Saliva proteins, adsorption

Exposing the saliva protein mixture to the brushed surfaces reveals two remarkable features (a) the brush, even at a-1 = 12 nm2, strongly suppresses adsorption, whereas (2) the shift in the zeta potential is still relatively large. These observations suggest that the small amounts of saliva protein deposited at the brushed surface are positively charged and that small proteins (i.e. of the size of that of LSZ) are hardly involved. 

K. Kawasaki, M. Kambara, H. Matsumura, and W. Norde, Protein adsorption at polymer-grafted hydroxyapatite surfaces comparison between a mixture of saliva proteins and some well-defined model proteins, Biofouling 19, 355-363 (2003). 

The only authors to study the more relevant protein adsorption characteristics to date have been Ruan et al. [97], However, they observed neither qualitative nor quantitative differences in adsorption from 1 1 mixed parotid -submandibular saliva samples, from 6 caries-free and 6 caries-active subjects, onto powdered enamel and cementum. The small number of samples compared may be the reason for a lack of discrimination. The authors did find that much more proline-rich protein and cysteine-containing protein were adsorbed to enamel than to cementum though they could not explain why. 

The rapid initial phase of salivary protein adsorption is followed by a second, comparatively slower phase of protein adsorption onto the protein-coated enamel surface. The second stage of pellicle formation is characterised by a continuous adsorption of biopolymers from saliva. This process involves protein-protein interactions between already adsorbed proteins, immobilised in the pellicle layer, and proteins as well as protein aggregates from saliva. Amino acid and Auger analyses of the pellicle layer formed on buccally carried enamel slabs [18] indicate that the adsorbed proteins reach an initial thickness in about 2-3 min, and stay at that level for about 30 min. The thickness of the pellicle then increases to about three times its initial thickness and reaches a plateau after 30-90min [5, 18, 27], Within 60min, the thickness of the in situ-formed pellicle will further increase to between 100 and lOOOnm [17, 28], dependent on the supply of locally available salivary biopolymers and the prevailing intraoral conditions [17,28,29] (fig. 2). 

Even though zinc is at a low level of only 2% in the alloy, it cannot be overlooked in regard to its effect upon the alloy s interaction with protein. Admittedly, the presence of zinc in the material compounds the issues of protein adsorption that are under investigation. Zinc binds to proteins in various ways, and in some instances, an active competition for zinc exists between certain proteins and amino acids (42). In normal human sera, between 2 and 8% of zinc is ultrafilterable, implying that the remainder is bound to protein. Zinc in human saliva is likewise bound to various molecular... 

A variety of dental alloys were submitted to adsorption experiments with human saliva. FT-IR and SIMS were used to analyze the surface films. lEF compared the protein patterns from surface extracts and salivas used in protein adsorptions to those from unexposed saliva controls. Results support both selective and nonselective adsorption processes. The SIMS spectrum showed variabilities in elemental intensities between substrates of different compositions, while lEF patterns of surface extracts from eleven different compositions of powder all appeared to contain the same acidic protein bands. FT-IR spectrum showed variabilities in the protein to carbohydrate intensity ratios at different sites on the same alloy surface, and suggested that other factors besides substrate material may be important in protein adsorption. 

When biomaterials come into contact with various biological fluids (blood, saliva, tears) protein adsorption at the solid-liquid interface is the first phenomenon which occurs. This primary adsorption process then exerts a profound influence over subsequent events and me y give rise to such well recognized and undesired processes as thrombus formation, formation of dental plaque or dry spot formation in the case of contact lenses. 

A possible source of some of the variation in the above studies may well be degradation of salivary proteins by proteolytic enzymes in the mouth. Bennick et al. [98] found that pellicles formed in situ on pieces of enamel and more than 24 h old showed degradation of adsorbed proline-rich proteins, and that old pellicle from extracted teeth contained very little of these proteins. A more recent report from the same laboratory [99] described large numbers of small phosphoproteins in samples of whole saliva, which were mostly fragments of acidic proline-rich proteins and indicated rapid degradation. In apparent contrast, Lamkin et al. [100] found that the magnitude of proteolysis of whole saliva samples was much smaller than they had expected, albeit by an ex vivo adsorption technique. 

Formation of the acquired salivary pellicle is the result of biopolymer adsorption at the tooth-saliva interface. The term acquired pellicle was first suggested in a review of the nomenclature of the enamel surface integuments by Dawes et al. [1], to describe the cuticular material formed on the enamel surface after eruption. The pellicle consists of adsorbed proteins and other macromolecules from the oral environment (saliva, crevicular fluids) and is clearly distinguished from the microbial biofilm (plaque) (fig. 1). 

Pellicle formation is determined by adsorption of components from saliva, crevicular fluid and bacteria onto the enamel surface [2-13], Formation of the acquired pellicle is a highly selective process, since only a fraction of the proteins available in saliva is found in the pellicle [14,15],... 

Studies on pellicle composition are hampered by the fact that only limited amounts (minute quantities) of pellicle material can be collected and recovered from human teeth in vivo for analytical investigations. It has been calculated that the pellicle layer formed per labial surface of a tooth over 2 h in vivo only contains approximately 1 xg of protein [39], Therefore, much work has been performed using in vitro models to mimic the formation of the salivary pellicle. Glandular salivary secretions or whole saliva supernatants are used to form a pellicle-like protein layer adsorbed on hydroxyapatite or tooth enamel. Although considerable insight into the selectivity and affinity characteristics of salivary proteins during adsorption onto these surfaces has been obtained from... 

Jensen JL, Lamkin MS, Oppenheim FG Adsorption of human salivary proteins to hydroxyapatite a comparison between whole saliva and glandular salivary secretions. J Dent Res 1992 71 1569-1576. 

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