An In Vitro Study of Local Oxygen Therapy as Adjunctive Antimicrobial Therapeutic Option for Patients with Periodontitis

Periodontitis is a common global disease caused by bacterial dysbiosis leading to tissue destruction, and it is strongly associated with anaerobic bacterial colonization. Therapeutic strategies such as oxygen therapy have been developed to positively influence the dysbiotic microbiota, and the use of oxygen-releasing substances may offer an added benefit of avoiding systemic effects commonly associated with antibiotics taken orally or hyperbaric oxygen therapy. Therefore, the oxygen release of calcium peroxide (CaO₂) was measured using a dissolved oxygen meter, and CaO₂ solutions were prepared by dissolving autoclaved CaO₂ in sterile filtered and deionized water. The effects of CaO₂ on planktonic bacterial growth and metabolic activity, as well as on biofilms of Streptococcus oralis and Porphyromonas gingivalis, were investigated through experiments conducted under anaerobic conditions. The objective of this study was to investigate the potential of CaO₂ as an antimicrobial agent for the treatment of periodontitis. Results showed that CaO₂ selectively inhibited the growth and viability of P. gingivalis (p < 0.001) but had little effect on S. oralis (p < 0.01), indicating that CaO₂ has the potential to selectively affect both planktonic bacteria and mono-species biofilms of P. gingivalis. The results of this study suggest that CaO₂ could be a promising antimicrobial agent with selective activity for the treatment of periodontitis.

Antiplanktonic and Antibiofilm Activity of Rheum palmatum against Streptococcus oralis and Porphyromonas gingivalis

Periodontitis and peri-implantitis are inflammatory conditions with a high global prevalence. Oral pathogens such as Porphyromonas gingivalis play a crucial role in the development of dysbiotic biofilms associated with both diseases. The aim of our study was to identify plant-derived substances which mainly inhibit the growth of “disease promoting bacteria”, by comparing the effect of Rheum palmatum root extract against P. gingivalis and the commensal species Streptococcus oralis. Antiplanktonic activity was determined by measuring optical density and metabolic activity. Antibiofilm activity was quantified using metabolic activity assays and live/dead fluorescence staining combined with confocal laser scanning microscopy. At concentrations of 3.9 mg/L, R. palmatum root extract selectively inhibited planktonic growth of the oral pathogen P. gingivalis, while not inhibiting growth of S. oralis. Selective effects also occurred in mature biofilms, as P. gingivalis was significantly more stressed and inhibited than S. oralis. Our studies show that low concentrations of R. palmatum root extract specifically inhibit P. gingivalis growth, and offer a promising approach for the development of a potential topical agent to prevent alterations in the microbiome due to overgrowth of pathogenic P. gingivalis.

Antimicrobial agents in dental restorative materials: a on polymerization, short-term drug release and biological impact

With the aim to design bioactive dental restorative material, the present study investigated the influence of the antimicrobial agents chlorhexidine diacetate (CHX) and octinidine (di)hydrochloride (ODH) when incorporated in two different materials. Selected parameters were polymerization enthalpy, short-term drug release, and the effect on Streptococcus mutans as well as human gingival fibroblasts. Samples were made by mixing a nano-hybrid ormocer (O) and a methacrylate-based nano-hybrid composite (C), each with a mass fraction of 2% CHX or ODH. Release profiles and concentrations of active agents from the resins were assessed, and the cell proliferation of human gingival fibroblasts as well as Streptococcus mutans cultured with the eluates were evaluated. The influence on polymerization was assessed by means of differential scanning calorimetry. Both drugs, especially ODH, showed a decreasing effect on polymerization enthalpies associated with a lowered crosslinking degree. At the same time ODH appeared to be released more persistently than CHX. Moreover, ODH was more efficient with regard to bacteria growth inhibition but also more cytotoxic in terms of reduction of cell viability. ODH is deemed more appropriate for application in a dental resin-based drug delivery system, because of the more persistent drug release than seen for CHX.

Evaluation of biofilm colonization on multi-part dental implants in a rat model

Background

Peri-implant mucositis and peri-implantitis are highly prevalent biofilm-associated diseases affecting the tissues surrounding dental implants. As antibiotic treatment is ineffective to fully cure biofilm mediated infections, antimicrobial modifications of implants to reduce or prevent bacterial colonization are called for. Preclinical in vivo evaluation of the functionality of new or modified implant materials concerning bacterial colonization and peri-implant health is needed to allow progress in this research field. For this purpose reliable animal models are needed.

Methods

Custom made endosseous dental implants were installed in female Sprague Dawley rats following a newly established three-step implantation procedure. After healing of the bone and soft tissue, the animals were assigned to two groups. Group A received a continuous antibiotic treatment for 7 weeks, while group B was repeatedly orally inoculated with human-derived strains of Streptococcus oralis, Fusobacterium nucleatum and Porphyromonas gingivalis for six weeks, followed by 1 week without inoculation. At the end of the experiment, implantation sites were clinically assessed and biofilm colonization was quantified via confocal laser scanning microscopy. Biofilm samples were tested for presence of the administered bacteria via PCR analysis.

Results

The inner part of the custom made implant screw could be identified as a site of reliable biofilm formation in vivo. S. oralis and F. nucleatum were detectable only in the biofilm samples from group B animals. P. gingivalis was not detectable in samples from either group. Quantification of the biofilm volume on the implant material revealed no statistically significant differences between the treatment groups. Clinical inspection of implants in group B animals showed signs of mild to moderate peri-implant mucositis (4 out of 6) whereas the mucosa of group A animals appeared healthy (8/8). The difference in the mucosa health status between the treatment groups was statistically significant (p = 0.015).

Conclusions

We developed a new rodent model for the preclinical evaluation of dental implant materials with a special focus on the early biofilm colonization including human-derived oral bacteria. Reliable biofilm quantification on the implant surface and the symptoms of peri-implant mucositis of the bacterially inoculated animals will serve as a readout for experimental evaluation of biofilm-reducing modifications of implant materials.

The Influence of Connection on the Microleakage Development of Implant- Supported Fixed Bridges

PURPOSE

If bacteria penetrate through the implant-abutment connection, they may initiate inflammatory reactions in the peri-implant tissue. It seems that the type of connection plays a key role in the development of peri-implantitis. The aim of the present in vitro study was to compare the microleakage of implant-supported fixed complete arch bridges at the levels of abutment and implant.

METHODS

Ten identical polyurethane model bases containing six implants each were produced using an edentulous model of the upper jaw. These models were prepared with two types of implant-supported complete arch prostheses. Five specimens were fixed at implant level and five at abutment level. The inner parts implants were inoculated with Escherichia coli (E.coli). Each implant was surrounded with closed bacteria-proof vessels to observe bacterial migration from the inner parts of implants to the nutrient solution. Samples of nutrient solution were taken at different time points up to 2 to 10 days and colony forming units were determined.

RESULTS

The bacterial accumulation in the implant-supported bridges at the implant level was significantly lower than at the abutment-level (p=0.00953).

CONCLUSION

For implant-supported fixed complete arch prostheses, bacterial accumulation was lower at the implant level than at the abutment-level.

Plant-based oral care product exhibits antibacterial effects on different stages of oral multispecies biofilm development in vitro

Background

Excessive biofilm formation on surfaces in the oral cavity is amongst the main reasons for severe infection development like periodontitis and peri-implantitis. Mechanical biofilm removal as well as the use of adjuvant antiseptics supports the prevention of pathogenic biofilm formation. Recently, the antibacterial effect of the oral care product REPHA-OS^®, based on medicinal plant extracts and essential oils, has been demonstrated on oral pathogens grown on agar plates. In the present study, the effectiveness of the product on medical relevant oral biofilm development should be demonstrated for the first time.

Methods

An established in vitro oral multispecies biofilm, composed of Streptococcus oralis, Actinomyces naeslundii, Veillonella dispar and Porphyromonas gingivalis, was used to analyze the antibacterial effect of different REPHA-OS^® concentrations on planktonic bacteria, biofilm formation and mature biofilms. It was quantified using metabolic activity assays and live/dead fluorescence staining combined with three-dimensional confocal laser-scanning microscopy. Additionally, effects on species distribution inside the biofilm were assessed by means of quantitative real-time PCR.

Results

REPHA-OS^® showed statistically significant antimicrobial effects on all stages of biofilm development: a minimal inhibitory concentration of 5% could be detected for both, for planktonic bacteria and for biofilm formation. Interestingly, only a slightly higher concentration of 10% was necessary to completely kill all bacteria in mature biofilms also. In contrast, an influence on the biofilm matrix or the species distribution could not be observed. The effect could be attributed to the herbal ingredients, not to the contained ethanol.

Conclusion

The strong antibacterial effect of REPHA-OS^® on different stages of oral biofilm development strengthens its application as an alternative adjuvant in oral care therapies.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12903-021-01504-4.

Liquid-Infused Structured Titanium Surfaces: Antiadhesive Mechanism to Repel Streptococcus oralis Biofilms

To combat implant-associated infections, there is a need for novel materials which effectively inhibit bacterial biofilm formation. In the present study, the antiadhesive properties of titanium surface functionalization based on the "slippery liquid-infused porous surfaces" (SLIPS) principle were demonstrated and the underlying mechanism was analyzed. The immobilized liquid layer was stable over 13 days of continuous flow in an oral flow chamber system. With increasing flow rates, the surface exhibited a significant reduction in attached biofilm of both the oral initial colonizer  Streptococcus oralis and an oral multispecies biofilm composed of S. oralis, Actinomyces naeslundii, Veillonella dispar, and Porphyromonas gingivalis. Using single cell force spectroscopy, reduced S. oralis adhesion forces on the lubricant layer could be measured. Gene expression patterns in biofilms on SLIPS, on control surfaces, and expression patterns of planktonic cultures were also compared. For this purpose, the genome of S. oralis strain ATCC 9811 was sequenced using PacBio Sequel technology. Even though biofilm cells showed clear changes in gene expression compared to planktonic cells, no differences could be detected between bacteria on SLIPS and on control surfaces. Therefore, it can be concluded that the ability of liquid-infused titanium to repel S. oralis biofilms is mainly due to weakened bacterial adhesion to the underlying liquid interface.

Development and characterization of an oral multispecies biofilm implant flow chamber model

Peri-implant infections are the most common cause of implant failure in modern dental implantology. These are caused by the formation of biofilms on the implant surface and consist of oral commensal and pathogenic bacteria, which harm adjacent soft and hard tissues and may ultimately lead to implant loss. In order to improve the clinical situation, there has to be a better understanding of biofilm formation on abiotic surfaces. Therefore, we successfully developed a system to cultivate an oral multispecies biofilm model in a flow chamber system, optimized for the evaluation of biofilm formation on solid materials by direct microscopic investigation. The model contains four relevant oral bacterial species: Streptococcus oralis, Actinomyces naeslundii, Veillonella dispar and Porphyromonas gingivalis in ratios similar to the native situation. The reliability of the developed “Hanoverian Oral Multispecies Biofilm Implant Flow Chamber” (HOBIC) model was verified. Biofilm volume and live/dead distribution within biofilms were determined by fluorescence staining and confocal laser scanning microcopy (CLSM). The individual species distribution was analyzed using quantitative real time PCR with propidium monoazide pretreatment (PMA-qRT-PCR) and by urea-NaCl fluorescence in situ hybridization (urea-NaCl-FISH). This in vitro model may be used to analyze biofilm formation on dental implants in more detail and to develop future implant systems with improved material properties.

An oral multispecies biofilm model for high content screening applications

Peri-implantitis caused by multispecies biofilms is a major complication in dental implant treatment. The bacterial infection surrounding dental implants can lead to bone loss and, in turn, to implant failure. A promising strategy to prevent these common complications is the development of implant surfaces that inhibit biofilm development. A reproducible and easy-to-use biofilm model as a test system for large scale screening of new implant surfaces with putative antibacterial potency is therefore of major importance. In the present study, we developed a highly reproducible in vitro four-species biofilm model consisting of the highly relevant oral bacterial species Streptococcus oralis, Actinomyces naeslundii, Veillonella dispar and Porphyromonas gingivalis. The application of live/dead staining, quantitative real time PCR (qRT-PCR), scanning electron microscopy (SEM) and urea-NaCl fluorescence in situ hybridization (urea-NaCl-FISH) revealed that the four-species biofilm community is robust in terms of biovolume, live/dead distribution and individual species distribution over time. The biofilm community is dominated by S. oralis, followed by V. dispar, A. naeslundii and P. gingivalis. The percentage distribution in this model closely reflects the situation in early native plaques and is therefore well suited as an in vitro model test system. Furthermore, despite its nearly native composition, the multispecies model does not depend on nutrient additives, such as native human saliva or serum, and is an inexpensive, easy to handle and highly reproducible alternative to the available model systems. The 96-well plate format enables high content screening for optimized implant surfaces impeding biofilm formation or the testing of multiple antimicrobial treatment strategies to fight multispecies biofilm infections, both exemplary proven in the manuscript.