Surface modification of urchin-like serried hydroxyapatite with sol-gel method and its application in dental composites

The novel surface modification method of urchin-like serried hydroxyapatite (USHA) was reported in this work, and the effect of this method on mechanical and the remineralization performances of dental composites were also explored. A silica sol-gel layer (SSL) was firstly coated onto USHA surface using a sol-gel method with tetraethoxysilane (TEOS) as precursor, and the coating thickness of SSL was adjusted by the reaction time. The obtained TUSHA material was further modified with 3-methacryloxypropyl trimethoxysilane (gamma-MPS) to get silanized TUSHA (STUSHA). Then, these STUSHA fillers with different loading fractions were used as the reinforcement for dental composites, and the unfilled resin matrix was used as control. The results demonstrated that the reaction time of the sol-gel method had a prominent effect on the morphologies of TUSHA, and the synthesized TUSHA-4 h (reaction time: 4 h) exhibited the entire urchin-like structure and the desirable SSL thickness. In addition, at the filler loading of 50 wt%, the composite reinforced with STUSHA-4 h presented the excellent overall performance, especially for flexural strength, and the desirable matrix/filler interfacial bonding. In vitro remineralization of this composite confirmed that thick and dense layers were covered on its surface. Therefore, the existence of SSL coating effectively enhanced the mechanical performance of dental composites without compromising the remineralization activity.