Effect of Pore Size and Porosity on the Biomechanical Properties and Cytocompatibility of Porous NiTi Alloys.

Five types of porous Nickel-Titanium (NiTi) alloy samples of different porosities and pore sizes were fabricated. According to compressive and fracture strengths, three groups of porous NiTi alloy samples underwent further cytocompatibility experiments. Porous NiTi alloys exhibited a lower Young's modulus (2.0 GPa ~ 0.8 GPa). Both compressive strength (108.8 MPa ~ 56.2 MPa) and fracture strength (64.6 MPa ~ 41.6 MPa) decreased gradually with increasing mean pore size (MPS). Cells grew and spread well on all porous NiTi alloy samples. Cells attached more strongly on control group and blank group than on all porous NiTi alloy samples (p < 0.05). Cell adhesion on porous NiTi alloys was correlated negatively to MPS (277.2 µm ~ 566.5 µm; p < 0.05). More cells proliferated on control group and blank group than on all porous NiTi alloy samples (p < 0.05). Cellular ALP activity on all porous NiTi alloy samples was higher than on control group and blank group (p < 0.05). The porous NiTi alloys with optimized pore size could be a potential orthopedic material.

Binding of corroded ions to human saliva.

Employing equilibrium dialysis, the binding abilities of Cu, Al, Co and Cr ions from corroded Cu-Al and Co-Cr dental casting alloys towards human saliva and two of its gel chromatographic fractions were determined. Results indicate that both Cu and Co bind to human saliva i.e. 0.045 and 0.027 mg/mg protein, respectively. Besides possessing the largest binding ability, Cu also possessed the largest binding capacity. The saturation of Cu binding was not reached up to the limit of 0.35 mg protein/ml employed in the tests, while Co reached full saturation at about 0.2 mg protein/ml. Chromium showed absolutely no binding to human saliva while Al ions did not pass through the dialysis membranes. Compared to the binding with solutions that were synthetically made up to contain added salivary-type proteins, it is shown that the binding to human saliva is about 1 order of magnitude larger, at least for Cu ions.

Metal release from dental biomaterials.

Levels of corrosion products released from dental alloys in natural or synthetic saliva, i.e. from amalgams, cobalt, gold, nickel, iron, or titanium based alloys have been surveyed. The amounts of Ag, Au, Cd, Co, Cr, Cu, Hg, Mo, Ti or Ni released from such alloys, either in vitro or in vivo during animal tests or during clinical usage have been compiled. The quantities released have been adapted to a 'standard restored man' with a specified number of restorations or a specified construction with a defined surface area, and compared to man's food and drink intake of similar elements. This was done as one approach to a security analysis of wearing dental alloys. In view of the assessment of extensive corrosion testing using electrochemical methods, rather scarce information seems presently available pertinent to release kinetics of specific elements in various biological environments like saliva or saliva substitutes. Several examinations indicate that mercury released from amalgams could be a substantial part of man's daily intake of this element, e.g. in the initial period following insertion, as well as on a long-term basis. From a copper amalgam cadmium could be released in vitro in amounts close to food and drink intake. The mercury release from the amalgam surface seems to be strongly influenced by the interaction of mechanical forces, e.g. chewing, and seems to be released according to a cyclic pattern. From a base metal alloy with high nickel content nickel could be released in vitro at the same level as from food and drink intake. However, from cobalt based alloys the nickel release seems insignificant in this context. The elemental release from the other alloys seemed to be far below the intake of similar elements from food and drink. Release under static and dynamic conditions has been discussed.

In vitro evaluation of the effect of freshly mixed amalgam and gallium-based alloy on the viability of primary periosteal and osteoblast cell cultures.

The effect of freshly mixed specimens of a gallium-based alloy Galloy and a high copper spherical amalgam Tytin on the viability of primary periosteal and osteoblast cells was investigated. The cells were grown from the parietal bones of 2-3 day old Albino Wistar rats and were seeded in multi-well plates and exposed to the test materials for 1 or 6 days. The number of viable cells in each test group was determined using the Trypan blue dye exclusion test and compared with the controls. The area of cell death around the test specimens was also measured. Statistical analysis (ANOVA, Tukey's pairwise comparisons) showed a significant effect of the test materials on cell viability (P < 0.01). The viability of cultures containing Tytin was significantly lower than cultures with Galloy and the controls (P < 0.05). The viability of cultures containing Galloy was significantly lower (P < 0.05) than controls except for periosteal cells after 1 day. The culture media was analysed using atomic absorption spectrophotometry (AAS) for metal ion content. The results suggested that mercury (Hg) was the main element released from the dental amalgam followed by copper (Cu) and silver (Ag) whilst gallium (Ga) was the main element released from the gallium-based alloy followed by indium (In), Ag and Cu.

Laser fusion of selected dental casting alloys.

Laser-fused precious, nonprecious, and mixed metal welds were investigated for optimum weld energy requirement as determined by tensile strength tests. These strengths were compared to soldered unions. Laser fusion is as good as, or better than, unions created by conventional dental joining methods.

Fibroblast growth on surface-modified dental implants: an in vitro study.

A major consideration in designing dental implants is the creation of a surface that provides strong attachment between the implant and bone, connective tissue, or epithelium. In addition, it is important to inhibit the adherence of oral bacteria on titanium surfaces exposed to the oral cavity to maintain plaque-free implants. Previous in vitro studies have shown that titanium implant surfaces coated with titanium nitride (TiN) reduced bacterial colonization compared to other clinically used implant surfaces. The aim of the present study was to examine the support of fibroblast growth by a TiN surface that has antimicrobial characteristics. Mouse fibroblasts were cultured on smooth titanium discs that were either magnetron-sputtered with a thin layer of titanium nitride, thermal oxidized, or modified with laser radiation (using a Nd-YAG laser). The resulting surface topography was examined by scanning electron microscopy (SEM), and surface roughness was estimated using a two-dimensional contact stylus profilometer. A protein assay (BCA assay) and a colorimetric assay to examine fibroblast metabolism (MTT) were used. Cellular morphology and cell spreading were analyzed using SEM and fluorescence microscopy. Fibroblasts on oxidized titanium surfaces showed a more spherical shape, whereas cells on laser-treated titanium and on TiN appeared intimately adherent to the surface. The MTT activity and total protein were significantly increased in fibroblasts cultured on titanium surfaces coated with TiN compared to all other surface modifications tested. This study suggests that a titanium nitride coating might be suitable to support tissue growth on implant surfaces.

Mercury from maternal "silver" tooth fillings in sheep and human breast milk. A source of neonatal exposure.

Neonatal uptake of mercury (Hg) from milk was examined in a pregnant sheep model, where radioactive mercury (Hg203)/silver tooth fillings (amalgam) were newly placed. A crossover experimental design was used in which lactating ewes nursed foster lambs. In a parallel study, the relationship between dental history and breast milk concentration of Hg was also examined in 33 lactating women. Results from the animal studies showed that, during pregnancy, a primary fetal site of amalgam Hg concentration is the liver, and, after delivery, the neonatal lamb kidney receives additional amalgam Hg from mother's milk. In lactating women with aged amalgam fillings, increased Hg excretion in breast milk and urine correlated with the number of fillings or Hg vapor concentration levels in mouth air. It was concluded that Hg originating from maternal amalgam tooth fillings transfers across the placenta to the fetus, across the mammary gland into milk ingested by the newborn, and ultimately into neonatal body tissues. Comparisons are made to the U. S. minimal risk level recently established for adult Hg exposure. These findings suggest that placement and removal of "silver" tooth fillings in pregnant and lactating humans will subject the fetus and neonate to unnecessary risk of Hg exposure.

A study on the influence of Ni-Ti M-Wire in the flexural fatigue life of endodontic rotary files by using Finite Element Analysis.

The aim of this paper is to analyze the cyclic performance of two different Ni-Ti endodontic rotary files made from different alloys under bending using Finite Element Analysis (FEA). When experimentation is not available, this is not a trivial task and most papers on the subject rely on static analysis only. Two Ni-Ti rotary instruments are selected, ProFile GT and a GT Series X (GTX). The latter file is made from M-Wire, which has been thermo-mechanically processed to have larger flexibility, according to its manufacturer. The mechanical response was studied by considering different scenarios in the FEA package, in which the material properties were introduced according to existing literature. The method and results are presented and discussed so that this paper can be used as a guideline for future works. Although not fully reflective of the instrument's behavior in a dynamic rotation intra-canal system, the models used constitute a good approximation when a comparison between two instruments is at stake. It is shown that the GTX file has a lower risk of fatigue fracture during its clinical use when compared to the GT file, especially when the root canal makes the file deform into an extreme geometry. However, if the root canal does not make the file deform more than a certain amount, the GT file is equally good from the point of view of mechanical endurance.

Release of metal ions from orthodontic appliances: an in vitro study.

In this paper, we report the results of an in vitro experiment on the release of metal ions from orthodontic appliances composed of alloys containing iron, chromium, nickel, silicon, and molybdenum into artificial saliva. The concentrations of magnesium, aluminum, silicon, phosphorus, sulfur, potassium, calcium, titanium, vanadium, manganese, iron, cobalt, copper, zinc, nickel, and chromium were significantly higher in artificial saliva in which metal brackets, bands, and wires used in orthodontics were incubated. In relation to the maximum acceptable concentrations of metal ions in drinking water and to recommended daily doses, two elements of concern were nickel (573 vs. 15 µg/l in the controls) and chromium (101 vs. 8 µg/l in the controls). Three ion release coefficients were defined: α, a dimensionless multiplication factor; ß, the difference in concentrations (in micrograms per liter); and γ, the ion release coefficient (in percent). The elevated levels of metals in saliva are thought to occur by corrosion of the chemical elements in the alloys or welding materials. The concentrations of some groups of dissolved elements appear to be interrelated.

Oral keratinocyte responses to nickel-based dental casting alloys in vitro.

Adverse reactions of oral mucosa to nickel-based dental casting alloys are probably due to corrosion metal ion release. We exposed H400 oral keratinocytes to two Ni-based dental alloys (Matchmate and Dsign10) as well as NiCl( 2) (1-40 microg/mL Ni(2+)). Alloy derived Ni(2+) media concentrations were determined. Direct culture on both alloys resulted in inhibited growth with a greater effect observed for Dsign10 (higher ion release). Indirect exposure of cells to conditioned media from Dsign10 negatively affected cell numbers (approximately 64% of control by 6 days) and morphology while Matchmate-derived media did not. Exposure to increasing NiCl(2) negatively affected cell growth and morphology, and the Granulocyte-macrophage colony-stimulating factor (GM-CSF) transcript was significantly up-regulated in cells following direct and indirect exposure to Dsign10. NiCl(2) exposure up-regulated all cytokine transcripts at 1 day. At day 6, IL-1beta and IL-8 transcripts were suppressed while GM-CSF and IL-11 increased with Ni(2+) dose. Accumulation of Ni(2+) ions from alloys in oral tissues may affect keratinocyte viability and chronic inflammation.

Corrosion of copper, nickel, and gold dental casting alloys: an in vitro and in vivo study.

The corrosion behavior of commercially available copper, nickel, and gold alloys for dental castings was investigated. The alloys investigated included: three copper alloys (76-87Cu, 6-11A1, 0-12Zn, 1-5Ni, 0-4Fe, 0.5-1.2Mn), two nickel alloys (68-78Ni, 12-16Cr, 4-14Mo, 0-1.7Be), and one gold alloy (77Au, 14Ag, 8Cu, 1Pd). Anodic and cathodic polarization curves, long-term immersion tests in saline and artificial saliva solutions, and dog crown studies were conducted to evaluate both the in vitro and in vivo corrosion characteristics of the alloys. All evaluations conducted demonstrated that the copper alloys were highly susceptible to corrosion attack. High corrosion currents were observed in the in vitro tests, and SEM of the alloys specimens showed significantly altered surfaces. The anodic polarization curves predicted that the beryllium-containing nickel alloy should be susceptible to localized corrosion and SEM revealed an etched surface with corrosion of certain microstructural features. No significant corrosion was predicted or observed for the non-beryllium nickel alloy and the gold alloy. The in vitro corrosion evaluations predicted the in vivo corrosion behavior for the alloys. Since the three copper alloys and the beryllium-containing nickel alloy demonstrated significant corrosion under the tested conditions, the use of these alloys for restorative procedures is questionable due to the release of significant levels of selected ions to the oral cavity.

Release and detection of dental corrosion products in vivo: development of an experimental model in rabbits.

An experimental animal model was developed to investigate the release of metal ions from nonprecious dental alloys. Cast specimens of five Ni-Cr-alloys and Co-Cr-alloys were implanted intramuscularly in rabbits for periods of 2, 4, 8, and 12 weeks. The concentrations of nickel, chromium, cobalt, and molybdenum in the implant-loaded muscles were determined by electrothermal atomic absorption spectrometry (AAS) and neutron activation analysis (NAA). Reference muscle samples of each animal were analyzed to determine the individual control values. Significant increases in the tissue concentrations of these metals occurred in the immediate vicinity of the implants. Concentration gradients of the corrosion products were found between the implant contact tissue and the implant periphery (p less than 0.001). Tissue concentrations of nickel and chromium correlated (r less than 0.7). Microprobe analysis before and after implantation of the alloy specimens indicated an even corrosive loss of the alloy surfaces and changes in the surface element distributions. Advantages and limitations of this animal model are discussed, as well as its application in future studies.

Autoradiographic study of distribution patterns of metals which occur as corrosion products from dental restorations.

Radioactive chromium, cobalt, gold and mercury, all of which may occur as corrosion products from dental restorations, were injected in single doses via the tail vein of mice and an in vivo analysis of their distribution was performed using whole-body autoradiography. Gold seemed to be inert and went mainly to the liver and bones. The other elements studied were distributed widely in the body and remained for a long period of time in specific target organs and tissues.

In vitro kinetic evaluation of titanium alloy biodegradation.

The present controlled in vitro experiment evaluated the dissolution kinetics of titanium (Ti), aluminum (Al) and vanadium (V). Titanium alloy (Ti90Al6V4) dental implants were inserted in 1.8 ml sterile tubes, containing equal volumes of NaCl 0.9% (w/v) and human serum. Metallic elements released by the atomic process of corrosion were measured at pH 7.2 and 37 C by atomic absorption spectrophotometer at 1, 3, 6, 9, 15, 21, 27, 33, 42, 51, 60, 69, 78, 87 and 96 days. Ti dissolution averaged 16+/-5 ng/cm2/day and 1565 ng/cm2 over the experimental period. Al dissolution was stable at 9+/-5 ng/cm2/day and averaged 945 ng/cm2 over the 96-day period. V dissolution was stable at 0.15+/-0.18 ng/cm2/day after the sixth day of incubation and averaged 42 ng/cm2 over the 96-day period. Major disparities in atomic dissolution were detected among implants. No local or systemic reaction to titanium has been documented. In contrast, 4% toxic V and 6% Al may suffice to elicit local and systemic reactions or inhibit cellular proliferation and differentiation.

Relating nickel-induced tissue inflammation to nickel release in vivo.

Nickel has a number of adverse biological effects that have made the use of nickel in biomedical implants controversial. Yet information about the distribution of nickel in tissues around nickel-containing implants is scarce. The purpose of the current study was to use a laser ablation technique, combined with inductively coupled mass spectroscopy, to assess the spatial distribution of nickel around nickel-containing implants in vivo. Polyethylene, pure nickel wire, or a nickel-containing alloy (Ni-Cr) were implanted subcutaneously into rats for 7 days. The tissues were analyzed for Ni content and inflammation at 1-mm intervals up to 5 mm away from the implants. The sham surgery sites and the polyethylene caused mild to moderate inflammation 1-2 mm from the implant site with no detectable nickel in the tissue. The nickel wire caused severe inflammation up to 5 mm away from the implant site with necrosis for 1 mm around the implant. Nickel concentrations reached 48 microg/g near the implants, falling exponentially to undetectable levels at 3-4 mm from the implants. The Ni-Cr wire caused inflammation equivalent to polyethylene, with less than 4 microg/g of nickel present in the tissue for 1-2 mm around the implants. The current study showed that the laser-ablation technique was well suited for the analysis of soft tissues for metal-ion content, and that the nickel distribution in tissues correlated well with overt tissue inflammation.

Averiguaçäo radiográfica de possíveis defeitos de fundiçäo em armaçöes de próteses parciais removíveis / Quality evaluation of removable partial denture framework by x-rays

Cientes das grandes variáveis que podem determinar a ocorrência de fraturas em armaçöes de cobalto-cromo no momento de sua adaptaçäo pelo cirurgiäo-dentista e/ou durante o uso pelos pacientes, procurou-se, por meio de uma técnica radiográfica simples, identificar a presença de defeitos estruturais (áreas de maior ou menor radioluscência), a fim de evitar perda de tempo e despesas envolvidas com o uso de laboratório, protético, ou a responsabilizaçäo do paciente pela fratura. Foram realizadas armaçöes de P. P. R. para os pacientes atendidos na Clínica de Prótese da Faculade de Odontologia de Bauru-USP, utilizando-se as ligas Still-Dent e Alloy, respectivamente nos anos de 1990 e 1991, tendo sido radiografadas 82 armaçöes previamente identificadas e numeradas. O processamento das películas radiográficas expostas foi realizado, obedecendo-se rigorosamente às recomendaçöes do fabricante, e as películas foram avaliadas por 2 examinadores previamente calibrados. As armaçöes fundidas com liga Alloy apresentaram uma melhor qualidade que as em Still-Dent. Somente por intermédio de radiografias das armaçöes, feitas rotineiramente, poder-se-ía identificar possíveis defeitos estruturais que culminariam em fracasso do aparelho