Calcium Phosphate Oligomers as Inorganic Glue for Microcrack Repair in Teeth

Inorganic materials are easily cracked due to their brittle nature, and the repair of these cracks, especially microsized cracks, by inherent inorganic components is a long-term challenge. In addition to dental caries and periodontal disease, tooth cracks and structural fractures are increasingly considered important factors leading to tooth loss in clinical practice. Herein, we propose a calcium phosphate oligomer (CPO) glue by systematically elucidating its mass transport behavior in microcracks, realizing the repair of tooth cracks with an improvement of mechanical properties. We discovered a critical concentration of the CPO ethanol solution that can efficiently infiltrate tooth microcracks and deliver sufficient calcium phosphate for millimeter-scale crack remineralization. The CPO glue-based repair eliminated the gaps between remineralized calcium phosphate and enamel, which cannot be achieved by clinical resins or other inorganic nanoparticles. After oral condition-induced crystallization, the microcracks can be fully sealed, leading to an improvement in both the macroscopic load-bearing capacity and the microscopic local mechanical property. This work provides a theoretical foundation for the design of tooth-cracked materials. Moreover, this work establishes a promising strategy for the repair of inorganic microcracks, which commonly occur in biological hard tissues, construction materials, and cultural heritage.