Ultrastructural study of early dental plaque formation

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Abstract
Initial Colonization and early plaque formation were studied using hydroxyapatite splint segments attached to buccal surfaces of maxillary molar and premolar teeth in six young adults given a low‐sucrose diet. Segments were removed at intervals of 2, 4, 6, 12, 24 and 48 hr. Bacteria were first regularly seen in 4 or 6 hr specimens where they occurred as individual cells or as small groups of cells. No structures resembling preformed aggregates or hemispherical bacterial “globules” could be demonstrated. The bacteria most frequently attached to the pellicle surface diectly by their cell wall and gram‐positive cocci were most abundant. Another mode of bacterial attachment to pellicle was by means of fine bifbrils or coarser thread‐like structures. Occasionally organisms were seen attaching to apatite surfaces without interjacent pellicle material and sometimes they appeared to be completely embedded in the pellicle. Bacteria colonizing on epithelial cells regularly displayed a “fuzzy coat”. Extensions of organic material from the pellicle surface sometimes made it difficult to distinguish between pellicle and plaque matrix. No clear indication of bacteria metabolizing the pellicle was seen. Trilaminar vesicles probably originating from the surface of degenerating cells were especially abundant in areas with Gramnegative bacteria. In areas with Gram‐positive cells the amount of plaque matrix was greater and a number of cells displayed surface threads. The outer surface of the plaque ordinarily did not show a layer of extracellular organic material although a granular laer could be seen in local areas. These findings lend support to a concept of plaque formation as a sequential build‐up resulting from selective attachment and growth of individual organisms rather than resulting from attachment of aggregates of bacteria or a passive entrapment of organisms in a matrix.