Koichi Fujii

Light transmittance characteristics of light-cured composite resins

OBJECTIVES The purpose of this study was: (1) to examine the light transmittance characteristics of various shades of light-cured composite resins, and (2) to evaluate the effect of light transmittance characteristics on the color of the resins. METHODS Eleven shades of two composite resins were used. Specimens with four different thicknesses (0.5, 1.0, 2.0 and 3.0 mm) were prepared. The transmittance at wavelengths from 400 to 700 nm was measured. Also, the color values and the color differences among thicknesses of a specimen on the CIE L*a*b* color system were determined by a digital chroma meter. The differences in the transmittance, color values and color difference were determined by using a one-way analysis of variance (ANOVA) combined with a Tukey multiple-range test. RESULTS Significant differences were found in the wavelength dependence of transmittance between the two materials, and among shades of each material. The transmittances of the darker shades of one material were significantly lower at lower wavelengths than the other shades, but were nearly equal or significantly higher at higher wavelengths. There was a significant correlation between the changing ratio of transmittance and the color difference. Two materials showed significant differences in delta a* and delta b* of the chromatic component of color difference. SIGNIFICANCE The results of this study indicate that light transmittance characteristics, including the wavelength dependence, play an important role for the color of a composite resin. The significant difference in light transmittance characteristics among materials and shades will affect their clinical appearance.

Micro-CT Analysis of New Bone Formation Around Implant with Electrochemically Deposited Apatite

Micro-CT was employed to determine the volume of new bone formed ar ound the implants with and without the electrochemically deposited apatite. With the accumulation of new bone area in the 2-dimensional images, the volumes of new bone around implants were deriv d. Linear regression analysis revealed a correlation ( r=0.704) between the pull-out bonding strengths and the volume of new bone of rabbit femora around the implants. Introduction We reported that the electrochemical deposition of apatite have som advantages: i.e. it can easily create a homogeneous apatite coating on substrates having complicate d sh pes such as dental implants, and requires only simple and small devices. Furthermore , varying the electrochemical conditions can easily control the morphology of deposited apatite [1-6]. The bonding strength of the implant with the electrochemically deposited apatite depended on the morphology of apatite [7, 8]. The apatite deposited at 100 ̊C showed the best bioactivity in vitro [6, 8]. At 3-week implantation, the boundary of the implant coated at 100 ̊C was completely fill d with new bone, whereas that at 200 ̊C was not filled with it [9]. On the other hand, micro-computed tomography (CT) recently is applied to osteology [10-12]. The purpose of the pres ent tudy was to quantitatively determine the volume of new bone formed around the implants with and without the electrochemical apatite coating using micro-CT and to discuss the relation between the amount of new-bone and their bonding strengths. Materials and Methods The electrolyte was heated in stainless steel-autoclave asse mbled two electrodes, a stirring screw, a pressure gauge, a pressure valve, a thermo-couple and an electric hea ter. A platinum plate, 20 x 20 x 0.5 mm, was used as the counter electrode and commercially pur e titanium bars, 2 x 12 mm, were employed as the working electrode. The electrolyte was prepared by dissolving given amounts of reagent-grade chemicals of 137.8 mM of NaCl, 1.67 mM of K 2HPO4, and 2.5 mM of CaCl2·2H2O into distilled water. The solution was buffered to pH value of 7.2 wi th 50 mM tris(hydroxymethyl)aminomethane [(CH 2OH)3CNH2] and an adequate amount of hydrochloric acid. The electrolyte was heated at 100, 150, and 200 ̊C using electric heater and agitated by a stainless screw. The current was maintained at 12.5 mA/cm 2 by DC power supply for 1 hr. After loading of the constant current, the titanium bars loaded as cathodes were r insed with distilled water and dried at 37 ̊C in air. These titanium bars with and without the electrochemically depos it d apatite were implanted into the femora of Japanese white rabbit. The rabbits were sacrific ed at 3 weeks after implantation and the femora were taken out from the bodies. Immediately, the fem ora were used for radiographic Key Engineering Materials Online: 2003-05-15 ISSN: 1662-9795, Vols. 240-242, pp 611-614 doi:10.4028/www.scientific.net/KEM.240-242.611

Composite Mesh Consisting of Titanium, Apatite and Biodegradable Copolymer

Apatites were formed on pure titanium mesh using a hydrothermalelectrochemical method. The mesh covered with apatites was dipped in the solution of dichloromet hane and poly-lactic acid/poly-glycolic acid copolymer (PLGA) and dried in air. SEM obs ervations showed that the apatites were well embedded in the PLGA film having many pores left by the evaporation of dichloromethane and the tips of the apatites were mostly exposed. These results imply that PLG A does not interfere with the bioactivity of apatite and maintain the mechanical strengt h of the coating during operation and initial stage of bone formation.

A Study on Porcelain Laminate Veneer Crown. Part 2. Setting Characteristics of Light-Curing Luting Materials.

On the assumption that porcelain laminate veneer crown had been bonded to the abutment tooth with the light-curing luting material, setting characteristics of four light-curing luting materials were evaluated for linear shrinkage from the start of exposing, water absorption, Vickers hardness and compressive strength after exposing the materials to visible light. The results were as follows : 1. The light-curing luting materials rapidly shrank as soon as exposed to light passing through a cover glass or a plate made of porcelain. When exposed to light through the laminate veneer plate, the shrinkage of materials was less than that of materials exposed to light through a cover glass. The result suggested that the curing process was delayed because of a shade effect of the laminate veneer plate. 2. The compressive strength was shown to have a tendency to increase with the elapse of time. The compressive strength of luting materials stored in air at 37•Ž was larger than that of materials immersed in distilled water at 37•Ž, and such a tendency was remarkable from 1 to 4 weeks after exposing. 3. The values of Vickers hardness of light-curing luting materials were almost the same from 1 to 4 weeks after exposing, and the hardness values of the materials in air at 37•Ž was larger than those of materials immersed in distilled water at 37•Ž. 4. The amounts of water absorption (wt%) increased rapidly after the luting materials were immersed in distilled water at 37•Ž, but were hardly increased 8 weeks after exposing the materials to visible light.

Studies on Mechanical properties of Soft Lining Materials

Viscoelastic properties of silicone material (code-named MDX-4-4210) and 4 commercial soft liners and related materials (Kurepate, Neo-Snugger, Super-Soft and Viscogel) were examined using a stress relaxation testing instrument. All measurements were preformed in water at a temperature of 37±0.5°C.In the case of other 4 materials, except Visco-gel, the decreasing rates of relative stress {f(t)/f(0)} with time were relatively small. Furthermore, the decreases of stress relaxation modulus {Er(t)} of these materials with period soaked in water at 37°C were also very small, with exception of Visco-gel. Code-named MDX-4-4210 showed the most superior elastic properties in materials used. The relative stress in Visco-gel diminished markedly with time.These results indicate that all materials, excluding Visco-gel, have possessed the favourable properties as soft liners and related materials since it is necessary for these materials to remain in oral cavity for long period of month.