Yohji Imai

Effect of blending calcium compounds on hydrolytic degradation of poly(DL-lactic acid-co-glycolic acid).

To clarify the effect of blending calcium compounds with different acidity or basicity on the degradation of poly(DL-lactic acid-co-glycolic acid) (PLGA). composite materials composed of PLGA incorporated with 30 mass% of calcium dihydrogenphosphate (CDHP), calcium hydrogenphosphate, calcium phosphate, and calcium carbonate (CC) were prepared by mixing in dioxane followed by freeze-drying. The porous composite materials were then compressed to yield nonporous films with 0.5 mm thickness. The blend films and the unfilled films as a control were immersed in phosphate-buffered saline (pH 7.4) at 37 degrees C. Specimens were removed at 1, 2, 3, 4, 6, and 8 weeks and subjected to measuring of water absorption, mass loss, thickness change, and molecular weight. The temporal changes in appearance and measurements for the five materials differed from each other; especially, the CC blend differed from the other four materials. The degradation of PLGA decreased with increasing basicity of the calcium compounds blended. The most basic CC was most effective to delay the degradation, while the most acidic CDHP was least effective. However, even CDHP had appreciable degradation-delaying effects compared with unfilled PLGA. Thus, the findings of the present study suggest that degradation of PLGA can be varied by blending inorganic compounds with different basicity.

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.

Microf racture Mechanisms of Dental Resin Composites Containing Spherically-shaped Filler Particles

The effects of spherically-shaped filler particles on bending strength, bending elastic modulus, and fracture toughness of resin composites were studied. The filler content was changed by 0, 20, 40, 60, and 70 wt%. Bending properties and fracture toughnesses were determined on three-point bending specimens. Acoustic Emission (AE), i.e., the elastic wave released from a localized source in the material, was detected by sensors of a high-sensitivity and low-noise resonance type during the fracture toughness test. Detected acoustic emission signals were analyzed for parameters such as amplitude, events, and locations. The fractured surf ace was examined by a scanning electron microscope. The bending strength and the fracture toughness showed almost the same trend in their increasing rates by filler content, but the elastic modulus showed a much higher increasing rate. A microfracture mechanism of the dental resin composites containing spherically-shaped filler particles is proposed based on the results obtained from the AE-releasing pattern, two-dimensional AE location, and fracture surface findings. In addition to the toughening effects of crack pinning and crack branching, which are observed in the usual commercial resin composites, crack-deflecting effects are confirmed in this new type of dental resin composites.

Synthesis of poly(ethylene glycol)-silk fibroin conjugates and surface interaction between L-929 cells and the conjugates

Poly(ethylene glycol) (PEG)-silk fibroin (SF) conjugates (PEG2-SF) were prepared by the chemical modification of solubilized SF with 2,4-bis[O-methoxypoly(ethylene glycol)]-6-chloro-s-triazine (actPEG2) in borate buffer at 37 degrees C. The IR spectra and DSC curves of PEG2-SF and SF suggested the introduction of PEG into SF by the modification and the beta-sheet structure of both SF and PEG2-SF induced by the treatment with methanol aqueous solutions. The content of the PEG component in PEG2-SF was evaluated to be 67% by weight from the melting enthalpy change of PEG observed on the DSC thermogram of PEG2-SF. Water content and contact angle measurements of SF before and after the modification indicated that the hydrophilicity of the PEG2-SF surface increased compared with that of SF. The attachment and growth of fibroblast cells (L-929) on the matrix of PEG2-SF were studied by a cell culture method. PEG2-SF exhibited very low cell attachment and growth, though SF exhibited high cell attachment and growth. The filopodium of the cells attached to PEG2-SF could not be found, and the cells aggregated to form masses in scanning electron microscopy images. These results could be explained in terms of the increased hydrophilicity of the PEG2-SF surface.

Properties of a new injectable type of root canal filling resin with adhesiveness to dentin

The properties of a new, injectable type of root canal wall, adhesive filling resin, which we developed, were studied for its physical properties, adhesiveness to dentin and the root canal, and sealing ability. The new resin consisted of a powder composed of a specially selected poly(methyl methacrylate) and barium sulfate radiopacifier and liquid composed of methyl methacrylate monomer and tributylborane catalyst. A mixture of both components had a consistency suitable for injection. The physical properties, including radiopacity, were evaluated according to the ISO standard. The adhesiveness to dentin and the root canal was investigated by bond strength testing or by scanning electron microscopy. The apical sealing ability of the new resin was compared by a dye penetration test with that of gutta-percha/sealer. The findings of this study indicated that the new filling resin had physical properties satisfying all the ISO requirements for dental root canal sealing materials: a tensile bond strength to dentin of 7.3 MPa, a significantly better sealing ability compared with gutta-percha/sealer, the capability of forming resin tags in dentinal tubules, and removability.

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.

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.

Dentin Bonding and Sealing Ability of a New Root Canal Resin Sealer

The aims of this study were to find a dentin bonding system suitable for root canal treatment using a newly developed root canal resin sealer, and to examine its sealing ability. The sealer was composed of vinylidene fluoride/hexafluoropropylene copolymer, methyl methacrylate, zirconia, and tributylborane catalyst. The effects of dentin conditioners and primers on dentin bonding were studied by tensile bond strength testing and scanning electron microscopy. Apical and coronal leakage were evaluated at 1-, 4-, and 12-wk intervals by a dye penetration test using a methylene blue solution. Pulp Canal Sealer EWT and Sealapex were used as controls. Significantly high bond strength was obtained by treating dentin with EDTA, followed by application of a glutaraldehyde/2-hydroxyethyl methacrylate primer. The experimental resin sealer produced a significantly superior coronal seal at 12 wk when compared with the two control sealers (p < 0.05). Scanning electron microscopic examination revealed few gaps at the resin sealer-dentin interface.

Primer for bonding resin to metal.

OBJECTIVES The purpose was to examine the effect on the bond strength and durability of a resin bond to metal of modification of a primer consisting of thiophosphoric methacrylate with phosphoric methacrylates and/or benzoyl peroxide. METHODS Acrylic rods were bonded with a luting resin consisting of poly(methyl methacrylate) powder and a mixture of methyl methacrylate and tributylborane initiator to silver-palladium alloy (Ag-Pd), gold-silver alloy (Au-Ag), cobalt-chromium alloy (Co-Cr), and titanium (Ti) surfaces treated with various primers. The bonded samples were thermocycled for 2,000 cycles and the mean bond strengths were compared using one-way ANOVA and Duncans new multiple range test at p < 0.05. RESULTS Using primers of thiophosphoric methacrylate or phosphoric methacrylates alone, the bond strengths of Ag-Pd decreased significantly (p < 0.05) after thermocycling. The durability was significantly improved (p < 0.05) when thiophosphoric methocrylate was used in combination with the phosphate monomers. The additional use of benzoyl peroxide and heat treatment resulted in a significant increase (p < 0.05) in the durability of two groups; the mean bond strengths over 20 MPa and the lowest values remained unchanged even after 2,000 thermocycles. SIGNIFICANCE The highest level of bond strength and durability to dental noble metals was achieved using a mixture of thiophosphoric and phosphoric methacrylates and benzoyl peroxide. These bond strength results are comparable to values obtained for base metals.

Osteoinductive potential of freeze-dried, biodegradable, poly(glycolic acid-co-lactic acid) disks incorporated with bone morphogenetic protein in skull defects of rats

Biodegradable, porous, polymer implant disks with an osteoinductive potential were prepared by a freeze-drying technique by incorporating bovine bone morphogenetic protein (BMP) in poly (glycolic acid-co-lactic acid) (PGLA). The PGLA disks with and without BMP were implanted in rat skull defects, and the defect sites were studied radiographically and histologically for 2 and 4 weeks after implantation. A quantitative radiographic analysis showed significantly thicker radiopacity for the disks with BMP than those without BMP (P < 0.01). After 2 weeks, chondrogenesis and new bone formation were observed on the BMP-incorporated disks. After 4 weeks, PGLA was completely replaced by new bone in the defects with implantation of the BMP-incorporated disks, whereas the defects implanted with PGLA alone were filled with fibrous connective tissue. The results suggest that BMP-incorporated PGLA is an ideal bone substitute with osteoinductive potential.