The surface free energy of human dental enamel

The surface free energy is a definite factor in the adhesion of micro-organisms to host surfaces, such as tooth surfaces. The surface free energy gamma s can experimentally be determined by means of a series of contact angle measurements with various liquids. Employing the concept of polar and dispersion components, it was found, that gamma s of ground and polished human enamel is 88 +/- 9 erg.cm-2. This value is of the same order of magnitude as obtained for hydroxyapatite (the main mineral component of enamel) and fluorapatite. Fluoride applications on human enamel, frequently employed in dentistry, greatly influence the surface free energy. Application of various fluorides gave different results: Aminfluorides reduced gamma s to 62 +/- 5 erg.cm-2; APF raised gamma s to 107 +/- 11 erg.cm-2; NaF hardly influenced gamma s X gamma s remained 87 +/- 9 erg.cm-2. Adsorption of salivary proteins (pellicle formation) influences these differences. In vivo pellicle formation on FEP (gamma s = 17 erg.cm-2) increased gamma s to 41 erg.cm-2, Diacryl (gamma s = 76 erg.cm-2) increased gamma s to 117 erg.cm-2, while on sintered hydroxyapatite (gamma s = 80 erg.cm-2) gamma s increased to 118 erg.cm-2.