Transmission electron microscopy comparison of methods for collecting in situ formed enamel pellicle

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.

Salivary pellicle modulates biofilm formation on titanium surfaces

OBJECTIVES

The present study aimed to evaluate the potential of the salivary pellicle (SP) formed on titanium (Ti) surfaces to modulate the formation of a biofilm composed of Streptococcus gordonii, Actinomyces naeslundii, Fusobacterium nucleatum, and Porphyromonas gingivalis.

MATERIALS AND METHODS

Ti substrates were incubated for 2 h with a pool of saliva samples obtained from 10 systemically and periodontally healthy subjects. Enamel substrates were included as a biological reference. Scanning electron microscopy (SEM) and Raman spectroscopy analysis were used to analyze the formation of the salivary pellicle. After the SP formation, the surfaces were incubated for 12 h with a mix of Streptococcus gordonii, Actinomyces naeslundii, Fusobacterium nucleatum, and Porphyromonas gingivalis. The number of bacterial cells attached to each surface was determined by the XTT assay while bacterial viability was analyzed by fluorescence microscopy using the LIVE/DEAD® BacLightTM kit.

RESULTS

The SEM and Raman spectroscopy analysis confirmed the presence of a salivary pellicle formed on the tested surfaces. Regarding the biofilm formation, the presence of the SP decreases the number of the bacterial cells detected in the test surfaces, compared with the uncover substrates. Even more, the SP-covered substrates showed similar bacterial counts in both Ti and enamel surfaces, meaning that the physicochemical differences of the substrates were less determinant than the presence of the SP. While on the SP-uncover substrates, differences in the bacterial adhesion patterns were directly related to the physicochemical nature of the substrates.

CONCLUSIONS

The salivary pellicle was the main modulator in the development of the biofilm consisting of representative oral bacteria on the Ti substrates.

CLINICAL RELEVANCE

The results of this study provide valuable information on the modulatory effect of the salivary pellicle on biofilm formation; such information allows us to understand better the events involved in the formation of oral biofilms on Ti dental implants.

Rinsing solutions containing natural extracts and fluoride prevent enamel erosion in vitro

BACKGROUND

Polyphenols interact with salivary proteins and thus can improve the pellicle's erosion protective properties. This effect could be exploited to create rinsing solutions with polyphenols as active ingredients for erosion prevention. Different from the current gold standard for erosion protective rinsing solutions, these rinses would not rely on stannous ions. This would offer alternatives for patients with concerns regarding the composition of rinsing solutions and preferring bio-products.

OBJECTIVE

To develop an erosion-preventive rinsing solution containing natural polyphenol-rich extracts.

METHODOLOGY

Solutions were prepared with polyphenols from either grapeseed extract or cranberry extract, 500 ppm fluoride added, and additionally flavors and sweeteners. Controls were deionized water, 500 ppm fluoride solution, and the gold standard rinse in the field (Sn2+/F-). In total, 135 enamel specimens (n=15/group) were subjected to five cycles of salivary pellicle formation (30 min, 37°C), modification with the solutions (2 min, 25°C), further salivary pellicle formation (60 min, 37°C), and erosive challenge (1 min, 1% citric acid, pH 3.6). Relative surface microhardness (rSMH), surface reflection intensity (rSRI), and amount of calcium release (CaR) were investigated. Data were analyzed with Kruskal-Wallis and Wilcoxon rank sum tests (α=0.05).

RESULTS

The polyphenol solutions containing fluoride, as well as additional flavors, protected enamel better than fluoride alone, and similar to the Sn2+/F- solution, when investigating both rSMH and CaR. When measuring rSRI, Sn2+/F- showed the best protection, while the polyphenol solutions were similar to fluoride.

CONCLUSION

For two of the three assessed parameters (rSMH and CaR), both developed polyphenol-rich rinsing solutions were able to protect enamel from erosion, improving/potentializing the effect of fluoride and matching the protection offered by the current gold standard rinsing solution.

New insights into the protective effect of statherin-derived peptide for different acquired enamel pellicle formation times on the native human enamel surfaces

OBJECTIVES

This study evaluated the protective impact of acquired enamel pellicle (AEP) engineering with statherin-derived peptide (StatpSpS), considering different AEP formation times.

DESIGN

A total of 120 native human enamel specimens were divided into 2 main groups: 1) No AEP engineering and 2) AEP engineering with StatpSpS (pretreatment for 1 min; 37 °C, under agitation). Each group was further divided into 4 subgroups: No pellicle, or 1, 60-and-120 min AEP formation times (human saliva; 37 °C). The specimens were then subjected to an erosive challenge (1% citric acid; pH 3.6; 1 min; 25 °C). This procedure was repeated for 5 cycles. Relative surface reflection intensity (%SRI) was measured and scanning electron microscopy (SEM) of the enamel surface was done.

RESULTS

All AEP engineering groups protected against initial dental erosion in comparison with No pellicle (p < 0.001), likewise all groups with AEP, independent of engineering or formation times (p 0.001). Furthermore, engineering with StatpSpS even without the presence of AEP protected the enamel when compared to the No engineering/No pellicle group (p < 0.0001). No difference was observed regarding the protection from the different AEP formation times (p > 0.05). Regarding the SEM analysis, in the "No AEP engineering & No AEP" group, a more severe effect of citric acid was observed, with more enamel prism heads and scratches on the surface when compared with the other groups.

CONCLUSIONS

AEP provides almost instant protection at formation times even as short as 1 min, protecting the native enamel against erosion. Treatment with StatpSpS by itself provides similar protection as the AEP.

Synergistic effect between plant extracts and fluoride to protect against enamel erosion: An in vitro study

Polyphenol-rich solutions, such as plant extracts and teas, can modify the salivary pellicle and improve the protection against dental erosion. In this study, we further explored how these polyphenol-rich plant extracts solutions behave in the presence of fluoride. We distributed enamel specimens into 9 groups (n = 15): Control_No_F- (Deionized water); Control_F- (500 ppm F-), Grape_Seed_No_F- (Grape seed extract), Grape_Seed_F- (Grape seed extract + 500 ppm F-), Grapefruit_Seed_No_F- (Grapefruit seed extract), Grapefruit_Seed_F- (Grapefruit seed extract + 500 ppm F-), Blueberry_No_F- (Blueberry extract), Blueberry_F- (Blueberry extract + 500 ppm F-), and Sn2+/F-_Rinse (commercial solution containing 800 ppm Sn2+ and 500 ppm F-). The specimens were submitted to 5 cycles (1 cycle per day), and each cycle consisted of: salivary pellicle formation (human saliva, 30 min, 37°C), modification of the pellicle (2 min, 25°C), pellicle formation (60 min, 37°C), and an erosive challenge (1 min, citric acid). Between cycles, the specimens were kept in a humid chamber. Relative surface hardness (rSH), relative surface reflection intensity (rSRI) and calcium released to the acid were analysed, using general linear models, and Kruskal-Wallis with post-hoc Dunn's tests. We observed that the presence of fluoride in synergy with the extract solutions provided better protection than the groups containing extract or fluoride only. For rSH, we observed a significant main effect of extracts (F(4,117) = 9.20; p<0.001) and fluoride (F(1,117) = 511.55; p<0.001), with a significant interaction (F(3,117) = 6.71; p<0.001). Grape_Seed_F- showed the best protection, better than fluoride, and Sn2+/F-_Rinse. Calcium results also showed greater protection for the groups containing fluoride, whereas for rSRI, despite a significant interaction between extract and fluoride (F(3,117) = 226.05; p<0.001), the differences between the groups were not as clearly observed. We conclude that polyphenols from plant extracts, when combined with fluoride, improve the protective effect of salivary pellicles against enamel erosion.

Pellicle modification with natural bioproducts: Influence on tooth color under erosive conditions

Salivary pellicle was modified with bioproducts and we assessed the change in tooth color and the protection of enamel to erosion. Human enamel specimens were assigned to one of three solutions: grape seed extract or black tea (bioproducts), or deionized water (negative control); after which one half the specimens underwent erosive challenges. The specimens underwent 15 cycles involving salivary pellicle formation (10 min, 37°C), incubation in solution (2 min, 25°C), subsequent pellicle formation (90 min, 37°C). Half of the specimens was kept in a humid chamber and the other half was submitted to erosion (2 min, 1% citric acid). After 15 such cycles, the pellicle was removed. Tooth color and the surface reflection intensity were assessed after every five cycles and after pellicle removal. For non-eroded specimens, the exposure to bioproducts promoted significantly greater color change than the deionized water, with increases in yellow appearance. After pellicle removal, the color was similar in all non-eroded specimens. The bioproducts increased the surface reflection intensity over cycles. For the erosion-exposed specimens, erosion itself resulted in color change. Black tea and deionized water resulted in increased yellow appearance. Exposure to the bioproducts resulted in higher relative surface reflection intensity values over time, but only grape seed extract resulted in higher relative surface reflection intensity value at the time of pellicle removal. The bioproducts caused transient staining effect, which was reduced after pellicle removal. For enamel submitted to erosion, grape seed extract resulted in less color change and better protection of enamel against erosion than black tea or water.

Influence of periodic milk or cream treatment on the anti-erosive potential of the acquired enamel pellicle

OBJECTIVE

The purpose of the present study was to assess the anti-erosive potential of the acquired enamel pellicle formed in situ under the influence of periodic milk or cream treatment.

METHODS

The pellicle was formed on bovine enamel specimens in the oral cavity at buccal and palatal sites of upper molars in 6 subjects, using removable acrylic splints. During 6-h of intraoral exposure, splints were removed from the oral cavity every 25 min, treated with milk or cream for 5 min, and subsequently re-inserted into the oral cavity. After 6 h, pellicle covered specimens were immersed in citric acid (0.1 or 1.0 %) for 1 min, and processed for measurement of surface microhardness, determination of calcium release by atomic absorption spectroscopy, scanning and transmission electron microscopy. Statistical analysis was performed with SAS.

RESULTS

Statistical analysis did not indicate major differences between erosive surface alterations on enamel specimens covered by pellicles treated with cream or milk, and those covered by control pellicles. In addition, TEM analysis did not reveal any differences concerning the ultrastructure of the different pellicle treatments during acid exposure. All pellicles were dissolved in part after exposure to 0.1 % citric acid and were nearly completely removed after treatment with 1.0% citric acid.

CONCLUSIONS

It is concluded that periodic treatment with milk or cream during pellicle formation in situ does not improve the protective potential of the acquired enamel pellicle against erosion.

CLINICAL SIGNIFICANCE

Modification of the pellicle by consumption of milk or cream prior to an acidic challenge cannot sufficiently protect enamel from erosion.

The dentin pellicle - A neglected topic in dental research

OBJECTIVE

All soft and solid surfaces exposed to the oral cavity are covered by an acquired pellicle. While the pellicle adsorbed on enamel is well researched, only limited data are available on the dentin pellicle. The purpose of the present review is to summarize studies considering the composition, structure and properties of the dentin pellicle and compare them with the current state of research on enamel pellicle.

METHODS

The literature search was conducted using Medline database and Google Scholar, including checking reference lists of journal articles by handsearching. Thereby, 19 studies were included in the present review.

RESULTS AND CONCLUSION

The dentin pellicle has a similar ultrastructure to the enamel pellicle, which is up to 1 μm thick depending on pellicle formation time and localization in the oral cavity. In contrast, due to the lack of studies on the dentin pellicle regarding its composition and properties, a comparison to the enamel pellicle is difficult. So far, only one study showed anti-abrasive properties and data on anti-erosive properties were controversial. Despite becoming more and more clinically relevant due to the increasing frequency of dentin exposure, the dentin pellicle is largely unexplored. For further investigations it is not only necessary to standardize dentin specimens, but also to assess fundamental research on dentin itself, as its complex morphology and composition may have a crucial influence on pellicle formation. Furthermore, a more detailed knowledge of the dentin pellicle may also reveal target sites for modification in favor of its protective properties.

Analysing Complex Oral Protein Samples: Complete Workflow and Case Analysis of Salivary Pellicles

Studies on small quantity, highly complex protein samples, such as salivary pellicle, have been enabled by recent major technological and analytical breakthroughs. Advances in mass spectrometry-based computational proteomics such as Multidimensional Protein Identification Technology have allowed precise identification and quantification of complex protein samples on a proteome-wide scale, which has enabled the determination of corresponding genes and cellular functions at the protein level. The latter was achieved via protein-protein interaction mapping with Gene Ontology annotation. In recent years, the application of these technologies has broken various barriers in small-quantity-complex-protein research such as salivary pellicle. This review provides a concise summary of contemporary proteomic techniques contributing to (1) increased complex protein (up to hundreds) identification using minute sample sizes (µg level), (2) precise protein quantification by advanced stable isotope labelling or label-free approaches and (3) the emerging concepts and techniques regarding computational integration, such as the Gene Ontology Consortium and protein-protein interaction mapping. The latter integrates the structural, genomic, and biological context of proteins and genes to predict protein interactions and functional connections in a given biological context. The same technological breakthroughs and computational integration concepts can also be applied to other low-volume oral protein complexes such as gingival crevicular or peri-implant sulcular fluids.

Effect of nonionic and amphoteric surfactants on salivary pellicles reconstituted in vitro

Surfactants are important components of oral care products. Sodium dodecyl sulfate (SDS) is the most common because of its foaming properties, taste and low cost. However, the use of ionic surfactants, especially SDS, is related to several oral mucosa conditions. Thus, there is a high interest in using non-ionic and amphoteric surfactants as they are less irritant. To better understand the performance of these surfactants in oral care products, we investigated their interaction with salivary pellicles i.e., the proteinaceous films that cover surfaces exposed to saliva. Specifically, we focused on pentaethylene glycol monododecyl ether (C12E5) and cocamidopropyl betaine (CAPB) as model nonionic and amphoteric surfactants respectively, and investigated their interaction with reconstituted salivary pellicles with various surface techniques: Quartz Crystal Microbalance with Dissipation, Ellipsometry, Force Spectroscopy and Neutron Reflectometry. Both C12E5 and CAPB were gentler on pellicles than SDS, removing a lower amount. However, their interaction with pellicles differed. Our work indicates that CAPB would mainly interact with the mucin components of pellicles, leading to collapse and dehydration. In contrast, exposure to C12E5 had a minimal effect on the pellicles, mainly resulting in the replacement/solubilisation of some of the components anchoring pellicles to their substrate.

The salivary pellicle on dental biomaterials

The salivary pellicle, an adlayer formed by adsorption of salivary components on teeth and dental biomaterials, has direct consequences on basic outcomes of dentistry. Here, we provide an overview of salivary pellicle formation processes with a critical focus on dental biomaterials. We describe and critique the array of salivary pellicle measurement techniques. We also discuss factors that may affect salivary pellicle formation and the heterogeneity of the published literature describing salivary pellicle formation on dental biomaterials. Finally, we survey the many effects salivary pellicles have on dental biomaterials and highlight its implications on design criteria for dental biomaterials. Future investigations may lead to rationally designed dental biomaterials to control the salivary pellicle and enhance material function and patient outcomes.

Effects of Octenidine on the Formation and Disruption of Dental Biofilms: An Exploratory In Situ Study in Healthy Subjects

Dental biofilms are highly structured, complex multispecies communities that, if left untreated, lead to severe oral complications such as caries and periodontal diseases. Therefore, antibiofilm agents are often recommended for both preventive and therapeutic measures. However, biofilm management can be challenging due to the low sensitivity of biofilms to antimicrobial treatments. Octenidine dihydrochloride (OCT) is a highly effective antibacterial agent. Because the OCT antibiofilm efficacy has not been studied in situ, this exploratory crossover study aimed to evaluate the effects of OCT mouth rinsing on biofilm formation and on the disruption of mature biofilms. Moreover, a comparison to the gold-standard chlorhexidine (CHX) was conducted. The biofilms were formed intraorally by 5 healthy volunteers on enamel specimens fixed to acrylic splints. For biofilm formation analysis, OCT, CHX, or water rinses were applied for 30 s every 12 h. The samples evaluation took place at 24-and 48-h time points. For biofilm disruption analysis, sample assessment was performed before and directly after the first OCT or CHX rinse on 48-h mature biofilms. A second rinse was carried out 12 h later. The last assessment was applied to 72-h mature biofilms. The biofilms were analyzed by fluorescence microscopy and transmission electron microscopy. The results showed OCT significantly reducing biofilm formation and bacterial vitality in situ. Simultaneously, the biofilm thickness was strongly decreased. Moreover, a single application of OCT to a 48-h mature biofilm induced substantial biofilm disruption. In addition, the efficacy of OCT compared favorably to CHX. These findings show that OCT rinses prevent biofilm formation and disrupt preexisting mature biofilms formed by healthy subjects. This work suggests that OCT might be used for dental biofilm management as a part of the medical treatment of oral diseases. Future studies with a larger subject heterogeneity and number are needed to confirm the observed OCT effects.

Chlorhexidine rinsing inhibits biofilm formation and causes biofilm disruption on dental enamel in situ

OBJECTIVES

This in situ study aims to evaluate the effects of chlorhexidine (CHX) mouth rinsing on biofilm formation and moreover on the disruption of existing mature dental biofilms.

METHODS

Biofilms were formed in situ by five volunteers on bovine enamel specimens fixed to individual acrylic splints. For biofilm formation analysis, the volunteers intraorally exposed the splint for 48 h. Mouth rinsing using 10 ml of 0.2% CHX or water as control was performed for 30 s every 12 h. For analysis of biofilm disruption, the biofilm was formed on enamel specimens for 48 h. Then, the first CHX rinse was carried out. A second rinse followed after an additional 12 h, again for 30 s using 10 ml of 0.2% CHX. Biofilm vitality was imaged by fluorescence microscopy after vital fluorescence staining. Additionally, the ultrastructure of the biofilm was examined by transmission electron microscopy.

RESULTS

Rinses with 0.2% CHX significantly reduced biofilm formation on enamel. Both biofilm colonization and vitality were dramatically impaired. Moreover, a considerable biofilm disruption induced by the CHX rinses was observed. Remarkably, a single application of CHX to a 48-h mature biofilm causes biofilm ultrastructure alterations and induces a substantial reduction in biofilm thickness and bacterial vitality.

CONCLUSIONS

CHX mouth rinses induced a significant inhibition of biofilm formation on native enamel. Furthermore, an important biofilm disrupting effect under in situ conditions was detected.

CLINICAL RELEVANCE

CHX rinses could be used as a short-term treatment protocol for biofilm management focused on patients unable to reach adequate oral hygiene.

Erosion-Protective Capacity of the Salivary Pellicle of Female and Male Subjects Is Not Different

This study aimed to analyse if the erosion-protective potential of the salivary pellicle is different between female and male subjects. Bovine enamel and dentin specimens (each n = 3) were exposed to the oral cavity of healthy female or male volunteers (each n = 25, females: 25.8 ± 3.5 years, males: 26.7 ± 4.0 years) for 120 min to form a salivary pellicle. Subsequently, each 2 enamel and 2 dentin specimens were eroded with hydrochloric acid (pH 2.6, 60 s). Specimens of the control group (each n = 30) were eroded without presenting a salivary pellicle. Calcium release into the acid was determined photometrically. Additionally, total protein content in the pellicle (each n = 1 enamel and dentin specimen/volunteer) and different salivary parameters (flow rate, pH, buffer capacity, protein, albumin, calcium, phosphate, fluoride) were assessed. Statistical analyses were performed by one-way ANOVA, t tests, multiple linear regressions and Pearson correlations (p < 0.05). The erosion-protective capacity was not significantly different among female (calcium release [% of control]: enamel: 82.6 ± 28.1, dentin: 80.7 ± 24.0) and male (enamel: 76.0 ± 27.5, dentin: 87.1 ± 34.9) subjects. The protein content of the pellicle was not different between female and male subjects. The protein content and pH of unstimulated saliva were significantly reduced in female compared to male volunteers. Calcium release was neither correlated with the protein content of the salivary pellicle nor with salivary parameters. Under the conditions of the present study, the erosion-protective capacity of the salivary pellicle of female and male subjects is not different.

Frequency of Application of AmF/NaF/SnCl2 Solution and Its Potential in Controlling Human Enamel Erosion Progression: An in situ Study

Although several studies have demonstrated the efficacy of AmF/NaF/SnCl2 solution in inhibiting dental erosion progression, measures for further improvement in its effectiveness are paramount. Thus, this in situ study evaluated whether the protective effect promoted by the AmF/NaF/SnCl2 solution would be enhanced by increasing its frequency of use. The study was conducted with 12 volunteers, a 4-phase (5 days each) randomized, crossover model. Extraoral erosive challenges (0.5% citric acid, pH 2.6, 6 × 2 min/day) and rinsing protocol (1 or 2 × 2 min/day) were performed. Before the in situ phase, human enamel samples were subjected to an in vitro surface softening (1% citric acid, pH 4.0, for 3 min). Four treatment protocols were tested using samples in replicas (n = 12): group G1 - deionized water (negative control); G2 - NaF solution (positive control, 500 ppm F-, pH 4.5); G3 - AmF/NaF/SnCl2 solution (500 ppm F-, 800 ppm Sn2+, pH 4.5) once a day; G4 - AmF/NaF/SnCl2 solution twice a day. Tissue loss and morphological changes were determined by optical profilometry (n = 12) and scanning electron microscopy (n = 3) analysis, respectively. Data were statistically analyzed by ANOVA with subsequent pairwise comparison of treatments. Tissue loss means (±SD in µm) for each treatment protocol and statistical differences were found as follows: G1 4.55 ± 2.75, G2 4.59 ± 2.13, G3 2.64 ± 1.55, and G4 1.34 ± 1.16. Although there was no difference between the 2 AmF/NaF/SnCl2 solution application regimens (once or twice a day), application of the product twice a day was the only treatment that was able to control erosion progression, differing from the control groups.

Structural and compositional changes in the salivary pellicle induced upon exposure to SDS and STP

Sodium dodecyl sulphate (SDS) and sodium tripolyphosphate (STP) act to remove stained pellicle from dentition and loosen deposits on tooth surfaces that may become cariogenic over time. This study investigated how SDS and STP impact the salivary pellicle adsorbed onto hydroxyapatite and silica sensors using a dual polarisation interferometer and a quartz-crystal microbalance with dissipation. After the pellicle was exposed to SDS and STP the remaining pellicle, although weaker, due to the loss of material, became less dense but with a higher elastic component; suggesting that the viscous component of the pellicle was being removed. This would imply a structural transformation from a soft but dense structured pellicle, to a more diffuse pellicle. In addition, the majority of proteins displaced by both SDS and STP were identified as being acidic in nature; implying that the negatively charged groups of SDS and STP may be responsible for the displacement of the pellicle proteins observed.

A comprehensive method for determination of fatty acids in the initial oral biofilm (pellicle)

The acquired pellicle is a tenacious organic layer covering the surface of teeth, protecting the underlying dental hard tissues. Lipids account for about one quarter of the pellicle's dry weight and are assumed to be of considerable importance for their protective properties. Nevertheless, only preliminary information is available about the nature of lipids in the pellicle. Gas chromatography coupled with electron impact ionization mass spectrometry was used to establish a convenient analytical protocol in order to obtain a qualitative and quantitative characterization of a wide range of FAs (C(12)-C(22)). In situ biofilm formation was performed on bovine enamel slabs mounted on individual splints carried by 10 subjects. A modified Folch extraction procedure was adopted to extract the lipids from the detached pellicle, followed by transesterification to fatty acid methyl esters using methanol and concentrated hydrochloric acid. Tridecanoic and nonadecanoic acid were used as internal standards suitable and reliable for robust, precise and accurate measurements. The present study demonstrates, for the first time, a procedure based on a combination of innovative specimen generation and convenient sample preparation with sensitive GC-MS analysis for the determination of the fatty acid profile of the initial oral biofilm.

Friction force spectroscopy as a tool to study the strength and structure of salivary films

In this work, we employ atomic force microscopy based friction force spectroscopy to study the strength and structure of salivary films. Specifically, films formed on model hydrophobic (methylated silica) and hydrophilic (clean silica) substrata have been studied in water at pHs in the range 3.3-7. Results reveal that films formed on both types of substrata can be described in terms of two different fractions, with only one of them being able to diffuse along the underlying substrata. We also show how the protective function of the films is reduced when the pH of the surrounding medium is lowered. Specifically, lowering of pH causes desorption of some components of the films formed on hydrophobic methylated surfaces, leading to weaker layers. In contrast, at low pHs, saliva no longer forms a layer on hydrophilic silica surfaces. Instead, an inhomogeneous distribution of amorphous aggregates is observed. Our data also suggest that hydrophobic materials in the oral cavity might be more easily cleaned from adsorbed salivary films. Finally, reproducible differences are observed in results from experiments on films from different individuals, validating the technique as a tool for clinical diagnosis of the resistance to erosion of salivary films.

Bacterial and Candida albicans adhesion on different root canal filling materials and sealers

INTRODUCTION

Microbial adhesion and subsequent biofilm formation on endodontic root canal filling materials and sealers lead to survival of microorganisms in treated root canals and subsequently to endodontic treatment failures. The present study focused on initial microbial adhesion to different endodontic filling materials.

METHODS

The following endodontic biomaterials were tested: AH-Plus, Tubli Seal, gutta-percha, Real Seal SE, EndoREZ, Apexit Plus, GuttaFlow, and dentin. Samples of each material were prepared. Bovine dentin samples were used as a control. The initial adhesions of salivary bacteria as well as the subsequent single species were quantified by determination of colony-forming units (CFUs) and visualized by scanning electron microscopy and confocal microscopy (CLSM): Enterococcus faecalis, Streptococcus mutans, Streptococcus sanguis, Candida albicans, and Prevotella nigrescens.

RESULTS

Initially adherent microorganisms could be detected and microscopically visualized on each of the materials tested. Considering the values of the CFUs and the covering grade as detected by CLSM, there were significant differences among the materials. Fewer bacteria tended to adhere to Apexit Plus, whereas Real Seal SE and the widely used gutta-percha showed the highest number of adherent bacteria. This tendency was not detected for C. albicans.

CONCLUSIONS

Endodontic microorganisms have a high affinity to root canal filling materials and sealers, especially to gutta-percha. Because of this high level of bacterial adhesion, subsequent biofilm formation on these materials could be suggested as leading to the persistence of microorganisms in root canals.

Protein adhesion on dental surfaces-a combined surface analytical approach

Protein adsorption is a field of huge interest in a number of application fields. Information on protein adhesion is accessible by a variety of methods. However, the results obtained are significantly influenced by the applied technique. The objective of this work was to understand the role of adhesion forces (obtained by scanning force spectroscopy, SFS) in the process of protein adsorption and desorption. In SFS, the protein is forced to and retracted from the surface, even under unfavorable conditions, in contrast to the natural situation. Furthermore, adhesion forces are correlated with adhesion energies, neglecting the entropic part in the Gibbs enthalpy. In this context, dynamic contact angle (DCA) measurements were performed to identify the potential of this method to complement SFS data. In DCA measurements, the protein diffuses voluntarily to the surface and information on surface coverage and reversibility of adsorption is obtained, including entropic effects (conformational changes and hydrophobic effect). It could be shown that the surface coverage (by DCA) of bovine serum albumin on dental materials correlates well with the adhesion forces (by SFS) if no hydrophobic surface is involved. On those, the entropic hydrophobic effect plays a major role. As a second task, the reversibility of the protein adsorption, i.e., the voluntary desorption as studied by DCA, was compared to the adhesion forces. Here, a correlation between low adhesion forces and good reversibility could be found as long as no covalent bonds were involved. The comparative study of DCA and SFS, thus, leads to a more detailed picture of the complete adsorption/desorption cycle.

Targeted immobilisation of lysozyme in the enamel pellicle from different solutions

Mouthwashes containing protective enzymes are required especially for patients suffering from xerostomia. The present study aimed to investigate the possibilities of modulating the immobilisation of lysozyme in the in situ pellicle layer. In situ formed pellicles were incubated in vitro for 10 min with various enzymatic buffer solutions containing lysozyme and additive enzymes such as transglutaminase or trypsin as well as polyphenolic compounds (cistus tea). After the rinses, the pellicle samples were incubated in collected whole saliva or in desorption solutions for 0, 20 and 40 min and the enzyme activities were measured. Furthermore, accumulation of lysozyme in the pellicle was visualised in ultrathin sections of the pellicle using the gold immunolabelling technique and transmission electron microscopy. Hen egg white lysozyme was accumulated in the in situ pellicle tenaciously. Up to 2.8-fold higher activities than in controls were observed. The addition of transglutaminase did not enhance the immobilisation of lysozyme activity, whereas the polyphenolic compound had no adverse effect. Accumulation of lysozyme in the acquired pellicle was confirmed by gold immunolabelling. Targeted and tenacious immobilisation of lysozyme in the acquired pellicle is possible. Poylphenolic compounds might be a relevant additive for mouthwashes containing lysozyme.

Polyphenolic beverages reduce initial bacterial adherence to enamel in situ

OBJECTIVES

Polyphenols are antibacterial and anti-oxidative natural agents. The present in situ study aimed to investigate the effect of different polyphenolic beverages on initial bacterial adherence to enamel in the oral cavity.

METHODS

Initial biofilm formation was performed on bovine enamel specimens mounted buccally on individual upper jaw splints and carried by six subjects. After 1 min of pellicle formation, oral rinses with black tea, green tea, grape juice, Cistus tea or red wine were performed for 10 min. Afterwards the slabs were carried for another 19 or 109 min, respectively. Samples exposed to the oral fluids for 30 and 120 min served as controls. Following intraoral exposure, the slabs were rinsed with saline solution. The amount of adherent bacteria was determined with DAPI-staining (4',6-diamidino-2-phenylindole) and with fluorescence-in situ hybridization (FISH) of eubacteria and streptococci.

RESULTS

Rinses with all beverages reduced the amount of detectable bacteria. Lowest number of adherent bacteria was found following rinses with red wine, Cistus tea and black tea as measured with DAPI (up to 66% reduction of adherent bacteria vs. controls). Also FISH revealed significant impact of most tested beverages.

CONCLUSIONS

Rinses with certain polyphenolic beverages as well as consumption of these foodstuffs may contribute to prevention of biofilm induced diseases in the oral cavity.

The composition of enamel salivary films is different from the ones formed on dental materials

This study utilized two-dimensional gel electrophoresis (2DE) to illustrate the compositional differences between in vitro salivary conditioning films (denoted pellicles) formed on human enamel as well as on the dental materials titanium and poly(methyl methacrylate). The salivary pellicles were formed by immersing each surface in individual tubes containing small volumes of freshly collected whole saliva. Saliva remaining in the tubes after the pellicle formation for 2 h was visualized by means of 2DE and silver staining. The results showed that the protein patterns in 2DE of the liquid phase of saliva left after the exposure to the respective surfaces, regarding proteins <100 kDa in size, were different depending on the surface used. Several protein groups and/or individual proteins were shown to be distinct for each surface used.

Validation of mechanically-assisted sodium dodecyl-sulphate elution as a technique to remove pellicle protein components from human enamel

The salivary film, denoted the pellicle, formed on oral surfaces is of great importance for oral health and comfort. The present study describes mechanically-assisted sodium dodecyl sulphate (SDS) elution of the in vivo pellicle formed on human enamel and visualisation of the desorbed pellicle proteins using two-dimensional gel electrophoresis (2-DE). To verify this removal of the pellicle, a combined mechanical and surfactant procedure was additionally performed on an in vitro pellicle formed on human enamel, and the effectiveness was validated by mechanical removal in combination with HCl. As indicated by protein quantitation and one dimensional gel electrophoresis, rubbing with polyamide fibre pellets soaked in a 0.5% SDS solution was optimal for completely removing the adsorbed proteins from the enamel surface, and yet provided separation of the proteins by 2-DE to enable identification in future studies.

Fluorescence microscopic visualization and quantification of initial bacterial colonization on enamel in situ

OBJECTIVE

The acquired salivary pellicle has been defined as proteinaceous film free of bacteria. However, due to the large numbers of microorganisms existent in the oral fluids, it is conceivable that adherent bacteria are already present in the initial pellicle. The aim of this in situ study was to visualize and to quantify these bacteria.

DESIGN

Initial biofilm formation was performed on bovine enamel slabs mounted buccally on individual splints and carried in situ by six subjects for 3, 30 and 120 min, respectively. After intraoral exposure, the slabs were rinsed with saline solution and the adherent bacteria were investigated with the following fluorescence microscopic methods: staining with 4',6-diamidino-2-phenylindole (DAPI), staining of vital and nonvital bacteria with fluoresceinediacetate and ethidiumbromide (live/dead staining) and fluorescence in situ hybridization (FISH) of eubacteria and streptococci, respectively. In addition, determination of colony forming units after ultrasonically induced detachment of bacteria was performed.

RESULTS

With all the methods, bacteria were detected in the initial in situ biofilm irrespective of the formation time. The numbers of bacteria revealed high intraindividual and interindividual variability and the microorganisms were distributed randomly in small aggregates. The results of the epifluorescence microscopic techniques corresponded well. The mean number of adherent bacteria detected was in the range of 10-20x10(4)cm(-2).

CONCLUSION

Already after 3 min, adherent bacteria are present in the initial pellicle. For the first time, DAPI-staining as well as FISH have proven success for visualization of initial intraoral colonization of enamel specimens.

The erosion-inhibiting effect of TiF4, SnF2, and NaF solutions on pellicle-covered enamel in vitro

OBJECTIVE

The aim of this study was to compare the protective effect of TiF(4), SnF(2), and NaF treatment on the development of erosion-like lesions in pellicle-covered human enamel.

MATERIAL AND METHODS

Twelve human molars were each divided into 5 specimens, 4 of which were immersed in saliva for 2 h. Three pellicle-covered specimens from each tooth were treated with a TiF(4), SnF(2), or NaF solution (all 0.5 M F) for 2 min. Control specimens, one with and one without pellicle, were included. Immersion in acid (0.01 M HCl) was carried out stepwise (2+2+2+2 min). The etching depths (in microm) were measured using white light interferometry.

RESULTS

Compared with the control with pellicle, TiF(4) reduced enamel loss by 100% after 2 min and by 24% after 8 min of acid exposure. The corresponding values for SnF(2) were 45% and 14%. NaF provided no significant protection of the surface. The pellicle-covered specimens showed reduced lesion depths after 6 and 8 min compared to the controls without pellicle.

CONCLUSIONS

TiF(4) gave the best protection against acid attack. SnF(2) provided significant protection only after 2 min of acid exposure, while NaF had no significant protective effect.

Human saliva forms a complex film structure on alumina surfaces

Films formed from saliva on surfaces are important for the maintenance of oral health and integrity by protection against chemical and/or biological agents. The aim of the present study was to investigate adsorbed amounts, thickness, and structure of films formed from human whole saliva on alumina surfaces by means of in situ ellipsometry, neutron reflectivity, and atomic force microscopy. Alumina (Al2O3, synthetic sapphire) is a relevant and interesting substrate for saliva adsorption studies as it has an isoelectric point close to that of tooth enamel. The results showed that saliva adsorbs rapidly on alumina. The film could be modeled in two layers: an inner and dense thin region that forms a uniform layer and an outer, more diffuse and thicker region that protrudes toward the bulk of the solution. The film morphology described a uniformly covering dense layer and a second outer layer containing polydisperse adsorbed macromolecules or aggregates.

Identification of protein components in in vivo human acquired enamel pellicle using LC-ESI-MS/MS

The acquired enamel pellicle is a thin protein film forming upon exposure of tooth enamel surfaces to saliva. The structural analysis of this integument relies on efficient pellicle harvesting and protein identification procedures. Material from three individual subjects and two pooled samples yielded the identification by LC-ESI-MS/MS of 130 pellicle proteins of which 89 were found in three or more experiments. A high intersubject consistency in pellicle composition was observed.

Non-destructive visualisation of protective proteins in the in situ pellicle

Several salivary anti-microbial and buffering components are part of the acquired in vivo pellicle. The purpose of the present in situ study was to visualise these proteins within the in situ formed pellicle and to investigate their distribution with respect to pellicle formation time and intra-oral localisation. Bovine enamel slabs were fixed on individual splints. They were carried by 6 subjects buccally and palatally in the region of the upper first molar teeth over 30 and 120 min, respectively, for in situ pellicle formation. After intra-oral exposure, enamel specimens were processed for transmission electron microscopy. Secretory immunoglobulin A (sIgA), lactoferrin, lysozyme, carbonic anhydrase (CA) I and II were visualised successfully in the in situ pellicle layer by gold immuno-labelling. All components were found to be distributed randomly within all layers of the pellicle. Significantly higher amounts of the proteins were detected after 120 min of formation time. Furthermore, significantly more labelled lactoferrin and lysozyme were found on buccal surfaces compared with palatal sites. For CA I, CA II and sIgA, no significant influence of the localisation was detected. All investigated anti-bacterial and buffering proteins are distributed randomly in the in situ formed pellicle layer and thus could contribute to its protective properties as an early defence barrier.

Salivary Mucin MUC5B Could Be an Important Component of in Vitro Pellicles of Human Saliva: An in Situ Ellipsometry and Atomic Force Microscopy Study

This paper describes a combined investigation of the salivary and MUC5B films structure and topography in conditions similar to those found in the oral cavity in terms of ionic strength, pH, and protein concentration. AFM and ellipsometry were successfully used to give a detailed picture of the film structure and topography both on hydrophilic and on hydrophobic substrata. Regardless of the substrata, the salivary film can be described as having a two sublayer structure in which an inner dense layer is decorated by large aggregates. However, the shape and height of these larger aggregates largely depend on the type of substrata used. Additionally, we show that the adsorption of MUC5B is controlled by the type of substrata and the MUC5B film topography is similar to that of the larger aggregates present in the salivary films, especially on hydrophobic substrates. Therefore, we conclude that MUC5B is a major component in the salivary film when formed on hydrophobic substrates. Furthermore, we studied how resistant the salivary and MUC5B films are against elutability by buffer rinsing and addition of SDS solution. We conclude that the adsorbed proteins contain fractions with varying binding strengths to the two types of surfaces. Specifically, we have shown that the large MUC5B biomacromolecules on the hydrophobic substrates are especially resistant to both elution with buffer solution and SDS. Therefore, these large mucins can be responsible for the increased resistance of HWS films on hydrophobic substrates and can protect the intraoral surfaces against surface-active components present in oral health care products.

Influence of different restorative materials on lysozyme and amylase activity of the salivary pellicle in situ

Lysozyme and amylase are the most abundant enzymatic components in the salivary pellicle. The purpose of the present study was to determine the influence of different substrata on amylase and lysozyme activity in salivary pellicles formed in situ. Slabs (5 mm diameter) of bovine dentine and enamel, of titanium, gold alloy, resin composite, PMMA, amalgam, and feldspar ceramic were fixed on the buccal sites of individual splints worn by six subjects for 30 min to allow pellicle formation. Thereafter, slabs were removed from the trays and rinsed with running water. Lysozyme activity was determined via lysis of Micrococcus lysodeicticus. Amylase activity was measured with a photometric method using 2-chloro-4-nitrophenyl-4-O-beta-D-galactopyranosylmaltotriosid (GalG2CNP) as substrate. Both pellicle enzymes were evaluated in the immobilized as well as in the desorbed state. Salivary enzyme activities were also measured. All investigated pellicles exhibited lysozyme and amylase activity. Great intraindividual and interindividual differences were observed. Over all samples, immobilized amylase activity amounted to 0.65 +/- 0.64 mU/cm2. Immobilized lysozyme activity was 5.04 +/- 1.55 U/cm2. There were no major effects of the substratum on pellicle-bound amylase and lysozyme activity. Immobilized and desorbed enzyme activities revealed a strong correlation (lysozyme: r = 0.700; amylase: r = 0.990). Salivary enzyme activities had only little impact on pellicle-bound enzyme activities. Amylase and lysozyme are incorporated in the acquired in situ pellicle on different solid surfaces in an active conformation. Dental material and enzyme activity in the saliva have only little impact on enzymatic activity in the pellicle in situ.