Implant decontamination facing the biofilm challenge

With an estimated prevalence between 40 and 45%, peri-implantitis emerges as a major biological complication, threatening the longevity of restorations on Roxolid® implants and SLActive® surfaces. While current protocols rely on mechanical and chemical decontamination, the complete removal of bacterial biofilm on these micro-rough surfaces remains a major clinical challenge. This study specifically addresses this obstacle by exploring the potential of microwave argon plasma, an innovative physical technology aimed at disrupting complex microbial communities.

Objective and mechanisms of action tested

The objective of this work is to evaluate the bacterio-inhibitory efficacy of cold plasma in a 3D experimental model simulating a mandibular socket. The authors seek to quantify the effect of the plasma on Streptococcus mutans NBIMCC 1786, a reference oral pathogen. The central hypothesis is based on the ability of reactive oxygen and nitrogen species (RONS) generated by the plasma to induce lethal oxidative and nitrosative stress to the cell, measured here by the protein modification marker 3-nitrotyrosine. The study thus analyses the post-exposure recovery dynamics as a function of dose and time to validate the viability of this approach in peri-implant conditions.

Experimental design and simulation model

This in vitro study is based on a 3D-printed mandibular segment model, simulating a clinical bone socket. The device accommodates a Straumann BLX RB implant (16 mm x 4 mm) made of Roxolid® alloy (85% titanium, 15% zirconium). The SLActive® surface, selected for its sandblasted and acid-etched microtopography, exhibits high surface energy and hydrophilicity promoting protein adsorption.

Microbial models studied

The protocol compares two strains with distinct biological characteristics to evaluate the response to treatment:

• Streptococcus mutans NBIMCC 1786: opportunistic oral pathogen, facultative anaerobe and extracellular matrix producer.
• Chromohalobacter canadensis NBIMCC 9077: Gram-negative extremophile bacterium, moderate halophile (optimal growth at 8-10% NaCl), used as a comparative model for its cellular resilience in hostile environments.

Exposure protocol and analysis

The experiment uses a low-temperature microwave argon plasma for the decontamination of the implant surface. The analysis focuses on the following points:

• Evaluation of the bacterio-inhibitory effect according to a dose-time relationship.
• Study of post-exposure recovery dynamics.
• Measurement of oxidative and nitrosative stress induced by reactive oxygen and nitrogen species (RONS) generated by plasma.
• Identification of 3-nitrotyrosine formation as a marker of protein modification and cellular apoptosis.

Epidemiological data and characterisation of the experimental model

The data compiled in this study highlight the magnitude of the clinical challenge posed by peri-implant pathologies. The analysed systematic reviews and epidemiological surveys report prevalence rates of peri-implantitis ranging between 40% and 45%. These figures, although variable depending on the diagnostic thresholds used, confirm the major socio-economic impact of this complication during the clinical lifespan of dental restorations.

Distribution of bacterial strains

The study focuses on Streptococcus mutans, identified as a key player in the architecture of dental plaque due to its ability to convert sucrose into extracellular glucan polymers. The distribution of S. mutans serotypes isolated from human dental plaque, reported by the authors, follows a specific pattern:

This microbiological profile is complemented by the use of Chromohalobacter canadensis, a moderate halophilic extremophile, serving as a comparative model to evaluate resistance to plasma treatments. The latter exhibits optimal growth at NaCl concentrations of 8 to 10%, within a pH range of 5.0 to 10.0.

Characterisation of the implant and substrate

The experimental model uses a Straumann BLX RB implant (16 mm / 4 mm) whose physicochemical properties are decisive for bacterial adhesion. The Roxolid® alloy used consists of:

• 85% Titanium (Ti)
• 15% Zirconium (Zr)

This composition combines the biocompatibility of titanium with the increased mechanical strength of zirconium. The SLActive® surface, characterised by a sandblasted and acid-etched microtopography, exhibits high surface energy and marked hydrophilicity, favouring the rapid adsorption of proteins but also posing a challenge for the complete decontamination of bacterial biofilms.

Conclusion

The study emphasises that despite current technologies, the complete elimination of biofilms on moderate and rough surfaces remains a major challenge. The use of microwave argon plasma emerges as an innovative approach to disrupt these complex ecosystems without altering the properties of the implant.

A promising physical alternative to chemical decontamination

The efficacy of microwave argon plasma on Streptococcus mutans biofilms highlights the potential of this technology in the treatment of peri-implantitis. This study demonstrates the plasma's ability to induce oxidative and nitrosative stress via the generation of reactive oxygen and nitrogen species (RONS). For the clinician, these results are significant: the plasma acts as a physical disrupting agent capable of reaching the micro-crevices of modified titanium surfaces, where traditional chemotherapeutic agents and mechanical debridement often show their limitations.

However, the significance of these findings must be tempered by the simplified nature of the experimental model used. Although the study validates the bactericidal mechanism of action, the use of a single-species culture does not reflect the ecological complexity and resilience of the polymicrobial biofilms encountered in real clinical settings. Furthermore, the post-exposure recovery dynamics and the dose-time relationship warrant further investigation to optimise chairside decontamination protocols.

Compared to implantoplasty methods or the use of antiseptics, low-temperature plasma offers a less invasive approach to preserve the integrity of the implant surface while aiming for re-osseointegration. These data confirm that, despite the experimental stage, plasma represents a serious avenue to overcome the challenges posed by modified and rough surfaces, particularly vulnerable to bacterial recolonisation.

Summary of the challenges and experimental model

Faced with a peri-implantitis prevalence reaching 45%, this study evaluates the efficacy of a microwave argon plasma on a 3D model of a Roxolid implant (85% Ti, 15% Zr) with an SLActive surface. The approach specifically targets S. mutans, whose serotype c represents 75% of clinical strains and acts as a biofilm architect via the production of glucans and acidification of the environment.

In practical terms, for the practitioner:

• Systematic vigilance: Anticipate a risk of biological complication in nearly one in two patients, requiring a rigorous maintenance protocol from the time of loading.
• Early biofilm targeting: The control of S. mutans is decisive; its neutralisation prevents the formation of the extracellular matrix that protects more aggressive pathogens.
• Limitations of conventional methods: On high-energy surfaces (SLActive), mechanical decontamination alone is often insufficient; cold plasma technologies are emerging as a promising physical adjunct to treat the complex microtopography.

Technical glossary of the study

Streptococcus mutans (NBIMCC 1786): Gram-positive facultative anaerobic coccus, identified as a major aetiological agent of caries. It plays a key role in biofilm architecture through its ability to convert sucrose into extracellular glucan polymers, creating a resilient matrix that promotes plaque maturation.

Chromohalobacter canadensis (NBIMCC 9077): Gram-negative aerobic bacterium, extreme halophile (optimal growth at 8-10% NaCl). It serves here as a comparative model to evaluate the plasma resistance of an organism adapted to extreme environmental conditions.

3-nitrotyrosine: Specific biomarker of protein modification resulting from nitrosative stress. In this study, its formation is used as a potential indicator of apoptosis induction following plasma exposure.

Acid tolerance response: Transcriptional and physiological adaptive mechanism enabling microorganisms to survive drops in pH. This process includes cytoplasmic buffering and modification of the fatty acid composition of the cell membrane.

Microwave argon plasma: Low-temperature cold plasma technology used for decontamination. It generates active species capable of disrupting bacterial biofilms on titanium surfaces, without excessive thermal damage.

Acidogenicity: Metabolic capacity of a bacterium to convert a wide range of carbohydrates into organic acids, contributing to the creation of a low-pH ecosystem favouring peri-implant biological complications.

Aciduricity: Biological property enabling a microorganism to survive and grow in highly acidic pH conditions, a crucial virulence factor for the persistence of pathogenic biofilms.

Chemoorganotrophy: Metabolic mode of organisms (such as Chromohalobacter canadensis) that derive their energy and carbon from the oxidation of organic compounds, reflecting their physiological adaptation capabilities.

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