Acquired enamel pellicle and biofilm engineering with a combination of acid-resistant proteins (CaneCPI-5, StN15, and Hemoglobin) for enhanced protection against dental caries - in vivo and in vitro investigations

OBJECTIVE

This study was designed in two-legs. In the in vivo, we explored the potential of a rinse solution containing a combination (Comb) of 0.1 mg/mL CaneCPI-5 (sugarcane-derive cystatin), 1.88 × 10- 5M StN15 (statherin-derived peptide) and 1.0 mg/mL hemoglobin (Hb) to change the protein profile of the acquired enamel pellicle(AEP) and the microbiome of the enamel biofilm. The in vitro, was designed to reveal the effects of Comb on the viability and bacterial composition of the microcosm biofilm, as well as on enamel demineralization.

MATERIALS AND METHODS

In vivo study, 10 participants rinsed (10mL,1 min) with either deionized water (H2O-control) or Comb. AEP and biofilm were collected after 2 and 3 h, respectively, after rinsing. AEP samples underwent proteomics analysis, while biofilm microbiome was assessed via 16 S-rRNA Next Generation Sequencing(NGS). In vitro study, a microcosm biofilm protocol was employed. Ninety-six enamel specimens were treated with: 1)Phosphate-Buffered Solution-PBS(negative-control), 2)0.12%Chlorhexidine, 3)500ppmNaF and 4)Comb. Resazurin, colony-forming-units(CFU) and Transversal Microradiography(TMR) were performed.

RESULTS

The proteomic results revealed higher quantity of proteins in the Comb compared to control associated with immune system response and oral microbial adhesion. Microbiome showed a significant increase in bacteria linked to a healthy microbiota, in the Comb group. In the in vitro study, Comb group was only efficient in reducing mineral-loss and lesion-depth compared to the PBS.

CONCLUSIONS

The AEP modification altered the subsequent layers, affecting the initial process of bacterial adhesion of pathogenic and commensal bacteria, as well as enamel demineralization.

CLINICAL RELEVANCE

Comb group shows promise in shaping oral health by potentially introducing innovative approaches to prevent enamel demineralization and deter tooth decay.

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.

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.

Targeted metabolomics of pellicle and saliva in children with different caries activity

Pellicle is the initial proteinaceous layer that is formed almost instantaneously on all solid surfaces in the oral cavity. It is of essential relevance for any interactions and metabolism on the tooth surface. Up to now, there is no information on the metabolome of this structure. Accordingly, the present study aims to characterise the metabolomic profile of in-situ pellicle in children with different caries activity for the first time in comparison to saliva. Small molecules such as carbohydrates, amino acids, organic acids, and fatty acids, putatively involved in the formation of caries were quantified using mass spectrometry (MS)-based techniques, such as (stable isotope dilution analysis)-ultra-performance liquid chromatography-tandem MS and gas chromatography/electron ionisation-MS. Pellicle and corresponding saliva samples were collected from caries-active, caries-free and caries-rehabilitated 4- to 6-year-old children. The most abundant analytes in pellicle were acetic acid (1.2-10.5 nmol/cm2), propionic acid (0.1-8.5 nmol/cm2), glycine (0.7-3.5 nmol/cm2), serine (0.08-2.3 nmol/cm2), galactose (galactose + mannose; 0.035-0.078 nmol/cm2), lactose (0.002-0.086 nmol/cm2), glucose (0.018-0.953 nmol/cm2), palmitic acid (0.26-2.03 nmol/cm2), and stearic acid (0.34-1.81 nmol/cm2). Significant differences depending on caries activity were detected neither in saliva nor in the corresponding pellicle samples.

Proteome analysis of the salivary pellicle formed on titanium alloys containing niobium and zirconium

The chemical composition of biomaterials can drive their biological responses; therefore, this in vitro study aimed to evaluate the proteomic profile of the salivary pellicle formed on titanium (Ti) alloys containing niobium (Nb) and zirconium (Zr). The experimental groups consisted of Ti35NbxZr (x = 5 and 10 wt%) alloys, and commercially pure titanium (cpTi); titanium aluminium vanadium (Ti6Al4V) alloys were used as controls. The physical and chemical characteristics of the Ti materials were analysed. The proteomic profile was evaluated by liquid chromatography coupled with tandem mass spectrometry. Bacterial adhesion (2 h) of mixed species (Streptococcus sanguinis and Actinomyces naeslundii) was investigated as colony-forming units (n = 6). This paper reports the finding that salivary pellicle composition can be modulated by the composition of the Ti material. The Ti35NbxZr group showed a significant ability to adsorb proteins from saliva, which can favour interactions with cells and compatibility with the body.

Comprehensive measurements of salivary pellicle thickness formed at different intraoral sites on Si wafers and bovine enamel

The salivary pellicle is a thin acellular film formed on orally exposed surfaces by adsorption of macromolecules from the oral fluids and serves as a protective layer in the maintenance of oral health. Pellicle thickness measurements are a central tool helping to understand how exogenous manipulations may influence pellicle formation. This is of particular importance for the investigation of new preventive and therapeutic approaches. In the present study we determined the kinetics of the in situ pellicle thickness formation at different intraoral sites and investigated how pellicle formation occurs in different individuals. To address the kinetic aspect, the thickness of the in situ pellicle was determined after formation periods of 3 min, 30 min and 120 min. The thickness of the pellicle was either measured on silicon wafers by ellipsometry or on bovine enamel by transmission electron microscopy. We found a physiologically important rapid pellicle formation phase within the first minutes and a slow pellicle formation phase between 30 min and 120 min. Furthermore, our results identify significant inter-individual differences both for the pellicle thickness and for the formation kinetics, indicating the consideration of individual-specific differences of the pellicle layer as an important aspect for future studies.

Acquired Enamel Pellicle Engineered Peptides: Effects on Hydroxyapatite Crystal Growth

The aim of this study was to test the hypothesis that duplication/hybridization of functional domains of naturally occurring pellicle peptides amplified the inhibitory effect of hydroxyapatite crystal growth, which is related to enamel remineralization and dental calculus formation. Histatin 3, statherin, their functional domains (RR14 and DR9), and engineered peptides (DR9-DR9 and DR9-RR14) were tested at seven different concentrations to evaluate the effect on hydroxyapatite crystal growth inhibition. A microplate colorimetric assay was used to quantify hydroxyapatite crystal growth. The half-maximal inhibitory concentration (IC50) was determined for each group. ANOVA and Student-Newman-Keuls pairwise comparisons were used to compare the groups. DR9-DR9 increased the inhibitory effect of hydroxyapatite crystal growth compared to single DR9 (p < 0.05), indicating that functional domain multiplication represented a strong protein evolution pathway. Interestingly, the hybrid peptide DR9-RR14 had an intermediate inhibitory effect compared to DR9 and DR9-DR9. This study used an engineered peptide approach to investigate a potential evolution protein pathway related to duplication/hybridization of acquired enamel pellicle's natural peptide constituents, contributing to the development of synthetic peptides for therapeutic use against dental caries and periodontal disease.

Identification of in vivo Pellicle Constituents by Analysis of Serum Immune Responses

Human acquired enamel pellicle is composed of molecules that selectively adsorb from saliva onto tooth surfaces and provides a protective interface between the tooth enamel and the oral environment. To identify the micro-amounts of components present in pellicle, we immunized mice with in vivo-formed human acquired enamel pellicle and analyzed the serum immune responses. Selective reactivities of the serum (OD > 1.0 above background) against albumin, amylase, carbonic anhydrase II, sIgA, IgG, IgM, lactoferrin, lysozyme, proline-rich proteins, statherin, histatin 1, and mucous glycoprotein 1 were observed. We further confirmed the presence of proline-rich proteins, lactoferrin, lysozyme, and carbonic anhydrase II by probing in vivo pellicle with specific polyclonal anti-sera. The polyclonal antibody approach provided a powerful method for the identification of various pellicle proteins, including some which show mineral homeostasis or antimicrobial activity.

Structural modifications of the salivary conditioning film upon exposure to sodium bicarbonate: implications for oral lubrication and mouthfeel

The salivary conditioning film (SCF) that forms on all surfaces in the mouth plays a key role in lubricating the oral cavity. As this film acts as an interface between tongue, enamel and oral mucosa, it is likely that any perturbations to its structure could potentially lead to a change in mouthfeel perception. This is often experienced after exposure to oral hygiene products. For example, consumers that use dentifrice that contain a high concentration of sodium bicarbonate (SB) often report a clean mouth feel after use; an attribute that is clearly desirable for oral hygiene products. However, the mechanisms by which SB interacts with the SCF to alter lubrication in the mouth is unknown. Therefore, saliva and the SCF was exposed to high ionic strength and alkaline solutions to elucidate whether the interactions observed were a direct result of SB, its high alkalinity or its ionic strength. Characteristics including bulk viscosity of saliva and the viscoelasticity of the interfacial salivary films that form at both the air/saliva and hydroxyapatite/saliva interfaces were tested. It was hypothesised that SB interacts with the SCF in two ways. Firstly, the ionic strength of SB shields electrostatic charges of salivary proteins, thus preventing protein crosslinking within the film and secondly; the alkaline pH (≈8.3) of SB reduces the gel-like structure of mucins present in the pellicle by disrupting disulphide bridging of the mucins via the ionization of their cysteine's thiol group, which has an isoelectric point of ≈8.3.

Protective effects of SnF2 - Part II. Deposition and retention on pellicle-coated enamel

Deposition of an acid-resistant barrier onto enamel represents a potentially superior means for delivering protection against dietary, erosive acid challenges.

PURPOSE

The purpose of this study was to demonstrate the ability of a stabilised stannous fluoride (SnF2 ) dentifrice to: (1) deposit a SnF2 barrier layer onto pellicle-coated enamel surfaces; (2) increase the intensity of the barrier layer over time; and (3) be retained on the enamel surface for hours after product use.

METHODS

Squares of human enamel were exposed to pooled saliva for 1 hour (pellicle formation) and separated into six sets. Set 1 was treated with the supernatant of a 1:3 slurry of the test dentifrice (Crest(®) Pro-Health(®) : water for 2 minutes), then rinsed. Set 2 was treated in the same manner and then placed into saliva (6 hours). Set 3 was cycled through seven repeated treatments. Set 4 was treated for seven cycles and then placed into saliva (6 hours). Set 5 was a water control, and set 6 was a water control that remained in saliva for 6 hours. Surface analysis of specimens was done using laser ablation Inductively Coupled Plasma Mass Spectroscopy (ICP-MS).

RESULTS

Deposition of a barrier layer was demonstrated, beginning with the initial treatment, with Sn (using isotopes (117) Sn + (120) Sn) measured on the enamel surface as the reference marker. Deposition of the barrier layer was greater after seven cycles, and the retention of this layer was highly significant (P = 0.05, anova: 6 hours).

CONCLUSIONS

This study confirms that: (1) the stabilised SnF2 dentifrice deposits a barrier layer onto the enamel surface, beginning with the first use of the product; (2) this barrier is enhanced following multiple treatments; and (3) the barrier layer is retained on the enamel surface for hours after product use.

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.

Lubrication and load-bearing properties of human salivary pellicles adsorbed ex vivo on molecularly smooth substrata

In a series of Surface Force Balance experiments, material from human whole saliva was adsorbed to molecularly smooth mica substrata (to form an 'adsorbed salivary film'). Measurements were taken of normal (load bearing, F (n)) and shear (frictional, F (s)*) forces between two interacting surfaces. One investigation involved a salivary film formed by overnight adsorption from undiluted, centrifuged saliva, with the adsorbed film rinsed with pure water before measurement. Measurements were taken under pure water and 70 mM NaNO(3). In a second investigation, a film was formed from and measured under a solution of 7% filtered saliva in 10 mM NaNO(3). F (n) results for both systems showed purely repulsive layers, with an uncompressed thickness of 35-70 nm for the diluted saliva investigation and, prior to the application of shear, 11 nm for the rinsed system. F (s)* was essentially proportional to F (n) for all systems and independent of shear speed (in the range 100-2000 nm s(-1)), with coefficients of friction μ ≈ 0.24 and μ ≈ 0.46 for the unrinsed and rinsed systems, respectively. All properties of the rinsed system remained similar when the pure water measurement environment was changed to 70 mM NaNO(3). For all systems studied, shear gave rise to an approximately threefold increase in the range of normal forces, attributed to the ploughing up of adsorbed material during shear to form debris that stood proud of the adsorbed layer. The results provide a microscopic demonstration of the wear process for a salivary film under shear and may be of particular interest for understanding the implications for in vivo oral lubrication under conditions such as rinsing of the mouth cavity. The work is interpreted in light of earlier studies that showed a structural collapse and increase in friction for an adsorbed salivary film in an environment of low ionic strength.

Biology of Streptococcus mutans-derived glucosyltransferases: role in extracellular matrix formation of cariogenic biofilms

The importance of Streptococcus mutans in the etiology and pathogenesis of dental caries is certainly controversial, in part because excessive attention is paid to the numbers of S. mutans and acid production while the matrix within dental plaque has been neglected. S. mutans does not always dominate within plaque; many organisms are equally acidogenic and aciduric. It is also recognized that glucosyltransferases from S. mutans (Gtfs) play critical roles in the development of virulent dental plaque. Gtfs adsorb to enamel synthesizing glucans in situ, providing sites for avid colonization by microorganisms and an insoluble matrix for plaque. Gtfs also adsorb to surfaces of other oral microorganisms converting them to glucan producers. S. mutans expresses 3 genetically distinct Gtfs; each appears to play a different but overlapping role in the formation of virulent plaque. GtfC is adsorbed to enamel within pellicle whereas GtfB binds avidly to bacteria promoting tight cell clustering, and enhancing cohesion of plaque. GtfD forms a soluble, readily metabolizable polysaccharide and acts as a primer for GtfB. The behavior of soluble Gtfs does not mirror that observed with surface-adsorbed enzymes. Furthermore, the structure of polysaccharide matrix changes over time as a result of the action of mutanases and dextranases within plaque. Gtfs at distinct loci offer chemotherapeutic targets to prevent caries. Nevertheless, agents that inhibit Gtfs in solution frequently have a reduced or no effect on adsorbed enzymes. Clearly, conformational changes and reactions of Gtfs on surfaces are complex and modulate the pathogenesis of dental caries in situ, deserving further investigation.

The structure, dynamics, and energetics of protein adsorption-lessons learned from adsorption of statherin to hydroxyapatite

Proteins are found to be involved in interaction with solid surfaces in numerous natural events. Acidic proteins that adsorb to crystal faces of a biomineral to control the growth and morphology of hard tissue are only one example. Deducing the mechanisms of surface recognition exercised by proteins has implications to osteogenesis, pathological calcification and other proteins functions at their adsorbed state. Statherin is an enamel pellicle protein that inhibits hydroxyapatite nucleation and growth, lubricates the enamel surface, and is recognized by oral bacteria in periodontal diseases. Here, we highlight some of the insights we obtained recently using both thermodynamic and solid state NMR measurements to the adsorption process of statherin to hydroxyapatite. We combine macroscopic energy characterization with microscopic structural findings to present our views of protein adsorption mechanisms and the structural changes accompanying it and discuss the implications of these studies to understanding the functions of the protein adsorbed to the enamel surfaces.

Chitosan adsorption to salivary pellicles

The salivary pellicle is a negatively charged protein film, to which oral bacteria readily adhere. Chitosans are cationic biomolecules with known antimicrobial properties that can be modified in different ways to enhance its antimicrobial activity. Here, we determined the changes in surface chemical composition using X-ray photoelectron spectroscopy (XPS), in hydrophobicity by analyzing water contact angles, in charge through measuring streaming potentials, and evaluated morphology using atomic force microscopy (AFM), of salivary pellicles upon adsorption of different chitosans. The adsorption of chitosans to pellicles was chemically evident from altered carbon functionalities and the presence of an N(1s) peak at 401.1 eV as a result of protonated amines in XPS. Chitosan adsorption made the pellicle (zeta potential of untreated pellicles 29 mV) positively charged and more hydrophobic. A chemically modified chitosan (CL) and an unmodified chitosan (UC) caused aggregation of adsorbed salivary proteins, and AFM revealed clumps of protein after treatment with these chitosans, yielding an increase in pellicle surface roughness from 5.1 nm to between 16.3 and 35.6 nm for CL and UC, respectively. In summary, chitosans have a clear tendency to adsorb to salivary pellicles with a profound effect on the surface properties of the pellicle. Therefore, chitosans may provide anchoring molecules to affix antimicrobials to pellicle surfaces.

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.

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.

Peptidomic analysis of human acquired enamel pellicle

Human acquired enamel pellicle is the result of a selective interaction of salivary proteins and peptides with the tooth surface. In the present work, the characterization of the peptides as well as the type of interactions established with the enamel surface was performed. Peptides from in vivo bovine enamel implants in the human oral cavity were sequentially extracted using guanidine and trifluoroacetic acid solutions and the fractions obtained were analysed by LC-MS and LC-MS/MS. Based on the LC-MS data, six phosphorylated peptides were identified in an intact form, strongly adsorbed to the enamel surface. Data from the LC-MS/MS analyses allowed us to identified 30 fragment peptides non-covalently bonded to enamel [basic proline-rich proteins, histatins (1 and 3) and acidic proline-rich protein classes]. The tandem mass spectrometry experiments showed the existence of a pattern of amide bond cleavage for the different identified peptide classes suggesting a selective proteolytic activity. For histatins, a predominance of cleavage at Arg, Lys and His residues was observed, while for basic proline-rich proteins, cleavage at Arg and Pro residues prevailed. In the case of acidic proline-rich proteins, a clearly predominance of cleavage of the Gln-Gly amide bond was evident.

Two-dimensional electrophoresis study of in vitro pellicle formation and dental caries susceptibility

In the present study, a proteomic approach was applied to evaluate the influence of salivary protein composition on in vitro dental pellicle formation and its possible correlation with dental caries. Whole saliva, collected from caries-free and caries-susceptible subjects, was analyzed by two-dimensional electrophoresis, and protein spots were identified by mass spectrometry. Data analysis of salivary protein composition showed a statistically significant correlation between the quantity of acidic proline-rich proteins (PRPs), lipocalin, cystatin SN and cystatin S, and samples from the caries-free group of subjects [decayed, missing or filled teeth (DMFT) = 0]. Samples from subjects with a high DMFT index appear to be correlated with high levels of amylase, immunoglobulin A, and lactoferrin. In vitro pellicle-composition experiments showed the same correlations found for whole saliva. As cystatins are known physiological inhibitors of cathepsins, the higher quantities of lipocalin, and cystatins S and SN found in the samples from the caries-free subjects suggest that inhibition of proteolytic events on other salivary proteins may indirectly provide tooth protection. The correlation between higher levels of the phosphorylated acidic PRPs 1/2 with samples from the caries-free group also suggests a protective role for these proteins.

Adhesion of salivary components to Streptococcus mutans peptides

Streptococcus mutans is the main microorganism associated to dental caries; it adheres to the dental enamel by interacting with the acquired film's proteins and the cell surface adhesin, called variously antigen PAc. At least two distinct sites in PAc interact with salivary receptors in vitro, these are within residues 816-1213, the most conserved portion of PAc, and within residues 186-469, the alanine-rich sequence. Our purpose was to establish differences or similarities in PAc's peptides interactions with the salivary components of individuals with and without previous caries experience. 40 saliva samples were obtained from patients with (n=20) and without (n=20) caries. The acquired film's proteins were extracted using hydroxyapatite, and subjected to interaction with three synthetic PAc peptides (PAc (301-319), PAc (365-377), and PAc (1025-1044)) synthesized from PAc's bonding sites to the salivary components. The results show low interaction between the acquired pellicle components and the peptides in all patients. This suggests that the examined PAc's are not relevant as far as the initial adhesion of Streptococcus mutans to the tooth's surface is concerned, as defined by the similarities in the results for healthy and affected individuals.

Understanding the chemistry of dental erosion

The mineral in our teeth is composed of a calcium-deficient carbonated hydroxyapatite (Ca10-xNax(PO4)6-y(CO3)z(OH)2-uFu). These substitutions in the mineral crystal lattice, especially carbonate, renders tooth mineral more acid soluble than hydroxyapatite. During erosion by acid and/or chelators, these agents interact with the surface of the mineral crystals, but only after they diffuse through the plaque, the pellicle, and the protein/lipid coating of the individual crystals themselves. The effect of direct attack by the hydrogen ion is to combine with the carbonate and/or phosphate releasing all of the ions from that region of the crystal surface leading to direct surface etching. Acids such as citric acid have a more complex interaction. In water they exist as a mixture of hydrogen ions, acid anions (e.g. citrate) and undissociated acid molecules, with the amounts of each determined by the acid dissociation constant (pKa) and the pH of the solution. Above the effect of the hydrogen ion, the citrate ion can complex with calcium also removing it from the crystal surface and/or from saliva. Values of the strength of acid (pKa) and for the anion-calcium interaction and the mechanisms of interaction with the tooth mineral on the surface and underneath are described in detail.

Supramolecular pellicle precursors

Saliva contacting with solid surfaces in the oral cavity forms a coat termed the pellicle. However, its formation is not fully understood. Although indications for the existence of supramolecular pellicle precursors have been reported, the possible relationship between them and pellicle formation is unclear. This study investigates the ability of supramolecular precursors to form the pellicle via interaction with a solid surface. Fixed and unfixed salivary globes were spread onto a microscopic grid and examined by transmission electron microscopy. Biochemical pretreatment of saliva revealed that neither disulphide links nor transglutaminase-mediated crosslinking are responsible for maintaining the salivary globes, i.e. supramolecular pellicle precursors. However, the detergent, sodium dodecyl sulphate, caused dissociation of the salivary globes, indicating their micellar nature. Saliva contacting a formvar film for 10 s did not form a complete surface coating, but single supramolecular pellicle precursors were observed attached to the surface. After extension of the contact time to 60 s, a surface layer was formed by clustering and fusion of the supramolecular pellicle precursors. The supramolecular pellicle precursors are unstable and attain a thermodynamically more favourable state by adhesion to a solid surface. As a result, a layer of fused precursors covering the solid surface is formed -- the salivary pellicle.

Initial salivary pellicle formation on solid substrates studied by AFM

Organic layers of salivary biopolymers adsorbed on soft and hard oral tissues, referred to also as salivary pellicle, play a critical role with respect to all surface phenomena taking place in the oral cavity. The initial stages of pellicle formation are of great interest since they determine the ensuing processes of salivary biopolymer adsorption and subsequent adherence of bacteria. In spite of the important physiological role of the pellicle in protecting the enamel surface against short-term acidic attacks, the composition and ultrastructure of the pellicle layer are not yet understood and resolved in detail. The present study utilized atomic force microscopy (AFM), for the first time, to elucidate the morphogenesis and ultrastructural pattern of initial salivary pellicle formation taking place in situ on solid substrates of mica, silicon wafer and graphite. Using tapping mode AFM, salivary pellicles were found in all intraorally exposed specimens and revealed a globular surface morphology of the adsorbed protein layer. The average diameter and height of the adsorbed salivary proteins were determined to be 15 +/- 3 nm and 2.0 +/- 0.5 nm, respectively. It was also found that the surface energy of the substrates affects the rate of pellicle formation, while the overall size of the adsorbed salivary proteins appears to be identical on all studied substrates.

Influence of Oral Detergents and Chlorhexidine on Soft-Layer Electrokinetic Parameters of the Acquired Enamel Pellicle

Electron microscopy has described the salivary pellicle as an 'uneven, knotted structure'. This study describes a novel soft-layer model of salivary pellicles, based on measured electrophoretic mobilities and the influence of dentifrices and a chlorhexidine mouthwash on the parameters of the model. The enamel surface was found to possess a high number of fixed, negative charges (zN = -62 mM) and to be electrophoretically hard (1/lambda = 0.6 nm), i.e. impenetrable to fluid flow. Adsorption of a salivary pellicle resulted in a fourfold reduction in the surface fixed charge density (zN = -15 mM) along with an increase in electrophoretic softness (1/lambda = 2.3 nm). Exposure of pellicles to various dentifrices containing sodium fluoride as an active component and sodium lauryl sulfate as a detergent had little effect on the surface fixed charge densities (varying between -15 and -30 mM, depending on the dentifrice involved) and electrophoretic softnesses (varying between 2.3 and 3.4 nm). Exposure of pellicles to a dentifrice containing sodium fluoride and hexametaphosphate as an additional detergent yielded soft (8.0 nm) pellicles, penetrable to fluid flow, with few fixed, negative charges (1 mM). This is opposite to the effects of chlorhexidine, which created an electrophoretically hard pellicle (1.7 nm). This soft-layer electrokinetic model quantitatively shows that the degree to which pellicles are penetrable to fluid flow differs upon exposure to dentifrices, with relevance for plaque formation, de- and remineralization and staining processes.

Adsorption from black tea and red wine onto in vitro salivary pellicles studied by ellipsometry

The adsorption of black tea and red wine components onto a pellicle-like protein layer formed in vitro by adsorption from whole unstimulated saliva on hydroxyapatite discs were studied by in situ ellipsometry. It was found that components from black tea readily adsorbed to the pellicle. Subsequent exposure to saliva led to further adsorption of salivary components to give an overall increase in the amounts adsorbed. The amounts adsorbed increased still further following a third tea and saliva exposure. Components of red wine gave significantly greater amounts of adsorption to the pellicle than black tea. The adsorption of components of black tea gave a concomitant increase in colour or stain as measured by a reflectance chromameter. In all cases, the black tea- and red wine-modified pellicles were not eluted by either phosphate buffer or sodium dodecyl sulphate (SDS) rinses. Thus, black tea and red wine components have been shown to have a profound effect on in vitro pellicle maturation, causing thickened layers of stained material to build up, which are not readily removed.