Effect of Silica Nanoparticles Silanized by Functional/Functional or Functional/Non-Functional Silanes on the Physicochemical and Mechanical Properties of Dental Nanocomposite Resins  
[PERSON]  
1 Laboratory of Polymer and Color Chemistry and Technology, Department of Chemistry, Aristotle University Thessaloniki, 541 24 Thessaloniki, Greece; [EMAIL_ADDRESS]  
[PERSON]  
2 Division of Dental Tissues' Pathology and Therapeutics (Basic Dental Sciences, Endodontology and Operative Dentistry), School of Dentistry, Aristotle University Thessaloniki, 541 24 Thessaloniki, Greece; [EMAIL_ADDRESS] (A.K.N. ); [EMAIL_ADDRESS] (E.A.K.) [PERSON]  
2 Division of Dental Tissues' Pathology and Therapeutics (Basic Dental Sciences, Endodontology and Operative Dentistry), School of Dentistry, Aristotle University Thessaloniki, 541 24 Thessaloniki, Greece; [EMAIL_ADDRESS] (A.K.N. ); [EMAIL_ADDRESS]. condensation reaction between the silanol groups of filler and the corresponding intermediate silanols of silane produced after the hydrolysis of its alkoxy segments [6]. Hence, the derived siloxane Si-O-Si linkages lead to the formation of interface adhesion between the organic matrix and inorganic filler. This, in turn, might facilitate the stress transition from the flexible matrix to the stiffer filler particles resulting in improved mechanical performance of the dental composite resin [7; 8; 9]. Besides, this link contributes to the enhancement of the overall performance of the composite by protecting the filler against fracture while improving the resistance to hydrolytic degradation [10; 11; 12]. The successful matrix-filler bonding depends on the optimal matching between the organic functional group of the resin monomer and the functional group of the silane [13]. Undoubtedly, the most commonly functional silane coupling agent used in dental composites is 3-(trimethoxysilyl)propyl methacrylate (\(\gamma\)-MPS), which is proven to provide high interfacial stability, thus ensuring promising ultimate physicochemical and mechanical properties of the composite resin [14; 15; 16; 17; 18; 19; 20; 21; 22; 23]. Other typical organofunctional silane coupling agents such as 3-acrylopropyltrimethoxysilane (ACPS) [24], N-alkylaminopropyltrimethoxysilane [25], quaternary ammonium silane compounds (QASiC) [26], 3-styrylethyltrimethoxysilane [24], vinyltrimethoxysilane [24], 3-(isocyanato)propyltriethoxysilane (UDMS) [24; 27; 28], 3-aminopropyltriethoxysilane (APTES), 3-glycidoxypropyltrimethoxysilane (GPS) [29; 30], and styrylethyltrimethoxysilane (SETMS) [31] have also been extensively studied in the research field of dental composite resins. Except for functional organosilanes, non-functional silanes containing an additional hydrolysable alkoxy group instead of a C=C group can also be utilized. For instance, the hydrophobic nature of octyltrimethoxysilane (OTMS) usually renders it preferable toward the limitation of the hydrolysis phenomena over the matrix-filler interfacial region [27; 31; 32; 33] in dental composites, even if it interacts through weaker van der Waals forces. In some cases, non-functional silanes may have two silicon atoms, each one with three alkoxy groups capable of forming extensive cross-linking networks [34] into the composite. The bis-1,2-(triethoxysilyl)ethane (BTSE) [13; 24; 35; 36; 37; 38; 39], bis-[3-(trimethoxysilyl)propyl]amine [37], bis-1,6-(trichloroxysilyl)ethane (BISET), bis-1,6-(trichloroxysilyl)hexane (BISHEX), and bis-1,8-(trichloroxysilyl)octane (BISOCT) [40] are considered to serve as typical cross-linker silanes. In such a way, the formed stiff siloxane films can hinder the diffusion of water molecules inside the network [13], increasing the hydrolytic stability of the composite resin. On the other hand, dual silanization is a process of inorganic filler modification with blends of functional with non-functional silanes in diverse mass ratios.