en Infectious disease (Molecular and Cellular aspects) Infectious disease (Molecular and Cellular aspects) Original Article Original Article <p><span style="font-size:12px;"><span style="font-family:Tahoma;"><span style="line-height:107%">Dental caries is among the most prevalent chronic diseases. It arises from bacterial biofilm formation on tooth surfaces due to metabolic activity. <a name="_Hlk191490384"></a><a name="_Hlk191490346"><i>Streptococcus</i> <i>mutans</i> </a>(<i>S</i>. <i>mutans</i>) is a key pathogen implicated in the development of dental caries. As bacterial resistance to conventional treatments increases, there is a growing interest in using novel compounds that possess antibacterial and antibiofilm properties. This study evaluated the effect of <a name="_Hlk191491341">chitosan-arginine nanoparticles (CS-Arg NPs)</a> and <a name="_Hlk191491365">sodium fluoride (NaF) </a>on inhibiting <i>S</i>. <i>mutans</i>&#39; growth.<b> </b>After synthesizing CS-Arg NPs, their size, morphology, and chemical structure were evaluated. The broth microdilution method determined the minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of CS-Arg NPs and NaF. The combined antibacterial and antibiofilm effect of CS-Arg NPs and NaF was assessed using the checkerboard method.<b> </b>The CS-Arg NPs had an average size of 269.9 nm with a zeta potential of +38.3 mV. The MIC of <i>S</i>. <i>mutans</i> for CS-Arg NPs and NaF was 312 &micro;g/mL and 625 &micro;g/mL, respectively, and the MBC for these NPs and NaF was 625 &micro;g/mL and 2500 &micro;g/mL, respectively. The fractional inhibitory concentration index (FICI) of the combination of CS-Arg NPs and NaF showed an additive effect (FICI = 1). The inhibitory effect of different concentrations of CS-Arg NPs and NaF, alone or in combination, on biofilm formation in the studied strain ranged from approximately 12% to 81%.<b> </b>This study demonstrated that CS-Arg NPs have antibacterial and antibiofilm properties against <i>S</i>. <i>mutans</i>, and their combination with NaF can enhance these antibacterial effects. These findings suggest that CS-Arg NPs and NaF, as a novel combination, could effectively develop oral hygiene products.</span><br> &nbsp;</span></span></p> Chitosan, Arginine, Sodium fluoride, Streptococcus mutans. 637 645 http://ijmcmed.org/browse.php?a_code=A-10-8232-1&slc_lang=en&sid=1 Fahimeh Daneshyar Fa.daneshyar70@gmail.com 100319475328460034590 100319475328460034590 No Department of Pediatric dentistry, Faculty of Dentistry, Hamadan University of Medical Sciences, Hamadan, Iran Mohammad Yousef Alikhani alikhani43@yahoo.com 100319475328460034591 100319475328460034591 No Infectious disease research center, Avicenna Institute of Clinical Sciences, Hamadan University of Medical Sciences, Hamadan, Iran Soudeh Tayebi soudeh_t_1986@yahoo.com 100319475328460034592 100319475328460034592 No Department of Pediatric dentistry, Faculty of Dentistry, Hamadan University of Medical Sciences, Hamadan, Iran Delaram Abedi Firouzjaei abedidelaram@yahoo.com 100319475328460034593 0009-0009-2166-482X Yes Department of Pediatric dentistry, Faculty of Dentistry, Hamadan University of Medical Sciences, Hamadan, Iran