In vitro investigation of coupling-agent-free dental restorative composite based on nano-porous alumina fillers.

Objectives: The study aims at demonstrating the feasibility of a novel type of coupling-agent-free resin composite based on nano-porous fillers.

Methods: The fillers were obtained by ball-milling anodic alumina membranes. Composites were prepared with standard resin at maximum loading of 50% by weight. The resin matrix penetration into the pores was verified visually by scanning electron microscopy and mechanically by atomic force microscopy in force modulation mode. The dynamic flexural modulus at 1Hz was measured by dynamic mechanical analysis. Silver nanoparticles were also synthesized in the pores and their release was investigated with inductive coupled plasma optical emission spectrometry.

Results: A storage modulus of 5GPa was measured, similar to the ∼6GPa ones of two coupling-agent-based dental restorative composites used for comparison, which is a promising starting point, additionally showing better one-year equivalent ageing as compared to both commercial materials. Loading the pores with silver nanoparticles was demonstrated as well as their subsequent release in a model system.

Significance: The alumina micro-particles with interconnected nano-pores allow mechanical interlocking between fillers and matrix without the need for chemical bonding. This material is also promising for being made bio-active, after pore filling with different agents.