Dry mouth: saliva substitutes which adsorb and modify existing salivary condition films improve oral lubrication

Biomedical applications of functional hydrogels: Innovative developments, relevant clinical trials and advanced products

Functional hydrogels are used for numerous biomedical applications such as tissue engineering, wound dressings, lubricants, contact lenses and advanced drug delivery systems. Most of them are based on synthetic or natural polymers forming a three-dimensional network that contains aqueous media. Among synthetic polymers, poly(meth)acrylates, polyethyleneglycols, poly(vinylalcohols), poly(vinylpyrrolidones), PLGA and poly(urethanes) are of high relevance, whereas natural polymers are mainly polysaccharides such as hyaluronic acid, alginate or chitosan and proteins such as albumin, collagen or elastin. In contrast to most synthetic polymers, natural polymers are biodegradable. Both synthetic and natural polymers are often chemically modified in order to improve or induce favorable properties and functions like high mechanical strength, stiffness, elasticity, high porosity, adhesive properties, in situ gelling properties, high water binding capacity or drug release controlling properties. Within this review we provide an overview about the broad spectrum of biomedical applications of functional hydrogels, summarize innovative approaches, discuss the concept of relevant functional hydrogels that are in clinical trials and highlight advanced products as examples for successful developments.

Influence of irradiated dentin, biofilm and different artificial saliva formulations on root dentin demineralization

The aim of this study was evaluated the influence of radiation as well as of new formulations of artificial saliva on the development of root dentin lesions. Bovine root samples were divided into: irradiated (70 Gy) dentin or not; the type of biofilm (from irradiated patient-experimental or non-irradiated patient-control) and the type of artificial saliva (for the condition irradiated dentin/biofilm from irradiated patient): Control Artificial Saliva (inorganic); Control Saliva + 1 mg/ml hemoglobin; Control Saliva +0.1 mg/ml cystatin; Control Saliva + hemoglobin + cystatin; Bioextra (positive control) and deionized water (DiW, negative control) (n = 12/group). Biofilm was produced using human biofilm and McBain saliva (0.2 % of sucrose, 37o C and 5 % CO2); the treatments were done 1x/day, for 5 days. Colony-forming units (CFU) counting was performed; demineralization was quantified by transversal microradiography. Two-way ANOVA/Bonferroni or Sidak test for the comparison between biofilm x dentin and ANOVA/Tukey or Kruskal-Wallis/Dunn for comparing artificial saliva were done (p < 0.05). The type of biofilm had no influence on CFU and demineralization. Sound dentin under control biofilm presented the lowest Lactobacillus ssp. and Streptococcus mutans CFU and the lowest mean mineral loss (R) (25.6 ± 2.2; 23.7 ± 2.9 %) compared to irradiated dentin (26.1 ± 2.8; 28.1 ± 3.3, p < 0.004) for both types of biofilms (experimental and control, respectively). Bioextra was the only artificial saliva that reduced R (10.8 ± 2.5 %) and Lesion Depth (LD) (35 ± 15 μm) compared to DiW (17.3 ± 3.3 %, 81 ± 18 μm, p < 0.0001). Irradiation has impact on caries development; the experimental saliva were unable to reduce its occurrence.

In vitro effect of TiF4/NaF solution on the development of radiation-induced dentin caries

OBJECTIVE

To evaluate the protective effect of an experimental solution containing TiF4/NaF on the development of radiation-induced dentin caries lesions.

METHODOLOGY

bovine root samples were irradiated (70Gy) and distributed as following (n=12/group): Commercial Saliva (BioXtra), NaF (500 ppm F-), TiF4 (500 ppm F), TiF4/NaF (TiF4: 300 ppm F-, NaF: 190 ppm F-), and Phosphate buffer solution (PBS, negative control). Biofilm was produced using biofilm from irradiated patients and McBain saliva (0.2% of sucrose, at 37oC and 5% CO2) for five days. The treatments were applied 1x/day. Colony-forming units (CFU) were counted and demineralization was quantified by transversal microradiography. The ANOVA/Tukey test was applied for all parameters.

RESULTS

All treatments reduced CFU for total microorganisms. TiF4 reduced Lactobacillus sp. (7.04±0.26 log10 CFU/mL) and mutans streptococci (7.18±0.28) CFU the most, when compared to PBS (7.58±0.21 and 7.75±0.17) and followed by NaF (7.12±0.31 and 7.34±0.22) and TiF4/NaF (7.16±0.35 and 7.29± 0.29). TiF4 and Commercial saliva showed the lowest integrated mineral loss (ΔZ-vol%.mm) (1977±150 and 2062±243, respectively) when compared to PBS (4540±335), followed by NaF (2403±235) and TiF4/NaF (2340±200). Commercial saliva was the only to significantly reduce mineral loss (LD-µm) (111±25) compared to PBS (153±24).Mean mineral loss (R-vol%) decreased by 35.2% for TiF4 (18.2±3.3) when compared to PBS (28.1±2.9) Conclusion: TiF4/NaF has a comparable anti-cariogenic effect to TiF4 and Commercial saliva under the model in this study.

Evaluation and management of dry mouth and its complications in rheumatology practice

INTRODUCTION

The symptom of dry mouth has multiple potential etiologies and can be a diagnostic clue to the presence of common systemic diseases encountered in rheumatology practice. The presence of decreased saliva flow (i.e. salivary hypofunction) defines a subset of dry mouth patients in whom there may be reversible drug effects, an iatrogenic insult such as head and neck irradiation, or a disease that directly involves the salivary glands (e.g. Sjögren's disease). The assessment of salivary hypofunction includes sialometry, salivary gland imaging, salivary gland biopsy, and an assessment for relevant systemic diseases. Optimal management of dry mouth requires accurate definition of its cause, followed by general measures that serve to alleviate its symptoms and prevent its complications.

AREAS COVERED

Through a literature search on xerostomia and salivary hypofunction, we provide an overview of the causes of dry mouth, highlight the potential impact of salivary hypofunction on oral and systemic health, detail routine evaluation methods and treatment strategies, and emphasize the importance of collaboration with oral health care providers.

EXPERT OPINION

Our Expert Opinion is provided on unmet needs in the management of dry mouth and relevant research progress in the field.

Benchmarking of a microgel-reinforced hydrogel-based aqueous lubricant against commercial saliva substitutes

Xerostomia, the subjective sensation of 'dry mouth' affecting at least 1 in 10 adults, predominantly elders, increases life-threatening infections, adversely impacting nutritional status and quality of life. A patented, microgel-reinforced hydrogel-based aqueous lubricant, prepared using either dairy or plant-based proteins, has been demonstrated to offer substantially enhanced lubricity comparable to real human saliva in in vitro experiments. Herein, we present the benchmarking of in vitro lubrication performance of this aqueous lubricant, both in its dairy and vegan formulation against a range of widely available and employed commercial saliva substitutes, latter classified based on their shear rheology into "liquids", "viscous liquids" and "gels", and also had varying extensional properties. Strikingly, the fabricated dairy-based aqueous lubricant offers up to 41-99% more effective boundary lubrication against liquids and viscous liquids, irrespective of topography of the tested dry mouth-mimicking tribological surfaces. Such high lubricity of the fabricated lubricants might be attributed to their limited real-time desorption (7%) from a dry-mouth mimicking hydrophobic surface unlike the tested commercial products including gels (23-58% desorption). This comprehensive benchmarking study therefore paves the way for employing these microgel-based aqueous lubricant formulations as a novel topical platform for dry mouth therapy.

Stability and cytotoxicity of biopolymer-coated liposomes for use in the oral cavity

This study investigates the stability and cytotoxicity of biopolymer-coated liposomes for use in the oral cavity. Liposomes (3 mM and 6 mM) were prepared by the thin film method and hydrated with phosphate buffer (PB) or glycerol phosphate buffer (G-PB). For coating, liposomes were added to a biopolymer solution of opposite charge. Particle stability was evaluated by measuring the size, polydispersity index, and zeta potential for up to 60 weeks. In vitro interaction of fluorescent-labelled biopolymer-coated liposomes and dysplastic oral keratinocytes was analyzed by confocal microscopy. Potential cytotoxicity was assessed in dysplastic oral keratinocytes by cell proliferation and cell viability. All three biopolymers showed good coating abilities for both concentrations and hydration media. The alginate coated liposomes in PB, 3 mM chitosan-coated liposomes in PB, and chitosan-coated liposomes in G-PB were stable for up to 60 weeks. In vitro studies demonstrated low cytotoxicity for all coated liposomes and non-specific cellular uptake of biopolymer-coated liposomes, independent of biopolymer, surface charge, lipid concentration and hydration media. All three formulations demonstrated low cytotoxicity and were considered safe. Alginate- and chitosan-coated liposomes demonstrated good stability over time and may be promising agents for use in the oral cavity and should be investigated further.

Antibacterial, antibiofilm and anticaries effect of BioXtra® mouthrinse for head and neck cancer (HNC) patients under a microcosm biofilm model

BACKGROUND AND PURPOSE

Considering the lack of studies investigating salivary substitutes to control post-radiation caries for patients with head and neck cancer (HNC), this study aimed to evaluate the antibacterial, antibiofilm, and anticaries effects of BioXtra® on the microcosm biofilm formed on different enamel types (non-irradiated and irradiated) and from distinct saliva sources (control and HNC patients).

MATERIALS AND METHODS

Non-irradiated and irradiated enamel specimens were treated with BioXtra®, phosphate-buffered-saline (PBS; negative control), or 0.12% chlorhexidine (CHX; positive control) for 1 min. Biofilm was produced from human saliva (healthy participants with normal salivary flow for the control group or irradiated HNC patients with hyposalivation for the HNC group), mixed with McBain saliva, under 0.2% sucrose exposure, daily submitted to the treatments (1 min), for 5 days. Bacterial metabolic activity, biofilm viability, CFU counting, and enamel demineralization were determined.

RESULTS

BioXtra® significantly reduced the bacterial metabolic activity for both enamel types and the inoculum sources, being more effective for the irradiated enamel or for the saliva from the control group. Similarly, BioXtra® significantly reduced the biofilm viability, the CFU for total microorganisms, mutans streptococci, and lactobacilli, and was able to significantly reduce the mineral loss and the lesion depth compared to PBS. CHX was an effective treatment to significantly reduce all parameters, performing better than BioXtra® and reinforcing its reliable efficiency as a positive control.

CONCLUSION

Regardless of the enamel type and the inoculum source, BioXtra® presented antibacterial, antibiofilm, and anticaries effects under this experimental model, which should be confirmed in further clinical studies.

Salivary gland function, development, and regeneration

Salivary glands produce and secrete saliva, which is essential for maintaining oral health and overall health. Understanding both the unique structure and physiological function of salivary glands, as well as how they are affected by disease and injury, will direct the development of therapy to repair and regenerate them. Significant recent advances, particularly in the OMICS field, increase our understanding of how salivary glands develop at the cellular, molecular, and genetic levels: the signaling pathways involved, the dynamics of progenitor cell lineages in development, homeostasis, and regeneration, and the role of the extracellular matrix microenvironment. These provide a template for cell and gene therapies as well as bioengineering approaches to repair or regenerate salivary function.

Novel impacts of saliva with regard to oral health

The maintenance of balanced oral homeostasis depends on saliva. A readily available and molecularly rich source of biological fluid, saliva fulfills many functions in the oral cavity, including lubrication, pH buffering, and tooth mineralization. Saliva composition and flow can be modulated by different factors, including circadian rhythm, diet, age, drugs, and disease. Recent events have revealed that saliva plays a central role in the dissemination and detection of the SARS-CoV-2 coronavirus. A working knowledge of saliva function and physiology is essential for dental health professionals.

Lectin-Functionalized Polyethylene Glycol for Relief of Mucosal Dryness

The importance of lubrication between oral surfaces provided by the salivary film is most acutely apparent when it is disrupted, a prevalent consequence of salivary gland hypofunction experienced with aging, a symptom of certain diseases, or a side effect of some medical interventions. Sufferers report difficulty with speech and oral food processing and collectively is detrimental to quality of life. Polyethylene glycol (PEG) is widely employed as a successful biocompatible boundary lubricant in engineering and biomedical applications. It is hypothesized that the immobilization of PEG to biological materials such as oral epithelial cells and tissue can mimic the salivary film and provide durable relief from the symptoms of mucosal dryness. To do so, PEG is functionalized with a sugar binding lectin (wheat germ agglutinin) to enhance epithelial adhesion through lectin-sugar interactions. Retention and lubricity are characterized on an ex vivo oral tissue tribology rig. WGA-PEG coats and retains on mucin films, oral epithelial cells, and porcine tongue tissue, and offers sustained reduction in coefficient of friction (COF). WGA-PEG could be developed into a useful topical treatment for reducing oral friction and the perception of dry mouth.

Therapeutic Recommendations for the Management of Older Adult Patients with Sjögren's Syndrome

Primary Sjögren's syndrome (SjS) is a systemic autoimmune disease most commonly diagnosed in middle-aged women. Although the disease can occur at all ages, it is diagnosed between 30 and 60 years of age in two-thirds of patients. In more than 20% of cases, the people are older than 65 years. In this review, we focus on the therapeutic management of primary SjS in older patients, following the recently published 2020 European League Against Rheumatism (EULAR) recommendations for the management of the disease with topical and systemic therapies. These recommendations are applicable to all patients with primary SjS regardless of age at diagnosis, although the therapeutic management in older patients requires additional considerations. Older patients are more likely to have pulmonary, liver, kidney, or heart-related comorbidities (even cognitive disturbances); caution is required when most drugs are used, including muscarinic agents, systemic corticosteroids and synthetic immunosuppressants. It is also important to monitor the use of eye drops containing steroids due to the increased risk of developing cataracts, a frequent ocular complication in the older population. In contrast, the majority of drugs that can be used topically (pilocarpine rinses, eye drops containing topical non-steroidal anti-inflammatory drugs (NSAIDs) or cyclosporine A, topical dermal formulations of NSAIDs) have shown an acceptable safety profile in older patients, as well as rituximab. A rigorous evaluation of the medical history of older patients is essential when drugs included in the EULAR guidelines are prescribed, with special attention to factors frequently related to ageing, such as polypharmacy, the existence of organ-specific comorbidities, or the enhanced susceptibility to infections.

Dry mouth diagnosis and saliva substitutes-A review from a textural perspective

The aim of this review is to assess the objective and subjective diagnosis, as well as symptomatic topical treatment of dry mouth conditions with a clear focus on textural perspective. We critically examine both the current practices as well as outline emerging possibilities in dry mouth diagnosis and treatment, including a patent scan for saliva substitutes. For diagnosis, salivary flow rates and patient-completed questionnaires have proven to be useful tools in clinical practice. To date, objective measurements of changes in mechanical properties of saliva via rheological, adsorption, and tribological measurements and biochemical properties of saliva such as assessing protein, mucins (MUC5B) are seldom incorporated into clinical diagnostics; these robust diagnostic tools have been largely restricted to application in non-clinical settings. As for symptomatic treatments of dry mouth, four key agents including lubricating, thickening, adhesive, and moisturizing agents have been identified covering the overall landscape of commercial saliva substitutes. Although thickening agents such as modified celluloses, polysaccharide gum, polyethylene glycol, and so forth are most commonly employed saliva substitutes, they offer short-lived relief from dry mouth and generally do not provide boundary lubrication properties of real human saliva. Innovative technologies such as self-assembly, emulsion, liposomes, and microgels are emerging as novel saliva substitutes hold promise for alternative approaches for efficient moistening and lubrication of the oral mucosa. Their adoption into clinical practice will depend on their efficacies, duration of relief, and ease of application by the practitioners and patient compliance.

Influence of lubricating conditions on the two-body wear behavior and hardness of titanium alloys for biomedical applications

Commercially pure titanium and titanium alloys are often preferred in biomedical applications due to their high biocompatibility behavior. However, the inadequate wear, fatigue and corrosion resistance of titanium alloys limit their use as a biomaterial in the human body. Furthermore, these alloys may contain such as aluminum and vanadium elements that can damage the nervous system. The aim of this in vitro study was to evaluate the influence of lubrication conditions on the two-body wear behavior of pure titanium, Ti-2.5Si-5Zr, Ti-5Si-5Zr, and Ti-6Al-4V using dual-axis computer-controlled wear simulator device. The mean wear volume loss of all test specimens after the two-body wear test procedures were determined to use a non-contact 3D profilometer. The alloys hardness and microstructures were evaluated using the Vickers indention method, scanning electron microscopy (SEM), X-ray spectroscopy (EDS), and X-ray diffraction (XRD) analysis. The hardness of Ti-6Al-4V titanium alloy material was significantly greater than the other alloy materials and cp-Ti. The mean wear volume loss of Ti-5Si-5Zr test specimens was lower than the other test group specimens irrespective of lubrication conditions. It was concluded, the two-body wear resistance of the alloy formed with the addition of silica to the pure titanium is increased after both wear test procedures. However, for the test materials in this study considered, correlations between the two-body wear resistance and hardness were found to be insignificant.

Next Generation Salivary Lubrication Enhancer Derived from Recombinant Supercharged Polypeptides for Xerostomia

Insufficient retention of water in adsorbed salivary conditioning films (SCFs) because of altered saliva secretion can lead to oral dryness (xerostomia). Patients with xerostomia sometimes are given artificial saliva, which often lacks efficacy because of the presence of exogenous molecules with limited lubrication properties. Recombinant supercharged polypeptides (SUPs) improve salivary lubrication by enhancing the functionality of endogenously available salivary proteins, which is in stark contrast to administration of exogenous lubrication enhancers. This novel approach is based on establishing a layered architecture enabled by electrostatic bond formation to stabilize and produce robust SCFs in vitro. Here, we first determined the optimal molecular weight of SUPs to achieve the best lubrication performance employing biophysical and in vitro friction measurements. Next, in an ex vivo tongue-enamel friction system, stimulated whole saliva from patients with Sjögren syndrome was tested to transfer this strategy to a preclinical situation. Out of a library of genetically engineered cationic polypeptides, the variant SUP K108cys that contains 108 positive charges and two cysteine residues at each terminus was identified as the best SUP to restore oral lubrication. Employing this SUP, the duration of lubrication (Relief Period) for SCFs from healthy and patient saliva was significantly extended. For patient saliva, the lubrication duration was increased from 3.8 to 21 min with SUP K108cys treatment. Investigation of the tribochemical mechanism revealed that lubrication enhancement is because of the electrostatic stabilization of SCFs and mucin recruitment, which is accompanied by strong water fixation and reduced water evaporation.

Artificial Saliva in Diabetic Xerostomia (ASDIX): Double Blind Trial of Aldiamed® Versus Placebo

Xerostomia is a symptom frequently present in patients with type 1 (T1DM) and type 2 diabetes mellitus (T2DM). In the present trial, the activity of an artificial saliva (aldiamed^® spray) in comparison to a placebo spray were used to evaluate the xerostomia and the saliva antioxidant capacity (SAT). Sixty patients of both genders with T1DM or T2DM were randomized into two groups of 30 subjects each. The experiment was a double-blind study approved by the Ethics Committee of the “G. d’Annunzio University” of Chieti and Pescara. Moreover, measurements of the stimulated saliva flow rate and the ultrasonography of the submandibular and parotid glands were performed at both the study time points. The results demonstrated statistically significant differences between the treatments in terms of the xerostomia average score. Specifically, the values were at baseline and after 30 days 2.9 ± 1.31 and 3.0 ± 1.44 and 1.4 ± 1.48 and 2.4 ± 0.99 for aldiamed^® spray and the placebo, respectively. Meanwhile, no statistically significant differences were shown between the two groups for the other variables, such as the salivary flow rate, the antioxidant capacity of the saliva, and the ultrasonography of the major salivary glands.