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.

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 continously 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.