Tehran University of Medical Sciences Frontiers in Dentistry 2676-296X 23 0 2026 10 10 4925 4925 EN Kamonchanok T angsapsathit Department of Pediatric Dentistry, Faculty of Dentistry, Thammasat University, Pathum Thani, Thailand Visakha Aupaphong Department of Oral Biology, Faculty of Dentistry, Thammasat University, Pathum Thani, Thailand Chiravoot Pechyen Department of Materials and Textile Technology, Faculty of Science and Technology, Thammasat University, Pathum Thani, Thailand Parinda Tasanarong Department of Pediatric Dentistry, Faculty of Dentistry, Thammasat University, Pathum Thani, Thailand 2023 08 25 2024 09 24 Objectives: Azadirachta indica var. siamensis Valeton, also known as neem, possesses various beneficial biological properties, including antibacterial activity. Neem paste (NZ-paste) was developed to enhance its application. This study aimed to investigate the antibacterial activity of NZ-paste against Lactobacillus rhamnosus (L. rhamnosus), its penetration ability, and its cytotoxicity for human dental pulp stem cells (hDPSCs). Materials and Methods: The active compounds of the neem extract were identified using high-performance liquid chromatography (HPLC). The rheological and physicochemical characteristics of 20mg/g NZ-paste were evaluated by pH measurement, penetration testing, and rheometer analysis. The antibacterial activity of NZ-paste against L. rhamnosus was assessed using agar disc diffusion and live/dead BacLight® assays in dentin, and confirmed by confocal laser stereomicroscopy (CLSM). The methyl thiazolyl tetrazolium assay was used to determine its cytotoxicity for hDPSCs. Results: HPLC analysis identified azadirachtin, quercetin, nimbin, and nimbidin as the main bioactive compounds. NZ-paste had a smooth, fluid-like texture, was water-soluble, and exhibited a pH of 7.09. Although its inhibition zone was comparable to that of Ca(OH)₂, NZ-paste demonstrated superior antibacterial efficacy in the dentinal tubule invasion model, as indicated by the lowest live/dead ratio confirmed by CLSM. NZ-paste at concentrations up to 10mg/mL did not affect hDPSC viability. Conclusion: The novel NZ-paste exhibits antibacterial activity against L. rhamnosus, with suitable penetration ability and favorable biocompatibility with hDPSCs at low concentrations. https://fid.tums.ac.ir/index.php/fid/article/view/4925 https://fid.tums.ac.ir/index.php/fid/article/download/4925/2248