Curd M. L. Bollen

Bio: Curd M. L. Bollen is an academic researcher from Catholic University of Leuven. The author has contributed to research in topics: Full mouth disinfection & Periodontitis. The author has an hindex of 18, co-authored 21 publications receiving 4561 citations.

The influence of surface roughness and surface-free energy on supra- and subgingival plaque formation in man. A review of the literature.

Abstract: In the oral cavity, an open growth system, bacterial adhesion to the non-shedding surfaces is for most bacteria the only way to survive. This adhesion occurs in 4 phases: the transport of the bacterium to the surface, the initial adhesion with a reversible and irreversible stage, the attachment by specific interactions, and finally the colonization in order to form a biofilm. Different hard surfaces are available in the oral cavity (teeth, filling materials, dental implants, or prostheses), all with different surface characteristics. In a healthy situation, a dynamic equilibrium exists on these surfaces between the forces of retention and those of removal. However, an increased bacterial accumulation often results in a shift toward disease. 2 mechanisms favour the retention of dental plaque: adhesion and stagnation. The aim of this review is to examine the influence of the surface roughness and the surface free energy in the adhesion process. Both in vitro and in vivo studies underline the importance of both variables in supragingival plaque formation. Rough surfaces will promote plaque formation and maturation, and high-energy surfaces are known to collect more plaque, to bind the plaque more strongly and to select specific bacteria. Although both variables interact with each other, the influence of surface roughness overrules that of the surface free energy. For the subgingival environment, with more facilities for microorganisms to survive, the importance of surface characteristics dramatically decreases. However, the influence of surface roughness and surface-free energy on supragingival plaque justifies the demand for smooth surfaces with a low surface-free energy in order to minimise plaque formation, thereby reducing the occurrence of caries and periodontitis.

The influence of abutment surface roughness on plaque accumulation and peri-implant mucositis

Abstract: Bacterial adhesion to intra-oral, hard surfaces is firmly influenced by the surface roughness to these structures. Previous studies showed a remarkable higher subgingival bacterial load on rough surfaces when compared to smooth sites. More recently, the additional effect of a further smoothening of intra-oral hard surfaces on clinical and microbiological parameters was examined in a short-term experiment. The results indicated that a reduction in surface roughness below R(a) = 0.2 microns, the so-called "thresholds R(a)", had no further effect on the quantitative/qualitative microbiological adhesion or colonisation, neither supra- nor subgingivally. This study aims to examine the long-term effects of smoothening intra-oral hard transgingival surfaces. In 6 patients expecting an overdenture in the lower jaw, supported by endosseus titanium implants, 2 different abutments (transmucosal part of the implant): a standard machined titanium (R(a) = 0.2 microns) and one highly polished and made of a ceramic material (R(a) = 0.06 microns) were randomly installed. After 3 months of intra-oral exposure, supra- and subgingival plaque samples from both abutments were compared with each other by means of differential phase-contrast microscopy (DPCM). Clinical periodontal parameters (probing depth, gingival recession, bleeding upon probing and Periotest-value) were recorded around each abutment. After 12 months, the supra- and subgingival samples were additionally cultured in aerobic, CO2-enriched and anaerobic conditions. The same clinical parameters as at the 3-month interval were recorded after 12 months. At 3 months, spirochetes and motile organisms were only detected subgingivally around the titanium abutments. After 12 months, however, both abutment-types harboured equal proportions of spirochetes and motile organisms, 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 within one division of a logarithmic scale. The aerobic culture data showed a higher proportion of Gram-negative organisms in the subgingival flora of the rougher abutments. From the group of potentially "pathogenic" bacteria, only Prevotella intermedia and Fusobacterium nucleatum were detected for anaerobic culturing and again the inter-abutment differences 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 microns), has no major impact on the supra- and subgingival microbial composition.

The influence of titanium abutment surface roughness on plaque accumulation and gingivitis: short-term observations.

Abstract: The roughness of intraoral hard surfaces plays an important role in bacterial adhesion and colonization. Earlier studies have shown that rough surfaces accumulate up to 25 times more subgingival plaque than do smooth sites. In the present study, the influence of surface smoothing was studied. In six partially edentulous patients waiting for a fixed prosthesis supported by endosseous titanium implants, four titanium abutments with different surface roughness were randomly placed. After 1 month of intraoral exposure, subgingival plaque samples from each abutment were compared within each patient by means of differential phase-contrast microscopy. After 3 months, supragingival and subgingival plaque samples were taken from all abutments for differential phase-contrast microscopy and culturing. Probing depth, recession, and bleeding upon probing were scored at the same visit. Differential phase-contrast microscopy showed that subgingivally, only the two roughest abutments harbored spirochetes after 1 month. After 3 months, subgingivally, the composition of the flora showed little variation on the different abutment types, although spirochetes were only noticed around the roughest abutments. Anaerobic culturing resulted in comparable amounts of colony-forming units for all abutment types, both supragingivally and subgingivally. Subgingivally, the microbiologic composition did not show major interabutment differences. Clinically, small differences in probing depth were observed. The roughest abutment showed some attachment gain (0.2 mm) during 3 months, whereas all other abutments had an attachment loss ranging from 0.8 to greater than 1 mm. The results indicate that a reduction in surface roughness (less than a roughness of 0.2 micron) had no major effect on the microbiologic composition, supragingivally or subgingivally. These observations indicate the existence of a threshold roughness below which no further impact on the bacterial adhesion and/or colonization should be expected. However, clinical evaluation seems to indicate that a certain surface roughness is necessary for increased resistance to clinical probing.

An in vivo Study of the Influence of the Surface Roughness of Implants on the Microbiology of Supra- and Subgingival Plaque

Abstract: In nine patients with fixed prostheses supported by endosseous titanium implants, 2 titanium abutments (transmucosal part of the implant) were replaced by either an unused standard abutment or a roughened titanium abutment. After 3 months of habitual oral hygiene, plaque samples were taken for differential phase-contrast microscopy, DNA probe analysis, and culturing. Supragingivally, rough abutments harbored significantly fewer coccoid micro-organisms (64 vs. 81%), which is indicative of a more mature plaque. Subgingivally, the observations depended on the sampling procedure. For plaque collected with paper points, only minor qualitative and quantitative differences between both substrata could be registered. However, when the microbiota adhering to the abutment were considered, rough surfaces harbored 25 times more bacteria, with a slightly lower density of coccoid organisms. The presence and density of periodontal pathogens subgingivally were, however, more related to the patient's dental status than to the surface characteristics of the abutments. These results justify the search for optimal surface smoothness for all intra-oral and intra-sulcular hard surfaces for reduction of bacterial colonization and of periodontal pathogens.

Biofilms: Survival Mechanisms of Clinically Relevant Microorganisms

Abstract: Though biofilms were first described by Antonie van Leeuwenhoek, the theory describing the biofilm process was not developed until 1978. We now understand that biofilms are universal, occurring in aquatic and industrial water systems as well as a large number of environments and medical devices relevant for public health. Using tools such as the scanning electron microscope and, more recently, the confocal laser scanning microscope, biofilm researchers now understand that biofilms are not unstructured, homogeneous deposits of cells and accumulated slime, but complex communities of surface-associated cells enclosed in a polymer matrix containing open water channels. Further studies have shown that the biofilm phenotype can be described in terms of the genes expressed by biofilm-associated cells. Microorganisms growing in a biofilm are highly resistant to antimicrobial agents by one or more mechanisms. Biofilm-associated microorganisms have been shown to be associated with several human diseases, such as native valve endocarditis and cystic fibrosis, and to colonize a wide variety of medical devices. Though epidemiologic evidence points to biofilms as a source of several infectious diseases, the exact mechanisms by which biofilm-associated microorganisms elicit disease are poorly understood. Detachment of cells or cell aggregates, production of endotoxin, increased resistance to the host immune system, and provision of a niche for the generation of resistant organisms are all biofilm processes which could initiate the disease process. Effective strategies to prevent or control biofilms on medical devices must take into consideration the unique and tenacious nature of biofilms. Current intervention strategies are designed to prevent initial device colonization, minimize microbial cell attachment to the device, penetrate the biofilm matrix and kill the associated cells, or remove the device from the patient. In the future, treatments may be based on inhibition of genes involved in cell attachment and biofilm formation.

Effect of material characteristics and/or surface topography on biofilm development

Abstract: Background: From an ecological viewpoint, the oral cavity, in fact the oro-pharynx, is an ‘open growth system’. It undergoes an uninterrupted introduction and removal of both microorganisms and nutrients. In order to survive within the oro-pharyngeal area, bacteria need to adhere either to the soft or hard tissues in order to resist shear forces. The fast turn-over of the oral lining epithelia (shedding 3 ×/day) is an efficient defence mechanism as it prevents the accumulation of large masses of microorganisms. Teeth, dentures, or endosseous implants, however, providing non-shedding surfaces, allow the formation of thick biofilms. In general, the established biofilm maintains an equilibrium with the host. An uncontrolled accumulation and/or metabolism of bacteria on the hard surfaces forms, however, the primary cause of dental caries, gingivitis, periodontitis, peri-implantitis, and stomatitis. Objectives: This systematic review aimed to evaluate critically the impact of surface characteristics (free energy, roughness, chemistry) on the de novo biofilm formation, especially in the supragingival and to a lesser extent in the subgingival areas. Methods: An electronic Medline search (from 1966 until July 2005) was conducted applying the following search items: ‘biofilm formation and dental/oral implants/surface characteristics’, ‘surface characteristics and implants’, ‘biofilm formation and oral’, ‘plaque/biofilm and roughness’, ‘plaque/biofilm and surface free energy’, and ‘plaque formation and implants’. Only clinical studies within the oro-pharyngeal area were included. Results: From a series of split-mouth studies, it could be concluded that both an increase in surface roughness above the Ra threshold of 0.2 μm and/or of the surface-free energy facilitates biofilm formation on restorative materials. When both surface characteristics interact with each other, surface roughness was found to be predominant. The biofilm formation is also influenced by the type (chemical composition) of biomaterial or the type of coating. Direct comparisons in biofilm formation on different transmucosal implant surfaces are scars. Conclusions: Extrapolation of data from studies on different restorative materials seems to indicate that transmucosal implant surfaces with a higher surface roughness/surface free energy facilitate biofilm formation.