ABSTRAKPendahuluan: Penggunaan alat ortodonti dapat mempengaruhi ekosistem rongga mulut seperti meningkatnya jumlah bakteri Streptococcus mutans. Clear retainer merupakan alat ortodonti yang memerlukan sterilisasi sebelum dapat digunakan kembali. Penggunaan tanaman herbal kemangi (Ocimum basilicum) dikembangkan menjadi alternatif bahan sterilisasi alami. Penelitian ini bertujuan menganalisis daya antibakteri melalui zona hambat, konsentrasi hambat minimum (KHM), konsentrasi bunuh minimum (KBM), dan penghitungan jumlah koloni bakteri Streptococcus mutans pada clear retainer ortodonti yang telah disterilisasi dengan fraksi etil asetat daun kemangi dan Chlorhexidine. Metode: Jenis penelitian eksperimental laboratoris, menggunakan fraksi etil asetat kemangi 5%. Kontrol penelitian adalah Chlorhexidine 2%. Populasi dan sampel adalah satu ose Streptococcus mutans ATCC 25175. Pengujian zona hambat dan jumlah koloni dilakukan pada media agar yang sudah ditumbuhi bakteri setelah diinkubasi pada suhu 370C selama 48 jam, pengujian KHM KBM dilakukan dengan metoda mikrodilusi menggunakan microplate 96 yang diinkubasi pada suhu 370C selama 48 jam. Pengukuran KHM dan KBM menggunakan spektrofotometer pada ELISA reader. Hasil penelitian dianalisis dengan uji statistik t-test. Hasil: Terdapat zona hambat pada sampel kemangi dengan konsentrasi 5%, sedangkan Chlorhexidine 2%. KHM dan KBM daun kemangi pada 3125 ppm dan 6250 ppm, sedangkan Chlorhexidine pada 3,125 ppm dan 6,250 ppm. Uji statistik t-test memperlihatkan tidak terdapat perbedaan yang signifikan pada penurunan jumlah koloni bakteri Streptococcus mutans yang telah disterilisasi dengan daun kemangi dan Chlorhexidine. Simpulan: Fraksi etil asetat kemangi memiliki daya antibakteri terhadap Streptococcus mutans, terlihat dengan adanya zona hambat pada pemeriksaan KHM, KBM, dan penurunan koloni bakteri pada media agar. Kata kunci: uji daya antibakteri; Ocimum bacilicum; Streptococcus mutans ATCC 25175; clear retainer ABSTRACTIntroduction: Orthodontic appliances can affect the oral cavity ecosystem by increasing the number of Streptococcus mutans bacteria. A clear retainer is an orthodontic appliance that requires sterilisation prior to usage. The basil plant (Ocimum basilicum) was developed as an alternative natural sterilisation material. This study was aimed to analyse the inhibitory zone, minimum inhibitory concentration (MIC), minimum killing concentration (MKC), and count the number of Streptococcus mutans bacteria on clear retainers that have been sterilised with ethyl acetate fraction of basil leaves and chlorhexidine. Methods: This research was an experimental laboratory that used the 5% basil ethyl acetate fraction and 2% chlorhexidine as control. The population and sample were one ose of Streptococcus mutans ATCC 25175. Examination of the inhibitory zone and the number of colonies was performed on agar media with cultured bacteria after being incubated at 37°C for 48 hours. Microdilution testing was performed using the microdilution method using a 96 microplate incubated at 37°C for 48 hours. MIC and MKC were measured using a spectrophotometer on an ELISA reader. The results of the study were analysed with the t-test. Results: There was an inhibitory zone found in the basil group with a concentration of 5% and the control group (2% chlorhexidine). MIC and MBC of basil leave at 3,125 ppm and 6,250 ppm, while chlorhexidine at 3,125 ppm and 6,250 ppm, respectively. Statistical t-test results showed no significant difference in the decreasing number of Streptococcus mutans colonies after sterilisation with basil leaves and chlorhexidine. Conclusions: The ethyl acetate fraction of basil has antibacterial potential on Streptococcus mutans, as seen by the presence of an inhibitory zone during the MIC and MKC examination and decreasing number of bacterial colonies on agar media.Keywords: antibacterial potential; Ocimum basilicum; Streptococcus mutans; clear retainer