Modulated regeneration of acid-etched human tooth enamel by a functionalized dendrimer that is an analog of amelogenin

In the bioinspired repair process of tooth enamel, it is important to simultaneously mimic the organic-matrix-induced biomineralization and increase the binding strength at the remineralization interface. In this work, a fourth-generation polyamidoamine dendrimer (PAMAM) is modified by dimethyl phosphate to obtain phosphate-terminated dendrimer (PAMAM-PO₃H₂) since it has a similar dimensional scale and peripheral functionalities to that of amelogenin, which plays important role in the natural development process of enamel. Its phosphate group has stronger affinity for calcium ion than carboxyl group and can simultaneously provide strong hydroxyapatite (HA)-binding capability. The MTT assay demonstrates the low cytotoxicity of PAMAM-PO₃H₂. Adsorption tests indicate that PAMAM-PO₃H₂ can be tightly adsorbed on the human tooth enamel. Scanning electron microscopy and X-ray diffraction are used to analyze the remineralization process. After being incubated in artificial saliva for 3 weeks, there is a newly generated HA layer of 11.23 μm thickness on the acid-etched tooth enamel treated by PAMAM-PO₃H₂, while the thickness for the carboxyl-terminated one (PAMAM-COOH) is only 6.02 μm. PAMAM-PO₃H₂ can regulate the remineralization process to form ordered new crystals oriented along the Z-axis and produce an enamel prism-like structure that is similar to that of natural tooth enamel. The animal experiment also demonstrates that PAMAM-PO₃H₂ can induce significant HA regeneration in the oral cavity of rats. Thus PAMAM-PO₃H₂ shows great potential as a biomimetic restorative material for human tooth enamel.