Purpose:　To　investigate　the　inhibition　of　Streptococcus　mutans　(S.mutans)　and　its　biofilm　by　AgBr-nanoparticles　(NP)　@CTMAB　(cetyltrimethyl-ammonium　bromide)　and　evaluate　the　changes　in　Polymethyl　methacrylate　(PMMA)＇s　surface　roughness　(Ra),　microhardness,　and　flexural　strength　during　prolonged　immersion　in　AgBr-NP@CTMAB　for　application　in　the　denture　cleaning　industry.　Patients　and　Methods:　The　antibacterial　activity　of　AgBr-NP@CTMAB　against　S.mutans　was　measured　colony　formation　assay,　OD600　and　laser　confocal　microscopy.　Changes　in　the　specimens＇　values　for　surface　roughness,　microhardness,　and　flexural　strength　(MPa)　were　measured　after　immersion　solutions　for　180　or　360　days.　Results:　The　AgBr-NP@CTMAB　solution　exhibited　a　robust　antibacterial　effect　on　planktonic　S.　mutans,　with　a　minimum　bactericidal　concentration　of　5　mu　g/mL.　The　10　mu　g/mL　AgBr-NP@CTMAB　solution　efficiently　inhibited　S.　mutans　biofilm　formation.　(2)　No　significant　difference　in　surface　roughness　after　immersion　in　AgBr-NP@CTMAB　(10　mu　g/mL　and　20　mu　g/mL)　comparing　with　distilled　water　(P　＞　0.05)　and　Polident　had　significantly　higher　than　distilled　water　(P　＜　0.05).　There　was　a　significant　decrease　in　the　surface　hardness　of　the　PMMA　specimens　that　were　immersed　in　the　Polident　compared　with　those　in　distilled　water　(P　＜　0.05).　While,　no　significant　differences　in　surface　hardness　after　immersion　in　the　AgBr-NP@CTMAB　(P　＞　0.05).　The　result　of　flexural　strength　suggested　that　there　was　no　statistically　significant　difference　(P　＜　0.05)　between　AgBr-NP@CTMAB　as　well　as　Polident　and　water.　Conclusion:　AgBrNP@CTMAB　can　efficiently　inhibit　the　growth　of　plankton　S.mutans　and　biofilm　formation,　without　affecting　the　flexural　strength,　microhardness,　or　surface　roughness　of　PMMA.　Therefore,　AgBrNP@CTMAB　holds　promise　as　a　new　denture　cleaning　agent.