Periodontal diseases and preterm birth: Pathophysiological mechanisms and the evidence for treatment-based prevention

Background Preterm birth is a leading cause of neonatal morbidity. Periodontal disease is common in pregnancy and associated with preterm birth, yet mechanisms remain unclear and treatment evidence conflicts. Methods Scoping review using Joanna Briggs Institute methodology, reported per PRISMA-ScR. PubMed/MEDLINE, Scopus and the Cochrane Library were searched in June 2026 (2000-2025); 44 studies were included: 15 randomized and prospective trials, 17 systematic reviews and meta-analyses, 7 mechanistic and 5 observational studies. Bias was assessed with RoB 2 and AMSTAR 2. Results Two pathways were identified: direct hematogenous dissemination of oral bacteria to the feto-placental unit and indirect mediation by inflammatory cytokines (IL-1β, IL-6, TNF-α, PGE2). Mechanical therapy improves periodontal health, but adequately powered trials found no reduction in preterm birth. The largest meta-analysis (14 trials) reported a pooled risk ratio of 0.85 (95% CI 0.71-1.02), moderate certainty. Benefit appeared only in adjunctive-antiseptic subgroups or lower-quality trials, not at low risk of bias. Observational syntheses report larger associations, consistent with confounding. By contrast, a cluster-randomized trial of periconception xylitol gum (n = 10,069) reduced preterm birth (RR 0.76, 95% CI 0.57-0.99), suggesting daily, early-initiated interventions differ from episodic debridement. The 17 syntheses draw on 14 trials, so their concordance reflects a shared trial base, not replication. Conclusions Periodontal diseases are observationally associated with preterm birth and biologically plausible, but randomized evidence does not establish that mechanical therapy reduces it. Treatment is safe and indicated on oral health grounds alone, so prenatal oral health assessment is warranted on that basis, not as demonstrated prevention. The null applies to mechanical therapy as tested, not to oral-health intervention generally. Trials in defined periodontitis, intervening before or early in gestation with preterm birth as primary outcome, are needed.