Corrosion kinetics and topography analysis of Ti–6Al–4V alloy subjected to different mouthwash solutions

Zirconia Dental Implant Designs and Surface Modifications: A Narrative Review

Titanium currently has a well-established position as the gold standard for manufacturing dental implants; however, it is not free of flaws. Mentions of possible soft-tissue discoloration, corrosion, and possible allergic reactions have led to the development of zirconia dental implants. Various techniques for the surface modification of titanium have been applied to increase titanium implants' ability to osseointegrate. Similarly, to achieve the best possible results, zirconia dental implants have also had their surface modified to promote proper healing and satisfactory long-term results. Despite zirconium oxide being a ceramic material, not simply a metal, there have been mentions of it being susceptible to corrosion too. In this article, we aim to review the literature available on zirconia implants, the available techniques for the surface modification of zirconia, and the effects of these techniques on zirconia's biological properties. Zirconia's biocompatibility and ability to osseointegrate appears unquestionably good. Despite some of its mechanical properties being, factually, inferior to those of titanium, the benefits seem to outweigh the drawbacks. Zirconia implants show very good success rates in clinical research. This is partially due to available methods of surface treatment, including nanotopography alterations, which allow for improved wettability, bone-to-implant contact, and osteointegration in general.

Oxide degradation precedes additively manufactured Ti-6Al-4V selective dissolution: An unsupervised machine learning correlation of impedance and dissolution compared to Ti-29Nb-21Zr

Additively manufactured (AM) Ti-6Al-4V devices are implanted with increasing frequency. While registry data report short-term success, a gap persists in our understanding of long-term AM Ti-6Al-4V corrosion behavior. Retrieval studies document β phase selective dissolution on conventionally manufactured Ti-6Al-4V devices. Researchers reproduce this damage in vitro by combining negative potentials (cathodic activation) and inflammatory simulating solutions (H2O2-phosphate buffered saline). In this study, we investigate the effects of these adverse electrochemical conditions on AM Ti-6Al-4V impedance and selective dissolution. We hypothesize that cathodic activation and H2O2 solution will degrade the oxide, promoting corrosion. First, we characterized AM Ti-6Al-4V samples before and after a 48 h -0.4 V hold in 0.1 M H2O2/phosphate buffered saline. Next, we acquired nearfield electrochemical impedance spectroscopy (EIS) data. Finally, we captured micrographs and EIS during dissolution. Throughout, we used AM Ti-29Nb-21Zr as a comparison. After 48 h, AM Ti-6Al-4V selectively dissolved. Ti-29Nb-21Zr visually corroded less. Structural changes at the AM Ti-6Al-4V oxide interface manifested as property changes to the impedance. After dissolution, the log-adjusted constant phase element (CPE) parameter, Q, significantly increased from -4.75 to -3.84 (Scm-2(s)α) (p = .000). The CPE exponent, α, significantly decreased from .90 to .84 (p = .000). Next, we documented a systematic decrease in oxide polarization resistance before pit nucleation and growth. Last, using k-means clustering, we established a structure-property relationship between impedance and the surface's dissolution state. These results suggest that AM Ti-6Al-4V may be susceptible to in vivo crevice corrosion within modular taper junctions.

The Addition of Hydroxyapatite Nanoparticles on Implant Surfaces Modified by Zirconia Blasting and Acid Etching to Enhance Peri-Implant Bone Healing

This study investigated the impact of adding hydroxyapatite nanoparticles to implant surfaces treated with zirconia blasting and acid etching (ZiHa), focusing on structural changes and bone healing parameters in low-density bone sites. The topographical characterization of titanium discs with a ZiHa surface and a commercially modified zirconia-blasted and acid-etched surface (Zi) was performed using scanning electron microscopy, profilometry, and surface-free energy. For the in vivo assessment, 22 female rats were ovariectomized and kept for 90 days, after which one implant from each group was randomly placed in each tibial metaphysis of the animals. Histological and immunohistochemical analyses were performed at 14 and 28 days postoperatively (decalcified lab processing), reverse torque testing was performed at 28 days, and histometry from calcified lab processing was performed at 60 days The group ZiHa promoted changes in surface morphology, forming evenly distributed pores. For bone healing, ZiHa showed a greater reverse torque, newly formed bone area, and bone/implant contact values compared to group Zi (p < 0.05; t-test). Qualitative histological and immunohistochemical analyses showed higher features of bone maturation for ZiHa on days 14 and 28. This preclinical study demonstrated that adding hydroxyapatite to zirconia-blasted and acid-etched surfaces enhanced peri-implant bone healing in ovariectomized rats. These findings support the potential for improving osseointegration of dental implants, especially in patients with compromised bone metabolism.

Exploring the effect of chlorhexidine concentration on the biocorrosion behavior of Ti6Al4V for dental implants

Corrosion of dental implants is one of the most critical factors in the failure of implant treatments. Generally, corrosion depends on the type of material used in implants and the chemical composition of the oral environment. Due to the antibacterial activities, mouthwashes and chlorhexidine gels are often used after implant surgery. Ti6Al4V is commonly used in manufacturing dental implants. The present study aims to investigate the corrosion behavior of the Ti6Al4V alloy under different concentrations of chlorhexidine (0.12%, 0.2%,and 2%) during 2- and 24-h immersion. This way corrosion may be minimized while obtaining an antibacterial environment around the implant. In this regard, the electrochemical behavior of the specimens was investigated using polarization and impedance tests, and then their morphology, cross-section and nano-tribological behavior were evaluated using atomic force microscopy, scanning electron microscopy, energy dispersive x-ray spectroscopy, and nano-scratch test. The results show that using chlorhexidine solution with a concentration of 0.12% could yield a lower corrosion rate and material loss after implant surgery. RESEARCH HIGHLIGHTS: Open circuit potential values increase with immersion time, which suggests multistage passivation of the surface during immersion in chlorhexidine. Specimens in 0.12% chlorhexidine show improved thermodynamic corrosion resistance. Nano-scratch testing demonstrates higher scratch resistance for specimens in 0.12% chlorhexidine solution after 2-h immersion. Higher chlorhexidine concentration than 0.12% and longer immersion times decrease the resistance of the formed passive layer.

The effect of three dental cement types on the corrosion of dental implant surfaces

Statement of problem

One of the main challenges facing dental implant success is peri-implantitis. Recent evidence indicates that titanium (Ti) corrosion products and undetected-residual cement are potential risk factors for peri-implantitis. The literature on the impact of various types of dental cement on Ti corrosion is very limited.

Purpose

This study aimed to determine the influence of dental cement on Ti corrosion as a function of cement amount and type.

Materials and methods

Thirty commercially pure Ti grade 4 discs (19 × 7mm) were polished to mirror-shine (Ra ≈ 40 nm). Samples were divided into 10 groups (n = 3) as a cement type and amount function. The groups were no-cement as control, TempBond NE (TB3mm, TB5mm, and TB8mm), FujiCEM-II (FC3mm, FC5mm, and FC8mm), and Panavia-F-2.0 (PC3mm, PC5mm, and PC8mm). Tafel's method estimated corrosion rate (icorr) and corresponding potential (Ecorr) from potentiodynamic curves. Electrochemical Impedance Spectroscopy (EIS) data was utilized to obtain Nyquist and Bode plots. An equivalent electrical circuit estimated polarization resistance (Rp) and double-layer capacitance (Cdl). Inductively coupled plasma mass spectrometry (ICP-MS) analysis was conducted to analyze the electrolyte solution after corrosion. pH measurements of the electrolyte were recorded before and after corrosion tests. Finally, the corroded surface was characterized by a 3D white-light microscope and scanning electron microscope. Statistical analysis was conducted using either one-way ANOVA followed by Tukey's Post Hoc test or Kruskal-Wallis followed by Dunn's test based on data distribution.

Results

Based on cement amount, FC and PC significantly increased icorr in higher amounts (FC8mm-icorr = 8.22 × 10-8A/cm2, PC8mm-icorr = 5.61 × 10-8A/cm2) compared to control (3.35 × 10-8A/cm2). In contrast, TB3mm decreased icorr significantly compared to the control. As a function of cement type, FC increased icorr the most. EIS data agrees with these observations. Finally, corroded surfaces had higher surface roughness (Ra) compared to non-corroded surfaces.

Conclusion

The study indicated that cement types FC and PC led to increased Ti-corrosion as a function of a higher amount. Hence, the implant stability could be impacted by the selection, excessive cement, and a potentially increased risk of peri-implantitis.

Effect of Enterococcus faecalis Biofilm on Corrosion Kinetics in Titanium Grade 4 Alloys with Different Surface Treatments

E. faecalis has been associated with bacteremia, sepsis, and bacterial endocarditis and peri-implantitis. This microorganism can remain in the alveolus even after extraction of the root remnant. This study aimed to evaluate the corrosion on different surfaces of commercially pure titanium (Ti) grade 4 (Ticp-G4) as a function of the bacterial biofilm effect of Enterococcus faecalis. A total of 57 discs were randomly divided according to their surface finish (n = 19). For microbiological analysis (n = 9), the discs were placed in 12-well plates containing E. faecalis culture and incubated at 37 °C for 7 days. The results show that for the intergroup analysis, considering the "electrolyte" factor, there was a difference between the groups. There was greater biofilm formation for the D.A.Zir group, with greater electrochemical exchange for Biofilm, and the presence of biofilm favored greater electrochemical exchange with the medium.

Bio-Tribocorrosion of Titanium Dental Implants and Its Toxicological Implications: A Scoping Review

Bio-tribocorrosion is a phenomenon that combines the essentials of tribology (friction, wear, and lubrication) and corrosion with microbiological processes. Lately, it has gained attention in implant dentistry because dental implants are exposed to wear, friction, and biofilm formation in the corrosive oral environment. They may degrade upon exposure to various microbial, biochemical, and electrochemical factors in the oral cavity. The mechanical movement of the implant components produces friction and wear that facilitates the release of metal ions, promoting adverse oro-systemic reactions. This review describes the bio-tribocorrosion of the titanium (Ti) dental implants in the oral cavity and its toxicological implications. The original research related to the bio-tribo or tribocorrosion of the dental implants was searched in electronic databases like Medline (Pubmed), Embase, Scopus, and Web of Science. About 34 studies included in the review showed that factors like the type of Ti, oral biofilm, acidic pH, fluorides, and micromovements during mastication promote bio-tribocorrosion of the Ti dental implants. Among the various grades of Ti, grade V, i.e., Ti6Al4V alloy, is most susceptible to tribocorrosion. Oral pathogens like Streptococcus mutans and Porphyromonas gingivalis produce acids and lipopolysaccharides (LPS) that cause pitting corrosion and degrade the TiO₂. The low pH and high fluoride concentration in saliva hinder passive film formation and promote metal corrosion. The released metal ions promote inflammatory reactions and bone destruction in the surrounding tissues resulting in peri-implantitis, allergies, and hyper-sensitivity reactions. However, further validation of the role of bio-tribocorrosion on the durability of the Ti dental implants and Ti toxicity is warranted through clinical trials.

Cathodic activation and inflammatory species are critical to simulating in vivo Ti-6Al-4V selective dissolution

In vivo retrievals of metallic orthopedic implants have shown selective dissolution of Ti-6Al-4V, where the vanadium-rich β phase preferentially corrodes from the surface. This damage, typically observed in crevices, is not directly caused by wear mechanics and the underlying electrochemical mechanism remains poorly understood. Previous studies show that fretting corrosion can cause negative potential drops, resulting in a decrease in surface oxide passivation resistance and the electrochemical generation of reactive oxygen species (ROS) at metallic surfaces. In this study, we combine cathodic activation and hydrogen peroxide to induce selective dissolution in vitro. After a 600 s -1 V hold and 4 h recovery in 20 °C 1 M H₂O₂ solution, the Ti-6Al-4V β phase was preferentially dissolved. An initial activation threshold of -0.5 V induced a significant increase in β dissolution (p = 0.000). Above this threshold, little selective dissolution occurred. In an Arrhenius-like fashion, decreasing solution concentration to 0.1 M required 72 h to generate β dissolution instead of 4 h at 1 M. Heating 0.1 M solution to body temperature (37 °C) resulted in a decrease in the time needed to replicate a similar level of β dissolution (>90%). Electrochemical impedance shows that both cathodic activation and inflammatory species are necessary to induce selective dissolution, where the combinatorial effect causes a significant drop in oxide passivation resistance from 10⁶ to 10² (p = 0.000). STATEMENT OF SIGNIFICANCE: Though hip arthroplasties are considered a successful procedure, revision rates of 2-4% result in tens of thousands of additional surgeries within the United States, subjecting patients to increased risk of complications. Corrosion is associated with implant failure and retrieval studies show that titanium and its alloys can severely corrode in vivo in ways not yet duplicated in vitro. Here, we reproduce selective dissolution of Ti-6Al-4V β phase simulating key characteristics of in vivo degradation observed in orthopedic retrievals. We establish both cathodically activated corrosion, a relatively unexplored concept, and the presence of inflammatory species as prerequisites, furthering our understanding of this clinically relevant damage mode. We introduce an Arrhenius-based approach to assess the concentration-temperature-time interactions present.

Impact of tribocorrosion and titanium particles release on dental implant complications - A narrative review

Titanium particles as a product of degradation have been detected in periimplant oral tissues and it has been assumed that implants were the source of these particles. Periimplantitis sites had higher concentrations of particles in comparison to healthy implant sites. Several factors have been identified in the degradation of dental implant surface, such as mechanical wear, contact with chemical agents, and the effects of biofilm adhesion. Titanium particles silently prompt the immune-system activation and generate a pro-inflammatory response in macrophages, T lymphocytes and monocytes. During the activation, inflammatory cytokines are released including, granulocyte-macrophage colony-stimulating factor (GM-CSF), prostaglandin, and TNF-α, IL-1β, IL-6. The nanoparticles depict unique features such as high level of biological reactivity and potentially harmful compared to microparticles since they have a relatively greater surface area to volume ratio. Allergic response to titanium as a cause of implant failure has not been well documented. Evidence demonstrating biological complication due to titanium particles release includes peri-implant tissue inflammation that lead terminally to implant loss. There is a biological probability for a relation between the presence of titanium particles and ions, biological complication, and corrosion, but there is no justifiable evidence for unidirectional series of causative actions.

A Comprehensive Review on the Corrosion Pathways of Titanium Dental Implants and Their Biological Adverse Effects

The main aim of this work was to perform a comprehensive review of findings reported by previous studies on the corrosion of titanium dental implants and consequent clinical detrimental effects to the patients. Most studies were performed by in vitro electrochemical tests and complemented with microscopic techniques to evaluate the corrosion behavior of the protective passive oxide film layer, namely TiO2. Results revealed that bacterial accumulation, dietary, inflammation, infection, and therapeutic solutions decrease the pH of the oral environment leading to the corrosion of titanium. Some therapeutic products used as mouthwash negatively affect the corrosion behavior of the titanium oxide film and promote changes on the implant surface. In addition, toothpaste and bleaching agents, can amplify the chemical reactivity of titanium since fluor ions interacting with the titanium oxide film. Furthermore, the number of in vivo studies is limited although corrosion signs have been found in retrieved implants. Histological evaluation revealed titanium macro- and micro-scale particles on the peri-implant tissues. As a consequence, progressive damage of the dental implants and the evolution of inflammatory reactions depend on the size, chemical composition, and concentration of submicron- and nanoparticles in the surrounding tissues and internalized by the cells. In fact, the damage of the implant surfaces results in the loss of material that compromises the implant surfaces, implant-abutment connections, and the interaction with soft tissues. The corrosion can be an initial trigger point for the development of biological or mechanical failures in dental implants.

Demonstration of a SiC Protective Coating for Titanium Implants

To mitigate the corrosion of titanium implants and improve implant longevity, we investigated the capability to coat titanium implants with SiC and determined if the coating could remain intact after simulated implant placement. Titanium disks and titanium implants were coated with SiC using plasma-enhanced chemical vapor deposition (PECVD) and were examined for interface quality, chemical composition, and coating robustness. SiC-coated titanium implants were torqued into a Poly(methyl methacrylate) (PMMA) block to simulate clinical implant placement followed by energy dispersive spectroscopy to determine if the coating remained intact. After torquing, the atomic concentration of the detectable elements (silicon, carbon, oxygen, titanium, and aluminum) remained relatively unchanged, with the variation staying within the detection limits of the Energy Dispersive Spectroscopy (EDS) tool. In conclusion, plasma-enhanced chemical vapor deposited SiC was shown to conformably coat titanium implant surfaces and remain intact after torquing the coated implants into a material with a similar hardness to human bone mass.

Surface analysis and corrosion behavior of pure titanium under fluoride exposure

STATEMENT OF PROBLEM

The corrosive effects of oral fluoride products on titanium have been reported, and chronic fluorosis, which causes hyperfluoemia, is one of the world's health problems. Nevertheless, the relationship between high serum fluoride and corrosion on the titanium surface, which might have adverse effects on titanium implant osseointegration, has not been elucidated.

PURPOSE

The purpose of this in vitro study was to investigate the corrosion behavior of pure titanium exposed to high serum fluoride with different pH values based on surface analysis.

MATERIAL AND METHODS

Pure titanium specimens, exposed to different electrolytes with 0.04 and 0.4 ppm NaF at pH 7.3 and 5.0 values, were examined for surface microstructure by using scanning electron microscopy (SEM) and for surface element composition with X-ray photoelectron spectroscopy (XPS). The corrosion behavior and metal ion release of specimens immersed in the Hanks' balanced salt solution (HBSS) containing 0.04 and 0.4 ppm serum fluoride concentrations (NaF) at 7.3 and 5.0 pH values were measured by electrochemical impedance spectroscopy (EIS) and inductively coupled plasma atomic emission spectrometry (ICP-AES).

RESULTS

Pitting holes were observed on pure titanium surfaces exposed to high serum fluoride. The surfaces became rougher with the increase of serum fluoride concentration, especially under acidic conditions. XPS analysis revealed a reduction of dominant titanium dioxide (TiO₂) on the pure titanium surface under serum fluoride exposure, corresponding to an increase in the relative level of F. EIS data showed an active corrosion behavior of pure titanium exposed to high serum fluoride and gradually decreased corrosion resistance with increasing concentration of serum fluoride, which was more severe under acidic conditions. The release of titanium ions was also induced by high serum fluoride and acidic conditions.

CONCLUSIONS

High serum fluoride had a negative influence on the corrosion behavior of pure titanium. The titanium oxide film barrier could be broken down in the fluoride ions condition, and the corrosion resistance of pure titanium decreased with the increasing concentration of serum fluoride. The increased corrosion susceptibility of pure titanium accelerated the release of titanium ions after exposure to high serum fluoride; this was more pronounced in an acidic environment.

Comparison between Plasma Electrolytic Oxidation Coating and Sandblasted Acid-Etched Surface Treatment: Histometric, Tomographic, and Expression Levels of Osteoclastogenic Factors in Osteoporotic Rats

Plasma electrolytic oxidation (PEO) has been a promising surface coating with better mechanical and antimicrobial parameters comparing to conventional treatment surfaces. This study evaluated the peri-implant bone repair using (PEO) surface coatings compared with sandblasted acid (SLA) treatment. For this purpose, 44 Wistar rats were ovariectomized (OVX-22 animals) or underwent simulated surgery (SS-22 animals) and received implants in the tibia with each of the surface coatings. The peri-implant bone subsequently underwent molecular, microstructural, bone turnover, and histometric analysis. Real-time PCR showed a higher expression of osteoprotegerin (OPG), receptor activator of nuclear kappa-B ligand (RANKL), and osteocalcin (OC) proteins in the SLA/OVX and PEO/SS groups (p < 0.05). Computed microtomography, confocal microscopy, and histometry showed similarity between the PEO and SLA surfaces, with a trend toward the superiority of PEO in OVX animals. Thus, PEO surfaces were shown to be promising for enhancing peri-implant bone repair in ovariectomized rats.

Initial investigation of the corrosion stability of craniofacial implants

STATEMENT OF PROBLEM

Although craniofacial implants have been used for retention of facial prostheses, failures are common. Titanium undergoes corrosion in the oral cavity, but the corrosion of craniofacial implants requires evaluation.

PURPOSE

The purpose of this in vitro study was to investigate the corrosion stability of commercially pure titanium (CP Ti) exposed to simulated human perspiration at 2 different pH levels (5.5 and 8).

MATERIAL AND METHODS

Fifteen titanium disks were divided into 3 groups (n=5 per group). The control group was subjected to simulated body fluid (SBF) (control). Disks from the 2 experimental groups were immersed in simulated alkaline perspiration (SA_KP) and simulated acidic perspiration (SA_CP). Electrochemical tests, including open circuit potential (3600 seconds), electrochemical impedance spectroscopy, and potentiodynamic tests were performed according to the standardized method of 3-cell electrodes. Data were analyzed by 1-way ANOVA and the Tukey honestly significant difference tests (α=.05).

RESULTS

Simulated human perspiration reduced the corrosion stability of CP Ti (P<.05). The SBF group presented the lowest capacitance values (P<.05). SA_KP and SA_CP groups showed increased values of capacitance and showed no statistically significant differences (P>.05) from each other. The increase in capacitance suggests that the acceleration of the ionic exchanges between the CP Ti and the electrolyte leads to a lower corrosion resistance. SA_KP reduced the oxide layer resistance of CP Ti (P<.05), and an increased corrosion rate was noted in both simulated human perspiration groups.

CONCLUSIONS

Craniofacial implants can corrode when in contact with simulated human perspiration, whereas alkaline perspiration shows a more deleterious effect. Perspiration induces a more corrosive effect than simulated body fluid.

Evaluation of corrosion resistance and surface characteristics of orthodontic wires immersed in different mouthwashes

BACKGROUND

Patients use mouthwashes in addition to mechanical cleaning during orthodontic treatment. The effects of mouthwashes on the archwires have not been examined yet.

OBJECTIVE

To compare the corrosion resistance of four different arch wires and corrosion effects of different mouthwashes to formulate a biocompatible and mechanically useful arch wire and mouthwash combination.

METHODS

Each group comprised of 4 wire samples of 2 cm 0.016 × 0.022 inch. 1st group: ion implanted nickel titanium (INT), 2nd group: nickel titanium, without ion implantation (NT), 3rd group: micro layered esthetic nickel titanium (ENT), 4th group: stainless steel (SS) wires. They were immersed inside 2 ml of artificial saliva solutions (AS) for the control, or AS (9%) combined with 1 of the 3 mouthwashes (91%) for study groups, for 24 hours. These mouthwashes were essential oil (EO), chlorhexidine (CHX), sodium-fluoride (NaF). An electrochemical analyzer was used for electrochemical impedance spectroscopy measurements.

RESULTS

High corrosion resistance was obtained for ENT than the other wires. The corrosion potentials are 0.007, -0.042, 0.074 and -0.015 V (Ag/AgCl) for ENT, INT, SS and NT in the artificial salivary, respectively. In NaF containing mouthwash Rp value of ENT is significantly high in comparison to others. The impedance responses of all materials increased significantly in the presence of NaF mouthwash as well as in the CHX mouthwash. Low frequencies are seen at all materials in EO mouthwash. Diameters of loops are 22, 5.9, 5.9 and 3.7 MΩ at ENT, INT, SS and NT.

CONCLUSIONS

In this study, micro layered esthetic nickel titanium wires are found biocompatible among other wires and NaF and CHX mouthwashes can be recommend for their good corrosion resistance during fixed orthodontic therapy.

Titanium: a review on exposure, release, penetration, allergy, epidemiology, and clinical reactivity

Exposure to titanium (Ti) from implants and from personal care products as nanoparticles (NPs) is common. This article reviews exposure sources, ion release, skin penetration, allergenic effects, and diagnostic possibilities. We conclude that human exposure to Ti mainly derives from dental and medical implants, personal care products, and foods. Despite being considered to be highly biocompatible relative to other metals, Ti is released in the presence of biological fluids and tissue, especially under certain circumstances, which seem to be more likely with regard to dental implants. Although most of the studies reviewed have important limitations, Ti seems not to penetrate a competent skin barrier, either as pure Ti, alloy, or as Ti oxide NPs. However, there are some indications of Ti penetration through the oral mucosa. We conclude that patch testing with the available Ti preparations for detection of type IV hypersensitivity is currently inadequate for Ti. Although several other methods for contact allergy detection have been suggested, including lymphocyte stimulation tests, none has yet been generally accepted, and the diagnosis of Ti allergy is therefore still based primarily on clinical evaluation. Reports on clinical allergy and adverse events have rarely been published. Whether this is because of unawareness of possible adverse reactions to this specific metal, difficulties in detection methods, or the metal actually being relatively safe to use, is still unresolved.

Surface treatment influences electrochemical stability of cpTi exposed to mouthwashes

The role of surface treatment on the electrochemical behavior of commercially pure titanium (cpTi) exposed to mouthwashes was tested. Seventy-five disks were divided into 15 groups according to surface treatment (machined, sand blasted with Al2O3, and acid etched) and electrolyte solution (artificial saliva — control, 0.12% chlorhexidine digluconate, 0.05% cetylpyridinium chloride, 0.2% sodium fluoride, and 1.5% hydrogen peroxide) (n = 5). Open-circuit-potential and electrochemical impedance spectroscopy were conducted at baseline and after 7 and 14 days of immersion in each solution. Potentiodynamic test and total weight loss of disks were performed after 14 days of immersion. Scanning electron microscopy, energy dispersive spectroscopy, white light interferometry and profilometry were conducted for surface characterization before and after the electrochemical tests. Sandblasting promoted the lowest polarization resistance (Rp) (P b .0001) and the highest capacitance (CPE) (P b .006), corrosion current density (Icorr) and corrosion rate (P b .0001). In contrast, acid etching increased Rp and reduced CPE, independent to the mouthwash; while hydrogen peroxide reduced Rp (P b .008) and increased Icorr and corrosion rate (P b .0001). The highest CPE values were found for hydrogen peroxide and 0.2% sodium fluoride. Immersion for longer period improved the electrochemical stability of cpTi (P b .05). In conclusion, acid etching enhanced the electrochemical stability of cpTi. Hydrogen peroxide and sodium fluoride reduced the resistance to corrosion of cpTi, independent to the surface treatment. Chlorhexidine gluconate and cetylpyridinium chloride did not alter the corrosive behavior of cpTi.

Influence of stress corrosion on the mechanical properties of laser-welded titanium

STATEMENT OF PROBLEM

Whether laser-welded (LW) titanium can resist the stress corrosion produced by the combination of fluoride ions and stress in the oral environment is unknown.

PURPOSE

The purpose of this in vitro study was to investigate the influence of stress corrosion on the mechanical properties of LW titanium.

MATERIAL AND METHODS

Twenty-seven titanium bars (25×2 mm) with a circular cross-section were cut in half and laser-welded, while another 27 nonwelded (NW) bars were used as the control. Thirty bars were submitted to a flexural load of 480 N at 1 Hz and immersed in artificial saliva at pH 6 (S1) or in 1000 ppm fluoride-containing saliva at pH 6.0 (S2) or 2.0 (S3) at room temperature for up to 4000 cycles. After the stress corrosion simulation, the tensile strength and Vickers microhardness were determined (n=5). Twelve LW and NW bars were submitted to the corrosion immersion test media for 51 days (n=2) to determine polarization curves (n=2) in an artificial saliva media. The corroded surface was examined with scanning electron microscopy (SEM).

RESULTS

The combination of fluoride and low pH significantly decreased the tensile strength of LW (P<.05). Stress corrosion did not affect the hardness of LW or NW (P>.05). NW bars immersed in S3 exhibited progressive surface dissolution, while LW bars spontaneously fractured at the welded area after 25 days of immersion in the same medium. SEM images demonstrated pitting corrosion without the presence of cracks in both groups immersed in S3.

CONCLUSIONS

Stress corrosion caused by acidic fluoride-containing saliva and flexural load cycling decreased the tensile strength and hardness of LW titanium bars.