67 - Development of a Magnetic Nanorod Reinforced Bulk Fill Composite

Abstract

The purpose of this study is to develop a magnetically active dental composite that has improved mechanical properties. Methods of resin formulation were explored for nanomaterials incorporation and to monitor the effect on mechanical reinforcement. Magnetically-active composite resins (MCRs) were formulated up to 0.05% (w/w) of iron oxide nanorods (GetNanoMaterials) with Filtek (A2 Shade) dental composite resins. Control samples (Filtek OneBulk and Flowable) were prepared in the same manner as MCRs but without nanorods. These formulations were dispensed into 3-D printed molds and photocured (3 M Elipar DeepCure-S and Paradigm LEDs at 1470 and 1200 mW/cm 2 , respectively) for 20 s on one or both sides depending on analyses. Physical and chemical evaluations of MCRs were analyzed by depth-of-cure (DoC) testing (ISO 4049), shade determination (Vita shade guide and Vita Easyshade), shear bond and compressive strength using the Alliance test system by Materials Test System (MTS). Results were analyzed using one-way ANOVA / post-hoc Tukey test (alpha = 0.05). Compared to the flowable controls, 0.01% (w/w) MCRs were found to have: (1) change in hue, value, and chroma, having D4 instead of A2 shade due to the dark color of the MCRs. (2) statistical reduction in DoC (2.4 0.1 vs 3.4 0.2 mm, N=10, p<0.0001) and compressive strength (231.0 34.8 vs 252.1 52.9 N/mm 2 , N=10, p<0.05). However, shear bond tests were not statistically different (2.9 1.3 vs 4.1 3.0 N/mm 2 , N=10, p>0.05). Alternatively, 0.001% (w/w) MCRs (C2 shade) showed no statistical differences (p>0.05, N=10) for compression, shear bond, and DoC with the controls, at 241.2 61.8 N/mm 2 , 2.6 1.1 N/mm 2 , and 3.4 0.1 mm, respectively. Notably, one bulk sample revealed a similar trend as flowable samples when compared to their controls. Overall, magnetic nanorod integration into commercial composites were promising; however, MCRs mechanical and bond strengths were mixed. Theoretically, the random orientation of the magnetic nanorods could be a probable cause for decreased compressive strength and depth of cure. Future work will involve nanorod alignment using external magnetic fields during curing to strengthen the framework, followed by the investigation of 3-D printing applications.