Quantitative affinity parameters of synthetic hydroxyapatite and enamel surfaces in vitro

Abstract

Particulate synthetic hydroxyapatite (HAP) is rapidly gaining importance as a biomimetic agent in oral care products. The prerequisite for an adequate effect of the treatment is an efficient attachment of the HAP particles to the tooth substance. However, quantitative data about the interaction and affinity parameters involved are scarce. The authors used an in vitro approach with standardized bovine tooth enamel surfaces and aqueous dispersions of chemically pure synthetic HAP particles as a model system. Structural characterization of the HAP powder using high-resolution scanning electron microscopy (SEM) shows that the particles are micrometer-sized stable clusters of crystallites that closely resemble the structure of natural enamel. Using SEM image analysis, the authors investigated the influence of HAP particle concentration and particle size on the efficiency of attachment to bovine tooth enamel based on pure mineral-mineral interaction. The results show that both play an important role and can be tailored for optimizing the efficiency of corresponding oral care formulations. The results also reveal the presence of structures resembling mineral bridges at the interfaces between HAP particles and enamel that provide indications for possible interaction mechanisms.