H.J. Busscher

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

In nine patients with fixed prostheses supported by endosseous titanium implants, 2 titanium abutments (trans-mucosal 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 us. 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 patients 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.

EFFECT OF SPREADING PRESSURE ON SURFACE FREE-ENERGY DETERMINATIONS BY MEANS OF CONTACT-ANGLE MEASUREMENTS

Abstract Contact angle measurements have been carried out on various solid substrates using water-propanol mixtures and α-bromonaphthalene as wetting liquids. These substrates were: polytetrafluorethylene, Parafilm, polyethylene, polyurethane, polystyrene, polymethylmethacrylate, fluorapatite, and hydroxyapatite. The dispersion and the polar components of the surface free energy, γsd and γsp have been calculated from the geometric mean equation. Two approaches have been considered: (1) neglecting the spreading pressure πe and (2) taking πe into account (Danns method). The results show that both approaches actually yield the same results for the surface free energy, γs, if a proper interpretation of the approaches is considered. All data indicate, that approach (1) gives γs values determined on the adsorbed liquid layer, whereas in approach (2) the free energies of the bare solid surfaces are found.

Effect of Zeta Potential and Surface Energy on Bacterial Adhesion to Uncoated and Saliva-coated Human Enamel and Dentin

Physicochemical surface characteristics of early plaque-forming bacteria and of human tooth surfaces were measured to establish their role in bacterial adhesion to intact dental tissue slabs. In addition, the influence of an experimental salivary pellicle was evaluated. Strains of S. mutans, S. sanguis, S. salivarius, A. viscosus, and A. odontolyticus showed relatively high surface free energies (range, 99-128 mJ.m-2) and carried a negative surface charge, at both physiological (μ = 0.057) and low (μ = 0.020) ionic strengths of the medium. Very large differences in hydrophobicity were detected when the hexadecane adsorption test was used for measurement. Powdered enamel and dentin were also negatively charged at low ionic strength but were slightly positively charged in the physiological buffer. The surface free energy of enamel and dentin increased upon saliva coating, whereas the surface charge was always negative. The adhesion experiments showed: (1) large differences in the binding of various bacteria to the same surface; (2) an up to 20-fold difference in the binding of the same bacterium to different surfaces, although the binding of some strains was relatively independent of the type of surface or presence of a salivary pellicle; (3) a significant decrease in adhesion when the ionic strength of the medium was lowered, due to increased electrostatic repulsion (however, the adhesion of some bacteria was independent of the ionic strength of the medium); (4) different time-dependent adherence kinetics, depending on both the bacteria and nature of the solid surface; and (5) a propensity for plaque streptococci to bind to uncoated dentin.

Direct probing by atomic force microscopy of the cell surface softness of a fibrillated and nonfibrillated oral streptococcal strain

In this paper, direct measurement by atomic force microscopy (AFM) of the cell surface softness of a fibrillated oral streptococcal strain Streptococcus salivarius HB and of a nonfibrillated strain S. salivarius HBC12 is presented, and the data interpretation is validated by comparison with results from independent techniques. Upon approach of the fibrillated strain in water, the AFM tip experienced a long-range repulsion force, starting at approximately 100 nm, attributed to the compression of the soft layer of fibrils present at the cell surface. In 0.1 M KCl, repulsion was only experienced when the tip was closer than approximately 10 nm, reflecting a stiffer cell surface due to collapse of the fibrillar mass. Force-distance curves indicated that the nonfibrillated strain, probed both in water and in 0.1 M KCl, was much stiffer than the fibrillated strain in water, and a repulsion force was experienced by the tip at close approach only (20 nm in water and 10 nm in 0.1 M KCl). Differences in cell surface softness were further supported by differences in cell surface morphology, the fibrillated strain imaged in water being the only specimen that showed characteristic topographical features attributable to fibrils. These results are in excellent agreement with previous indirect measurements of cell surface softness by dynamic light scattering and particulate microelectrophoresis and demonstrate the potential of AFM to directly probe the softness of microbial cell surfaces.

Hydrophobic recovery of repeatedly plasma-treated silicone rubber. Part 1. Storage in air

Silicone rubber is used for a wide variety of biomedical and industrial applications due to its good mechanical properties, combined with a hydrophobic surface. Frequently, however, it is desirable to alter the surface hydrophobicity of silicone rubber. Often this is done by plasma treatments but the effects are usually transient. In this study, surfaces of medical grade silicone rubber have been repeatedly modified by means of oxygen, argon, carbon dioxide, and ammonia RF plasma treatments with a 24 h time interval in between treatments. Treated samples were stored in air prior to surface characterization by water contact angle measurements, X-ray photoelectron spectroscopy (XPS), streaming potential measurements, and profilometry for surface roughness. The carbon percentage of the surfaces decreased after plasma treatment, while the silicon and oxygen percentages increased irrespective of the plasma used. The formation of Si-O-Si bridges between siloxane chains after plasma treatment was demonstrated by...

Wetting Properties of Human Saliva and Saliva Substitutes

Contact angle measurements were employed so that we could study the wetting properties of human whole saliva and saliva substitutes containing mucins or carboxymethylcellulose (CMC) on human oral mucosa (in vivo) and on ground and polished human enamel (in vitro). A new approach was introduced for measuring contact angles on human oral mucosa in vivo. It was shown that the wetting properties of CMC- and mucin-containing saliva substitutes on human enamel were significantly better than those of human whole saliva. On human oral mucosa, the wetting properties of CMC-containing saliva substitutes and human whole saliva were comparable, but were surpassed by those of the mucin-containing saliva substitutes. Mucin-containing substitutes thus provide good wetting properties on ground and polished enamel as well as on oral mucosa.

Deposition of leuconostoc mesenteroides and streptococcus thermophilus to solid substrata in a parallel plate flow cell

Deposition of two microbial strains encountered in the dairy industry (Leuconostoc mesenteroides and Streptococcus thermophilus) to substrata with different wettabilities was studied in a parallel plate flow cell. Deposition was studied both from a bacterial suspension in water and in potassium phosphate buffer (pH 70). L. mesenteroides adhered rather weakly and showed no clear preference for any of the substrata. Conversely, S. thermophilus adhered much better to substrata with a high wettability than to low wettability substrata. Using real‐time image analysis, it was observed that after an initially high deposition of S. thermophilus from water to glass, cells subsequently desorbed leaving a biosurfactant layer on the surface to which freshly cultured cells did not adhere. Presumably this layer is due to biosurfactants produced by the adhering cells themselves. Such a biological anti‐adhesive coating might have great potential for the control of microbial fouling in dairy processing.

Bacterial deposition to fluoridated and non-fluoridated polyurethane coatings with different elastic modulus and surface tension in a parallel plate and a stagnation point flow chamber

Deposition of three marine bacterial strains with different cell surface hydrophobicities from artificial seawater to polyurethane coatings on glass with different surface tensions and elastic modulus was studied in situ in a parallel plate (PP) and stagnation point (SP) flow chamber. Different surface tensions of the coatings were established by changing the amount of fluorine, whereas using more or less branched polymers made different elastic moduli. Surface tensions of the coating, derived from measured contact angles with liquids, ranged from 11.9 to 44.9 mJ m-2, while the elastic moduli, derived from force-distance curves as measured with an atomic force microscope were between 1.5 and 2.2 GPa. In both flow chambers, the most hydrophilic bacterium Halomonas pacifica adhered preferentially to the more hydrophilic, non-fluoridated coating, whereas the most hydrophobic bacterium Marinobacter hydrocarbonoclasticus showed a greater preference for the more hydrophobic coating. Bacterial adhesion in the PP flow chamber was not influenced by the elastic modulus of the coatings, but in the SP flow chamber bacteria adhered in higher numbers to hard surfaces than to coatings of lower elastic moduli.

Spreading pressures of water and n-propanol on polymer surfaces

Spreading pressures of water and n-propanol on polytetrafluoroethylene (PTFE), polystyrene (PS), polymethylmethacrylate (PMMA), polycarbonate (PC), and glass are determined from ellipsometrically measured adsorption isotherms by graphical integration, yielding for water 9, 37, 26, 33, and 141 erg·cm−2 on PTFE, PS, PMMA, PC, and glass, respectively, while for n-propanol 5, 38, 26, 23, and 37 erg·cm−2, respectively. The spreading pressures for water as well as n-propanol are comparable to values previously obtained from contact angle data with water, water/n-propanol mixtures and α-bromonaphthalene using the geometric mean equation. This method yielded spreading pressures of 9, 14, 30, 27, and 70 erg·cm−2 for PTFE, PS, PMMA, PC, and glass, respectively. The numerical correspondence between the spreading pressures for water and n-propanol determined ellipsometrically with the values derived from contact angles indicates the necessity as well as the validity of taking the spreading pressures of water/n-propanol mixtures into account as a constant, if surface free energies of high energy substrata are approximated by contact angle measurements.

Bond Strengthening in Oral Bacterial Adhesion to Salivary Conditioning Films

ABSTRACT Transition from reversible to irreversible bacterial adhesion is a highly relevant but poorly understood step in initial biofilm formation. We hypothesize that in oral biofilm formation, irreversible adhesion is caused by bond strengthening due to specific bacterial interactions with salivary conditioning films. Here, we compared the initial adhesion of six oral bacterial strains to salivary conditioning films with their adhesion to a bovine serum albumin (BSA) coating and related their adhesion to the strengthening of the binding forces measured with bacteria-coated atomic force microscopy cantilevers. All strains adhered in higher numbers to salivary conditioning films than to BSA coatings, and specific bacterial interactions with salivary conditioning films were accompanied by stronger initial adhesion forces. Bond strengthening occurred on a time scale of several tens of seconds and was slower for actinomyces than for streptococci. Nonspecific interactions between bacteria and BSA coatings strengthened twofold faster than their specific interactions with salivary conditioning films, likely because specific interactions require a closer approach of interacting surfaces with the removal of interfacial water and a more extensive rearrangement of surface structures. After bond strengthening, bacterial adhesion forces with a salivary conditioning film remained stronger than those with BSA coatings.