Preparation, microstructure, and mechanical properties of enamel-like nanocomposites for dental repair application

Tooth enamel, as the hardest and the most resilient bioceramic material (~95.5 wt% apatite minerals) in human body, forms complex, highly ordered, hierarchical hetero-phase array structure over millions of years of evolution. This multiscale complex structure endows tooth enamel with excellent mechanical stability (especially the resistance to fracture, wear, and impact), high chop efficiency, and superb durability. However, in the complex oral environment, several factors such as oral bacteria, acidic foods, and mechanical collisions, can cause the dissolution of apatite crystals and even the damage of the enamel, resulting in a series of lesions such as dental caries that severely affects human health and life quality. Therefore, the urgent need for restoring to the normal function of natural teeth by repairing enamel has motivated researchers to develop advanced synthetic strategies for constructing artificial enamels. In this review, based on the understanding of the hierarchical heterogeneous structure-mechanical property-function relationship of natural human tooth enamel, we firstly introduced several synthetic strategies of biomimetic enamel nanocomposites such as cell-based tissue engineering, organic matrix-guided crystal growth, microgel-based microenvironment mineralization, amorphous precursor mineralization, and physicochemical methods, as well as presenting their microstructures and mechanical properties published in recent years. Finally, we discussed the biological safety of these artificial enamel nanocomposites and their dental repair applications.