Mariana Lima da Costa Valente

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.

In vitro analysis of the influence of surface treatment of dental implants on primary stability

Surface treatment interferes with the primary stability of dental implants because it promotes a chemical and micromorphological change on the surface and thus stimulates osseointegration. This study aimed to evaluate the effects of different surface treatments on primary stability by analyzing insertion torque (IT) and pullout force (PF). Eight samples of implants with different surface treatments (TS - external hexagon with acid surface treatment; and MS - external hexagon, machined surface), all 3.75 mm in diameter X 11.5 mm in length, were inserted into segments of artificial bones. The IT of each sample was measured by an electronic torquemeter, and then the pullout test was done with a universal testing machine. The results were subjected to ANOVA (p < 0.05), followed by Tukeys test (p < 0.05). The IT results showed no statistically significant difference, since the sizes of the implants used were very similar, and the bone used was not highly resistant. The PF values (N) were, respectively, TS = 403.75 ± 189.80 and MS = 276.38 ± 110.05. The implants were shown to be different in terms of the variables of maximum force (F = 4.401, p = 0.0120), elasticity in maximum flexion (F = 3.672, p = 0.024), and relative stiffness (F = 4.60, p = 0.01). In this study, external hexagonal implants with acid surface treatment showed the highest values of pullout strength and better stability, which provide greater indication for their use.

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.

Influence of torsional strength on different types of dental implant platforms.

Aim:The study assessed deformation of implant components submitted to torsion tests of 80 and 120 N·cm using an optical stereomicroscope. Material and Methods:The following 3 types of Titaniumfix conical implant connections (n = 5) measuring Ø 4.0 × 11.5 mm were used: external, internal hexagon and Morse taper connections. The diagonal and lateral measurements of the hexagon implant platform were measured before and after the torsion test. Results:The torsion test using torque of 80 and 120 N·cm altered the implant dental platforms. All groups presented deformation of implant component after torque of 80 N·cm with no statistical difference among them. During torque of 120 N·cm, a difference in the Morse taper connection in relation to the internal and external hexagon connection was observed. The Morse taper connection implant, followed by the internal hex implant, underwent less deformation. Greater deformation occurred in the external hex implants. Conclusion:For all the implants, high insertion torques deformed the implant platform preventing long-term maintenance and stability of 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.

In Vitro Microstructural Analysis of Dental Implants Subjected to Insertion Torque and Pullout Test

The change in the implant microstructure during handling may reduce the potential of surface treatment on the osteoinduction and, therefore, on the osseointegration. The aim of this study was to evaluate by energy-dispersive X-ray spectroscopy (EDX) the effect of insertion torque and pullout test on the microstructure of dental implants with different shapes. Four shapes of implants (n=8) were selected: conical with surface treatment (COTS), cylindrical with surface treatment (CTS), cylindrical with double surface treatment (CTSD) and cylindrical with machined surface (CSU). Before and after performing the mechanical tests, the screw surfaces were subjected to analysis of chemical composition by EDX. The results obtained by the microstructural analysis showed presence of three main chemical elements: Ti, C and O. There was a significant change in the concentration of Ti and C. The implant with double surface treatment (CTSD) showed the greatest Ti reduction and the greatest C increase. It may be concluded that the mechanical manipulation may alter the implant surfaces as regards their microstructure. Therefore, surgical planning should take into consideration the choice of surface treatment because the characteristics of the implants may be modified as they are inserted and removed from the bone site.

Estudo in vitro da influência do formato e do tratamento de superfície de implantes odontológicos no torque de inserção, resistência ao arrancamento e frequência de ressonância

OBJECTIVE: The purpose of the study was to evaluate the influence of the shape and surface treatment on the primary stability of dental implants inserted in different substrates through association methods such as insertion torque, pullout strength and resonance frequency. MATERIAL AND METHOD: 32 implants were used with 8 cylindrical treatment Porous (CA), 8 machined cylindrical (MS), 8 cylinder dual treatment Porous (MP) and 8 tapered untreated (CC). The substrates used for inclusion were: pork rib;

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.

Analysis of the surface deformation of dental implants submitted to pullout and insertion test.

OBJECTIVE The aim of the present study was to evaluate the possible deformations in the surface of dental implants submitted to pullout and insertion test in polyurethane synthetic bone, using scanning electron microscopy. MATERIAL AND METHODS Four different types of implants were used: Master Screw, Master Porous, Master Conect AR and Master Conect Conical (n = 8). These implants were into the femoral head synthetic bone (Synbone) and removed through the pullout test, performed with a universal testing machine (EMIC MEM 2000). All the screws, before and after the mechanical tests, were micro structurally analyzed in a Scanning Electron Microscope (SEM - Zeiss EVO50), utilizing a magnification of 35 times. The results were subjected to ANOVA and Tukey tests (α =0.05). RESULTS Only the Master Conect Conical and Master Porous implants presented statistically significant difference to pullout and maximum deformation (P = 0.014 and P = 0.009, respectively). The SEM images did not show morphological changes of the implants when compared before and after the mechanical tests. CONCLUSION We concluded that Master Porous presented higher pullout resistance, suggesting a greater primary stability.