Surface charge on polymeric implants and calcified tissues: interfacial implications

Samples of human bone, dentin, and enamel were analyzed through the technique known as thermally stimulated discharge (TSD). It is possible through this technique to detect current flow resulting from appearance or loss of net polarization in a material. Samples of freshly extracted tissue give rise to well-defined TSD current maximal without having been exposed to external electrical potentials. Calculation of activation energies for these currents and their thermal range suggests the involvement of collagen denaturation in the loss of appearance of a net surface charge on bone and dentin surfaces. In the case of enamel samples, TSD current maxima are possibly the result of dipolar alignment in water or biopolymers by surface charges in the mineral phase. Interfacial implications of surface charge were studied through the measurement of adhesive strength in dentin/acrylic polymer joints. Enhancement of joint strength by a factor of two or higher was observed when powder particles of the experimental adhesive carried externally induced surface charge. It is hypothesized that electrostatic coupling between polarization domains on the tissue surface and the setting implant improves wetting and produces stronger interfaces.