Development of a Magnetic Nanorod Reinforced Bulk Fill Composite

Objectives: Resin-based composites have been used in clinical dentistry as direct dental restorative materials for decades. Traditionally, these materials are used in the anterior and smaller, less load-bearing, posterior areas. However in recent years, there has been an increase in the use of direct packable and bulk-fill composite materials for larger posterior tooth restorations, which require higher strength and longer durability due to higher masticatory forces. Recent studies have shown that these physical properties of composites can be significantly improved by the incorporation of nanomaterials and fiber-reinforcement. In industry, the utilization of magnetically aligned nanorods into resin materials have been used to dramatically improve their physical properties (ie. mechanical strength and fracture resistance). In this current work, the objective is to develop a dental composite with magnetically active nanostructures which can be utilized to enhance mechanical strength inherently and actively through magnetic field alignment.
Methods: Magnetically-active composite resins were formulated by mixing up to 0.05% (w/w) of commercial superparamagnetic iron oxide nanorods and low-viscosity bulk flowable composite resins. Physical and chemical evaluations of magnetic resins, such as depth of cure, shade determination, and compressive strength were performed.
Results: Results demonstrated that inclusion of nanorods at 0.05% (w/w) significantly darkened the shade of the resin beyond the limit of the guide (D4). Additionally at this weight percentage, the mechanical strength was only 38% of the control with a depth of cure of 71%. However, when reduced to 0.005% (w/w), there was a minimal effect on the shade of the resin (B2) with the resin maintaining 86% of the compressive strength.
Conclusions: Overall, the results demonstrated successful integration of magnetic nanorods into composite resins. Future work involves nanorod alignment using an external magnetic field before photo-curing to assess any improvements in the physical and mechanical properties of the magnetic resin.