K. Wakasa

Analysis of Photo-initiators in Visible-light-cured Dental Composite Resins

Seven commercial visible-light-cured (VL) dental composite resins were analytically studied for identification of the photo-initiator consisting of photo-sensitizer and reducing agent. Gas-liquid chromatography (GC) was used for the determination of the dilute components extracted from the composite resin. Mass spectroscopy (GC-MS) was used for confirmation of the qualitative data obtained by GC. The results showed that all composite resins examined included camphorquinone (CQ) as a photo-sensitizer. The concentration of CQ in the resin phase, however, ranged from 0.17 to 1.03% w/w. The composite resin with hybrid-sized filler tended to have a higher concentration of CQ than did the micro-filled composite resin. As for the reducing agent, two out of seven brands contained dimethylaminoethyl methacrylate (DMAEMA), and one included dimethyl-p-toluidine (DMPTI). The mixing ratio between CQ and the amine in these three composite resins also varied. Another four brands did not contain either DMAEMA or DMPTI, and would utilize different reducing agents.

Refractive-index-adjustable Fillers for Visible-light-cured Dental Resin Composites: Preparation of TiO 2-SiO2 Glass Powder by the Sol-gel Process

New fillers have been prepared for visible-light-cured (VL) dental resin composites with the refractive index adjustable to that of the resin phase. These SiO2 glass powders containing TiO2 up to 20 wt% were formed by heating to 1000°C ground gels made from a mixture of Ti[OCH(CH3)2] 4 and Si(OC2H5)4· With increasing TiO2 content, the refractive index of the prepared powder increased linearly, while the optical transmittance at 467 nm decreased linearly. The experimentally formulated VL-cured resin composites, consisting of (TEGDMA and Bis-GMA) monomer mixture and TiO2-SiO2 glass filler, had greater transmittance when the refractive index of the filler matched that of the monomer mixture, resulting in a greater degree of monomer conversion upon irradiation with VL.

Cutting effectiveness and wear of carbide burs on eight machinable ceramics and bovine dentin.

As a first approach in evaluating the feasibility of industrial machinable ceramics in dentistry, we performed weight-load-cutting tests on eight machinable ceramics and bovine dentin, using #1557 carbide burs driven by an air-turbine handpiece. While the transverse load applied to the bur was cyclically varied between 20 and 80 g, we measured the cutting speed (i.e., the steady-state handpiece speed during cutting) and the cutting volume. The greater the applied load, the more the cutting speed decreased and the cutting volume increased. The degree of this trend, however, differed among the workpieces. When dentin and mica-based glass ceramics were being cut, the cutting speed was moderately reduced, the cutting effectiveness of the bur remained high, and the wear of the bur was small. When other ceramics--such as AIN-based, Si3N4-based, and CaO.SiO2-based ceramics--were being cut, however, the cutting speed was less diminished, and the cutting efficiency of the bur was smaller and decreased rapidly, along with extensive wear of the bur. We speculate that mica-based glass ceramics could be used as the substitute for dentin in the pre-clinical cutting exercise, and that another potential use of machinable ceramics examined might be in the production of future machined dental prostheses.

Curing performances of four experimental bis-GMA based binary monomer mixtures for dental visible-light-cured composite resin inlays

Visible-light-cured (VLC) composite resins have been widely accepted in dental clinics because of their aesthetic merit and ease in handling [1]. Visible light (VL) irradiation of composite resins at intraoral temperature is, however, said to be insufficient for maximum polymerization, leading to wear and discoloration problems [2-4]. To offset these drawbacks, a method for post-curing by heat has been introduced. These composites are now used as V L C inlay composite resins [5]. For the purpose of providing VLC inlay composite resins with improved clinical performances, it seems necessary to study the monomer mixture suitable for both VL and heat curing. Bisphenol A glycidyl dimethacrylate (bis-GMA) has been proven to be a useful base monomer for various dental composite resins [6]. Due to its high viscosity, however, bis-GMA has to be added with diluent monomers to render the handling and incorporation of filler easier [7]. Although some attempts have been made to examine the influence of diluent monomers on the curing behaviour of bis-GMA based binary monomer mixtures [8], such effects are still not well clarified. Therefore, the objectives of this study were, firstly, to prepare four bis-GMA based binary monomer mixtures and evaluate their curing performance by VL and by VL plus heat with residual monomer measurements and mechanical strength (diametral tensile strength) measurements and, secondly, to assess the effects of post-curing by heat on the properties of the once photo-cured copolymers. Table I shows the formulation of four bis-GMA (D-GMA, Shin Nakamura Co., Japan; lot no. 1105K) based binary monomer mixtures, in which one of the following four monomers was used as the diluent monomer: triethyleneglycol dimethacrylate

CURE PERFORMANCE OF MULTIFUNCTIONAL MONOMERS TO PHOTO-INITIATORS : A THERMOANALYTICAL STUDY ON BIS-GMA-BASED RESINS

In order to assess cure performance in experimental monomer systems containingbis-GMA and 3G, differential scanning calorimetry was used to obtain heat for curing, and residual monomers present within the resin systems were measured by high-performance liquid chromatography. Visible light-activated polymerization of these monomer systems was studied using camphorquinone (CQ) and reducing agents of dimethylaminoethyl methacrylate (DMAEMA) and dimethyl-para-toluidine (DMPT). For unfilledbis-GMA-based resin (60 wt%bis-GMA and 40 wt% 3 G) containing CQ (0.5 wt%) and DMAEMA (0.5 wt%) indicating approximately 100% polymerization, less residual monomer and larger hardness than the other monomer systems were observed.

Application of multifunctional base monomer to dental composite resins

Experimental composite resin systems were prepared with visible-light-cured multifunctional matrices to which various amounts of organic composite filler were added. In comparison with the unfilled resins, the filled resin systems were tested for Knoop hardness, compressive and diametral tensile tests, thermal properties, and water sorption. Analyses of the results obtained for the unfilled resins indicate that the increased hardness and mechanical strength were dependent on the multifunctional base monomer. The effective composite resin system was the one that was filled with organic composite filler in the multifunctional comonomer having triethylene glycol dimethacrylate as a diluent monomer.

High-temperature oxidation behaviour of base metal elements in nickel-base alloys

Oxidation of non-precious metals nickel, chromium and copper, nickel-base alloys in an air atmosphere was studied under differential thermal analysis. The results suggest that adding chromium and copper to high-purity nickel metal reduces the amount of oxidation and gives a slower oxidation than in untreated high-purity metals. It is then shown that the activation energy for oxidation in nickel-base alloys is almost the same as that in high-purity nickel metal when alloying elements are added to nickel.

DENTAL APPLICATION OF POLYFUNCTIONAL URETHANE COMONOMERS TO COMPOSITE RESIN VENEERING MATERIALS

Urethane monomer/diluent monomer mixtures were used in dental composite resin veneering materials filled with various ratios of powder (filler)/liquid (comonomer), P/L. Hardness values of unfilled resins containing benzoyl peroxide only (BP0; 0.5 wt%), and filled resins (included trimethylol propane trimethacrylate (TMPT) composite filler) were tested. Significant increases in hardness were obtained with the use of TMPT composite filler in the resins. Also, their modulus values measured by bend test showed an increasing trend, compared to a commercial composite resin veneering material (a control sample; CONT) with a lower filler content (50 wt%). The DME–DPMDC/HPDM comonomer (dimethacryloxyethyl diphenylmethane-4,4′-dicarbamate/hydroxypropyl dimethacrylate), which showed a smaller fraction of surface porosity, gave greater mechanical strength values at P/L ratios of 0.55 (17.8 wt% filler content) to 1.20 (27.3 wt%) than a CONT resin. The coefficient of thermal expansion was smaller in urethane-based filling materials than a CONT resin. Also, greater activation energy of thermal decomposition was observed in the resin samples with P/L ratio 0.75 to 1.20 than in a CONT resin. Thermally-induced decomposition occurred with smaller weight loss in the experimental filled resins than in a CONT resin.

Effect of filler content on mechanical strength in bis-GMA-based resins with urethane linkages

Bis-GMA-based visible-light-cured resins containing urethane linkages exhibited improved hardness and strength by addition of filler to the unfilled resins. The urethane monomers in the resins strengthened the resin matrix, exhibiting an increased Shore hardness value. Urethane monomer derived from 2HEMA and N3500 was more effective than that from 2HEMA and HT. The increased strength in the resin matrix occurred after storage in water at 37°C. Addition of filler to bis-GMA-based resins increased compressive strength (110 MPa as the maximum), while diametral strength values of 20 MPa were obtained.

Corrosive properties in experimental Ni-Cu-Mn-based alloy systems for dental purposes

Experimental Ni-Cu-Mn-based alloys containing additives were studied to find their corrosive properties in tarnishing tests. The microstructural features revealed interdendritic areas with small corroded regions. In 30Ni-30Cu-40Mn-based alloys which were respectively substituted by aluminium, tin, aluminium and indium (Al-In), Al-Sn and Al-Sn-In the maximum roughness values in the surface roughness curves ranged from 2.0 to 7.2µm. Each corrosion-resistant alloy system which contained additive elements of Al-In, Al-Si, Ca-Si-C and P-Fe had a smooth surface with a maximum roughness value of 0.8 to 2.0 µm.