Restoration of human tooth enamel

Human tooth enamel, consisting of hydroxyapatite nanocrystals (∼85–88 vol%), proteins (∼2-3 vol%), and requisite water (∼10–12 vol%), is 1–3 mm thick at the outer layer of the tooth. It possesses remarkable properties such as high stiffness, hardness, strength, and viscoelasticity. However, when tooth enamel undergoes deterioration due to various factors, including unhealthy dietary habits, wear and tear of the enamel and others, it progresses from surface stains to enamel loss, ultimately necessitating entire tooth enamel replacement. This is because the tooth enamel lacks the ability to generate cells on the damaged side of the tooth after eruption, preventing self-repair. Thus, enamel repair materials are in urgent demand, but clinical tooth enamel restorative materials nowadays cannot fully replicate the microstructure and function of natural tooth enamel. Numerous efforts have been made to develop the next generation restorative materials for tooth enamel to address different types of damage, including stains, defects, and loss. Here, we introduce the fundamental characteristics of tooth enamel at the beginning. Then, we provide a summary of the preparation process and function of existing tooth enamel restorative materials based on the various types of tooth enamel defects in detail. Finally, suggestions and development directions in the field of tooth enamel restoration are presented, with the aim of providing a theoretical reference for the creation of tooth enamel restorative materials that better match the microstructure and function of natural tooth enamel.