Comparative evaluation of antibacterial efficacy against <i>Streptococcus mutans</i> and shear bond strength of <i>Azadirachta indica</i> infused orthodontic adhesive primer: an in vitro study

Purpose Orthodontic appliances promote plaque accumulation, enamel demineralization, and bacterial adhesion, increasing the risk of tooth decay. Integrating antimicrobial agents into orthodontic adhesives offers a potential solution. Neem (Azadirachta indica), known for its antimicrobial and anti-inflammatory properties, may inhibit bacterial colonization when incorporated into orthodontic primers. This study evaluates the antibacterial efficacy, shear bond strength (SBS), and adhesive remnant index (ARI) of Neem-infused Transbond XT (TXT) primers compared to conventional formulations.Materials and Methods Ethanolic Neem extract was prepared and added to TXT primer at 2%, 4% and 6% concentrations. Sixty extracted premolars were randomly assigned to four groups (n = 15 each): a control group using unmodified TXT primer and three experimental groups with modified primer at different Neem concentrations. Brackets were bonded following a standardized protocol, and SBS was assessed using a universal testing machine. Antibacterial efficacy against Streptococcus mutans was evaluated using a disc agar diffusion assay, while ARI scores were determined post-debonding using stereomicroscopy. One-way ANOVA and Tukey’s post hoc test were applied for statistical analysis (p < 0.05).Results The 6% Neem-modified primer exhibited the highest antibacterial efficacy (17.43 ± 1.36 mm zone of inhibition, p < 0.05). However, SBS decreased with increasing Neem concentration, with the 6% formulation showing the lowest SBS (7.80 ± 1.09 MPa). ARI scores indicated moderate adhesive retention across experimental groups.Conclusion Neem-modified orthodontic primers enhance antibacterial efficacy but compromise SBS. The 4% Neem concentration provides the best balance between bacterial inhibition and bond strength.