Intraoral lubrication of PRP-1, statherin and mucin as studied by AFM

The Contribution of Scanning Force Microscopy on Dental Research: A Narrative Review

Scanning force microscopy (SFM) is one of the most widely used techniques in biomaterials research. In addition to imaging the materials of interest, SFM enables the mapping of mechanical properties and biological responses with sub-nanometer resolution and piconewton sensitivity. This review aims to give an overview of using the scanning force microscope (SFM) for investigations on dental materials. In particular, SFM-derived methods such as force-distance curves (scanning force spectroscopy), lateral force spectroscopy, and applications of the FluidFM® will be presented. In addition to the properties of dental materials, this paper reports the development of the pellicle by the interaction of biopolymers such as proteins and polysaccharides, as well as the interaction of bacteria with dental materials.

Dysphagia in Parkinson Disease: Part I - Pathophysiology and Diagnostic Practices

Purpose of Review

Dysphagia affects the majority of individuals with Parkinson disease (PD) and is not typically diagnosed until later in disease progression. This review will cover the current understanding of PD pathophysiology, and provides an overview of dysphagia in PD including diagnostic practices, gaps in knowledge, and future directions.

Recent Findings

Many non-motor and other motor signs of PD appear in the prodrome prior to the manifestation of hall- mark signs and diagnosis. While dysphagia often presents already in the prodrome, it is not routinely addressed in standard neurology examinations.

Summary

Dysphagia in PD can result in compromised efficiency and safety of swallowing, which significantly contributes to malnutrition and dehydration, decrease quality of life, and increase mortality. The heterogeneous clinical presentation of PD complicates diagnostic procedures which often leads to delayed treatment. Research has advanced our knowledge of mechanisms underlying PD, but dysphagia is still largely understudied, especially in the prodromal stage.

Effects of Streptococcus mutans and their metabolites on the wear behavior of dental restorative materials

The wear behavior of dental restorative materials is highly related to the biolubricating medium in the oral environment. Bacteria, along with their metabolic products, are essential substances in the oral cavity and have not been studied as a potential factor affecting lubrication performance during mastication. In this study, the effects of the Streptococcus mutans bacterial cells and their metabolites were investigated on the wear behavior of resin composites, polymer-infiltrated ceramic networks and zirconium-lithium silicate glass-ceramics. A reciprocating friction test and quantitative analysis of the wear morphology were utilized to determine the coefficient of friction (COF) and wear resistance of the test materials. The results showed that the bacterial metabolite medium significantly reduces the COF and wear rate of the three restorative materials and provide better protection against superficial abrasion. When tested under lactic acid medium, a key acid production in bacterial metabolites, similar wear reduction results were observed in the three materials, which confirmed that lactic acid should be accountable for the excellent lubricating property of bacterial metabolites. Furthermore, the resin composite with lower wettability exhibited a more significant wear reduction than the other two materials when lubricating with a bacterial metabolite medium. These findings provide novel insights into the biological basis of lubrication mechanisms in the oral cavity under high-loading and low-velocity conditions.

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.

Effects of oral lubrication on satiety, satiation and salivary biomarkers in model foods: A pilot study

With a dramatic increase in overweight and population with obesity over the last decades, there is an imminent need to tackle this issue using novel strategies. Addressing obesity issues by generating satiety in food to reduce energy intake has been one of those prominent strategies and often textural interventions have been used to generate satiety, specifically in short-term trials. This study aimed to investigate the role of preloads varying in their oral lubricating properties on appetite sensations, food intake, salivary friction and concentration of salivary biomarkers (proteins, α-amylase and mucins) in collected human saliva (n = 17 healthy participants). The preloads were model foods (flavoured hydrogels) either high or low in their lubricating properties, assessed both by instrumental and sensorial measurements. The results showed that hunger and desire to eat decreased immediately after preload and remained decreased for 10 and 20 min, respectively, after preload in the high lubricating condition compared to control (all p < 0.05). Fullness increased immediately after preload and remained increased for 10 and 20 min, respectively, after preload in high lubricating condition compared to control (p < 0.05). However, after controlling the values for baseline, such significant effect of the intervention did not exist anymore. Only the effect of time is observed. Consuming high lubricating hydrogels showed no effect on food intake and salivary biomarkers in this pilot study. Salivary lubrication correlated with feeling of fullness. Considering the issue of large time-interval (30 min) between preload and next meal in this study, it is worthwhile investigating the immediate effects of oral lubrication on appetite control, food intake and salivary biomarkers.

Protein-saliva interactions: a systematic review

Food industries are challenged to reformulate foods and beverages with higher protein contents to lower fat and sugar content. However, increasing protein concentration can reduce sensory acceptability due to astringency perception. Since the properties of food-saliva mixtures govern mouthfeel perception, understanding how saliva and protein interact is key to guide development of future protein-rich reformulations with optimal sensory attributes. Hence, this systematic review investigated protein-saliva interaction using both model and real human saliva, including a quality assessment. A literature search of five databases (Medline, Pubmed, Embase, Scopus and Web of Science) was undertaken covering the last 20 years, yielding 36 604 articles. Using pre-defined criteria, this was reduced to a set of 33 articles with bulk protein solutions (n = 17), protein-stabilized emulsions (n = 13) and protein-rich food systems (n = 4). Interaction of dairy proteins, lysozyme and gelatine with model or human saliva dominated the literature. The pH was shown to have a strong effect on electrostatic interaction of proteins with negatively-charged salivary mucins, with greater interactions occurring below the isoelectric point of proteins. The effect of protein concentration was unclear due to the limited range of concentrations being studied. Most studies employed a 1 : 1 w/w protein : saliva ratio, which is not representative of true oral conditions. The interaction between protein and saliva appears to affect mouthfeel through aggregation and increased friction. The searches identified a gap in research on plant proteins. Accurate simulation of in vivo oral conditions should clarify understanding of protein-saliva interaction and its influence on sensory perception.

Production and Application of Triblock Hydrolysis Lignin-Based Anionic Copolymers in Aqueous Systems

Although lignin is currently an under-utilized biopolymer, it has the potential to be valorized through different modification pathways to yield alternative products to petroleum-based ones. In this work, hydrolysis lignin (HL) was copolymerized with acrylamide (AM) and acrylic acid (AA) under acidic conditions to generate the lignin/AM polymer (HM), lignin/AA polymer (HA), and lignin/AM/AA copolymer (HAM) with different negative charge densities and molecular weights. Lignin-based polymers characterized by advanced tools, such as proton nuclear magnetic resonance (1H NMR), gel permission chromatography (GPC), and elemental analysis confirmed the successful polymerization of HL with AM, AA, or AM/AA monomers. The adsorption analysis using a quartz crystal microbalance (QCM) revealed that compared to diblock HM and HA, the triblock copolymers of HAM adsorbed more on the Al2O3 surface and generated a bulkier adsorbed layer, which is important for lignin-based coating formulation. HAM1 with a lower charge density yielded a higher surface excess density, while HAM2 with a larger R h occupied more space (153.7 Å2) at the interface of water and Al2O3. In suspension systems, because of the higher M w, R h, and adsorption affinity, the bridging performance of HAM2 was more remarkable than that of the other lignin derivatives for Al2O3 particles via forming stronger flocs (with a deflocculation parameter, T df, of 80.6 s). However, the diblock lignin-AA (HA1) polymer showed the fastest floc regrowth capability after reducing the shear forces (with a reflocculation parameter, T rf, of 62.5 s). The high thermal stability, T g, and rheological characteristics of the HAM copolymer proved that it can be an excellent material for coating formulations and flocculants for wastewater treatment systems.

Lubricating properties of chewing stimulated whole saliva from patients suffering from xerostomia

OBJECTIVES

The study aimed to quantify the lubricating properties of chewing stimulated whole saliva from healthy controls (n = 22), from patients suffering from primary Sjögren's syndrome (n = 37) and from patients undergoing head-and-neck radiotherapy (n = 34).

MATERIALS AND METHODS

All participants had to complete the Xerostomia Inventory questionnaire to score dry mouth sensation. Lubrication was measured using an ex vivo tongue-enamel friction system in terms of Relief and Relief period. MUC5b and total protein concentrations of the saliva samples were measured by an enzyme-linked immunosorbent assay and a bicinchoninic acid assay, respectively.

RESULTS

Relief of Sjögren's patients' saliva and post-irradiation patients' saliva was similar compared with healthy controls, but saliva from post-irradiation patients lubricated significantly better than saliva from Sjögren's patients. The Relief period was similar between the three groups. The Relief and Relief period were higher for saliva samples post-irradiation compared to pre-irradiation. MUC5b and total protein concentrations were comparable in all groups. MUC5b and total protein output were significantly lower in patients subjected to radiotherapy compared to saliva from healthy controls and pre-irradiation patients. MUC5b concentrations positively correlated with lubricating properties of post-irradiation patient saliva.

CONCLUSIONS

The lubricating properties of patient saliva were not any worse than healthy controls. Lower flow rate leads to lower availability of saliva in the oral cavity and decreases the overall output of protein and MUC5b, which might result in an insufficient replenishing of the mucosal salivary film.

CLINICAL RELEVANCE

An insufficient replenishing might underlie the sensation of a dry mouth and loss of oral function.

A comparison between the structures of reconstituted salivary pellicles and oral mucin (MUC5B) films

HYPOTHESIS

Salivary pellicles i.e., thin films formed upon selective adsorption of saliva, protect oral surfaces against chemical and mechanical insults. Pellicles are also excellent aqueous lubricants. It is generally accepted that reconstituted pellicles have a two-layer structure, where the outer layer is mainly composed of MUC5B mucins. We hypothesized that by comparing the effect of ionic strength on reconstituted pellicles and MUC5B films we could gain further insight into the pellicle structure.

EXPERIMENTS

Salivary pellicles and MUC5B films reconstituted on solid surfaces were investigated at different ionic strengths by Force Spectroscopy, Quartz Crystal Microbalance with Dissipation, Null Ellipsometry and Neutron Reflectometry.

FINDINGS

Our results support the two-layer structure for reconstituted salivary pellicles. The outer layer swelled when ionic strength decreased, indicating a weak polyelectrolyte behavior. While initially the MUC5B films exhibited a similar tendency, this was followed by a drastic collapse indicating an interaction between exposed hydrophobic domains. This suggests that mucins in the pellicle outer layer form complexes with other salivary components that prevent this interaction. Lowering ionic strength below physiological values also led to a partial removal of the pellicle inner layer. Overall, our results highlight the importance that the interactions of mucins with other pellicle components play on their structure.

Artificial oral fluid characterisation: Potential for use as a reference matrix in drug testing

Quality assurance schemes for drug-screening programmes require access to large quantities of biological matrices for reference or control samples. This presents problems when the availability of a matrix, such as oral fluid (OF) for screening or for confirmatory purposes, limits the collection of large volumes. In such cases, synthetic alternatives of OF may provide a solution. The preparation of an artificial (synthetic) oral fluid (AOF) was conducted by dissolving its components (salts, surfactant, antimicrobial agent and mucin) in water. We characterised the physical properties of AOF to determine its suitability as a matrix for quality assurance purposes. The evaluation of pH, specific gravity (SG), conductivity (mS cm^-1 ), freezing point depression (°C), light-scattering and kinematic viscosity (mm² s^-1 ) showed AOF to be a stable, reliable matrix. Synthetic OF was prepared using components (mucin, surfactants and so on) obtained from different suppliers and a comparison was performed. Our results suggest that AOF is a feasible matrix for the preparation of quality assurance samples for confirmatory or drug screening programmes.

Salivary lubricity (ex vivo) enhances upon moderate exercise: A pilot study

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Moderate intensity exercise leads to enhanced lubrication performance of saliva.

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Such enhanced lubrication performance was sustained after 60 min of rest.

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Protein content and α-amylase activity in saliva was elevated post-exercise.

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Protein content and α-amylase activity returned to baseline with an hour.

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Effects of exercise on salivary mucin (MUC5B) content was not observed.

Objective

This study sought to examine the effects of moderate intensity exercise on lubrication performance of saliva. We hypothesized that exercise would result in enhanced salivary lubricity by direct sympathetic stimulation of the salivary proteins.

Study design

In total, 11 healthy young pre-menopausal female participants (mean age: 24.4 ± 1.8 years, BMI: 22.1 ± 1.9 kg/m²) were included in a within-subjects repeated measures experimental design. Unstimulated whole saliva was collected at rest (S₀), immediately after 45 min of moderate intensity cycling at ∼70 % maximum heart rate (mean: 133.4 ± 0.8 bpm) or time-match quiet rest (S₁), and after a 60 min of recovery period (S₂). Ex vivo salivary lubricity were measured using soft tribology. Total protein content, mucin (MUC5B) concentration, and α-amylase activity were determined.

Results

Tribology results revealed that moderate intensity exercise resulted in enhanced lubricity of saliva with an order-of-magnitude lower friction coefficients in the boundary regime at S₁ and S_2, with frictional forces being significantly lower at S₁ (p < 0.001) and S₂ (p < 0.001) as compared to the Control procedure. Total protein and α-amylase secretion also increased in the Exercise procedure at S₁ (p < 0.05), but concentrations returned to baseline levels at S₂.

Conclusions

Moderate intensity exercise leads to an increase in α-amylase and total protein secretion resulting in enhanced lubrication performance of the saliva. However, the lubrication performance was not related to MUC5B content, suggesting the role of other proteinaceous species acting as lubricants. This proof-of-concept study serves as the first step to design exercise interventions in populations with dry mouth conditions.

Human saliva and model saliva at bulk to adsorbed phases - similarities and differences

Human saliva, a seemingly simple aqueous fluid, is, in fact, an extraordinarily complex biocolloid that is not fully understood, despite many decades of study. Salivary lubrication is widely believed to be a signature of good oral health and is also crucial for speech, food oral processing and swallowing. However, saliva has been often neglected in food colloid research, primarily due to its high intra- to inter-individual variability and altering material properties upon collection and storage, when used as an ex vivo research material. In the last few decades, colloid scientists have attempted designing model (i.e. 'saliva mimicking fluid') salivary formulations to understand saliva-food colloid interactions in an in vitro set up and its contribution on microstructural aspects, lubrication properties and sensory perception. In this Review, we critically examine the current state of knowledge on bulk and interfacial properties of model saliva in comparison to real human saliva and highlight how far such model salivary formulations can match the properties of real human saliva. Many, if not most, of these model saliva formulations share similarities with real human saliva in terms of biochemical compositions, including electrolytes, pH and concentrations of salivary proteins, such as α-amylase and highly glycosylated mucins. This, together with similarities between model and real saliva in terms of surface charge, has led to significant advancement in decoding various colloidal interactions (bridging, depletion) of charged emulsion droplets and associated sensory perception in the oral phase. However, model saliva represents significant dissimilarity to real saliva in terms of lubricating properties. Based on in-depth examination of properties of mucins derived from animal sources (e.g. pig gastric mucins (PGM) or bovine submaxillary mucin (BSM)), we can recommend that BSM is currently the most optimal commercially available mucin source when attempting to replicate saliva based on surface adsorption and lubrication properties. Even though purification via dialysis or chromatographic techniques may influence various physicochemical properties of BSM, such as structure and surface adsorption, the lubricating properties of model saliva formulations based on BSM are generally superior and more reliable than the PGM counterpart at orally relevant pH. Comparison of mucin-containing model saliva with ex vivo human salivary conditioning films suggests that mucin alone cannot replicate the lubricity of real human salivary pellicle. Mucin-based multi-layers containing mucin and oppositely charged polyelectrolytes may offer promising avenues in the future for engineering biomimetic salivary pellicle, however, this has not been explored in oral tribology experiments to date. Hence, there is a strong need for systematic studies with employment of model saliva formulations containing mucins with and without polycationic additives before a consensus on a standardized model salivary formulation can be achieved. Overall, this review provides the first comprehensive framework on simulating saliva for a particular bulk or surface property when doing food oral processing experiments.

Interactions of Fly Ash Particles with Mucin and Serum Albumin

Fly ash particles can contribute to haze and adverse health outcomes. In this study, two mucins, one from bovine submaxillary glands (bovine submaxillary mucin, BSM) and one from porcine stomach (porcine gastric mucin), as well as bovine serum albumin (BSA), which served as the physical barriers against foreign substances entering the tissues and the blood protein, respectively, were chosen as models for the investigations of the interactions between the proteins and the fly ash particles. Their adsorption behaviors were studied using spectroscopy and a quartz crystal microbalance with a dissipation monitor (QCM-D). The results indicated that the fly ash particles can induce the loosening of mucins and BSA, probably via the formation of complexes. Further, the secondary structure of proteins changed in the presence of fly ash particles. The α-helix content decreased with an increasing fly ash particle concentration. The addition of fly ash particles into protein solutions led to fluorescence quenching, which suggested that there were interactions between these particles and the mucins and BSA. The association constants ( K_a) for BSM and BSA were 5.35 and 4.18 L/g, respectively. Furthermore, the results of QCM-D analyses showed that the amount decreased on the mucin surface but increased slightly on the BSA surface, which indicated that the fly ash particles disrupted the mucin layer upon adsorption. These findings provide clear evidence of the interactions between the fly ash particles and the mucins and BSA, which can lead to structural changes. This study contributes to a better understanding of the interactions and adsorptions of atmospheric particulate pollutants with the proteins in the human body.

β-CD-Functionalized Microdevice for Rapid Capture and Release of Bacteria

Most procedures for detecting pathogens in liquid media require an initial concentration step. In this regard, carbohydrates have proven to be attractive affinity ligands for the solid-phase capture of bacteria that use lectins for adhesion to host cell membranes. However, the use of cyclodextrin-immobilized substrates to selectively trap bacteria has not been explored before. Here, using quartz-crystal microbalance with dissipation monitoring experiments, we demonstrate that functionalization of surfaces by β-cyclodextrin (β-CD) can not only allow for rapid and efficient capture of bacterial cells in liquid but also their facile elution with an aqueous solution of a selectively methylated β-CD derivative as a competitive molecule. This capture/elution strategy, which is based on host-guest interactions between membrane components of the bacterial cell and the CD cavities, is performed in physiological conditions and can be integrated in a microchip. Indeed, proof-of-concept studies showed the potential of β-CD-modified micropillar-integrated microfluidic devices for concentration of bacteria. The results obtained with Escherichia coli suggest that this approach could be broadly applicable among Gram-negative bacteria, which share common cell membrane structures.

Synergies in lubrication

In living organisms the aqueous medium is used for providing low friction forces. This is achieved by synergistic actions of different biomolecules that together accomplish a high load bearing capacity and sustain an easily sheared water layer.

Solid liquid liquid extraction of porcine gastric mucins from homogenized animal material

With solid liquid liquid extraction as a new capture step for the purification of porcine gastric mucins from crude homogenate, yield and productivity was optimized.

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.

Designing food delivery systems: challenges related to the in vitro methods employed to determine the fate of bioactives in the gut

This review discussesin vitroavailable approaches to study delivery and uptake of bioactive compounds and the associated challenges.

An optimized purification process for porcine gastric mucin with preservation of its native functional properties

The purification of porcine gastric mucin was optimized and key properties such as gel formation at acidic pH, lubrication behavior and interactions of mucins with charged molecules were preserved.

Biomechanical factors related to occlusal load transfer in removable complete dentures

Owing to economic conditions, removable dentures remain popular despite the discomfort and reduced chewing efficiency experienced by most denture wearers. However, there is little evidence to confirm that the level of mucosal load exceeds the pressure pain threshold. This discrepancy stimulated us to review the current state of knowledge on the biomechanics of mastication with complete removable dentures. The loading beneath dentures was analyzed in the context of denture foundation characteristics, salivary lubrication, occlusal forces, and the biomechanics of mastication. The analysis revealed that the interpretation of data collected in vivo is hindered due to the simultaneous overlapping effects of many variables. In turn, problems with determining the pressure beneath a denture and analyzing frictional processes constitute principal limitations of in vitro model studies. Predefined conditions of finite element method simulations should include the effects of oblique mastication forces, simultaneous detachment and sliding of the denture on its foundation, and the stabilizing role of balancing contacts. This review establishes that previous investigations may have failed because of their unsubstantiated assumption that, in a well-working balanced occlusion, force is only exerted perpendicular to the occlusal plane, allowing the denture to sit firmly on its foundation. Recent improvements in the simulation of realistic biomechanical denture behavior raise the possibility of assessing the effects of denture design on the pressures and slides beneath the denture.

New Insights into the Composition and Functions of the Acquired Enamel Pellicle

The acquired enamel pellicle (AEP) is a thin acellular film that forms on tooth surfaces upon exposure to the oral environment. It consists predominantly of salivary proteins, but also includes non-salivary-derived proteins, carbohydrates, and lipids. Since it is the interface between teeth and the oral environment, the AEP plays a key role in the maintenance of oral health by regulating processes including lubrication, demineralization, and remineralization and shaping the composition of early microbial flora adhering to tooth surfaces. Knowledge of the 3D structure of the AEP and how that correlates with its protective functions may provide insight into several oral pathological states, including caries, erosion, and periodontal disease. This review intends to update readers about the latest discoveries related to the formation, ultrastructure, composition, and functions of the AEP, as well as the future of pellicle research, with particular emphasis on the emerging role of proteomic and microscopy techniques in oral diagnosis and therapeutics.

Boundary lubrication by brushed salivary conditioning films and their degree of glycosylation

Objectives

Toothbrushing, though aimed at biofilm removal, also affects the lubricative function of adsorbed salivary conditioning films (SCFs). Different modes of brushing (manual, powered, rotary–oscillatory or sonically driven) influence the SCF in different ways. Our objectives were to compare boundary lubrication of SCFs after different modes of brushing and to explain their lubrication on the basis of their roughness, dehydrated layer thickness, and degree of glycosylation. A pilot study was performed to relate in vitro lubrication with mouthfeel in human volunteers.

Materials and methods

Coefficient of friction (COF) on 16-h-old SCFs after manual, rotary–oscillatory, and sonically driven brushing was measured using colloidal probe atomic force microscopy (AFM). AFM was also used to assess the roughness of SCFs prior to and after brushing. Dehydrated layer thicknesses and glycosylation of the SCFs were determined using X-ray photoelectron spectroscopy. Mouthfeel after manual and both modes of powered brushing were evaluated employing a split-mouth design.

Results

Compared with unbrushed and manually or sonically driven brushed SCFs, powered rotary–oscillatory brushing leads to deglycosylation of the SCF, loss of thickness, and a rougher film. Concurrently, the COF of a powered rotary–oscillatory brushed SCF increased. Volunteers reported a slightly preferred mouthfeel after sonic brushing as compared to powered rotating–oscillating brushing.

Conclusion

Deglycosylation and roughness increase the COF on SCFs.

Clinical relevance

Powered rotary–oscillatory brushing can deglycosylate a SCF, leading to a rougher film surface as compared with manual and sonic brushing, decreasing the lubricative function of the SCF. This is consistent with clinical mouthfeel evaluation after different modes of brushing.

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.

Normal and frictional interactions of purified human statherin adsorbed on molecularly-smooth solid substrata

Human salivary statherin was purified from parotid saliva and adsorbed to bare hydrophilic (HP) mica and STAI-coated hydrophobic (HB) mica in a series of Surface Force Balance experiments that measured the normal (F(n)) and friction forces (F(s)*) between statherin-coated mica substrata. Readings were taken both in the presence of statherin solution (HP and HB mica) and after rinsing (HP mica). F(n) measurements showed, for both substrata, monotonic steric repulsion that set on at a surface separation D ~20 nm, indicating an adsorbed layer whose unperturbed thickness was ca 10 nm. An additional longer-ranged repulsion, probably of electrostatic double-layer origin, was observed for rinsed surfaces under pure water. Under applied pressures of ~1 MPa, each surface layer was compressed to a thickness of ca 2 nm on both types of substratum, comparable with earlier estimates of the size of the statherin molecule. Friction measurements, in contrast with F(n) observations, were markedly different on the two different substrata: friction coefficients, μ ≡ ∂F(s)*/∂F(n), on the HB substratum (μ ≈ 0.88) were almost an order of magnitude higher than on the HP substratum (μ ≈ 0.09 and 0.12 for unrinsed and rinsed, respectively), and on the HB mica there was a lower dependence of friction on sliding speed than on the HP mica. The observations were attributed to statherin adsorbing to the mica in multimer aggregates, with internal re-arrangement of the protein molecules within the aggregate dependent on the substratum to which the aggregate adsorbed. This internal re-arrangement permitted aggregates to be of similar size on HP and HB mica but to have different internal molecular orientations, thus exposing different moieties to the solution in each case and accounting for the very different friction behaviour.

Friction force spectroscopy of β- and κ-casein monolayers

Friction force spectroscopy (FFS) has been applied to study the tribological properties of β- and κ-casein layers on hydrophobic substrates in aqueous solutions. Nanometer-sized imaging tips were employed. This allowed exerting and determining the high pressures needed to remove the layers and registering the topographic evolution during this process. Both β- and κ-casein layers showed similar and not particularly high initial frictional responses (friction coefficient of ∼1 when measured with a silicon nitride tip). The pressures needed to remove the layers were of the same order of magnitude for both proteins, ∼10(8) Pa, but slightly higher for those composed of β-casein. The technique has also shown to be useful in studying the two-dimensional lateral diffusion of the proteins and the wear on the layers they form.

Structural characterization of a new statherin from pig parotid granules

This study describes the identification and structural characterization of Sus scrofa statherin. HPLC-electrospray ionization mass spectrometry analysis on pig parotid secretory granule extracts evidenced a peptide with a molecular mass value of 5381.1 +/- 0.6 Da and its truncated form, devoid of the C-terminal Ala residue, with a molecular mass value of 5310.1 +/- 0.6 Da. The complete sequence of pig statherin gene was determined by sequencing the full-length cDNA obtained by rapid amplification of cDNA ends. The gene is 549 base pairs long and contains an open reading frame of 185 nucleotides, encoding a 42-amino acid secretory polypeptide with a signal peptide of 19 residues. This sequence presents some typical features of the four statherins characterized till now, showing the highest degree of amino acid identity with bovine (57%) and human statherin (39%). Pig statherin is mono-phoshorylated on Ser-3, while primate statherins already characterized are di-phosphorylated on Ser-2 and Ser-3. This difference, probably connected to the Asp-4 --> Glu substitution, suggests the involvement of the Golgi-casein kinase, which strictly recognizes the SX(E/pS) consensus sequence.

Sequential adsorption of bovine mucin and lactoperoxidase to various substrates studied with quartz crystal microbalance with dissipation

Mucin and lactoperoxidase are both natively present in the human saliva. Mucin provides lubricating and antiadhesive function, while lactoperoxidase has antimicrobial activity. We propose that combined films of the two proteins can be used as a strategy for surface modification in biomedical applications such as implants or biosensors. In order to design and ultilize mixed protein films, it is necessary to understand the variation in adsorption behavior of the proteins onto different surfaces and how it affects their interaction. The quartz crystal microbalance with dissipation (QCM-D) technique has been used to extract information of the adsorption properties of bovine mucin (BSM) and lactoperoxidase (LPO) to gold, silica, and hydrophobized silica surfaces. The information has further been used to retrieve information of the viscoelastic properties of the adsorbed film. The adsorption and compaction of BSM were found to vary depending on the nature of the underlying bare surface, adsorbing as a thick highly hydrated film with loops and tails extending out in the bulk on gold and as a thinner film with much lower adsorbed amount on silica; and on hydrophobic surfaces, BSM adsorbs as a flat and much more compact layer. On gold and silica, the highly hydrated BSM film is cross-linked and compacted by the addition of LPO, whereas the compaction is not as pronounced on the already more compact film formed on hydrophobic surfaces. The adsorption of LPO to bare surfaces also varied depending on the type of surface. The adsorption profile of BSM onto LPO-coated surfaces mimicked the adsorption to the underlying surface, implying little interaction between the LPO and BSM. The interaction between the protein layers was interpreted as a combination of electrostatic and hydrophobic interactions, which was in turn influenced by the interaction of the proteins with the different substrates.

Adsorption of the Flexible Salivary Proteins Statherin and PRP-1 to Negatively Charged Surfaces – A Monte Carlo Simulation and Ellipsometric Study

The structural properties of the salivary proteins, acidic proline rich PRP-1 and statherin, adsorbed onto negatively charged surfaces have been studied by Monte Carlo simulations and ellipsometry. It is shown that both proteins adsorb to negatively charged surfaces, although their net charges are negative. Experimentally, an initial fast mass-controlled film build-up was detected for both proteins, and plateaus were reached within 10 min. The isotherm shape and the adsorbed amounts were similar for PRP-1 to hydrophilic and hydrophobic surfaces, while statherin adsorbs to a greater extent to the hydrophobic surface. These results could be explained from the simulation results by considering the proteins as diblock polyampholytes. It has also been shown that the adsorption of PRP-1 to a negatively charged surface may be purely electrostatically driven, while pure electrostatic interaction is not sufficient to drive adsorption of statherin,i.e., an extra short-ranged attractive interaction is necessary to account for the experimental observations.

Viscous boundary lubrication of hydrophobic surfaces by mucin

The lubricating behavior of the weakly charged short-side-chain glycoprotein mucin "Orthana" (Mw=0.55 MDa) has been investigated between hydrophobic and hydrophilic PDMS substrates using soft-contact tribometry. It was found that mucin facilitates lubrication between hydrophobic PDMS surfaces, leading to a 10-fold reduction in boundary friction coefficient for rough surfaces. The presence of mucin also results in a shift of the mixed lubrication regime to lower entrainment speeds. The observed boundary lubrication behavior of mucin was found to depend on the bulk concentration, and we linked this to the structure and dynamics of the adsorbed mucin films, which are assessed using optical waveguide light spectroscopy. We observe a composite structure of the adsorbed mucin layer, with its internal structure governed by entanglement. The film thickness of this adsorbed layer increases with concentration, while the boundary friction coefficient for rough surfaces was found to be inversely proportional to the thickness of the adsorbed film. This link between lubrication and structure of the film is consistent with a viscous boundary lubrication mechanism, i.e., a thicker adsorbed film, at a given sliding speed, results in a lower local shear rate and, hence, in a lower local shear stress. The estimated local viscosities of the adsorbed layer, derived from the friction measurements and the polymer layer density, are in agreement with each other.

Normal and friction forces between mucin and mucin-chitosan layers in absence and presence of SDS

Employing the colloidal probe AFM technique we have investigated normal and friction forces between flat mica surfaces and silica particles coated with mucin and combined mucin-chitosan layers in presence and absence of anionic surfactant, SDS, in 30 mM NaCl solution. We have shown that the normal interactions between mucin coated mica and silica surfaces are dominated by long-range steric repulsion on both compression and decompression. Friction forces between such mucin layers are characterized by a low effective friction coefficient, mu(eff)=0.03+/-0.02, which is lower than the value of 0.13+/-0.02 observed when chitosan layers were adsorbed. Forces between combined mucin-chitosan layers have also been measured. Adsorption of chitosan on mucin results in considerable compaction of the layer, and development of attractive forces detectable on separation. Friction between mucin-chitosan layers in 30 mM NaCl solution is high, with mu(eff) approximately 0.4. Adsorption of additional mucin to this layer results in no improvement with respect to lubrication as compared to the mucin-chitosan layer, and mu(eff) approximately 0.4 is observed. We argue that the layers containing both mucin and chitosan are not strictly layered but rather strongly entangled. As a result attractive interactions between oppositely charged moieties of sialic acid residues from mucin and amine groups from chitosan residing on the opposing surfaces contribute to the increased friction. The effects of SDS on normal and friction forces between combined mucin-chitosan layers were also investigated. The relation between surface interactions and friction properties is discussed.

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.

Saliva as research material: Biochemical, physicochemical and practical aspects

Whole saliva is a complex mixture of proteins and other molecules which originate from several sources. The biochemical and physicochemical properties of saliva contribute to the numerous functions of saliva in, e.g., speech, maintaining oral and general health, and food processing. Interest in saliva has increased in the last few years for its potential to diagnose viral, bacterial and systemic diseases. The use of saliva as research material may pose particular problems due to its inherent variability and instability. This review describes practical aspects of salivary as research material with emphasis on protein biochemistry and physical chemistry.

Charge and interfacial behavior of short side-chain heavily glycosylated porcine stomach mucin

The current accepted model for high-molecular-weight gastric mucins of the MUC family is that they adopt a polydisperse coil conformation in bulk solutions. We develop this model using well-characterized highly purified porcine gastric mucin and examine the molecules' charge and interfacial adsorption. "Orthana" mucin has short side-chains, low levels of sialic acid residues, and includes minute amounts of cystine residues that can be responsible for the self-polymerization of mucin. Atomic force microscopy and transmission electron microscopy are used to examine the interfacial behavior of the mucin and clearly demonstrate the existence of discrete spherical subunits within the mucin molecules, with sizes in agreement with static light scattering, dynamic light scattering, and zeta potential measurements. Furthermore images indicate the combs are assembled with a beads on a string conformation; the daisy chain model. Zeta potential measurements establish the polyampholyte nature of the mucin molecules, which is used to explain their adsorption behavior on similarly charged surfaces.

Adsorption and viscoelastic properties of fractionated mucin (BSM) and bovine serum albumin (BSA) studied with quartz crystal microbalance (QCM-D)

The adsorption profile and viscoelastic properties of bovine submaxillary gland mucin (BSM) and bovine serum albumin (BSA), extracted from a commercial mucin preparation, adsorbing to polystyrene surfaces has been studied using quartz crystal microbalance with dissipation monitoring (QCM-D). A significant difference in the adsorption properties of the different proteins was detected; with the BSA adsorbing in a flat rigid layer whilst the mucin adsorbed in a diffuse, highly viscoelastic layer. Subsequent addition of BSA to the preadsorbed mucin layer resulted in stiffening of the protein layer which was attributed to complexation of the mucin by BSA. In contrast, a preadsorbed layer of BSA prevented mucin adsorption altogether. Combined mixtures of mucin and BSA in well defined ratios revealed intermediate properties between the two separate protein species which varied systematically with the protein ratios. The results shed light on the synergistic effects of complexation of lower molecular weight biomolecular species with mucin. The possibility to selectively control protein uptake and tailor the physical properties of the adsorbed layer makes mucin an attractive option for application in biomaterial coatings.