Eiichi Masuhara

4-META Opaque Resin — A New Resin Strongly Adhesive to Nickel-Chromium Alloy

Opaque resins lacking adhesion and mechanical retention devices are required in positioning crowns; the average bond strength in such cases is 60-70 kg/cm2. An adhesive opaque resin containing 4-methacryloxyethyl trimellitate anhydride was prepared for use with acrylic veneer crowns, and its bond strength and durability of adhesion with an alloy were studied. Its bonding strength between cured resin and dental nickel-chromium alloy etched with HCl and oxidized with HNO3 was an average 250 kg/cm2 after immersion in water at 37°C for 30 wk.

Studies on Hemolytic Activity of Bisphenol A Diglycidyl Methacrylate (BIS-GMA)

To clarify the high hemolytic activity of BIS-GMA, the molar concentration producing 50% hemolysis (H 50) and the partition coefficient in-octanol-water were determined using BIS-GMA and various types of methacrylates. It is suggested that the strong hemolytic potency of BIS-GMA is due to the high hydrophobic nature of the compound.

Binding of Eugenol and O-ethoxybenzoic Acid to Bovine Serum Albumin

The binding constants (log K) of eugenol, o-ethoxybenzoic acid, and their analogues, plus other organic compounds widely used in dentistry with bovine serum albumin, were examined with respect to the partition coefficients of these compounds in octanol-water (log P). Linear relationships between log K and log P values were obtained with high relative coefficients. Eugenol and o-ethoxybenzoic acid showed a relatively large log K value.

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.

Evaluation of the Biologic Effects of Dental Materials Using a New Cell Culture Technique

The biological effects of seven dental cements — including zinc oxide-eugenol, EBA, silicate, zinc phosphate, silico-phosphate, polycarboxylate, and glass ionomer — and a composite resin were evaluated by a new cell culture technique. The agar overlay containing serum was proposed as a dentin model. The effects of thickness and serum concentration of the agar overlay on cell growth were studied and compared to in vivo findings. Some correlative phenomena between the cell culture results and in vivo data are presented.

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.

Soft denture liner of fluoroethylene copolymer and its clinical evaluation

The acrylic resins are acrylic copolymers to which plasticizers are added occasionally. Inasmuch as the monomers used are generally solvents for the denture base resins, reasonably good adhesion of the liner to the denture should be expected. On the other hand, acrylic soft resins absorb water, swell, and eventually deteriorate; the plasticizer molecules are leached out by the saliva, and the liners gradually harden. Their intraoral efficacy is short lived, and they are not satisfactory for extended clinical use. The silicone rubbers excel in their resiliency and their initial resistance to water absorption. However, in time they also will absorb water and begin to deteriorate. The liners are attached to denture base resins by an adhesive; but the bond is a poor one, and separations between the two materials often occur. Furthermore, they cannot be polished or trimmed properly. Another objection to the silicone lining materials is the possibility of microbial degradation. We developed fluoropolymer soft liners (Kurepeet, Kurecha Co., Tokyo, Japan) that are chemically stable and show good resistance to solvents and abrasion. In addition, their water absorption is low. We have used the liners clinically and observed their behavior in vivo more than 2 years. The objective of this

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.

Spherical powder for retaining thermosetting acrylic resin veneers.

1. Nine different sizes of spherical powder were prepared, and their effectiveness as retentive devices was evaluated against those available commercially. 2. Smaller-diameter spherical powder (No. 5) gave the best results of all retaining devices tested. 3. The physical properties of the resins play an important role in the retentive strength with No. 5 retention beads. The retentive strength was reduced when brittle resin was used. 4. The retentive strength of the resin veneer was greatly affected by the angle of stress at the incisal resin. The retentive strength increased as the angle between the longitudinal axis of the specimen and the direction of stress decreased.

Nuclear Magnetic Resonance Spectroscopic Studies of the Interaction of Phospholipids with Stabilizing Lysosome Agents

The interaction between phospholipids and stabilizing lysosome agents such as acetylsalicylic acid (ASA), colchicine (CC), prednisolone (PD), etc., was studied using NMR spectroscopy. The peak intensity of protons arising from these compounds was reduced in liposomes containing lecithin and various agents with a molar ratio of 1:1 in D2O. The reduced percentage of protons in the agents differed due to their molecular structures: ASA was about 20%, CC about 30%, and PD about 100%.