The protective nature of the salivary pellicle

Mass spectrometry-based proteomic approaches for salivary protein biomarkers discovery and dental caries diagnosis: A critical review

Dental caries is a multifactorial chronic disease resulting from the intricate interplay among acid-generating bacteria, fermentable carbohydrates, and several host factors such as saliva. Saliva comprises several proteins which could be utilized as biomarkers for caries prevention, diagnosis, and prognosis. Mass spectrometry-based salivary proteomics approaches, owing to their sensitivity, provide the opportunity to investigate and unveil crucial cariogenic pathogen activity and host indicators and may demonstrate clinically relevant biomarkers to improve caries diagnosis and management. The present review outlines the published literature of human clinical proteomics investigations on caries and extensively elucidates frequently reported salivary proteins as biomarkers. This review also discusses important aspects while designing an experimental proteomics workflow. The protein-protein interactions and the clinical relevance of salivary proteins as biomarkers for caries, together with uninvestigated domains of the discipline are also discussed critically.

Effect of three different remineralising agents on prevention against acidic erosion of primary teeth: an in vitro study

PURPOSE

This study aimed to evaluate and compare the protective effect of fluoride varnish (Enamelast™, Ultradent Inc., Cologne, Germany), casein phosphopeptide-amorphous calcium phosphate fluoride/CPP-ACPF (MI Paste Plus, GC Corp., Tokyo, Japan) and self-assembling P11-4 peptide (Curodont™ Protect, Credentis AG, Windisch, Switzerland), against acidic erosion of primary teeth.

METHODS

Forty primary anterior teeth were randomly assigned to four groups (n = 10): group 1: control, group 2: fluoride varnish, group 3: CPP-ACPF and group 4: self-assembling P11-4 peptide. After applying remineralising agents, except for the control group, all specimens underwent an erosive challenge of carbonated soft drink and artificial saliva for 15 cycles of 6 s each at 6-h intervals for a day. Groups were compared in terms of surface microhardness, roughness readings, and surface scanning with an extra-oral scanner (D800; 3Shape A/S) before and after the erosive process.

RESULTS

All experimental groups showed superior results than the control group regarding microhardness, surface roughness, and substance loss. The fluoride varnish group showed significantly favourable results in microhardness change. There was no significant difference between the experimental groups regarding surface roughness and enamel loss measurements.

CONCLUSION

5% NaF fluoride varnish, CPP-ACPF and self-assembling P11-4 peptide protect the enamel of primary teeth against erosion compared to artificial saliva alone.

Protease-inhibitors added to saliva in vitro influence the erosion protective effect of enamel pellicles

In contrast to pellicles formed in vivo, pellicles formed in vitro provide little to no erosion protection for enamel, possibly due to protein degradation from proteases during pellicle formation. With the objective to achieve a more similar effect as observed for in vivo pellicles, the effects of adding protease inhibitors (PI) to saliva in vitro, and/or exchanging saliva repeatedly during pellicle formation were investigated in a cyclic model of pellicle formation and erosion with human enamel specimens. We repeatedly assessed surface microhardness (SMH), measured initial and final surface reflection intensity (SRI), and determined calcium released during erosion. For all the parameters tested, we observed a clear positive effect on erosion protection when adding PI to saliva for pellicle formation: SMH remained harder, SRI remained higher, and less calcium was released. Additionally, exchanging saliva with fresh one during pellicle formation led to a protective effect, but not as strong as the addition of PI. We conclude that adding protease inhibitors to saliva in vitro for pellicle formation leads to an erosion protective effect, which was further increased by repeatedly exchanging the saliva. Whether the pellicle itself more closely resembles in vivo pellicles remains to be investigated.

Advanced non-fluoride approaches to dental enamel remineralization: The next level in enamel repair management

In modern dentistry, a minimally invasive management of early caries lesions or early-stage erosive tooth wear (ETW) with synthetic remineralization systems has become indispensable. In addition to fluoride, which is still the non-plus-ultra in these early caries/ETW treatments, a number of new developments are in the test phase or have already been commercialized. Some of these systems claim that they are comparable or even superior to fluoride in terms of their ability to remineralize enamel. Besides, their use can help avoid some of the risks associated with fluoride and support treatments of patients with a high risk of caries. Two individual non-fluoride systems can be distinguished; intrinsic and extrinsic remineralization approaches. Intrinsic (protein/peptide) systems adsorb to hydroxyapatite crystals/organics located within enamel prisms and accumulate endogenous calcium and phosphate ions from saliva, which ultimately leads to the re-growth of enamel crystals. Extrinsic remineralization systems function on the basis of the external (non-saliva) supply of calcium and phosphate to the crystals to be re-grown. This article, following an introduction into enamel (re)mineralization and fluoride-assisted remineralization, discusses the requirements for non-fluoride remineralization systems, particularly their mechanisms and challenges, and summarizes the findings that underpin the most promising advances in enamel remineralization therapy.

Effect of Artificial Aging on Mechanical and Tribological Properties of CAD/CAM Composite Materials Used in Dentistry

With easy-to-process 3D printing materials and fast production, the quality of dental services can be improved. In the conventional procedure, the dentist makes temporary crowns directly in the patient’s mouth, e.g., from the most commonly used bis-acrylic composites. Temporary crowns made directly in the office without the use of CAD/CAM are often of inferior quality, which directly results in impaired hygiene, poorer masticatory mechanics, greater deposition of plaque, calculus and sediment, and may adversely affect periodontal and gum health. The mechanical strength, resistance to aging and abrasion of 3D printing materials are higher than those of the soft materials used in conventional methods. This translates into durability. The patient leaves the surgery with a restoration of higher utility quality compared to the conventional method. The objective of the paper was to determine the influence of aging in artificial saliva of AM (additive manufacturing) orthodontic composites on their functional properties. For the purpose of the study, fillings well-known worldwide were selected. These were traditional UV-curable resins (M I, M II, M III, M V) and a hybrid material based on a UV-curable resin (M VI). Samples were stored in artificial saliva at 37 ± 1 °C in a thermal chamber for 6 months. Indentation hardness, frictional tests and sliding wear measurements were conducted. A comparison between various materials was made. Descriptive statistics, degradation coefficients, H²E, Archard wear and specific wear rate were calculated. The Weibull statistical test for indentation hardness was performed and Hertzian contact stresses for the frictional association were calculated for unaged (M I, M II, M III, M V, M VI) and aged (M I AS, M II AS, M III AS, M V AS, M VI AS) samples. M I exhibited the lowest average hardness among the unaged materials, while M III AS had the lowest average hardness among the aged materials. Comparably low hardness was demonstrated by the M I AS material. The coefficient of friction values for the aged samples were found to be higher. The lowest wear value was demonstrated by the M I material. The wear resistance of most of the tested materials deteriorated after aging. The M VI AS material had the highest increase in wear. According to the results provided, not only the chemical composition and structure, but also aging have a great impact on the indentation hardness and wear resistance of the tested orthodontic materials.

Functional biomedical materials derived from proteins in the acquired salivary pellicle

In the oral environment, the acquired salivary pellicle (ASP) on the tooth surface comprises proteins, glycoproteins, carbohydrates, and lipids. The ASP can specifically and rapidly adsorb on the enamel surface to provide effective lubrication, protection, hydration, and remineralisation, as well as be recognised by various bacteria to form a microbial biofilm (plaque). The involved proteins, particularly various phosphoproteins such as statherins, histatins, and proline-rich proteins, are vital to their specific functions. This review first describes the relationship between the biological functions of these proteins and their structures. Subsequently, recent advances in functional biomedical materials derived from these proteins are reviewed in terms of dental/bone therapeutic materials, antibacterial materials, tissue engineering materials, and coatings for medical devices. Finally, perspectives and challenges regarding the rational design and biomedical applications of ASP-derived materials are discussed.

The dentin pellicle - A neglected topic in dental research

OBJECTIVE

All soft and solid surfaces exposed to the oral cavity are covered by an acquired pellicle. While the pellicle adsorbed on enamel is well researched, only limited data are available on the dentin pellicle. The purpose of the present review is to summarize studies considering the composition, structure and properties of the dentin pellicle and compare them with the current state of research on enamel pellicle.

METHODS

The literature search was conducted using Medline database and Google Scholar, including checking reference lists of journal articles by handsearching. Thereby, 19 studies were included in the present review.

RESULTS AND CONCLUSION

The dentin pellicle has a similar ultrastructure to the enamel pellicle, which is up to 1 μm thick depending on pellicle formation time and localization in the oral cavity. In contrast, due to the lack of studies on the dentin pellicle regarding its composition and properties, a comparison to the enamel pellicle is difficult. So far, only one study showed anti-abrasive properties and data on anti-erosive properties were controversial. Despite becoming more and more clinically relevant due to the increasing frequency of dentin exposure, the dentin pellicle is largely unexplored. For further investigations it is not only necessary to standardize dentin specimens, but also to assess fundamental research on dentin itself, as its complex morphology and composition may have a crucial influence on pellicle formation. Furthermore, a more detailed knowledge of the dentin pellicle may also reveal target sites for modification in favor of its protective properties.

Progress and limitations of current surface registration methods when measuring natural enamel wear

OBJECTIVES

Our ability to detect dental wear on sequential scans is improving. This experiment aimed to determine if widely used surface registration methods were sufficiently accurate to distinguish differences between intervention groups on early wear lesions.

METHODS

Baseline measurements were taken on human molar buccal enamel samples (n = 96) with a confocal scanning profilometer (Taicaan, UK). Samples were randomly assigned to subgroups of brushing (30 linear strokes 300 g force) before or after an acid challenge (10 min citric acid 0.3% immersion) for four test dentifrices (medium abrasivity NaF, medium abrasivity SnF₂, low abrasivity NaF and a water control). Post-experimental profilometry was repeated. 3D step height was analysed using WearCompare (www.leedsdigitaldentistry.co.uk/wearcompare, UK). Percentage Sa change was calculated using Boddies (Taicaan Technologies, Southampton, UK). Data were analysed in SPSS (IBM, USA).

RESULTS

The mean 3D step height (SD) observed when samples were brushed before the erosive challenge was -2.33 µm (3.46) and after was -3.5 µm (5.6). No significant differences were observed between timing of toothbrushing or dentifrice used. The mean % Sa change for the low abrasivity group (water control and low abrasivity NaF) was -10.7% (16.8%) and +28.0% (42.0%) for the medium abrasivity group (medium abrasivity NaF and SnF₂).

CONCLUSIONS

Detectable wear scars were observed at early stages of wear progression. However standard deviations were high and the experiment was underpowered to detect significant changes. Brushing with a low abrasivity dentifrice or water control produced a smoother surface whereas brushing with a high abrasivity dentifrice produced a rougher surface.

CLINICAL SIGNIFICANCE

The methodology currently used to align sequential scans of teeth and measure change is too imprecise to measure early wear on natural enamel surfaces unless a large sample size is used. Further improvements are required before we can fully assess early wear processes on natural teeth using profilometry.

Effect of nonionic and amphoteric surfactants on salivary pellicles reconstituted in vitro

Surfactants are important components of oral care products. Sodium dodecyl sulfate (SDS) is the most common because of its foaming properties, taste and low cost. However, the use of ionic surfactants, especially SDS, is related to several oral mucosa conditions. Thus, there is a high interest in using non-ionic and amphoteric surfactants as they are less irritant. To better understand the performance of these surfactants in oral care products, we investigated their interaction with salivary pellicles i.e., the proteinaceous films that cover surfaces exposed to saliva. Specifically, we focused on pentaethylene glycol monododecyl ether (C12E5) and cocamidopropyl betaine (CAPB) as model nonionic and amphoteric surfactants respectively, and investigated their interaction with reconstituted salivary pellicles with various surface techniques: Quartz Crystal Microbalance with Dissipation, Ellipsometry, Force Spectroscopy and Neutron Reflectometry. Both C12E5 and CAPB were gentler on pellicles than SDS, removing a lower amount. However, their interaction with pellicles differed. Our work indicates that CAPB would mainly interact with the mucin components of pellicles, leading to collapse and dehydration. In contrast, exposure to C12E5 had a minimal effect on the pellicles, mainly resulting in the replacement/solubilisation of some of the components anchoring pellicles to their substrate.

Analysis of the Statistical Comparability of the Hardness and Wear of Polymeric Materials for Orthodontic Applications

Background: Clinical success depends on the contact strength and wear resistance of medical devices made of polymer materials. The scientific goal resulted from the problem of using different methods of surface evaluation of materials used in the production of orthodontic appliances. The purpose of the work was an experimental comparative assessment of indentation hardness and scratch hardness and the sliding wear of four selected polymeric materials used in the manufacture of orthodontic appliances. Methods: Four commercial materials were compared. Shore hardness tests and a scratch test with a Rockwell indenter were performed. A sliding wear test was performed using the ball-on-disc method. Statistical PCA and correlation analyses were performed. Results: The results of scratch hardness measurements using a contact profilometer correlated with the Shore hardness to a greater extent than measurements made using an optical microscope. PCA showed that Shore hardness explains 45% of the total variance in all the results across the materials. Conclusions: The scratch hardness method allows for a more explicit ranking of orthodontic polymeric materials when measurements are made with a profilometer. The ranking of sliding wear resistance should be made separately.

The salivary pellicle on dental biomaterials

The salivary pellicle, an adlayer formed by adsorption of salivary components on teeth and dental biomaterials, has direct consequences on basic outcomes of dentistry. Here, we provide an overview of salivary pellicle formation processes with a critical focus on dental biomaterials. We describe and critique the array of salivary pellicle measurement techniques. We also discuss factors that may affect salivary pellicle formation and the heterogeneity of the published literature describing salivary pellicle formation on dental biomaterials. Finally, we survey the many effects salivary pellicles have on dental biomaterials and highlight its implications on design criteria for dental biomaterials. Future investigations may lead to rationally designed dental biomaterials to control the salivary pellicle and enhance material function and patient outcomes.

Acquired salivary pellicle and oral diseases: A literature review

As soon as saliva contacts the teeth surface, salivary proteins adhere to the tooth surface to form acquired salivary pellicle. The formation of this acquired salivary pellicle is a dynamic and selective process of macromolecular adsorption and desorption. Although acquired salivary pellicle contains proteins and peptides, it also contains lipids, and other macro-molecules, all of which contribute to its protective properties. Acquired salivary pellicle is related to the development of common oral diseases, such as erosion, dental caries, and periodontal disease. Acquired salivary pellicle acts as a natural barrier to prevent a tooth's surface from making direct contact with acids and to protect it from erosive demineralization. It contributes to the control of dental erosion by modulating calcium and phosphate concentrations on the tooth surface. It also influences the initial colonizer of oral biofilm and affects the transportation pathway of the acidic products of cariogenic bacteria, which affects the development of dental caries. In addition, it influences periodontal disease by acting on the colonization of periodontal pathogens. This paper's aim is to provide an overview of the acquired salivary pellicle, highlighting its composition, structure, function, role in common oral diseases, and modification for the prevention of oral diseases.

Effect of the usage of Er,Cr:YSGG laser with and without different remineralization agents on the enamel erosion of primary teeth

The aim of the present study was to evaluate the effects of different remineralization agents associated with erbium, chromium:yttrium-scandium-gallium-garnet (Er,Cr:YSGG) (0.5 W power, 20 Hz frequency, 60% water, 40% air, 25 mJ pulse energy, 8.84 J/cm² fluence, 60 μs pulse duration, 600 μm tip diameter, and an approximate 1-1.5 mm distance to the target) laser irradiation on erosion induced by the consumption of carbonated drinks in human primary enamel. There were 8 groups and 10 primary teeth in each g0roup. The distribution was as follows: group 1, casein phosphopeptide-amorphous calcium phosphate with fluoride (CPP-ACPF); group 2, Er,Cr:YSGG laser+CPP-ACPF; group 3, fluor varnish; group 4, Er,Cr:YSGG Laser+fluoride varnish; group 5, ROCS® medical mineral gel; group 6, Er,Cr:YSGG laser + ROCS® medical mineral gel; group 7, Er,Cr:YSGG laser; and group 8, artificial saliva. The samples in the groups were submerged in artificial saliva and acid twice a day for 6 s at 6-h intervals and were then exposed to an erosion cycle 15 times. In the groups in which the Er,Cr:YSGG laser was applied in combination with the remineralization agents, the laser application was made first, and then the remineralization agents were applied for 4 min in each group. The Friedman and Wilcoxon signed-rank tests and the Bonferroni correction were used in statistical analyses, and the significance level was taken as p < 0.05. According to the results, all agents had a statistically significant difference (groups 1, 2, 3, 4, and 6: p = 0.005, p < 0.017; groups 5 and 7: p = 0.007, p < 0.017) between BL-RM periods. However, all agents had a statistically significant remineralization effect on primary teeth enamel (groups 1, 2, 3, 6, and 7: p = 0.005, p < 0.017; group 4: p = 0.011, p < 0.017) except that group 5 (p = 0.074, p < 0.017) between DM-RM periods. The coadministration of an agent with the laser did not make any difference at a statistical level (p = 0.804, p > 0.05). The results were supported by scanning electron microscopy (SEM) and X-ray diffraction (XRD) analysis. As a result of this study, CPP-ACPF had a notable impact in terms of the remineralization effect on eroded enamel, and the Er,Cr:YSGG laser alone may be an alternative method, which may be related to the modified hydroxyapatite structure, 38.5% H_0.56Ca_4.56O₁₃P₃Y_0.44, that was determined in XRD analysis.

Characterization of the in situ pellicle ultrastructure formed under the influence of bovine milk and milk protein isolates

OBJECTIVES

The present study aimed to investigate if bovine milk or milk protein isolates, respectively, alter the ultrastructure of thein situ pellicle and might therefore have an influence on oral health.

METHODS

In situ pellicle samples were formed on bovine enamel slabs exposed in the oral cavity of three subjects for 6, 30, 60 or 120 min. After 3 min of pellicle formation, mouthrinses were performed for 3 min with (non-)homogenized UHT- or fresh milk (0.3% or 3.8% fat), 30% UHT-treated cream or different types of casein- or milk protein isolates containing preparations. The specimens were removed after the exposure times and transmission electron microscopy (TEM) was performed. Native pellicle samples served as controls.

RESULTS

Topical ultrastructural pellicle modifications were detected after mouthrinses with all types of homogenized UHT- or fresh milk and after the application of a 3% native casein micelles containing experimental solution. Atypical globular protein structures, identified as casein micelles, were temporarily adsorbed onto the pellicle. They were closely associated with lipid droplets. Furthermore, the mouthrinses occasionally affected the morphology of salivary bacteria. However, no notable ultrastructural alterations remained after 120 min of pellicle formation.

CONCLUSION

For the first time, bovine milk- and micellar casein-induced pellicle modifications were revealed by TEM. The adsorption of micellar casein is possibly due to its molecular interactions.

CLINICAL SIGNIFICANCE

Bovine milk or micellar caseins provide some potential for the development of preventive strategies against bacterial biofilm formation or erosive processes at the tooth surface.

In situ Effect of Chewing Gum with and without CPP-ACP on Enamel Surface Hardness Subsequent to ex vivo Acid Challenge

The erosion-protective effect of casein phosphopeptide-amorphous calcium phosphate (CPP-ACP) is controversial. This study aimed to investigate the ability of CPP-ACP chewing gum to prevent a single event of erosive demineralization in situ. Bovine enamel blocks (n = 120) were randomly assigned to 3 phases according to the baseline surface hardness: phase I (PI) - chewing gum with CPP-ACP, phase II (PII) - chewing gum without CPP-ACP, and control phase (PIII) - salivary effect without stimulation (no gum). Nineteen volunteers participated in this study during 3 crossover phases of 2 h. In PI and PII, the volunteers wore intraoral palatal appliances for 120 min and chewed a unit of the corresponding chewing gum for the final 30 min. In the control phase the volunteers wore the appliance for 2 h, without chewing gum. Immediately after intraoral use, the appliances were extraorally immersed in a cola drink for 5 min to promote erosive demineralization. The percentage of surface hardness loss was calculated. The data were analyzed by ANOVA models and Tukey's test. Lower enamel hardness loss was found after the use of chewing gum with CPP-ACP (PI: 32.7%) and without CPP-ACP (PII: 33.5%) compared to the salivary effect without stimulation (PIII: 39.8%) (p < 0.05). There was no difference between PI and PII (p > 0.05). The results suggest that the use of chewing gum immediately before an erosive demineralization can diminish enamel hardness loss. However, the presence of CPP-ACP in the chewing gum cannot enhance this protective effect.

Protective effects of SnF2 - Part III. Mechanism of barrier layer attachment

OBJECTIVE

To assess the ability of various fluoride salts to protect enamel against acid attack via a barrier mechanism.

METHODS

Extracted human enamel specimens were cleaned and rinsed, then soaked in pooled human saliva for 1 hour to initiate formation of an early pellicle. Groups of three specimens each were etched for 10 minutes in 1% citric acid (pH 2.3), treated in a 1:3 slurry of dentifrice [1,100 ppm F as stannous fluoride (SnF2 ), 1,100 ppm F as sodium fluoride (NaF), 1,000 ppm F as sodium monofluorophosphate (SMFP), or 1,400 ppm F as amine fluoride (AmF)] and saliva for 2 minutes, exposed to 2% alizarin red-S (a calcium-selective dye) and rinsed again. The relative ability of each test product to deposit a barrier layer on the enamel surface was measured by its ability to protect against attachment of the calcium-selective dye.

RESULTS

Specimens treated with the SnF2 dentifrice showed the least dye attachment, indicating a high level of surface protection. On a five-point scale, with 0 being no dye deposition (100% protection) and four being complete dye coverage (0% protection), the SnF2 -treated specimens scored an average of 0.25, with NaF scoring 3.4, SMFP scoring 3.4 and AmF scoring 3.7. Protection of the enamel surface was significantly higher for the SnF2 product than for the other products (P < 0.05), with no significant differences among the other three F salts.

CONCLUSIONS

These results demonstrate that after an aggressive acid challenge, SnF2 deposits a barrier layer onto the pellicle-coated enamel surface, and the barrier layer which attaches onto acid challenged tooth surfaces is different from any that might be provided by treatment with the other fluoride compounds tested.

Friction force spectroscopy as a tool to study the strength and structure of salivary films

In this work, we employ atomic force microscopy based friction force spectroscopy to study the strength and structure of salivary films. Specifically, films formed on model hydrophobic (methylated silica) and hydrophilic (clean silica) substrata have been studied in water at pHs in the range 3.3-7. Results reveal that films formed on both types of substrata can be described in terms of two different fractions, with only one of them being able to diffuse along the underlying substrata. We also show how the protective function of the films is reduced when the pH of the surrounding medium is lowered. Specifically, lowering of pH causes desorption of some components of the films formed on hydrophobic methylated surfaces, leading to weaker layers. In contrast, at low pHs, saliva no longer forms a layer on hydrophilic silica surfaces. Instead, an inhomogeneous distribution of amorphous aggregates is observed. Our data also suggest that hydrophobic materials in the oral cavity might be more easily cleaned from adsorbed salivary films. Finally, reproducible differences are observed in results from experiments on films from different individuals, validating the technique as a tool for clinical diagnosis of the resistance to erosion of salivary films.

In vitro cleaning, abrasion and fluoride efficacy of a new silica based whitening toothpaste containing blue covarine

OBJECTIVES

To investigate the stain removal ability, abrasivity towards enamel and dentine, and fluoride efficacy of a new silica based blue covarine whitening toothpaste in vitro.

METHODS

Stain removal was assessed by brushing artificially stained bovine specimens with slurries of either the new toothpaste or one of two whitening products or a non-whitening silica product. Toothpaste abrasivity was assessed by brushing enamel/dentine specimens with slurries of either the new toothpaste, a whitening toothpaste or a non-whitening toothpaste and measuring the wear via a combination of changes in geometry of Knoop indents and surface profilometry. Fluoride efficacy was assessed using remineralisation, demineralisation and fluoride-uptake methods.

RESULTS

The in vitro cleaning study showed that the silica based blue covarine whitening toothpaste removed significantly (p < 0.05) more stain than the non-whitening toothpaste and was as effective as the two marketed silica based whitening toothpastes. This enhanced tooth whitening benefit did not give rise to a concomitant statistically significant increase in the level of wear to enamel and dentine compared to the non-whitening silica based toothpaste. The fluoride efficacy was superior to a non-fluoridated control and was as effective as a clinically tested formulation containing the same fluoride source.

CONCLUSIONS

The studies show that the new whitening toothpaste is effective in extrinsic stain removal, does not have an undue degree of abrasivity to enamel or dentine compared to other relevant commercially available products, and is an efficacious source of fluoride.

The measurement of enamel wear by four toothpastes

OBJECTIVES

To determine the enamel abrasivity of three whitening toothpastes and a silica toothpaste and to measure the brushing forces used.

METHODS

Polished human enamel blocks were indented with a Knoop diamond and attached to dentures of adult volunteers. The blocks were brushed ex vivo, twice per day with either a whitening toothpaste containing Perlite (White System), a commercial whitening toothpaste (A and B) or a silica toothpaste. After four and twelve-weeks, one block per subject was removed and the Knoop indent remeasured. From the changes in the indent length, the amount of enamel wear was calculated.

RESULTS

The mean enamel wear (sd) for White System, silica toothpaste, whitening toothpaste A and B after four-weeks was 0.14 (0.15), 0.09 (0.16), 0.14 (0.12) and 0.89 (0.93) and after twelve-weeks was 0.24 (0.21), 0.37 (0.73), 0.36 (0.52) and 1.04 (0.98) microm respectively. After four-weeks, the differences in enamel wear between whitening toothpaste B and all other toothpastes were of statistical significance (p < 0.003), but not after twelve-weeks. The mean ex vivo normal brushing force (sd) was 2.67 (1.33) N.

CONCLUSIONS

All three whitening toothpastes did not give significantly more enamel wear than a silica toothpaste after twelve-weeks in situ with ex vivo brushing.

Protective effect of the in situ pellicle on dentin erosion–an ex vivo pilot study

AIM

The acquired pellicle is well known as an anti-erosive proteinaceous layer on enamel, but its protective properties on dentin have not been investigated in detail until now. The aim of the present ex vivo study was to evaluate the erosive effects on pellicle coated dentin.

METHODS

Bovine dentin slabs were exposed to the oral cavity of one subject for 120 min for in situ pellicle formation. Subsequently, the slabs were incubated with HCl (pH 2.3) in vitro for 5 min and erosive calcium-release was measured photometrically. In addition, the acid treated specimens were evaluated by transmission electron microscopy (TEM). Pellicle free samples served as controls.

RESULTS

Calcium erosion from the pellicle coated dentin slabs amounted to 23.5+/-2.9 microg Ca/min (pellicle free samples: 32.2+/-4.2 microg Ca/min). The difference was statistically significant (p < or = 0.05). In pellicle coated as well as in uncoated dentin samples, TEM-evaluation showed a demineralised dentinal surface layer which thickness ranged between 3 and 6 microm. The pellicle itself was partially dissolved but not removed by hydrochloric acid treatment.

CONCLUSION

The protective properties of the acquired pellicle against an erosive challenge of the dentinal surface are limited. The dentinal pellicle functions like an ion permeable network rather than a barrier.

Influence of different restorative materials on lysozyme and amylase activity of the salivary pellicle in situ

Lysozyme and amylase are the most abundant enzymatic components in the salivary pellicle. The purpose of the present study was to determine the influence of different substrata on amylase and lysozyme activity in salivary pellicles formed in situ. Slabs (5 mm diameter) of bovine dentine and enamel, of titanium, gold alloy, resin composite, PMMA, amalgam, and feldspar ceramic were fixed on the buccal sites of individual splints worn by six subjects for 30 min to allow pellicle formation. Thereafter, slabs were removed from the trays and rinsed with running water. Lysozyme activity was determined via lysis of Micrococcus lysodeicticus. Amylase activity was measured with a photometric method using 2-chloro-4-nitrophenyl-4-O-beta-D-galactopyranosylmaltotriosid (GalG2CNP) as substrate. Both pellicle enzymes were evaluated in the immobilized as well as in the desorbed state. Salivary enzyme activities were also measured. All investigated pellicles exhibited lysozyme and amylase activity. Great intraindividual and interindividual differences were observed. Over all samples, immobilized amylase activity amounted to 0.65 +/- 0.64 mU/cm2. Immobilized lysozyme activity was 5.04 +/- 1.55 U/cm2. There were no major effects of the substratum on pellicle-bound amylase and lysozyme activity. Immobilized and desorbed enzyme activities revealed a strong correlation (lysozyme: r = 0.700; amylase: r = 0.990). Salivary enzyme activities had only little impact on pellicle-bound enzyme activities. Amylase and lysozyme are incorporated in the acquired in situ pellicle on different solid surfaces in an active conformation. Dental material and enzyme activity in the saliva have only little impact on enzymatic activity in the pellicle in situ.

Lysozyme activity in the initially formed in situ pellicle

Lysozyme is one of the most abundant enzymatic components in the salivary pellicle. The purpose of the present in situ study was to determine if and to which extent lysozyme immobilised in pellicles exposes enzymatic activity. Influence of different oral sites and pellicle formation time on enzyme activity was also evaluated. Bovine enamel slabs (5mm diameter) were fixed on buccal and oral sites of individual trays worn by six subjects for 3 and 30 min on different days. After pellicle formation, slabs were removed from the trays and rinsed with running water. Afterwards, pellicle-bound lysozyme activity was determined via lysis of Micrococcus lysodeicticus photometrically in two steps. In a first step, lysozyme was desorbed in phosphate buffer and dissolved activity was measured. In a second step, slabs were incubated in phosphate buffer with the substrate and remaining immobilised activity was determined. All investigated pellicles exhibited lysozyme activity. Great intra- and inter-individual differences were observed. Mean desorbed activity of 3 min-pellicles amounted to 26.06+/-17.81 U/cm(2) (30 min; 26.79+/-17.48). The remaining immobilised activity was 13.54+/-11.42 for 3 min-pellicles and 16.08+/-12.81 for 30 min-pellicles. Pellicle derived lysozyme showed a Michaelis type kinetic.

CONCLUSION

In situ pellicle exposes lysozyme activity even after a 3 min formation period. Exposed enzyme activity is neither influenced by pellicle formation time nor by the site of pellicle formation. It shows great inter- and intra-individual differences.

The measurement in vitro of enamel and dentine wear by toothpastes of different abrasivity

OBJECTIVES

To investigate the in vitro enamel and dentine wear by toothpastes with a range of Relative Dentine Abrasivity (RDA) and Relative Enamel Abrasivity (REA) values.

METHODS

Human enamel/dentine (approximately 50:50) blocks (approximately 4 x 4 mm) were polished and the enamel indented with four Knoop indents. The step across the enamel-dentine junction was measured by interference microscopy. Specimens were brushed in vitro with toothpastes with a range of RDA/REA values using a flat trim toothbrush mounted in a Wira brushing machine for 360 s and a load of 375 g. After brushing the Knoop indent length and the enamel-dentine step were remeasured and the amount of wear to the enamel and dentine was calculated.

RESULTS

The mean enamel wear ranged from 0.05 to 0.40 microns, with the highest wear for the highest REA product. The mean dentine wear for all toothpaste products tested was positively correlated with RDA value (R2 = 0.897). The correlation was further improved if median wear values were used (R2 = 0.930).

CONCLUSIONS

This study has demonstrated a rapid technique for the simultaneous investigation of the abrasive wear of toothpaste on enamel and dentine. There was a good correlation between median dentine wear and RDA values.

Relationship between enamel erosion and liquid flow rate

The association of severe erosion with certain habits of consuming soft drinks prompted a study of erosion in relation to fluid flow. In the main experiments, citric acid solution (pH 3.2) was directed at polished enamel surfaces at flow rates of 26, 67 or 126 ml min(-1) through outlets of diameters 1.0, 2.6 or 5.0 mm for up to 20 min. Erosion depth increased with time of exposure and total volume of solution, with increasing flow rate and with decreasing outlet diameter. Scanning electron microscopy of acid-treated surfaces and of the subsurface enamel indicated that the clearance of dissolution products, rather than the mechanical dislodgement of partly dissolved crystal bundles, was the main process involved. For an exposure time of 20 min, erosion increased with (liquid velocity)(1/4). In a secondary experiment, it was found that the erosive potential of a low-erosive drink did not increase with increasing liquid velocity. The rapid increase in the rate of erosion caused by citric acid at low liquid velocities shows that reproducible stirring is essential for precision and intercomparison of in vitro studies. It also accounts for the rapid erosion seen when erosive drinks are consumed from a straw placed labial to the anterior teeth, or are "swished" between the teeth.

Abrasion of human enamel and dentine caused by toothpastes of differing abrasivity determined using an in situ wear model

OBJECTIVES

To determine the rates of enamel and dentine wear in situ during tooth brushing with a range of five toothpastes of differing RDA and REA values.

METHODS

Enamel/dentine inserts were placed in the buccal aspects of full upper dentures of human volunteers. Enamel wear was determined by change in Knoop indent length and dentine wear was determined from the enamel-dentine step height, measured using optical profilometry.

RESULTS

Significant differences between the test products were found for both enamel and dentine (p < 0.05). However for the conventional toothpastes the rate of wear was similar and differences between the products were not generally statistically significant for either enamel or dentine, despite the fact that their RDA values differed by more than a factor of two. The rate of wear was found to decrease throughout the duration of the study.

CONCLUSIONS

The study demonstrated that the methodology used is capable of assessing enamel and dentine wear in situ within a relatively short period of time. The data suggest that whilst in vitro tests have value in understanding differences in abrasivity between products, they cannot be used to predict in vivo effects.

The measurement of enamel and dentine abrasion by tooth whitening products using an in situ model

OBJECTIVES

To determine the enamel and dentine wear of two whitening toothpastes using an in situ model with ex vivo brushing.

METHODS

Human enamel/dentine (approximately 50:50) blocks (approximately 4 x 4mm) were placed in the upper buccal aspects of full or partial dentures of a group of 25 subjects. Subjects brushed the specimens ex vivo with either a calcium carbonate/perlite or silica containing whitening toothpaste under exaggerated conditions as compared to normal for 30 s, twice per day. Specimens were removed after 4, 8 and 12 weeks and the wear to the enamel and dentine was determined. Enamel wear was determined by change in Knoop indent length and dentine wear was determined from the enamel-dentine step height, measured using optical profilometry.

RESULTS

The mean wear after 12 weeks was for enamel 0.27 and 0.19 microns, and for dentine 34.3 and 61.1 microns, for the calcium carbonate/perlite and silica toothpastes respectively. There were no significant differences between products after 12 weeks. The rate of wear was found to decrease throughout the duration of the study.

CONCLUSION

There were no significant differences between the two whitening toothpastes in terms of enamel and dentine wear after 12 weeks brushing.

Enzymes in the acquired enamel pellicle

The acquired pellicle is a biofilm, free of bacteria, covering oral hard and soft tissues. It is composed of mucins, glycoproteins and proteins, among which are several enzymes. This review summarizes the present state of research on enzymes and their functions in the dental pellicle. Theoretically, all enzymes present in the oral cavity could be incorporated into the pellicle, but apparently enzymes are adsorbed selectively onto dental surfaces. There is clear evidence that enzymes are structural elements of the pellicle. Thereby they exhibit antibacterial properties but also facilitate bacterial colonization of dental hard tissues. Moreover, the immobilized enzymes are involved in modification and in homeostasis of the salivary pellicle. It has been demonstrated that amylase, lysozyme, carbonic anhydrases, glucosyltransferases and fructosyltransferase are immobilized in an active conformation in the pellicle layer formed in vivo. Other enzymes, such as peroxidase or transglutaminase, have been investigated in experimental pellicles. Despite the depicted impact of enzymes on the formation and function of pellicle, broader knowledge on their properties in the in vivo-formed pellicle is required. This might be beneficial in the development of new preventive and diagnostic strategies.

Ellipsometry analysis of the in vitro adsorption of tea polyphenols onto salivary pellicles

The adsorption of components from black tea and of purified tea polyphenols onto a whole unstimulated salivary pellicle-like protein layer, formed in vitro on hydroxyapatite discs, was studied by in situ ellipsometry. It was found that components from black tea and the purified polyphenols epicatechin-3-gallate (ECG), epigallocatechin-3-gallate (EGCG) and theaflavin readily adsorbed onto the pellicle. Further investigations showed that under the experimental conditions of this study, no black tea- or purified polyphenol-modified pellicles were eluted by either phosphate buffer or sodium dodecyl sulphate rinses. Therefore, black tea and its polyphenol components are indicated to have a profound effect on in vitro pellicle modification. Similar effects were observed for tannic acid.

Protective effect of the in situ formed short-term salivary pellicle

Salivary pellicle, as previously investigated, protects the enamel surface after certain processes of maturation against the influence of acidic agents. The aim of the present study was to investigate the protective effect of the short-term salivary pellicle formed in situ over periods of 3, 60 and 120 min. Six human volunteers used intraoral acrylic splints with bovine enamel samples fixed at the buccal and palatal sites of the maxillary first molars and second premolars. Enamel specimens (n = 252) with and without pellicle were immersed for 60 s in 1.0% citric acid solution under agitation. Knoop surface hardness (KHN) of uneroded polished enamel was measured as a baseline and estimated immediately after erosive treatment reflecting the microhardness loss (DeltaKHN). The amounts of calcium dissolved from the eroded enamel surface were analysed by atomic absorption spectroscopy and scored in mg/l per 10 mm2 of enamel surface area. In addition, the scanning electron microscope was used for the micromorphological examination of the erosive alterations of the enamel surface. The average microhardness loss values after erosion of the enamel samples with buccally/palatally formed pellicle layers were measured as 139.1/144.9 DeltaKHN for 3 min pellicle, 145.9/146.9 DeltaKHN for 60 min pellicle and 141.7/138.6 DeltaKHN for 120 min pellicle. Calcium release values from the specimens with buccal/palatal pellicles were amounted to 15.0/14.9, 16.5/15.9 and 15.3/17.4 mg/l per 10 mm2 for 3, 60 and 120 min-old pellicles, respectively. No significant differences were related to the pellicle formation time and intraoral site (buccal or palatal) in all tested series (ANOVA, P < 0.05). However, significant protection of the enamel surface provided by the pellicle layer was observed on all pellicle-covered surfaces if compared to the non-covered enamel samples (calcium release: 25.6 mg/l per 10 mm2; microhardness loss 187.0 DeltaKHN). These data were in accordance with the morphologic alterations caused by citric acid on the pellicle-covered and pellicle non-covered specimens. It could be concluded that salivary pellicle formed in situ within a period of 3 min offers protection of enamel against citric acid. However, pellicle does not completely inhibit the erosive action of citric acid under the conditions of the present study.

Transmission electron microscopy comparison of methods for collecting in situ formed enamel pellicle

The in vivo formed salivary pellicle is composed of an outer globular and a densely structured basal layer. This study developed a method for selective recovering of these pellicle layers from the enamel surface. Two-hour in situ pellicles were formed by intraoral exposure of enamel specimens in two adults. Pellicle-covered enamel specimens were treated either mechanically (scraping with scaler, curette or razor blade, or rubbing with a sponge) or chemically (phosphate buffer, NaCl, NaOCl, CaCl2, NaSCN, urea, tetrahydrofurane, guanidine, SDS, HCl, or EDTA with or without additional ultrasonication). Specimens were processed for transmission electron microscopic analysis to detect pellicle residues remaining on the enamel surface after the different treatments. Most of the chemical treatments caused partial, incomplete removal of the globular layer. Complete removal of the globular layer without disruption of the basal layer was obtained by sponge rubbing or by CaCl2 combined with ultrasonication, whereas scraping caused partial disruption of the basal layer. Removal of the basal layer was observed after treatment with HCl, EDTA, or NaOCl combined with ultrasonication. Electrophoretical analysis of recovered pellicle fractions indicate that combination of sponge-rubbing followed by EDTA treatment can be recommended for stepwise removal of the globular and basal pellicle layers.

Supramolecular pellicle precursors

Saliva contacting with solid surfaces in the oral cavity forms a coat termed the pellicle. However, its formation is not fully understood. Although indications for the existence of supramolecular pellicle precursors have been reported, the possible relationship between them and pellicle formation is unclear. This study investigates the ability of supramolecular precursors to form the pellicle via interaction with a solid surface. Fixed and unfixed salivary globes were spread onto a microscopic grid and examined by transmission electron microscopy. Biochemical pretreatment of saliva revealed that neither disulphide links nor transglutaminase-mediated crosslinking are responsible for maintaining the salivary globes, i.e. supramolecular pellicle precursors. However, the detergent, sodium dodecyl sulphate, caused dissociation of the salivary globes, indicating their micellar nature. Saliva contacting a formvar film for 10 s did not form a complete surface coating, but single supramolecular pellicle precursors were observed attached to the surface. After extension of the contact time to 60 s, a surface layer was formed by clustering and fusion of the supramolecular pellicle precursors. The supramolecular pellicle precursors are unstable and attain a thermodynamically more favourable state by adhesion to a solid surface. As a result, a layer of fused precursors covering the solid surface is formed -- the salivary pellicle.

Immobilisation and activity of human α-amylase in the acquired enamel pellicle

Amylase is an important salivary component and structural element of the acquired enamel pellicle. Aim of the study was to establish a method for precise and direct determination of pellicle bound amylase activity in order to analyse kinetics and activity of the immobilised enzyme. Six bovine enamel slabs (5mm diameter) were fixed on individual maxillary trays and worn by five subjects for different times (3, 30 and 120 min) on buccal and palatal sites on different days. Slabs were removed from the trays and rinsed with aqua dest. Afterwards, pellicle bound amylase activity was determined directly with a photometric method using 2-chloro-4-nitrophenyl-4-O-beta-D-galactopyranosylmaltotriosid (GalG2CNP) as substrate yielding the coloured product chloronitrophenolate (CNP). All investigated pellicles exhibited immobilised amylase activity. Mean activity was 1.39 +/- 187 mU/cm(2) (n=87, range 0.14-11.5 mU/cm(2)). Product formation of CNP by immobilised amylase was linear over time. Pellicle bound amylase showed a Michaelis type kinetic (Km = 3.3 x 10(-3) M). Immobilised activity on buccal surfaces ranged between 0.25 and 11.1 mU/cm(2) (palatal slabs: 0.14-3.06 mU/cm(2)). Thirty minutes pellicles formed on buccal sites exhibited significantly higher immobilised amylase activity (2.85 +/- 3.65 mU/cm(2)) than palatal ones (0.63 +/- 0.32 mU/cm(2)). Amylase activity showed great intraindividual variability when comparing same positions on different days.

CONCLUSION

Pellicle bound amylase activity can be determined directly with GalG2CNP and shows a Michaelis Menten kinetic. Enzyme activity of the amylase immobilised in the in situ pellicle reveals great intra- and interindividual differences.

Evaluation of a 6% hydrogen peroxide tooth whitening gel on enamel and dentine microhardness in vitro

OBJECTIVES

The aims of this study were to evaluate the effects of a novel 6% hydrogen peroxide containing tooth whitener, Xtra White (XW), on enamel and dentine microhardness in vitro.

METHODS

Polished human enamel and dentine specimens were prepared and baseline microhardness determined. In study 1, enamel specimens were exposed to 20 min cycles of either water, XW or Sprite Light for up to 28 cycles. In studies 2 and 3, enamel specimens were treated with 20 min cycles of either XW or water and exposed to whole saliva at all other times. In study 3, an additional exposure to a fluoride containing toothpaste was conducted. In total, 28 treatments were conducted in order to simulate a 2 weeks product use. In study 4, dentine specimens were treated as per study 3. Final microhardness measurements were taken and for studies 3 and 4 colour measurements were additionally taken.

RESULTS

XW and water gave no statistically significant (p>0.05) changes in enamel and dentine microhardness after 28 treatments. Sprite Light gave a significant (p<0.00002) reduction in enamel microhardness after one 20 min treatment. XW showed significant bleaching of enamel and dentine specimens as compared to the water control.

CONCLUSIONS

XW does not have any significant effect on enamel and dentine microhardness.