Evaluation of Ion Release from Two Base-Metal Alloys at Various pH Levels

Clinical Evaluation of Corrosion Resistance, Ion Release, and Biocompatibility of CoCr Alloy for Metal-Ceramic Restorations Produced by CAD/CAM Technologies

BACKGROUND

CAD/CAM technologies facilitate using powder CoCr alloys to produce metal-ceramic dental restorations. However, base alloys may induce oxidative stress in the oral cavity due to corrosion and ion release. This study evaluated resistance to corrosion and release of metal ions from 3D printed CoCr dental alloy and their effect on oral oxidative stress.

METHODS

Metal-ceramic crowns with 3D printed copings from CoCr alloy EOS CobaltChrome SP2 (EOS, Germany) were fabricated for 35 patients. Inductively coupled plasma mass spectrometry (ICP-MS) was used for measuring the concentration of Co and Cr ions in non-stimulated saliva before prosthetic treatment (BPT), at 2 h and 7 days after the dental treatment (APT2, APT7, respectively). Open circuit potentials (Eocp) were evaluated at APT2 and APT7. Estimating oral oxidative stress, measurements of 8-isoprostaglandin F2-alpha were conducted using liquid chromatography-tandem mass spectrometry (LC-MS/MS) at stages BPT, APT2, and APT7.

RESULTS

Salivary Co level increased at APT2 and decreased to the initial levels at APT7. No statistical difference was found between the levels of 8-isoPGF2-alpha measured, and between the Eocp measurements at APT2 and APT7.

CONCLUSIONS

The studied alloy showed stable corrosion resistance and the metal ion release did not induce oral oxidative stress.

Mechanical Characterization of Dental Prostheses Manufactured with PMMA-Graphene Composites

The use of a PMMA composite with graphene is being commercialized for application as dental prostheses. The different proportions of fibers provide a wide range of colors that favors dental esthetics in prostheses. However, there are no studies that have explained the influence that graphene has on the mechanical properties. In this contribution, we studied the PMMA and PMMA material with graphene fibers (PMMA-G) in the form of discs as supplied for machining. The presence of graphene fibers has been studied by Raman spectroscopy and the Shore hardness and Vickers micro hardness were determined. Mechanical compression tests were carried out to obtain the values of maximum strength and Young’s modulus (E) and by means of pin-on-disc wear tests, the specific wear rate and the friction coefficients were determined following the established international standards. Finally, the samples were characterized by field emission scanning electron microscopy (FESEM) to characterize the graphene’s morphology inside the PMMA. The results showed the presence of graphene in PMMA and was estimated in an amount of 0.1027% by weight in G-PMMA. The Shore hardness and Vickers microhardness values did not show statistically significant differences. Differences were observed in the compression maximum strength (129.43 MPa for PMMA and 140.23 for PMMA-G) and E values (2.01 for PMMA and 2.89 GPa for PMMA-G) as well as in the lower wear rate for the G-PMMA samples (1.93 × 10−7 for PMMA and 1.33 × 10−7 mm3/N·m) with a p < 0.005. The coefficients of friction for PMMA-G decreased from 0.4032 for PMMA to 0.4001 for PMMA-G. From the results obtained, a slight content in graphene produced a significant improvement in the mechanical properties that could be observed in the prosthesis material. Therefore, we can state that the main attraction of this material for dental prosthesis is its esthetics.

Citric Acid in the Passivation of Titanium Dental Implants: Corrosion Resistance and Bactericide Behavior

The passivation of titanium dental implants is performed in order to clean the surface and obtain a thin layer of protective oxide (TiO2) on the surface of the material in order to improve its behavior against corrosion and prevent the release of ions into the physiological environment. The most common chemical agent for the passivation process is hydrochloric acid (HCl), and in this work we intend to determine the capacity of citric acid as a passivating and bactericidal agent. Discs of commercially pure titanium (c.p.Ti) grade 4 were used with different treatments: control (Ctr), passivated by HCl, passivated by citric acid at 20% at different immersion times (20, 30, and 40 min) and a higher concentration of citric acid (40%) for 20 min. Physical-chemical characterization of all of the treated surfaces has been carried out by scanning electronic microscopy (SEM), confocal microscopy, and the 'Sessile Drop' technique in order to obtain information about different parameters (topography, elemental composition, roughness, wettability, and surface energy) that are relevant to understand the biological response of the material. In order to evaluate the corrosion behavior of the different treatments under physiological conditions, open circuit potential and potentiodynamic tests have been carried out. Additionally, ion release tests were realized by means of ICP-MS. The antibacterial behavior has been evaluated by performing bacterial adhesion tests, in which two strains have been used: Pseudomonas aeruginosa (Gram-) and Streptococcus sanguinis (Gram+). After the adhesion test, a bacterial viability study has been carried out ('Life and Death') and the number of colony-forming units has been calculated with SEM images. The results obtained show that the passivation with citric acid improves the hydrophilic character, corrosion resistance, and presents a bactericide character in comparison with the HCl treatment. The increasing of citric acid concentration improves the bactericide effect but decreases the corrosion resistance parameters. Ion release levels at high citric acid concentrations increase very significantly. The effect of the immersion times studied do not present an effect on the properties.

Effect of chemical passivation on corrosion behavior and ion release of a commercial chromium-cobalt alloy

Background. Corrosion resistance and ion release of alloys play a crucial role in biomedical applications. The present study aimed to investigate an increase in corrosion resistance and reduction in ion release in a commercial Co-Cr-Mo alloy by the chemical passivation method. Methods. Based on ADA97, 20 samples of Flexicast alloy were cast, surface-polished, and electrolytically passivated at room temperature for 24 h in a sodium sulfate solution. Corrosion and ion release of the alloys before and after passivation were studied in normal saline solution. Corrosion resistance and the ion release rates were measured by the weight loss method and atomic absorption spectroscopy, respectively, before and after passivation after 1, 2, 3, and 4 weeks. The surface morphology of the samples was examined using scanning electron microscopy (SEM). The results were analyzed with Kruskal-Wallis and Mann-Whitney tests using SPSS 20 at a significance level of <0.05. Results. The corrosion rate in the passivated samples was significantly lower than the non-passivated samples at the intervals (1, 2, 3, and 4 weeks) (P<0.05). The passivation of the alloy significantly reduced Co and Cr ion release in the first and fourth weeks, and in the first, second, and fourth weeks, respectively (P<0.05). SEM images revealed localized pitting associated with the corrosion, which was less significant in passivated samples. Conclusion. Chemical passivation of the CR-Co alloy significantly reduced corrosion and ionic release of Cr and Co over time.

Corrosion Resistance and Ion Release of Dental Prosthesis of CoCr Obtained by CAD-CAM Milling, Casting and Laser Sintering

Corrosion resistance and ion release behavior have been evaluated for thirty dental restoration samples obtained by three different manufacturing systems: computer-aided design and manufacturing (CAD-CAM), traditional casting and laser sintering. The alloy used was the CoCr alloy (same batch) generally used in clinical dentistry. Corrosion resistance has been evaluated by electrochemical testing in an artificial saliva medium at 37 °C. Corrosion parameters such as critical current density (icr), corrosion potential (Ecorr), and passive current density (ip), have been determined. Cobalt and Chromium ions released from the different samples have also been analyzed in an artificial saliva medium at 37 °C by Inductively Coupled Plasma Mass Spectrometry (ICP-MS) at different immersion times. The casted samples showed higher corrosion rates and ion-release levels. The CAD-CAM milled samples presented lower ion-release levels and better corrosion resistance due to the total solubility of the chemical elements in only one phase with the same chemical composition. This homogeneity avoids the formation of electrochemical corrosion. Moreover, the absence of defects and residual stresses increases the corrosion resistance. Casted and laser sintered prostheses have shown the presence of Cr, W, and Nb rich-precipitates which are detrimental to the corrosion resistance. These precipitates produce a decrease in the Cr content on the surface. It is well known that the corrosion resistance increases with the Cr content by the formation of Chromium oxide on the surface that increases passivation. Consequently, the decrease in Cr induces an increase in corrosion and ion release.

Effect of recasting on element release from base metal dental casting alloys in artificial saliva and saline solution

Aim:

The aim of this study was to quantitatively estimate the concentration of ion release from recasted base metal alloys in various pH conditions using atomic absorption spectroscopy (AAS).

Materials and Methods:

Specimens of commercially available dental casting alloys (cobalt [Co]-chromium [Cr] and nickel [Ni]- chromium [Cr]) were prepared using lost-wax casting techniques and were stored in the test solution for 1 week and 4 weeks, and ions released during chemical corrosion were detected using AAS.

Results:

An increase in the quantity of ion release was observed with recasting. These changes were higher after twice recasting in Ni-Cr alloy.

Evaluation of metal ion release from Ti6Al4V and Co-Cr-Mo casting alloys: in vivo and in vitro study

PURPOSE

The aim of this study was to evaluate the amount of ions released from Ti6Al4V and Co-Cr-Mo alloys both in vivo and in vitro.

MATERIALS AND METHODS

Twenty-one discs of each alloy were constructed and divided into seven groups. Three specimens from each group were immersed in a buffered saline solution over a period of 1, 3, 5, 7, 14, 21, and 28 days. Twenty-eight participants were also included in the study, where the study group consisted of 14 mandibular partially edentulous patients, and the control group consisted of 14 volunteers. The study group was further divided into two equal groups: the first group received removable partial dentures (RPDs) constructed from Co-Cr-Mo alloy, while the second group received RPDs constructed from Ti6Al4V alloy. Saliva samples were collected from each participant over the same study period. The conditioning media and saliva samples were analyzed using a spectrophotometer. One-way ANOVA and Tukey tests were used for statistical analysis (p < 0.05).

RESULTS

The concentrations of metal ions released from the studied alloys were significantly higher in the in vitro than in the in vivo study group during the follow-up periods. A statistically significant increase in ion concentrations of the different elements for both alloys was found with time (p < 0.05).

CONCLUSION

The amounts of released metallic ions from Co-Cr-Mo and Ti6Al4V alloys were higher in the buffered saline solutions than in the studied saliva samples and control groups; however, these amounts were still within the physiological limit of trace elements in the human body.

Urinary levels of nickel and chromium associated with dental restoration by nickel-chromium based alloys

This paper aims to investigate if the dental restoration of nickel–chromium based alloy (Ni–Cr) leads to the enhanced excretions of Ni and Cr in urine. Seven hundred and ninety-five patients in a dental hospital had single or multiple Ni–Cr alloy restoration recently and 198 controls were recruited to collect information on dental restoration by questionnaire and clinical examination. Urinary concentrations of Ni and Cr from each subject were measure by graphite furnace atomic absorption spectrometry. Compared to the control group, the urinary level of Ni was significantly higher in the patient group of <1 month of the restoration duration, among which higher Ni excretions were found in those with either a higher number of teeth replaced by dental alloys or a higher index of metal crown not covered with the porcelain. Urinary levels of Cr were significantly higher in the three patient groups of <1, 1 to <3 and 3 to <6 months, especially in those with a higher metal crown exposure index. Linear curve estimations showed better relationships between urinary Ni and Cr in patients within 6-month groups. Our data suggested significant increased excretions of urinary Ni and Cr after dental restoration. Potential short- and long-term effects of Ni–Cr alloy restoration need to be investigated.