Heat-cured poly(methyl methacrylate) resin incorporated with different food preservatives as an anti-microbial denture base material.

BACKGROUND/PURPOSE: The colonization of microorganisms onto denture bases is one common problem that can contribute to oral diseases. Herein, three food preservatives, including zinc oxide, potassium sorbate, and sodium metabisulfite were introduced as anti-microbial additives into a heat-polymerized poly(methyl methacrylate) (PMMA). MATERIALS AND METHODS: Relative microbial reductions of the modified PMMA resins against Staphylococcus aureus, Pseudomonas aeruginosa, and Candida albicans were evaluated. The in vitro cytotoxicity of the materials was measured against mouse fibroblast L929 cells. A three-point flexural test was performed to determine a flexural strength and modulus properties of the materials. RESULTS: The incorporation of all preservative agents into the material diminished the microbial growth of three microbial species. The PMMA resin combined with sodium metabisulfite exhibited the greatest anti-microbial activity that reduced almost all bacterial cells and about 40% of C. albicans. All modified resins showed no significant cytotoxicity against L929 cells. The addition of food preservatives did not significantly alter the flexural strength of the PMMA resin (∼84-92 MPa). However, the flexural modulus of the PMMA incorporated with food preservatives (∼2,024-2,144 MPa) was significantly lower than the unmodified PMMA. CONCLUSION: Three food preservatives, especially sodium metabisulfite, could be applied as anti-microbial additives into the denture base resin. The PMMA incorporated with the additives did not show cytotoxicity. Although, the addition of the food preservatives altered the mechanical properties, the materials still provided acceptable flexural properties.

Effect of Piper betle extract on anti-candidal activity, gelation time, and surface hardness of a short-term soft lining material.

The purpose of this study was to evaluate anti-candidal activity, gelation time, and surface hardness of a short-term soft lining material incorporated with varying concentrations of Piper betle extract (0.25 to 20% w/w). Agar-diffusion assay was conducted to evaluate an inhibitory effect against Candida albicans. The gelation time was assessed and surface hardness was measured at 2 h and 7 days by Shore AO durometer. A soft liner containing at least 5% w/w of P. betle extract was observed the inhibitory effect against C. albicans. An increasing of P. betle concentrations provided larger inhibition zone. Incorporating 5% w/w of P. betle extract into the soft liner did not significantly alter its gelation time and surface hardness (ANOVA; p>0.05). The optimum composition at 5% w/w of P. betle extract can be used as an additive in the soft liner to provide the anti-candidal activity without significantly affect these two main properties.

Contrast ratio of six zirconia-based dental ceramics.

PURPOSE: The objective of this study was to determine the effect of thickness and brands on the contrast ratio of six zirconia dental ceramics. MATERIALS AND METHODS: Six brands of yttria-stabilized tetragonal zirconia polycrystalline (Y-TZP) ceramics (ZENO® Translucent, Lava™ Plus High Translucency, inCoris TZI, Cercon® Base, Zeno®Zr, Lava™) were used in this study. Disc-shaped specimens with 15 mm diameter were prepared in five thickness levels (0.3, 0.6, 0.9, 1.2, 1.5 mm, n = 10) for each brand. The contrast ratio (CR = Y(b) /Y(w) ) was determined from the luminous reflectance over black (Y(b) ) and white (Y(w) ) backgrounds using a spectrophotometer. Two-way ANOVA was performed to determine the significant differences among thicknesses and brands at α = 0.05. RESULTS: The mean contrast ratio values of six zirconia ceramics were significantly different and influenced by both the thickness and brand. The mean contrast ratio values of all groups increased as their thickness increased from 0.3 to 1.5 mm. inCoris TZI was the most translucent, with the lowest contrast ratio at a thickness of 0.6 to 1.5 mm. The mean contrast ratio values of Lava™ and Lava™ Plus were significantly lower than those of Zeno®Zr, ZENO® Translucent, and Cercon® Base. CONCLUSIONS: The thickness and brands had significant effects on the contrast ratio of six zirconia dental ceramics. The mean contrast ratio values of inCoris TZI, Lava™, and Lava™ Plus High Translucency were significantly lower than those of Cercon® Base, Zeno®, and ZENO® Translucent at all thicknesses.

Mechanical properties of experimental silicone soft lining materials.

The purpose of this study was to evaluate the mechanical properties of experimental silicone elastomers, Silastic(®) MDX 4-4210 reinforced with silica fillers, to assess its potential as a denture soft lining material. The mechanical properties measured included tensile strength, percentage elongation, tear strength, and Shore A hardness. Using one-way ANOVA and Tukey's HSD test, the results indicated that silicone elastomers with filler loadings of 6, 8, and 10 phr had significantly greater tensile strength, percentage elongation, tear strength with a softer surface compared with commercial materials (p<0.001). In conclusion, the experimental silicone elastomers revealed acceptable mechanical properties to be used as denture soft lining materials.

Dynamic viscoelastic properties of experimental silicone soft lining materials.

The purpose of this study was to evaluate the dynamic viscoelastic properties of experimental silicone soft lining materials, Silastic MDX 4-4210 reinforced with silica fillers. Storage modulus (E'), loss modulus (E") and damping factor (tan delta) were determined using a dynamic mechanical analyzer under a deformation strain level of 0.27% at test frequency and a temperature range of 1 Hz and 0 to 60 degrees C, respectively. The degree of silica dispersion was also studied using a field emission scanning electron microscopy (FE-SEM). One-way ANOVA and Tukey's HSD test results indicated that the prepared silicone elastomers provided a significantly greater damping factor, but less storage modulus than GC Reline Soft and Tokuyama Sofreliner Tough (p<0.001). The storage moduli, loss moduli and damping factor of the experimental silicone elastomers increased with increasing amounts of fumed silica. In conclusion, the experimental silicone elastomers revealed acceptable dynamic viscoelastic properties to be used as denture soft lining materials.

The effect of base materials with different elastic moduli on the fracture loads of machinable ceramic inlays.

This study investigated the effect of two base materials with different elastic moduli (F2000 and Vitrebond) on the fracture load of machinable ceramic inlays. Standardized MOD cavities were prepared in 18 human maxillary first or second premolars. The teeth were randomly assigned to three groups of six premolars each; Group 1 (control: no base); Group 2 (base with a polyacid-modified resin composite: F2000); Group 3 (base with a resin-modified glass-ionomer cement: Vitrebond). The inlays were fabricated from Vitablocs Mark II using a Cerec II machine. After the inlays were cemented with Tetric Ceram and the Syntac adhesive system, using the Ultrasonic Insertion Technique (USI), they were stored in distilled water at 37 degrees C for 24 hours prior to fracture testing in a universal testing machine using a crosshead speed of 0.5 mm/minute. The static transverse elastic moduli of base materials were measured using a three-point bending test. The mean fracture loads and standard deviations of the Cerec inlays in Groups 1, 2 and 3 were 1.15 +/- 0.39 KN, 1.13 +/- 0.36 KN and 0.58 +/- 0.11 KN, respectively. Statistical analysis showed that the mean fracture load of Group 3 was significantly lower than that of Groups 1 and 2 (p < .05). There was no significant difference in fracture load between Groups 1 and 2. The means and standard deviations of the elastic moduli of F2000 and Vitrebond were 15.63 +/- 0.32 and 2.16 +/- 0.55 GPa, respectively. The results indicated that the fracture load increased significantly as the elastic modulus of a base material increased.