Viscosity of whole saliva

Volatile sulfur compounds, biofilm, and salivary parameters in patients with periodontal disease: a cross-sectional study

This cross-sectional study aimed to evaluate the interplay between volatile sulfur compounds (VSC), biofilm, salivary parameters, and periodontal status in patients with and without periodontal disease. Sixty-four subjects diagnosed with periodontitis and 60 periodontally healthy individuals were included. Probing depth, clinical attachment level, bleeding on probing, tongue coating index, plaque index, number of teeth, spinnability of unstimulated whole saliva, and salivary flow rate were evaluated. The concentrations of VSC were quantified using a portable gas chromatograph. The mean differences in hydrogen sulfide, methyl mercaptan, salivary flow, spinnability, and plaque index did not exhibit statistically significant variances between the two groups. However, a pronounced tongue coating index and a diminished tooth count showed statistical significance in the periodontitis group (p = 0.039; p < 0.001). Unstimulated salivary flow rate less than 0.25 mL/min was statistically significant in the periodontitis group (p = 0.032). After controlling for confounding factors, bleeding on probing remained significant. A positive correlation between periodontal parameters and VSC concentration was found. An inverse correlation was also noted between the spinnability of saliva and tongue coating index (-0.34; p < 0.001). Salivary parameters may contribute to the formation of tongue coating and are correlated with periodontal status. Bleeding on probing, clinical attachment level, and probing depth were identified as potential contributors to VSC formation.

The effect of contaminating media on the static and dynamic mechanical resilience of dental implant abutments' screws: In vitro study

INTRODUCTION

This in vitro study aims to biomechanically evaluate the influence of medium contamination for example, saliva, blood, chlorhexidine (liquid and gel), and fluoride mouthwash on the biomechanical behavior of implant abutments' screws under static and dynamic loading.

METHODS

Forty five Ti6Al4V commercial dental implants and abutments were tested in this study. Two main mechanical tests were carried out in the selected media. The first, static, aimed to evaluate the torque loss after the first tightening. The second, dynamic, involved a random cyclic load range between 0 and 200 N to evaluate torque loss due to mastication. In addition, metallographic longitudinal and cross-sections of the abutment-implant apparatus were examined to evaluate the abutment screw-abutment-implant interface.

RESULTS

The static torque test showed that irrespective of the media, no statistical difference in static torque loss was found prior to dynamic loading. For the dynamic tests, torque-angle evolution analysis during tightening to 30 Ncm and after the spectrum loading, showed the same global mechanical behavior for all media, but the statistical analysis indicated a difference between the groups in reverse torque values (RTV) and in the torque loss due to dynamic loading. The medium groups CHX, CHX-gel, and Fluoride mouthwash, showed a meaningful torque loss due to loading, but the medium groups, control (no medium), blood and saliva showed an opposite trend and required a higher torque to open the abutment screws. The microstructural analysis revealed clear signs of cold-welding/galling, post-dynamic loading in these latter groups.

CONCLUSIONS

The presence of lubrication/contamination media (CHX mouthwash/CHX-gel/Fluoride mouthwash) reduces the preload generated due to tightening but prevents damage due to galling. The observed reduction of RTV clearly emphasizes the need for frequent abutment screw retightening for implant-supported prosthetic long-term stability.

Pinching dynamics, extensional rheology, and stringiness of saliva substitutes

Saliva substitutes are human-made formulations extensively used in medicine, food, and pharmaceutical research to emulate human saliva's biochemical, tribological, and rheological properties. Even though extensional flows involving saliva are commonly encountered in situations such as swallowing, coughing, sneezing, licking, drooling, gleeking, and blowing spit bubbles, rheological evaluations of saliva and its substitutes in most studies rely on measured values of shear viscosity. Natural saliva possesses stringiness or spinnbarkeit, governed by extensional rheology response, which cannot be evaluated or anticipated from the knowledge of shear rheology response. In this contribution, we comprehensively examine the rheology of twelve commercially available saliva substitutes using torsional rheometry for rate-dependent shear viscosity and dripping-onto-substrate (DoS) protocols for extensional rheology characterization. Even though most formulations are marketed as having suitable rheology, only three displayed measurable viscoelasticity and strain-hardening. Still, these too, failed to emulate the viscosity reduction with the shear rate observed for saliva or match perceived stringiness. Finally, we explore the challenges in creating saliva-like formulations for dysphagia patients and opportunities for using DoS rheometry for diagnostics and designing biomimetic fluids.

Analysis of Covarine Particle in Toothpaste Through Microfluidic Simulation, Experimental Validation, and Electrical Impedance Spectroscopy

Covarine, copper phthalocyanine, a novel tooth whitening ingredient, has been incorporated into various toothpaste formulations using diverse technologies such as larger flakes, two-phase pastes, and microbeads. In this study, we investigated the behavior of covarine microbeads (200 μm) in Colgate advanced white toothpaste when mixed with artificial and real saliva. Our analysis utilized a custom-designed microfluidic mixer with 400 μm wide channels arranged in serpentine patterns, featuring a Y-shaped design for saliva and toothpaste flow. The mixer, fabricated using stereolithography 3D printing technology, incorporated a flexible transparent resin (Formlabs' Flexible 80A resin) and PMMA layers. COMSOL simulations were performed by utilizing parameters extracted from toothpaste and saliva datasheets, supplemented by laboratory measurements, to enhance simulation accuracy. Experimental assessments encompassing the behavior of covarine particles were conducted using an optical profilometer. Viscosity tests and electrical impedance spectroscopy employing recently developed all-carbon electrodes were employed to analyze different toothpaste dilutions. The integration of experimental data from microfluidic chips with computational simulations offers thorough insights into the interactions of covarine particles with saliva and the formation of microfilms on enamel surfaces.

The use of biological fluids in microfluidic paper-based analytical devices (μPADs): Recent advances, challenges and future perspectives

The use of microfluidic paper-based analytical devices (μPADs) for aiding medical diagnosis is a growing trend in the literature mainly due to their low cost, easy use, simple manufacturing, and great potential for application in low-resource settings. Many important biomarkers (proteins, ions, lipids, hormones, DNA, RNA, drugs, whole cells, and more) and biofluids are available for precise detection and diagnosis. We have reviewed the advances μPADs in medical diagnostics have achieved in the last few years, focusing on the most common human biofluids (whole blood/plasma, sweat, urine, tears, and saliva). The challenges of detecting specific biomarkers in each sample are discussed, along with innovative techniques that overcome such limitations. Finally, the difficulties of commercializing μPADs are considered, and future trends are presented, including wearable devices and integrating multiple steps in a single platform.

The biomolecular gastrointestinal corona in oral drug delivery

The formation of a biomolecular corona on exogenous particles in plasma is well studied and is known to dictate the biodistribution and cellular interactions of nanomedicine formulations. In contrast, while the oral route is the most favorable administration method for pharmaceuticals, little is known about the formation and composition of the corona formed by biomolecules on particles within the gastrointestinal tract. This work reviews the current literature understanding of (1) the formation of drug particles after oral administration, (2) the formation of a biomolecular corona within the gastrointestinal tract ("the gastrointestinal corona"), and (3) the possible implications of the formation of a gastrointestinal corona on the interactions of drug particles with their biological environment. In doing so, this work aims to establish the significance of the formation of a gastrointestinal corona in oral drug delivery to ultimately arrive at new avenues to control the behavior of orally administered pharmaceuticals.

A Comparative Evaluation of Physical Parameters of Saliva and Correlation with Periodontal Condition in Down Syndrome Children and Healthy Controls

AIM

The aim of this study was to assess the significance and role of physical parameters of saliva on periodontal health in children with Down syndrome (DS).

MATERIALS AND METHODS

A comparative evaluation of physical parameters of saliva such as flow rate, viscosity, pH, quantity and buffering capacity, and buffer capacity was carried out using GC Saliva-Check Buffer kit and correlated with periodontal condition examined using community periodontal index of treatment needs (CPITN) in 40 DS subjects (group I) and 40 healthy controls (group II) aged 8-15 years.

RESULTS

Down syndrome subjects had a low resting salivary flow rate, moderately acidic saliva, very low quantity of stimulated saliva, and low buffering capacity. On correlating salivary parameters with the periodontal condition, DS subjects with CPITN code 1 had low resting salivary flow rate, normal viscosity, moderately acidic pH, very low quantity of stimulated saliva, and low buffering capacity. Down syndrome subjects with CPITN code 2 had low resting flow rate, increased viscosity, very low quantity of stimulated saliva, low buffering capacity, and moderately acidic pH. Healthy controls with CPITN code 0 had normal resting flow rate, viscosity of saliva, quantity of stimulated saliva, buffering capacity, and moderately acidic pH.

CONCLUSION

Compared to healthy controls, DS subjects showed decreased values for resting flow rate, pH, quantity of stimulated saliva, and buffering capacity. A statistically significant correlation was observed between the physical parameters of saliva and periodontal condition in DS subjects (p < 0.05).

CLINICAL SIGNIFICANCE

Periodontal diseases start at a very early age and periodontal health deteriorates at a faster rate in DS children for which saliva also plays its part. Prime importance should be given to frequent oral hygiene and preventive measures in DS children thus preventing accumulation of debris and plaque.

Superhydrophobic 3D-Assembled Metallic Nanoparticles for Trace Chemical Enrichment in SERS Sensing

The performance of surface-enhanced Raman spectroscopy (SERS) is determined by the interaction between highly diluted analytes and boosted localized electromagnetic fields in nanovolumes. Although superhydrophobic surfaces are developed for analyte enrichment, i.e., to concentrate and transfer analytes toward a specific position, it is still challenging to realize reproducible, uniform, and sensitive superhydrophobic SERS substrates over large scales, representing a major barrier for practical sensing applications. To overcome this challenge, a superhydrophobic SERS chip that combines 3D-assembled gold nanoparticles on nanoporous substrates is proposed, for a strong localized field, with superhydrophobic surface treatment for analyte enrichment. Intriguingly, by concentrating droplets in the volume of 40 µL, the sensitivity of 1 nm is demonstrated using 1,2-bis(4-pyridyl)-ethylene molecules. In addition, this unique chip demonstrates a relative standard deviation (RSD) of 2.2% in chip-to-chip reproducibility for detection of fentanyl at 1 µg mL^-1 concentration, revealing its potential for quantitative sensing of chemicals and drugs. Furthermore, the trace analysis of fentanyl and fentanyl-heroin mixture in human saliva is realized after a simple pretreatment process. This superhydrophobic chip paves the way toward on-site and real-time drug sensing to tackle many societal issues like drug abuse and the opioid crisis.

Effect of Surface Porosity on SARS-CoV-2 Fomite Infectivity

Previous reports indicated the low stability of severe actute respiratory syndrome coronovirus 2 (SARS-CoV-2) on various porous surfaces, but the role of porosity was unclear because there was no direct comparison between porous and nonporous solids of the same chemistry. Through comparing pairs of solids with very similar chemistry, we find that porosity is important: porous glass has a much lower infectivity than nonporous glass. However, porosity is not sufficient to lower infectivity; permeability, which is the ability of a liquid to move through a material, is the important parameter. We show this by comparing a pair of porous CuO coatings where the pores are accessible in one case and inaccessible in the other case. When the pores are inaccessible, the infectivity remains similar to that for nonporous solids. Thus, for both glass and CuO, it is the access to porosity that decreases the infectivity of extracted liquid droplets. Having established the importance of permeability, there is the open question of the mechanism of changing the infectivity of SARS-CoV-2. Several hypotheses are possible, such as increasing the difficulty of extracting the virus from the solid, changing the drying time, increasing the surface area of active ingredient, etc. Reverse transcriptase quantitative polymerase chain reaction (RT-qPCR) measurements show that less viral DNA is extracted from a permeable surface, suggesting that the virus becomes trapped in the pores. Finally, we consider the effect of drying. We show that permeability and the water contact angle on the solid have effects on the drying time of a contaminated droplet, which may in turn affect infectivity.

Comparison of diagnosis of cracked tooth using contrast-enhanced CBCT and micro-CT

OBJECTIVES

To evaluate the diagnostic accuracy using sodium iodide (NaI) and dimethyl sulfoxide (DMSO) as contrast agent in cone beam computed tomography (CBCT) scanning, and compare this with micro-CT.

METHODS

18 teeth were cracked artificially by soaking them cyclically in liquid nitrogen and hot water. After pre-treatment with artificial saliva, the teeth were scanned in four modes: CBCT routine scanning without contrast agent (RS); CBCT with meglumine diatrizoate (MD) as contrast agent (ES1); CBCT with NaI + DMSO as contrast agent (ES2); and micro-CT (mCT). The number of crack lines was evaluated in all four modes. Depth of crack lines and number of cracks presented from the occlusal surface to the pulp cavity (Np) in ES2 and micro-CT images were evaluated.

RESULTS

There were 63 crack lines in all 18 teeth. 45 crack lines were visible on ES2 images as against four on the RS and ES1 images (p<0.05) and 37 on micro-CT images (p>0.05). Further, 34 crack lines could be observed on both ES2 and micro-CT images, and the average depth presented on ES2 images was 4.56 ± 0.88 mm and 3.89 ± 1.08 mm on micro-CT images (p<0.05). More crack lines could be detected from the occlusal surface to the pulp cavity on ES2 images than on micro-CT images (22 vs 11).

CONCLUSION

CBCT with NaI +DMSO as the contrast agent was equivalent to micro-CT for number of crack lines and better for depth of crack lines. NaI + DMSO could be a potential CBCT contrast agent to improve diagnostic accuracy for cracked tooth.

Application of centrifugal microfluidics in immunoassay, biochemical analysis and molecular diagnosis

Rapid diagnosis plays a vital role in daily life and is effective in reducing treatment costs and increasing curability, especially in remote areas with limited availability of resources. Among the various common methods of rapid diagnosis, centrifugal microfluidics has many unique advantages, such as less sample consumption, more precise valve control for sequential loading of samples, and accurately separated module design in a microfluidic network to minimize cross-contamination. Therefore, in recent years, centrifugal microfluidics has been extensively researched, and it has been found to play important roles in biology, chemistry, and medicine. Here, we review the latest developments in centrifugal microfluidic platforms in immunoassays, biochemical analyses, and molecular diagnosis, in recent years. In immunoassays, we focus on the application of enzyme-linked immunosorbent assay (ELISA); in biochemical analysis, we introduce the application of plasma and blood cell separation; and in molecular diagnosis, we highlight the application of nucleic acid amplification tests. Additionally, we discuss the characteristics of the methods under each platform as well as the enhancement of the corresponding performance parameters, such as the limit of detection, separation efficiency, etc. Finally, we discuss the limitations associated with the existing applications and potential breakthroughs that can be achieved in this field in the future.

Cupric Oxide Coating That Rapidly Reduces Infection by SARS-CoV-2 via Solids

The ongoing COVID-19 pandemic has created a need for coatings that reduce infection from SARS-CoV-2 via surfaces. Such a coating could be used on common touch surfaces (e.g., door handles and railings) to reduce both disease transmission and fear of touching objects. Herein, we describe the design, fabrication, and testing of a cupric oxide anti-SARS-CoV-2 coating. Rapid loss of infectivity is an important design criterion, so a porous hydrophilic coating was created to allow rapid infiltration of aqueous solutions into the coating where diffusion distances to the cupric oxide surface are short and the surface area is large. The coating was deposited onto glass from a dispersion of cuprous oxide in ethanol and then thermally treated at 700 °C for 2 h to produce a CuO coating that is ≈30 μm thick. The heat treatment oxidized the cuprous oxide to cupric oxide and sintered the particles into a robust film. The SARS-CoV-2 infectivity from the CuO film was reduced by 99.8% in 30 min and 99.9% in 1 h compared to that from glass. The coating remained hydrophilic for at least 5 months, and there was no significant change in the cross-hatch test of robustness after exposure to 70% ethanol or 3 wt % bleach.

Viscosity and mixing properties of artificial saliva and four different mouthwashes

BACKGROUND

Numerous functions of saliva depend on its biophysical properties. Mouth rinses react with saliva and change both their own properties and properties of saliva.

OBJECTIVE

The aim of this study was to define the level of mixing of artificial saliva and mouth rinses, and define their viscosity and its changes at room and body temperature.

METHODS

Artificial saliva, fluoride solutions, chlorhexidine, zinc-hydroxyapatite solution and casein phosphopeptide amorphous calcium phosphate were used. To simulate their mixing, Y-channel PVC chips were used, in two different microfluidics systems. The experiments were recorded with a microscope, then the proportion of mixing was calculated using Matlab. For viscosity measurements rotational viscometer was used.

RESULTS

The results show partial mixing of all solutions with artificial saliva. Measurements with a viscometer indicate different viscosities of all used solutions. Viscosity of a mixture of solution and artificial saliva is always in the range of viscosity of the artificial saliva and the solution separately. Moreover, viscosity of all solutions, as well as mixture with artificial saliva, significantly decreases at higher temperature.

CONCLUSION

Intraoral administration of mouth rinses results in change of biophysical properties of both saliva and mouth rinses. Those changes can affect preventive and therapeutic effect, and therefore oral health.

Eliminating viscosity bias in lateral flow tests

Despite the widespread application of point-of-care lateral flow tests, the viscosity dependence of these assay results remains a significant challenge. Here, we employ centrifugal microfluidic flow control through the nitrocellulose membrane of the strip to eliminate the viscosity bias. The key feature is the balancing of the sample flow into the cassette of the lateral flow test with the air flow out of the cassette. A viscosity-independent flow rate of 3.01 ± 0.18 µl/min (±6%) is demonstrated for samples with viscosities ranging from 1.1 mPas to 24 mPas, a factor greater than 20. In a model human IgG lateral flow assay, signal-intensity shifts caused by varying the sample viscosity from 1.1 mPas to 2.3 mPas could be reduced by more than 84%.

Evaporation-Driven Flow in Micropillar Arrays: Transport Dynamics and Chemical Analysis under Varied Sample and Ambient Conditions

Microfluidic flow in lab-on-a-chip devices is typically very sensitive to the variable physical properties of complex samples, e.g., biological fluids. Here, evaporation-driven fluid transport (transpiration) is achieved in a configuration that is insensitive to interfacial tension, salinity, and viscosity over a wide range. Micropillar arrays ("pillar cuvettes") were preloaded by wicking a known volatile fluid (water) and then adding a microliter sample of salt, surfactant, sugar, or saliva solution to the loading zone. As the preloaded fluid evaporates, the sample is reliably drawn from a reservoir through the pillar array at a rate defined by the evaporation of the preloaded fluid (typically nL/s). Including a reagent in the preloaded fluid allows photometric reactions to take place at the boundary between the two fluids. In this configuration, a photometric signal enhancement is observed and chemical analysis is independent of both humidity and temperature. The ability to reliably transport and sense an analyte in microliter volumes without concern over salt, surfactant, viscosity (in part), humidity, and temperature is a remarkable advantage for analytical purposes.

The sorptivity and durability of gelling fibre dressings tested in a simulated sacral pressure ulcer system

Wound‐dressing performances are affected by exudate viscosity, resistance to flow because of gravity, and bodyweight loads, the level of which is related to the body position. Here, we focussed on two dressing properties: (a) Sorptivity—the ability of dressings to transfer exudate away from the wound bed by capillary action—and (b) Durability—the capacity of dressings to maintain their integrity over time and during their removal. Both properties are critically important for avoiding further tissue damage but require the development of new laboratory tests for their measurement. A computer‐controlled phantom of an exuding sacral pressure ulcer has therefore been developed and used to compare the performances of Exufiber (Mölnlycke Health Care) vs an alternative market‐leading dressing. Sorptivity was determined using weight tests, and durability was measured through tensile tests of the used dressings. For a supine configuration, the Exufiber dressing demonstrated ~three times higher sorptivity and better durability, withstanding ~five times greater strain energy than the other product before failure occurred. This work paves the way for quantitative, standardised testing of dressings in all aspects of exudate management. The reported tests are further suitable for testing dressing combinations or how dressings interact with negative pressure wound therapy.

A stepwise approach investigating salivary responses upon multisensory food cues

Exposure to sensory food cues such as smell, vision, taste and/or texture may trigger anticipatory physiological responses such as salivation, participating on adequate metabolism of the signaled food. However, the individual contribution of each sensory modality as well as the impact of particular food products on salivation and salivary composition remains unclear. Therefore, by systematically varying sensory modalities and nutrient content of food stimuli, we investigated their effect on saliva secretion, α-amylase activity and other salivary characteristics (pH level, buffering capacity, MUC5B concentration, and total protein content). Over 3 sessions, 46 normal-weight healthy participants were exposed to 12 conditions, consisting of 4 levels of sensory stimulation (odor, odor + vision, odor + vision + taste, and odor + vision + taste + mastication) and 3 types of stimuli (bread, high-in-starch; cucumber, low-in-starch; and parafilm as non-food control) during which saliva was collected. Linear mixed models showed a significant increase in salivation with increasing levels of sensory stimulation. α-amylase secretion rate increased upon the highest level of stimulation, which involved mastication, compared to odor and odor + visual level of stimulation. Other salivary characteristics varied with the level of sensory stimulation, which might be related to the total volume of salivation. The type of stimuli did not influence the saliva composition (α-amylase concentration nor other salivary components). Our findings indicate that cumulative sensory information, rather than specific (food) product, play a vital role in anticipatory salivary responses.

Automated Pre-Analytic Processing of Whole Saliva Using Magnet-Beating for Point-of-Care Protein Biomarker Analysis

Saliva offers many advantages for point-of-care (PoC) diagnostic applications due to non-invasive, easy, and cost-effective methods of collection. However, the complex matrix with its non-Newtonian behavior and high viscosity poses handling challenges. Several tedious and long pre-analytic steps, incompatible with PoC use, are required to liquefy and homogenize saliva samples before protein analysis can be performed. We apply magnet-beating to reduce hands-on time and to simplify sample preparation. A magnet in a chamber containing the whole saliva is actuated inside a centrifugal microfluidic cartridge by the interplay of centrifugal and magnetic forces. Rigorous mixing, which homogenizes the saliva sample, is then initiated. Consequently, fewer manual steps are required to introduce the whole saliva into the cartridge. After 4 min of magnet-beating, the processed sample can be used for protein analysis. The viscosity of whole saliva has been reduced from 10.4 to 2.3 mPa s. Immunoassay results after magnet-beating for three salivary periodontal markers (MMP-8, MMP-9, TIMP-1) showed a linear correlation with a slope of 0.99 when compared to results of reference method treated samples. Conclusively, magnet-beating has been shown to be a suitable method for the pre-analytic processing of whole saliva for fully automated PoC protein analysis.

Salivary Theranostics in Pediatric and Special Care Dentistry

Saliva as a microfluidic system offers numerous advantages for both general and oral health diagnostic and therapeutic procedures since its assembly is quick, stress-free, inexpensive and non-invasive. Moreover, saliva is frequently referred to as a mirror of the body due to the fact that it can reflect the physiological and pathological state of the body. More than a decade ago the term “Salivaomics” has been introduced with the aim of emphasizing the development of research, knowledge and applications of five salivary constituents: proteome, transcriptome, micro-RNA, metabolome, and microbiome. Contemporary oral health care delivery in pediatric and special care dentistry is focused toward the development of new diagnostic and therapeutical procedures that are essentially noninvasive due to common issue of intolerability to invasive procedures among these patients, with the possibility of increasing participation rates. Besides the criteria of being easily and non-invasive collected, there are additional standards that should be met before routine application in everyday clinical practice; the existence of specific biomarkers for a disease, and ability of having its biomarkers detected using present-day equipment. For example, there are recent suggestions that a salivary RNA panel could objectively differentiate children with autism spectrum disorder from their neurotypical peers. In addition, due to the ease of the administration, the oral cavity is an attractive site for the drug delivery systems development because through this route it is possible to realize mucosal and transmucosal, systemic effect. All these contemporary advances extended the salivary diagnostic approach from the oral to general health pointing towards a promising future of salivary diagnostics for personalized medicine devices.

The effect of environment (Dry and Natural Saliva) on clasp retention: In vitro study - Part I

Objective:

The purpose of this study was to investigate the importance of environments (dry and wet) to dislodge the clasp.

Materials and Methods:

Mandibular test models with natural premolar and molar teeth were used to test four types of clasp (each 12) (Akers, rest plate Akers [RPA], half and half [H-H], and ring clasp) in dry and natural fresh saliva environments. Each clasp was pulled out 10 times with a crosshead speed of 10 mm/min and the force required to withdraw each was measured.

Statistical Analysis Used:

A paired sample t-test and Wilcoxon test were used.

Results:

There were significant differences between the dry and wet (natural fresh saliva) environment. However, while the mean of the environment for RPA and ring clasp type was significantly different, the H-H and Akers clasp type was not.

Conclusion:

The environment has an effect on dislodging the clasp but differs according to the type of clasp.

Reduced Salivary Mucin Binding and Glycosylation in Older Adults Influences Taste in an In Vitro Cell Model

Background: Taste loss is a significant problem in older adults, affecting quality of life and nutrition. Altered salivary rheology and loss of mucin function may contribute to taste loss by reducing mucosal defences in the oral cavity, impairing sensitivity to oral stimulants. This study aimed to investigate the effects of salivary rheology on taste loss in ageing. Salivary mucin glycosylation and binding to the oral epithelium was investigated in older and younger adults. A cell-based model was utilised to consider the role of saliva in taste loss. Methods: Human subjects aged >60 years (n = 25) and 18–30 (n = 30) provided saliva samples which were analysed for viscosity, mucin composition and mucin binding to oral epithelial cells (TR146/MUC1). Oral epithelial cells (TR146/MUC1 and SCC090) provided models for taste receptor activation. Results: Reduced levels and sialylation of MUC7 were evident in saliva of older adults which may lead to reduced viscoelasticity, while viscosity is unaffected. Impaired muco-adhesion of saliva from older adults was also observed. Saliva from older adults facilitated the bitter taste receptor activation less well than saliva from younger adults. The causes of taste dysfunction in older adults are unknown, but this study supports a role of saliva in facilitating the activation of taste receptors.

Exosomes and other extracellular vesicles in oral and salivary gland cancers

Extracellular vesicles (EVs, including exosomes) are a group of heterogeneous nanometer-sized vesicles that are released by all types of cells and serve as functional mediators of cell-to-cell communication. This ability is primarily due to their capacity to package and transport various proteins, lipids, and nucleic acids-namely DNA and messenger RNA (mRNA), but also microRNAs (miRNAs) and long non-coding RNAs (lncRNAs). These contents can influence the function and fate of both recipient and donor cells. More and more studies have shown that EVs are involved in every phase of cancer development, mediating bidirectional cross talk between cancer cells and their tissue microenvironment. More specifically, EVs can promote tumor progression by modifying vesicular contents and establishing a distant premetastatic niche with molecules that favor cancer cell proliferation, migration, invasion, metastasis, angiogenesis, and even drug resistance. Given that the packaging of these molecules is known to be tissue-specific, EVs can not only serve as novel prognostic and diagnostic markers but also be used as potential therapeutic targets and vehicles for drug delivery. The present review discusses the current understanding of the multifaceted roles of EVs in the progression of oral and salivary gland cancers, as well as their potential use in clinical applications.

Rheological parameters of saliva in comparison with taste examination

BACKGROUND

It is generally unknown if taste sensitivity is dependent upon saliva viscosity. The rheological properties of saliva result from many factors and it has been shown to behave as a non-Newtonian fluid whose viscosity decreases with increasing shear rate. Taste sensitivity may be quantitatively assayed by electro-gustometry.

OBJECTIVES

The aim of this work was to compare saliva rheological properties, obtained with a rotary-oscillating rheometer, to quantitative measures of taste sensitivity, using electro-gustometry.

METHODS

Saliva samples were taken from 27 healthy non-smoking donors - 7 men and 20 women aged 18-65 years (mean age - 37 years). After thresholds of taste sensation were measured, the saliva samples were taken and characterized in terms of their rheological properties and pH. Saliva viscosity was measured in the order of decreasing shear rate in the range 100-0.01 s-1. Viscoelastic properties were examined under constant frequency oscillations (with f = 0.5 Hz) and with decreasing shear effective amplitude γeff'.

RESULTS AND CONCLUSIONS

Saliva viscosity was found to decrease with increasing shear rate and varied with time. Analysis of the dependence of the viscosity values of saliva and components of complex viscosity did not show a significant correlation with taste sensation. A dependency of taste sensation on pH could not be discerned due to the narrow range of naturally occurring pH.

Electrofluidic Circuit-Based Microfluidic Viscometer for Analysis of Newtonian and Non-Newtonian Liquids under Different Temperatures

This paper reports a microfluidic viscometer with an integrated pressure sensor based on electrofluidic circuits, which are electrical circuits constructed by ionic liquid-filled microfluidic channels. The electrofluidic circuit provides a pressure-sensing scheme with great long-term and thermal stability. The viscosity of the tested fluidic sample is estimated by its flow resistance, which is a function of pressure drop, flow rate, and the geometry of the microfluidic channel. The viscometer can be exploited to measure viscosity of either Newtonian or non-Newtonian power-law fluid under various shear rates (3-500 1/s) and temperatures (4-70 °C) with small sample volume (less than 400 μL). The developed sensor-integrated microfluidic viscometer is made of poly(dimethylsiloxane) (PDMS) with transparent electrofluidic circuit, which makes it feasible to simultaneously image samples under tests. In addition, the entire device is disposable to prevent cross-contamination between samples, which is desired for various chemical and biomedical applications. In the experiments, viscosities of Newtonian fluids, glycerol water solutions with different concentrations and a mixture of pyrogallol and sodium hydroxide (NaOH), and non-Newtonian fluids, xanthan gum solutions and human blood samples, have been characterized. The results demonstrate that the developed microfluidic viscometer provides a convenient and useful platform for practical viscosity characterization of fluidic samples for a wide variety of applications.

Effect of clasp type and pullout location on clasp retention in different environment: In vitro study

Objective:

The purpose of this study was to investigate the importance of pullout location and clasp types in two different environments to dislodge the clasp.

Materials and Methods:

Mandibular test models with natural premolars and molar teeth were used to test four types of clasp (each 12) (Akers, Rest plate Akers, Half and Half, and Ring clasp) with three different pullout location for each type (ring on the rest, loop on the saddle, and wax arising from both rests) in dry and natural fresh saliva environment. Each clasp was pulled out 10 times with a crosshead speed of 10 mm/min, and the force required to withdraw each was measured.

Statistical Analysis Used:

A one-way ANOVA and Tukey test were used.

Results:

The ring on the saddle pullout location has the highest retention force while ring on the rest was the lowest. In addition, ring clasp has the highest retention force.

Conclusion:

Clasp type and pullout location had a significant effect on the retentive force.

Critical view on drug dissolution in artificial saliva: A possible use of in-line e-tongue measurements

Proper monitoring of drug's dissolution is a prerequisite for assessing of taste masking efficacy of pharmaceuticals. Corresponding dissolution procedure is likely to be performed with water. Since the objective of these tests is to examine fate of a pharmaceutical formulation in oral cavity, this choice of solvent seems unsuitable because physical and chemical properties of human saliva are quite far from those of water. Obviously, dissolution profiles registered in water may differ significantly from what really happens with a drug in a mouth cavity. In order to address this discrepancy we examined three different compositions of artificial saliva in dissolution test context in present study. It was found that certain compositions preclude the employment of traditional UV-vis spectroscopy as a detection tool due to strong light scattering in the media caused by viscosity and protein composition modifiers. This issue was circumvented by the use of in-line applied potentiometric multisensor system (e-tongue) and the potential of this new approach for more biorelevant dissolution tests was demonstrated with two model formulations of quinine and ibuprofen.

Isolation of human salivary extracellular vesicles by iodixanol density gradient ultracentrifugation and their characterizations

Diagnostic methods that focus on the extracellular vesicles (EVs) present in saliva have been attracting great attention because of their non-invasiveness. EVs contain biomolecules such as proteins, messenger RNA (mRNA) and microRNA (miRNA), which originate from cells that release EVs, making them an ideal source for liquid biopsy. Although there have been many reports on density-based fractionation of EVs from blood and urine, the number of reports on EVs from saliva has been limited, most probably because of the difficulties in separating EVs from viscous saliva using density gradient centrifugation. This article establishes a protocol for the isolation of EVs from human saliva using density gradient centrifugation. The fractionated salivary EVs were characterized by atomic force microscopy, western blot and reverse transcription polymerase chain reaction. The results indicate that salivary EVs have a smaller diameter (47.8±12.3 nm) and higher density (1.11 g/ml) than EVs isolated from conditioned cell media (74.0±23.5 nm and 1.06 g/ml, respectively). Additionally, to improve the throughput of density-based fractionation of EVs, the original protocol was further modified by using a fixed angle rotor instead of a swinging rotor. It was also confirmed that several miRNAs were expressed strongly in the EV-marker-expressing fractions.

Blood, sweat, and tears: developing clinically relevant protein biosensors for integrated body fluid analysis

Biosensors are being developed to provide rapid, quantitative, diagnostic information to clinicians in order to help guide patient treatment, without the need for centralised laboratory assays. The success of glucose monitoring is a key example of where technology innovation has met a clinical need at multiple levels – from the pathology laboratory all the way to the patient's home. However, few other biosensor devices are currently in routine use. Here we review the challenges and opportunities regarding the integration of biosensor techniques into body fluid sampling approaches, with emphasis on the point-of-care setting.

Viscoelasticity of biofilms and their recalcitrance to mechanical and chemical challenges

We summarize different studies describing mechanisms through which bacteria in a biofilm mode of growth resist mechanical and chemical challenges. Acknowledging previous microscopic work describing voids and channels in biofilms that govern a biofilms response to such challenges, we advocate a more quantitative approach that builds on the relation between structure and composition of materials with their viscoelastic properties. Biofilms possess features of both viscoelastic solids and liquids, like skin or blood, and stress relaxation of biofilms has been found to be a corollary of their structure and composition, including the EPS matrix and bacterial interactions. Review of the literature on viscoelastic properties of biofilms in ancient and modern environments as well as of infectious biofilms reveals that the viscoelastic properties of a biofilm relate with antimicrobial penetration in a biofilm. In addition, also the removal of biofilm from surfaces appears governed by the viscoelasticity of a biofilm. Herewith, it is established that the viscoelasticity of biofilms, as a corollary of structure and composition, performs a role in their protection against mechanical and chemical challenges. Pathways are discussed to make biofilms more susceptible to antimicrobials by intervening with their viscoelasticity, as a quantifiable expression of their structure and composition.

Recalcitrance of biofilms against mechanical and chemical challenges has been looked at for ages from a microbiological perspective, but an approach based on viscoelastic properties of biofilms yields new insights in this recalcitrance.

Saliva viscosity as a potential risk factor for oral malodor

OBJECTIVES

The objective of this study was to assess whether saliva viscosity, measured by a viscometer, was a predictor of oral malodor.

MATERIALS AND METHODS

The subjects were 617 patients who visited an oral malodor clinic. The organoleptic test (OT) was used for diagnosis of oral malodor. An oral examination assessed the numbers of teeth present and decayed teeth as well as the presence or absence of dentures. Further, periodontal pocket depths (PD), gingival bleeding, dental plaque and tongue coating were investigated. Unstimulated saliva were collected for 5 min. Saliva viscosity was measured with a viscometer. Logistic regression analysis with oral malodor status by OT as a dependent variable was performed. Possible confounders including age, gender, number of teeth present, number of decayed teeth, number of teeth with PD ≥ 4 mm, number of teeth with bleeding on probing, presence or absence of dentures, plaque index, area of tongue coating, saliva flow rate, saliva pH and saliva viscosity were used as independent variables.

RESULTS

Saliva viscosity (p = 0.047) along with the number of teeth with PD ≥4 mm (p = 0.001), plaque index (p = 0.037) and area of tongue coating (p < 0.001) were significant variables for oral malodor. Subjects with a higher number of teeth with PD ≥ 4 mm (OR = 1.32), plaque index (OR = 2.13), area of tongue coating (OR = 3.17) and saliva viscosity (OR = 1.10) were more likely to have oral malodor compared to those with lower values.

CONCLUSIONS

The results suggested that high saliva viscosity could be a potential risk factor for oral malodor.

Tooth wear and the role of salivary measures in general practice patients

OBJECTIVES

The goal of this study was to investigate the association between tooth wear and salivary measures in a random sample of patients from practices of dentist members of a practice-based research network.

MATERIALS AND METHODS

Patients completed a questionnaire on oral self-care, health, dietary habits, medications, and socio-demographic variables. Six salivary characteristics (consistency, resting salivary flow, resting salivary pH, stimulated salivary flow, stimulated salivary pH, and buffering capacity) were measured, and a dental examination included categorizing patients according to the dentist's judgment of the degree of tooth wear (i.e., none/minimal, some, or severe/extreme). Bivariate and multinomial logistic regression models were used to relate salivary characteristics and other factors to the outcome of tooth wear.

RESULTS

Data are reported from 1,323 patients (age range 16-97 years) from 61 practices. Patient age, gender, number of teeth, and perception of dry mouth were associated with tooth wear, but salivary and dietary factors were either weakly or not related.

CONCLUSIONS

The findings of this cross-sectional assessment suggest that using these salivary tests and dietary assessments in real-life clinical settings is unlikely to be useful in assessing tooth wear risk. Suggestions are offered about risk assessment for tooth wear.

CLINICAL RELEVANCE

Assessing a dental patient's risk of tooth wear using salivary measures and dietary assessments as described is not recommended for general dental practice until stronger evidence exists indicating its utility.

Rapid saliva processing techniques for near real-time analysis of salivary steroids and protein

INTRODUCTION

Point-of-care (POC) measurements using saliva samples have immense potential to assess systemic health and wellbeing, but sample viscosity and contaminants can affect analyses. We sought a portable clean-up method for whole saliva appropriate for use with POC measurement techniques such as biosensors.

METHODS

Whole saliva from each of 13 male subjects was split into 5 fractions. Each fraction was treated with a different clean-up process: a freeze-thaw-centrifuge (FTC) step; centrifugation alone; or passage through a Mini-UniPrep polyethersulfone filter, cotton Salivette, or foam Oracol device. Following clean-up, each subject's treated saliva fractions were assayed for cortisol, testosterone, dehydroepiandrosterone (DHEA), and protein concentrations. The effects of clean-up methods on nonspecific binding (NSB) in a biosensor were also assessed.

RESULTS

Compared with FTC, no analytes were affected by centrifugation alone. Cotton Salivettes significantly altered all analytes, with increases in cortisol (+64%), testosterone (+126%), and DHEA (off-scale) levels, and decreased protein (-21%) and biosensor NSB (-75%). Oracol foam devices decreased DHEA levels by 28%. Mini-UniPrep filtration decreased testosterone (-45%) and DHEA (-66%) concentrations while increasing cortisol (+40%).

CONCLUSION

No method was optimal for all analytes, highlighting the need for validation of saliva treatment methods before their adoption in rapid POC analyses.

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.

Interfacial instabilities affect microfluidic extraction of small molecules from non-Newtonian fluids

As part of a project to develop an integrated microfluidic biosensor for the detection of small molecules in saliva, practical issues of extraction of analytes from non-Newtonian samples using an H-filter were explored. The H-filter can be used to rapidly and efficiently extract small molecules from a complex sample into a simpler buffer. The location of the interface between the sample and buffer streams is a critical parameter in the function of the H-filter, so fluorescence microscopy was employed to monitor the interface position; this revealed apparently anomalous fluorophore diffusion from the samples into the buffer solutions. Using confocal microscopy to understand the three-dimensional distribution of the fluorophore, it was found that the interface between the non-Newtonian sample and Newtonian buffer was both curved and unstable. The core of the non-Newtonian sample extended into the Newtonian buffer and its position was unstable, producing a fluorescence intensity profile that gave rise to the apparently anomalously fast fluorophore transport. These instabilities resulted from the pairing of rheologically dissimilar fluid streams and were flowrate dependent. We conclude that use of non-Newtonian fluids, such as saliva, in the H-filter necessitates pretreatment to reduce viscoelasticity. The interfacial variation in position, stability and shape caused by the non-Newtonian samples has substantial implications for the use of biological samples for quantitative analysis and analyte extraction in concurrent flow extraction devices.

Salivary secretion, taste and hyposalivation

Saliva has many essential functions. As the first digestive fluid in the alimentary canal, saliva is secreted in response to food, assisting intake and initiating the digestion of starch and lipids. During this process, saliva acts as a solvent of taste substances and affects taste sensitivity. Clinically, a more important role is in the maintenance of oral health, including the protection of teeth and mucosa from infections, maintenance of the milieu of taste receptors, and communication ability through speech. Variations in salivary flow can be affected, reversibly or irreversibly, by numerous physiological and pathological factors. Decreased salivary flow results in clinically significant oral discomfort that may manifest as increased caries, susceptibility to oral candidiasis, altered taste sensation or as a host of other problems. Hyposalivation is a condition that is frequently encountered in dental practice. The most common cause is the use of certain systemic medications, which put the elderly at greater risk because they are usually more medicated. Other causes include high doses of radiation and certain diseases such as Sjögren's syndrome. This article reviews the mechanism of salivary secretion, effect of saliva on taste, importance of saliva in oral health, and hyposalivation in relation to ageing, medicine and/or disease and management of hyposalivation.