Anton H. Weerkamp

The Influence of Surface Free-energy on Planimetric Plaque Growth in Man

The purpose of this study was to examine the change in plaque area over nine days in vivo on four materials with different surface free-energies (s.f.e.). Twelve healthy dental students participated in a crossover, split-mouth, double-blind study. Supragingival plaque formation was recorded over a nine-day period, on four different materials: fluorethylenepropylene (Teflon) (FEP), parafilm (PAR), cellulose acetate (CA), and enamel (E) with s.fe. of 20, 26, 57, and 88 erg/cm2, respectively. Strips made from the first three materials were stuck to the buccal surface of an upper incisor. The remaining incisor was carefully polished and served as an enamel surface. The increase in plaque was evaluated after three, six, and nine days. A planimetrical analysis was used so that the plaque area could be expressed as a percentage of the total buccal tooth surface. This procedure was repeated on each subject, so that at the end, each pair of central or lateral incisors received the four tested materials. The results indicated that the adherence of micro-organisms on pellicle-coated substrata was influenced by the materials s.f.e.; there was an association between the s.f.e. of the substrata and the supragingival plaque extension in vivo. High surface free-energy substrata in the oral cavity attracted more micro-organisms than did low energetic materials. Additionally, the bacterial adhesion seemed very weak on surfaces with a low s.f.e.

REAL-TIME ENUMERATION OF ADHERING MICROORGANISMS IN A PARALLEL PLATE FLOW CELL USING AUTOMATED IMAGE-ANALYSIS

Abstract A parallel plate flow cell has been developed allowing real-time enumeration of microorganisms adhering to solid substrata using automated image analysis. A detailed description is given of the flow cell system, microscope illumination facilities and specifichydrodynamic conditions in the flow cell. In addition, a method is presented for the distinction of adhering microorganims into singlets and multicellular aggregates.

ADHESION OF ORAL STREPTOCOCCI FROM A FLOWING SUSPENSION TO UNCOATED AND ALBUMIN-COATED SURFACES

A flow cell system was developed which allowed the study of bacterial adhesion to solid substrata at well-defined shear rates. In addition, the system enabled the solid surfaces to be coated with a proteinaceous film under exactly the same shear conditions. In this flow cell system, adhesion of three strains of oral streptococci from a phosphate-buffered solution onto three different substrata was studied as a function of time in the absence and presence of a bovine serum albumin (BSA) coating at a shear rate of 21 s-1. To obtain a wide range in surface free energies (gamma) representative strains (gamma b 38-117 mJ m-2) and solid substrata (gamma s 20-109 mJ m-2) were selected. The number of bacteria adhering was counted microscopically. In the absence of a BSA coating a linear relation was found between the number of bacteria adhering at saturation (nb,s) and the calculated interfacial free energy of adhesion (delta Fadh) for each of the three strains. In the presence of a BSA coating the number of bacteria adhering was greatly decreased in all cases. However, despite the presence of the BSA coating there was still a linear relation between the number of bacteria adhering at saturation and the interfacial free energy of adhesion, calculated on the basis of the surface free energy of the uncoated substrata. It can be concluded that the bare, uncoated substratum still influenced bacterial adhesion in spite of the marked influence of a BSA coating.

MICROBIAL FACTORS IN A THERMODYNAMIC APPROACH OF ORAL STREPTOCOCCAL ADHESION TO SOLID SUBSTRATA

Abstract In this paper surface modification of bacterial adhesion sites on glass by excreted macromolecular substances from Streptococcus mitis BMS cells was investigated by probing the affinity of Streptococcus mutans NS cells for the glass surface. Excreted substances which were different from the fibrillar surface appendages of this strain affected the adhesion sites and hence the adhesive behavior of S. mutans and the producer strain itself. Such surface modifications caused by excreted substances can occur frequently but until now their effects have been neglected in a thermodynamic approach on bacterial adhesion to solid substrata. Recently we proposed that the number of bacteria adhering at equilibrium to solid substrate, n e , is linearly related to the interfacial free energy of adhesion according to n e = a (Δ F adh − 23.1) + 1.2 (I. H. Pratt-Terpstra, A. H. Weerkamp, and H. J. Busscher, Curr. Microbiol. 16 , 311 (1988)). In this relation a denotes a strain-specific microbial factor with a characteristic value for each strain which was associated with the absence or presence of fibrillar surface appendages. In the present study we showed that the low a factor of S. mitis BMS is due to surface modifications caused by its excretion of antiadhesive substances. Recalculations of data provided by various other authors confirmed these results, independent of whether the thermodynamic approach employed involved the equation of state or the dispersion and polar components concept. Therefore the inclusion of an a factor can be done in a general approach to bacterial adhesion to solid substrata. Tentatively this strain-specific a factor must be considered as a parameter because of its possible dependence on temperature, pH, ionic strength, and shear rate, but it is expected that this factor can be evolved to a purely strain-dependent constant by changing the variables and extending the above equation.

ON A RELATION BETWEEN INTERFACIAL FREE ENERGY-DEPENDENT AND NONINTERFACIAL FREE ENERGY-DEPENDENT ADHERENCE OF ORAL STREPTOCOCCI TO SOLID SUBSTRATA

In several systems bacterial adhesion occurs despite a positive interfacial free energy of adhesion, ΔFadh; this implies that other interactions are involved. We hypothesize that the number of bacteria adhering at ΔFadh=0 represents their ability to adhere by other, i.e., non-ΔFadh-dependent interactions. Eight strains of oral streptococci were allowed to adhere to three solid substrata with different surface free energies in a flow cell system. Strain-specific linear relations were found between the numbers of bacteria adhering at saturation, nb,s, and ΔFadh. When for all strains the numbers of adhering bacteria at ΔFadh=0 were plotted versus the slopes, denoting the sensitivity to ΔFadh, a linear relationship (r=0.92) was observed. It is, therefore, concluded that one strain-specific factor influences both ΔFadh-dependent and non-ΔFadh-dependent adherence. The numerical value of this factor, together with a surface energetic analysis, predicts the number of streptococci that will adhere to a given nonbiological substratum.

Secretory IgA adsorption and oral streptococcal adhesion to human enamel and artificial solid substrata with various surface free energies

In this paper, secretory IgA adsorption from a single component sIgA solution and from human whole saliva onto human enamel and artificial solid substrata with various surface free energies was studied as a function of time. ELISA indicated that screening or displacement of adsorbed sIgA by other salivary proteins occurred only on low surface free energy substrata, not on high surface free energy substrata such as enamel. In addition, the adhesion of three oral streptococcal strains (Streptococcus mitis BMS, S. sanguis 12, and S. mutans NS), also having widely different surface free energies, to sIgA-coated surfaces was studied. The adhesion of all three streptococcal strains was significantly reduced in the presence of a sIgA coating. However, ranking the adhesion data with respect to the various substrata revealed a similar order to that in the case of uncoated substrata, indicating that substratum properties were at least partly transferred by the adsorbed protein film to the interface with adhering micro-organisms. For S. sanguis 12 and S. mitis BMS, adhesion decreased proportionally with the amounts of sIgA detected by ELISA, but for S. mutans NS such relations with the amounts of sIgA detected on the protein-coated substrata were not found. Thus, for S. mutans NS a specific antibody effect seems to exist in addition to a non-specific protein effect like that observed for S. sanguis 12 and S. mitis BMS.