The purpose of this study was to characterize and compare by scanning electron microscopy (SEM) the maturation of supragingival microbial plaque on enamel and smooth titanium and that of subgingival plaque on cementum, plasma-sprayed titanium and hydroxyapatite surfaces. Specimens (6.5 x 2 x 1 mm) were obtained from titanium implants with smooth transmucosal collars and plasma-sprayed endosseous posts of titanium or hydroxyapatite. Unerupted third molars were sectioned to similar dimensions that included equal lengths of enamel and root surface. Ten patients with post-treatment pocket depths of > 6 mm on 3 non-adjacent teeth were selected and each had 1 set of the 3 specimen types bonded by random assignment to the selected teeth. Specimens were positioned so that enamel and/or smooth titanium surfaces were supragingival and cementum and titanium or hydroxyapatite plasma-sprayed surfaces were subgingival. Patients were instructed to stop oral hygiene, after which 2 specimen sets were removed at 1, 3, 5, 7 and 10 days. Two specimens of each type were examined by SEM at each time interval for supra- and subgingival plaque. The sequence of appearance of various microbial morphotypes in supra- and subgingival plaque was similar regardless of surface. In both supra- and subgingival plaque, depending on time interval, cocci, rods of various lengths, filamentous organisms, fusiforms, spirochetes and corn-cob formations were observed. Mineralized plaque was noted on most subgingival specimens by day 10. These observations indicate that surface of natural teeth, smooth titanium and plasma-sprayed titanium and hydroxyapatite support the maturation of microbial plaque with the successive inclusion of a variety of morphotypes.