Microbial corrosion of metallic biomaterials in the oral environment

A wide variety of microorganisms have been closely linked to metal corrosion in the form of adherent surface biofilms. Biofilms allow the development and maintenance of locally corrosive environments and/or permit direct corrosion including pitting corrosion. The presence of numerous genetically distinct microorganisms in the oral environment poses a threat to the integrity and durability of the surface of metallic prostheses and implants used in routine dentistry. However, the association between oral microorganisms and specific corrosion mechanisms is not clear. It is of practical importance to understand how microbial corrosion occurs and the associated risks to metallic materials in the oral environment. This knowledge is also important for researchers and clinicians who are increasingly concerned about the biological activity of the released corrosion products. Accordingly, the main goal was to comprehensively review the current literature regarding oral microbiologically influenced corrosion (MIC) including characteristics of biofilms and of the oral environment, MIC mechanisms, corrosion behavior in the presence of oral microorganisms and potentially mitigating technologies. Findings included that oral MIC has been ascribed mostly to aggressive metabolites secreted during microbial metabolism (metabolite-mediated MIC). However, from a thermodynamic point of view, extracellular electron transfer mechanisms (EET-MIC) through pili or electron transfer compounds cannot be ruled out. Various MIC mitigating methods have been demonstrated to be effective in short term, but long term evaluations are necessary before clinical applications can be considered. Currently most in-vitro studies fail to simulate the complexity of intraoral physiological conditions which may either reduce or exacerbate corrosion risk, which must be addressed in future studies. STATEMENT OF SIGNIFICANCE: A thorough analysis on literature regarding oral MIC (microbiologically influenced corrosion) of biomedical metallic materials has been carried out, including characteristics of oral environment, MIC mechanisms, corrosion behaviors in the presence of typical oral microorganisms and potential mitigating methods (materials design and surface design). There is currently a lack of mechanistic understanding of oral MIC which is very important not only to corrosion researchers but also to dentists and clinicians. This paper discusses the significance of biofilms from a biocorrosion perspective and summarizes several aspects of MIC mechanisms which could be caused by oral microorganisms. Oral MIC has been closely associated with not only the materials research but also the dental/clinical research fields in this work.

Antibiofilm peptides enhance the corrosion resistance of titanium in the presence of Streptococcus mutans

Titanium alloys have gained popularity in implant dentistry for the restoration of missing teeth and related hard tissues because of their biocompatibility and enhanced strength. However, titanium corrosion and infection caused by microbial biofilms remains a significant clinical challenge leading to implant failure. This study aimed to evaluate the effectiveness of antibiofilm peptides 1018 and DJK-5 on the corrosion resistance of titanium in the presence of Streptococcus mutans. Commercially pure titanium disks were prepared and used to form biofilms. The disks were randomly assigned to different treatment groups (exposed to S. mutans supplied with sucrose) including a positive control with untreated biofilms, peptides 1018 or DJK-5 at concentrations of 5 μg/mL or 10 μg/mL, and a negative control with no S. mutans. Dynamic biofilm growth and pH variation of all disks were measured after one or two treatment periods of 48 h. After incubation, the dead bacterial proportion, surface morphology, and electrochemical behaviors of the disks were determined. The results showed that peptides 1018 and DJK-5 exhibited significantly higher dead bacterial proportions than the positive control group in a concentration dependent manner (p < 0.01), as well as far less defects in microstructure. DJK-5 at 10 μg/mL killed 84.82% of biofilms and inhibited biofilm growth, preventing acidification due to S. mutans and maintaining a neutral pH. Potential polarization and electrochemical impedance spectroscopy data revealed that both peptides significantly reduced the corrosion and passive currents on titanium compared to titanium surfaces with untreated biofilms, and increased the resistance of the passive film (p < 0.05), with 10 μg/mL of DJK-5 achieving the greatest effect. These findings demonstrated that antibiofilm peptides are effective in promoting corrosion resistance of titanium against S. mutans, suggesting a promising strategy to enhance the stability of dental implants by endowing them with antibiofilm and anticorrosion properties.

Influence of a D-enantiomeric peptide on the anticorrosion ability of titanium with different surface roughness against Streptococcus mutans biofilms

OBJECTIVE

To investigate the effectiveness of a d-enantiomeric antibiofilm peptide (DJK-5) on the anticorrosion ability of titanium (Ti) with different surface roughness against Streptococcus mutans biofilms.

METHODS

Commercially pure Ti disks with machined (MA, smooth) or sandblasted + acid-etched (SLA, rough) surfaces were prepared and characterized. All disks were divided into three groups: a positive control (PC) group with S. mutans, a DJK-5-treated group, and a negative control (NC) group without S. mutans. Biofilm formation and corrosion on Ti surfaces were determined by confocal laser scanning microscopy and scanning electron microscopy after 2 and 6 days, and the electrochemical properties were evaluated.

RESULTS

Ten μg/mL of DJK-5 killed 83.3 % and 87.4 % of biofilms on SLA and MA Ti surfaces, respectively after 2 days, and 72.9 % and 77.7 % after 6 days, with more bacteria surviving on SLA surfaces with higher roughness (p < 0.05). DJK-5 treatment induced less surface defects with tiny pit corrosion than PC. DJK-5 treatment when compared to PC, led to electrochemical properties more reflecting NC surfaces, including significantly less negative corrosion potential, lower corrosion current, and higher passive film resistance (p < 0.05). SLA surfaces exhibited higher current density and lower resistance than MA surfaces (p < 0.05).

CONCLUSION

DJK-5 effectively enhanced the corrosion resistance of Ti with different surface roughness while killing S. mutans biofilms, and smooth surfaces were more susceptible to peptide treatment.

CLINICAL SIGNIFICANCE

The antibiofilm peptide is promising for promoting the anticorrosion ability of Ti against biofilms, thereby preventing biofilm-related infections.

Nanoscale Chemical Surface Analyses of Recycled Powder for Direct Metal Powder Bed Fusion Ti-6Al-4V Root Analog Dental Implant: An X-ray Photoelectron Spectroscopy Study

Over the past couple of decades, additive manufacturing and the use of root-analogue-printed titanium dental implants have been developed. Not all powder particles are sintered into the final product during the additive manufacturing process. Reuse of the remaining powder could reduce the overall implant manufacturing cost. However, Ti-6Al-4V powder particles are affected by heat, mechanical factors, and oxidization during the powder bed fusion manufacturing process. Degradation of the powder may harm the final surface composition and decrease the biocompatibility and survival of the implant. The uncertainty of the recycled powder properties prevents implant fabrication facilities from reusing the powder. This study investigates the chemical composition of controlled, clean, and recycled titanium alloy powder and root-analogue implants (RAI) manufactured from these powders at three different depths. The change in titanium's quantity, oxidization state, and chemical composition in powder and RAI implants have been demonstrated and analyzed. While not identical, the surface chemical composition of the recycled powder implant and the implant manufactured from unused powder are similar. The results also indicate the presence of TiO₂ on all surfaces. Many studies confirmed that titanium dioxide on the implant's surface correlates with better osteointegration, reduced bacterial infection, and increased corrosion resistance. Considering economic and environmental aspects, surface chemical composition comparison of clean and reused powder is crucial for the future manufacturing of cost-effective and biocompatible implants.

Efficacy of combined chemical and electrochemical decontamination treatments on contaminated healing abutments and their effect on surface topography: An in vitro study

OBJECTIVE

To evaluate the efficacy of four decontamination protocols on contaminated healing abutments (HAs) and their effects on surface topography.

METHODS

Eighty contaminated single-use HA samples collected from human participants were stained with phloxine B and examined microscopically. The retrieved HAs were randomly divided into four test groups: (1) Autoclaving only (AU), (2) 5.25% sodium hypochlorite (NaOCl) + AU, (3) Electrochemical treatment (EC) + AU, (4) NaOCl + EC + AU, and positive control (contaminated without any treatment). Four new unused HAs served as negative controls (NC). The surface features were analyzed using stereo microscopy (SM), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and optical profilometry.

RESULTS

The lowest decontamination efficacy was observed for the AU group. The NaOCl + AU and EC + AU groups effectively removed residual contamination, whereas EC + AU showed better decontamination results than NaOCl + AU. SM, SEM, and EDS analyses revealed the best decontamination efficacy in the combined NaOCl + EC + AU group compared to the other groups. Surface roughness (Sa), developed surface area ratio (Sdr), and texture-aspect ratio (Str) in AU, NaOCl + AU, EC + AU, and NaOCl + EC + AU groups were not statistically significant compared to the NC group.

CONCLUSIONS

The combination of NaOCl with subsequent EC can remove soft and hard deposits from the surface of HAs compared to NaOCl alone and EC alone, without altering the surface topography of HAs.

The role of bacterial corrosion on recolonization of titanium implant surfaces: An in vitro study

BACKGROUND

Inflammation triggered by bacterial biofilms in the surrounding tissue is a major etiological factor for peri-implantitis and subsequent implant failure. However, little is known about the direct effects of bacterial corrosion and recolonization on implant failure PURPOSE: To investigate the influence of oral commensals on bacterial corrosion and recolonization of titanium surfaces.

MATERIALS AND METHODS

Streptococcus sanguinis (S. sanguinis) and Porphyromonas gingivalis (P. gingivalis), which are key bacteria in oral biofilm formation, were cultured on commercially pure titanium and titanium-aluminum-vanadium (Ti6Al4V) plates in artificial saliva/brain heart infusion medium under aerobic or anaerobic conditions. Biofilm formation was examined after 7 and 21 days by crystal violet and live/dead staining. Titanium ions released into culture supernatants were analyzed over a period of 21 days by atomic absorption spectrometry. Visual changes in surface morphology were investigated using scanning electron microscopy. Biofilm formation on sterilized, biocorroded, and recolonized implant surfaces was determined by crystal violet staining.

RESULTS

S. sanguinis and P. gingivalis formed stable biofilms on the titanium samples. Bacterial corrosion led to a significant increase in titanium ion release from these titanium plates (p < 0.01), which was significantly higher under aerobic conditions on pure titanium (p ≤ 0.001). No obvious morphological surface changes, such as pitting and discoloration, were detected in the titanium samples. During early biofilm formation, the addition of titanium ions significantly decreased the number of live cells. In contrast, a significant effect on biofilm mass was only detected with P. gingivalis. Bacterial corrosion had no influence on bacterial recolonization following sterilization of titanium and Ti6Al4V surfaces.

CONCLUSION

Bacterial corrosion differs between oral commensal bacteria and leads to increased titanium ion release from titanium plates. The titanium ion release did not influence biofilm formation or bacterial recolonization under in vitro conditions.

Effects of Dicationic Imidazolium-Based Ionic Liquid Coatings on Oral Osseointegration of Titanium Implants: A Biocompatibility Study in Multiple Rat Demographics

Dicationic imidazolium-based ionic liquids with amino acid anions, such as IonL-phenylalanine (IonL-Phe), have been proposed as a multifunctional coating for titanium (Ti) dental implants. However, there has been no evaluation of the biocompatibility of these Ti coatings in the oral environment. This study aims to evaluate the effects of IonL-Phe on early healing and osseointegration of Ti in multiple rat demographics. IonL-Phe-coated and uncoated Ti screws were implanted into four demographic groups of rats to represent biological variations that could affect healing: young males (YMs) and females (YFs), ovariectomized (OVXFs) females, and old males (OMs). Samples underwent histopathological and histomorphometric analysis to evaluate healing at 7 and 30 days around IonL-coated and uncoated Ti. The real-time quantitative polymerase chain reaction was also conducted at the 2- and 7-day YM groups to evaluate molecular dynamics of healing while the IonL-Phe was present on the surface. IonL-coated and uncoated implants demonstrated similar histological signs of healing, while coated samples’ differential gene expression of immunological and bone markers was compared with uncoated implants at 2 and 7 days in YMs. While YMs presented suitable osseointegration for both uncoated and IonL-Phe-coated groups, decreased success rate in other demographics resulted from lack of supporting bone in YFs and poor bone quality in OVXFs and OMs. Overall, it was found that IonL-coated samples had increased bone-to-implant contact across all demographic groups. IonL-Phe coating led to successful osseointegration across all animal demographics and presented the potential to prevent failures in scenarios known to be challenged by bacteria.

Zinc- and strontium- co-incorporated nanorods on titanium surfaces with favorable material property, osteogenesis, and enhanced antibacterial activity

Early infection and peri-implantitis after implant restoration are major reasons for dental implant failure. Implant-associated infections are majorly attributed to biofilm formation. In this study, co-incorporated zinc- (Zn-) and strontium- (Sr-) nanorod coating on sandblasted and acid-etched (SLA) titanium (SLA-Zn/Sr) was fabricated by hydrothermal synthesis. It was aimed at promoting osteogenesis while inhibiting biofilm formation. The nanorod-like particles (φ 30-50 nm) were found to be evenly formed on SLA-Zn/Sr (Zn: 1.49 ± 0.16 wt%; Sr: 21.69 ± 2.74 wt%) that was composed of well-crystallized ZnTiO₃ and SrTiO₃ phases. With a sufficient interface bonding strength (42.00 ± 3.00 MPa), SLA-Zn/Sr enhanced the corrosion resistance property of titanium. Besides, SLA-Zn/Sr promoted the cellular initial adhesion, proliferation and osteogenic differentiation of rBMSCs in vitro while inhibiting the adhesion of Staphylococcus aureus and Porphyromonas gingivalis . In addition, through down-regulating icaA gene expression, this novel surface reduced the secretion of polysaccharide intercellular adhesion (reduced by 87.9% compared to SLActive) to suppress the S. aureus biofilm formation. We, therefore, propose a new chemical modification on titanium for multifunctional implant material development. Due to the Zn/Sr co-doping in coating, material properties, early osteogenic effect and antibacterial ability of titanium can be simultaneously enhanced, which has the potential to be applied in dental implantation in the future.

Oral prosthetic microbiology: aspects related to the oral microbiome, surface properties, and strategies for controlling biofilms

The oral cavity is an environment that allows for the development of complex ecosystems; the placement of prosthetic devices as a consequence of partial or total tooth loss may alter the diversity of microbial communities. Biofilms on the surface of materials used in dental prostheses can promote important changes in the mechanic and aesthetic properties of the material itself and may cause local and systemic diseases for the prosthetic wearer. This review presents the main features of the oral microbiome associated with complete or partial dentures and dental implants. The main diseases associated with microbial colonization of prosthetic surfaces, factors that may affect biofilm formation on prosthetic materials, as well as novel alternative therapies aiming to reduce biofilm formation and/or to eradicate biofilms formed on these materials are also explored.

Effects of multiple implantations of titanium healing abutments: Surface characteristics and microbial colonization

OBJECTIVE

Very few studies have investigated dental implant components involved in the early stage of healing, especially the implant healing abutment (IHA), despite its vital role in soft tissue contouring and shaping after implant placement. Although these components are labelled by the manufacturer for "single-use only," it is a common clinical practice to clean, sterilize, and reuse them.

METHODS

In the present study, IHAs after single and multiple implantations were retrieved as per standard procedures, and biological material isolated from the surface was subjected to 16S rRNA sequence analysis. The microbiome analysis was followed by cleaning and sterilization in order to replicate clinical sterilization techniques. Following sterilization, retrievals were subjected to surface characterization with optical and scanning electron microscopy to investigate surface features, and electrochemical testing was performed to evaluate corrosion behavior.

RESULTS

The microbiota was comprised of early colonizers including Streptococcus species and secondary anaerobic colonizers such as Fusobacterium, Capnocytophaga, and Prevotella species. The surface analysis revealed that irrespective of the cleaning and sterilization techniques, the pristine, homogeneous surface of the new, unused IHAs could not be restored. Both single and multiple-use IHAs had severe surface changes including discoloration, major abrasions, biological contamination, and the IHA retrievals exhibited higher corrosion rate as compared to control specimens.

SIGNIFICANCE

Reusing IHAs multiple times may not be a prudent practice as the microbial colonization and surface changes caused by using this component multiple times may affect the performance of IHAs in soft tissue healing.

Bone loss around implants-is it metallosis?

Most would agree that the etiology of dental implant failure is related to oral biofilm. At present one group of scientists and clinicians feel that biofilm is solely responsible for bone loss around the devices. However, there is strong evidence that particles and ions of titanium released into the surrounding tissues by the action of biofilm and/or mechanical forces, a process termed metallosis, can be responsible for bone loss around some dental implants. These findings are reinforced by similar responses found around failed metal on metal joint prostheses. Both possible etiologies are discussed in detail in this commentary.

Spectroscopic Methods Used in Implant Material Studies

It is recognized that interactions between most materials are governed by their surface properties and manifest themselves at the interface formed between them. To gain more insight into this thin layer, several methods have been deployed. Among them, spectroscopic methods have been thoroughly evaluated. Due to their exceptional sensitivity, data acquisition speed, and broad material tolerance they have been proven to be invaluable tools for surface analysis, used by scientists in many fields, for example, implant studies. Today, in modern medicine the use of implants is considered standard practice. The past two decades of constant development has established the importance of implants in dentistry, orthopedics, as well as extended their applications to other areas such as aesthetic medicine. Fundamental to the success of implants is the knowledge of the biological processes involved in interactions between an implant and its host tissue, which are directly connected to the type of implant material and its surface properties. This review aims to demonstrate the broad applications of spectroscopic methods in implant material studies, particularly discussing hard implants, surface composition studies, and surface-cell interactions.

The role of bacterial biofilm and mechanical forces in modulating dental implant failures

Currently many assume that bacteria are the primary etiological factor associated with failure of titanium dental implants. However, emerging data indicates a possible role for mechanical forces in implant failure. This study is based on the hypothesis that the synergistic effect of mechanical forces and bacterial biofilm can lead to surface damage resulting in in vivo release of metallic particles. The primary aim of the study was to develop a dynamic fatigue test method for dental implants immersed in wet environments such as; (i) 0.01 M phosphate buffer saline (PBS); (ii) lactic acid (pH = 5); (iii) bacterial polyculture. Four dental implants each were subjected to fatigue loading from 45 N to 450 N at 4 Hz for 2 million cycles while immersed in (i) PBS (negative control); (ii) bacterial culture (test); and (iii) lactic acid (positive control). Post-testing, optical microscopy, x-ray photoelectron spectroscopy, and electrochemical corrosion tests were performed to evaluate the surface morphology, chemistry, and potential, respectively, of titanium implants. Post-testing, surface discoloration was evident in all three groups. However, the surface damage was further established in XPS analyses of test specimens, which showed that the interplay of bacterial biofilm and mechanical forces resulted in thinning of the TiO₂. Lower corrosion potential (Ecorr) of the test specimens compared to positive and negative controls also illustrated damage to the oxide layer. However, other electrochemical parameters such as linear polarization resistance (LPR) and corrosion rate (CR) were comparable among the groups indicating the corrosion resistance post-testing. The synergistic effect of cyclic occlusal loading and bacteria biofilm could negatively affect the surface of titanium dental implants.

Biological characterization of surface-treated dental implant materials in contact with mammalian host and bacterial cells: titanium versus zirconia

Early-colonizing oral bacterial adhesion and mammal cell proliferation were similar on surface-treated titanium and zirconia.