Secondary caries due to biofilm acids is a primary cause of dental composite restoration failure.To date,there have been no reports of dental composites that can repel protein adsorption and inhibit bacteria attachment.The objectives of this study were to develop a protein-repellent dental composite by incorporating 2-methacryloyloxyethyl phosphorylcholine(MPC) and to investigate for the first time the effects of MPC mass fraction on protein adsorption,bacteria attachment,biofilm growth,and mechanical properties.Composites were synthesized with 0(control),0.75%,1.5%,2.25%,3%,4.5%and 6%of MPC by mass.A commercial composite was also tested as a control.Mechanical properties were measured in three-point flexure.Protein adsorption onto the composite was determined by the microbicinchoninic acid method.A human saliva microcosm biofilm model was used.Early attachment at 4 h,biofilm at 2 days,live/dead staining and colony-forming units(CFUs) of biofilms grown on the composites were investigated.Composites with MPC of up to 3%had mechanical properties similar to those without MPC and those of the commercial control,whereas 4.5%and 6%MPC decreased the mechanical properties(P<0.05).Increasing MPC from 0 to 3%reduced the protein adsorption on composites(P<0.05).The composite with 3%MPC had protein adsorption that was 1/12 that of the control(P<0.05).Oral bacteria early attachment and biofilm growth were also greatly reduced on the composite with 3%MPC,compared to the control(P<0.05).In conclusion,incorporation of MPC into composites at 3%greatly reduced protein adsorption,bacteria attachment and biofilm CFUs,without compromising mechanical properties.Protein-repellent composites could help to repel bacteria attachment and plaque build-up to reduce secondary caries.The protein-repellent method might be applicable to other dental materials. Secondary caries due to biofilm acids is a primary cause of dental composite restoration failure. To date, there have been no reports of dental composites that can repel protein adsorption and inhibit bacteria attachment. These objectives of this study were to develop a protein-repellent dental composite by incorporating 2-methacryloyloxyethyl phosphorylcholine (MPC) and to investigate for the first time the effects of MPC mass fraction on protein adsorption, bacteria attachment, biofilm growth, and mechanical properties. Composites were synthesized with 0 (control), 0.75%, 1.5 %, 2.25%, 3%, 4.5% and 6% of MPC by mass. A commercial composite was also tested as a control. Mechanical properties were measured in three-point flexure. Protein adsorption onto the composite was determined by the microbicinchoninic acid method .A human saliva microcosm biofilm model was used. Early attachment at 4 h, biofilm at 2 days, live / dead staining and colony-forming units (CFUs) of biofilms grown on the composites were investigated 4.5% and 6% MPC decreased the mechanical properties (P <0.05). Increasing MPC from 0 to 3% reduced the composite with 3% MPC had protein adsorption that was 1/12 that of the control (P <0.05) .Oral bacteria early attachment and biofilm growth were also significantly reduced on the composite with 3% MPC, compared to the control (P <0.05). In conclusion, incorporation of MPC into composites at 3% greatly reduced protein adsorption, bacteria attachment and biofilm CFUs, without compromising mechanical properties. Protein-repellent composites could help to repel bacteria attachment and plaque build-up to reduce secondary caries.The protein-repellent method might be applicable to other dental materials.