In the prior investigation, a spacer was reported to improve the adaptability of MOD define composite resin inlays, but a spacer made of condensation cured silicone interfered with the double bond conversion of light-cured composite resins.This study evaluated a new experimental spacer of addition cured silicone.The experimental spacer improved the adaptability of the resin inlays mede from a Lite-fil CR Inlay and a 3M Resin Inlay more than the separating agent which was prepared according to the manufacturer's instructions.However, the experimental spacer did not improve the adaptability of the resin inlays made from a Clearfil CR Inlay.The film thickness of the new spacer was from 3 to 13μm on every MOD cavity wall of the stone dies.The Vickers hardness of the resin inlays on the new spacer was lower than that on a polyester matrix, but higher than that on a spacer made of a condensation cured silicone.A spacer is very useful for a composite resin inlay because the spacer fills the micro-undercuts of the stone dies and makes it easy to remove the resin inlay from a stone die.However, there is still room for improvement of the material of the spacer and the procedures for applying it to a stone die.

View full abstract

To improve the mechanical properties of crown and bridge resins, organic and/or inorganic fillers are added.However, heavy filler loading results in increased rigidity of the cured resin which then tends to fracture easily.Experimental crown and bridge resins were prepared by curing TEGDMA, BdDMA and BMA as liquid components with silica powder as a filler.The mechanical properties of these experimental crown and bridge resins were examined.The water sorption of the crown and bridge resins decreased as the concentration of BdDMA in the matrix resin increased.The transverse strength showed a maximum value of 203MPa at a concentration of 5vol% BdDMA in the crown and bridge resin containing 80wt% inorganic filler.Despite the high modulus of elasticity, the deflection of the cured resin was about 1.5 times as high as that without BdDMA.

View full abstract

A heat-cured crown and bridge resin with good mechanical properties, was designed using cross-linked polymer and micro silica(MF)as a filler.Thus, the micro cross-linked polymer and microcapsular filler(MCP)reinforced with MF obtained by the phase separation method, and organic filler with MF were prepared as fillers.The mechanical properties of these three experimental resins with various fillers were investigated.The results were obtained as follows:1.MCP which was surface-treated showed better adhesion at the polymer-matrix-interface than the cross-linked polymer.2.Transverse strength was influenced by adhesion at the filler-matrix interface, and increased by increasing the MF content relative to the cross-linked polymer.The transverse strength of resins using non-surface-treated filler was 80% of those using surface-treated filler.3.The elastic modulus and the Knoop hardness increased with increases in the filler content.4.Abrasion loss decreased with increases in the MF content.The abrasion loss of MCP was less than that of the organic filler.Since the particle size of MCP was smaller than that of organic filler, the distance between MCP particles was shorter than that between organic filler particles.Therefore, MCP reinforces the matrix more effectively than organic filler.5.MCP filler containing 60% MF showed good adhesion at the MCP-matrix interface, since MF located at the surface was treated with γMPTS.

View full abstract

In this study radiopaque self-curing acrylic resins were prepared by adding ZrO₂ micro particles to the polymer beads, then their radiopacities, physical properties, discoloration and adherence of oral bacteria were evaluated for clinical use.Acrylic resin containing more than 21.3wt% ZrO₂ demonstrated sufficient radiopacity, but the sterngth decreased as ZrO₂ contents increased.Therefore, the most desirable ZrO₂ content for clinical application was estimated to be about 21.3wt%.The other physical properties, discoloration and adherence of oral bacteria did not significantly differ from those of commercially available self-curing resins.This suggests that the present method using polymer beads polymerized with ZrO₂ would more effectively obtain high radiopacity compared with that obtained by mixing ZrO₂ powder with polymer beads.

View full abstract

Fabrication of titanium extracoronal attachments was investigated using a numerically controlled wire type electric discharge machining(EDM).Even when the machining properties of titanium plates and castings differed, high machining accuracy was achieved by selecting suitable machining conditions.Retention between male and female parts was adjusted by the taper of attachments and the machining programs.The female was designed on the computer and fabricated on the pontic of the titanium casting crowns using a wire type EDM.The male was designed to fit the female on the computer and fabricated from titanium plate using a wire type EDM.The fabrication system investigated was considered a practical application of EDM to prosthetic works.

View full abstract

This study investigated the relationship between fluorine(F)release from glass-ionomer cement(GIC)and disintegration of the cement.Two kinds of GIC products and one kind of light cured GIC were used.Immersion in distilled water began, 5, 10 or 60 minutes after the start of mixing.After immersion for two weeks, the solutions were analyzed to determine the amounts of F, Al and Si.The amount of dissolved F was higher and the disintegration of GICs, indicated by the amounts of Al and Si dissolved, was greater, the sooner immersion began after mixing.The influence of early immersion on disintegration was smaller in light cured GIC, which disintegrated less than the other GICs.The results demonstrated that F release from GIC which was immersed sooner, was strongly related to disintegration of the cement.F release from both GICs, which had been immersed later, and from light cured GIC, seemed to be related to diffusion of F through the GIC matrix.

View full abstract

Functionally gradient materials(FGM)were made for dental applications.Mixed powders with different ratios of metals(titanium, palladium)and ceramics(hydroxyapatite, zirconia)were packed into silicone rubber molds changing the concentration gradually from one end to the other.The specimens were compressed under a pressure of 400MPa by cold isostatic press(CIP)and sintered in an argon gas atmosphere by high frequency induction heating at a temperature of 1, 300℃.Mechanical tests were performed using the uniform composite sintered specimens.The relation of the mechanical properties with the micro structure was investigated by SEM observation.With increases in hydroxyapatite, the titanium-apatite specimens showed lower values in both flexural strength and deflection, but maximum values in both the elastic modulus and apparent density were found in specimens containing 95% titanium.There was a close corelation between apparent density and elastic modulus of titanium-zirconia specimens.The modes of fracture were brittle on both the flexural test and diametral test, in contrast with the ductile properties in the compressive test.At the same volumetric content, the titanium-apatite composite showed the same flexural strength as the titanium-zirconia composite, and higher values in elastic modulus and strain.By adding 5% palladium to titanium, sintering was improved and the strengthening effect of alloying was prominent at the higher range of apatite concentration.By inserting titanium plate or coil, a 50% increase of flexural strength and 80% increase of elastic modulus were obtained structurally.Using functionally gradient materials specimens in the shape of column, implants and rods were made gradually changing the ceramics content from pure titanium at one end to 50% ceramics at the other end.The micro-hardness numbers of these specimens were distributed gradually relative to the ceramics content.

View full abstract

We examined the effect of five kinds of monomers, MMA, TEGDMA, Bis-GMA, UDMA and HEMA, which are widely used for dental restorations, on L-929 cells in serum-free culture.The effects of serum concentration on monomer cytotoxicity were also examined.In serum-free cultures, the 50% inhibitory concentration(IC50)of Bis-GMA was 4.2μg/ml, the lowest, while MMA showed 8, 992μg/ml, the highest.Serum-free culture induced a considerable reduction in IC50 of TEGDMA, Bis-GMA, and UDMA.The order of cytotoxicity as a whole was Bis-GMA>UDMA>TEGDMA>HEMA>MMA.However, IC50 was increased two to thirty-five times when serum was added to the culture.Increasing the quantity of serum added by 1, 5 and 10% resulted in decreases in the cytotoxicity level of each monomer.However, their order remained unchanged.The order of cytotoxicity in culture containing 10% serum was Bis-GMA>UDMA>HEMA>TEGDMA>MMA, therefore TEGDMA and HEMA reversed order between serum-free and serum containing cultures.These findings suggest that cytotoxicity tests without the influence of serum are necessary to evaluate the cytotoxicity of monomer itself and consider the interaction between monomer and protein.

View full abstract

To clarify the interface reaction between porcelain and pure titanium during porcelain firing, an electron probe microanalyzer(EPMA), X-ray diffraction and Fourier transform infrared spectroscopy(FTIR)were used to characterize the interface that was revealed after mechanically peeling.Separation occurred partly at the interface between titanium and porcelain and partly slightly inside the porcelain after firing three times at 760℃.In the surface layer of the titanium side, only oxygen was detected as a diffusing element.Redox reaction was deduced from the X-ray diffraction results which indicated a decrease in SnO₂ and revealed β-Sn(metallic Sn).A considerable amount of Ti₂O was formed at the interface when fired at 760℃ for two minutes.

View full abstract

Thiobarbituric acid monomers, 5-allyl-2-thiobarbituric acid(5AS)and 5-(4-vinylbenzyl)-2-thiobarbituric acid(5VS), were utilized to treat the surface of dental metals to enhance the durability of adhesion against water at the adhesion interface between resin and metal.Treatment agents were prepared by dissolving 5AS or 5VS in various solvents.The agent was applied to metal surfaces polished to a mirror-like finish, and the two specimens were butt jointed with MMA-PMMA/TBBO resin.Tensile bond strength measurements were made after 2000 thermal cyclings in water, and the durability of adhesion was evaluated.The introduction of the treatment with the thiobarbituric acid monomers yielded statistically superior bond strengths, and the agent containing 5VS was more effective than that containing 5AS in almost all cases.Ethanol was generally the most suitable solvent for the agent, although acetone demonstrated a specific adhesion to noble metal alloys with the highest bond strength.The bond strengths also depended on the concentration of the monomers in the agent, and excellent adhesion durability against water was observed even at the low concentration of 0.001mole%.Results suggested that treatment with 5VS provided high bond strengths to noble metal alloys rather than base metal alloys and that this bond was durable against water penetration.

View full abstract

The effect of surface treatment on structural change of dentinal collagen and the durability of its adhesiveness to resin was examined and the mechanism considered.From transmisson electron microscopy(TEM), scanning electron microscopy(SEM)and adhesive strength test for acid-etched dentin, treated with an aqueous solution of 2-hydroxyethyl methacrylate(HEMA), the following results were obtained.The microfibril structures of dentinal collagen fibers were transformed following the application of HEMA.The resin was impregnated layer produced by this procedure considerably thicker than that without HEMA.Respective adhesive and tensile strengths of 12.07 and 11.75MPa were obtained after immersion in water 37℃ for one day or after 20, 000 thermal cycles, indicating only a slight decrease.

View full abstract