Ibrahim Yusufoglu

Flexural properties of repaired heat-polymerising acrylic resin after wetting with monomer and acetone.

OBJECTIVES Repair strength can be improved by treating fractured surfaces of a denture. BACKGROUND This study investigated flexural properties of heat-polymerised acrylic resin specimens repaired with auto-polymerising and visible light curing (VLC) resins after the repair surfaces were wetted with monomers or acetone. MATERIALS AND METHODS Fifty-four specimens (65 x 10 x 2.5 mm) were prepared and 48 of them were sectioned to simulate denture fracture. Butt-joint designed repair surfaces were wetted with heat-, auto-polymerising monomers and acetone for 180 s and repaired with auto-polymerising and VLC resins. After repairs, specimens were subjected to three-point bending test and flexural strength, strain, fracture load, modulus of elasticity and deflection values were recorded. Data were analysed with Student t and LSD tests (p < or = 0.05). RESULTS Overall flexural strength, strain, fracture load and deflection values of specimens repaired with VLC resin were significantly higher than the specimens repaired with auto-polymerising resin for all types of wetting agent (p < 0.05). Within the wetting agents, heat- and auto-polymerising monomers produced the best mechanical properties, while wetting with acetone did not provide superior effect over both monomers. CONCLUSION In clinical use, wetting the repair surfaces may result in stronger repairs. The use of bonding agent in VLC resin repairs in combination with wetting agent results in improved flexural properties.

Kinetic investigation of dissolution of CaWO4 in oxalic acid solution

Abstract In this study, the effects of stirring speed, temperature, H2C2O4 concentration and particle size on the dissolution rate of CaWO4 in H2C2O4 solutions were investigated. CaWO4 was dissolved in H2C2O4 solutions as series parallel type reaction. In the first step which took place according to Langmuir-Hinshelwood Mechanism, H2C2O4 was adsorbed as a mobile adsorption layer on the surface of CaWO4, reacted to form adsorbed calcium aqua oxalato tungstate (Ca[WO3(C2O4)H2O]) intermediate product and the adsorbed Ca[WO3(C2O4)H2O] was desorbed into the solution. In the second step, Ca[WO3(C2O4)H2O] hydrolysed and formed H2WO4 which reacted with H2C2O4 to form hydrogen aqua oxalato tungstate (H2[WO3(C2O4)H2O]) as end product together with solid CaC2O4H2O. Model kinetic equations were derived which showed the relationships of the fractional conversion of CaWO4, the concentration of Ca[WO3(C2O4)H2O] and the concentration of H2[WO3(C2O4)H2O] with time. The diagrams drawn according to the model kinetic equations were in good agreement with the experimentally obtained diagrams (R2>0·99). Dans cette étude, on a examiné les effets de la vitesse d’agitation, de la température, de la concentration d’H2C2O4 et de la taille de particule sur la vitesse de dissolution de CaWO4 dans des solutions d’H2C2O4. On a dissous le CaWO4 dans des solutions d’H2C2O4 en une réaction de type série-parallèle. Dans la première étape, qui avait lieu d’après le Mécanisme de Langmuir-Hinshelwood, l’H2C2O4 était adsorbé en une couche mobile d’adsorption à la surface du CaWO4, réagissait pour former le produit intermédiaire adsorbé, aqua oxalato tungstate de calcium (Ca[WO3(C2O4)H2O]), et ce Ca[WO3(C2O4)H2O] adsorbé était désorbé dans la solution. Dans la seconde étape, le Ca[WO3(C2O4)H2O] était hydrolysé et formait l’H2WO4 qui réagissait avec l’H2C2O4 pour former de l’aqua oxalato tungstate d’hydrogène (H2[WO3(C2O4)H2O]) comme produit final avec le CaC2O4H2O solide. On a dérivé les équations cinétiques du modèle, lesquelles montraient les relations de la conversion fractionnelle du CaWO4, de la concentration de Ca[WO3(C2O4)H2O] et de la concentration d’H2[WO3(C2O4)H2O] en fonction du temps. Les diagrammes dessinés d’après les équations cinétiques du modèle étaient en bon accord avec les diagrammes obtenus expérimentalement (R2>0·99).

Structural and optical characterizations of porous anodic alumina–aluminum nanocomposite films on borofloat substrates

Abstract. Structural and optical properties of the porous anodic alumina (PAA)–aluminum (Al) nanocomposite and the PAA-nanostructured films on borofloat substrates are studied. The films are fabricated by the anodization of 170- to 200- and 295- to 330-nm-thick Al sputtered onto the borofloat. The anodization process is stopped at different times in order to form the PAA–Al nanocomposite films with different layer thicknesses. Then, the pore widening is applied to 189- to 210- and 430- to 495-nm-thick PAA films in 5- and 10-min intervals, respectively. The structural properties of the films are characterized by a scanning electron microscopy. The nanocomposite films are also characterized optically by total reflection and directional transmission measurements in the wavelength range between 250 and 800 nm. Our results indicate that controlling the thicknesses of both Al and the PAA layers by anodization time and the morphology of the nanostructures by chemical etching duration in the PAA layer provides unique PAA–Al nanocomposite films with desired optical properties.