Katsuichiro Inoue

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.

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.