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Residual melanins have been detected in multimillion-year-old animal body fossils, however, confident identification and characterization of these natural pigments remain challenging due to loss of chemical signatures during diagenesis. Here, we simulate this post-burial process through artificial maturation experiments using three synthetic and one natural eumelanin exposed to mild (100 &deg, C/100 bar) and harsh (250 &deg, C/200 bar) environmental conditions, followed by chemical analysis employing alkaline hydrogen peroxide oxidation (AHPO) and time-of-flight secondary ion mass spectrometry (ToF-SIMS). Our results show that AHPO is sensitive to changes in the melanin molecular structure already during mild heat and pressure treatment (resulting, e.g., in increased C-C cross-linking), whereas harsh maturation leads to extensive loss of eumelanin-specific chemical markers. In contrast, negative-ion ToF-SIMS spectra are considerably less affected by mild maturation conditions, and eumelanin-specific features remain even after harsh treatment. Detailed analysis of ToF-SIMS spectra acquired prior to experimental treatment revealed significant differences between the investigated eumelanins. However, systematic spectral changes upon maturation reduced these dissimilarities, indicating that intense heat and pressure treatment leads to the formation of a common, partially degraded, eumelanin molecular structure. Our findings elucidate the complementary nature of AHPO and ToF-SIMS during chemical characterization of eumelanin traces in fossilized organismal remains.

This study evaluated the long-term efficacy of denture cleansers against Candida spp. biofilm recolonization on liner surface. Specimens were fabricated of a poly(methyl methacrylate)-based denture liner and had their surface roughness evaluated at baseline and after cleansing treatments. C. albicans or C. glabrata biofilms were formed on liner surface for 48 h, and then the specimens were randomly assigned to one of cleaning treatments: two alkaline peroxides (soaking for 3 or 15 min), 0.5% sodium hypochlorite (10 min) or distilled water (control; 15 min). After the treatments, the specimens were sonicated to disrupt the biofilm, and residual cells were counted (cell/mL). Long-term effectiveness of the cleaning processes was determined by submitting a set of cleaned specimens to biofilm growth conditions for 48 h followed by estimation of cell counts. The topography of specimens after cleaning treatments was analyzed by SEM. Data were analyzed by ANOVA and Tukey's test (α; = 0.05). Results of cell count estimation showed significant differences in cleanliness among the treatments (p < 0.001), and it could be observed by SEM. However, no significant difference (p > 0.05) was observed among the Candida species regarding the recolonization condition. Alkaline denture cleansers showed similar cleaning performance and both differed from the control (p < 0.001). Sodium hypochlorite was the only treatment that removed biofilm efficiently, since no viable cells were found after its use. In conclusion, alkaline peroxide denture cleansers were not effective in removing Candida spp. biofilm from denture liner surfaces and preventing biofilm recolonization.

Aim: The objective of this study was to measure the microbial contamination released from dental unit air lines (DUAL) and dental unit water lines (DUWL). Materials and methods: Emissions from DUAL and DUWL from five dental units supplied by a central water source (tap) and a centralised air supply were sampled three times over a five- week period. Air was forced through sterile water and then plated onto selective agar using apparatus designed to spread the sample solution evenly, and then incubated at room temperature for seven days. Colonies were then counted and the concentration of bacteria present was determined and expressed as colony forming units per millilitre (cfu/ml) per minute. The same procedure was used to evaluate five other dental units, which had attached independent water reservoir (bottle) systems (IWR). Only deionised water was added to the bottles and unit waterlines were cleaned weekly with alkaline peroxide based solution. Values were expressed as cfu/ml. Results: Air and water specimens obtained from dental units supplied with tap water had microbial counts significantly (t-test, p < 0.05) greater than IWR dental units. Conclusions: Results indicate that IWR can reduce the numbers of micro-organisms released from DUWL. However, the effectiveness of such systems should be routinely monitored. Emissions from DUAL seems to reflect the levels of microbial contamination present in DUWL.