Paulo Maurício Batista da Silva

Effect of repeated cycles of chemical disinfection on the roughness and hardness of hard reline acrylic resins

OBJECTIVE The aim of this study was to assess the effect of repeated cycles of five chemical disinfectant solutions on the roughness and hardness of three hard chairside reliners. METHODS A total of 180 circular specimens (30 mm x 6 mm) were fabricated using three hard chairside reliners (Jet; n = 60, Kooliner; n = 60, Tokuyama Rebase II Fast; n = 60), which were immersed in deionised water (control), and five disinfectant solutions (1%, 2%, 5.25% sodium hypochlorite; 2% glutaraldehyde; 4% chlorhexidine gluconate). They were tested for Knoop hardness (KHN) and surface roughness (microm), before and after 30 simulated disinfecting cycles. Data was analysed by the factorial scheme (6 x 2), two-way analysis of variance (anova), followed by Tukeys test. RESULTS For Jet (from 18.74 to 13.86 KHN), Kooliner (from 14.09 to 8.72 KHN), Tokuyama (from 12.57 to 8.28 KHN) a significant decrease in hardness was observed irrespective of the solution used on all materials. For Jet (from 0.09 to 0.11 microm) there was a statistically significant increase in roughness. Kooliner (from 0.36 to 0.26 microm) presented a statistically significant decrease in roughness and Tokuyama (from 0.15 to 0.11 microm) presented no statistically significant difference after 30 days. CONCLUSIONS This study showed that all disinfectant solutions promoted a statistically significant decrease in hardness, whereas with roughness, the materials tested showed a statistically significant increase, except for Tokuyama. Although statistically significant values were registered, these results could not be considered clinically significant.

Microscopical analysis of Candida albicans biofilms on heat-polymerised acrylic resin after chlorhexidine gluconate and sodium hypochlorite treatments

The ability of Candida albicans to form biofilms on denture surfaces is a significant cofactor in the pathogenesis of denture stomatitis. In this study, we applied a differential staining approach and scanning electron microscopy (SEM) to analyse the effect of sodium hypochlorite and chlorhexidine gluconate on the viability, removal and morphology of C. albicans forming biofilms on denture acrylic using an in vitro model. Immediately after treatment, to distinguish live from dead C. albicans cells in the remaining biofilms, the specimens were stained differentially and analysed by confocal scanning laser microscopy. Moreover, morphological alterations of fungal cells were investigated using scanning electron microscopy. All disinfectant solutions killed all remaining fungal cells on the specimens. Interestingly, 4% chlorhexidine did not remove these cells from the acrylic resin surface whereas sodium hypochlorite solutions (1% and 2%) provided almost complete biofilm removal. Furthermore, treating the specimens with sodium hypochlorite induced cell morphology alterations, as seen in the residual fungal cells. Finally, according to our findings, it can be suggested that sodium hypochlorite solutions are the first choice as denture cleanser when compared with 4% chlorhexidine because those solutions not only killed C. albicans biofilms but also removed them from the heat‐polymerised acrylic resin.

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.

INFLUENCE OF DIFFERENT ADHESIVE SYSTEMS ON THE PULL-OUT BOND STRENGTH OF GLASS FIBER POSTS

This in vitro study evaluated the tensile bond strength of glass fiber posts (Reforpost – Angelus-Brazil) cemented to root dentin with a resin cement (RelyX ARC – 3M/ESPE) associated with two different adhesive systems (Adper Single Bond - 3M/ESPE and Adper Scotchbond Multi Purpose (MP) Plus – 3M/ESPE), using the pull-out test. Twenty single-rooted human teeth with standardized root canals were randomly assigned to 2 groups (n=10): G1- etching with 37% phosphoric acid gel (3M/ESPE) + Adper Single Bond + #1 post (Reforpost – Angelus) + four #1 accessory posts (Reforpin – Angelus) + resin cement; G2- etching with 37% phosphoric acid gel + Adper Scotchbond MP Plus + #1 post + four #1 accessory posts + resin cement. The specimens were stored in distilled water at 37°C for 7 days and submitted to the pull-out test in a universal testing machine (EMIC) at a crosshead speed of 0.5 mm/min. The mean values of bond strength (kgf) and standard deviation were: G1- 29.163 ± 7.123; G2- 37.752 ±13.054. Statistical analysis (Students t-test; α=0.05 showed no statistically significant difference (p<0.05) between the groups. Adhesive bonding failures between resin cement and root canal dentin surface were observed in both groups, with non-polymerized resin cement in the apical portion of the post space when Single Bond was used (G1). The type of adhesive system employed on the fiber post cementation did not influence the pull-out bond strength.

Manipulação do genoma humano: ética e direito

The molecular biology has provided the basic tool for geneticists deepening in the molecular mechanisms that influence different diseases. It should be noted the scientific and moral responsibility of the researchers, because the scientists should imagine the moral consequences of the commercial application of genetic tests, since this fact involves not only the individual and their families, but the entire population. Besides being also necessary to make a reflection on how this information from the human genome will be used, for good or bad. The objective of this review was to bring the light of knowledge, data on characteristics of the ethical application of molecular biology, linking it with the rights of human beings. After studying literature, it might be observed that the Human Genome Project has generated several possibilities, such as the identification of genes associated with diseases with synergistic properties, but sometimes modifying behavior to genetically intervene in humans, bringing benefits or social harm. The big challenge is to decide what humanity wants on this giant leap.

Effects of repeated long-term sodium hypochlorite disinfection treatment on surface hardness and roughness of self-polymerizing reline acrylic resins

Denture stomatitis is the most common alteration on the palate of denture wearers and deficient denture hygiene is an important predisposing factor, because it facilitates both the presence of Candida albicans and bacteria in saliva and their colonization on the oral mucosa and denture surfaces. Sodium hypochlorite is an efficient chemical disinfectant to eliminate denture biofilm, but the effect of long-term disinfection on reline acrylic resins was not studied. Purpose: This study investigated the hardness and roughness of three self-polymerizing reline resins after repeated long-term sodium hypochlorite disinfections. Material and methods: Forty round specimens (30 x 6mm) were made from each material: Jet, Kooliner and Tokuyama Rebase II Fast, and divided in 4 groups (n=10). The control group was stored in water and the others were disinfected with 1%, 2%, 5.25% sodium hypochlorite, respectively. The specimens were tested for knoop hardness (KHN) and roughness (Ra) before disinfection and after 30, 90 and 180 disinfection cycles. Data were analyzed by analysis of variance followed by the Tukey test at 5%. Results: The hardness of Jet resin varied from 18.74 ± 0.47 to 13.75 ± 0.95 KHN, Kooliner varied from 14.09 ± 1.63 to 7.52 ± 0.88 KHN, and Tokuyama Rebase II Fast from 12.57 ± 0.94 to 8.28 ± 0.39 KHN. Statistically significant decrease in hardness of the three reline acrylic resins was observed early after the first 30 disinfection cycles. Conclusion: The hardness of the tested materials decreased after immersion in water and after repeated long-term chemical disinfections