Denise Tornavoi de Castro

Evaluation of antibiofilm and mechanical properties of new nanocomposites based on acrylic resins and silver vanadate nanoparticles.

OBJECTIVE The purpose of this study was evaluate, for the first time, the impact of incorporation of nanostructured silver vanadate (β-AgVO3) in antibiofilm and mechanical properties of dental acrylic resins (poly(methyl methacrylate), PMMA). DESIGN The β-AgVO3 was synthesized and characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy, and microanalysis (SEM/EDS). Resins specimens were prepared with 0-10% wt.% β-AgVO3 and characterized by SEM, XRD and optical microscopy. The antibiofim activity of the samples against Candida albicans and Streptococcus mutans was investigated by XTT reduction test, colony-forming units (CFUs), and confocal laser scanning microscopy (CLSM). The flexural strength, hardness, and surface roughness of the samples containing β-AgVO3 were compared with the pure PMMA matrix. RESULTS The incorporation of 10% β-AgVO3 significantly reduced the metabolic activity of C. albicans and S. mutans (p<0.05). There was a reduction in microbial load (CFU/mL) of microorganisms for the different concentrations used (p<0.05), which was confirmed by confocal microscopy. The addition of β-AgVO3 did not change the mechanical properties of hardness and surface roughness of the resins (p>0.05). However, flexural strength decreased with the addition of amounts greater than 1% (p<0.05). CONCLUSIONS β-AgVO3 additions in dental acrylic resin may have an impact on inhibition of biofilm of main microorganisms associated with dental prostheses. However, the viability of clinical use should be evaluated in function of changed promoted in some mechanical properties.

Development of a novel resin with antimicrobial properties for dental application

The adhesion of biofilm on dental prostheses is a prerequisite for the occurrence of oral diseases. Objective To assess the antimicrobial activity and the mechanical properties of an acrylic resin embedded with nanostructured silver vanadate (β-AgVO3). Material and Methods The minimum inhibitory concentration (MIC) of β-AgVO3 was studied in relation to the species Staphylococcus aureus ATCC 25923, Streptococcus mutans ATCC 25175, Pseudomonas aeruginosa ATCC 27853, and Candida albicans ATCC 10231. The halo zone of inhibition method was performed in triplicate to determine the inhibitory effect of the modified self-curing acrylic resin Dencor Lay - Clássico®. The surface hardness and compressive strength were examined. The specimens were prepared according to the percentage of β-AgVO3 (0%-control, 0.5%, 1%, 2.5%, 5%, and 10%), with a sample size of 9x2 mm for surface hardness and antimicrobial activity tests, and 8x4 mm for the compression test. The values of the microbiologic analysis were compared and evaluated using the Kruskal-Wallis test (α=0.05); the mechanical analysis used the Shapiro-Wilks tests, Levenes test, ANOVA (one-way), and Tukeys test (α=0.05). Results The addition of 10% β-AgVO3 promoted antimicrobial activity against all strains. The antimicrobial effect was observed at a minimum concentration of 1% for P. aeruginosa, 2.5% for S. aureus, 5% for C. albicans, and 10% for S. mutans. Surface hardness and compressive strength increased significantly with the addition of 0.5% β-AgVO3 (p<0.05). Higher rates of the nanomaterial did not alter the mechanical properties of the resin in comparison with the control group (p>0.05). Conclusions The incorporation of β-AgVO3 has the potential to promote antimicrobial activity in the acrylic resin. At reduced rates, it improves the mechanical properties, and, at higher rates, it does not promote changes in the control.

Microstructure and Mechanical Properties of Composite Resins Subjected to Accelerated Artificial Aging

The aim of this study was to investigate the influence of accelerated artificial aging (AAA) on the microstructure and mechanical properties of the Filtek Z250, Filtek Supreme, 4 Seasons, Herculite, P60, Tetric Ceram, Charisma and Filtek Z100. composite resins. The composites were characterized by Fourier-transform Infrared spectroscopy (FTIR) and thermal analyses (Differential Scanning Calorimetry - DSC and Thermogravimetry - TG). The microstructure of the materials was examined by scanning electron microscopy. Surface hardness and compressive strength data of the resins were recorded and the mean values were analyzed statistically by ANOVA and Tukeys test (α=0.05). The results showed significant differences among the commercial brands for surface hardness (F=86.74, p<0.0001) and compressive strength (F=40.31, p<0.0001), but AAA did not affect the properties (surface hardness: F=0.39, p=0.53; compressive strength: F=2.82, p=0.09) of any of the composite resins. FTIR, DSC and TG analyses showed that resin polymerization was complete, and there were no differences between the spectra and thermal curve profiles of the materials obtained before and after AAA. TG confirmed the absence of volatile compounds and evidenced good thermal stability up to 200 °C, and similar amounts of residues were found in all resins evaluated before and after AAA. The AAA treatment did not significantly affect resin surface. Therefore, regardless of the resin brand, AAA did not influence the microstructure or the mechanical properties.

Analyzing the Influence of a New Dental Implant Design on Primary Stability.

BACKGROUND The macrogeometry of dental implants strongly influences the primary stability and hence the osseointegration process. PURPOSE Compare the performance of conventional and modified implant models in terms of primary stability. MATERIALS AND METHODS A total of 36 implants (Neodent®) with two different formats (n = 18): Alvim CM (Conical CM, Ø 4.3 mm × 10 mm in length) and Titamax Ti (Cylindrical HE, Ø 4.0 mm × 11 mm in length) were inserted into artificial bone blocks. Nine implants from each set were selected to undergo external geometry changes. The primary stability was quantified by insertion torque and resonance frequency using an Osstell device and the pullout test. One-way analysis of variance and Tukeys test were used for statistical evaluation. RESULTS The comparative analysis of the implants showed a significant increase of the insertion torque for the modified Conical CM implants (p = 0.000) and Cylindrical HE (p = 0.043); for the resonance frequency the modified Cylindrical HE showed a lower statistical mean (p = 0.002) when compared to the conventional model, and in the pullout test both modified implants showed significant reduction (p = 0.000). CONCLUSIONS Within the limitations of this study, the proposed modification showed good stability levels and advantages when compared to the conventional implants.

Effect of casting atmosphere on the marginal deficiency and misfit of Ni-Cr alloys with and without beryllium

Statement of problem. The marginal adaptation of prosthetic crowns is still a significant clinical problem. Purpose. The purpose of this in vitro study was to evaluate the marginal deficiency and misfit of Ni‐Cr alloys with and without beryllium under different casting conditions. Material and methods. Four casting conditions were selected: flame‐torch, induction/argon, induction/vacuum, and induction/air; and 2 alloys were used, Ni‐Cr‐Be and Ni‐Cr. For each group, 10 metal specimens were prepared. Silicone indirect impressions and analysis of the degree of rounding were used to evaluate the marginal deficiencies of metal copings, and a standardized device for the setting pressure associated with optical microscopy was used to analyze the marginal misfit. Results were evaluated with 2‐way ANOVA (&agr;=.05), followed by the Tukey honest significant difference post hoc test, and the Pearson correlation test (&agr;=.05). Results. Alloy (P<.001) and casting technique (P<.001) were shown to affect marginal deficiencies. The Ni‐Cr cast using the torch technique showed the highest marginal deficiency, and the Ni‐Cr‐Be cast in a controlled argon atmosphere showed the lowest (P<.001). Alloy (P=.472) and casting techniques (P=.206) did not affect the marginal misfit, but significant differences were found in the interaction (P=.001); the lowest misfit was achieved using the Ni‐Cr‐Be, and the highest misfit occurred with the molten Ni‐Cr, using the cast torch technique. No correlation was found between deficiency and marginal misfit (r=.04, P=.69). Conclusions. The interactions demonstrated that the alloy containing beryllium that was cast in an argon atmosphere led to reduced marginal deficiency. Improved marginal adaptation can be achieved for the same alloy by using the torch technique.

Comparative analysis of stress in a new proposal of dental implants

The purpose of this study was to compare, through photoelastic analysis, the stress distribution around conventional and modified external hexagon (EH) and morse taper (MT) dental implant connections. Four photoelastic models were prepared (n=1): Model 1 - conventional EH cylindrical implant (Ø 4.0mm×11mm - Neodent®), Model 2 - modified EH cylindrical implant, Model 3 - conventional MT Conical implant (Ø 4.3mm×10mm - Neodent®) and Model 4 - modified MT conical implant. 100 and 150N axial and oblique loads (30° tilt) were applied in the devices coupled to the implants. A plane transmission polariscope was used in the analysis of fringes and each position of interest was recorded by a digital camera. The Tardy method was used to quantify the fringe order (n), that calculates the maximum shear stress (τ) value in each selected point. The results showed lower stress concentration in the modified cylindrical implant (EH) compared to the conventional model, with application of 150N axial and 100N oblique loads. Lower stress was observed for the modified conical (MT) implant with the application of 100 and 150N oblique loads, which was not observed for the conventional implant model. The comparative analysis of the models showed that the new design proposal generates good stress distribution, especially in the cervical third, suggesting the preservation of bone tissue in the bone crest region.

Bioglass® and resulting crystalline materials synthesized via an acetic acid-assisted sol–gel route

In this study, we report on the synthesis of a bioactive glass powder with the original 45S5 composition (Bioglass®) by means of an acetic acid-assisted sol–gel route. A glassy material was obtained after the gels underwent a thermal stabilization treatment at 600 °C for 3 h. Above this temperature, the heat-treated gels crystallized partially, forming a sodium-calcium-silicate Na2CaSi2O6 phase. Even after crystallization, this material showed in vitro bioactivity in simulated body fluid after 12 h, when the formation of hydroxycarbonate apatite on the material surface was identified by X-ray diffraction. Not surprisingly, microbiological assays revealed that these gel-derived materials appear to have an antibacterial effect against Pseudomonas aeruginosa (ATCC 27853)—a Gram-negative bacterium that is noted for its environmental survival versatility, ability to produce biofilm and resistance to some antibiotics. Thus, using common precursors that are widely available, relatively cheap, simple to use, and which result in gels with low stabilization temperature, it was possible to explore the versatility of sol–gel processing to obtain the golden standard 45S5 bioglass.Graphical Abstract

Analysis of the oral microbiome on the surface of modified dental polymers

OBJECTIVES This study characterized the microbial diversity of formed biofilm on the surface of acrylic resins modified with nanostructured silver vanadate decorated with silver nanoparticles (AgVO3) after incubation in human saliva. DESIGN Resin specimens prepared with AgVO3 at concentrations 0%, 1%, 2.5%, and 5% by either vacuum mixing or polymer solubilization were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). After 24 h and 7 days of saliva incubation, biofilm samples were collected from the surface of the specimens. The 16S rDNA genes were amplified, sequenced with the 454-Roche next-generation sequencing platform and analyzed to identify the Operational Taxonomic Units at the genus or higher level. RESULTS Significant differences in the dispersion pattern of the nanoparticles were observed among the two different methods of AgVO3 incorporation. In the microbiological analysis, a total of 103 genera and 7 more inclusive taxa, representing the phyla Bacteroidetes, Firmicutes and Proteobacteria were identified colonizing resin surfaces. The incorporation method of the AgVO3 had little to no significant effect on the microbiota of samples. Significant time and concentration-dependent responses to AgVO3 caused changes in the taxonomic profile at the phylum and genus level. CONCLUSIONS The results show differences in relation to the microbial diversity of modified resins during the initial phase of biofilm maturation. The incorporation of AgVO3 seems to significantly affect the colonizing microbiota.

Effect of incorporation of a new antimicrobial nanomaterial on the physical-chemical properties of endodontic sealers

Objectives: The objective of the study is to incorporate the nanostructured silver vanadate (AgVO3) decorated with silver nanoparticles at endodontic sealers AH Plus, Sealapex, Sealer 26, and Endofill, at concentrations of 2.5%, 5%, and 10%, and to evaluate physical-chemical properties. Materials and Methods: The study was to evaluate the radiopacity using digital radiography (n = 5), the tooth color change in 48 incisors (n = 3) for 7, 30, 90, and 180 days in a spectrophotometer, and the topographic distribution in a confocal laser (n = 5). The radiopacity was analyzed by Kruskal–Wallis test and the permutation (α = 0.05) and the color and topographical distribution by descriptive statistical analysis. Results: The AgVO3 had no effect on the radiopacity of Endofill and Sealapex (P > 0.05) and at 2.5% concentrations increased the radiopacity of Sealer 26 and AH Plus (P < 0.05). The Endofill 10% showed less color change, and the major changes were the modified groups in 180 days. The AgVO3 showed a circular topographic distribution in areas of the sealers. Conclusion: It was found that the addition of AgVO3 did not affect the radiopacity of Endofill and Sealapex however, increased the radipacity of Sealer 26 and AH Plus. For modified groups, the greatest color change was promoted after 180 days, except for Endofill with 10%. Topographic distribution of nanomaterial affected the color change of theevaluated sealers.