fa Original article Original article <strong><span dir="LTR">Background and aim: </span></strong><span dir="LTR">Reduction of oral pathogens is very important in the healing of oral ulcers and infections. The side effects of chemical drugs have attracted more attention to medicinal plants. The present study assessed the effect of clove, thyme, garlic, and cinnamon ethanolic extracts on the growth of Streptococcus mutans (S. mutans) and Lactobacillus by measuring the inhibition zone diameter.</span><br> <strong><span dir="LTR">Materials and methods: </span></strong><span dir="LTR">In this in-vitro experimental study, suspensions of standard strains of S. mutans (PTCC5027) and Lactobacillus (PTCC1608) were inoculated on M&uuml;ller-Hinton agar using a sterile swab. 10 g of crushed and dried plants was dissolved in 100 ml of ethanol, and an ethanolic extract was obtained</span> <span dir="LTR">after passing through a filter and evaporation. 10 &mu;l of each extract was poured onto blank discs which were placed on plates containing bacteria. A disc containing the control groups, including 0.2% chlorhexidine and a blank disc, was also placed on the plates.</span><span dir="LTR"> The </span><span dir="LTR">plates were placed in a jar for 24 hours at 37&deg;C and then the</span> <span dir="LTR">inhibition zone diameter around each disc was measured. Ten replicates were performed</span> <span dir="LTR">for each herbal extract. Data were analyzed by analysis of variance (ANOVA) and post hoc tests.</span><br> <strong><span dir="LTR">Results:</span></strong><span dir="LTR"> All four ethanolic herbal extracts were able to inhibit the growth of S. mutans and Lactobacilli. For both bacteria, the largest inhibition zone was observed with chlorhexidine, followed by clove, thyme, garlic, and cinnamon, respectively. There was a significant difference between the inhibition zone diameters formed by the extracts (P<0.01).</span><br> <strong>Conclusion:</strong> Ethanolic extract of clove showed more prominent antibacterial effects than ethanolic extracts of thyme, garlic, and cinnamon. Clove, Thyme, Garlic, Cinnamon, Chlorhexidine, Streptococcus mutans, Lactobacillus, Microbial Sensitivity Tests 7 13 http://jrdms.dentaliau.ac.ir/browse.php?a_code=A-10-557-1&slc_lang=fa&sid=1 N Moezzi ghadim dr.nahid.moezzi@gmail.com 10031947532846008963 10031947532846008963 No Assistant professor, Oral Medicine Dept, Dental Branch of Tehran, M Taghibakhsh mehrdad.taghibakhsh@yahoo.com 10031947532846008964 10031947532846008964 Yes Assistant professor, Oral Medicine Dept, Dental Branch of Tehran, H Godarzi hgod500@yahoo.com 10031947532846008965 10031947532846008965 No Professor, shahid beheshti university of medical sciences N Liravinezhad hoseini nahidliravi@yahoo.com 10031947532846008966 10031947532846008966 No Dentist S Alirezaei dr.somayehalirezaei@gmail.com 10031947532846008967 10031947532846008967 No Assistant professor,Oral Medicine Dept, Dental Branch of Tehran,