The formation of salivary coating (SC) and dental plaque on top of Vestopal W and enamel inlays was studied with scanning and transmission electron microscopy. No clear morphological differences were found between SC and dental plaque formed on either material. A thin continuous SC was formed on the supporting material in all volunteers within 30 minutes' oral exposure. The SC appeared smooth and contained numerous protruding small round bodies (40-200 nm in size), the numbers of which increased with increasing time. Bacterial colonization of the SC started between 6 and 12 hours' oral exposure. After 24 hours' oral exposure, bacterial colonies were confluenting and partly obscuring the subjacent SC. No evidence was obtained in this study contraindicating the use of Vestopal W as supporting material for experimental plaque studies.