The Surface Free Energy of Human Dental Enamel

Abstract

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 γs 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 γs 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 γs to 62 ± 5 erg.cm⁻²; APF raised γs to 107 ± 11 erg.cm⁻²; NaF hardly influenced γs. γs remained 87 ± 9 erg.cm⁻². Adsorption of salivary proteins (pellicle formation) influences these differences. In vivo pellicle formation on FEP (γs = 17 erg.cm⁻²) increased γs to 41 erg.cm⁻², Diacryl (γs = 76 erg.cm⁻²) increased γs to 117 erg.cm⁻², while on sintered hydroxyapatite (γs = 80 erg.cm⁻²) γs increased to 118 erg.cm⁻²