Role of Mucins from Human Whole Saliva in the Protection of Tooth Enamel against Demineralization in vitro

Abstract
The influence of salivary pellicles on the demineralization of human dental enamel by 1% citric acid was studied. The pellicles were formed on embedded human tooth surfaces incubated in vitro with various solutions for periods of up to 6 days. Pellicles induced by unstimulated whole saliva gave an approximately 45% and those from parotid saliva a 25% inhibition of demineralization. On the other hand, a pellicle formed from mixed submandibular and sublingual (SM-SL) saliva in 30 min gave a retardation in lesion formation of at least 40% and after a 60-min exposure to SM-SL saliva, the lesion formation was completely prevented. In contrast, when the mucins were removed from SM-SL saliva by ultracentrifugation, protection against demineralization by the pellicle formed on exposure to the supernatant was only 30%. The effect of pellicles obtained by isolated salivary mucins was also studied. Human whole salivary mucins (HWSM) were isolated from both human SM-SL saliva and whole saliva of two individuals with blood group A. The mucins contained 18% protein, 72% carbohydrate, 1.4% sulfate and 0.14% phosphate. The major components of the protein moiety were threonine (14.7%), valine (12.6%) and serine (10.8%). The molar ratio of the sugar residues was: galactose: N-acetylglucosamine: N-acetylgalactose: fucose: N-acetylneuraminic acid = 6:4.5:4:7:1. A pellicle formed by a 3-day exposure to salivary mucins in vitro gave 100% protection of the tooth surface against demineralization by citric acid. These data suggest that the mucins in human saliva contribute to a large extent to its protective effect against acidic attacks on the tooth surface.

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