en علوم پایه پزشکی Basic Medical Sciences تحقیقی Original article <strong>Background and objectives:</strong> The association of oral micro-organisms with infectious diseases such as bacterial endocarditis is a concern in dentistry. Bacterial endocarditis is a serious disease with a mortality rate of 40%. The present study was conducted to investigate the effect of using chlorhexidine mouthwash on concentrations of some groups of bacteria in gingival sulcus, which is the main contact point of oral flora with circulating blood during scaling.<br> <strong>&shy;&shy;&shy; Methods</strong>: In this Randomized controlled clinical trial, participants were selected among referrals to the department of gingival diseases of Yazd dental school. Participants underwent determining plaque index and after scaling, sampling of the buccal and lingual gingival groove of mandibular central and lateral teeth was performed by paper with walking movement.<br> <strong>Results:</strong> participants were 53 patients who divided into two groups. Group A consisted of 27 patients <u>(</u>15 women and 12 men) ranging in age from 21 to 54 years mean of 35) who used 50 mL chlorhexidine mouthwash and Group B consisted of 26 patients <u>(</u>13 females and 13 males) ranging in age from 19 to 51 years old with a mean of 35.76 who used 50 mL normal saline before scaling. Study groups were not significantly different in terms of age, sex and plaque index. (P-values= 0.755, 0.348 and 0.708)<br> Mann Whitney-Wilcoxon test compared the counted values of <em>Streptococcus viridance</em> and <em>Staphylococcus aureus</em> in control group was significantly higher than the study group. (P-value = 0.000)<br> <strong>Conclusion</strong>: according to the results of our study chlorhexidine mouthwash prior to scaling teeth significantly reduced <em>Streptococcus viridance</em> and <em>Staphylococcus aureus</em> colony counts and could be recommended as a complementary agent for antibiotic prophylaxis in high risk patients prone to endocarditis, or as the only agent in moderate risk cardiac patients that antibiotic prophylaxis does not been used. Infectious endocarditis,Streptococcus viridance,chlorhexidine 22 30 http://goums.ac.ir/jorjanijournal/browse.php?a_code=A-10-505-1&slc_lang=en&sid=1 Mohammad-Hassan Akhavan Karbassi pooriakarbassi@gmail.com 10031947532846005694 10031947532846005694 No Department of Oral Medicine, Shahid Sadoughi University of Medical Science, Yazd, Iran Assistant Professor, Department of Oral Medicine, Shahid Sadoughi University of Medical Science, Yazd, Iran Fatemeh Owlia dr.owlia@gmail.com 10031947532846005695 10031947532846005695 No Department of Oral Medicine, Shahid Sadoughi University of Medical Science, Yazd, Iran Assistant Professor, Department of Oral Medicine, Shahid Sadoughi University of Medical Science, Yazd, Iran Henghameh Zandi hengameh_zandi@yahoo.com 10031947532846005696 10031947532846005696 No Department of Medical Microbiology, Shahid Sadoughi University of Medical Science, Yazd, Iran Assistant Professor, Department of Oral Medicine, Shahid Sadoughi University of Medical Science, Yazd, Iran Samira Hajimaghsoodi dents1390@gmail.com 10031947532846005697 10031947532846005697 Yes Department of Oral Medicine, Shahid Sadoughi University of Medical Science, Yazd, Iran Assistant Professor, Department of Oral Medicine, Shahid Sadoughi University of Medical Science, Yazd, Iran