Development of binary and ternary titanium alloys for dental implants

OBJECTIVE

The aim of this study was to develop binary and ternary titanium (Ti) alloys containing zirconium (Zr) and niobium (Nb) and to characterize them in terms of microstructural, mechanical, chemical, electrochemical, and biological properties.

METHODS

The experimental alloys - (in wt%) Ti-5Zr, Ti-10Zr, Ti-35Nb-5Zr, and Ti-35Nb-10Zr - were fabricated from pure metals. Commercially pure titanium (cpTi) and Ti-6Al-4V were used as controls. Microstructural analysis was performed by means of X-ray diffraction and scanning electron microscopy. Vickers microhardness, elastic modulus, dispersive energy spectroscopy, X-ray excited photoelectron spectroscopy, atomic force microscopy, surface roughness, and surface free energy were evaluated. The electrochemical behavior analysis was conducted in a body fluid solution (pH 7.4). The albumin adsorption was measured by the bicinchoninic acid method. Data were evaluated through one-way ANOVA and the Tukey test (α=0.05).

RESULTS

The alloying elements proved to modify the alloy microstructure and to enhance the mechanical properties, improving the hardness and decreasing the elastic modulus of the binary and ternary alloys, respectively. Ti-Zr alloys displayed greater electrochemical stability relative to that of controls, presenting higher polarization resistance and lower capacitance. The experimental alloys were not detrimental to albumin adsorption.

SIGNIFICANCE

The experimental alloys are suitable options for dental implant manufacturing, particularly the binary system, which showed a better combination of mechanical and electrochemical properties without the presence of toxic elements.

Retention force and fatigue strength of overdenture attachment systems

This study evaluated retention force and fatigue resistance of two overdenture attachment systems. Twenty samples (O-ring and Bar-Clip) from two manufacturers (Conexão Sistemas de Prótese and Lifecore Biomedical) were prepared and divided into four groups: (i) Conexão/O-ring; (ii) Conexão/Bar-Clip; (iii) Lifecore/O-ring and (iv) Lifecore/Bar-Clip, with five samples in each group. They were submitted to mechanical fatigue test using a servohydraulic machine performing 5500 cycles of insertion and removal (f=0.8 Hz), immersed in artificial saliva. Retention force values were obtained three times (0, 3000 and after 5500 cycles) simulating the clinical service, using a tensile strength at 1 mm min(-1) and load cell of 1 kN. Data were analysed with analysis of variance and Tukey's test at 5% level. Results showed that Conexão/Bar-Clip specimens had significantly higher retention values than Lifecore/Bar-Clip (44.61 and 18.44 N, respectively), Conexão/O-ring specimens had significantly lower values than Lifecore/O-ring (13.91 and 19.75 N, respectively). Conexão/Bar-Clip values were always significantly higher than those of Conexão/O-ring group (44.61 and 13.91 N, respectively). Lifecore (O-ring and Bar-Clip) presented similar values (19.75 and 18.44 N, respectively). The systems evaluated showed satisfactory retention force values, before and after fatigue testing. Conexão/Bar-Clip specimens presented the highest values. A 5-year simulation of insertion and removal did not decrease retention values or fracture components.

The volumetric fraction of inorganic particles and the flexural strength of composites for posterior teeth

OBJECTIVE

To evaluate the content of inorganic particles and the flexural strength of new condensable composites for posterior teeth in comparison to hybrid conventional composites.

METHOD

The determination of the content of inorganic particles was performed by mass weighing of a polymerized composite before and after the elimination of the organic phase. The volumetric particle content was determined by a practical method based on Archimedes' principle, which calculates the volume of the composite and their particles by differential mass measured in the air and in water. The flexural strength of three points was evaluated according to the norm ISO 4049:1988.

RESULTS

The results showed the following filler content: Alert, 67.26%; Z-100, 65.27%; Filtek P 60, 62.34%; Ariston pHc, 64.07%; Tetric Ceram, 57.22%; Definite, 54.42%; Solitaire, 47.76%. In the flexural strength test, the materials presented the following decreasing order of resistance: Filtek P 60 (170.02 MPa)>Z-100 (151.34 MPa)>Tetric Ceram (126.14 MPa)=Alert (124.89 MPa)>Ariston pHc (102.00 MPa)=Definite (93.63 MPa)>Solitaire (56.71 MPa).

CONCLUSION

New condensable composites for posterior teeth present a concentration of inorganic particles similar to those of hybrid composites but do not necessarily present higher flexural strength.

Neutrophils have a protective role during early stages of Leishmania amazonensis infection in BALB/c mice

Neutrophils are involved in the early stages of immune responses to pathogens. Here, we investigated the role of neutrophils during the establishment of Leishmania amazonensis infection in BALB/c and C57BL/6 mice. First, we showed an accumulation of neutrophils between 6 and 24 h post-infection, followed by a reduction in neutrophil numbers after 72 h. Next, we depleted neutrophils prior to infection using RB6-8C5 or 1A8 mAb. Neutrophil depletion led to faster lesion development, increased parasite numbers and higher arginase activity during the first week of infection in BALB/c mice, but not in C57BL/6 mice. Increased susceptibility was accompanied by augmented levels of anti-L. amazonensis IgG and increased production of IL-10 and IL-17. Because IL-10 is a mediator of susceptibility to Leishmania infection, we blocked IL-10 signalling in neutrophil-depleted mice using anti-IL-10R. Interestingly, inhibition of IL-10 signalling abrogated the increase in parasite loads observed in neutrophil-depleted mice, suggesting that parasite proliferation is at least partially mediated by IL-10. Additionally, we tested the effect of IL-17 in inflammatory macrophages and observed that IL-17 increased arginase activity and favoured parasite growth. Taken together, our data indicate that neutrophils control parasite numbers and limit lesion development during the first week of infection in BALB/c mice.

Lipases and esterases: a review of their sequences, structure and evolution

This chapter aims to provide a brief review on the enzyme family of lipases and esterases. The sequences, 3D structures and pH dependent electrostatic signatures are presented and analyzed. Since the family comprises more than 100 sequences, we have tried to focus on the most interesting features from our perspective, which translates into finding similarities and differences between members of this family, in particular in and around the active sites, and to identify residues that are partially or totally conserved. Such residues we believe are either important for maintaining the structural scaf-fold of the protein or to maintain activity or specificity. The structure function relationship for these proteins is therefore of central interest. Can we uniquely identify a protein from this large family of sequences--and if so, what is the identifier? The protein family displays some highly complex features: many of the proteins are interfacially activated, i.e. they need to be in physical contact with the aggregated substrate. Access to the active site is blocked with either a loop fragment or an alpha-helical fragment in the absence of interfacial contact. Although the number of known, relevant protein 3D structures is growing steadily, we are nevertheless faced with a virtual explosion in the number of known or deduced amino acid sequences. It is therefore unrealistic to expect that all protein sequences within the foreseeable future will have their 3D structure determined by X-ray diffractional analysis or through other methods. When feasible the gene and/or the amino acid sequences will be analyzed from an evolutionary perspective. As the 3D folds are often remarkably similar, both among the triglyceride lipases as well as among the esterases, the functional diversities (e.g. specificity) must originate in differences in surface residue utilization, in particular of charged residues. The pH variations in the isopotential surfaces of some of the most interesting lipases are presented and a qualitative interpretation proposed. Finally we illustrate that NMR has potential for becoming an important tool in the study of lipases, esterases and their kinetics.

Effect of the Association of Nystatin with a Tissue Conditioner on its Ultimate Tensile Strength

PURPOSE

This study evaluated the ultimate tensile strength of a tissue conditioner without nystatin incorporation (GI-control group) and the same tissue conditioner modified by the addition of nystatin in two concentrations: GII-500,000 International Units (U) and GIII-1,000,000 U, in which each milligram of the medicament corresponded to 6079 U.

MATERIALS AND METHODS

Dumbbell-shaped specimens (N= 7) with a central cross-sectional area of 33 x 6 x 3 mm were produced for the three experimental groups. After polymerization following manufacturer's instructions, specimens were immersed in distilled water at 37 degrees C for either 24 hours or 7 days and then tested in tension in the MTS 810 at 40 mm/minute. Data were analyzed by two-way ANOVA followed by Tukey's test, at 95% level of confidence.

RESULTS

The means (force-grams (gf) +/- standard deviation) of the ultimate tensile strength were: GI-634.29 +/- 122.80; GII-561.92 +/- 133.56; and GIII-547.30 +/- 73.47 for 24-hour storage, and GI-536.68 +/- 54.71; GII-467.50 +/- 143.51; and GIII-500.62 +/- 159.76 for 7-day storage. There were no statistically significant differences among the three experimental groups (p > 0.05). The ultimate tensile strength means of all experimental groups after 7 days were significantly lower than those observed after 24 hours (p= 0.04).

CONCLUSIONS

The results of this study suggest that the addition of nystatin into the tissue conditioner investigated in concentrations below 1,000,000 U did not affect its ultimate tensile strength.

Proteome analysis of the salivary pellicle formed on titanium alloys containing niobium and zirconium

The chemical composition of biomaterials can drive their biological responses; therefore, this in vitro study aimed to evaluate the proteomic profile of the salivary pellicle formed on titanium (Ti) alloys containing niobium (Nb) and zirconium (Zr). The experimental groups consisted of Ti35NbxZr (x = 5 and 10 wt%) alloys, and commercially pure titanium (cpTi); titanium aluminium vanadium (Ti6Al4V) alloys were used as controls. The physical and chemical characteristics of the Ti materials were analysed. The proteomic profile was evaluated by liquid chromatography coupled with tandem mass spectrometry. Bacterial adhesion (2 h) of mixed species (Streptococcus sanguinis and Actinomyces naeslundii) was investigated as colony-forming units (n = 6). This paper reports the finding that salivary pellicle composition can be modulated by the composition of the Ti material. The Ti35NbxZr group showed a significant ability to adsorb proteins from saliva, which can favour interactions with cells and compatibility with the body.

Porosity control of hydroxyapatite implants

Conformation of hydroxyapatite (HAp) bodies was carried out using a multiple slip-casting technique, in order to obtain dual-layer samples with differential sized porosities. The external layer, because of its porosity, controlled by the addition of organic compounds (polyvinyl polyacrylate, PVC), will promote bone ingrowth. The internal denser layer, due to the addition of lithium phosphate (Li3PO4) as sintering additive, will give mechanical resistance to the implant. HAp aqueous suspensions were characterized by rheological measurements. Scanning electron microscopy (SEM) and intrusion mercury porosimetry (MP) were used to characterize sintered bodies. It can be concluded that it is possible to introduce gross porosity in HAp bodies by the addition of organic compounds. The results show that a compatible shrinking of the layers during the sintering process and a good frequency of pores with an appropriate size in the external layer can be achieved with the use of organic additives.

Compressive fatigue in titanium dental implants submitted to fluoride ions action

The aim of this study was to assess the influence of a fluoridated medium on the mechanical properties of an internal hexagon implant-abutment set, by means of compression, mechanical cycling and metallographic characterization by scanning electronic microscopy. Five years of regular use of oral hygiene with a sodium fluoride solution content of 1500 ppm were simulated, immersing the samples in this medium for 184 hours, with the solutions being changed every 12 hours. Data were analyzed at a 95% confidence level with Fisher's exact test. After the action of fluoride ions, a negative influence occurred in the mechanical cycling test performed in a servohydraulic machine (Material Test System-810) set to a frequency of 15 Hz with 100,000 cycles and programmed to 60% of the maximum resistance of static compression test. The sets tended to fracture by compression on the screw, characterized by mixed ruptures with predominance of fragile fracture, as observed by microscopy. An evidence of corrosion by pitting on sample surfaces was found after the fluoride ions action. It may be concluded that prolonged contact with fluoride ions is harmful to the mechanical properties of commercially pure titanium structures.

Differences between Experienced and Novice Rugby Union Players during Small-Sided Games

The purpose of this study was to compare physical exertion and game performance indicators of experienced and novice Rugby Union players when playing small-sided games. Forty male players ( M age = 21.6 yr., SD = 3.6; M Height = 177.7 cm, SD = 7.4; M body mass 81.2 kg, SD = 10.2) participated in eight 6 vs 6 small-sided games over a 4-wk. period, with 12 min. continuous duration in a 60 × 40 m playing area. All players wore GPS units and heart rate belts. No statistically significant differences in the physical exertion measures between experienced and novice players were found. However, the manual notational analysis revealed substantial differences between players in all game performance indicators, with better performance by the experienced players (Passes made ES = 0.5; Tackles made ES = 1.0; Tries ES = 0.5). These results suggest the possibility that specific physical conditioning might be achieved without also achieving technical and tactical excellence.

Mechanical, physical, and chemical characterization of Ti-35Nb-5Zr and Ti-35Nb-10Zr casting alloys

Titanium is used due its excellent properties in medical and dentistry areas. With the objective of exploiting better mechanical properties, not altering its biocompatibility, it was intended to add niobium and zirconium to the titanium, being formulated two alloys Ti-35%Nb-5%Zr (alloy 1) and Ti-35%Nb-10%Zr (alloy 2) wt% produced by an arc melting method. The chemical analysis of the samples was accomplished by X-ray fluorescence, and the microstrutural evaluation by scanning electron microscopy and X-ray diffraction. The mechanical tests were: Vickers hardness, tensile strength, mechanical cycling, and fracture analysis. The results allowed characterizing the alloy 1 as alpha + beta type and the alloy 2 as beta type. It is found that the alloy 1 presented larger hardness and smaller tensile strength than the alloy 2. The fractures, after the tensile test, were of the ductile type and, after the mechanical cycling, they were of the mixed type for both alloys.

Comparison of the tensile bond strengths of cast metal crowns luted with resin cements

The limitation of photoactivation of dual-polymerized resin cements along the margins of metal restorations may adversely affect the mechanical properties of these cements, thus impairing the retention of restorations. The aim of this study was to assess the bond strength of cast metal crowns cemented with three dual-polymerized resin cements, using a chemically-activated resin cement and zinc phosphate as controls. Fifty nickel-chromium alloy crowns were cast and randomly assigned to five groups of equal size. Castings were cemented on their corresponding metal dies with one of the tested luting agents: Scotchbond Resin Cement, Enforce and Panavia F (dual-polymerized resin cements), Cement-It (chemically-activated resin cement) and Zinc Phosphate Cement (zinc phosphate cement). Specimens were stored in distilled water at 37 degrees C for 24 h and then loaded in tension until failure. Panavia F and Zinc Phosphate Cement provided the highest and lowest bond strength means, respectively. Scotchbond Resin Cement, Enforce and Cement-It cements exhibited similar intermediate values, but with statistically significant difference compared to the other materials (P < 0.05). Even with the restriction or absence of light activation, all tested dual-polymerized resin cements produced significantly higher bond strength than did the zinc phosphate cement and yielded similar or better results than the chemically activated cement. It should be pointed out that the findings of this study relate to a test scenario which does not mimic clinical circumstances and that further work is required to identify the clinical significance of the reported tensile bond strength differences between the different luting materials.

Compressive strength and compressive fatigue limit of conventional and high viscosity posterior resin composites

The purpose of this study was to compare the compressive strengths and compressive fatigue limits of three posterior composite resins (Filtek P-60, Surefil and Prodigy Condensable) and a universal restorative composite (Z-100). Cylindrical specimens (8 mm in length x 4 mm in diameter) were used. The dynamic test was performed using the staircase method, and the ratio between compressive fatigue limit and compressive resistance was also calculated (n = 15). The compressive strength and compressive fatigue limit data were analyzed by Anova and Tukeys test. The Z-100 composite demonstrated higher compression strength (307.20 MPa) than Surefil (266.93 MPa) and Prodigy Condensable (222.08 MPa). The resistance of Filtek P-60 (270.44 MPa) was similar to the resistances of Z-100 and Surefil, while Prodigy Condensable presented the lowest compressive strength. In the compressive fatigue limit tests, Filtek P-60 demonstrated a higher value (184.20 MPa) than Prodigy Condensable (155.50 MPa). Surefil (165.74 MPa) and Z-100 (161.22 MPa) presented limits similar to those of Filtek P-60 and Prodigy Condensable. The compressive fatigue limit/compressive strength ratio was 70.01% for Prodigy Condensable, 68.11% for Filtek P-60, 62.09% for Surefil and 52.48% for Z-100. It was concluded that the Z-100 universal composite was more sensitive to the dynamic test than the high viscosity materials.

Spirometric tests to assess the prevalence of childhood asthma at Portuguese rural areas: influence of exposure to high ozone levels

The study here reported aimed to: i) evaluate the prevalence of childhood asthma at a Portuguese rural area with high ozone concentrations through lung function tests, validating the previously estimated one assessed through questionnaires (similar to those of the ISAAC); ii) compare the achieved prevalence with the one reported at an unexposed area (with low ozone concentrations), aiming to evaluate the influence of exposure to high ozone levels; and iii) determine potential risk factors. Ninety-five of the original 478 children that completed the questionnaires, mentioned to have at least one of asthma symptoms (wheeze, dyspnea or cough) and were therefore evaluated by spirometry. FEV(1) was in average 89.7% for asthmatics and 102.8% for non-asthmatics. For the studied sample the risk was higher for girls with a tendency to be higher from 8 to 10 years old. Lifetime prevalence of childhood asthma at the exposed area was 9.2%. Children living at the exposed area had 3 times higher risk of having asthma than those living at the unexposed area. Considering that ozone concentrations were the main difference between both areas, it can be suggested that ozone pollution increased asthma prevalence. Nevertheless, it should be remarked that further studies should be done to confirm these results.

Pre-heating mitigates composite degradation

Dental composites cured at high temperatures show improved properties and higher degrees of conversion; however, there is no information available about the effect of pre-heating on material degradation. Objectives This study evaluated the effect of pre-heating on the degradation of composites, based on the analysis of radiopacity and silver penetration using scanning electron microscopy/energy-dispersive X-ray spectroscopy (SEM/EDS). Material and Methods Thirty specimens were fabricated using a metallic matrix (2x8 mm) and the composites Durafill VS (Heraeus Kulzer), Z-250 (3M/ESPE), and Z-350 (3M/ESPE), cured at 25°C (no pre-heating) or 60°C (pre-heating). Specimens were stored sequentially in the following solutions: 1) water for 7 days (60°C), plus 0.1 N sodium hydroxide (NaOH) for 14 days (60°C); 2) 50% silver nitrate (AgNO3) for 10 days (60°C). Specimens were radiographed at baseline and after each storage time, and the images were evaluated in gray scale. After the storage protocol, samples were analyzed using SEM/EDS to check the depth of silver penetration. Radiopacity and silver penetration data were analyzed using ANOVA and Tukey's tests (α=5%). Results Radiopacity levels were as follows: Durafill VS<Z-350<Z-250 (p<0.05). The depth of silver penetration into the composites ranked as follows: Durafill VS>Z-350>Z-250 (p<0.05). After storage in water/NaOH, pre-heated specimens presented higher radiopacity values than non-pre-heated specimens (p<0.05). There was a lower penetration of silver in pre-heated specimens (p<0.05). Conclusions Pre-heating at 60°C mitigated the degradation of composites based on analysis of radiopacity and silver penetration depth.

Asthma prevalence and risk factors in early childhood at Northern Portugal

Asthma is the commonest and most important chronic non-infectious disease in childhood and it has become more prevalent in recent years. There is a shortage of studies in relation to early childhood and so, as part of the INAIRCHILD project, this cross-sectional study aimed to assess the prevalence of asthma and its associated risk factors, namely demographic, environmental, psychosocial and clinical factors for infants and preschoolers living in Northern Portugal. Data concerning asthma prevalence were collected through questionnaires based on those from the International Study of Asthma and Allergies in Childhood (ISAAC-derived), the questionnaires were distributed to 1042 children attending the 17 nurseries involved in the INAIRCHILD project (10 in urban and suburban context, and 7 in rural context). The response rate was 48%. Prevalence of asthma based on symptomatology and odds ratio was calculated. Around 52% of the studied children presented at least one of the respiratory symptoms investigated (wheeze, dyspnea and cough) in the absence of upper respiratory infections. The prevalence of asthma was 10.7%, comparable to the figures for Portuguese schoolchildren (6-7 years old) reported by the national Directorate-General of Health, thus showing that an early diagnosis might be possible and helpful for the mitigation of childhood asthma. Environmental context (urban, suburban or rural), gender and family asthma history showed clear associations with asthma prevalence, namely non-rural location, male gender, and having an asthmatic parent were found to be risk factors.

Differences in the force system delivered by different beta-titanium wires in elaborate designs

Objective:

Evaluation of the force system produced by four brands of b-Ti wires bent into an elaborate design.

Methods:

A total of 40 T-loop springs (TLS) hand-bent from 0.017 x 0.025-in b-Ti were randomly divided into four groups according to wire brand: TMA^TM(G1), BETA FLEXY^TM (G2), BETA III WIRE^TM (G3) and BETA CNA^TM (G4). Forces and moments were recorded by a moment transducer, coupled to a digital extensometer indicator adapted to a testing machine, every 0.5 mm of deactivation from 5 mm of the initial activation. The moment-to-force (MF) ratio, the overlapping of the vertical extensions of the TLSs and the load-deflection (LD) ratio were also calculated. To complement the results, the Young's module (YM) of each wire was determined by the slope of the load-deflection graph of a tensile test. The surface chemical composition was also evaluated by an energy dispersive X-ray fluorescence spectrometer.

Results:

All groups, except for G2, produced similar force levels initially. G3 produced the highest LD rates and G1 and G4 had similar amounts of overlap of the vertical extensions of the TLSs in "neutral position". G1 and G3 delivered the highest levels of moments, and G2 and G3 produced the highest MF ratios. b-Ti wires from G3 produced the highest YM and all groups showed similar composition, except for G2.

Conclusion:

The four beta-titanium wires analyzed produced different force systems when used in a more elaborate design due to the fact that each wire responds differently to bends.

Assisted navigation based on shared-control, using discrete and sparse human-machine interfaces

This paper presents a shared-control approach for Assistive Mobile Robots (AMR), which depends on the user's ability to navigate a semi-autonomous powered wheelchair, using a sparse and discrete human-machine interface (HMI). This system is primarily intended to help users with severe motor disabilities that prevent them to use standard human-machine interfaces. Scanning interfaces and Brain Computer Interfaces (BCI), characterized to provide a small set of commands issued sparsely, are possible HMIs. This shared-control approach is intended to be applied in an Assisted Navigation Training Framework (ANTF) that is used to train users' ability in steering a powered wheelchair in an appropriate manner, given the restrictions imposed by their limited motor capabilities. A shared-controller based on user characterization, is proposed. This controller is able to share the information provided by the local motion planning level with the commands issued sparsely by the user. Simulation results of the proposed shared-control method, are presented.