Comparison of human enamel and polymer-infiltrated-ceramic network material ENAMIC through micro- and nano-mechanical testing

The mechanical behaviours of a polymer-infiltrated-ceramic-network (PICN) material and human enamel were compared using micro- and nano-mechanical testing. The Vickers hardness and fracture resistance of the two materials were evaluated by the micro-indentation technique. A comparison of the microstructure and crack propagation of both materials was performed by scanning electron microscopy (SEM). From the micro-mechanical level, the Vickers hardness of PICN (3.31 +/- 0.11 GPa) was similar to that of human enamel (3.43 +/- 0.16 GPa), and the micro-creep behaviours of both materials were also alike. However, the average indentation fracture resistance (K-C) of the enamel (1.26 +/- 0.05 MPa.m(1/2)) was significantly lower than that of the PICN (1.81 +/- 0.08 MPa.m(1/2)). Cracks in human enamel are prone to propagate along the rod sheath, while within the PICN, these mainly extend through the ceramic matrix, and are deflected at the polymer-ceramic interfaces. From the nano-mechanical testing, the nanohardness, elastic modulus and nanoindentation creep response of PICN were significant different from that of human enamel. Furthermore, the creep capacity of the PICN was mainly influenced by the infiltrated polymer matrix. Overall, PICN has been found to be more effective than human enamel in crack growth resistance at the microscopic level. The mutually chimeric network structure improves PICN's nano-mechanical behaviour, and the infiltrated polymer matrix facilitates time-dependent deformation that helps dissipate strain energy and prevent fracture. (C) 2016 Published by Elsevier Ltd.