Effect of Coating Fillers with HEMA-Phosphate Copolymer on the Mechanical Properties of an Experimental Composite Resin

Purpose：Silane-treated dental fillers can degrade through water sorption and hydrolysis. The study evaluates a hydrophobic HEMA-phosphate copolymer as a filler surface treatment and its effect on an experimental composite resin.

System and methods：A HEMA-phosphate copolymer was synthesized and coupled to nano-silica. FTIR and TGA confirmed the coating, and 78 composite specimens with different copolymer levels were tested for three-point flexural strength, microhardness and degree of conversion.

Key findings and mechanism：A HEMA-phosphate copolymer was coupled to nano-silica, with FTIR and TGA confirming the coating. Seventy-eight composite specimens with different copolymer levels were tested for flexural strength, microhardness and degree of conversion. Increasing copolymer content reduced hardness but non-linearly increased flexural strength and conversion, with clearer interfacial improvement when combined with silane. The hydrophobic HEMA-phosphate copolymer reduces water uptake and silane hydrolysis at the filler surface. Phosphate groups interact with silica, while methacrylate groups participate in the resin network, creating an interface that is both more hydrophobic and more covalently connected.

Application value and limits：Phosphate copolymer treatment can complement silane by modifying filler surface chemistry and improving interfacial durability. Hardness, aesthetics and long-term hydrolytic stability still require formulation optimization. The study is based on dental composites and cannot be transferred directly to all industrial fillers. Coating uniformity, filler moisture, resin viscosity and cure must be controlled. The trade-off between improved flexural strength and reduced hardness also requires application-specific balancing.