Mitsuru Atsuta

Effect of different etching periods on the bond strength of a composite resin to a machinable porcelain

OBJECTIVES The purpose of this study was to evaluate microstructure changes of Cerec 2 Vitablocs Mark II porcelain etched by a 5% hydrofluoric acid and examine the effect of different etching times on the bond strength between the porcelain and a composite resin. METHODS Six different etching times (0, 5, 30, 60, 120 and 180 s) were used to etch the surfaces of the porcelain, respectively. Etched relief patterns were observed by means of a scanning electron microscope and the bond strength was determined between a dual-cured composite luting agent and the porcelain. RESULTS The results showed that composite resin did not bond to unetched porcelain but bonded to etched porcelain, the 120 s etch giving the highest bond strength. CONCLUSION The bond strength values corresponded well to the microstructure changes caused by etching.

Effect of ceramic surface treatments on the bond of four resin luting agents to a ceramic material

PURPOSE This study evaluated the effect of various ceramic surface treatments on the shear bond strengths of four resin luting agents to Cerec 2 ceramic material. MATERIAL AND METHODS Four ceramic surface treatments were performed. All groups were subjected to the control treatment, which was abrasion with No. 600 silicon carbide paper. The other three group treatments were etching with phosphoric acid gel, application of bonding agent containing silane coupler, and application of silane coupling agent after etching with phosphoric acid gel. Cerec 2 ceramic specimens were treated with one of the four methods and then cemented together with each of the four resin luting agents (Super-Bond C&B, Panavia 21, Clapearl, and Vita Cerec Duo Cement). Half of the specimens were stored in water and the other half were thermal cycled before shear bond strength testing. RESULTS Treatment with the silane coupler improved the shear bond strength compared only with the abrasion with carbide paper (control). When the ceramic material was treated with the silane coupler or the silane coupling agent after etching with phosphoric acid gel, no significant differences in bond strength were noted between water storage and 20,000 thermal cycles for any of the four resin luting agents. After 20,000 thermal cycles, all specimens treated with the silane coupling agent with phosphoric acid gel except those cemented with Super-Bond C&B resin luting agent after etching showed cohesive failures within the ceramic. CONCLUSION Combined surface treatment of etching with phosphoric acid and application of silane coupling agent provides the highest bond strengths of resin luting agents to Cerec 2 ceramic material after thermal cycling.

Photo‐induced hydrophilicity enhances initial cell behavior and early bone apposition

OBJECTIVE The anatase form of titanium dioxide (TiO(2)) exhibits photo-induced hydrophilicity when it is irradiated with ultraviolet (UV) light. In the present study, the effect of photo-induced hydrophilicity on initial cell behavior and bone formation was evaluated. MATERIALS AND METHODS Plasma source ion implantation method and post-annealing were employed for coating the anatase form of TiO(2) to the surface of the titanium disk and implant. Half of the disks and implants were illuminated with UV for 24 h beforehand, whereas the other halves were blinded and used as controls. Photo-induced hydrophilicity was confirmed by a static wettability assay. The effects of this hydrophilicity on cell behavior were evaluated by means of cell attachment, proliferation and morphology using pluripotent mesenchymal precursor C2C12 cells. Thereafter, bone formation around the hydrophilic implant inserted in the rabbit tibia was confirmed histomorphometrically. RESULTS The water contact angle of the photo-induced hydrophilic disk decreased markedly from 43.5 degrees to 0.5 degree. Cell attachment and proliferation on this hydrophilic disk showed significant improvement. The cell morphology on this hydrophilic disk was extremely flattened, with an elongation of the lamellipodia, whereas a round/spherical morphology was observed on the control disk. The photo-induced hydrophilic implant enhanced the bone formation with the bone-to-metal contact of 28.2% after 2 weeks of healing (control: 17.97%). CONCLUSION The photo-induced hydrophilic surface used in the current study improves the initial cell reactions and enhances early bone apposition to the implant.

Bond strength and durability of porcelain bonding systems

Because the most effective bonding system for ceramic restorations has not been documented, this study examined bond strength and durability of bonding systems joined to a feldspathic porcelain. Disks of porcelain specimens were fired on refractory investment materials and were air-abraded with alumina. The disks were then bonded with six combinations of five silane primers and six luting agents. Durability of the bond was evaluated by means of a thermocycling machine. Shear bond strengths were determined before and after thermocycling. The results showed that reduction in bond strengths after thermocycling was remarkable for five systems (p < 0.05). However, three systems exhibited shear bond strength greater than 20 MPa after 20,000 cycles.

Effect of Pressure Difference on the Quality of Titanium Casting

In casting titanium using a two-compartment casting machine, Herø et al. (1993) reported that the pressure difference between the melting chamber and the mold chamber affected the soundness of the castings. This study tested the hypothesis that differences in pressure produce castings with various amounts of porosity and different mechanical properties values. Plastic dumbbell-shaped patterns were invested with an alumina-based, phosphate-bonded investment material. Both chambers of the casting machine were evacuated to 6 x 10-2 torr; the argon pressure difference was then adjusted to either 50, 150, 300, or 450 torr. The porosity of the cast specimens was determined by x-ray radiography and quantitative image analysis. Tensile strength and elongation were measured by means of a universal testing machine at a strain rate of 1.7 x 10-4/s. The fractured surfaces were examined by SEM. Changes in Vickers hardness with depth from the cast surface were measured on polished cross-sections of the specimens. Raising the argon pressure difference to 300 and 450 torr caused a significant increase in internal porosity and a resultant decrease in the engineering tensile strength and elongation. The highest tensile strength (- 540 MPa), elongation (- 10%), bulk hardness (HV50g 209), and lowest porosity level (- 0.8%) occurred in the specimens cast at 150 torr. Turbulence of the metal during casting was thought to be responsible for the increase in porosity levels with the increase in argon pressure difference. By choosing an argon pressure difference (around 150 torr) suitable for this geometry, we could produce castings which have adequate mechanical properties and low porosity levels.

A New Ion-coating Surface Treatment of Alloys for Dental Adhesive Resins

4-META and new phosphate-methacrylate resins adhere strongly to dental alloys. However, for strengthening the water durability of the adhesive interface, the oxidation of the alloy surface is indispensable. A new oxidation method using ion-sputtering was developed, and the effectiveness of this surface treatment on two dental alloys-a type IV gold alloy and Ni-Cr-Be alloy-was investigated. As an endurance test, thermocycling for a maximum of 100, 000 cycles was adopted, and the tensile adhesive bond strength was then measured. Ion-coating the surface of the alloys resulted in strong bonds with adhesive resins, and after 100, 000 thermocycles, a bond strength of above 20 MPa was maintained.

Heterogeneity in the expression pattern of two ganglioside synthase genes during mouse brain development

Abstract: Gangliosides are synthesized by sequential catalytic reaction of multiple glycosyltransferases. GM2/GD2 synthase and GD3 synthase are key enzymes for ganglioside synthesis, because their relative activities regulate the main profiles of ganglioside expression. Mouse GD3 synthase (EC 2.4.99.8) cDNA was cloned by eukaryotic expression cloning, and its mRNA expression as well as that of GM2/GD2 synthase gene during the development of the mouse CNS was analyzed by using northern blotting, reverse transcription‐polymerase chain reaction, and in situ hybridization. When brain tissue was analyzed as a whole mass, a typical pattern corresponding to the reported findings obtained by biochemical analyses was observed, i.e., high expression of GD3 synthase gene in the early stage and gradual increase of GM2/GD2 synthase gene expression in the late stage of the development. However, the results of in situ hybridization of these two genes revealed that the expression kinetics of these two genes were heterogeneous among various sites in the brain under development. These findings suggest that various expression patterns of the two genes reflect differences in the course of the development of individual sites, and also different ganglioside components are required in individual portions of the brain for development and maintenance of the function.

A new porcelain repair system with a silane coupler, ferric chloride and adhesive opaque resin

A new porcelain repair system was developed which uses a two-liquid primer, self-cured opaque resin, and light-cured composite. The primer consisted of two liquids. One component was 4% 3-trimethoxysilylpropyl methacrylate in methyl methacrylate, and the other component was 0.5% ferric chloride in ethanol. A self-curing opaque resin, 4-META/MMA-TBB opaque resin, was used as an adhesive to bind the porcelain and the composite. Adhesive opaque resin was applied on the roughened and primed porcelain. Light-cured composite was placed over the 4-META opaque layer. A shear test was performed for investigation of the strength and durability of the bonding. The result was that for all specimens after 20,000 thermocycles, fracture or crack propagation during the shear test occurred in the porcelain, rather than in the bond. This system may be used to repair fractured porcelain facings without removal of prostheses.

Effect of adhesive primers on bonding a prosthetic composite resin to metals

Abstract The effect of three adhesive metal primers on the shear bond strength of a light-cured prosthetic composite resin bonded to cobalt-chromium or silver-palladium-copper-gold casting alloy was evaluated. The adhesive metal primers used were New Metacolor opaque bonding liner, Cesead opaque primer, and 0.5% VBATDT in acetone. A newly prepared light-cured opaque resin was used to bond a light-cured veneering resin to dental alloys. The specimens were thermocycled in water for up to 20,000 cycles between 4 °C and 60 °C, and shear bond strengths were recorded. The light-cured composite resin bonded most strongly to Co-Cr alloy primed with Cesead primer and to Ag-Pd-Cu-Au alloy with the VBATDT primer. These adhesive metal primers may be clinically acceptable for bonding a light-cured prosthetic composite resin to base or precious metal.

Surface treatment of gold alloys for adhesion

A lthough several efforts have been made to develop adhesives and bonding methods for dental gold alloys, the results failed to provide adequate attachment to counteract the severe conditions in the oral cavity.le3 Poor water resistance of the adhesives or lack of effective surface pretreatment of the gold alloys were the main reasons for failure. Previous studies found that adhesives containing 4methacryloxyethyl trimellitate anhydride (CMETA), a synthesized adhlesion-promoting monomer, provided strong adhesion 1.0 nonprecious alloys.4,5 In addition, the bonding durability of the 4-META resin with these alloys was much improved by oxidation of the metal surface. To apply these findings to gold alloys, various trials using experimental thermosetting type 4-META resins were conducted. This research resulted in two kinds of surface oxidation, singleand double-heating.6 Because the clinical use of a thermosetting resin is less frequent than that of a self-curing resin, the effectiveness of both surface treatments with a self-curing type 4-META resin was investigated.‘,* Favorable bonding strength of greater than 200 kg/cm2 was obtained after 20,000 thermocycles in both treatment methods. In addition, the single-heating method was studied for application to fixed partial dentures and other adhesionretained restorat:ions.