Dental caries is a common infectious disease worldwide. Current conventional therapies lack specific antimicrobial effects against Streptococcus mutans, a key bacterium that induces caries. A promising alternative approach is bacteriophage (phage) therapy. Recently, SMHBZ8 phage targeting S. mutans was isolated and characterized. The aim of this study was to evaluate the caries-prevention efficacy of SMHBZ8 using in vitro and in vivo caries models. Hemi-mandibles dissected from euthanized healthy mice were subjected to caries-promoting conditions in vitro. Jaws treated with phage therapy in suspension and in formulation with a sustained-release delivery system showed no carious lesions, similar to control and chlorhexidine-treated jaws. Subsequently, SMHBZ8 phage suspension also prevented carious lesion development in a murine caries model in vivo. In both models, caries lesions were analyzed clinically and radiographically by µCT scans. This study shows how SMHBZ8 phage therapy targeting S. mutans can serve as an efficient caries-prevention modality, in suspension or with a sustained-release delivery system, by in vitro and in vivo mouse models.

In vitro and in vivo models simulating the dental caries process enable the evaluation of anti-caries modalities for prevention and treatment. Animal experimentation remains important for improving human and animal health. Nonetheless, reducing animal sacrifice for research is desirable. The aim of the study was to establish a new reproducible in vitro caries model system and compare it to an in vivo model using similar conditions. Hemi-mandibles were extracted from previously euthanized healthy 10-week-old BALB/C female mice. Jaws were subjected to saliva, high-sucrose diet, and dental caries bacteria Streptococcus mutans UA159 for 5 days. Similar caries induction protocol was used in vivo in fifteen BALB/c female mice (6–7 weeks old) and compared to the in vitro model. Caries lesions were assessed clinically by photographic analysis and µCT analysis, and bacterial growth was evaluated. Under in vitro experimental conditions, carious lesions evolved within 5 days, prominently in the depth of the occlusal fissures in the control group as depicted by photographic analysis, µCT analysis, and bacterial growth. The developed in vitro caries model presented in this study may be a novel animal sparing model for caries disease studies and can be used widely to evaluate the efficacy of different antibacterial dental materials.

Streptococcus mutans (S. mutans) is the main cariogenic bacterium with acidophilic properties, in part due to its acid-producing and -resistant properties. As a result of this activity, hard tooth structures may demineralize and form caries. Trans-cinnamaldehyde (TC) is a phytochemical from the cinnamon plant that has established antibacterial properties for Gram-positive and -negative bacteria. This research sought to assess the antibacterial and antibiofilm effects of trans-cinnamaldehyde on S. mutans. TC was diluted to a concentration range of 156.25–5000 μg/mL in dimethyl sulfoxide (DMSO) 0.03–1%, an organic solvent. Antibacterial activity was monitored by testing the range of TC concentrations on 24 h planktonic growth compared with untreated S. mutans. The subminimal bactericidal concentrations (MBCs) were used to evaluate the bacterial distribution and morphology in the biofilms. Our in vitro data established a TC MBC of 2500 μg/mL against planktonic S. mutans using a microplate spectrophotometer. Furthermore, the DMSO-only controls showed no antibacterial effect against planktonic S. mutans. Next, the sub-MBC doses exhibited antibiofilm action at TC doses of ≥625 μg/mL on hydroxyapatite discs, as demonstrated through biofilm analysis using spinning-disk confocal microscopy (SDCM) and high-resolution scanning electron microscopy (HR-SEM). Our findings show that TC possesses potent antibacterial and antibiofilm properties against S. mutans. Our data insinuate that the most effective sub-MBC of TC to bestow these activities is 625 μg/mL.

Background: Dental caries, primarily caused by Streptococcus mutans (S. mutans), is a prevalent condition with significant global impact. Trans-cinnamaldehyde (TC), a phytochemical derived from the cinnamon plant, has shown promising antibacterial and antibiofilm activity against S. mutans. This study aimed to evaluate the anti-cariogenic effects of TC on S. mutans using an innovative mouse jaw explant model. Methods: TC was diluted in an organic solvent across various concentrations. Initially, cytotoxicity assays were performed at all tested TC concentrations. Sub-minimum bactericidal concentrations were then used to examine the distribution and morphology of S. mutans biofilms. Hemi-mandibles were dissected from euthanized, healthy, seven-week-old female mice to study the impact of TC on the cariogenic activity of S. mutans using stereoscopic analysis. Finally, pH changes during exposure to cariogenic conditions and post-treatment bacterial viability were measured. Results: In vitro data demonstrate that TC doses of ≤625 µg/mL were non-cytotoxic. Treatment groups exposed to TC exhibited altered bacterial morphology, including abnormal and incomplete cell division. In the mouse jaw explant model, TC doses of ≥625 µg/mL showed anti-cariogenic effects, evidenced by the absence of visible carious lesions. Additionally, pH changes and post-treatment viable bacterial counts corresponded with the observed anti-cariogenic activity. TC doses ≤625 µg/mL led to a pH drop over time and the presence of bacterial colonies. Conclusions: TC exhibits significant anti-cariogenic activity against S. mutans in the mouse model. Our findings suggest that 625 µg/mL is the lowest non-toxic concentration of TC that effectively inhibits cariogenic activity.