Mixed Bacillus species—primarily strains of Bacillus subtilis, Bacillus coagulans, and Bacillus clausii—have been explored as oral probiotics for the adjunctive management of gingivitis. The rationale stems from their ability to compete with pathogenic oral bacteria, modulate the host immune response, and produce antimicrobial substances such as bacteriocins. Several small-scale randomized controlled trials and pilot studies (e.g., using Bacillus coagulans or Bacillus subtilis in lozenges or mouth rinses) have shown modest benefits in reducing gingival inflammation and plaque indices compared to placebo. Proposed mechanisms include inhibition of periodontopathogens, reduction of pro-inflammatory cytokines, and support of oral microbial homeostasis.

However, the clinical evidence base remains limited. Most studies are of short duration, involve small sample sizes, and often lack rigorous blinding or standardized outcome measures. Systematic reviews of oral probiotics for periodontal health typically focus more on Lactobacillus and Bifidobacterium species, with Bacillus receiving less attention. There is currently no high-quality, large-scale clinical trial establishing the efficacy of mixed Bacillus for gingivitis. Thus, while there is some scientific exploration and preliminary support, the strength of evidence is moderate to low (rated 2/5), and further research is needed before firm conclusions or recommendations can be made.