Yoshinori Kadoma

1H and 13C NMR Studies of the Interaction of Eugenol, Phenol, and Triethyleneglycol Dimethacrylate with Phospholipid Liposomes as a Model System for Odontoblast Membranes

To clarify the mechanism of the interaction of eugenol with odontoblast membranes compared with that of phenol and triethyleneglycol dimethacrylate (TEGDMA), we employed dipalmitoylphosphatidylcholine (DPPC) liposomes as a model system for odontoblast membranes. 1H and 13C nuclear magnetic resonance spectroscopy (NMR) was used as the spectroscopic approach in the study of this interaction. No signals of 1H and 13C due to eugenol in the DPPC/eugenol liposomes were observed, indicating that the mobility of eugenol was strongly disturbed by DPPC and that eugenol did not diffuse from the liposomes once it was incorporated. The change in chemical shifts due to phenol between the free state and the DPPC/phenol liposomes was not found, indicating that phenol resides in the aqueous phase or near the surfaces of liposomes, its interaction being markedly weaker than that of eugenol. The signals due to TEGDMA in the DPPC/ TEGDMA liposomes were split into two peaks: a lower-field peak (free TEGDMA) and a higher-field one (membrane-bound TEGDMA). TEGDMA with ethyleneglycol groups seemed to be activated on the liposomes as a surfactant-like agent.

Incorporation into Human Enamel of Fluoride Slowly Released from a Sealant in vivo

Fluoride incorporation into human enamel from an experimental sealant resin in vivo was investigated. The sealant consisted of a newly synthesized methacryloyl fluoride-methyl methacrylate (MF-MMA) copolymer resin, which contains acidic fluoride covalently bonded to carbonyl groups and releases fluoride ions slowly by hydrolysis in an aqueous environment. This experimental sealant was applied to the enamel of permanent pre-molars and the control sealant without MF-MMA copolymer to that of the contralateral teeth. Fluoride concentration was determined by an enamel biopsy procedure with acid-etching four weeks after the sealant application. As much as 3500 ppm fluoride was found to be deposited at 10 μm depth in the enamel under the MF-MMA copolymer sealant. The increase in fluoride concentration was significant even at 60 μm. Of the fluoride incorporated into the enamel, from 70 to 80% was present as a tightly bound form. This resin sealant is expected to protect the enamel from caries attack even after detachment of the sealant.

Kinetic evaluation of the reactivity of flavonoids as radical scavengers

The reactivity of flavonoids as radical scavengers was investigated under kinetic considerations using radical polymerization of methyl methacrylates initiated by benzoyl peroxide. The number of radicals which are trapped by each molecule of phenol (the stoichiometric factors, n values) decreased in the order of epigallocatechin-3- O -gallate (ECG) (5.5) > catechin (3.5) > resveratrol (2.4) > quercetin (1.9)> n -propylgallate (1.5) > hesperetin (1.0). The inhibition rate constants ( k inh ) (1-3 ‐ 10 3 l/(mol s)) for the flavonoids were not different from each other, and, therefore, the radical scavenging activity depend on n values. The n values of the fully oxidized flavonoids were estimated from the frontier orbital theory, using PM3 semiempirical molecular orbital calculation. The experimental n values were consistent with the calculated values.

A study on the adsorption structure of an adhesive monomer for precious metals by surface-enhanced Raman scattering spectroscopy

In order to clarify the role of a primer on the adhesion between dental precious metals and resin, surface-enhanced Raman scattering (SERS) technique has been applied to the structural analysis of the adhesive monomer, 6-(N-(4-vinylbenzyl)propylamino)-1,3,5-triazine-2, 4-dithione (VBATDT) adsorbed on colloidal Au surfaces. VBATDT is one of the major components of commercial primers. A mixture of a methanol solution of VBATDT and aqueous Au colloid was illuminated by the 647.1 nm line from a Kr ion laser to obtain the SERS. The most intense peak at 458 cm-1 due to C = S stretching in the Raman spectrum of solid VBATDT disappears completely in the SERS, while all the other peaks due to vinylbenzyl group vibrations remain unchanged. It suggests that some structural change occurs in VBATDT upon adsorption on Au which involves the C = S bonds and that the molecule undergoes thione-thiol-type tautomerization in the adsorption process. The SERS spectrum of a commercial primer containing VBATDT exhibits a similar spectral pattern. The present results lead us to conclude that some specific interactions exist between the sulfur atoms of VBATDT and Au surface to form chemical bond likes, which are effective to improve the bond strength between dental precious metals and resin. The ambivalent properties of the primer, chemical stability in storage and chemical affinity to Au, are also explained by the thione-thiol-type tautomerization of VBATDT on the basis of the spectroscopic evidence.

Effects of Photoinitiators for the Visible-light Resin System on Hemolysis of Dog Erythrocytes and Lipid Peroxidation of Their Components

The visible-light (VL) polymerizing resin system with photoinitiators (photosensitizer and reducing agent) is widely used in modern dentistry. In this system, polymerization is initiated by photochemical reactions between the photosensitizers (aromatic or aliphatic ketones) and reducing agents (tertiary amines) during VL irradiation. In order to simulate the VL resin-induced toxicity in dental pulps, the present investigation was conducted to determine whether hemolysis of dog erythrocytes and lipid peroxidation of their components occur on exposure to a VL resin system containing aromatic (9-fluorenone, benzil) or aliphatic ketones (camphoroquinone) plus tertiary amine [2-(dimethylamino) ethyl methacrylate]. It was demonstrated that the hemolysis and lipid peroxidation with aromatic ketones were markedly higher than with those of aliphatic ketones, even when the latter were used at higher concentrations. It was clear that peroxidation-induced hemolysis occurred and, further, that surface-active complexes between photosensitizers and reducing agents, which are formed by irradiation, promote hemolytic activity due to their hydrophobic interactions. VL resin-induced responses to dental pulps are probably promoted due to the double effects of unpolymerized monomers and of both radicals and surface-active complexes formed during irradiation.

Action of Drugs, Detergents, and Monomers on Liposomes

Interactions of 14 organic compounds, such as phenols, aromatic carboxylic acids, steroids, and methacrylates with the multi-lamellar lecithin-cholesterol liposomes, were monitored in biological systems. It was found that their actions with our artificial liposomes were quite similar to those of biological membranes described previously.

Studies on dental fluoride-releasing polymers IV: Fluoridation of human enamel by fluoride-containing sealant

An experimental fluoride-containing acrylic sealant was prepared using methacryloyl fluoride-methyl methacrylate copolymer as powder component. The in vitro fluoride acquisition by human enamel coated with the sealant after 11, 21, 41 and 84 days of incubation in a phosphate buffer of pH7 at 37 degrees C was determined. Fluoride penetration and uptake were increased by prolonging the exposure time of enamel to the sealant. Most of the fluoride retained in enamel was found to be present as fluorapatite. The discharge of fluoride in the sealant was about 12% of initial load after 84 days of immersion.

Kinetics of the radical scavenging activity of β-carotene-related compounds

To clarify the non-enzymatic radical-scavenging activity of β-carotene-related compounds and other polyenes, we used differential scanning calorimetry to study the kinetics of radical polymerization of methyl methacrylate (MMA) by 2,2′-azobisisobutyronitrile (AIBN) or benzoyl peroxide (BPO) in the absence or presence of polyenes under nearly anaerobic conditions at 70°C, and analyzed the results with an SAR approach. The polyenes studied were all-trans retinol, retinol palmitate, calciferol, β-carotene and lycopene. Polyenes produced a small induction period. The stoichiometric factor (n) (i.e. the number of radicals trapped by each inhibitor molecule) of polyenes was close to 0. Tetraterpenes (β-carotene, lycopene) suppressed significantly more of the initial rate of polymerization (R inh) than did diterpenes (retinol, retinol palmitate). The inhibition rate constants (k inh) for the reaction of β-carotene with AIBN-or BPO-derived radicals were determined to be 1.2–1.6 × 105  l / mol s, similar to published values. A linear relationship between k inh and the kinetic chain length (KCL) for polyenes was observed; as k inh increased, KCL decreased. KCL also decreased significantly as the number of conjugated double bonds in the polyenes increased. Polyenes, particularly β-carotene and lycopene, acted as interceptors of growing poly-MMA radicals.

A review of the developments of self-etching primers and adhesives-Effects of acidic adhesive monomers and polymerization initiators on bonding to ground, smear layer-covered teeth

This paper reviews the developments of self-etching primers and adhesives, with a special focus on the effect of acidic adhesive monomers and polymerization initiators on bonding to ground, smear layer-covered teeth. Ionized acidic adhesive monomers chemically interact with tooth substrates and facilitate good bonding to ground dentin. Polymerization initiators in self-etching primers further promote effective bonding to ground dentin. To promote bonding to both dentin and enamel, phosphonic acid monomers such as 6-methacryloyloxyhexyl phosphonoacetate (6-MHPA) were developed. These novel adhesive monomers also have a water-soluble nature and are hence endowed with sufficient demineralization capability. A new single-bottle, self-etching, 2-hydroxyethyl methacrylate (HEMA)-free adhesive comprising 6-MHPA and 4-acryloyloxyethoxycarbonylphthalic acid (4-AET) was developed. This novel adhesive enabled strong adhesion to both ground enamel and dentin, but its formulation stability was influenced by pH value of the adhesive. To develop hydrolytically stable, single-bottle, self-etching adhesives, hydrolytically stable, radical-polymerizable acidic monomers with amide or ether linkages have been developed.

Radical-Scavenging Activity of Dietary Phytophenols in Combination with co-Antioxidants Using the Induction Period Method

The radical-scavenging activity of dietary phytophenols has been investigated by many researches due to their antioxidant, anti-inflammatory and anticancer property but the radical-scavenging effect of 2-phytophenol and the phytophenol:co-antioxidants, vitamin C and thiol combination under nearly anaerobic conditions still remains unknown. The radical-scavenging activity for seventeen phytophenols and for six synthetic phenols (positive controls) was investigated using the induction period method in the polymerization of methyl methacrylates (MMA) initiated by thermal decomposition of benzoyl peroxide (BPO) by monitoring differential scanning calorimetery (DSC). The kinh for the phytophenols was likely with the range 0.5 × 103 M−1s−1−2.2 × 103 M−1s−1, whereas that for synthetic phenols, hydroquinone and galvinoxyl, was with the range 7 × 103 M−1s−1−8 × 103 M−1s−1. Also, the additive scavenging effect of the (−)-epigallocatechin (EGC):(−)-epicatechin (EC) and the (+)-catechin:epicatechin (EC) combination was observed at 1:1 molar ratio, whereas that of the EC:quercetin combination showed the cancel (prooxidative) effect. Furthermore, the EGC:ASDB (L-ascorbyl 2,6-dibutylate) or 2-ME (2-mercaptoethanol) combination showed the prooxidative effect. Such enhancement of prooxidation in the combination may increase their toxic effects due to their cooxidation. Also, the synergic, additive or cancel effects of the flavonoid:vitamins E combination on the induction period in the BPO (a PhCOO* radical) and 2,2′-azobisisobutyronitrile (AIBN, an R* radical) systems are discussed.