Emanuel Santos

Relation between in-vitro wear and nanomechanical properties of commercial light-cured dental composites coated with surface sealants

This work investigates the correlation between the in-vitro wear resistance and the nanomechanical properties of dental sealants commercially available. Mechanical properties, namely hardness (H) and elastic modulus (E), were assessed by nanoindentation technique. The coated samples presented lower H and E values than the Z250 composite resin substrate. Such measurements were used to calculate H/E ratios. Wear tests were carried out in water by using a pin-on-plate apparatus. Scars formed on the samples were qualitatively examined by optical microscopy, while their wear depths were measured by contact profilometry. Based on the findings, an empirical correlation between the wear depths and H/E was obtained. A high H/E ratio was associated to surfaces with enhanced wear resistance. For the tribological conditions here employed, the H/E ratio could be, therefore, considered a useful parameter for ranking the in-vitro wear of dental sealants.

Infrared spectroscopy, nano-mechanical properties, and scratch resistance of esthetic orthodontic coated archwires

OBJECTIVE To evaluate the material composition, mechanical properties (hardness and elastic modulus), and scratch resistance of the coating of four commercialized esthetic orthodontic archwires. MATERIALS AND METHODS The coating composition of esthetic archwires was assessed by Fourier-transform infrared spectroscopy (FTIR). Coating hardness and elastic modulus were analyzed with instrumented nano-indentation tests. Scratch resistance of coatings was evaluated by scratch test. Coating micromorphologic characteristics after scratch tests were observed in a scanning electron microscope. Statistical differences were investigated using analysis of variance and Tukey post hoc test. RESULTS The FTIR results indicate that all analyzed coatings were markedly characterized by the benzene peak at about 1500 cm(-1). The coating hardness and elastic modulus average values ranged from 0.17 to 0.23 GPa and from 5.0 to 7.6 GPa, respectively. Scratch test showed a high coating elasticity after load removal with elastic recoveries >60%, but different failure features could be observed along the scratches. CONCLUSION The coatings of esthetic archwires evaluated are probably a composite of polyester and polytetrafluoroethylene. Delamination, crack propagation, and debris generation could be observed along the coating scratches and could influence its durability in the oral environment.

Effect of resin infiltration on the nanomechanical properties of demineralized bovine enamel.

Objective: The aim of the present study was to evaluate the efficacy of resin infiltration in preventing in vitro lesion progression. Materials and Methods: Buccal surfaces of bovine incisors were divided into mesial and distal regions and, at the center, nail varnish was applied (1.0 mm width) to protect the enamel surface against any further treatment. In order to create artificial enamel lesions in the unprotected areas, each specimen was soaked in a demineralizing solution. After that, specimens had two enamel lesions. One lesion in each sample was etched with 15% HCl for 120 s and infiltrated with a commercial infiltrating resin for 3 min, while the other lesion was not treated (control). Each specimen was cross-sectionally halved and randomly allocated to two groups: Group 1 was immediately processed and Group 2 was submitted to a new demineralization process. The samples were analyzed by means of cross-sectional hardness measurements using a nanoindenter equipment. Hardness data were statistically analyzed by non-parametric Kruskal-Wallis and MannWhitney tests (α = 0.05). Results: The findings showed statistical difference between treatments at the same analyzed distance range from the outer surface of the enamel (P < 0.05). Conclusion: The untreated lesion showed lower hardness values for distances near the outer surface of the enamel. The resin infiltration was efficient in preventing further in vitro demineralization of bovine enamel lesions.

Preliminary results of osteoblast adhesion on titanium anodic films

Osteoblast adhesion on metallic titanium coated with anodic films was evaluated. The anodic oxidation treatment was carried out on commercially pure-titanium (cp-Ti) substrate under the following conditions: 1.0M H2SO4/150V and 1.0M Na2SO4/100V. Osteoblast cells were cultured onto the samples for 4 hours. The morphologies of both Ti anodic films and cells were observed by scanning electron microscopy (SEM). The oxide films are rough with porous structure. Statistical differences in average surface roughness (Ra) values are found among both anodic films and substrate (abraded cp-Ti), measured by contact profilometry. The oxide films prepared in H2SO4 had greater contact angle, whereas there is no statistical significance between the values for the Ti anodic films produced in Na2SO4 and the substrate surface. Despite the some differences in morphology, roughness and contact angle between the treated and non-treated samples, cell morphologies were similar on all surfaces after 4h of culture. Further, was not clearly observed a correlation between the surface characteristics with cell behavior.

In Vitro Behavior of Two Distinct Titanium Surfaces Obtained by Anodic Oxidation

Two different Ti oxide films produced by anodic oxidation were submitted to in vitro bioactivity and cell culture tests. The oxide films were produced in 1.0M H2SO4/150V and 1.0M Na2SO4/100V. Surfaces were found to be homogeneous and rough, with the presence of pores. Both oxide films presented anatase and rutile phases. Ti oxide film produced in Na2SO4 was rougher than the film grown with H2SO4 and composed of a rutile-rich phase. Both films were constituted by TiO2 and Ti2O3 oxides. Despite the differences observed, after 7 days, a calcium phosphate layer was precipitated on both surfaces. Indeed, these two treatment conditions seem to be efficient to spread and attach osteoblast-like cells within 4h.

Nanomechanical Properties of Bioactive Ti Surfaces Obtained by NaOH-Based Anodic Oxidation and Alkali Treatment

Titanium has been used in the production of dental implants and orthopedic prostheses due to the low tendency to corrosion and good biocompatibility. Meanwhile, the surface of titanium is not bioactive. Several surface treatments have been developed to make the surface of such metals bioactive. The aim of this work was to evaluate two of these modification processes in commercially pure titanium grade 2, both of them using NaOH solutions: the anodic oxidation and the alkali treatment. The surface morphology was evaluated by SEM/EDS, the crystal structure by XRD, and the mechanical properties and scratch resistance by instrumented indentation. The anodic oxidation (AO) was carried out using NaOH electrolyte 0.1 mol/L and constant current density of 150 mA/cm² for one minute. The alkaline treatment (AT) was performed by soaking the Ti sample in NaOH 5 mol/L solution at 60 °C for 24 hours; after this, the sample was heat treated at 600 °C for one hour in atmospheric air. The AO produced a TiO2 layer on Ti, whereas a thin sodium titanate layer was obtained by AT. Each surface modification resulted in a specific morphology, but both of them presented the increase in roughness as a common characteristic. The alkali treated Ti surfaces showed the lowest elastic modulus and hardness values. The largest increase in hardness between the treated surfaces was obtained for Ti after anodic oxidation. Scratch test indicates that the TiO2 film from AO has higher strength to tangential loading than the Ti substrate. In addition, for the Ti submitted to AT, the scratch test indicates that the modified surface layer has a poor adhesion with the substrate. Based on these results it is possible to conclude that, using NaOH solutions, Ti surfaces treated by anodic oxidation present improved mechanical properties than the alkali-treated ones.

Effect of Hot Swaging on Microstructure and Properties of Aged Ti-10Mo-20Nb Alloy

Mechanical properties of metastable β-Ti alloys are highly dependent on the final microstructure, which is controlled by the thermomechanical processing. These alloys are used for biomedical applications and require a high mechanical strength as well as a low Young’s modulus to avoid stress shielding. Previous work on the development of cold swaged Ti-10Mo-20Nb alloy showed that the best compromise strength and Young ́s modulus was obtained when the forming is followed by an aging heat treatment at 500 oC. In this work, Ti-10Mo-20Nb alloy was hot swaged and aged at 500 oC for 10 min, 4h and 24h. The microstructure was analyzed by X-ray diffraction, optical microscopy and transmission electron microscopy. Mechanical characterization was based on Vickers microhardness tests and Young’s modulus measurements. Aging at 500 oC for 10 min after hot swaging resulted in a nearly 100% β phase microstructure while aging at 500°C for 4h or 24h led to a bimodal microstructure consisting on α precipitates dispersed in the β matrix. The higher hardness to Young’s modulus ratio was obtained for the sample aged at 500 °C for 4h. This value was higher than those obtained for the Ti-6Al-4V alloy and commercially pure Ti.

Tribological Characterization of Porous TiO2 Coatings Produced by Electrodeposition

In this work, the resistance to scratch and wear (pin-on-flat) tests of five different porous TiO2 films were compared. Such tribological tests were carried out under dry conditions. The coatings were electrodeposited on commercially pure-Ti by anodic oxidation method in different electrolyte solutions at constant voltages. The scratch tests were conducted by applying increasing normal loads up to 400 mN. The coefficient of friction (COF) varied from 0.2 up to 0.5, and increased at larger penetrations depths. When the electrolyte concentration was changed from 0.5 into 1.0M H2SO4, the COF slightly decreased. Scanning electron microscopy indicated that the coatings produced in H2SO4/150V and Na2SO4/100V did not have their substrates revealed. In addition, the samples anodized in H2SO4/150V had the highest elastic recoveries. Therefore, such coatings seem to be more resistant to scratch tests than the others. The wear tests were carried out with Berkovich tip as counter-face under constant normal loads of 10 mN in 10 forward-backward cycles. The coatings deposited in H2SO4/150V had the lowest wear volume rates. The findings suggest that the porous Ti oxide coatings electrodeposited above their rupture voltages are more suitable to both scratch- and wear-resistance compared to those prepared at the lowest voltage (H2SO4/100V).