Biomedical subjects

Y Kadoma

Publications and source records attributed to Y Kadoma.

At least 19 recordsLinked to original sources

PubMed1992

Effect of phenolic compounds on the polymerization of methyl methacrylate.

The inhibitory effects of six phenolic compounds and two analogues on the polymerization of methyl methacrylate (MMA) by azobisisobutyronitrile (AIBM) were examined. Differential scanning calorimetry was used to determine the induction period (IP) and initial rate of polymerization (IRP). The IP values (minutes) decreased in the order: eugenol > thymol > hydroquinone > cresol > guaiacol > phenol >>> safrole > methol. The IRP values of all compounds tested ranged from 0.8 to 1.2 percent per minute, except for hydroquinone (0.2 percent per minute). Phenolic compounds inhibited the polymerization of MMA by scavenging radicals, and eugenol was the most potent inhibitor.

Cresols↗

PubMed1992

Hemolytic activity of a dental adhesive monomer (N-methacryloyloxy-5-aminosalicylic acid, MASA) and its interaction with phospholipid liposomes as studied by NMR and DSC.

N-methacryloyloxy-5-aminosalicylic acid (MASA) has recently been used as an adhesive primer in restorative resin systems. To monitor the biological activity of MASA, we studied changes in NMR-chemical shifts (delta H) and the differential scanning calorimetry (DSC) phase transition temperature (Tm) of dipalmitoylphosphatidylcholine (DPPC)/MASA liposomes with or without the presence of albumin and collagen. The delta H and the Tm did not alter significantly and the interaction of MASA with DPPC was found to be small. Hemolytic activity of MASA was markedly smaller than that of the phosphate monomer (MDP) in bonding agents widely used. These findings suggest that using a MASA primer in resin systems has an acceptable biocompatibility for dentin-pulp, involving its adsorption and adhesion to hard tooth tissues.

1,2-Dipalmitoylphosphatidylcholine↗

PubMed1991

Importance of polymerization initiator systems and interfacial initiation of polymerization in adhesive bonding of resin to dentin.

Although various adhesive resins for dentin have been developed and used clinically, most attention has been directed to adhesion-promoting monomers and pre-treatment agents. The role of polymerization initiator systems in bonding has been overlooked. The purpose of this work was to study the role of initiators from the viewpoint of interfacial initiation of polymerization in dentin bonding. The bond strength between dentin and methyl methacrylate resin was significantly improved by a possible interfacial initiation with (1) the combination of ferric chloride, adsorbed onto dentin, and oxidized tri-n-butylborane (TBBO) and (2) the addition of tertiary butyl peroxymaleic acid (containing a carboxylic acid group, which has an affinity with dentin) to chemically- or light-activated initiator systems.

Acid Etching, Dental↗

PubMed1991

Changes in 1H-NMR chemical shifts of Bis-GMA and its related methacrylates induced by their interaction with phosphatidylcholine/cholesterol liposomes.

To clarify the hemolytic mechanism of Bis-GMA and its related methacrylates, the interaction of five methacrylates (Bis-GMA, MMA, NPGDMA, TEGDMA, and UDMA) with DPPC/Cholesterol (CS) liposomes, as a model for erythrocyte membranes, was studied by 1H-NMR spectroscopy. Exogenous Bis-GMA partitioning into the DPPC/CS liposomes caused disappearances of its proton signals. With NPGDMA, its signals broadened markedly in DPPC/CS liposomes. UDMA partitioning caused changes in chemical shifts to a higher field, whereas MMA and TEGDMA partitioning did not cause any changes in chemical shifts. It was concluded from these observations that Bis-GMA has a stronger interaction with the DPPC/CS liposomes than the other methacrylates used. The high hemolytic activity of Bis-GMA reported previously seemed to be due to its migration into the lipid bilayer of phospholipids containing CS in erythrocyte membranes.

1,2-Dipalmitoylphosphatidylcholine↗

PubMed1990

Changes in NMR chemical shifts of methacrylates induced by their interactions with the phospholipid and the phospholipid/cholesterol liposome system.

The interaction of methyl methacrylate (MMA), ethylene dimethacrylate (EDMA) and triethyleneglycol dimethacrylate (TEGDMA), which are widely used in dentistry, with the dipalmitoyl phosphatidylcholine (DPPC) and the DPPC/cholesterol (CS) liposome system was studied by 1H and 13C nuclear magnetic resonance spectroscopy (NMR). EDMA and TEGDMA have a larger interaction with the DPPC liposome system compared to MMA, resulting in changes in chemical shifts. The 13C chemical shift differences of C = C-C-O were larger than those of other carbon portions in methacrylate, indicating that double bonds interact predominantly with DPPC liposomes due to the hydrophobicity of methacrylates. At 37 degrees C, 1H signals from TEGDMA appeared in the DPPC/CS/TEGDMA liposome system, while signals due to H2C = C-C-OCH2CH2 did not appear in the DPPC/TEGDMA liposome system.

1,2-Dipalmitoylphosphatidylcholine↗

PubMed1990

Hemolysis mechanism of dental adhesive monomer (methacryloyloxydecyl dihydrogen phosphate) using a phosphatidylcholine liposome system as a model for biomembranes.

To clarify the mechanism of interaction of dental adhesive monomers with biological membranes at the molecular level, we studied the interaction of methacryloyloxydecyl dihydrogen phosphate (MDP) and methacrylic acid (MAA) with the dipalmitoylphosphatidylcholine (DPPC) liposome system using NMR and DSC. MDP-DPPC interaction became apparent through broadening of the DPPC phase transition as pH decreased, finally the enthalpy of MDP-DPPC (1:1 mol ratio) reduced to zero at pH 2.5. Proton chemical shifts of MDP enhanced shielding and proton signals due to the phosphatidylcholine polar group (O-CH2-CH2-N bond) of DPPC were observed. MAA-DPPC interaction was smaller than that of MDP-DPPC, even at low pH. It was concluded that the strong hemolytic activity of MDP may be due to its interaction with the phospholipid bilayers of erythrocyte membranes.

1,2-Dipalmitoylphosphatidylcholine↗

PubMed1990

[Visible-light initiator system using thiobarbituric acid derivatives with methyl substituent].

Seven 2-thiobarbituric acid derivatives with methyl substituents were synthesized. Experimental visible-light curing resins were prepared using these compounds as a reducing agent in the dl-camphorquinone (CQ)-reducing agent initiator system. The effects of methyl substitution for thiobarbituric acid on initiation behavior of CQ-thiobarbituric acid initiator system were examined by analysis of polymerization of triethylene glycol dimethacrylate (3 G) in DSC and depth of cure. The solubility of thiobarbituric acid derivatives in 3 G was markedly changed by the introduction of the methyl group. Although the methyl group substitution at position 1 (3) in thiobarbituric acid improved the solubility of the acid in 3 G, it did not enhance the initiation ability. Maximum exothermic rate, time at maximum exothermic peak, amount of insufficiently polymerized layer and depth of cure were significantly improved by the introduction of one methyl group at the position 5. Thus the initiation ability was enhanced by the substitution. However, the introduction of two methyl groups at position 5 did not promote polymerization, but the inhibitory effect became apparent as the concentration of the reducing agent was increased.

Composite Resins↗

PubMed1990

[Study on visible-light curing soft resins consisting of fluoropolymers. 2. Effect of fluoroalkyl alpha-fluoroacrylate monomers].

New experimental visible-light cured soft resins were prepared by combining a vinylidene fluoride/hexafluoropropylene copolymer (2-6 F), or a vinylidene fluoride/tetrafluoroethylene/hexafluoropropylene copolymer (2-4-6 F) with 2,2,3,3-tetrafluoropropyl alpha-fluoroacrylate (4 FFA), 2,2,3,3,3-pentafluoropropyl alpha-fluoroacrylate (5 FFA), 2,2,3,3,4,4,5,5-octafluoropentyl alpha-fluoroacrylate (8 FFA), or 2,2,3,3,4,4,5,5,6,6,7,7-dodecafluoroheptyl alpha-fluoracrylate (12 FFA). Some properties of the resins prepared were measured to determine whether they would be candidate materials for the soft denture liner. Water contact angles increased with the increase in the number of fluorine atoms contained in the monomers: 85-90 degrees in 4 FFA, 90-93 degrees in 8 FFA, and 92-93 degrees in 12 FFA. Softer resins were obtained with 2-4-6 F, especially by the combination with 8 FFA giving the softest resin with a hardness of 43-46 (JIS A). Water sorption after 10 weeks was considerably low: 0.4-2%: 0.4-0.9% in 4 FFA/2-6 F and about 2% in 8 FFA/2-4-6 F. Solubility was 0.2-0.4% in the resins with 4 FFA and 1.0-1.4% with 8 FFA or 12 FFA. Amount of residual monomer was low, and the maximum was 0.4% in the resin with 12 FFA. Thus hardness and water sorption of the resins prepared were superior to those of the commercial soft materials.

Denture Liners↗

PubMed1990

[Study on visible-light curing soft resins consisting of fluoropolymers. (3) Application of low molecular weight fluoropolymer].

New experimental visible-light cured soft resins were prepared by combining a low molecular weight vinylidene fluoride/hexafluoropropylene copolymer (2-6 FL), or vinylidene fluoride/tetrafluoroethylene/hexafluoropropylene copolymer (2-4-6 FL) with 2,2,3,3-tetrafluoropropyl alpha-fluoroacrylate (4 FFA), or 2,2,3,3,4,4,5,5-octafluoropentyl alpha-fluoroacrylate (8 FFA). Some properties of the resins prepared were measured to determine whether they would be candidate material for a soft denture liner. Water contact angle was 90-92 degrees with 4 FFA, and 90-94 degrees with 8 FFA. The resins combined with 2-4-6 FL were sufficiently soft: 42-46 (JIS A hardness) in 4 FFA, and 33-39 in 8 FFA. Generally the hardness decreased by 5-10 with the use of a low molecular weight of fluoropolymer. Water sorption after 10 weeks was 0.8-1.2% in 2-6 FL/4 FFA, 1.3-1.7% in 2-6 FL/8 FFA, about 1% in 2-4-6 FL/4 FFA, and about 2% in 2-4-6 FL and 8 FFA. Solubility was 0.4-0.5% in 2-6 FL/4 FFA, 0.3-0.4% in 2-4-6 FL/4 FFA, 1.5-1.9% in 2-6 FL/8 FFA, and 1.1-1.5% in 2-4-6 FL/8 FFA. Amount of residual monomer was very low, and the maximum was 0.1%. Tensile strength of the resins was reduced to 40-70% of that of the similar resins obtained in the previous study. Thus softer resins could be prepared by using lower molecular weight fluoropolymers.

Denture Liners↗

PubMed1990

[Study on visible-light curing soft resins consisting of fluoropolymers. 1. Effect of fluoroalkyl methacrylate monomers].

New experimental visible-light cured soft resins were prepared by combining 4 kinds of fluoroalkyl methacrylate monomers with a vinylidene fluoride/hexafluoropropylene copolymer, or a vinylidene fluoride/tettrafluroethylene/hexafluoropropylene copolymer. Some properties of the resins prepared were examined to determine their value as a soft denture liner material. Water contact angles were more than 90 degrees in all cases and increased with the increase in the number of fluorine atoms in the fluoroalkyl groups. Hardness (JIS A) was less than 50 for the softes resin. Water sorption after 10 weeks was 3-4.5 wt %. Solubility 0.1-0.3 wt% and amount of residual monomer 0.2 wt% were very low. The properties of these new experimental resins were comparable or superior to the commercial soft materials available.

Acrylic Resins↗

PubMed1990

[Study on adhesion mechanism of MMA-TBBO resin to dentin. A model experiment using decalcified dentin].

As a model experiment to understand the mechanism of adhesion of the MMA-TBBO resin to dentin, MMA-TBBO was polymerized using a decalcified dentin sheet treated with aqueous citric acid (CA) solutions of copper fluoride (CF), ferric fluoride (FF), or ferric chloride (FC), which are usually used as treating agents in the bonding of the resin to dentin. The curing time for MMA-TBBO resin was considerably reduced on the decalcified dentin sheet treated with FC-CA, CF-CA or FF-CA at an appropriate concentration. Polymerization of MMA-TBBO resin was accelerated in the presence of a fluoride ion. Molecular weight of PMMA depended on the site of polymerization; PMMA polymerization inside the decalcified dentin sheet gave the highest and that outside gave the lowest molecular weight in the presence of an appropriate amount of ferric or cupric ion. These results suggested that ferric compounds adsorbed to decalcified dentin are involved in the polymerization of MMA and thus will influence the bond strength of the MMA-TBBO resin to dentin.

Acrylic Resins↗

PubMed1990

[New low temperature initiator system for dental adhesive resins. Application of peroxyesters with carboxyl group].

Adhesion between dentin and MMA resin was investigated using chemically activated initiator system consisting of 1,3,5-trimethyl-2-thiobarbituric acid, cupric salt, chloride ion, and tert.-butyl peroxymaleic acid (MA) with carboxyl group which usually has affinity to tooth. The adhesive strength of the MMA/PMMA resin to bovine dentin increased significantly to 8-10 MPa by addition of MA, while the adhesive strength was 4 MPa without MA. When the bonding broke at higher than 7 MPa, the adhesive resin layer usually fractured cohesively and the interfacial fracture did not occur. The bond strength obtained in this experiment was comparable to that obtained with MMA resin using TBBO and ferric ion initiator system which is known as the best initiator system for dentin available.

Acrylic Resins↗

PubMed1990

[Adhesion mechanism of MMA/TBBO resin containing 4-META to decalcified dentin].

As a model experiment to understand the mechanism of adhesion of the 4-META-MMA/TBBO resin to dentin, 4-META-MMA/TBBO was polymerized in the presence of decalcified dentin sheet treated with citric acid (CA) aqueous solution containing ferric chloride (FC). Curing time of MMA/TBBO resin was reduced by the addition of 4-META to MMA. Addition of 4-META increased molecular weight of PMMA. PMMA polymerized inside the decalcified dentin sheet was insoluble in acetone. PMMA obtained from the monomer liquid used in commercial Super-Bond C & B was all insoluble and no soluble fraction was obtained. These results suggested that 4-META accelerated polymerization of MMA-TBBO resin in the presence of ferric ion and was effective to enhance molecular weight of PMMA. These effects seemed to be related to high bond strength of Super-Bond with dentin.

Acrylic Resins↗

PubMed1989

Nuclear magnetic resonance spectroscopic studies of the interaction of methyl methacrylate and ethylene dimethacrylate with phosphatidylcholine liposomes as a model for biomembranes.

The interaction of methyl methacrylate (MMA) and ethylene dimethacrylate (EDMA) with dipalmitoyl phosphatidylcholine (DPPC) liposomes was studied by 1H and 13C nuclear magnetic resonance spectroscopy (NMR). It was found that the changes in the 1H chemical shift of EDMA were larger than those of MMA when comparing membrane-bound state with free state and that the amount of EDMA incorporated into DPPC liposomes was approximately 74%, whilst MMA was approximately 41%. The major changes in chemical shifts of EDMA appeared to be due to its interaction with the acyl chains of DPPC liposomes.

1,2-Dipalmitoylphosphatidylcholine↗

PubMed1989

Nuclear magnetic resonance spectroscopic studies of interaction of bis-GMA analogues with phosphatidylcholine liposomes as a model for biomembranes.

The interaction of bis-GMA analogues with dipalmitoylphosphatidylcholine liposomes was studied by 1H and 13C nuclear magnetic resonance spectroscopy. It was found that bis-GMA analogues did not diffuse from liposomes once they were incorporated into the lipid bilayers of dipalmitoylphosphatidylcholine. The mobility of iso-bis-GMA was strongly disturbed by dipalmitoylphosphatidylcholine. The large changes in nuclear magnetic resonance spectra of iso-bis-GMA indicated that the interaction of iso-bis-GMA with dipalmitylphosphatidylcholine was larger than that of bis-GMA. This seems to be due to the chemical structure of iso-bis-GMA with the primary hydroxyl group.

Biocompatible Materials↗

PubMed1989

[Degradation of polyurethanes in aqueous environment].

The effect of in vitro exposure to aqueous environments on the change of properties of polyurethanes was studied as a model experiment for understanding the in vivo degradation of polyurethanes. Films of three commercially available medical polyurethanes consisting of diphenylmethane diisocyanate (MDI) (Biomer, Cardiothane and TM-3) and an experimental segmented polyurethane based on hydrogenated MDI (HMDI) were immersed in phosphate buffer or HEPES buffer containing lithium chloride at pH 7.4 at 70 degrees C for up to one year. Samples were subjected to ATR-FTIR measurement, tensile testing and viscosity measurement. Stability to hydrolytic degradation increased in the order: HMDI, TM-3, Biomer and Cardiothane. This ranking was consistent with that obtained in vivo. The results suggest that an in vitro model experiment is helpful for understanding and predicting degradation performance of polyurethanes in vivo.

Hydrolysis↗

PubMed1989

[Recovery of fluoride orally on the acid-etched tooth surface].

There are many reports concerning the recovery phenomenon of acid-etched enamel surfaces of teeth. Many studies of surface hardness, acid resistant properties, radiolucency, and surface morphology suggest that orally the acid-etched enamel reverts to a state nearly similar to that of the intact enamel before the acid etching. This study was conducted in order to verify the existence of the recovery phenomenon of fluoride on acid-etched enamel, because the surface layer of a high fluoride concentration is removed from the surface enamel by the acid etching. The deciduous upper central incisors of both sides were etched with phosphoric acid. The fluoride content of one incisor was measured immediately after the etching and that of the opposite incisor was also measured in vivo after 4 weeks, during which period no special fluoride was used. The fluoride content of the tooth surface in the mouth after 4 weeks significantly increased by about 50 ppm, when compared to that immediately after the acid etching. No significant relationship was found between the fluoride increase and the fluoride concentration of the patients' saliva and drinking water which were the probable supply sources of fluoride for the teeth. No relationship was found between the fluoride increase and the number of second deciduous molars with defects or fillings, which was counted as a measure of the patient's susceptibility to caries.

Acid Etching, Dental↗

PubMed1989

[Studies on visible-light initiator system using thiobarbituric acid derivatives].

Experimental visible-light curing resins were prepared by the combination of dl-camphorquinone and a thiobarbituric acid derivative, such as 5-methyl-2-thiobarbituric acid (5 MS), 5-n-butyl-2-thiobarbituric acid (5 BS), and 1,3,5-trimethyl-2-thiobarbituric acid (135 MS). The ability of their initiator systems to polymerize resins was investigated and was also compared with that of initiator systems containing 5-n-butyl-barbituric acid (5 B) or N,N-dimethylaminoethyl methacrylate (DMAEMA) as the most popular reducing agent. The amount of insufficiently polymerized layer was small in 135 MS at a low concentration, and in DMAEMA at a high concentration, respectively. 135 MS was superior to DMAEMA in curing time, maximum exothermic rate and depth of cure at a concentration of 1.0 mole%. 135 MS, therefore, seemed comparable or superior to DMAEMA. The order of increasing activity as a reducing agent was 5 BS less than 5 MS less than DMAEMA less than or equal to 135 MS. When analogous 5 B and 5 BS were compared, the sulfur-containing 5 BS was more effective as a reducing agent.

Acrylic Resins↗