 4-META/MMA-TBB resin. These findings suggest differences in functional property between 4-META and p-substituted Phenyl-P (or Phenyl-P Cl).

View full abstract