Takahito Kanie

Flexural properties and impact strength of denture base polymer reinforced with woven glass fibers

OBJECTIVES The present investigation was undertaken to determine the reinforcing effect of woven glass fibers on deflection, flexural strength, flexural modulus and impact strength of acrylic denture base polymer. METHODS Three silanized or unsilanized woven glass fibers were used. Specimens were made by heating the denture cure resin dough containing glass fibers, which were sheathed in the dough. Specimens with four different thicknesses and of five different types were made, incorporating the glass fiber. Three-point flexural test and flywheel type impact test were employed to determine the flexural properties and impact strength. RESULTS When specimens contained unsilanized glass fiber, the flexural strength in specimens of 1 and 2 mm thickness and the impact strength in specimens of 2 mm thickness were higher than those of specimens without glass fiber (p < 0.01). On the contrary, the flexural strength and deflection in specimens reinforced with silanized glass fiber of 1 mm thickness were significantly higher (p < 0.01, p < 0.05) than those of unreinforced specimens. Further, the impact strength in specimens reinforced with silanized glass fiber of 2 mm thickness was significantly higher (p < 0.01) than that of unreinforced specimens. Statistically significant differences were found in the flexural strength (p < 0.05) and in the impact strength (p < 0.01) when specimens of 4 mm thickness were reinforced with two or three unsilanized glass fibers. SIGNIFICANCE The reinforcement with glass fiber was effective in thin specimens, and the reinforcing effect increased with the increase of the number of glass fibers in the case of thick specimens.

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.

Comparison of the mechanical properties of 2 prosthetic mini-implants.

Two prosthetic mini-implants (MTI and MDI), which have very similar shapes, are widely used. In this investigation, the mechanical and physical properties of 2 prosthetic mini-implants were investigated. The flexural properties were measured with a universal testing machine. The surface image was observed by SEM with EDX. X-ray analyses were performed. The maximum strength and proportion limit for the different implants differed significantly ( P <0.01); however, elastic modulus did not differ significantly ( P >0.01). Although the surface of the MTI was smooth, the MDI had a rough surface. The elemental analysis detected titanium (Ti) in the MTI, and Ti, aluminum, and vanadium in the MDI. From the x-ray diffraction pattern, the MTI, which is composed of pure titanium, had a narrow, sharp Ti (syn) peak, whereas the corresponding peak for the MDI was small and broad. Although the 2 devices have similar shapes and dimensions, their surfaces and mechanical properties differ greatly. MTI is easy to remove and wrought in clinical use, and MDI is excellent in flexural properties compared with MTI. (Implant Dent 2004;13:251–256)

A comparison of stress relaxation in temporary and permanent luting cements

PURPOSE The stress relaxation and compressive strength of resin, resin-modified glass ionomer, glass ionomer, polycarboxylate, and zinc oxide eugenol cements were measured to determine the characteristics of these materials after setting. METHODS A total of 19 luting cements including 12 permanent cements and 7 temporary cements were used. Cylindrical cement specimens (10mm long and 6mm in diameter) were obtained by chemical setting or light curing. The specimens were stored for 24-36 h in water at 37°C and were then used for the stress relaxation and compression tests. The stress relaxation test was carried out using three constant cross-head speeds of 5, 50, and 100 mm/min. Upon reaching the preset dislocation of 0.5 mm, the cross-head movement was stopped, and the load was recorded for 60s. Fractional stress loss at 1s was calculated from the relaxation curves. The compressive strength and modulus were measured at a cross-head speed of 1mm/min. Data were analyzed with the Kruskal-Wallis test and Holms test. RESULTS A zinc oxide eugenol cement [TempBOND NX] exhibited the largest fractional stress loss. A resin cement [ResiCem] showed the largest compressive strength, while a glass ionomer cement [HY-BOND GLASIONOMER CX] showed the largest compressive modulus among all tested cements (p<0.05). CONCLUSION The fractional stress loss could not be classified by the cement type. Two implant cements [Multilink Implant and IP Temp Cement] showed similar properties with permanent resin cements and temporary glass ionomer cements, respectively. Careful consideration of the choice of cement is necessary.

Factors Affecting on the Bond Strength of Dental Zirconia to Veneering Porcelains

The bond strengths between two kinds of zirconia and three kinds of feldspathic veneering porcelains were measured. The specimens were prepared at four firing temperatures for three holding periods, respective opaque porcelain was painted and vacuum-fired. Then, each dentin porcelain was condensed in an acrylic resin mold and vacuum-fired under the conditions mentioned above. Cross sections of the interface between zirconia and porcelain were observed with a scanning electron microscope. The specimens were fixed to specimen holder on a universal testing machine. Data of the bonding test were statistically analyzed. The results showed that all the four factors statistically affected the bonding strength (p<0.01). The contribution of the firing temperature was highest and that of the porcelain type was lowest (p<0.01).

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.