Objectives: This electron  microscopic study aimed at investigating effects of oral astringen I stimuli on the enamel pellicle's morphology.

Methods: Pellicles  were  formed  in situ within  30 min on  bovine  enamel  slabs,  fixed  to individuals' upper  jaw

splints.  The pellicle-coated  specimens  were  immersed  in vicro in seven  diverse  astringent solutions  and  subse­ quently  analyzed  by scanning  electron  microscopy (SEM), energy dispersive X-ray (EDX) spectroscopy, as weil as Iransmission  electron  microscopy  (TEM). Four  biocompatible astringents, namely  the  polyphenol  epigalloca­ techin gallate,  the metal salt iron(III) sulfate,  the basic protein  Iysozyme, and the aminopolysaccharide chitosan, were additionally applied  in situ. After rinsing the oral cavity  with these compounds,  the pellicle's ultrastructure was imaged  by SEM and TEM, respectively. Untreated  pellicle samples  served  as controls.

Results: Exposure  to  polyphenols  and  Iysozyme  induced  particularly thicker  and  electron-denser pellicles  in comparison  to the control  pellicle with simi l ar characteristics in vicro and in situ . In contrast,  acidic chitosan  and meta! salt solutions, respectively,  revealed  minor  pellicle  alterations. The  incorporation of Fe and  Al into  the pellic!es treated  with  the corresponding inorganic  salts was verified  by EDX analysis.

Conclusions: Astringent-induced  pellicle  modifications were  for the  first  time  visualized  by TEM. The  ultra­

structural a lterations of the dental  pellicle may  partly  expla in the  tooth-roughening effect causcd  by oral  as­

tringent  stimuli.

Clinical significance: Astriogents  might  modify  the  pellicle's  proteelive properlies against  dental  erosion, attri­ tion,  as weil as bacterial  adhesion,  and  by this means  may  influence  tooth  health. The findings  may  thus  be particularly relevant  for preventive  dentistry.