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Objectives: Lactobacilli and Streptococcus mutans are stigmatized as cariogenic bacteria, but few studies have simultaneously examined the quantitative and qualitative aspects of lactobacilli and S. mutans in childhood dental caries. Therefore, this study aimed to detect the presence of S. mutans and lactobacilli in dental caries using Snyder's test, colony counting, and PCR in the primary teeth of Iranian children with dental caries., Material and Methods: A cross-sectional study was conducted in Kerman, Iran, from March to Jun 2024. After dental examinations, 120 eligible children aged 5-9 were chosen using simple random sampling and classified into four groups based on their decayed, missing, and filled (primary) teeth (dmft) index: Group 1 (dmft = 0), Group 2 (dmft = 4-6), Group 3 (dmft = 7-9), and Group 4 (dmft = 10-13). The salivary levels of lactobacilli and S. mutans were calculated using colony counting (CFU/ml). Moreover, Snyder's test was applied to evaluate caries activity. PCR was also performed for molecular detection of lactobacilli (16S rRNA gene) and S. mutans (gftB gene). Lastly, the association between bacterial counting, molecular findings, and Snyder's test was estimated through statistical methods using SPSS 27., Results: Significant differences were found between the age and the PCR results of lactobacilli and S. mutans among all dmft Groups (p < 0.05). Moreover, positive significant correlations were observed between the counts of lactobacilli and S. mutans in dmft Group 1 compared to other dmft Groups (p < 0.05). Furthermore, the counts of these two bacteria differed significantly in Snyder's test (p < 0.05). However, Snyder's test differed significantly from the S. mutans PCR (p < 0.05), but not from the lactobacilli PCR (p > 0.05)., Conclusions: The results of the study could potentially be considered a promising and cost-effective screening program to identify children who are susceptible to dental caries., (© 2024 The Author(s). Clinical and Experimental Dental Research published by John Wiley & Sons Ltd.)

Background. Stainless steel crowns (SSCs) of the opposing maxillary deciduous molar teeth are used in mandibular deciduous first molars with decreased proximal surfaces due to caries. However, the SSCs of maxillary deciduous molar teeth are different from those of the mandibular deciduous molars in terms of the occlusal surface morphology, the buccal margin, and the proximal surface contour. Therefore, it is possible to prepare the buccal and lingual surfaces to use the SSC of the lower deciduous molar teeth and compare microleakage. Methods. Eighty extracted mandibular deciduous first molars were randomly assigned to two groups. In the case group (BLP), the buccal (B) and lingual (L) surfaces were prepared in addition to the proximal (P) surface, and an SSC was placed on the mandibular first deciduous teeth. Only the proximal surface was prepared in the control (P) group, and the SSC of the opposing tooth (maxillary deciduous first molar teeth) was placed. After dissecting the teeth, the extent of dye penetration was measured. Results. The difference in microleakage on the buccal aspect between the case and control groups was significant ( P =0.02); however, the difference in microleakage on the lingual aspect between the case and control groups was not significant ( P =0.89). Conclusion. Microleakage at the buccal margin of the SSC of mandibular deciduous first molars was less than the maxillary deciduous first molar SSC, with no significant differences in the lingual margin., (©2022 The Author(s).)