Surface‐free energy and bacterial adhesion

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Abstract
Conflicting reports have been presented on the rôle of substratum surface free energy (s.f.e.) on bacterial adherence. It is the aim of the present study to evaluate the effect of the s.f.e. of substrata on bacterial adherence in vivo. The following substrata with s.f.e. varying from 23.3.–124.9 erg·cm−2 were cut into facings of 5 by 6 mm. polished and cleaned: polytetrafluorethylene (PTFE). Parafilm. polyvinylchloride (PVC). polymethylmethacrylate (PMMA), bovine dentin, bovine enamel and glass. In 5 beagle dogs, 7–9 years old. part of the buccal periodontium of the upper cuspids was excised and crowns were made and cemented with a non-fluoridated cement. The facings were placed in the crowns and placed in the oral cavity for 2 h. After removal, the facings were rinsed in saline. S.f.e. was assessed from contact angles with water, water/n-propanol mixtures and a-bromonaphthalene. according to the concept of dispersion and polar components, firstly on clean air dried facings and later on facings exposed to the oral cavity for 2 h. Immediately after rinsing, the water contact angle was measured as a function of time, to monitor the evaporation of free water from the protein layer adsorbed on the substrata which had been exposed to the oral cavity. It appeared that after a rapid increase in contact angle, a stable maximum value was obtained after 40–120 min depending on the substratum. S.f.e.'s of the protein-coated substrata were subsequently determined after a 120 min drying period. Following the contact angle determinations, the exposed facings were stained with ethidram bromide, enabling fluorescence microscopical counting of the adhered microorganisms. The oral environment markedly changed the substratum s.f.e.'s. Salivary protein adsorption reduced differences originally present in s.f.e. Low values increased, while high values decreased, yielding an average value of about 80 erg·cm−2. More micro-organisms adhered to substrata with an initially high s.f.e. than to substrata with an initially low s.f.e. (PTFE and Parafilm). The highest number of micro-organisms adhered to PVC (60·104 cm−2), the lowest to Parafilm (60·104 cm−2). It is interesting to note, that this relation was obtained, despite the fact that surfaces in the oral cavity are almost immediately covered with an adsorbed protein layer, shielding the physicochemical characteristics of the underlying substrata.