Eleven RCTs (n = 2,810) were included in the review. Study quality was mixed, with eight RCTs reporting methods of randomisation, none reporting allocation concealment, all using blinded assessment and six reporting reasons for losses to follow-up.
Gingivitis (eight RCTs): The overall WMD at the end of study was -0.32 (95% CI: -0.46, -0.19, p < 0.00001) in favour of the intervention, although baseline analysis revealed no difference between the groups. The results for subgroups of studies using the MGI and the GI were also significantly in favour of the essential oils mouthrinse. There was significant heterogeneity in the overall analysis, but not in the subgroup analyses.
Plaque (seven RCTs): There was a significant effect in favour of the intervention at end of study (WMD -0.83, 95% CI: -1.13, -0.53, p < 0.00001) but not at baseline. There was significant heterogeneity in the analysis.
Results for interproximal gingivitis and interproximal plaque were also reported and showed significant effects in favour of the intervention (with the exception of interproximal gingivitis in the comparison with dental floss).