Hydroxyapatite Pellets as Versatile Model Surfaces for Systematic Adhesion Studies on Enamel: A Force Spectroscopy Case Study

Abstract

Research into materials for medical application draws inspiration from naturally occurring or synthesized surfaces, just like many other research directions. For medical application of materials, particular attention has to be paid to biocompatibility, osseointegration, and bacterial adhesion behavior. To understand their properties and behavior, experimental studies with natural materials such as teeth are strongly required. The results, however, may be highly case-dependent because natural surfaces have the disadvantage of being subject to wide variations, for instance in their chemical composition, structure, morphology, roughness, and porosity. A synthetic surface which mimics enamel in its performance with respect to bacterial adhesion and biocompatibility would, therefore, facilitate systematic studies much better. In this study, we discuss the possibility of using hydroxyapatite (HAp) pellets to simulate the surfaces of teeth and show the possibility and limitations of using a model surface. We performed single-cell force spectroscopy with single Staphylococcus aureus cells to measure adhesion-related parameters such as adhesion force and rupture length of cell wall proteins binding to HAp and enamel. We also examine the influence of blood plasma and saliva on the adhesion properties of S. aureus. The results of these measurements are matched to water wettability, elemental composition of the samples, and the change in the macromolecules adsorbed over time on the surface. We found that the adhesion properties of S. aureus were similar on HAp and enamel samples under all conditions: Significant decreases in adhesion strength were found equally in the presence of saliva or blood plasma on both surfaces. We therefore conclude that HAp pellets are a good alternative for natural dental material. This is especially true when slight variations in the physicochemical properties of the natural materials may affect the experimental series.

Improve Dentin Bonding Performance Using a Hydrolytically Stable, Ether-Based Primer

“…On the other hand, enamel and dentin layers in the tooth's structure are predominantly composed of HA crystals [48]. Therefore, hydroxyapatite crystals have been used as versatile model surfaces that mimic enamel in their performance concerning bacterial adhesion [49], remineralization/demineralization [50], tooth staining [51], and other properties [52]. Although dentin only contains ~70wt% of HA, HA crystals were used in this study to confirm that primers can chemically bond to HA (and presumably the tooth surface), to compare the hydrophilicity of two primers, and to test the stability of the bonded primers against esterase challenge.…”