Enhanced mechanical properties and reduced polymerization shrinkage in a light-cured flowable dental nanocomposite via incorporation of silane-functionalized ScYSZ nanoparticles

The present investigation centers on the formulation and characterization of a light-cured nanohybrid dental composite, which incorporates a newly-proposed hybrid filler system composed of barium glass microparticles alongside surface-engineered zirconia nanoparticles. Notably, scandia- and yttria-stabilized zirconia nanoparticles (ScYSZ NPs) are introduced here for the first time within a methacrylate-based resin matrix. To improve interfacial compatibility, these nanoparticles were treated with γ-methacryloxypropyltrimethoxysilane (MPS), and three distinct dispersion techniques were systematically evaluated to secure a uniform particle distribution. Following identification of the optimal processing route, surface-modified ScYSZ (F-ScYSZ) was loaded at 1, 2.5, and 5 wt.% into a base resin already containing 48 wt.% barium glass. The resulting composites underwent thorough characterization through FT-IR, XRD, MTT and FE-SEM analysis. Mechanical response was quantified through three-point bending tests and Vickers indentation, whereas polymerization shrinkage was determined in line with ISO 17304 guidelines. The analyses verified the successful attachment of MPS moieties onto the nanoparticle surfaces and confirmed the retention of the non-transformable tetragonal (t′) polymorph within the ScYSZ structure. Incorporation of F-ScYSZ at 1 and 2.5 wt.% brought about substantial gains in mechanical performance; the best-performing formulation at 2.5 wt.% delivered a flexural strength of 134.33 MPa, an elastic modulus of 4.58 GPa, and a microhardness of 39.4 HV. At the 5 wt.% level, however, observable particle agglomeration occurred, which was accompanied by a pronounced deterioration in overall properties. Meanwhile, a consistent drop in polymerization shrinkage was noted with increasing filler loading. A side-by-side comparison against commercially available resin‑based composites reveals that the newly developed ScYSZ-reinforced nanohybrid achieves an attractive trade-off between enhanced mechanical strength and lower volumetric shrinkage, underscoring its viability as a high-performance flowable material for restorative dentistry applications.