Intraoral pH measurement of carious lesions with qPCR of cariogenic bacteria to differentiate caries activity Megumi Kuribayashi a , Yuichi Kitasako a, *, Khairul Matin a , Alireza Sadr b , Kanako Shida a , Junji Tagami a,b a Cariology and Operative Dentistry, Department of Restorative Sciences, Graduate School of Medical and Dental Sciences, Tokyo Medical and Dental University, Tokyo, Japan b Global Center of Excellence Program, International Research Center for Molecular Science in Tooth and Bone Diseases, Graduate School, Tokyo Medical and Dental University, Tokyo, Japan j o u r n a l o f d e n t i s t r y 4 0 ( 2 0 1 2 ) 2 2 2 – 2 2 8 a r t i c l e i n f o Article history: Received 25 July 2011 Received in revised form 14 December 2011 Accepted 15 December 2011 Keywords: Caries pH Micro-pH sensor Cariogenic bacteria qPCR a b s t r a c t Objectives: A low pH environment is created by cariogenic bacteria. This study was aimed to measure pH of carious lesions intraorally using a micro-pH sensor, and assess predominant acid-producing cariogens by qPCR to differentiate caries activities. Methods: 103 dentine lesions classified as active or arrested caries based on the clinical and radiological examinations were collected from patients after intraoral measurement of the lesion surface pH using a micro-pH sensor. Quantitative detection of genomic DNA copies of target cariogenic bacteria (mutans streptococci and Lactobacillus spp.) in each lesion was performed using real-time PCR. Correlation between the pH ranges and the number of bacterial species was examined by Spearman test. Results: 50 samples were diagnosed as active and 53 as arrested lesions. Statistically significant difference was observed on average surface pH value between active and arrested lesions ( p < 0.05). Prevalence of Lactobacillus spp. was higher in active lesions than in arrested lesions (76% vs. 58% of samples, respectively). When the carious lesions were categorised into four different pH ranges (up to 5.5, from 5.6 to 5.8, from 5.9 to 6.1 and 6.2 or above), increased prevalence of Lactobacillus spp. was observed with decrease of pH levels. A significant negative relationship was found between pH value and number of Lactobacillus spp. (r = 0.209, p < 0.05) but no such correlation was found for mutans streptococci. Conclusions: Intraoral pH measurement might be clinically useful to determine acidity of the local environment of carious lesions as one aspect of the caries activity assessment. Clinical significance: The population of certain bacteria may indicate activity of carious lesions. Intraoral pH measurement of the carious lesions using a micro-pH sensor may be a clinically feasible method for assessment of lesion acidity. # 2011 Elsevier Ltd. All rights reserved. * Corresponding author at: Cariology and Operative Dentistry, Department of Restorative Sciences Graduate School of Medical and Dental Sciences, Tokyo Medical and Dental University, 5-45 Yushima 1-chome, Bunkyo-ku, Tokyo 113-8549, Japan. Tel.: +81 3 5803 5483; fax: +81 3 5803 0195. E-mail address: kitasako.ope@tmd.ac.jp (Y. Kitasako). Available online at www.sciencedirect.com journal homepage: www.intl.elsevierhealth.com/journals/jden 0300-5712/$ – see front matter # 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.jdent.2011.12.013