Effects of Antimicrobial Agents Used for Dental Treatments: Impacts on the Human Oral Ecosystem and the Resistome

Antimicrobial resistance (AMR) is a major public health concern, especially with regard to bacterial resistance to antibiotics. Dentists are responsible for approximately 10% of all antibiotic prescriptions. In addition, there seems to be a lack of awareness of potential resistance toward antiseptics and biocides such as chlorhexidine digluconate (CHX) or cetylpyridinium chloride (CPC), which are commonly used in dental practice but also included in over-the-counter products. In comparison to the gut microbiome, only a small number of studies have investigated the impact of antibiotics on the oral microbiome. Amoxicillin is a commonly prescribed antibiotic in dentistry, often used in combination with metronidazole. Several studies have addressed its impact on the oral microbiome. Similarly, the effects of ciprofloxacin, clindamycin, cephazolin, and benzylpenicillin have also been examined in various studies. However, due to variations in study designs, it is difficult to compare the effects of antibiotics on the oral microbiota, and conclusions can only be drawn at the phyla level. In contrast, studies on CPC and CHX have also focused on the genus level. The oral resistome mainly contains genes involved in resistance to macrolides, MLSB (macrolide, lincosamide, and streptogramin B), lincosamide and streptogramin A, fluoroquinolone, tetracycline, or penicillin. The oral cavity therefore serves as a reservoir for antibiotic resistance genes (ARGs), which are of crucial importance both for inflammations in the oral cavity and for the treatment of the entire human organism. Therefore, dentists must weigh up the benefits and risks of using antibiotics very carefully.

Bacteremia caused by Veillonella parvula: Two case reports and a review of the literature

Veillonella parvula is a non-motile gram-negative coccus that forms part of the normal microbiota in several body sites and which has been rarely isolated as cause of infections in human population, particularly in bacteremias. Here we give the overview of characteristics of genus Veillonella and the summary of its role in infections, particularly in bacteremia. We additionally report two patients with bacteremia due to V. parvula. Two sets of blood cultures of each patient yielded a pure culture of an anaerobic microorganism identified as V. parvula by MALDI-TOF MS, and confirmed by 16S rRNA gene sequencing. The two patients were male and one of them had risk factors for anaerobic bacteremia. The isolates were susceptible to most antibiotics and the outcome was successful in both patients. Bacteremia due to V. parvula is still rare. MALDI-TOF MS appear to be an excellent tool for the correct identification of these species.

Biofilm volume and acidification within initial biofilms formed in situ on buccally and palatally exposed bracket material

PURPOSE

Acidification by bacterial biofilms at the bracket/tooth interface is one of the most common problems in fixed orthodontic treatments, which can lead to white spot lesions (WSL) and caries. As lingual brackets were shown to exhibit reduced WSL formation clinically, the aim of this in situ study was to compare initial intraoral biofilm formation and acidification on bracket-like specimens placed buccally and palatally in the upper jaw as a possible cause for this observation.

METHODS

Intraoral biofilm was collected from splints equipped with buccally and palatally exposed test specimens, which were worn by 12 volunteers for a total of 48 h. The test specimens consisted of standard bracket material cylinders on top of a hydroxyapatite disc to represent the bracket/tooth interface. They were analyzed for three-dimensional biofilm volume and live/dead distribution by fluorescence staining and confocal laser scanning microscopy as well as for acidification by fluorescence-based pH ratiometry.

RESULTS

Similar general biofilm morphology with regard to volume and viability could be detected for buccally and palatally exposed specimens. For pH values, biofilms from both positions showed increased acidification at the bottom layer. Interestingly, the pH value at the top layers of the biofilms was slightly lower on palatally than on buccally exposed specimens, which may likely be due to anatomic conditions.

CONCLUSION

Based on the results of this study, initial intraoral biofilm formation and acidification is almost similar on the bracket material/biomimetic tooth interface when placed buccally or palatally in the upper jaw. As lingual brackets were shown to exhibit reduced WSL formation clinically, future studies should investigate further factors like bracket geometry.

Interactions and effects of a stannous-containing sodium fluoride dentifrice on oral pathogens and the oral microbiome

Numerous studies have investigated the effects of stannous ions on specific microbes and their efficacy in reducing dental plaque. Nonetheless, our understanding of their impact on the oral microbiome is still a subject of ongoing exploration. Therefore, this study sought to evaluate the effects of a stannous-containing sodium fluoride dentifrice in comparison to a zinc-containing sodium fluoride dentifrice and a control group on intact, healthy oral biofilms. Utilizing the novel 2bRAD-M approach for species-resolved metagenomics, and FISH/CLSM with probes targeting periodontal and caries associated species alongside Sn2+ and Zn2+ ions, we collected and analyzed in situ biofilms from 15 generally healthy individuals with measurable dental plaque and treated the biofilms with dentifrices to elucidate variations in microbial distribution. Although significant shifts in the microbiome upon treatment were not observed, the use of a stannous-containing sodium fluoride dentifrice primarily led to an increase in health-associated commensal species and decrease in pathogenic species. Notably, FISH/CLSM analysis highlighted a marked reduction in representative species associated with periodontitis and caries following treatment with the use of a stannous-containing sodium fluoride dentifrice, as opposed to a zinc-containing sodium fluoride dentifrice and the control group. Additionally, Sn2+ specific intracellular imaging reflected the colocalization of Sn2+ ions with P. gingivalis but not with other species. In contrast, Zn2+ ions exhibited non-specific binding, thus suggesting that Sn2+ could exhibit selective binding toward pathogenic species. Altogether, our results demonstrate that stannous ions could help to maintain a healthy oral microbiome by preferentially targeting certain pathogenic bacteria to reverse dysbiosis and underscores the importance of the continual usage of such products as a preventive measure for oral diseases and the maintenance of health.

Optimizing the use of low-frequency ultrasound for bacterial detachment of in vivo biofilms in dental research-a methodological study

OBJECTIVES

Low-frequency, low-intensity ultrasound is commonly utilized in various dental research fields to remove biofilms from surfaces, but no clear recommendation exists in dental studies so far. Therefore, this study aims to optimize the sonication procedure for the dental field to efficiently detach bacteria while preserving viability.

MATERIALS AND METHODS

Initial biofilm was formed in vivo on bovine enamel slabs (n = 6) which were worn by four healthy participants for 4 h and 24 h. The enamel slabs covered with biofilm were then ultrasonicated ex vivo for various time periods (0, 1, 2, 4, 6 min). Colony-forming units were determined for quantification, and bacteria were identified using MALDI-TOF. Scanning electron microscopic images were taken to also examine the efficiency of ultrasonications for different time periods.

RESULTS

Ultrasonication for 1 min resulted in the highest bacterial counts, with at least 4.5-fold number compared to the non-sonicated control (p < 0.05). Most bacteria were detached within the first 2 min of sonication, but there were still bacteria detached afterwards, although significantly fewer (p < 0.0001). The highest bacterial diversity was observed after 1 and 2 min of sonication (p < 0.03). Longer sonication periods negatively affected bacterial counts of anaerobes, Gram-negative bacteria, and bacilli. Scanning electron microscopic images demonstrated the ability of ultrasound to desorb microorganisms, as well as revealing cell damage and remaining bacteria.

CONCLUSIONS

With the use of low-frequency, low-intensity ultrasound, significantly higher bacterial counts and diversity can be reached. A shorter sonication time of 1 min shows the best results overall.

CLINICAL RELEVANCE

This standardization is recommended to study initial oral biofilms aged up to 24 h to maximize the outcome of experiments and lead to better comparability of studies.

Aspects of oral streptococcal metabolic diversity: Imagining the landscape beneath the fog

It is widely acknowledged that the human-associated microbial community influences host physiology, systemic health, disease progression, and even behavior. There is currently an increased interest in the oral microbiome, which occupies the entryway to much of what the human initially encounters from the environment. In addition to the dental pathology that results from a dysbiotic microbiome, microbial activity within the oral cavity exerts significant systemic effects. The composition and activity of the oral microbiome is influenced by (1) host-microbial interactions, (2) the emergence of niche-specific microbial "ecotypes," and (3) numerous microbe-microbe interactions, shaping the underlying microbial metabolic landscape. The oral streptococci are central players in the microbial activity ongoing in the oral cavity, due to their abundance and prevalence in the oral environment and the many interspecies interactions in which they participate. Streptococci are major determinants of a healthy homeostatic oral environment. The metabolic activities of oral Streptococci, particularly the metabolism involved in energy generation and regeneration of oxidative resources vary among the species and are important factors in niche-specific adaptations and intra-microbiome interactions. Here we summarize key differences among streptococcal central metabolic networks and species-specific differences in how the key glycolytic intermediates are utilized.

Direct and indirect effects of different dentifrices on the initial bacterial colonization of enamel in situ overnight

OBJECTIVE

The aim of this study was to investigate the direct and indirect influence of fluoridated toothpastes and fluoride-free toothpaste with hydroxyapatite (HAP) as active ingredient on initial bacterial colonization on enamel in situ.

METHODS

For this clinical-experimental pilot study, eight subjects were instructed to brush their teeth with three different toothpastes (Elmex^® : 1400 ppm AmF, Meridol^® : 1400 ppm AmF +SnF2, Karex^® : HAP), using each for two consecutive days. As a control, brushing without toothpaste was performed. To evaluate bacterial colonization, subject wore splints with buccally placed bovine enamel platelets overnight. Two modes were tested. In a first pass (regimen A), the splints were inserted after toothbrushing to examine the indirect effects of the dentifrices. In order to investigate the direct effects, the specimens were brushed in situ in a second pass (regimen B). Biofilm formation was visualized and quantified using fluorescence microscopy (DAPI and BacLight) and transmission electron microscopy (TEM).

RESULTS

For brushing regimen A (indirect effect of dentifrices), no statistical differences were detected between any of the tested dentifrices or the control. Likewise, no statistically significant differences were recorded for brushing regimen B (direct effect of dentifrices). Furthermore, no differences between the different brushing techniques were determined with regard to the ultrastructure of the overnight biofilm.

CONCLUSION

Within the limitations of the present pilot study, it can be concluded that in patients with good oral hygiene, dentifrices and their chemical composition have no statistically significant effect on the initial bacterial colonization of enamel platelets in situ, irrespectively of the mode of application.

Biodentine Inhibits the Initial Microbial Adhesion of Oral Microbiota In Vivo

This study aimed to evaluate the in vivo initial microbial adhesion of oral microorganisms on the biomaterial Biodentine compared to MTA and AH Plus. Cylindrical samples of the materials were prepared, and dentin slabs served as a control. An individual intraoral lower jaw splint served as a carrier for the samples and was worn by six volunteers. The specimens were worn for 120 min. Adherent bacteria were quantified by determining the colony-forming units (CFUs), while the visualization and quantification of total adherent microorganisms were facilitated by using DAPI and live/dead staining combined with fluorescence microscopy. Bovine dentin had a significantly higher number of aerobic CFUs compared to Biodentine (p = 0.017) and MTA (p = 0.013). The lowest amounts of DAPI-stained adherent microorganisms were quantified for Biodentine (15% ± 9%) and the control (18% ± 9%), while MTA showed the highest counts of initially adherent microorganisms (38% ± 10%). Significant differences were found for MTA and Biodentine (p = 0.004) as well as for MTA and the control (p = 0.021) and for AH Plus and the control (p = 0.025). Biodentine inhibited microbial adherence, thereby yielding an antimicrobial effectivity similar to that of MTA.

Extended biofilm formation time by Streptococcus sanguinis modifies its non-cariogenic behavior, in vitro

Although the commensal Streptococcus sanguinis [ S. sanguinis] is isolated from caries-free people, it can ferment carbohydrates producing acids. We aimed to characterize S. sanguinis cariogenic potential as a function of different enamel biofilm formation periods, in vitro. Saliva-coated enamel slabs were inoculated with S. sanguinis to form initial biofilms for 8, 12 or 16 h in presence of sucrose and followed by a period in medium with glucose for 16, 12 or 8 h, respectively, until completion of 24 h. To simulate cariogenic challenges, S. sanguinis biofilms were exposed to 10% sucrose for 5 minutes, 3x/day for 5 days. Biofilm biomass, viable cells, total proteins, intracellular and extracellular polysaccharides production, acidogenicity and enamel demineralization were determined. Biofilms of Streptococcus mutans [ S. mutans ] served as caries-positive control. Biofilms of S. sanguinis forming on enamel for 12 and 16 h showed higher demineralization than those formed during 8 h, but lower than S. mutans biofilms, regardless of the initial biofilm formation time. No differences were detected in the biofilm properties among the different biofilm formation times tested for S. sanguinis . Increased enamel initial biofilm formation time by S. sanguinis appears to induce a cariogenic potential, but lower than S. mutans .

On the Pathogenicity of the Oral Biofilm: A Critical Review from a Biological, Evolutionary, and Nutritional Point of View

Plaque control is one of the most recommended approaches in the prevention and therapy of caries and periodontal diseases. However, although most individuals in industrialized countries already perform daily oral hygiene, caries and periodontal diseases still are the most common diseases of mankind. This raises the question of whether plaque control is really a causative and effective approach to the prevention of these diseases. From an evolutionary, biological, and nutritional perspective, dental biofilms have to be considered a natural phenomenon, whereas several changes in human lifestyle factors during modern evolution are not “natural”. These lifestyle factors include the modern “Western diet” (rich in sugar and saturated fats and low in micronutrients), smoking, sedentary behavior, and continuous stress. This review hypothesizes that not plaque itself but rather these modern, unnatural lifestyle factors are the real causes of the high prevalence of caries and periodontal diseases besides several other non-communicable diseases. Accordingly, applying evolutionary and lifestyle medicine in dentistry would offer a causative approach against oral and common diseases, which would not be possible with oral hygiene approaches used on their own.

The Influence of Cement Removal Techniques on In Situ Bacterial Adhesion and Biodegradation at the Marginal Interface of Ceramic Laminates

Objectives

This in situ study aimed to analyze the influence of different resin cement removal techniques on bacterial adhesion and biodegradation at the marginal interface of ceramic laminates.

Methods and Materials

Eighty feldspathic ceramic (F) blocks were prepared and cemented onto bovine enamel slabs (7×2.5×2 mm). Excess cement was removed using a microbrush (MBR), a scalpel blade (SCP), or a Teflon spatula (TSP). For the biodegradation analysis, 40 disc-shaped resin cement specimens were prepared (7×1.5 mm) using a Teflon mold. The specimens were randomly allocated into two groups: (1) No finishing procedure (only Mylar strip), and (2) with finishing and polishing procedures using the Jiffy system (Ultradent, South Jordan, UT, USA) (n=20). The in situ phase consisted of using an intraoral palatal device by 20 volunteers for 7 days. Each device contained five cylindrical wells (8×3 mm), where three dental blocks and two cement specimens were included in the wells. Surface roughness (Ra) was measured using a contact profilometer. A micromorphological analysis was performed under a stereomicroscope and a scanning electron microscope. Bacterial adhesion was quantitated based on the number of colony-forming units (CFU/mL) and their biofilm development potential.

Results

The cement removal techniques directly affected surface roughness at the marginal interface (p&lt;0.001), and the SCP technique produced higher mean roughness, regardless of the surface area analyzed. Surface polishing protected cement specimens from further biodegradation (p=0.148). There were no differences in CFU counts between the groups after the in situ phase (p=0.96). All specimens showed CFU with a strong ability to develop a biofilm.

Conclusions

The techniques used for cement removal increased the surface roughness of ceramic laminates, particularly SCP, but they did not affect bacterial adhesion at the marginal interface. Surface polishing of the resin cement is recommended to mitigate biodegradation.

The antimicrobial effect of Rosmarinus officinalis extracts on oral initial adhesion ex vivo

Objective

In the last few decades, there has been a growing worldwide interest in the use of plant extracts for the prevention of oral diseases. The main focus of this interest lies in the identification and isolation of substances that limit the formation of microbial biofilm which plays a major role in the development of caries, periodontitis, and peri-implantitis. In this clinical ex vivo study, we investigated the antimicrobial effects of Rosmarinus officinalis extract against oral microorganisms within in situ initial oral biofilms.

Materials and methods

Initial in situ biofilm samples (2 h) from six healthy volunteers were treated ex vivo with R. officinalis extract at concentrations of 20 mg/ml and 30 mg/ml. The number of viable bacterial cells was determined by counting the colony-forming units. All surviving bacteria were isolated in pure cultures and identified using MALDI-TOF and biochemical testing procedures. Additionally, live/dead staining in combination with epifluorescence microscopy was used for visualizing the antimicrobial effects in the initial biofilms.

Results

The number of colony-forming units in the R. officinalis–treated biofilms was significantly lower than in the untreated controls (p < 0.001). The reduction range of log10 was 1.64–2.78 and 2.41–3.23 for aerobic and anaerobic bacteria, respectively. Regarding the bacterial composition, large intra- and interindividual variability were observed. Except for Campylobacter spp., the average amount of all bacterial taxa was lower after treatment with R. officinalis than in the untreated biofilms. A total of 49 different species were detected in the untreated biofilms, while only 11 bacterial species were detected in the R. officinalis–treated biofilms. Live/dead staining confirmed that the R. officinalis–treated biofilms had significantly lower numbers of surviving bacteria than the untreated biofilms.

Conclusions

The treatment with R. officinalis extract has a significant potential to eliminate microbial oral initial biofilms.

Clinical relevance

The results of this study encourage the use of R. officinalis extracts in biofilm control and thus in the treatment of caries and periodontitis as a herbal adjuvant to synthetic substances.

Bioadhesion on Textured Interfaces in the Human Oral Cavity-An In Situ Study

Extensive biofilm formation on materials used in restorative dentistry is a common reason for their failure and the development of oral diseases like peri-implantitis or secondary caries. Therefore, novel materials and strategies that result in reduced biofouling capacities are urgently sought. Previous research suggests that surface structures in the range of bacterial cell sizes seem to be a promising approach to modulate bacterial adhesion and biofilm formation. Here we investigated bioadhesion within the oral cavity on a low surface energy material (perfluorpolyether) with different texture types (line-, hole-, pillar-like), feature sizes in a range from 0.7–4.5 µm and graded distances (0.7–130.5 µm). As a model system, the materials were fixed on splints and exposed to the oral cavity. We analyzed the enzymatic activity of amylase and lysozyme, pellicle formation, and bacterial colonization after 8 h intraoral exposure. In opposite to in vitro experiments, these in situ experiments revealed no clear signs of altered bacterial surface colonization regarding structure dimensions and texture types compared to unstructured substrates or natural enamel. In part, there seemed to be a decreasing trend of adherent cells with increasing periodicities and structure sizes, but this pattern was weak and irregular. Pellicle formation took place on all substrates in an unaltered manner. However, pellicle formation was most pronounced within recessed areas thereby partially masking the three-dimensional character of the surfaces. As the natural pellicle layer is obviously the most dominant prerequisite for bacterial adhesion, colonization in the oral environment cannot be easily controlled by structural means.

Veillonellae: Beyond Bridging Species in Oral Biofilm Ecology

The genus Veillonella comprises 16 characterized species, among which eight are commonly found in the human oral cavity. The high abundance of Veillonella species in the microbiome of both supra- and sub-gingival biofilms, and their interdependent relationship with a multitude of other bacterial species, suggest veillonellae to play an important role in oral biofilm ecology. Development of oral biofilms relies on an incremental coaggregation process between early, bridging and later bacterial colonizers, ultimately forming multispecies communities. As early colonizer and bridging species, veillonellae are critical in guiding the development of multispecies communities in the human oral microenvironment. Their ability to establish mutualistic relationships with other members of the oral microbiome has emerged as a crucial factor that may contribute to health equilibrium. Here, we review the general characteristics, taxonomy, physiology, genomic and genetics of veillonellae, as well as their bridging role in the development of oral biofilms. We further discuss the role of Veillonella spp. as potential “accessory pathogens” in the human oral cavity, capable of supporting colonization by other, more pathogenic species. The relationship between Veillonella spp. and dental caries, periodontitis, and peri-implantitis is also recapitulated in this review. We finally highlight areas of future research required to better understand the intergeneric signaling employed by veillonellae during their bridging activities and interspecies mutualism. With the recent discoveries of large species and strain-specific variation within the genus in biological and virulence characteristics, the study of Veillonella as an example of highly adaptive microorganisms that indirectly participates in dysbiosis holds great promise for broadening our understanding of polymicrobial disease pathogenesis.

Antimicrobial Effects of Inula viscosa Extract on the In Situ Initial Oral Biofilm

Given the undesirable side effects of commercially used mouth rinses that include chemically synthesized antimicrobial compounds such as chlorhexidine, it is essential to discover novel antimicrobial substances based on plant extracts. The aim of this study was to examine the antimicrobial effect of Inula viscosa extract on the initial microbial adhesion in the oral cavity. Individual test splints were manufactured for the participants, on which disinfected bovine enamel samples were attached. After the initial microbial adhesion, the biofilm-covered oral samples were removed and treated with different concentrations (10, 20, and 30 mg/mL) of an I. viscosa extract for 10 min. Positive and negative controls were also sampled. Regarding the microbiological parameters, the colony-forming units (CFU) and vitality testing (live/dead staining) were examined in combination with fluorescence microscopy. An I. viscosa extract with a concentration of 30 mg/mL killed the bacteria of the initial adhesion at a rate of 99.99% (log₁₀ CFU value of 1.837 ± 1.54). Compared to the negative control, no killing effects were determined after treatment with I. viscosa extract at concentrations of 10 mg/mL (log₁₀ CFU value 3.776 ± 0.831; median 3.776) and 20 mg/mL (log₁₀ CFU value 3.725 ± 0.300; median 3.711). The live/dead staining revealed a significant reduction (p < 0.0001) of vital adherent bacteria after treatment with 10 mg/mL of I. viscosa extract. After treatment with an I. viscosa extract with a concentration of 30 mg/mL, no vital bacteria could be detected. For the first time, significant antimicrobial effects on the initial microbial adhesion in in situ oral biofilms were reported for an I. viscosa extract.

Hydroxyapatite-Based Solution as Adjunct Treatment for Biofilm Management: An In Situ Study

Synthetic hydroxyapatite-based solution is a bioinspired material that may present anti-adhesive properties, restraining the dental biofilm formation without causing adverse effects. This in situ study aims to evaluate the effects of three different hydroxyapatite (HAP) watery solutions as a mouthwash against biofilm adhesion on different dental material surfaces under oral conditions. Hence, four volunteers carried maxillary splints containing enamel, titanium, ceramics, and polymethyl-methacrylate resin (PMMA) samples. Three HAP watery solutions (5%) were prepared with HAP particles presenting different shapes and sizes (HAP I, HAP II, HAP III). During 24 h, the volunteers rinsed two times with one of the following selected tested solution: HAP I, HAP II, HAP III, water, or chlorhexidine 0.2% (CHX). The first rinse was performed 3 min after pellicle formation; the second rinse occurred after a 12 h interval. The surface analysis was performed by scanning electron microscopy (SEM), fluorescence microscopy (FM), and transmission electron microscopy (TEM). Statistical and microscopic analysis showed that most samples treated with any HAP solution revealed reduced biofilm coverage presenting comparable results to CHX treated samples, however without altering the microorganisms' viability. In conclusion, the results of this investigation showed that a pure hydroxyapatite-based mouthrinse could be a promising bioinspired adjunct solution for biofilm management.

The Influence of Modified Experimental Dental Resin Composites on the Initial In Situ Biofilm-A Triple-Blinded, Randomized, Controlled Split-Mouth Trial

The purpose of the study was to investigate the bacterial viability of the initial biofilm on the surface of experimental modified dental resin composites. Twenty-five healthy individuals with good oral hygiene were included in this study. In a split-mouth design, they received acrylic splints with five experimental composite resin specimens. Four of them were modified with either a novel polymeric hollow-bead delivery system or methacrylated polymerizable Irgasan (Antibacterial B), while one specimen served as an unmodified control (ST). A delivery system based on Poly-Pore^® was loaded with one of the active agents: Tego^® Protect 5000 (Antiadhesive A), Dimethicone (Antiadhesive B), or Irgasan (Antibacterial A). All study subjects refrained from toothbrushing during the study period. Specimens were detached from the splints after 8 h and given a live/dead staining before fluorescence microscopy. A Friedman test and a post hoc Nemenyi test were applied with a significance level at p < 0.05. In summary, all materials but Antibacterial B showed a significant antibacterial effect compared to ST. The results suggested the role of the materials’ chemistry in the dominance of cell adhesion. In conclusion, dental resin composites with Poly-Pore-loaded active agents showed antibacterial effectiveness in situ.

Depth distributions of signaling molecules in Pseudomonas aeruginosa biofilms mapped by confocal Raman microscopy

Pseudomonas aeruginosa is an opportunistic human pathogen implicated in both acute and chronic diseases, which resists antibiotic treatment, in part by forming physical and chemical barriers such as biofilms. Here, we explore the use of confocal Raman imaging to characterize the three-dimensional (3D) spatial distribution of alkyl quinolones (AQs) in P. aeruginosa biofilms by reconstructing depth profiles from hyperspectral Raman data. AQs are important to quorum sensing (QS), virulence, and other actions of P. aeruginosa. Three-dimensional distributions of three different AQs (PQS, HQNO, and HHQ) were observed to have a significant depth, suggesting 3D anisotropic shapes-sheet-like rectangular solids for HQNO and extended cylinders for PQS. Similar to observations from 2D imaging studies, spectral features characteristic of AQs (HQNO or PQS) and the amide I vibration from peptide-containing species were found to correlate with the PQS cylinders typically located at the tips of the HQNO rectangular solids. In the QS-deficient mutant lasIrhlI, a small globular component was observed, whose highly localized nature and similarity in size to a P. aeruginosa cell suggest that the feature arises from HHQ localized in the vicinity of the cell from which it was secreted. The difference in the shapes and sizes of the aggregates of the three AQs in wild-type and mutant P. aeruginosa is likely related to the difference in the cellular response to growth conditions, environmental stress, metabolic levels, or other structural and biochemical variations inside biofilms. This study provides a new route to characterizing the 3D structure of biofilms and shows the potential of confocal Raman imaging to elucidate the nature of heterogeneous biofilms in all three spatial dimensions. These capabilities should be applicable as a tool in studies of infectious diseases.

The influence of biofilm maturation on fluoride's anticaries efficacy

OBJECTIVES

(1) To explore the influence of biofilm maturation and timing of exposure on fluoride anticaries efficacy and (2) to explore biofilm recovery post-treatment.

METHODS

Bovine enamel specimens were utilized in a pH cycling model (28 subgroups [n = 18]). Each subgroup received different treatments [exposure]: sodium fluoride [NaF]; stannous fluoride [SnF₂]; amine fluoride [AmF]; and de-ionized water [DIW], at a specific period: early: days 1-4; middle: days 3-6; and late: days 7-10. During non-exposure periods, pH cycling included DIW instead of fluorides. Objective 1: part 1 (cycling for 4, 6, or 10 days). Part 2 (cycling for 10 days). Objective 2: early exposure: three sample collection time points (immediate, 3 days, and 6 days post-treatment); middle exposure: two sample collection time points (immediate, 4 days post-treatment). The enamel and biofilm were analyzed ([surface microhardness; mineral loss; lesion depth]; [lactate dehydrogenase enzyme activity; exopolysaccharide amount; viability]). Data were analyzed using ANOVA (p = 0.05).

RESULTS

Objective 1: Early exposure to fluorides produced protective effects against lesion progression in surface microhardness and mineral loss, but not for lesion depth. Objective 2: Early exposure slowed the demineralization process. SnF₂ and AmF were superior to NaF in reducing LDH and EPS values, regardless of exposure time. They also prevented biofilm recovery.

CONCLUSION

Earlier exposure to SnF₂ and AmF may result in less tolerant biofilm. Early fluoride treatment may produce a protective effect against demineralization. SnF₂ and AmF may be the choice to treat older biofilm and prevent biofilm recovery.

CLINICAL RELEVANCE

The study provides an understanding of biofilm-fluoride interaction with mature biofilm (e.g., hard-to-reach areas, orthodontic patients) and fluoride's sustainable effect hours/days after brushing.

Modification of the Lipid Profile of the Initial Oral Biofilm In Situ Using Linseed Oil as Mouthwash

Lipids are of interest for the targeted modification of oral bioadhesion processes. Therefore, the sustainable effects of linseed oil on the composition and ultrastructure of the in situ pellicle were investigated. Unlike saliva, linseed oil contains linolenic acid (18:3), which served as a marker for lipid accumulation. Individual splints with bovine enamel slabs were worn by five subjects. After 1 min of pellicle formation, rinses were performed with linseed oil for 10 min, and the slabs' oral exposure was continued for up to 2 or 8 h. Gas chromatography coupled with electron impact ionization mass spectrometry (GC-EI/MS) was used to characterize the fatty acid composition of the pellicle samples. Transmission electron microscopy was performed to analyze the ultrastructure. Extensive accumulation of linolenic acid was recorded in the samples of all subjects 2 h after the rinse and considerable amounts persisted after 8 h. The ultrastructure of the 2 h pellicle was less electron-dense and contained lipid vesicles when compared with controls. After 8 h, no apparent ultrastructural effects were visible. Linolenic acid is an excellent marker for the investigation of fatty acid accumulation in the pellicle. New preventive strategies could benefit from the accumulation of lipid components in the pellicle.

Modification of in situ Biofilm Formation on Titanium by a Hydroxyapatite Nanoparticle-Based Solution

Oral biofilms play an essential role on peri-implant disease development. Synthetic hydroxyapatite nanoparticles (nHAP) are a bioinspired material that has structural and functional similarities to dental enamel apatite and may provide preventive properties against biofilm formation. This study aimed to investigate the effects of an experimental nHAP solution on biofilm formation on polished and non-polished titanium under oral conditions. Five volunteers carried maxillary splints with non-polished and polished titanium and followed a 48 h rinsing protocol with the proposed nHAP solution, and with chlorhexidine 0.2% (CHX) and water, as controls. Samples were analyzed by fluorescence microscopy (FM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). FM showed a significant reduction of biofilms on polished samples treated with nHAP (p = 0.0485) compared with water, without differences between nHAP and CHX (p > 0.9999). Analyzing biofilm viability, polished samples rinsed with nHAP showed significantly fewer dead bacteria than CHX (p = 0.0079), but there was no significant difference in viability between polished samples rinsed with water and nHAP (p = 0.9268). A significantly higher biofilm coverage was observed on the non-polished surfaces compared to the polished surfaces when nHAP was applied (p = 0.0317). This difference between polished and non-polished surfaces was not significant when water (p = 0.1587) or CHX (p = 0.3413) rinsing were applied. SEM and TEM analysis supported the FM findings, that polished samples rinsed with nHAP presented fewer biofilm coverage compared to samples rinsed with water. In conclusion, the nHAP solution reduced the biofilm formation on polished Ti surfaces without altering bacterial viability, providing a novel approach for the management of biofilm formation on biomaterials.

Microbial Composition of Oral Biofilms after Visible Light and Water-Filtered Infrared a Radiation (VIS+wIRA) in Combination with Indocyanine Green (ICG) as Photosensitizer

In view of increasing antibiotic resistance, antimicrobial photodynamic therapy (aPDT) is an alternative treatment method used to eradicate the microbial community of oral biofilms that can be responsible for different oral infections. In order to investigate changes in the microbial composition after application of aPDT with visible light and water-filtered infrared A (VIS+wIRA) in combination with indocyanine green (ICG), oral microorganisms of the initial and mature biofilm were evaluated by mass spectrometry (MALDI-TOF-MS). To determine surviving microorganisms using MALDI-TOF-MS, an in situ biofilm was irradiated with VIS+wIRA for five minutes in the presence of ICG (300 and 450 µg/mL, respectively). Treatment with chlorhexidine (0.2%) served as positive control. Identified microorganisms of the initial biofilm treated with ICG showed a clear reduction in diversity. The microbial composition of the mature oral biofilm also showed changes after the implementation of aPDT, which mainly resulted in a shift in the percentage of bacterial species. The resulting destruction of the microbial balance within the oral biofilm by aPDT using VIS+wIRA and ICG can be seen as an advantageous supplementary approach in the adjunctive treatment of periodontitis and peri-implantitis.

The anti-caries efficacy of three fluoride compounds at increasing maturation of a microcosm biofilm

OBJECTIVE

To explore the anti-caries efficacy of three fluoride compounds at increasing maturation of a microcosm biofilm.

DESIGN

Microcosm biofilm, obtained from saliva collected from three donors (IRB #1406440799), was grown on enamel samples (n = 18/group) for 24-h (Brain Heart Infusion; 0.2 % sucrose). Then, pH cycling model started. Three maturations were explored (4d, 8d, and 12d). The pH cycling consisted of daily 2 × 5 min treatments (NaF, SnF₂, AmF: 287.5 ppm F, and de-ionized water [DIW]), 4 × 10 min remineralization (BHI, no sucrose, pH 7.0), and 3 × 2:15 h demineralization (BHI, 1% sucrose, pH 4.5). We analyzed the enamel (surface microhardness [VHN_change], integrated mineral loss [ΔZ], lesion depth [L]), and the biofilm (viability [log₁₀ CFU/mL], lactic acid production [LDH], and exopolysaccharide [EPS] amount). Data were analyzed using two-way ANOVA (p = 0.05).

RESULTS

The interaction between tested variables was significant for VHN_change, viability, LDH, EPS (p = 0.0354, p = 0.0001, p < 0.0001, p < 0.0001), but not for L (p = 0.2412) or ΔZ (p = 0.6811). LDH and EPS analyses exhibited more tolerance of mature biofilm against NaF (LDH and EPS p < 0.0001); NaF-treated groups demonstrated significantly lower results than the control in the 12d group. The effect of SnF₂ and AmF continued over time. VHN_change, L, and ΔZ: The effect of SnF₂ and AmF was higher than NaF and DIW. L and ΔZ did not result in significant differences over time (all treatments). Within each maturation, fluoride compounds demonstrated statistically significantly lower L and ΔZ values than DIW.

CONCLUSIONS

Biofilm's maturation may influence the selection of fluoride compounds to achieve an optimum cariostatic effect.

Influence of salivary conditioning and sucrose concentration on biofilm-mediated enamel demineralization

INTRODUCTION

The acquired pellicle formation is the first step in dental biofilm formation. It distinguishes dental biofilms from other biofilm types.

OBJECTIVE

To explore the influence of salivary pellicle formation before biofilm formation on enamel demineralization.

METHODOLOGY

Saliva collection was approved by Indiana University IRB. Three donors provided wax-stimulated saliva as the microcosm bacterial inoculum source. Acquired pellicle was formed on bovine enamel samples. Two groups (0.5% and 1% sucrose-supplemented growth media) with three subgroups (surface conditioning using filtered/pasteurized saliva; filtered saliva; and deionized water (DIW)) were included (n=9/subgroup). Biofilm was then allowed to grow for 48 h using Brain Heart Infusion media supplemented with 5 g/l yeast extract, 1 mM CaCl2.2H2O, 5% vitamin K and hemin (v/v), and sucrose. Enamel samples were analyzed for Vickers surface microhardness change (VHNchange), and transverse microradiography measuring lesion depth (L) and mineral loss (∆Z). Data were analyzed using two-way ANOVA.

RESULTS

The two-way interaction of sucrose concentration × surface conditioning was not significant for VHNchange (p=0.872), ∆Z (p=0.662) or L (p=0.436). Surface conditioning affected VHNchange (p=0.0079), while sucrose concentration impacted ∆Z (p<0.0001) and L (p<0.0001). Surface conditioning with filtered/pasteurized saliva resulted in the lowest VHNchange values for both sucrose concentrations. The differences between filtered/pasteurized subgroups and the two other surface conditionings were significant (filtered saliva p=0.006; DIW p=0.0075). Growing the biofilm in 1% sucrose resulted in lesions with higher ∆Z and L values when compared with 0.5% sucrose. The differences in ∆Z and L between sucrose concentration subgroups was significant, regardless of surface conditioning (both p<0.0001).

CONCLUSION

Within the study limitations, surface conditioning using human saliva does not influence biofilm-mediated enamel caries lesion formation as measured by transverse microradiography, while differences were observed using surface microhardness, indicating a complex interaction between pellicle proteins and biofilm-mediated demineralization of the enamel surface.

Antimicrobial Photoinactivation Using Visible Light Plus Water-Filtered Infrared-A (VIS + wIRA) and Hypericum Perforatum Modifies In Situ Oral Biofilms

Due to increasing antibiotic resistance, the application of antimicrobial photodynamic therapy (aPDT) is gaining increasing popularity in dentistry. The aim of this study was to investigate the antimicrobial effects of aPDT using visible light (VIS) and water-filtered infrared-A (wIRA) in combination with a Hypericum perforatum extract on in situ oral biofilms. The chemical composition of H. perforatum extract was analyzed using ultra-high-performance liquid chromatography coupled with high resolution mass spectrometry (UPLC-HRMS). To obtain initial and mature oral biofilms in situ, intraoral devices with fixed bovine enamel slabs (BES) were carried by six healthy volunteers for two hours and three days, respectively. The ex situ exposure of biofilms to VIS + wIRA (200 mWcm^-2) and H. perforatum (32 mg ml^-1, non-rinsed or rinsed prior to aPDT after 2-min preincubation) lasted for five minutes. Biofilm treatment with 0.2% chlorhexidine gluconate solution (CHX) served as a positive control, while untreated biofilms served as a negative control. The colony-forming units (CFU) of the aPDT-treated biofilms were quantified, and the surviving microorganisms were identified using MALDI-TOF biochemical tests as well as 16 S rDNA-sequencing. We could show that the H. perforatum extract had significant photoactivation potential at a concentration of 32 mg ml^-1. When aPDT was carried out in the presence of H. perforatum, all biofilms (100%) were completely eradicated (p = 0.0001). When H. perforatum was rinsed off prior to aPDT, more than 92% of the initial viable bacterial count and 13% of the mature oral biofilm were killed. Overall, the microbial composition in initial and mature biofilms was substantially altered after aPDT, inducing a shift in the synthesis of the microbial community. In conclusion, H. perforatum-mediated aPDT using VIS + wIRA interferes with oral biofilms, resulting in their elimination or the substantial alteration of microbial diversity and richness. The present results support the evaluation of H. perforatum-mediated aPDT for the adjunctive treatment of biofilm-associated oral diseases.

Biogeography of the Oral Microbiome: The Site-Specialist Hypothesis

Microbial communities are complex and dynamic, composed of hundreds of taxa interacting across multiple spatial scales. Advances in sequencing and imaging technology have led to great strides in understanding both the composition and the spatial organization of these complex communities. In the human mouth, sequencing results indicate that distinct sites host microbial communities that not only are distinguishable but to a meaningful degree are composed of entirely different microbes. Imaging suggests that the spatial organization of these communities is also distinct. Together, the literature supports the idea that most oral microbes are site specialists. A clear understanding of microbiota structure at different sites in the mouth enables mechanistic studies, informs the generation of hypotheses, and strengthens the position of oral microbiology as a model system for microbial ecology in general.

Intraoral appliances for in situ oral biofilm growth: a systematic review

Background: Oral biofilms are the root cause of major oral diseases. As in vitro biofilms are not representative of the intraoral milieu, various devices have been manufactured over the years to develop Appliance Grown Oral Biofilm (AGOB). Objective: To review various intraoral appliances used to develop AGOB for microbiological analysis, and to judge the optimal means for such analyses. Design: Four databases (PubMed, Science Direct, Scopus and Medline) were searched by two independent reviewers, and articles featuring the key words 'device' OR 'splint' OR 'appliance'; 'Oral biofilm' OR 'dental plaque'; 'in vivo' OR 'in situ'; 'Microbiology' OR 'Bacteria' OR 'microbiome'; were included. The standard Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) were adopted for data gathering. Results: Of the 517 articles which met the initial inclusion criteria, 24 were deemed eligible for review. The age of the AGOB, sampled at various intervals, ranged from 30 min to 28 days. The most commonly used microbiome analytical methods were fluorescence microscopy, total cell count using conventional, and molecular tools including Next Generation Sequencing (NGS) platforms. Conclusions: No uniformly superior method for collecting AGOB could be discerned. NGS platforms are preferable for AGOB analyses.

Inactivation of oral biofilms using visible light and water-filtered infrared A radiation and indocyanine green

Aim: To investigate the antimicrobial photodynamic therapy (aPDT) of visible light and water-filtered infrared A radiation in combination with indocyanine green (ICG) on planktonic oral microorganisms as well as on oral biofilm. Methods: The irradiation was conducted for 5 min in combination with ICG. Treatment with chlorhexidine served as a positive control. The number of colony forming units and bacterial vitality were quantified. Results: All tested bacterial strains and salivary bacteria were killed at a level of 3log_10. The colony forming units of the initial mature oral biofilms were strongly reduced. The high bactericidal effect of aPDT was confirmed by live/dead staining. Conclusion: The aPDT using visible light and water-filtered infrared A radiation and ICG has the potential to treat periodontitis and peri-implantitis.

Candida Interactions with the Oral Bacterial Microbiota

The human oral cavity is normally colonized by a wide range of microorganisms, including bacteria, fungi, Archaea, viruses, and protozoa. Within the different oral microenvironments these organisms are often found as part of highly organized microbial communities termed biofilms, which display consortial behavior. Formation and maintenance of these biofilms are highly dependent on the direct interactions between the different members of the microbiota, as well as on the released factors that influence the surrounding microbial populations. These complex biofilm dynamics influence oral health and disease. In the latest years there has been an increased recognition of the important role that interkingdom interactions, in particular those between fungi and bacteria, play within the oral cavity. Candida spp., and in particular C. albicans, are among the most important fungi colonizing the oral cavity of humans and have been found to participate in these complex microbial oral biofilms. C. albicans has been reported to interact with individual members of the oral bacterial microbiota, leading to either synergistic or antagonistic relationships. In this review we describe some of the better characterized interactions between Candida spp. and oral bacteria.

Comparison of initial oral microbiomes of young adults with and without cavitated dentin caries lesions using an in situ biofilm model

Dental caries is caused by acids released from bacterial biofilms. However, the in vivo formation of initial biofilms in relation to caries remains largely unexplored. The aim of this study was to compare the oral microbiome during the initial phase of bacterial colonization for individuals with (CC) and without (NC) cavitated dentin caries lesions. Bovine enamel slabs on acrylic splints were worn by the volunteers (CC: 14, NC: 13) for in situ biofilm formation (2 h, 4 h, 8 h, 1 ml saliva as reference). Sequencing of the V1/V2 regions of the 16S rRNA gene was performed (MiSeq). The relative abundances of individual operational taxonomic units (OTUs) were compared between samples from the CC group and the NC group. Random forests models were furthermore trained to separate the groups. While the overall heterogeneity did not differ substantially between CC and NC individuals, several individual OTUs were found to have significantly different relative abundances. For the 8 h samples, most of the significant OTUs showed higher relative abundances in the CC group, while the majority of significant OTUs in the saliva samples were more abundant in the NC group. Furthermore, using OTU signatures enabled a separation between both groups, with area-under-the-curve (AUC) values of ~0.8. In summary, the results suggest that initial oral biofilms provide the potential to differentiate between CC and NC individuals.

Salivary density of Streptococcus mutans and Streptococcus sobrinus and dental caries in children and adolescents with Down syndrome

Streptococcus mutans and Streptococcus sobrinus are strongly associated with dental caries. However, the relationship between oral streptococci and dental caries in children with Down syndrome is not well characterized.

Effect of Tannic Acid on the Protective Properties of the in situ Formed Pellicle

OBJECTIVES

In the present in situ/ex vivo study the impact of tannic acid on the erosion-protective properties of the enamel pellicle was tested. Additionally, the antiadherent and antibacterial effects of tannic acid were evaluated.

METHODS

The pellicle was formed in situ on bovine enamel samples fixed on individual splints worn by 6 subjects. Following 1 min of pellicle formation the volunteers rinsed for 10 min with tannic acid. After further oral exposure for 19 min, 109 min, and 8 h overnight, respectively, slabs were incubated in HCl ex vivo (pH 2.0, 2.3, 3.0) over 120 s. Subsequently, kinetics of calcium and phosphate release were measured photometrically. Samples after a 1-min fluoride mouth rinse as well as enamel samples with and without a 30-min in situ pellicle served as controls. Antiadherent effects were evaluated after a 1-min rinse with tannic acid and oral exposure of the slabs overnight. DAPI (4',6-diamidino-2-phenylindole) combined with concanavalin A staining and live/dead staining was used for fluorescence microscopic visualization and quantification of adherent bacteria and glucans. Modification of the pellicle's ultrastructure by tannic acid was evaluated by transmission electron microscopy (TEM).

RESULTS

Tannic acid significantly improved the erosion-protective properties of the pellicle in a pH-dependent manner. Bacterial adherence and glucan formation on enamel were significantly reduced after rinses with tannic acid as investigated by fluorescence microscopy. TEM imaging indicated that rinsing with tannic acid yielded a sustainable modification of the pellicle; it was distinctly more electron dense.

CONCLUSION

Tannic acid offers an effective and sustainable approach for the prevention of caries and erosion.

Occlusal Caries: Biological Approach for Its Diagnosis and Management

The management of occlusal caries still remains a major challenge for researchers as well as for general practitioners. The present paper reviews and discusses the most up-to-date knowledge and evidence of the biological principles guiding diagnosis, risk assessment, and management of the caries process on occlusal surfaces. In addition, it considers the whole spectrum of the caries process on occlusal surfaces, ranging from the molecular ecology of occlusal biofilms to the management of deep occlusal caries lesions. Studies using molecular methods with focus on biofilms in relation to occlusal caries should explore the relationship between the function and the structural composition of these biofilms to understand the role of occlusal biofilms in caries development. State-of-the-art measures to evaluate risk for occlusal caries lesion activity, caries incidence, and progression should include the assessment of the occlusal biofilm and the stage of tooth eruption. Careful clinical examination of non-cavitated lesions, including assessment of the lesion activity status, remains the major tool to determine the immediate treatment need and to follow on the non-operative treatment outcome. Even medium occlusal caries lesions in the permanent dentition may be treated by non-invasive fissure sealing. By extending the criteria for non-invasive treatments, traditional restoration of occlusal surfaces can be postponed or even avoided, and the dental health in children and adolescents can be improved. Selective removal (incomplete) to soft dentin in deep carious lesions has greater success rates than stepwise excavation. Selective (complete) removal to firm dentin has a lower success rate due to increased pulp exposure.

Devices for In situ Development of Non-disturbed Oral Biofilm. A Systematic Review

Objective: The aim of this review was to assess the types of devices used for in situ development of oral biofilm analyzed microbiologically.

Materials and Methods: A systematic search of the literature was conducted to identify all in situ studies of oral biofilm which used an oral device; the Ovid MEDLINE and EMBASE databases complemented with manual search were used. Specific devices used to microbiologically analyze oral biofilm in adults were included. After reading of the selected full texts, devices were identified and classified according to the oral cavity zone and manufacturing material. The “ideal” characteristics were analyzed in every group.

Results: The search provided 787 abstracts, of which 111 papers were included. The devices used in these studies were classified as palatal, lingual or buccal. The last group was sub-classified in six groups based on the material of the device. Considering the analyzed characteristics, the thermoplastic devices and the Intraoral Device of Overlaid Disk-holding Splints (IDODS) presented more advantages than limitations.

Conclusions: Buccal devices were the most commonly used for the study of in situ biofilm. The majority of buccal devices seemed to slightly affect the volunteer's comfort, the IDODS being the closest to the “ideal” model.

Clinical Relevance: New devices for in situ oral biofilm microbiological studies should take into account the possible effect of their design on the volunteer's comfort and biofilm formation.

Monitoring of extracellular pH in young dental biofilms grown in vivo in the presence and absence of sucrose

Background and objective

pH in dental biofilms is of central importance for the development of caries. We used the ratiometric pH-sensitive dye C-SNARF-4 in combination with digital image analysis to monitor extracellular pH in dental biofilms grown in situ with and without sucrose supply.

Design

Dental biofilms (48 h) from 10 individuals were collected on glass slabs mounted on intra-oral appliances. During growth, appliances were immersed extra-orally in either physiological saline or 4% sucrose for 2 min, eight times per day. Fluorescence emissions of C-SNARF-4 in deep layers of the biofilms were recorded ex vivo with confocal microscopy for 15 min or for 1 h after exposure to 0.4% glucose. Extracellular pH was determined ratiometrically using digital image analysis.

Results

Extracellular pH dropped rapidly in most examined sites after addition of glucose. Distinct pH microenvironments were observed within single biofilms. The variation in pH was similar between sites within the same biofilm and sites from different individuals. pH drop patterns did not differ between biofilms exposed to sucrose-free and sucrose-rich environments.

Conclusion

The present study is the first of its kind to apply the combination of pH ratiometry and digital image analysis to systematically record extracellular pH in intact dental biofilms from several individuals for up to 1 h. We observed highly heterogeneous pH landscapes and the presence of acidogenic microenvironments – ‘acidogenic hotspots’ – within the biofilms. The data suggest that pH drops in young (48 h) dental biofilms are independent of the sucrose supply during growth.

The Oral Microbiota

The oral microbiota represents an important part of the human microbiota, and includes several hundred to several thousand diverse species. It is a normal part of the oral cavity and has an important function to protect against colonization of extrinsic bacteria which could affect systemic health. On the other hand, the most common oral diseases caries, gingivitis and periodontitis are based on microorganisms. While (medical) research focused on the planktonic phase of bacteria over the last 100 years, it is nowadays generally known, that oral microorganisms are organised as biofilms. On any non-shedding surfaces of the oral cavity dental plaque starts to form, which meets all criteria for a microbial biofilm and is subject to the so-called succession. When the sensitive ecosystem turns out of balance - either by overload or weak immune system - it becomes a challenge for local or systemic health. Therefore, the most common strategy and the golden standard for the prevention of caries, gingivitis and periodontitis is the mechanical removal of this biofilms from teeth, restorations or dental prosthesis by regular toothbrushing.

Antimicrobial Photoinactivation Using Visible Light Plus Water-Filtered Infrared-A (VIS + wIRA) Alters In Situ Oral Biofilms

Recently, growing attention has been paid to antimicrobial photodynamic therapy (aPDT) in dentistry. Changing the microbial composition of initial and mature oral biofilm by aPDT using visible light plus water-filtered infrared-A wavelengths (VIS + wIRA) has not yet been investigated. Moreover, most aPDT studies have been conducted on planktonic bacterial cultures. Therefore, in the present clinical study we cultivated initial and mature oral biofilms in six healthy volunteers for 2 hours or 3 days, respectively. The biofilms were treated with aPDT using VIS+wIRA (200 mW cm^-2), toluidine blue (TB) and chlorine e6 (Ce6) for 5 minutes. Chlorhexidine treated biofilm samples served as positive controls, while untreated biofilms served as negative controls. After aPDT treatment the colony forming units (CFU) of the biofilm samples were quantified, and the surviving bacteria were isolated in pure cultures and identified using MALDI-TOF, biochemical tests and 16S rDNA-sequencing. aPDT killed more than 99.9% of the initial viable bacterial count and 95% of the mature oral biofilm in situ, independent of the photosensitizer. The number of surviving bacterial species was highly reduced to 6 (TB) and 4 (Ce6) in the treated initial oral biofilm compared to the 20 different species of the untreated biofilm. The proportions of surviving bacterial species were also changed after TB- and Ce6-mediated aPDT of the mature oral biofilm, resulting in a shift in the microbial composition of the treated biofilm compared to that of the control biofilm. In conclusion, aPDT using VIS + wIRA showed a remarkable potential to eradicate both initial and mature oral biofilms, and also to markedly alter the remaining biofilm. This encourages the clinical use of aPDT with VIS + wIRA for the treatment of periimplantitis and periodontitis.

In situ antibiofilm effect of glass-ionomer cement containing dimethylaminododecyl methacrylate

OBJECTIVE

The aim of this study was to investigate antibiofilm effects of a recently developed glass ionomer cement (GIC) containing dimethylaminododecyl methacrylate (DMADDM) under oral conditions.

METHODS

Biofilms were allowed to form in situ on GIC specimens (n=216) which contained DMADDM (1.1wt.% or 2.2wt.%). Samples without DMADDM served as control (n=108). GIC specimens were fixed on custom made splints and exposed to the oral cavity in six healthy volunteers for 24, 48 and 72h, respectively. Biofilm viability and coverage were analyzed by fluorescence microscopy (FM) and evaluated by red/green ratios and an established scoring system. Bacterial morphology and biofilm accumulation were determined by scanning electron microscopy (SEM). Additionally, material properties as surface charge density of quaternary ammonium groups, surface roughness and DMADDM release were recorded.

RESULTS

FM results showed a higher ratio (24h: 0%: 0.5, 1.1%: 1.2, 2.2%: 2.5) of red/green fluorescence on GIC samples containing DMADDM. Biofilm coverage and viability scores were significantly reduced (24h: q1/median/q3 for: 0%: 3/4/5, 1.1%: 2/3/3, 2.2%: 1/2/2) on DMADDM containing samples compared to controls after 24h as well as 48 and 72h in situ (p<0.05). While surface charge density of quaternary ammonium groups and DMADDM release increased with the DMADDM concentration, surface roughness was lowest on specimens containing 2.2wt.% DMADDM.

SIGNIFICANCE

An in situ dental biofilm model was used to evaluate the novel GIC containing DMADDM. This material strongly inhibited biofilms in situ and is promising to prevent bacterial colonization on the surface of restorations.

Biofilm growth mode promotes maximum carrying capacity and community stability during product inhibition syntrophy

Sulfate-reducing bacteria (SRB) can interact syntrophically with other community members in the absence of sulfate, and interactions with hydrogen-consuming methanogens are beneficial when these archaea consume potentially inhibitory H₂ produced by the SRB. A dual continuous culture approach was used to characterize population structure within a syntrophic biofilm formed by the SRB Desulfovibrio vulgaris Hildenborough and the methanogenic archaeum Methanococcus maripaludis. Under the tested conditions, monocultures of D. vulgaris formed thin, stable biofilms, but monoculture M. maripaludis did not. Microscopy of intact syntrophic biofilm confirmed that D. vulgaris formed a scaffold for the biofilm, while intermediate and steady-state images revealed that M. maripaludis joined the biofilm later, likely in response to H₂ produced by the SRB. Close interactions in structured biofilm allowed efficient transfer of H₂ to M. maripaludis, and H₂ was only detected in cocultures with a mutant SRB that was deficient in biofilm formation (ΔpilA). M. maripaludis produced more carbohydrate (uronic acid, hexose, and pentose) as a monoculture compared to total coculture biofilm, and this suggested an altered carbon flux during syntrophy. The syntrophic biofilm was structured into ridges (∼300 × 50 μm) and models predicted lactate limitation at ∼50 μm biofilm depth. The biofilm had structure that likely facilitated mass transfer of H₂ and lactate, yet maximized biomass with a more even population composition (number of each organism) when compared to the bulk-phase community. Total biomass protein was equivalent in lactate-limited and lactate-excess conditions when a biofilm was present, but in the absence of biofilm, total biomass protein was significantly reduced. The results suggest that multispecies biofilms create an environment conducive to resource sharing, resulting in increased biomass retention, or carrying capacity, for cooperative populations.

Effect of CPP/ACP on initial bioadhesion to enamel and dentin in situ

The present in situ study investigated the influence of a preparation containing CPP/ACP (caseinphosphopeptide-amorphous calcium phosphate) (GC Tooth mousse) on initial bacterial colonization of enamel and dentin. Therefore, pellicle formation was performed in situ on bovine enamel and dentin specimens fixed to individual upper jaw splints worn by 8 subjects. After 1 min of pellicle formation GC Tooth mousse was used according to manufacturer's recommendations. Rinses with chlorhexidine served as positive controls. Specimens carried without any rinse served as negative controls. After 8 h overnight exposure of the splints, bacterial colonization was quantified by fluorescence microscopy (DAPI and BacLight live/dead staining). Additionally, the colony forming units (CFU) were determined after desorption. Furthermore, the effects on Streptococcus mutans bacteria were tested in vitro (BacLight). There was no significant impact of CPP/ACP on initial bacterial colonization proved with DAPI and BacLight. Determination of CFU showed statistical significance for CPP/ACP to reduce bacterial adherence on enamel. The in vitro investigation indicated no antimicrobial effects for CPP/ACP on Streptococcus mutans suspension. Under the chosen conditions, CPP/ACP (GC Tooth mousse) had no significant impact on initial biofilm formation on dental hard tissues. The tested preparation cannot be recommended for biofilm management.

Novel Broad-Spectrum Antimicrobial Photoinactivation of In Situ Oral Biofilms by Visible Light plus Water-Filtered Infrared A

Antimicrobial photodynamic therapy (APDT) has gained increased attention as an alternative treatment approach in various medical fields. However, the effect of APDT using visible light plus water-filtered infrared A (VIS + wIRA) on oral biofilms remains unexplored. For this purpose, initial and mature oral biofilms were obtained in situ; six healthy subjects wore individual upper jaw acrylic devices with bovine enamel slabs attached to their proximal sites for 2 h or 3 days. The biofilms were incubated with 100 μg ml(-1) toluidine blue O (TB) or chlorin e6 (Ce6) and irradiated with VIS + wIRA with an energy density of 200 mW cm(-2) for 5 min. After cultivation, the CFU of half of the treated biofilm samples were quantified, whereas following live/dead staining, the other half of the samples were monitored by confocal laser scanning microscopy (CLSM). TB- and Ce6-mediated APDT yielded a significant decrease of up to 3.8 and 5.7 log10 CFU for initial and mature oral biofilms, respectively. Quantification of the stained photoinactivated microorganisms confirmed these results. Overall, CLSM revealed the diffusion of the tested photosensitizers into the deepest biofilm layers after exposure to APDT. In particular, Ce6-aided APDT presented elevated permeability and higher effectiveness in eradicating 89.62% of biofilm bacteria compared to TB-aided APDT (82.25%) after 3 days. In conclusion, antimicrobial photoinactivation using VIS + wIRA proved highly potent in eradicating oral biofilms. Since APDT excludes the development of microbial resistance, it could supplement the pharmaceutical treatment of periodontitis or peri-implantitis.

In Situ Surface Biodegradation of Restorative Materials

This study aimed to evaluate the surface characteristics of restorative materials (roughness, hardness, chemical changes by energy-dispersive spectroscopy [EDX], and scanning electron microscopy [SEM]) submitted to in situ biodegradation. Fifteen discs of each material (IPS e.max [EM], Filtek Supreme [FS], Vitremer [VI], Ketac Molar Easymix [KM], and Amalgam GS-80 [AM]) were fabricated in a metallic mold (4.0 mm × 1.5 mm). Roughness, hardness, SEM, and EDX were then evaluated. Fifteen healthy volunteers used a palatal device containing one disc of each restorative material for seven days. After the biodegradation, the roughness, hardness, SEM, and EDX were once again evaluated. Data obtained from the roughness and hardness evaluations were submitted to Kolmogorov-Smirnov and Tukey-Kramer tests (p&lt;0.05). All esthetic restorative materials showed a significant increase in the roughness after biodegradation. Before biodegradation, significant differences in the hardness among the materials were seen: EM&gt;AM&gt;FS&gt;KM&gt;VI. After biodegradation, the hardness was significantly altered among the materials studied: EM&gt;AM&gt;FS=KM&gt;VI, along with a significant increase in the hardness for AM, KM, and VI. SEM images indicated degradation on the surface of all materials, showing porosities, cracks, and roughness. Furthermore, after biodegradation, FS showed the presence of Cl, K, and Ca on the surface, while F was not present on the VI and KM surfaces. EM and AM did not have alterations in their chemical composition after biodegradation. It was concluded that the dental biofilm accumulation in situ on different restorative materials is a material-dependent parameter. Overall, all materials changed after biodegradation: esthetic restorative materials showed increased roughness, confirmed by SEM, and the ionomer materials and silver amalgam showed a significantly higher hardness. Finally, the initial chemical composition of the composite resin and ionomer materials evaluated was significantly altered by the action of the biofilm in situ.

Multiplex fluorescence in situ hybridization (M-FISH) and confocal laser scanning microscopy (CLSM) to analyze multispecies oral biofilms

Multiplex fluorescence in situ hybridization (M-FISH) constitutes a favorable microbiological method for the analysis of spatial distribution of highly variable phenotypes found in multispecies oral biofilms. The combined use of confocal laser scanning microscopy (CLSM) produces high-resolution three-dimensional (3D) images of individual bacteria in their natural environment. Here, we describe the application of M-FISH on early (Streptococcus spp., Actinomyces naeslundii) and late colonizers (Fusobacterium nucleatum, Veillonella spp.) of in situ-formed oral biofilms, the acquisition of CLSM images, as well as the qualitative and quantitative analysis of these digitally obtained and processed images.

Initial Bacterial Adhesion on Different Yttria-Stabilized Tetragonal Zirconia Implant Surfaces in Vitro

Bacterial adhesion to implant biomaterials constitutes a virulence factor leading to biofilm formation, infection and treatment failure. The aim of this study was to examine the initial bacterial adhesion on different implant materials in vitro. Four implant biomaterials were incubated with Enterococcus faecalis, Staphylococcus aureus and Candida albicans for 2 h: 3 mol % yttria-stabilized tetragonal zirconia polycrystal surface (B1a), B1a with zirconium oxide (ZrO₂) coating (B2a), B1a with zirconia-based composite coating (B1b) and B1a with zirconia-based composite and ZrO₂ coatings (B2b). Bovine enamel slabs (BES) served as control. The adherent microorganisms were quantified and visualized using scanning electron microscopy (SEM); DAPI and live/dead staining. The lowest bacterial count of E. faecalis was detected on BES and the highest on B1a. The fewest vital C. albicans strains (42.22%) were detected on B2a surfaces, while most E. faecalis and S. aureus strains (approximately 80%) were vital overall. Compared to BES; coated and uncoated zirconia substrata exhibited no anti-adhesive properties. Further improvement of the material surface characteristics is essential.

Bacterial viability and physical properties of antibacterially modified experimental dental resin composites

PURPOSE

To investigate the antibacterial effect and the effect on the material properties of a novel delivery system with Irgasan as active agent and methacrylated polymerizable Irgasan when added to experimental dental resin composites.

MATERIALS AND METHODS

A delivery system based on novel polymeric hollow beads, loaded with Irgasan and methacrylated polymerizable Irgasan as active agents were used to manufacture three commonly formulated experimental resin composites. The non-modified resin was used as standard (ST). Material A contained the delivery system providing 4 % (m/m) Irgasan, material B contained 4 % (m/m) methacrylated Irgasan and material C 8 % (m/m) methacrylated Irgasan. Flexural strength (FS), flexural modulus (FM), water sorption (WS), solubility (SL), surface roughness Ra, polymerization shrinkage, contact angle Θ, total surface free energy γS and its apolar γS (LW), polar γS (AB), Lewis acid γS (+)and base γS (-) term as well as bacterial viability were determined. Significance was p < 0.05.

RESULTS

The materials A to C were not unacceptably influenced by the modifications and achieved the minimum values for FS, WS and SL as requested by EN ISO 4049 and did not differ from ST what was also found for Ra. Only A had lower FM than ST. Θ of A and C was higher and γS (AB) of A and B was lower than of ST. Materials A to C had higher γS (+) than ST. The antibacterial effect of materials A to C was significantly increased when compared with ST meaning that significantly less vital cells were found.

CONCLUSION

Dental resin composites with small quantities of a novel antibacterially doped delivery system or with an antibacterial monomer provided acceptable physical properties and good antibacterial effectiveness. The sorption material being part of the delivery system can be used as a vehicle for any other active agent.