Effects of amine fluoride on biofilm growth and salivary pellicles

The amine fluoride (AmF) N'-octadecyl-trimethylene-diamine-N,N,N'-tris(2-ethanol)-dihydro-fluoride is a cationic antimicrobial which can have beneficial effects on plaque formation. Here, we determine changes in pellicle and bacterial cell surface properties of the strains Actinomyces naeslundii HM1, Streptococcus mutans NS, S.mutans ATCC 700610, S. sobrinus HG1025 and S. oralis HM1 upon adsorption of this AmF and accompanying effects on bacterial adhesion and biofilm growth. In vitro pellicles had a zeta potential of -12 mV that became less negative upon adsorption of AmF. The chemical functionalities in which carbon and oxygen were involved changed after AmF adsorption and AmF-treated pellicles had a greater surface roughness than untreated pellicles. Water contact angles in vitro decreased from 56 to 45 degrees upon AmF treatment, which corresponded with water contact angles (44 degrees ) measured intraorally on the front incisors of volunteers immediately after using an AmF-containing toothpaste. All bacterial strains were negatively charged and their isoelectric points (IEP) increased upon AmF adsorption. Minimal inhibitory concentrations were smallest for strains exhibiting the largest increase in IEP. Adhesion to salivary pellicles and biofilm growth of the mutans streptococcal strains were significantly reduced after AmF treatment, but not of A. naeslundii or S. oralis. However, regardless of the strain involved, biofilm viability decreased significantly after AmF treatment. The electrostatic interaction between cationic AmF and negatively charged bacterial cell surfaces is pivotal in establishing reduced biofilm formation by AmF through a combination of effects on initial adhesion and killing. The major effect of AmF treatment, however, was a reduction brought about in biofilm viability.     

External radiolabelling of components of pellicle on human enamel and cementum

Enamel and cementum pellicles form by different adsorption of salivary and serum components to the tooth surface. The authors compared the constituents of surface pellicle formed on human enamel and cementum under three conditions: (1) natural pellicle, present on extracted teeth, which was formed by prolonged exposure to human salivary and serum components in vivo; (2) short-term in-vivo pellicle, formed by exposing enamel and cementum slabs to the oral environment for 0-60 min; (3) in-vivo pellicle, formed by incubating enamel and cementum slabs in a 1:1 mixture of parotid and submandibular/sublingual saliva for 0-60 min. Pellicle composition was characterized by external radiolabelling techniques specific for exposed carbohydrate (sialic acid and galactose) and amino-acid (tyrosine) residues. There were differences between cementum and enamel in the electrophoretic profiles of natural-pellicle components; notably, a major 180 kda 3H-labelled sialoglycoprotein, unique to the cementum pellicle, had the same electrophoretic mobility as the low-molecular-weight mucin from human submandibular/sublingual saliva. After alkaline-borohydride treatment, 3H-labelled natural-pellicle oligosaccharides chromatographed in the di- to tetrasaccharide region of a Bio-Gel P-2 column. The most prominently labelled components of short-term enamel and cementum pellicles in vivo and in vitro had the same electrophoretic mobility as the low-molecular-weight salivary mucin. The pellicle components formed in vitro, unlike those formed for the same period of time in vivo, were rapidly desorbed from the cementum, but not from the enamel surface. We conclude that: (1) external labelling techniques are useful for obtaining a profile of pellicle components; (2) submandibular/salivary mucins are major constituents of salivary pellicles on tooth surfaces; (3) glycoproteins that carry low-molecular-weight, sialic-acid-containing saccharides are important determinants of pellicle surface properties [corrected].     

Influence of oral detergents and chlorhexidine on soft-layer electrokinetic parameters of the acquired enamel pellicle

Electron microscopy has described the salivary pellicle as an 'uneven, knotted structure'. This study describes a novel soft-layer model of salivary pellicles, based on measured electrophoretic mobilities and the influence of dentifrices and a chlorhexidine mouthwash on the parameters of the model. The enamel surface was found to possess a high number of fixed, negative charges (zN = -62 mM) and to be electrophoretically hard (1/lambda = 0.6 nm), i.e. impenetrable to fluid flow. Adsorption of a salivary pellicle resulted in a fourfold reduction in the surface fixed charge density (zN = -15 mM) along with an increase in electrophoretic softness (1/lambda = 2.3 nm). Exposure of pellicles to various dentifrices containing sodium fluoride as an active component and sodium lauryl sulfate as a detergent had little effect on the surface fixed charge densities (varying between -15 and -30 mM, depending on the dentifrice involved) and electrophoretic softnesses (varying between 2.3 and 3.4 nm). Exposure of pellicles to a dentifrice containing sodium fluoride and hexametaphosphate as an additional detergent yielded soft (8.0 nm) pellicles, penetrable to fluid flow, with few fixed, negative charges (1 mM). This is opposite to the effects of chlorhexidine, which created an electrophoretically hard pellicle (1.7 nm). This soft-layer electrokinetic model quantitatively shows that the degree to which pellicles are penetrable to fluid flow differs upon exposure to dentifrices, with relevance for plaque formation, de- and remineralization and staining processes.     

Adsorption of chlorhexidine and black tea onto in vitro salivary pellicles, as studied by ellipsometry

The adsorption from 0.2% (w/w) chlorhexidine and black tea solutions onto an in vitro pellicle from whole unstimulated saliva on hydroxyapatite discs was studied by ellipsometry. It was found that chlorhexidine adsorbed to the pellicle and caused a modification of the pellicle properties, leading to a subsequent increase in adsorption of salivary and black tea components. There was a distinct order-of-addition effect, whereby chlorhexidine followed by black tea gave an overall greater adsorption of components compared with black tea followed by chlorhexidine. This increase in adsorption resulted in a concomitant increase in color or stain, as measured by a reflectance chromameter. The increase in adsorbed amounts and stain was modified, in part, by the adsorption of salivary fractions between the chlorhexidine and black tea treatments. In all cases, the chlorhexidine and black tea-modified pellicles were not readily removed by either phosphate or sodium dodecyl sulfate rinses. Thus, following exposure to chlorhexidine, the accelerated adsorption of salivary and black tea components can ultimately lead to increased staining of the pellicle.     

Ultrastructural investigation of pellicle morphogenesis at two different intraoral sites during a 24-h period

The purpose of the present in vivo study was to examine salivary pellicle formation on enamel surfaces at two different intraoral sites for periods of 1 min up to 24 h by means of transmission electron microscopy. Bovine enamel specimens were attached to the buccal and lingual surfaces of the upper first molars in three subjects using removable intraoral splints. Specimens were carried over periods of 1, 10, 30 and 60 min, 2, 6 and 24 h and were processed for transmission electron microscopy. After 1 min, an electron dense pellicle layer, 10–20 nm thick, was observed on the enamel surfaces. The subsequent adsorption of salivary biopolymers was governed by local influences of the oral cavity. Specimens located on the lingual aspect were covered within 2 h by a 20- to 80-nm-thick, homogeneous, predominantly granular-structured pellicle. The thickness of the surface coatings that were adsorbed on lingually carried specimens increased to 100–200 nm after 24 h. In contrast, on the buccally mounted specimen surfaces, a variably structured pellicle with granular and globular components could be detected after intraoral exposure for 2 h. The thickness of the 2-h buccal pellicles ranged between 200 and 700 nm. After 24 h, the buccally positioned specimens were covered by a dense globular pellicle layer varying in thickness from 1000 to 1300 nm. It is suggested that in vivo pellicle formation is initiated by adsorption of an electron-dense layer of salivary proteins. Further adsorption of salivary biopolymers leads to the formation of an outer loosely arranged pellicle layer. Under oral conditions, the locally available salivary biopolymers and the influence of locally effective shearing forces are of significance for the ultrastructural pattern and extent of pellicle formation. Received: 8 March 1999 / Accepted: 19 April 1999     

Influence of in vivo formed salivary pellicle on enamel erosion.

This study assessed the protective effect of the salivary pellicle formed in vivo during 24 h or 7 days against demineralization of bovine enamel caused by citric acid. In addition, the influence of acid treatment on the behavior of the pellicle was investigated. Enamel specimens with and without in vivo pellicles were immersed in citric acid (0.1, 1.0%) over 30, 60, and 300 s, and processed for scanning (SEM) and transmission electron microscopy (TEM), as well as for measurement of surface microhardness (SMH). Specimens coated with the in vivo formed pellicles revealed less extensive erosive demineralization of the enamel surface compared to uncovered enamel specimens. SEM analysis and SMH results did not indicate distinct differences between erosive surface alterations on enamel slabs covered with 24-hour pellicles and on those covered with 7-day pellicles. TEM analysis showed that the pellicle layer was dissolved in part from the enamel surface due to acid exposure. However, pellicle residues could be detected by TEM in all specimens, even after 5-min exposure to 1.0% citric acid. It is concluded that the in vivo salivary pellicle can resist the acidic action to some extent and provides protection to the underlying enamel surface against erosive destruction caused by short-term action of citric acid.     

Experimental salivary pellicles on the surface of orthodontic materials.

The purpose of this study was to define the composition of salivary pellicles that form on the surfaces of orthodontic materials and to further investigate whether qualitative differences exist between the composition of adsorbed salivary pellicles that form on 3 different orthodontic materials: stainless steel bracket metal, elastomeric ligature ring, and bracket bonding resin. Experimental pellicles were formed by incubating these materials in fresh human parotid or submandibular-sublingual saliva for 2 hours. Pellicles were extracted with sodium dodecyl sulfate buffer and lyophilized. They were then subjected to sodium dodecyl sulfate-polyacrylamide gel electrophoresis and immunoblotting to identify the adsorbed salivary components. Remarkable differences in the profiles of pellicle components were found, dependent on the type of orthodontic materials. The pellicle components on the bracket metal were almost the same as those found on the elastomeric ligature ring. Salivary protein adsorption patterns to bonding resin showed different features. Distinct differences were also found between the surface-binding affinities of the same salivary proteins from different glandular salivas. These results may be explained on the basis that binding sites for specific proteins on the surfaces of the materials are covered by molecules of submandibular-sublingual saliva, probably mucins. The results of this study provide valuable information concerning initial bacterial adhesion to the surfaces of orthodontic materials, as well as information that could be used in the development of orthodontic materials with enhanced surface properties.     

The carbohydrate composition of experimental salivary pellicles

Abstract. The carbohydrate compositions of pellicles formed in vivo and others formed in vitro from submandibular, parotid, and mixed (submandibular-parotid) saliva were determined using gas-liquid chromatography. Samples of the total pellicles as well as the relatively acid-soluble supernates and acid-insoluble sediments were collected, analyzed, and compared. The differences in carbohydrate composition between the supernates and sediments, particularly in the in vivo and in vitro mixed salivary pellicles, suggest that the total pellicle is composed of more than one component. In each instance obvious differences in composition between the pellicle and the saliva from which it was formed indicated that pellicle formation is a highly selective process.
Glucose: galactose ratios of approximately 1:1 were found in each of the total pellicles. These data suggest that at least one pellicle component is an unusual glycoprotein in that it contains high levels of glucose.
The total submandibular salivary pellicle and both its fractions were remarkably similar in carbohydrate composition to the counterparts formed from parotid saliva alone. The data strongly suggest that there are present in both submandibular and parotid saliva similar glycoproteins that are selectively deposited onto etched enamel as the initial pellicle.     

Protective properties of salivary pellicles from two different intraoral sites on enamel erosion

The purpose of this study was to investigate the protective effect and ultrastructure of salivary pellicles formed in vivo near the orifices of the ducts of parotid and submandibular/sublingual salivary glands. Pellicles were formed by exposing bovine enamel slabs to the oral environment at the buccal aspect of the upper first molars and at the lingual aspect of the lower incisors in 3 subjects over periods of 24 h. Enamel specimens with and without 24-hour pellicles were immersed in citric acid (0.1 and 1%) for periods ranging from 30 s to 5 min, and processed for measurement of surface microhardness (SMH) and transmission electron microscopy (TEM). In comparison to uncovered enamel specimen significantly less decrease in SMH due to acid exposure was observed in pellicle-coated enamel specimens. Pellicles formed at the buccal aspect of the upper molars were less effective in protecting the enamel against acid-induced softening as compared to pellicles formed at the lingual aspect of the lower incisors only after 5 min exposure in 1% citric acid. TEM analysis showed that pellicle layers were dissolved continuously due to acid exposure. However, even after 5 min exposure to 1% citric acid, a residual pellicle layer could be detected on the enamel surface. In conclusion, site-dependent differences of buccally and lingually in vivo formed 24-hour pellicles have minor importance concerning the pellicle-induced protection of the enamel surface against erosive changes.     

Amino acid composition of experimental salivary pellicles.

The amino acid compositions of pellicles formed in vitro from submandibular, parotid, and mixed saliva were determined and compared. Samples of the total pellicles as well as the relatively acid-soluble supernates and acid-insoluble sediments were collected and analyzed. In each instance striking differences in composition between the pellicle and the saliva from which it was formed indicate that pellicle formation is a highly selective process. The similarity in composition of the total and fractionated submandibular-parotid pellicle samples indicated a representative dissolution of the total mixed pellicle in the collection acid, rather than a preferential dissolution of part of the total pellicle. In the case of the pellicles formed from the isolated submandibular and parotid salivas, the supernate and the total pellicle were quite similar in composition, but differed somewhat from the sediment. Those results indicate that most of the salivary pellicle is soluble in the dilute acid used to collect the pellicle, and that a portion of the total submandibular or parotid salivary pellicle dissolves preferentially. The compositions of the total parotid pellicle and the parotid supernate and sediment were remarkable similar to the counterparts formed from submandibular saliva alone, suggesting similar origins and mechanisms of formation.     

Influence of salivary pellicle formation time on enamel demineralization – an in situ pilot study

This study assessed the protective potential of salivary pellicles formed in situ over periods ranging from 2 to 24 h. Pellicles were produced on enamel slabs mounted on the palatal aspect of removable acrylic splints and exposed to the oral environment in three subjects for 2, 6, 12 and 24 h. Enamel specimens with and without pellicles were immersed in citric acid (1%) for 60 s, and the amount of dissolved calcium was measured by atomic absorption spectroscopy. In addition, specimens were processed for transmission electron microscopy (TEM). Mean values (standard deviations) for calcium release (mg/l related to the specimen's surface area of 5×5 mm²) were: 2-h pellicle 6.94 (1.55); 6-h pellicle 6.69 (2.05); 12-h pellicle 6.57 (2.31); 24-h pellicle 5.71 (2.46); enamel without pellicle 8.95 (1.66). There were no significant differences in calcium release that were dependent on pellicle formation time, but in comparison to enamel specimens without pellicle, significantly less (p <0.05) demineralization of the enamel was observed in pellicle-covered specimens. TEM showed that the pellicle was partly, but not completely dissolved following acid exposure. It is concluded that even a 2-h in-situ-formed pellicle layer protects the enamel surface to a certain extent against demineralization.     

Adsorption from black tea and red wine onto in vitro salivary pellicles studied by ellipsometry

The adsorption of black tea and red wine components onto a pellicle-like protein layer formed in vitro by adsorption from whole unstimulated saliva on hydroxyapatite discs were studied by in situ ellipsometry. It was found that components from black tea readily adsorbed to the pellicle. Subsequent exposure to saliva led to further adsorption of salivary components to give an overall increase in the amounts adsorbed. The amounts adsorbed increased still further following a third tea and saliva exposure. Components of red wine gave significantly greater amounts of adsorption to the pellicle than black tea. The adsorption of components of black tea gave a concomitant increase in colour or stain as measured by a reflectance chromameter. In all cases, the black tea- and red wine-modified pellicles were not eluted by either phosphate buffer or sodium dodecyl sulphate (SDS) rinses. Thus, black tea and red wine components have been shown to have a profound effect on in vitro pellicle maturation, causing thickened layers of stained material to build up, which are not readily removed.     

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.     

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.     

Adsorption of whole saliva onto hydrophilic and hydrophobic solid surfaces: influence of concentration, ionic strength and pH

The influence of the concentration of salivary proteinaceous material from solutions of whole saliva on the kinetics of in vitro pellicle formation were studied together with the effects of ionic strength, pH and certain substrate characteristics. The pellicle formation was monitored by an automated Rudolph ellipsometer, equipped with a He-Ne laser (wavelength 632.8 nm). The substrates compared in the study were hydrophilic negatively charged silica surfaces and hydrophobic methylated silica surfaces. The results show that the adsorption of salivary proteins is a very rapid process on both types of surfaces. Part of the formed biofilm, however, desorbed upon rinsing, indicating that the proteinaceous material was adsorbed with varying binding strengths. Larger adsorbed amounts were recorded on hydrophobic than on hydrophilic surfaces. Increase of ionic strength caused larger amounts to be adsorbed on both types of surfaces but change of pH did not affect the adsorption on either of the studied surfaces. Ellipsometry was found to be a suitable technique to monitor the adsorption of salivary proteins at solid/liquid interfaces.     

Adsorption of whole saliva onto hydrophilic and hydrophobic solid surfaces: influence of concentration, ionic strength and pH.

The influence of the concentration of salivary proteinaceous material from solutions of whole saliva on the kinetics of in vitro pellicle formation were studied together with the effects of ionic strength, pH and certain substrate characteristics. The pellicle formation was monitored by an automated Rudolph ellipsometer, equipped with a He-Ne laser (wavelength 632.8 nm). The substrates compared in the study were hydrophilic negatively charged silica surfaces and hydrophobic methylated silica surfaces. The results show that the adsorption of salivary proteins is a very rapid process on both types of surfaces. Part of the formed biofilm, however, desorbed upon rinsing, indicating that the proteinaceous material was adsorbed with varying binding strengths. Larger adsorbed amounts were recorded on hydrophobic than on hydrophilic surfaces. Increase of ionic strength caused larger amounts to be adsorbed on both types of surfaces but change of pH did not affect the adsorption on either of the studied surfaces. Ellipsometry was found to be a suitable technique to monitor the adsorption of salivary proteins at solid/liquid interfaces.     

Surfactive and antibacterial activity of cetylpyridinium chloride formulations in vitro and in vivo

Aim: To compare effects of three cetylpyridinium chloride (CPC) formulations with and without alcohol and Tween80 on physico‐chemical properties of salivary pellicles, bacterial detachment in vitro and bacterial killing in vivo. Material and Methods: Adsorption of CPC to salivary pellicles in vitro was studied using X‐ray photoelectron spectroscopy and water contact angle measurements. Adhesion and detachment of a co‐adhering bacterial pair was determined in vitro using a flow chamber. Killing was evaluated after live/dead staining after acute single use in vivo on 24‐ and 72‐h‐old plaques after 2‐week continuous use. Results: The most pronounced effects on pellicle surface chemistry and hydrophobicity were observed after treatment with the alcohol‐free formulation, while the pellicle thickness was not affected by any of the formulations. All CPC formulations detached up to 33% of the co‐adhering pair from pellicle surfaces. Bacterial aggregate sizes during de novo deposition were enhanced after treatment with the alcohol‐free formulation. Immediate and sustained killing in 24 and 72 h plaques after in vivo, acute single use as well as after 2‐week continuous use were highest for the alcohol‐free formulation. Conclusions: CPC bioavailability in a formulation without alcohol and Tween80 could be demonstrated through measures of pellicle surface properties and bacterial interactions in vitro as well as bacteriocidal actions on oral biofilms in vivo.     

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.     

Non-contact removal of coadhering and non-coadhering bacterial pairs from pellicle surfaces by sonic brushing and de novo adhesion

Coadhesion between oral microbial pairs is an established factor in the spatiotemporal development and prevalence of mixed-species communities in early dental plaque in vivo. This study compares removal and de novo adhesion of pairs of coadhering and non-coadhering oral actinomyces and streptococci by sonic brushing on salivary pellicles in a non-contact mode as a function of the distance between the brush and the pellicle surface in vitro. First, actinomycetes were adhered to a pellicle surface, after which streptococci suspended in saliva were allowed to adhere. Removal was examined by non-contact, sonic brushing with a wetted brush on a either a wetted or a substratum immersed to a depth of 7 mm. After brushing, de novo adhesion of streptococci to brushed pellicles was studied. For coadhering and non-coadhering pairs, 34% and 9%, respectively, of the adhering bacteria were involved in aggregates comprising more than 10 organisms. Non-contact, sonic brushing removed up to 99% of the adhering bacteria, regardless of the state of immersion of the substratum. Bacterial removal decreased with increasing distance of up to 6 mm between brush and pellicle surface. For the non-coadhering pair, subsequent exposure of pellicles to a streptococcal suspension yielded about 6% of bacteria involved in large aggregates. Alternatively, de novo adhesion of the coadhering streptococcal strain to pellicles brushed on the wetted substratum yielded 31% of bacteria involved in large aggregates, but after brushing the immersed substratum only 12% of the adhering bacteria were found in large aggregates. It is concluded that non-contact sonic brushing, under immersion, removes high percentage of adhering bacterial pairs up to a distance of 6 mm between the brush and the pellicle surface. However, non-contact, sonic brushing with only a thin wet film on the substratum may leave footprints to which streptococci preferentially adhere.     

Microbubble-induced detachment of coadhering oral bacteria from salivary pellicles

The presence and maturity of the salivary pellicle influences microbial adhesion and its tenacity in the oral cavity, posing a challenge to different plaque-control systems. Some plaque-control systems rely on surface-tension forces arising from passing microbubbles sprayed over the pellicle. Passage of such bubbles is accompanied by a high fluid flow, but systematic studies are lacking on the contribution of fluid flow vs. microbubbles towards plaque removal. Therefore, the aim of this study was to determine the detachment efficacy of laminar fluid flow (wall shear rates 11,000-16,000 s(-1)), with and without microbubbles, towards the detachment of Actinomyces naeslundii T14V-J1 and Streptococcus oralis J22, and their coadhering aggregates, from salivary pellicles formed over 2 h or 16 h from reconstituted human whole saliva. Microbubbles in a fluid flow were more efficient at inducing single bacterial detachment, resulting in almost complete (97%) removal for S. oralis J22 and a 15-fold increase in A. naeslundii T14V-J1 removal as compared to the detachment caused by fluid flow alone. A. naeslundii was more difficult to remove and apparently formed the strongest bonds with high-molecular-weight proteins in 16-h pellicles. The detachment of coaggregates after 2 min left a substantial amount of adhered bacterial mass, including more than 60% of singly attached A. naeslundii on the pellicle surface, providing nucleation sites for the de novo adhesion of coadhering streptococci.