Synthetic hydroxyapatite: a perfect substitute for dental enamel in biofilm formation studies

In contact with saliva, tooth enamel is covered by biomolecules forming an initial biofilm. Microorganisms attach to the initial biofilm and form the bacterial biofilm, which can provoke diseases. Therefore, dental biofilms are the focus of preventive research. Enamel consists mainly of hydroxyapatite (HAP). Yet, the composition of dental apatite differs between individuals and influences enamel properties. Standardized surfaces might therefore be useful for biofilm research. Synthetic enamel-like HAP pellets perfectly meet the criteria for such well-defined samples. However, systematic investigations of synthetic HAP on oral biofilm formation have never been performed, especially not in comparison to enamel. Therefore, we systematically compared the in situ biofilm formation on synthetic HAP and enamel to investigate the suitability of HAP as a substitute for natural enamel in biofilm formation studies. We observed no differences in formation kinetics, microstructure and subject-specificity of the initial biofilm on both materials. Furthermore, at the proteome level the development of the biofilm on HAP follows the formation patterns observed for enamel. Formation kinetics and morphology of the bacterial biofilm were also subject-dependent and not distinguishable between the two materials. However, the bacterial viability on HAP was higher than on enamel. For bacterial biofilm viability studies, synthetic HAP may therefore even be the preferred substrate as it is more beneficial for identifying antimicrobial agents. In summary, the results prove synthetic HAP as perfect substrate for dental biofilm studies.