THE INFLUENCE OF ABUTMENT SURFACE-ROUGHNESS ON PLAQUE ACCUMULATION AND PERI-IMPLANT MUCOSITIS

Bacterial adhesion to intra-oral, hard surfaces is firmly influenced b y the surface roughness of these structures. Previous studies showed a remarkable higher subgingival bacterial load on rough surfaces when c ompared to smooth sites. More recently, the additional effect of a fur ther smoothening of intra-oral hard surfaces on clinical and microbiol ogical parameters was examined in a short-term experiment. The results indicated that a reduction in surface roughness below R(a)=0.2 mu m, the so-called ''threshold R(u)'', had no further effect on the quantit ative/qualitative microbiological adhesion or colonisation, neither su pra- nor subgingivally. This study aims to examine the long-term effec ts of smoothening intra-oral hard transgingival surfaces. In 6 patient s expecting an overdenture in the lower jaw, supported by endosseus ti tanium implants, 2 different abutments (transmucosal part of the impla nt): a standard machined titanium (R(a)=0.2 mu m) and one highly polis hed and made of a ceramic material (R(a)=0.06 mu m) were randomly inst alled. After 3 months of intra-oral exposure, supra- and subgingival p laque samples from both abutments were compared with each other by mea ns of differential phase-contrast microscopy (DPCM). Clinical periodon tal parameters (probing depth, gingival recession, bleeding upon probi ng and Periotest-value) were recorded around each abutment. After 12 m onths, the supra- and subgingival samples were additionally cultured i n aerobic, CO2-enriched and anaerobic conditions. The same clinical pa rameters as at the 3-month interval were recorded after 12 months. At 3 months, spirochetes and motile organisms were only detected subgingi vally around the titanium abutments. After 12 months, however, both ab utment-types harboured equal proportions of spirochetes and motile org anisms, both supra- and subgingivally. The microbial culturing (month 12) failed to detect large inter-abutment differences. The differences in number of colony- forming units (aerobic and anaerobic) were withi n one division of a logarithmic scale. The aerobic culture data showed a higher proportion of Gram-negative organisms in the subgingival flo ra of the rougher abutments. From the group of potentially ''pathogeni c'' bacteria, only Prevotella intermedia and Fusobacterium nucleatum w ere detected after anaerobic culturing and again the inter-abutment di fferences were negligible. Clinically the smoothest abutment showed a slightly higher increase in probing depth between months 3 and 12, and more bleeding on probing. The present results confirm the findings of our previous short-term study, indicating that a further reduction of the surface roughness, below a certain ''threshold R(a)'' (0.2 mu m), has no major impact on the supra- and subgingival microbial compositi on.