The clinical meaning of the surface roughness and the surface free energy of intra-oral hard substrata on the microbiology of the supra- and subgingival plaque: results of in vitro and in vivo experiments.

In the oral cavity, which may be considered as an open growth system, most bacteria can only survive if they adhere to the hard surfaces (teeth, filling materials, dental implants, or prostheses). Such bacterial adhesion occurs in four phases: transport to the surface, initial adhesion with a reversible and irreversible stage, attachment by specific interactions and finally colonization. During this process the roughness and the free energy of the surfaces play a key role. The reduction in roughness of a surface will result in a dramatic retardation of plaque formation and maturation. A reduction in surface free energy of the substratum will result in a decrease in plaque growth rate, a decrease in plaque retention capacity of the surface and in the selection of specific organisms. Although both parameters interact with each other, the influence of surface roughness is dominant. The importance of both parameters justifies the demand for smooth surfaces with a low surface free energy in order to prevent plaque formation, thereby reducing the occurrence of gingival inflammation.