Individual variations in saliva protein protection against enamel demineralisation

Objectives: Salivary proteins protect teeth against acid induced demineralisation by their pellicle forming properties on tooth surfaces. However, little is known about individual, gender and ethnic variations in this protective effect of the salivary proteins. Therefore, this study aimed to determine possible differences in saliva protein protection from ten healthy young Caucasians and ten healthy young non-Caucasians including both males and females. Methods: Parotid and submandibular saliva was collected from all subjects in closed systems, in response to drinking orange juice, and dialysed and afterwards lyophilised. Enamel was obtained from permanent bovine incisors that were sectioned in blocks and polished. The enamel blocks were pre-coated with either parotid or submandibular salivary proteins from one of the twenty individuals for 12 h and then exposed to a soft drink resembling solution (pH 2.3 and 5 mmol/L CaHPO4). Surface microhardness was determined for each enamel block before and after exposure as well as for sound enamel and uncoated enamel. Salivary protein analyses included total protein and carbohydrate as well as characterisation of individual protein profiles (1D and 2D) and MALDI-TOF mass fingerprinting on trypsin digested protein spots. Results: The results showed that protein coated enamel blocks were more resistant to the soft drink resembling solution than non-coated blocks (p<0.001). No systematic differences were found between males and females. However, considerable differences were found among individuals and between non-Caucasians and Caucasians. Non-Caucasians were as a group significantly better to protect enamel against acid-induced softening than Caucasians (p<0.001). Protein analyses revealed that samples of parotid saliva offering good protection against erosive challenges were high in the salivary cystatin SN isoform, contained more protein, and were less glycosylated than protein samples offering lower protection. Conclusions: Considerable individual variations in saliva protein protection may be expected and could be related to a high salivary cystatin level.