Effect of coupling agents on the local mechanical properties of bioactive dental composites by the nano-indentation technique

Objectives To examine the use of nano-indentation as a method of determining the interfacial mechanics of bioactive composites for mandibular bone substitutes. Methods Three coupling agents (PMMA-MAA, PMMA-MA and silane) were used to treat hydroxyapatite (HA) particles before incorporation into a polymethylmethacrylate (PMMA) matrix. Nano-indentation was used to determine the hardness and Youngʹs modulus on the HA particle surface, at the HA/PMMA interface and in the PMMA matrix region for each of the four groups. In addition bulk four-point bending tests were conducted on each of the four groups as a comparison. Results The findings resulted in significant differences in the local interfacial Youngʹs modulus between the polymer-treated composites and the uncoupled control specimens with a marked improvement (50%) in modulus with either polymertreated group. Similarly, the bending modulus of the polymer-treated groups was significantly higher than the un-treated control group; however, these differences were not as pronounced (approximately 15%). Significance The co-polymer-treated composites resulted in improved interfacial modulus as compared to the un-treated controls and that the nano-indentation technique is a powerful tool for understanding the local interfacial mechanics of bioactive composites.