en پژوهشی اصيل Original Research <span style="font-size:11pt"><span style="line-height:normal"><span style="text-autospace:none"><span sans-serif="" style="font-family:Calibri,"><b><span style="font-size:10.0pt"><span cambria="" style="font-family:"><span style="color:#1f497d">Aims:</span></span></span></b><span style="font-size:10.0pt"><span cambria="" style="font-family:"><span style="color:black"> Bacteria are one of the main factors involved in the process of tooth decay and are the main cause of pulp and periapical diseases. Their presence in the crown pulp and dental canal causes symptoms in the teeth. This study aimed to investigate the molecular analysis of anaerobic bacteria in primary and necrotic teeth of children and to determine the relationship between these bacteria and clinical signs and symptoms.</span></span></span></span></span></span></span><br> <span style="font-size:11pt"><span style="background:white"><span style="line-height:normal"><span sans-serif="" style="font-family:Calibri,"><b><span style="font-size:10.0pt"><span cambria="" style="font-family:"><span style="color:#1f497d">Materials & Methods:</span></span></span></b><b> </b><span style="font-size:10.0pt"><span cambria="" style="font-family:"><span style="color:black">In this analytical cross-sectional study, 90 children aged 4-12 years were divided into five equal groups (n=18), including reversible pulpitis without irritant pain, reversible pulpitis with irritant pain, irreversible pulpitis, necrosis with abscess, and necrosis without abscess. Clinical symptoms of the patient, such as history of pain, luxation, sensitivity to percussion, status of the dental pulp, and presence of swelling were recorded, and samples were taken from coronal pulp tissue and root canals during pulp treatment using sterile paper points. To identify anaerobic bacteria, clinical samples were cultured under anaerobic conditions. The <i>16s rRNA</i> sequencing was used for molecular identification of anaerobic bacteria at species level.</span></span></span></span></span></span></span><br> <span style="font-size:11pt"><span style="background:white"><span style="line-height:normal"><span sans-serif="" style="font-family:Calibri,"><b><span style="font-size:10.0pt"><span cambria="" style="font-family:"><span style="color:#1f497d">Findings:</span></span></span></b><span style="font-size:10.0pt"><span cambria="" style="font-family:"><span style="color:black"> In 90 </span></span></span><span style="font-size:10.0pt"><span cambria="" style="font-family:">patients, 9 different</span></span><b> </b><i><span style="font-size:10.0pt"><span cambria="" style="font-family:">Lactobacillus</span></span></i><span style="font-size:10.0pt"><span cambria="" style="font-family:"><span style="color:black"> spp. were identified which among them <i>L. fermentum</i> (37.8%), <i>L. rhamnosus</i> (15.6%), <i>L. salivarius</i> (10%), and <i>L. gasseri</i> (5.6%) were the most prevalent. <i>L. fermentum</i> was the most common species found in all clinical samples that was related to pain (p=0.034).</span></span></span><span dir="RTL" lang="AR-SA" style="font-size:10.0pt"><span style="color:black"></span></span></span></span></span></span><br> <span style="font-size:11pt"><span style="line-height:normal"><span sans-serif="" style="font-family:Calibri,"><b><span style="font-size:10.0pt"><span cambria="" style="font-family:"><span style="color:#1f497d">Conclusion:</span></span></span></b><span style="font-size:10.0pt"><span cambria="" style="font-family:"><span style="color:black"> <i>L. fermentum</i> is the most common species found in all clinical samples that is related to pain.</span></span></span></span></span></span><br> &nbsp; Lactobacillus,Primary Tooth,Signs and Symptoms, 113 120 http://jccs.yums.ac.ir/browse.php?a_code=A-10-231-1&slc_lang=en&sid=1 S.S. Khoramrooz khoramrooz@gmail.com 10031947532846005737 10031947532846005737 No Cellular and Molecular Research Centre, Yasuj University of Medical Sciences, Yasuj, Iran Z. Hashemi hashemi_kh11@yahoo.com 10031947532846005738 10031947532846005738 Yes Department of Pediatric Dentistry, Scholl of Dentistry, Yasuj University of Medical Sciences, Yasuj, Iran F. Kheirollahi farazkh27@gmail.com 10031947532846005739 10031947532846005739 No Department of Oral and Maxillo‐ facial Medicine, School of Dentistry, Arak University of Medical Sciences, Arak, Iran R. Alirezaei alirezaeirazyeh72@gmail.com 10031947532846005740 10031947532846005740 No Student Research Committee, Yasuj University of Medical Sciences, Yasuj, Iran M. Akbartabar Toori m_akbartabar@yahoo.com.uk 10031947532846005741 10031947532846005741 No Social Determinants of health Center, Yasuj University of Medical Sciences, Yasuj, Iran