Shuichi Yamagata

Mechanical properties and aesthetics of FRP orthodontic wire fabricated by hot drawing

The FRP wires 0.5 mm in diameter with a multiple fiber structure were fabricated by drawing the fiber polymer complex at 250 degrees C for an esthetic, transparent orthodontic wire. Biocompatible CaO-P2O5-SiO2-Al2O3 (CPSA) glass fibers of 8-20 microm in diameter were oriented unidirectionally in the longitudinal direction in PMMA matrix. The mechanical properties were investigated by 3-point flexural test. The FRP wire showed sufficient strength and a very good elastic recovery after deformation. Youngs modulus and the flexural load at deflection 1 mm were nearly independent of the fiber diameter and linearly increased with the fiber fraction. The dependence on fiber fraction obeys well the rule of mixture. This FRP wire could cover the range of strength corresponding to the conventional metal orthodontic wires from Ni-Ti used in the initial stage of orthodontic treatments to Co-Cr used in the final stage by changing the volume ratio of glass fibers with the same external diameter. The estheticity in external appearance was excellent. Thus the new FRP wire can satisfy both mechanical properties necessary for an orthodontic wire and enough estheticity, which was not possible for the conventional metal wire.

The fabrication and properties of aesthetic FRP wires for use in orthodontics

Transparent or translucent fibre-reinforced polymeric wires have been produced in an attempt to reproduce the mechanical properties of the metallic wires in current use in orthodontics. Two methods were employed: mould polymerization, and hot-drawing. Both methods produced wires of 0.5 mm diameter. Two polymers were investigated, poly(methyl methacrylate) and epoxy resin, and these were filled with either long silane-coated alumina fibres or fibres made from CPSA glass. Whilst mould-polymerized wires showed a linear increase in Youngs modulus with fibre content, they did not obey the rule of mixtures. However, the hot-drawn wires did, and they also demonstrated the rigidity, strength and good elastic recovery needed for use in orthodontics.

Electric Charge Dependence of Controlled Dye-Release Behavior in Glass Ionomer Cement Containing Nano-Porous Silica Particles

We investigated in controlled dye-release behavior of nanosized silica particles containing nanocavities (Nanoporous silica, NPS). To determine this, NPS were mixed with glass ionomer cement (GIC), which is a medical material used as a matrix. The dye-release behavior was observed using a UV-visible spectrometer. After cationic dye was charged into GIC pellet containing NPS, the pellet could gradually release cationic dye for up to two weeks. To understand the dependence of electric charge on the dye-release behavior, three types of dyes with different charge were also investigated. Dyes having a neutral or negative electric charge were quickly released from the pellet within a couple of days. These results suggest that the nanocavities present in NPS can selectively bind cationic dyes and allow for their gradual release. This result reveals the excellent sustained dye-release property of NPS.

Chemical modification to suppress metal ions elution of dental orthodontic wire surface

ABSTRACT In this study, we investigated on suppression of metal ions elution on dental orthodontic wire. To suppress metal ion elution from stainless wire, two types of surface chemical modifications were carried out. The obtained wire were immersed into several aqueous solution then the eluted ions (Cr and Ni, which are well known to cause a metal allergy) were determined using coupled plasma mass spectrometry (ICP-MS). By both electropolymerization and self-assembly monolayer formation, the ion elution was effectively reduced. These results suggested that these surface modifications succeeded to suppress the metal ions.

Effects of Surface Properties of Montmorillonite for their Cytocompatibility

We modified the surface of organically modified montmorillonite (OMMT) with the carboxyl group using the silane coupling reaction and assessed its characteristics and cytocompatibility. Scanning electron microscope observations show that while the size and morphology of the obtained OMMT (OMMT-COOH) was unchanged, the surface of OMMT-COOH was coarser than that of OMMT. Fourier transform infrared spectra showed characteristic strong peaks at 1210 and 1630 cm−1, corresponding to the peaks of the carboxyl group. X-ray diffraction analysis showed that the diffraction peak of OMMT-COOH corresponding to the (001) reflection was located at higher a 2θ value than that of OMMT. Results of the proliferation ratio and cell viability measurements indicated that the OMMT-COOH cytocompatibility is higher than that of OMMT. Based on these results, we conclude that cytocompatibility of montmorillonite would be improved by tuning the properties of the surface.

Controlled Ion Release Property of Glass Ionomer Cement Containing Nanoporous Silica Particles

Controlled ion release property of nanoporous silica particles (NPS) were investigated using cationic fluorescent dye, rhodamine B. The dye was charged into a glass ionomer cements (GIC) pellet containing the particles and then the pellet were immersed into distilled water. The dye-release behavior was observed using a UV-vis. spectrophotometer. GIC containing NPS can release the dye for a couple of weeks, where as other samples released it only a few days. This result suggests that NPS has excellent sustained dye-release property.

FRP Esthetic Orthodontic Wire and Development of Matrix Strengthening with Poly(methyl methacrylate)/Montmorillonite Nanocomposite

Orthodontic treatment using a multibracket appliance is the most popular and precise method for correcting misaligned dentition. We have been working to replace a conventional orthodontic metal wire with a fiber reinforced thermo-plastic (FRP) wire and have developed an esthetic transparent FRP wire containing biocompatible glass fibers and poly (methyl methacrylate) (PMMA). However, loss of mechanical properties carried by failure related with glass fibers has not yet been resolved. Meanwhile, we are working on developing a super-fiber (high-strength and high-modulus fibers) reinforced thermo-plastic wire; for this we will have to focus on improving the stiffness of PMMA without causing any deterioration in its flexibility. Transparent PMMA/layered silicate nanocomposites were fabricated by a solution intercalation method. Montmorillonite, organically modified with quaternary alkylammonium ions, was selected as the filler for reinforcement. The nanocomposites are transparent enough for their use as esthetic orthodontic wires. The flexural modulus of them was favorably improved. Those results encourage us to make them applicable for other dental use. To the best of our knowledge, there has been little or no research on polymer/layered silicate nanocomposites in the field of dentistry. A novelty and an application potentiality of our challenge are beneficial for evolving dentistry.

Preparation of a Poly(Lactic Acid)/Montmorillonite Nanocomposite

Poly (L-lactic acid)/organically modified montmorillonite (PLLA/OMMT) nanocomposites were fabricated by a solution intercalation method. OMMT, modified with quaternary alkylammonium ion, was prepared by alkyltrialkoxysilane. The differential scanning calorimetry measurement revealed that the crystallization temperatures of PLLA/OMMT nanocomposites were at around 110 °C regardless of the existence of OMMT or the weight fraction of them. X-ray diffraction patterns suggested that the (001) diffraction was around 2θ = 2.5°. The TEM image showed variously expanded interlayer galleries of OMMT and partially exfoliated silicate layer unit in the matrix. Board-shaped specimens for mechanical property tests were fabricated by compression-molding at 190 °C (including 30 min annealing at 110 °C). The flexural modulus of the nanocomposites increased with increasing content of OMMT. Vickers hardness of the nanocomposites were almost same independent on weight fraction of OMMT.

Biocompatibility and Biodistribution of Several Nano-Sized Ceramics Particles

We succeeded in determination the biodistribution of several nano-sized particles administered to mice through the tail vein. After administration, these particles were observed in the lung, liver and spleen. The distribution behaviors depend upon not only chemical species but also the particles size. To estimate their cytocompatibility, these particles were exposed to osteoblastic cell at several concentrations. When the concentration reached at 10 ppm, their viability remained at 80% or more even nano-sized particle contained rare earth element. Only CuO particles indicated the viability decrease. The effect depended on the particle size. These results suggested that the chemical species played a dominant key in the biodistribution and biocompatibility of nanoparticles compared with the size-effect.