bstract Polymer-based dental composites always face bulk/marginal fracture as one of the main challenges reducing this type of dental restorations' lifespan. In this study, the effect of mesoporous silica aerogel and poly (methyl methacrylate) (PMMA) mesocapsules containing ethyl 2-cyanoacrylate (EC) on the physical and mechanical properties of light-cured acrylic resin was evaluated separately. Silica aerogels were prepared according to the two-step sol-gel process and drying at ambient pressure. Also, silica aerogels were surface-modified by trimethylchlorosilane (TMCS) and 3-(trimethoxycyl) propyl methacrylate (?-MPS) silanes to investigate the surface properties of silica aerogels on the physical and mechanical properties of light acrylic-based resins. Characterization of silica aerogels was performed by nitrogen adsorption-desorption test, Fourier transform infrared spectroscopy (FTIR), and field emission scanning electron microscopy (FESEM). According to the results, mesoporous silica aerogels were prepared with high specific surface area (550-650 m2/g), high porosity (77%), mesometric pores (10-11 nm), and successful surface modification by silane agents. PMMA mesocapsules were also prepared by emulsion electrospray or single-nozzle electrospray method. Mesocapsules were characterized by FTIR, FESEM, and thermogravimetric analysis (TGA). According to the results, mesocapsules were prepared with spherical morphology and an average size of 520 nm containing two components of PMMA (shell) and EC (core). Next, light-cure resin composites were prepared based on bisphenol-A glyceroate dimethacrylate (BisGMA) and triethylene glycol dimethacrylate (TEGDMA) monomers. Composites containing silica aerogels (0 to 35 wt.%) and composites containing mesocapsules (0 to 4 wt.%) were prepared, and their physical and mechanical properties were evaluated. For this purpose, the flexural modulus (FM) and flexural strength (FS) of composites were measured according to the three-point bending method. Fracture toughness (FT) was also measured by single-edge V-notch beam three-point bending method (SEVNB). Fractography of the composites was also performed to understand how silica aerogels and mesocapsules influence the composites' mechanical properties. Also, the water contact angle test of the composites was performed to investigate silica aerogels' effect on the hydrophobicity of the composites. According to the results, the increase of mesocapsules content in the composite did not have a negative effect on FM and FS. Besides, according to the composites' fracture surface, it was observed that the mesocapsules were not able to break and trigger the self-healing property for the composite due to the weak adhesion strength of resin-mesocapsule interface. According to this study, SEVNB is not a suitable method for evaluating the self-healing efficiency of dental composites containing mesocapsules. On the other hand, increasing the silica aerogels fillers content increased the FM, FS, and FT of composites. Thus, increasing ?-MPS- and TMCS-modified silica aerogels in the range of 0-30 wt.% improved the FM by 86% and 42%, respectively. Also, composites containing 15 wt.% of ?-MPS-modified silica aerogel and composites containing 5% by weight of TMCS-modified silica aerogel showed the highest FM values 94.4 and 80.8 MPa, respectively. The increase of ?-MPS-modified silica aerogel (in the range of 5-30 wt.%) and TMCS-modified silica aerogel (in the range of 5-25 wt.%) improved the FT of the composites by 23%. According to fractography, the absence of exposed filler particles at all filler weight percentages indicated a strong interaction at the interface between the filler phase and the polymer matrix. Also, surface modification of silica aerogels by ?-MPS resulted in better wettability and penetration of the resin into silica aerogels' mesoporous structure. Fewer structural defects such as trapped air bubbles were detected in the fracture surface of composites containing ?-MPS-modified silica aerosols compared to composites containing TMCS-modified silica aerogels. Increasing silica aerogel fillers content increased the water contact angle of the resulting composites. According to this study, the use of PMMA mesocapsules did not have a negative effect on the mechanical properties of acrylic-based dental composites, and the use of silica aerogels as a filler enhanced the mechanical properties of acrylic-based dental composites. Keywords: acrylate-based light-cure composites, mechanical properties, mesoporous silica, poly (methyl methacrylate) mesocapsules containing ethyl 2-cyanoacrylate.