Abstract
The acquired enamel pellicle (AEP) is a thin acellular film that forms on tooth surfaces upon exposure to the oral environment. It consists predominantly of salivary proteins, but also includes non-salivary-derived proteins, carbohydrates, and lipids. Since it is the interface between teeth and the oral environment, the AEP plays a key role in the maintenance of oral health by regulating processes including lubrication, demineralization, and remineralization and shaping the composition of early microbial flora adhering to tooth surfaces. Knowledge of the 3D structure of the AEP and how that correlates with its protective functions may provide insight into several oral pathological states, including caries, erosion, and periodontal disease. This review intends to update readers about the latest discoveries related to the formation, ultrastructure, composition, and functions of the AEP, as well as the future of pellicle research, with particular emphasis on the emerging role of proteomic and microscopy techniques in oral diagnosis and therapeutics.
Introduction
The formation of the AEP is a highly selective and dynamic process influenced by several factors, including circadian cycles, oral microbial flora composition, the proteolytic capacity of the oral environment, and the physical and chemical properties of tooth surfaces, as well as location in the mouth (Lendenmann et al., 2000).
The initial stage of AEP formation is triggered within seconds of exposure to whole saliva and is characterized by an increase in pellicle thickness to 10 to 20 nm within a few minutes that remains stable for about 30 minutes (Lendenmann et al., 2000). Salivary proteins with a high affinity for hydroxyapatite, commonly referred to as ‘pellicle precursors’, initiate this process via electrostatic interactions with the enamel surface (Hay, 1973). In vitro studies identified aPRPs, statherin, and histatins as being among the first to adsorb to hydroxyapatite (Jensen et al., 1992; Lamkin et al., 1996). Besides those proteins, in situ studies have confirmed the presence of mucins (MUC5B and MUC7), amylase, cystatins, lysozyme, and lactoferrin as the most abundant proteins in the AEP (Appendix Table 1) (Vacca Smith and Bowen, 2000; Hannig and Joiner, 2006).
After this first increment, a rapid increase in AEP thickness is attributed to the adsorption of protein aggregates from saliva to AEP by means of protein-protein interactions. Thereafter, the pellicle thickness reaches a plateau, between 30 to 90 minutes, at a thickness of 100 to 1,000 nm, depending on its location within the oral cavity (Hannig, 1999). This characterizes the second or the maturational stage of pellicle formation. These protein aggregates could include heterotypic complexes (Iontcheva et al., 1997) and micelle-like globules (Young et al., 1999), which together are referred to as supramolecular precursors (Vitkov et al., 2004). A preliminary study in our laboratory explored the mechanism of in vivo AEP formation using ICAT (isotope-coded affinity tags). This novel proteomic technology covalently labels cysteine-containing peptides and provides a relative quantification in mass spectrometry level. In addition to ICAT, new proteomic approaches such as iTRAQ (isobaric tag for relative and absolute quantitation) can provide comprehensive exploration of salivary and AEP proteome (Siqueira and Dawes, 2011) and composition. Briefly, equal protein amounts of in vivo AEP samples collected after 5 and 120 minutes of pellicle formation were targeted with light-ICAT and heavy-ICAT, respectively (see details in Fig. 1) and subjected to liquid chromatography-electrospray ionization tandem mass spectrometry (LC-ESI-MS/MS) analysis for protein identification and relative quantitation. Salivary proteins such as neutrophil defensin 1 and lysozyme, which are known to interact with other proteins, showed a progressive increment in their contribution to the total pellicle proteome during the time-span covered; therefore, those proteins could be responsible for the formation of protein clusters in the AEP. In contrast, the abundance of proteins with recognized hydroxyapatite affinity, such as α-amylase, carbonic anhydrase 6, and cystatin S, was higher at 5 minutes in comparison with AEP collected at 120 minutes (Table). Analysis of the data demonstrated the high selectivity characteristic of the pellicle formation process and that proteomics can be assumed as the state-of-the-art tool for the investigation of the pellicle proteome on a quantitative basis down to femtomolar levels.
Schematic representation of peptide identification and relative quantitation by ICAT labeling approach. Relative peptide/protein abundance is calculated by comparison of the differences in intensity of the peptide ions in the MS data of the mixture of peptides derived from such sample groups.
ICAT Labeling of in vivo AEP Collected at 2 Different Time-points, 5-minute Pellicle Formation (Light-ICAT), and 120-minute Pellicle Formation (heavy-ICAT)
In addition, AEP is exposed to intrinsic and extrinsic maturation, which contribute to its insolubility and chemical resistance (Yao et al., 2000). As an example, transglutaminase, derived from oral epithelial cells, has been identified within the in situ pellicle in an active conformation (Hannig et al., 2009c), which may lead to the intrinsic AEP maturation due to crosslinking acidic or basic PRPs with statherin, as shown in vitro (Yao et al., 2000). Other enzymes, such as alkaline phosphatase and transaminase, have also been demonstrated within the in situ pellicle, supporting a potential role in the intrinsic maturation of the pellicle, whereas in situ studies have demonstrated little to no acid phosphatase or proteinase activity (Hannig et al., 2008b, 2009b).
Despite low proteolytic activity within the pellicle, salivary proteolysis plays an important role in the formation and extrinsic maturation of the pellicle, since many components of the AEP are actually peptide fragments (Siqueira et al., 2007b; Vitorino et al., 2007; Siqueira and Oppenheim, 2009), and this proteolysis can occur before (Helmerhorst et al., 2006) or after adsorption to hydroxyapatite (McDonald et al., 2011) (Fig. 2). Although the proteolytic fragmentation patterns show considerable inter- and intra-individual consistency, the proteolysis rate exhibits a high degree of variability among individuals (Lamkin et al., 2001). In addition, extrinsic factors such as abrasive toothpastes, whitening products, and the intake of acidic foods and beverages may also interfere with pellicle formation and maturation (Hara and Zero, 2010).
Mechanism of acquired enamel pellicle formation. The acquired enamel pellicle is formed by successive protein/peptide layers where selective proteins derived from salivary glands, gingival crevicular fluid, oral mucosa, and micro-organisms adsorb directly onto the enamel surface or by protein-protein interactions (circle). These proteins are presented in the pellicle in an intact form (purple proteins) or cleaved form (green proteins). The process of proteolytic cleavage is modulated by proteins (red proteins) also originating from salivary glands, gingival crevicular fluid, oral mucosa, and micro-organisms, where this process can happen in saliva or after protein adsorption (circle).
AEP Ultrastructure
Advances in high-resolution microscopy have allowed for the investigation of protein interactions with the enamel surface. Attempts to characterize the morphology and ultrastructure of the AEP used a wide range of techniques, including scanning electron microscopy, transmission electron microscopy (Deimling et al., 2007), field emission in-lens scanning electron microscopy (Hannig et al., 2008a), cryo-electron microscopy (Schüpbach et al., 2001), confocal laser scanning microscopy (Amaechi et al., 1999), and ellipsometry (Joiner et al., 2004; Cardenas et al., 2007). More recent microscopy techniques include multiphoton modulation microscopy, optical coherence tomography, and optical coherence microscopy (Baek et al., 2009). While the application of different approaches provides new insights into our knowledge of AEP structure, inherent limitations of each technique may contribute to data variability. Moreover, the surface on which the AEP is formed and the experimental model used (in vivo, in vitro, in situ) may also contribute to discrepancies within the results.
In addition, atomic force microscopy (AFM) has revolutionized the field of protein-mineral interaction, facilitating the investigation of a variety of protein/mineral surface properties at the atomic level, directly in aqueous solution (Vukosavljevic et al., 2011) (Fig. 3). Also, the development of revolutionary mass spectrometry has allowed for the proteomic investigation of protein-mineral interactions or biofilm-protein-mineral interactions. These powerful microscopic and proteomic techniques should be combined in investigations of the effect of AEP on biofilm formation, for a representative and comprehensive understanding of microbial responses to antimicrobial agents.
AFM image of the acquired enamel pellicle developed on hydroxyapatite substrata. This view highlights the three-dimensional topographic differences as a result of the pellicle layer adsorbed onto the surface. Moreover, the presence of protein clusters on the order of 16 to 80 nm provides evidence that the AEP is not a homogeneous layer in terms of the sizes and distribution of the proteins/peptides over the surface. Bright areas indicate high and dark areas low in height.
The ultimate structure, morphology, and thickness of the AEP differ with time of formation (Nyvad and Fejerskov, 1987), intra-oral location (Amaechi et al., 1999; Hannig, 1999), and primary vs. permanent dentition (Sonju Clasen et al., 1997), while also presenting inter-individual variability (Finke et al., 2002). The AEP is commonly described as a spongy mesh-work with a loosely arranged outer globular layer and a tightly bound, dense inner layer (Baek et al., 2009; Hannig and Hannig, 2009). Reports of in situ AEP thickness range from 20 nm to 500 nm at 2 hrs compared with 100 to 1,300 nm at 24 hrs (Hannig, 1999), with the thickest films forming in sheltered areas such as those found interproximally. While most AEP studies report a 2-layer globular appearance, fibrillar and granular morphologies as well as single layers have been demonstrated and may reflect time-dependent changes in the AEP as it matures (Hannig, 1999; Baek et al., 2009).
Composition
The AEP constituents derive from several sources, including glandular secretions, gingival crevicular fluid, oral epithelial cell products, and micro-organism products (Fig. 4) (Hannig and Joiner, 2006). Whereas intra-individual variability can be attributed to extrinsic factors (van der Mei et al., 2002; Joiner et al., 2004), studies support the temporal stability of the AEP composition and the high intra- and inter-individual reproducibility (Lamkin et al., 2001; Yao et al., 2003). Moreover, differences in AEP compositions between and among various areas of the dentition can be attributed to slight discrepancies in the availability of macromolecules in the local environment, induced by either physiologic (Carlén et al., 1998) or pathologic conditions (Rudiger et al., 2002).
Origin of major constituents of the acquired enamel pellicle.
Proteins and Peptides
Several experimental models have been used to study AEP protein composition, each with inherent advantages and disadvantages. The in vitro model consists of either hydroxyapatite powder or discs incubated with whole saliva, glandular secretions, or mixtures of purified proteins. The advantages of this system are that it overcomes the limited amounts of protein that can be harvested in vivo and difficulties in collection techniques (Jensen et al., 1992). However, this system does not reflect the dynamic conditions of the mouth, like the continuous flow and clearance of saliva. Consequently, several differences have been found between pellicles formed in vitro and those in vivo, including amino acid composition and electrophoretic/ chromatographic patterns, with more intact proteins found in vitro (Hannig, 1999; Li et al., 2004). Regardless, in vitro studies have provided valuable information on protein affinity for HA and the nature of those interactions. Some of the major proteins identified include albumin, amylase, carbonic anhydrase VI, cystatins, histatins, lysozyme, statherin, and PRPs.
The in situ model consists of bovine or human enamel slabs mounted in intra-oral appliances. Bovine enamel exhibits considerable structural similarity to that of human enamel and allows large amounts of protein to be harvested (Hannig et al., 2004; Hara et al., 2006). Also, in situ studies have provided valuable insight into enzyme activity within the AEP, including amylase, lysozyme, peroxidase, and transaminases, as well as its ultrastructure. Analysis of the in vivo AEP protein composition can be hindered by the minute amounts of harvested proteins (µg level) and the applied techniques’ sensitivity (Siqueira et al., 2007a). A combination of amino acid, immunogenic, histological, chromatographic, and electrophoretic approaches led to the identification of amylase, albumin, Igs, agglutinin, PRPs, statherin, histatin1, MUC5B, carbonic anhydrases, lactoferrin, lysozyme, and cystatins within the in vivo AEP. In recent years, the onset of the proteomics era and the development and application of increasingly sensitive techniques (at the picomole level) have led to a rapid expansion in our knowledge about the composition of the in vivo pellicle. These techniques include LC-ESI-MS/MS and MALDI-TOF-MS, which have facilitated a more direct and comprehensive characterization of AEP components than previous techniques such as enzymatic or immunogenic assays (Siqueira et al., 2007b). Two-dimensional SDS-PAGE of in vivo AEP, combined with mass spectrometry of excised gels, led to the identification of novel S100A9 and previously identified proteins such as histatins, lysozyme, and statherin (Yao et al., 2003). Application of a bottom-up ‘shotgun’ proteomics led to the identification of 130 proteins within the in vivo AEP, 113 of which were novel (Siqueira et al., 2007b). However, this technique was not adapted to the identification of naturally occurring peptides in the AEP.
The low-molecular-weight fraction of the in situ AEP has been explored by LC-ESI-MS/MS, which identified 30 peptides, only 6 of which had been previously identified (Vitorino et al., 2007). Similarly, LC-ESI-MS/MS techniques led to the identification of 78 peptide fragments derived from 29 different proteins within the in vivo pellicle (Siqueira and Oppenheim, 2009). The application of proteomic techniques with increasingly complex experimental designs has allowed for much more comprehensive and descriptive analysis of the AEP proteome/peptidome. Recently, a label-free quantitative proteomics approach was carried out to study the effects of NaF treatment on formation of AEP, demonstrating that fluoride treatment qualitatively and quantitatively modulates AEP formation (Siqueira et al., 2012). In summary, AEP is formed by a complex interaction between macromolecules and the enamel surface. Appendix Table 1 summarizes the known proteins identified in in vitro, in situ, and in vivo experiments. The details of this interaction have not yet been completely elucidated, although it is recognized that particular proteins/peptides have a greater affinity for enamel than others, based in part on their surface charges.
AEP Functions
Lubrication
The AEP is involved in the lubrication of tooth surfaces, which in turn enhances the efficiency of speech and mastication (Tabak et al., 1982). AEP constituents implicated in this process include mucins, statherin, and aPRP1 (Tabak, 1995; Hahn Berg et al., 2004). Although they all provide some level of lubrication, in vitro studies with AFM on silica surfaces suggest that aPRP1 is the most effective, followed by mucin, then statherin (Hahn Berg et al., 2004). Furthermore, AEP has been shown to reduce the frictional coefficient between silica surfaces 20x in vitro (Berg et al., 2003). The AEP has long been speculated to protect against abrasive damage because of its lubricating properties. It was recently demonstrated that the in situ pellicle can reduce toothbrush abrasion on enamel and dentin surfaces (Joiner et al., 2008). However, the overall extent to which the AEP protects against abrasive damage in vivo is unclear and requires further study.
Regulation of Mineral Homeostasis
Several in vitro and in situ studies support the protective role of the AEP against acid-induced demineralization caused by either chemical or bacterial agents (Hannig and Balz, 2001; Hara et al., 2006; Siqueira et al., 2010; Cheaib and Lussi, 2011). However, the mechanisms by which AEP proteins contribute to the enamel homeostasis may be related to a retarding effect on the demineralization process rather than an avoidance of the enamel mineral loss during acidic challenges. Moreover, the protective effect of this protein film appears limited to enamel, since the pellicle formed on dentin surfaces provides little protection against erosive challenge (Hannig et al., 2003; Hara et al., 2006).
Originally, maturation of the pellicle was believed to be necessary for its protective properties against demineralization; however, several studies cumulatively examining pellicle formation times from 3 minutes to 7 days suggest that aging of the pellicle has only minor relevance (Hannig and Balz, 2001; Hannig et al., 2003). In addition, protective function of the 1-hour AEP varies at different regions of the oral cavity (Amaechi et al., 1999), but location-based differences appear less important in the 24-hour pellicle (Hannig and Balz, 2001).
Regarding the ultrastructure of the AEP, exposure to acid removes the outer globular layer, but leaves the basal layer intact (Hannig and Joiner, 2006). Interestingly, histatins have been shown to provide protection against demineralization in vitro (Siqueira et al., 2010). Although all histatins provided some level of protection against acid challenge, phosphorylated histatins afforded a greater level of protection than unphosphorylated ones. It is also proposed that phosphorylated residues on phosphoproteins such as histatin 1 mediate their strong adsorption to enamel. Statherin, another phosphoprotein present within the AEP in both intact and fragmented forms (Li et al., 2004), also appears to contribute to the acid-protective nature of the AEP. In vivo fragments of statherin demonstrated protection against demineralization in vitro, and as histatins, fragments containing phosphorylated residues were more effective at enamel homeostasis (Richardson et al., 1993). Moreover, other AEP proteins such as mucins also contribute to acid resistance (Cheaib and Lussi, 2011).
Multiple components within the AEP also contribute to the overall protection against enamel demineralization. Regarding the role of ions in protein adsorption and acid demineralization, a comparison of dialyzed and undialyzed saliva found that all enamel surfaces coated with saliva were protected against demineralization in vitro to some extent compared with uncoated samples (Featherstone et al., 1993). However, the level of protection was enhanced in undialyzed compared with dialyzed saliva, suggesting that the ionic strength and composition of saliva and the AEP may work together to provide acid resistance.
Regarding the remineralization process, the AEP exhibits a permselective nature (Hannig and Joiner, 2006) in a porous mesh-like structure that may permit the diffusion of calcium, phosphate, and fluoride ions. Also, lacunae on the enamel surface after acid demineralization exhibit pellicle-like proteins beneath the basal layer of the AEP (Hannig et al., 2009a), which may provide a scaffold for remineralization (Kirkham et al., 2007). Of the 130 different proteins recently identified within the in vivo AEP, 15% have purported roles in the remineralization process (Siqueira et al., 2007b).
The AEP may prevent the continuous precipitation of calcium-phosphate minerals onto enamel and instead may favor subsurface precipitation. Several in vivo pellicle components, including aPRPs and statherin, have been shown to inhibit crystal deposition on enamel surfaces (Hay and Moreno, 1979). However, statherin appears to be the most potent inhibitor of primary and secondary calcium precipitation and the only one considered effective at physiologic concentrations (Tamaki et al., 2002). In addition, previous findings (Raj et al., 1992; Long et al., 1998) and recent in vitro studies from our laboratory exploring the functional domains of 5 naturally occurring in vivo AEP statherin fragments revealed that the N-terminal domain is involved in the inhibition of hydroxyapatite crystal growth and that the phosphate groups contribute significantly to its inhibitory effect.
Host Defense and Microbial Colonization
The AEP occupies a unique position as the interface between teeth and the oral environment. Its composition and functional properties may be important to the delicate balance between oral health and disease. Of the more than 100 proteins identified in the in vivo AEP, at least 8% have associated antimicrobial functions, including cystatins, lysozyme, myeloperoxidase, and histatins (Siqueira et al., 2007b). Some of these proteins are known to maintain biological activity in the adsorbed state (Hannig et al., 2005), while most remain uninvestigated. Furthermore, 11% and 12% have been associated with immune defense and inflammatory responses, respectively, suggesting that the in vivo AEP may play an active role in maintaining oral health (Siqueira et al., 2007b).
Microbial colonization onto tooth surfaces is determined by microbial recognition of specific receptors within the AEP, along with surface roughness and free energy (Whittaker et al., 1996). The AEP/microbial interaction occurs through specific and non-specific mechanisms (Bowden and Hamilton, 1998). Recognition in many cases is so specific that bacteria bind to adsorbed protein but not to the same one in solution (Gibbons et al., 1990). The overall flora depends on the complex interplay of AEP constituents that may promote or inhibit colonization (Appendix Table 2). For instance, histatins and statherin inhibit the adherence of S. mutans, but statherin itself promotes the adherence of several bacterial species, including A. naeslundii and F. nucleatum (Xie et al., 1991). Moreover, the development and virulence of oral biofilms can be modulated by non-host proteins incorporated into the AEP proteome. Glycosyltransferases (Gtfs), an enzyme secreted by S. mutans recently identified in the in vitro AEP, may enhance the cohesion between S. mutans cells and C. albicans cells (Gregoire et al., 2011). Therefore, the overall composition of the initial microbial colonizers of the pellicle will depend on the cumulative effect of all pellicle constituents.
Oral Diagnostics
The potential use of the AEP in salivary diagnostics has been overlooked due to limitations on the amount of material that can be harvested. However, with improvements to AEP collection techniques (for review, see Siqueira et al., 2007a) and the analytical tools available, it is now possible to determine the AEP composition of a single person or tooth.
The AEP shows considerable inter-individual consistency, as demonstrated by studies of its amino acid and protein composition (Lamkin et al., 2001; Siqueira et al., 2007b), which makes the compilation of AEP “fingerprints” for healthy and disease states, such as caries or periodontal disease, a potentially valuable diagnostic tool. Interestingly, few studies have evaluated the changes in AEP proteome during disease states. For instance, the AEP of individuals with gingival inflammation, in comparison with that of healthy individuals, presents a 2 to 10x higher amount of total pellicle proteins and increased lactoferrin abundance, as well as a significant increase in plasma proteins on the incisal portion of teeth (Rudiger et al., 2002). Gingival inflammation results in an increased flow of gingival crevicular fluid, altering the normal balance of local biopolymers, and thus changing the composition of the AEP.
Several potential biomarkers for periodontal disease have been identified within saliva and in gingival crevicular fluid (Taba et al., 2005) from which many components of the AEP derive, so it is reasonable to expect that changes in protein concentration in these fluids may be reflected in the AEP composition. With respect to the AEP in particular, more than 10% of the proteins identified have been associated with inflammatory responses and may serve as markers for oral inflammatory disease such as periodontal disease. Furthermore, elevated levels of transaminases have been found in the saliva of patients with periodontal disease (Nomura et al., 2006); as noted above, transaminase has been detected within the in situ pellicle (Hannig et al., 2009c). Overall, present evidence supports AEP proteome analyses as a useful tool for assessing the diagnosis of oral inflammatory diseases and monitoring responses to therapeutic interventions.
Comparison of in vitro pellicles formed from unstimulated whole saliva in caries-free and -susceptible individuals found higher levels of aPRP1, PRP3, lipocalcin, cystatins-SN and S, histatin-1, and statherin in the caries-free group and increased concentrations of amylase, IgA, and lactoferrin in caries-susceptible groups (Vitorino et al., 2005). Further research is necessary to elucidate the mechanism by which differences in AEP composition occur, but it is hypothesized that there are differences in proteolytic capacities of whole saliva in caries-susceptible and caries-resistant individuals (Vitorino et al., 2006). This theory is strengthened by previous reports that aPRP levels within parotid and submandibular secretions are similar in caries-susceptible and -resistant groups (Mandel and Bennick, 1983).
Future Perspectives—Therapeutic Potential
Knowledge of the 3D structure and composition of the AEP, along with an understanding of its functions, could lead to the development of new therapeutic options for the treatment and prevention of numerous oral diseases, such as dental caries, dental erosion, and periodontal disease. For instance, a possible path for the modulation of the AEP has been achieved via enzyme-containing toothpastes. Commercially available enzymatic toothpastes were shown to increase glucosidase and peroxidase activity in in situ pellicle (Hannig et al., 2010b). Whether these immobilized enzymes provide protection in vivo is unclear. Moreover, other vehicles assumed to deliver protective enzymes within the pellicle, such as mouthrinses, have had limited success, possibly because of pH or saturation issues (Hannig et al., 2010a).
In addition, the incorporation of protective non-enzymatic AEP proteins and/or peptides into mouthrinses should be considered. Histatins are subject to a rapid and extensive proteolytic degradation within the oral cavity (Jensen et al., 1992; Helmerhorst et al., 2006). However, both intact and fragmented forms, previously detected within the in vivo AEP (Siqueira et al., 2010), exhibit antimicrobial, anti-fungal, and wound-healing properties (Helmerhorst et al., 2006; Oudhoff et al., 2008). Recently, the adsorption of histatin 1 onto hydroxyapatite provided resistance against its proteolytic degradation (McDonald et al., 2011). Other phosphoproteins with high affinity to hydroxyapatite, such as statherin and aPRPs, have also demonstrated a significant resistance against proteolytic degradation when adsorbed onto hydroxyapatite (unpublished observations). In contrast, histatin 2 (or His 18/32), a degradation product from histatin 1 identified in the AEP, has been demonstrated to enhance epithelial and fibroblast migration in vitro, suggesting its importance in early wound healing without exhibiting cytotoxic, pro-inflammatory, or pro-fibrotic responses (Oudhoff et al., 2008). What role, if any, they play in the healing process of periodontal tissue requires further investigation. However, it is reasonable to imagine, in the near future, the incorporation of synthetic proteins/phosphoproteins, with biological functions similar to those of histatin 2, into mouthrinses or toothpaste. An important aspect is the challenging mass spectrometry identification and characterization of those proteins. As an example, tandem mass spectrometry analysis (MS/MS) by collision-induced dissociation (CID) intensifies the dissociation of phosphate groups during the CID fragmentation step; therefore, it must be considered in future investigations.
The first step in the initiation of dental caries and periodontal disease is the colonization of tooth surfaces by microbial flora. One area of research focusing on the prevention of these diseases is anti-adhesion therapy. Lectins are a heterogeneous group of carbohydrate-binding proteins, several of which have been shown to be capable of binding to sugars in the pellicle with various intensities and patterns (Teixeira et al., 2006). Glucose/mannose-specific lectins were most effective in reducing several strains of S. mutans adhesion to hydroxyapatite in vitro. Another area of anti-adhesion therapy is probiotic bacterial strains, some of which are available in commercial products that can alter pellicle composition and have been shown to inhibit adhesion of S. mutans and S. gordonii (Haukioja et al., 2008). In addition, dietary proteins (e.g., casein) can potentially amplify the biological function of specific or multiple AEP components. However, it remains to be seen whether these therapies can be combined to achieve an additive or synergistic reduction of bacterial adhesion. Moreover, toxicity studies of modifiers, such as lectins and casein, and their potential impact on pellicle function are required.
Conclusion
Recent evidence has demonstrated the increasingly sophisticated structure of the in vivo AEP, consisting predominantly of intact and fragmented proteins derived from several different sources and subject to modification within the oral environment. Our knowledge of its composition has undergone a rapid expansion due to the application of novel techniques. In summary, the balance between AEP composition and structure modulates the complex nature and biological function of this unique interface between the teeth and the oral environment. Moreover, the comprehension of the AEP can enhance our understanding of oral health and can lead to innovative therapeutic approaches regarding the diagnosis, prevention, and treatment of specific oral pathologies.
Footnotes
Preparation of this article was supported by the
The authors declare no potential conflicts of interest with respect to the authorship and/or publication of this article.
References
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