The isolation of fungi from laboratory dental pumice

Effect of comonomer of methacrylic acid on flexural strength and adhesion of Staphylococcus aureus to heat polymerized poly (methyl methacrylate) resin: An in vitro study

Aims and Objective:

The purpose of the present study was to evaluate and compare flexural strength and Staphylococcus aureus adhesion of heat-activated poly (methyl methacrylate [MMA]) resin modified with a comonomer of methacrylic acid (MAA) and MMA monomer.

Materials and Methods:

Comonomer preparation was done with the addition of varying concentration of MAA (0, 15, 20, and 25 wt %) to the MMA of conventional heat-activated denture base resin to prepare the specimens. Prepared specimens were stored in distilled water at 37°C for 1 day and 1 week before the evaluation of flexural strength and microbial adhesion. Flexural strength was measured using a universal testing machine at a crosshead speed for 2 mm/min (n = 10). Microbial adhesion (colony-forming unit [CFU]) was evaluated against S. aureus using a quadrant streaking method (n = 5). Data were subjected to one-way ANOVA, and the significant differences among the results were subjected to Tukey's HSD test. P < 0.05 was considered statistically significant.

Results:

Addition of MAA to the MMA monomer was found to significantly reduce the adhesion of S. aureus for all the groups. Reduction of CFU of S. aureus was found be more significant for Group 3 as compared to control, both at 1-day (P < 0.001) and 1-week (P < 0.002) storage in distilled water. However, no statistically significant changes in the flexural strength were observed with the addition of MAA at 1-day (P = 0.52) and 1-week (P = 0.88) time interval.

Conclusion:

Addition of MAA to conventional denture base resin reduced the microbial adhesion without significantly affecting the flexural strength.

Effect of repeated immersion solution cycles on the color stability of denture tooth acrylic resins

Objective

Chemical solutions have been widely used for disinfection of dentures, but their effect on color stability of denture tooth acrylic resins after repeated procedures is still unclear. The aim of this in vitro study was to evaluate whether repeated cycles of chemical disinfectants affected the color stability of two denture tooth acrylic resins.

Material and Methods

Sixty disc-shaped specimens (40 mm x 3 mm) were fabricated from two different brands (Artiplus and Trilux) of denture tooth acrylic resin. The specimens from each brand (n=30) were randomly divided into 6 groups (n=5) and immersed in the following solutions: distilled water (control group) and 5 disinfecting solutions (1% sodium hypochlorite, 2% sodium hypochlorite, 5.25% sodium hypochlorite, 2% glutaraldehyde, and 4% chlorhexidine gluconate). Tooth color measurements were made by spectrophotometry. Before disinfection, the initial color of each tooth was recorded. Further color measurements were determined after subjecting the specimens to 7, 21, 30, 45, 60, and 90 immersion cycles in each tested solution. Color differences (ΔE*) were determined using the CIE L*a*b* color system. Data were analyzed using two-way repeated measures analysis of variance (ANOVA) followed by Tukey tests. The significance level was set at 5%.

Results

There were statistically significant differences in ΔE* among the 5 disinfectants and water during the 90 cycles of immersion for both denture tooth acrylic resins. Distilled water promoted the greatest color change in both denture tooth acrylic resins, nevertheless none of tested disinfectants promoted ΔE* values higher than 1.0 on these acrylic materials during the 90 cycles of disinfection.

Conclusions

Repeated immersion cycles in disinfecting solutions alter ∆E* values, however these values do not compromise the color of the tested denture tooth acrylic resins because they are imperceptible to the human eye.

Disinfection of pumice

Pumice is a potential source of infection for the dental technician and of cross-contamination between different dentures and patients. In this study, the number of microorganisms in two different combinations of pumice and disinfectant was compared with a conventional mixture of pumice and water. The results revealed that under practical conditions the mix of Steribim (pumice containing benzoic acid added by the manufacturer) with water reduced the number of bacteria by 99% compared with a mix of a conventional pumice and water. The addition of an antiseptic product that contained octenidine as active agent to conventional pumice reduced the number of microorganisms by 99.999%.

The effectiveness of two disinfectants on denture base acrylic resin with an organic load

This study compared the biocidal effectiveness of chlorine dioxide and 5.25% sodium hypochlorite (diluted 1:10) on acrylic resin strips inoculated with Staphylococcus aureus, Candida albicans, or Escherichia coli in the presence of an organic load. Sterile acrylic resin strips were immersed in a solution containing 10% horse serum and 10(5) to 10(7) organisms/ml for each type of organism, then disinfected in chlorine dioxide, sodium hypochlorite, or 0.9 sterile saline for 30 seconds or 1, 2, or 4 minutes. After disinfection, the strips were neutralized and incubated for 72 hours. The results showed a difference between the ability of chlorine dioxide and sodium hypochlorite to kill the test organisms on acrylic resin strips when organic matter is present. Chlorine dioxide achieved complete disinfection of all three organisms within 2 minutes. Sodium hypochlorite achieved complete disinfection of all three organisms within 4 minutes.