Effect of calcium ions on in vitro pellicle formation from parotid and whole saliva

New insights into the protective effect of statherin-derived peptide for different acquired enamel pellicle formation times on the native human enamel surfaces

OBJECTIVES

This study evaluated the protective impact of acquired enamel pellicle (AEP) engineering with statherin-derived peptide (StatpSpS), considering different AEP formation times.

DESIGN

A total of 120 native human enamel specimens were divided into 2 main groups: 1) No AEP engineering and 2) AEP engineering with StatpSpS (pretreatment for 1 min; 37 °C, under agitation). Each group was further divided into 4 subgroups: No pellicle, or 1, 60-and-120 min AEP formation times (human saliva; 37 °C). The specimens were then subjected to an erosive challenge (1% citric acid; pH 3.6; 1 min; 25 °C). This procedure was repeated for 5 cycles. Relative surface reflection intensity (%SRI) was measured and scanning electron microscopy (SEM) of the enamel surface was done.

RESULTS

All AEP engineering groups protected against initial dental erosion in comparison with No pellicle (p < 0.001), likewise all groups with AEP, independent of engineering or formation times (p 0.001). Furthermore, engineering with StatpSpS even without the presence of AEP protected the enamel when compared to the No engineering/No pellicle group (p < 0.0001). No difference was observed regarding the protection from the different AEP formation times (p > 0.05). Regarding the SEM analysis, in the "No AEP engineering & No AEP" group, a more severe effect of citric acid was observed, with more enamel prism heads and scratches on the surface when compared with the other groups.

CONCLUSIONS

AEP provides almost instant protection at formation times even as short as 1 min, protecting the native enamel against erosion. Treatment with StatpSpS by itself provides similar protection as the AEP.

Colloidal dynamics of emulsion droplets in mouth

The interaction of emulsions with the tongue is key to the sensory appeal of food and can potentially be exploited for oral/buccal pharmaceutical delivery. Whilst there is good understanding of the different mucoadhesive forces governing emulsion interaction with the tongue, their relative importance is not well understood. In addition, the physical location of emulsions within the saliva papillae on the tongue is not understood at all. A combination of ex vivo salivary film, and in vivo oral coating experiments were used to determine the importance of different mucoadhesive forces. Mucoadhesion of cationic emulsions was largely driven by electrostatic complexation. SDS-PAGE of the in vivo saliva coating highlighted that mucins were largely responsible for cationic emulsion mucoadhesion. Anionic emulsions were bound via hydrophobic/steric interactions to small salivary proteins typically located away from the mucin anchor points. The physical location and clustering of emulsions relative to the salivary film/papillae was probed via the invention of a fluorescent oral microscope. Cationic emulsions were densely clustered close to the papillae whilst anionic emulsions were suspended in the salivary film above the papillae. Interestingly, non-ionic emulsions were also trapped within the salivary film above the papillae as individual droplets. These findings highlight that whilst electrostatic complexation with saliva is a powerful mucoadhesive force, hydrophobic and steric interactions also act to induce oral retention of emulsions. The differences in physical location and clustering of emulsions within the salivary film hint at the 3D locations of the different salivary proteins driving each mucoadhesive interaction. This novel understanding of emulsion saliva/papillae interactions has potential to aid efficacy of buccal pharmaceutical delivery and the reduction of astringency in plant-based foods.

Sialometry and concentration of phosphate and calcium in stimulated whole saliva and gingival crevicular fluid and its association with dental caries in schoolchildren

Introduction: The remineralizing properties of saliva contribute to maintain the physical and chemical integrity of the mineral structure of teeth, which protects it from the installation and evolution of dental caries. Objective: To relate sialometry, buffering capacity, calcium and phosphate concentration in whole stimulated saliva, and in gingival crevicular fluid with school children caries severity and activity. Materials and methods: We selected 36 schoolchildren aged 6 years: 18 with caries (International Caries Detection and Assessment System, ICDAS>1 group) and 18 without caries (ICDAS=0 group). The severity and activity of dental caries were diagnosed in the primary dentition: in the occlusal surface of molars and in the vestibular of the anterior teeth by ICDAS-II. Results: Caries in occlusal surface were more severe than in vestibular surface. The concentration of calcium in saliva and phosphate in healthy teeth gingival crevicular fluid were higher in the ICDAS>1 group. The concentration of calcium in gingival crevicular fluid was higher in the ICDAS=0 group than in the decayed teeth of the ICDAS>1 group. We found a statistically significant association between the frequency of active caries andthe concentration of phosphate in gingival crevicular fluid of teeth with caries, as well as between the severity of caries with buffering capacity and the concentration of phosphate in the gingival crevicular fluid of teeth with caries. Conclusion: We found an association between dental caries with buffering capacity and buccal calcium and phosphate.

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

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

The effect of different salivary calcium concentrations on the erosion protection conferred by the salivary pellicle

Different proportions of mineral ions in saliva can influence the protective effect the salivary pellicle provides against dental erosion. To investigate the effect of different calcium concentrations in human saliva on the protection against enamel erosion, enamel specimens were divided into 8 treatment groups: humid chamber (Ctrl); whole mouth stimulated human saliva (HS); artificial saliva containing different calcium concentrations (AS_low, AS_medium, AS_high); and dialysed human saliva containing different calcium concentrations (DS_low, DS_medium, DS_high). The specimens underwent 4 cycles of incubation in the treatment group followed by an erosive challenge. Surface hardness and calcium release were measured during the cycling process. All DS groups exhibited significantly higher enamel surface softening than HS and the corresponding AS groups. Among the DS groups, the surface softening was significantly higher in DS_low than in DS_high. No significant differences were found within the AS or DS groups regarding calcium release. The results of this study indicated that erosion protection conferred by saliva depends on an interplay between salivary proteins and ions. While both proteins and ions have a positive effect on their own, the combination of the two can lead to different degrees of protection or even negative effects, depending on the relative concentrations.

Chronophysiological features of the normal mineral composition of human saliva

BACKGROUND

The high rate of changes in the composition of saliva can be used for the monitoring of various biorhythms in order to study the physiological characteristics of the human body.

RESEARCH OBJECTIVE

The study of the dynamics of the near-24-h mineral composition of saliva in men and women.

METHODS

The study involved 20 men and 20 women, age 23.1±0.9years. Saliva samples were collected every 3h during the day within 10min. The mineral composition of saliva was defined by the capillary electrophoresis technique. The cross-group differences were evaluated using the non-parametric criterion.

RESULTS

It was shown that the maximum values of the mineralizing capacity fall to 7-8 a.m. and 18-19p.m., which is due to the change in the rate of saliva secretion. The near-24-h dynamics of the saliva pH practically coincides with the dynamics of the Ca/P ratio; there are evident maxima at 9:00 am and 15-18p.m. The values of the Na/K ratio are out of phase with the Ca/P ratio. There is one maximum, corresponding to 3 am in the night, and one minimum at 12-13p.m., which is due to a decreased level of sodium and increased potassium concentration. Statistically valid differences between men and women in pH (p<0.001), concentrations of inorganic phosphorus (p<0.001), as well as Ca/P coefficient (p=0.011) were identified.

CONCLUSION

The dynamics of the studied parameters during 24h is characterized by pronounced intervals.

Real-time formation of salivary films onto polymeric materials for dental applications: Differences between unstimulated and stimulated saliva

The formation of salivary films onto oral prostheses materials is of central importance for understanding their performance and interaction with oral tissue and flora. The aim of this work was to study and compare the salivary films formed from unstimulated and stimulated whole saliva on two common polymeric materials, polycarbonate and poly(methyl methacrylate). Irradiating these materials with UV light is a simple way to modify their wettability, roughness and ζ-potential. Therefore, the effect of UV exposure of polycarbonate and poly(methyl methacrylate) on saliva adsorption was also investigated. For this purpose a quartz crystal microbalance with dissipation and SDS-PAGE have been combined in order to associate the thicknesses and viscoelastic properties of the salivary films with their protein composition. SDS-PAGE results suggest that a larger diversity of proteins is involved in the formation of stimulated saliva pellicles. Furthermore, according to QCM-D, pellicles formed from stimulated saliva are thinner and stiffer than the ones formed from unstimulated saliva if the polymeric materials have not been exposed to UV light although both types of saliva form a biphasic layer. For UV-treated materials, the same is applied to polycarbonate but not to poly(methyl methacrylate) where stimulated saliva yields thicker and softer films than unstimulated saliva being the adsorption process of a multiphasic nature. These results highlight the importance of choosing the appropriate sample depending on the type of study to be performed.

Balancing microbial and mammalian cell functions on calcium ion-modified implant surfaces

Implant integration is a complex process mediated by the interaction of the implant surface with the surrounding ions, proteins, bacteria, and tissue cells. Although most implants achieve long-term bone-tissue integration, preventing pervasive implant-centered infections demands further advances, particularly in surfaces design. In this work, we analyzed classical microrough implant surfaces (only acid etched, AE; sandblasted then acid etching, SB + AE) and a new calcium-ion-modified implant surface (AE + Ca) in terms of soft- and hard-tissue integration, bacterial adhesion, and biofilm formation. We cultured on the surfaces primary oral cells from gingiva and alveolar bone, and three representative bacterial strains of the oral cavity, emulating oral conditions of natural saliva and blood plasma. With respect to gingiva and bone cells and in the presence of platelets and plasma proteins, AE + Ca surfaces yielded in average 86% higher adhesion, 44% more proliferation, and triggered 246% more synthesis of extracellular matrix biomolecules than AE-unmodified controls. Concomitantly, AE + Ca surfaces regardless of conditioning with saliva and/or blood plasma showed significantly less bacterial adhesion (67% reduction in average) and biofilm formation (40% reduction in average) than unmodified surfaces. These results highlight the importance of a calcium-rich hydrated interface to favor mammalian cell functions over microbial colonization at implant surfaces. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 421-432, 2018.

Erosion protection conferred by whole human saliva, dialysed saliva, and artificial saliva

During dental erosion, tooth minerals are dissolved, leading to a softening of the surface and consequently to irreversible surface loss. Components from human saliva form a pellicle on the tooth surface, providing some protection against erosion. To assess the effect of different components and compositions of saliva on the protective potential of the pellicle against enamel erosion, we prepared four different kinds of saliva: human whole stimulated saliva (HS), artificial saliva containing only ions (AS), human saliva dialysed against artificial saliva, containing salivary proteins and ions (HS/AS), and human saliva dialysed against deionised water, containing only salivary proteins but no ions (HS/DW). Enamel specimens underwent four cycles of immersion in either HS, AS, HS/AS, HS/DW, or a humid chamber (Ctrl), followed by erosion with citric acid. During the cycling process, the surface hardness and the calcium released from the surface of the specimens were measured. The different kinds of saliva provided different levels of protection, HS/DW exhibiting significantly better protection than all the other groups (p < 0.0001). Different components of saliva, therefore, have different effects on the protective properties of the pellicle and the right proportions of these components in saliva are critical for the ability to form a protective pellicle.

Dynamic interactions of amelogenin with hydroxyapatite surfaces are dependent on protein phosphorylation and solution pH

Amelogenin, the predominant extracellular matrix protein secreted by ameloblasts, has been shown to be essential for proper tooth enamel formation. In this study, amelogenin adsorption to hydroxyapatite (HAP) surfaces, a prototype for enamel mineral, has been studied using a quartz crystal microbalance (QCM) to interrogate effects of protein phosphorylation and solution pH. Dynamic flow-based experiments were conducted at pH 7.4 and 8.0 using native phosphorylated porcine amelogenin (P173) and recombinant non-phosphorylated porcine amelogenin (rP172). Loading capacities (μmol/m²) on HAP surfaces were calculated under all conditions and adsorption affinities (K_ad) were calculated when Langmuir isotherm conditions appeared to be met. At pH 8.0, binding characteristics were remarkably similar for the two proteins. However, at pH 7.4 a higher affinity and lower surface loading for the phosphorylated P173 was found compared to any other set of conditions. This suggests that phosphorylated P173 adopts a more extended conformation than non-phosphorylated full-length amelogenin, occupying a larger footprint on the HAP surface. This surface-induced structural difference may help explain why P173 is a more effective inhibitor of spontaneous HAP formation in vitro than rP172. Differences in the viscoelastic properties of P173 and rP172 in the adsorbed state were also observed, consistent with noted differences in HAP binding. These collective findings provide new insight into the important role of amelogenin phosphorylation in the mechanism by which amelogenin regulates enamel crystal formation.

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

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

The adsorption-desorption behaviour and structure function relationships of bile salts

The digestion of dietary components in the human gastrointestinal (GI) tract is a complex, dynamic, inherently heterogeneous process. A key aspect of the digestion of lipid in the GI tract is the combined action of bile salts, lipase and colipase in hydrolysing and solubilising dispersed lipid. The bile salts are a mixture of steroid acid conjugates with surfactant properties. In order to examine whether the different bile salts have different interfacial properties their dynamic interfacial behaviour was characterised. Differences in the adsorption behaviour to solid hydrophobic surfaces of bile salt species were studied using dual polarisation interferometry and atomic force microscopy (AFM) under physiological conditions. Specifically, the cholates adsorbed more slowly and a significant proportion were irreversibly adsorbed following buffer rinsing; whereas the deoxycholates and chenodeoxycholates adsorbed more rapidly and desorbed to a greater extent following buffer rinsing. The conjugating groups (taurine, glycine) did not influence the behaviour. AFM showed that the interfacial structures that remained following buffer rinsing were also different between these two groups. In addition, the adsorption-desorption behaviour affected the adsorption of colipase to a solid surface. This supports the idea that cooperative adsorption occurs between certain bile salts and colipase to facilitate the adsorption and activity of pancreatic lipase in order to restore lipolytic activity in the presence of bile salts. This study provides insights into how differences in bile salt structure could affect lipase activity and solubilisation of lipolysis products and other lipid-soluble bioactive molecules.

Structural and compositional changes in the salivary pellicle induced upon exposure to SDS and STP

Sodium dodecyl sulphate (SDS) and sodium tripolyphosphate (STP) act to remove stained pellicle from dentition and loosen deposits on tooth surfaces that may become cariogenic over time. This study investigated how SDS and STP impact the salivary pellicle adsorbed onto hydroxyapatite and silica sensors using a dual polarisation interferometer and a quartz-crystal microbalance with dissipation. After the pellicle was exposed to SDS and STP the remaining pellicle, although weaker, due to the loss of material, became less dense but with a higher elastic component; suggesting that the viscous component of the pellicle was being removed. This would imply a structural transformation from a soft but dense structured pellicle, to a more diffuse pellicle. In addition, the majority of proteins displaced by both SDS and STP were identified as being acidic in nature; implying that the negatively charged groups of SDS and STP may be responsible for the displacement of the pellicle proteins observed.