Oral telemetry of fluoride ion activity

Sensors for in situ monitoring of oral and dental health parameters in saliva

OBJECTIVES

The oral cavity is an easily accessible unique environment and open system which is influenced by the oral fluids, microbiota, and nutrition. Little is known about the kinetics and dynamics of metabolic processes at the intraoral surfaces. Real-time monitoring of salivary biomarkers, e.g., glucose, lactate, fluoride, calcium, phosphate, and pH with intraoral sensors is therefore of major interest. The aim of this review is to overview the existing literature for intraoral saliva sensors.

MATERIALS AND METHODS

A comprehensive literature search was performed to review the most relevant studies on intraoral saliva sensor technology.

RESULTS

There is limited literature about the in situ saliva monitoring of salivary biomarkers. Bioadhesion and biofouling processes at the intraoral surfaces limit the performances of the sensors. Real-time, long-term, and continuous intraoral measurement of salivary metabolites remains challenging and needs further investigation as only few well-functioning sensors have been developed until today. Until now, there is no sensor that measures reliably beyond hours for any analyte other than glucose.

CONCLUSIONS

Saliva's complex and dynamic structure as well as bioadhesion are key challenges and should be addressed in the future developments. Consequently, more studies that focus particularly on biofouling processes and interferential effects of the salivary matrix components on sensor surfaces are required.

CLINICAL RELEVANCE

By monitoring fluids in the oral cavity, as the entrance to the digestive system, extensive information can be obtained regarding the effects of foods and preventive agents on the oral microbiota and the tooth surfaces. This may lead to a better understanding of strategies to modulate oral and general health.

Nanostructured wearable electrochemical and biosensor towards healthcare management: a review

In recent years, there has been a rapid increase in demand for wearable sensors, particularly these tracking the surroundings, fitness, and health of people. Thus, selective detection in human body fluid is a demand for a smart lifestyle by quick monitoring of electrolytes, drugs, toxins, metabolites and biomolecules, proteins, and the immune system. In this review, these parameters along with the main features of the latest and mostly cited research work on nanostructured wearable electrochemical and biosensors are surveyed. This study aims to help researchers and engineers choose the most suitable selective and sensitive sensor. Wearable sensors have broad and effective sensing platforms, such as contact lenses, Google Glass, skin-patch, mouth gourds, smartwatches, underwear, wristbands, and others. For increasing sensor reliability, additional advancements in electrochemical and biosensor precision, stability in uncontrolled environments, and reproducible sample conveyance are necessary. In addition, the optimistic future of wearable electrochemical sensors in fields, such as remote and customized healthcare and well-being is discussed. Overall, wearable electrochemical and biosensing technologies hold great promise for improving personal healthcare and monitoring performance with the potential to have a significant impact on daily lives. These technologies enable real-time body sensing and the communication of comprehensive physiological information.

Electron transfer studies of a conventional redox probe in human sweat and saliva bio-mimicking conditions

Modern day hospital treatments aim at developing electrochemical biosensors for early diagnosis of diseases using unconventional human bio-fluids like sweat and saliva by monitoring the electron transfer reactions of target analytes. Such kinds of health care diagnostics primarily avoid the usage of human blood and urine samples. In this context, here we have investigated the electron transfer reaction of a well-known and commonly used redox probe namely, potassium ferro/ferri cyanide by employing artificially simulated bio-mimics of human sweat and saliva as unconventional electrolytes. Typically, electron transfer characteristics of the redox couple, [Fe(CN)₆]^3−/4− are investigated using electrochemical techniques like cyclic voltammetry and electrochemical impedance spectroscopy. Many different kinetic parameters are determined and compared with the conventional system. In addition, such electron transfer reactions have also been studied using a lyotropic liquid crystalline phase comprising of Triton X-100 and water in which the aqueous phase is replaced with either human sweat or saliva bio-mimics. From these studies, we find out the electron transfer reaction of [Fe(CN)₆]^3−/4− redox couple is completely diffusion controlled on both Au and Pt disc shaped electrodes in presence of sweat and saliva bio-mimic solutions. Moreover, the reaction is partially blocked by the presence of lyotropic liquid crystalline phase consisting of sweat and saliva bio-mimics indicating the predominant charge transfer controlled process for the redox probe. However, the rate constant values associated with the electron transfer reaction are drastically reduced in presence of liquid crystalline phase. These studies are essentially carried out to assess the effect of sweat and saliva on the electrochemistry of Fe^2+/3+ redox couple.

Wearable Biosensors: An Alternative and Practical Approach in Healthcare and Disease Monitoring

With the increasing prevalence of growing population, aging and chronic diseases continuously rising healthcare costs, the healthcare system is undergoing a vital transformation from the traditional hospital-centered system to an individual-centered system. Since the 20th century, wearable sensors are becoming widespread in healthcare and biomedical monitoring systems, empowering continuous measurement of critical biomarkers for monitoring of the diseased condition and health, medical diagnostics and evaluation in biological fluids like saliva, blood, and sweat. Over the past few decades, the developments have been focused on electrochemical and optical biosensors, along with advances with the non-invasive monitoring of biomarkers, bacteria and hormones, etc. Wearable devices have evolved gradually with a mix of multiplexed biosensing, microfluidic sampling and transport systems integrated with flexible materials and body attachments for improved wearability and simplicity. These wearables hold promise and are capable of a higher understanding of the correlations between analyte concentrations within the blood or non-invasive biofluids and feedback to the patient, which is significantly important in timely diagnosis, treatment, and control of medical conditions. However, cohort validation studies and performance evaluation of wearable biosensors are needed to underpin their clinical acceptance. In the present review, we discuss the importance, features, types of wearables, challenges and applications of wearable devices for biological fluids for the prevention of diseased conditions and real-time monitoring of human health. Herein, we summarize the various wearable devices that are developed for healthcare monitoring and their future potential has been discussed in detail.

Development of a Dental Implantable Temperature Sensor for Real-Time Diagnosis of Infectious Disease

Implantable sensors capable of real-time measurements are powerful tools to diagnose disease and maintain health by providing continuous or regular biometric monitoring. In this paper, we present a dental implantable temperature sensor that can send early warning signals in real time before the implant fails. Using a microfabrication process on a flexible polyimide film, we successfully fabricated a multi-channel temperature sensor that can be wrapped around a dental implant abutment wing. In addition, the feasibility, durability, and implantability of the sensor were investigated. First, high linearity and repeatability between electrical resistance and temperature confirmed the feasibility of the sensor with a temperature coefficient of resistance (TCR) value of 3.33 × 10^–3/°C between 20 and 100 °C. Second, constant TCR values and robust optical images without damage validated sufficient thermal, chemical, and mechanical durability in the sensor’s performance and structures. Lastly, the elastic response of the sensor’s flexible substrate film to thermal and humidity variations, simulating in the oral environment, suggested its successful long-term implantability. Based on these findings, we have successfully developed a polymer-based flexible temperature sensor for dental implant systems.

Wearable sensors: modalities, challenges, and prospects

Wearable sensors have recently seen a large increase in both research and commercialization. However, success in wearable sensors has been a mix of both progress and setbacks. Most of commercial progress has been in smart adaptation of existing mechanical, electrical and optical methods of measuring the body. This adaptation has involved innovations in how to miniaturize sensing technologies, how to make them conformal and flexible, and in the development of companion software that increases the value of the measured data. However, chemical sensing modalities have experienced greater challenges in commercial adoption, especially for non-invasive chemical sensors. There have also been significant challenges in making significant fundamental improvements to existing mechanical, electrical, and optical sensing modalities, especially in improving their specificity of detection. Many of these challenges can be understood by appreciating the body's surface (skin) as more of an information barrier than as an information source. With a deeper understanding of the fundamental challenges faced for wearable sensors and of the state-of-the-art for wearable sensor technology, the roadmap becomes clearer for creating the next generation of innovations and breakthroughs.

Organic Electronics for Point-of-Care Metabolite Monitoring

In this review we focus on demonstrating how organic electronic materials can solve key problems in biosensing thanks to their unique material properties and implementation in innovative device configurations. We highlight specific examples where these materials solve multiple issues related to complex sensing environments, and we benchmark these examples by comparing them to state-of-the-art commercially available sensing using alternative technologies. We have categorized our examples by sample type, focusing on sensing from body fluids in vitro and on wearable sensors, which have attracted significant interest owing to their integration with everyday life activities. We finish by describing a future trend for in vivo, implantable sensors, which aims to build on current progress from sensing in biological fluids ex vivo.

Wearable salivary uric acid mouthguard biosensor with integrated wireless electronics

This article demonstrates an instrumented mouthguard capable of non-invasively monitoring salivary uric acid (SUA) levels. The enzyme (uricase)-modified screen printed electrode system has been integrated onto a mouthguard platform along with anatomically-miniaturized instrumentation electronics featuring a potentiostat, microcontroller, and a Bluetooth Low Energy (BLE) transceiver. Unlike RFID-based biosensing systems, which require large proximal power sources, the developed platform enables real-time wireless transmission of the sensed information to standard smartphones, laptops, and other consumer electronics for on-demand processing, diagnostics, or storage. The mouthguard biosensor system offers high sensitivity, selectivity, and stability towards uric acid detection in human saliva, covering the concentration ranges for both healthy people and hyperuricemia patients. The new wireless mouthguard biosensor system is able to monitor SUA level in real-time and continuous fashion, and can be readily expanded to an array of sensors for different analytes to enable an attractive wearable monitoring system for diverse health and fitness applications.

Non-invasive mouthguard biosensor for continuous salivary monitoring of metabolites

The present work describes the first example of a wearable salivary metabolite biosensor based on the integration of a printable enzymatic electrode on a mouthguard. The new mouthguard enzymatic biosensor, based on an immobilized lactate oxidase and a low potential detection of the peroxide product, exhibits high sensitivity, selectivity and stability using whole human saliva samples. Such non-invasive mouthguard metabolite biosensors could tender useful real-time information regarding a wearer's health, performance and stress level, and thus hold considerable promise for diverse biomedical and fitness applications.

Study of saliva secretion and the salivary fluoride concentration of the human minor labial glands by a new method

Unstimulated and stimulated flow rate from minor lower labial glands and the fluoride concentration of resting whole and labial saliva were measured over 15 min using a novel method avoiding eversion of the lips. Resting salivary flow rate was measured as 1.09+/-0.44 microl/min/cm2 and stimulated flow rate as 3.13+/-1.05 microl/min/cm2. Secretion rates were significantly (p<0.001) increased during periods of continuous speaking. The increase in secretion elicited by labial movements and speaking may result from mechanical stimulation and/or activity of myoepithelial cells. Fluoride concentrations in resting whole saliva and in unstimulated minor labial gland saliva were 0.066+/-0.048 and 0.181+/-0.073 parts/10(6), respectively. The secretory capacity of the minor labial glands and the high F concentration in their secretions suggests a significant contribution to the F content of whole saliva. Our non-invasive method permits collection from the minor labial glands of a volume large enough for chemical analysis. It should prove useful for studying the effects of different secretory stimuli.

Intra-oral effects on acid-softened enamel of NaF lozenges administered in divided daily doses

The purpose of this investigation was to study the intra-oral effects of multiple daily applications of NaF lozenges upon acid-softened enamel. Bovine enamel slabs were softened with 0.1 mol/L lactate buffer at pH 4.0 for 14 hrs and subsequently mounted in a mandibular removable Hawley appliance. Control slabs were worn for seven days by eight adult male subjects who brushed their natural dentition daily with a fluoride-free dentifrice. Test slabs were exposed to one 0.55-mg NaF lozenge (0.25 mg F) 4x/day for seven days and the natural dentition brushed with a fluoride-free dentifrice. The efficacy of 0.25-mg F lozenges used 4x/day over that of a 1-mg F lozenge administered 1x/day was established by a pilot study with two subjects. Microhardness testing was performed after intra-oral exposure (IOE) and following immersion in 0.01 mol/L lactate buffer containing Ca and PO4 for 24 hrs at a pH of 4.0. Fluoride uptake was measured on separate control and test slabs after KOH wash and after acid-resistance-testing (ART). Recovery of microhardness following IOE was 40.9% for controls and 53.9% for treated slabs, while control slabs retained 1.3% resistance to ART, compared with 25.6% for test slabs. The F content of the control slabs was significantly less than that of lozenge-treated and lozenge-treated-ART slabs throughout the depth of the lesion. The F content of the lozenge-treated-ART slabs was significantly less than that of the lozenge-treated slabs only at the 0-5-microns depth.(ABSTRACT TRUNCATED AT 250 WORDS)

Distribution and retention of salivary fluoride from a sodium fluoride tablet following various intra-oral dissolution methods

The distribution and retention of salivary fluoride were investigated according to the following intra-oral dissolution methods of a sodium fluoride tablet: active chewing/swishing, active sucking/swishing, and passive dissolution in the maxillary and mandibular labial vestibule. The results suggested that the oral cavity was somewhat compartmentalized, in that homogeneous distribution of a dissolved fluoride tablet did not occur throughout the mouth, but rather each site sampled was influenced by various rates of clearance and retention. Tablet chewing may have an advantage over tablet sucking in terms of salivary fluoride retention, and there was a tendency for fluoride to be preferentially retained in the maxillary labial vestibule following swishing. The passive tablet dissolution methods resulted in a less homogeneous distribution of fluoride. Although the fluoride retention values for passive dissolution were impressively superior to either active dissolution method, the alarmingly high salivary fluoride concentrations (4000 ppm F) recorded at the passive dissolution sites should discourage its use until the potential cytotoxicity of this approach is thoroughly investigated.

Effects of a single application of sodium fluoride gel on dental plaque acidogenesis

Quantitative comparisons of the lactate and acetate produced by human dental plaque in vitro and in situ were made before and after five-minute exposures to 1% NaF gel. Assays included total ionic plaque fluoride by a fluoride electrode, L(+)- and D(-)-lactate by an enzyme method, and acetate by a standard GLC procedure. A single topical application of NaF gel increased plaque fluoride about eight-fold. Six hours after gel use, plaque fluoride had declined to about 20% above pretreatment levels. Plaque fluoride baseline levels and variation between and within subjects were greater than expected. This may have been due largely to non-standardized oral hygiene practice and/or the routine use of fluoride dentifrices and the wide variation in the natural fluoride content of drinking water. Fluoride gel use significantly reduced L(+)-lactate in vitro, but D(-)-lactate and acetate were virtually unaffected. Conversely, gel use significantly inhibited the in situ production of each of these acids. The findings of this study indicate that topically applied fluoride gel impairs plaque acidogenesis to an extent that could be meaningful in preventing dental caries.

Salivary fluoride and calcium concentrations, and their relationship to the secretion of saliva and caries experience

Samples were collected from the stimulated saliva of 113 students enrolled in institutions of higher education. The students were divided into three "carries-diagnostic groups" on the basis of indications given by the Dentocult saliva test, which shows the frequency of lactobacilli and other aciduric microorganisms in saliva. The frequency of such microorganisms in 1 ml saliva in Group A was less than or equal to 103, in Group B greater than 10(3), less than 10(4) and in Group C greater than or equal to 10(4). The rate of secretion of saliva in Group A was significantly higher than in Group C (P less than 0.05). On the average, a rise was noted in the fluoride and calcium concentrations with increasing "caries activity". In the material as a whole, there was a negative and highly significant correlation between the secretion rate of saliva and the concentrations of fluoride and calcium. In the examination by groups, significant correlations were observed between fluoride concentration and rate of saliva secretion in Group A, and with respect to fluoride and calcium only in Group C. The results suggest that the extra salivary fluoride is likely to be derived from the enamel.

The erupting first permanent molar--its place in stratified clinical field studies

Erupting first permanent molars of 5 1/2 to 6 1/2 year-olds are eminently suited for the clinical testing of potential caries-inhibiting techniques. Due to the rapid onset of caries in these teeth, accurate monitoring of new materials/regimes can be instituted and meaningful data obtained within one year of trial commencement. In addition, by concentrating on this age-group and by also stratifying for socio-economic status, deciduous caries experience and three-month wide age-bands, different trials' data can be readily compared. A further benefit is that these most caries-prone teeth can be protected thus saving the need for block injections in young subjects and alleviating later orthodontic problems.

Enamel biopsy results of children receiving fluoride tablets

This study measured the fluoride in tooth enamel of 338 schoolchildren after daily use of acidulated phosphate-fluoride (APF) tablets, and investigated the relationship between observed amounts of enamel fluoride and incidence of caries. Randomly selected study groups received under supervision either one placebo tablet, one APF tablet containing 1 mg fluoride, or 2 APF tablets (3 hours apart) each school day. An abrasive enamel-type biopsy of a maxillary central incisor was taken 30 months after the start of fluoride tablet treatments at the time of the follow-up examinations. Mean fluoride levels in the biopsied enamel from each of the three groups were similar despite a significant restriction in caries in the group receiving two APF tablets per day. These findings suggest that fluoride can restrict dental caries by some mechanism other than fluoride uptake in the enamel.

Retention of fluoride with chewable tablets and a mouthrinse

Fluoride concentration and volume of expectorates collected after chewing or rinsing with three different supplemental fluoride preparations were determined. Fluoride contained in the administered dose was measured and amount of fluoride in the collected volume was subtracted from it to yield the amount of fluoride retained. Retentions of 41, 20, and 7% of the dose were found with a NaF tablet, an APF tablet, and an APF rinse, respectively.