Abstract
Dental caries is a microbiome-driven disease in which acidogenic taxa dominated by Streptococcus mutans displace commensal genera and form a glucan-rich biofilm matrix that demineralises enamel. Chlorhexidine (CHX) is the standard chemical adjunct but causes staining, dysgeusia and broad commensal suppression, motivating evaluation of botanical alternatives that may rebalance the oral ecosystem. This study determined the antibiofilm and microbiome-modulatory effects of standardised Indonesian Syzygium aromaticum L. (clove, Myrtaceae) bud essential oil (SAEO) on saliva-derived polymicrobial cariogenic biofilms in vitro. SAEO was hydrodistilled, characterised by gas chromatography–mass spectrometry, and tested at 0.25%, 0.5% and 1.0% v/v against polymicrobial biofilms grown on hydroxyapatite discs from stimulated saliva of 60 caries-active adults; 0.12% CHX was the positive control (n = 6 biological replicates per arm). Endpoints were biofilm biomass, CFU on selective media, EPS, biofilm pH, lactate, 16S rRNA microbiome profiling and HGF-1 cytotoxicity. Eugenol (82.3%), β-caryophyllene (7.4%) and eugenyl acetate (4.8%) were the principal volatiles. SAEO 1.0% reduced biofilm biomass by 70.5% (95% CI 65.8–75.3; p < 0.001), S. mutans CFU by 3.22 log₁₀ and EPS by 67.9%, while raising Shannon diversity from 1.42 to 2.08 bits and restoring Neisseria and Corynebacterium relative abundance — a dysbiosis-reversal pattern absent under CHX. Cytotoxicity remained below 18% at 1.0% v/v versus 31.8% for CHX. Standardised SAEO is a credible complementary anticaries agent meriting clinical translation. Keywords: Syzygium aromaticum; clove essential oil; eugenol; oral microbiome; dental caries; antibiofilm.