Essential oil mouthwashes are used for many years in the prevention and treatment of periodontal disease. The effectiveness of the EO mouthwash in controlling plaque was demonstrated in many clinical trials, both long- and short-term. In short-term studies [30–33], EO significantly reduced plaque accumulation in the 4- and 21-days plaque regrowth models. However, when the EO rinse was compared to the CHX formulation, the latter showed better antiplaque effects. In contrast, recent studies [34, 35] have demonstrated that the EO rinse was as effective as the CHX rinse in inhibiting plaque regrowth. The effectiveness of the EO rinse was also demonstrated in long-term studies [5, 8, 9, 11, 36] in which it was used as a supplement to mechanical hygiene measures. In those studies, which varied in length from 3 to 9 months, the EO-containing mouthwash significantly reduced plaque accumulation and gingivitis when compared to the placebo. Although, EO formulations were less effective in reducing supragingival plaque accumulation than CHX , in contrast a more recent study  has demonstrated that the EO mouthwash and the CHX mouthwash have comparable antiplaque and antigingivitis activity. Furthermore, several studies have demonstrated that EO and CHX rinses were equally effective in reducing gingival index scores and the number of bleeding sites [9, 12, 37]. Finally, in a recent systematic review , the authors concluded that although the effects of CHX ensure higher control of plaque, there are no marked differences in the control of gingival inflammation. Therefore, the EO mouthwash appears to be a reliable alternative to the CHX mouthwash in those cases where the dental professional has judged that long-term anti-inflammatory oral care may be beneficial, while for indications where plaque control is the focus, a CHX mouthwash remains the first choice. All the studies reviewed refer to the EO mouthwash with its traditional formulation, containing alcohol. Alcohol is present in many mouthwashes and is used as a solvent of the ingredients and the preservative of the preparation. The antiseptic effect, however, seems to be negligible at the concentrations used in mouthwashes . In vitro studies have shown that the alcohol promotes the mucosal penetration of the various carcinogens found in tobacco , in addition causing direct damage on the oral mucosa . The bulk of the metabolism of alcohol is carried out in the liver but there is evidence that demonstrates the ability of some oral bacteria to metabolize alcohol to acetaldehyde, a carcinogenic substance . For many years, researchers have been discussing the safety of alcohol in mouthwashes for daily use and several case-control studies suggest the correlation of alcohol use in mouthwashes with oral cancer .
Epidemiological studies, however, are often inconsistent and many reviews conclude there are no data demonstrating the direct correlation between alcohol containing mouthwashes and oral cancer [42, 43]. Recently, Werner and Seymour  have reviewed the two most recent revisions on the role of alcohol in the onset of oral cancer [27, 45], stating that there is evidence showing the existence of this association, but these are still weak and inconclusive, and randomized clinical trials would be needed on a large sample to verify this hypothesis. These authors concluded that the benefit of alcohol in mouthwashes is negligible and it may carry a risk of oral cancer, which is difficult to quantify, and so it is preferable not to prescribe or recommend them.
The purpose of this study was to evaluate whether a new alcohol-free mouthwash with EO had the same characteristics as the antiplaque traditional alcohol-containing formulation, used as a control. It used a 3-day non-brushing model that allowed for plaque accumulation that was already used by several authors to evaluate the effects of various mouthwashes [29, 46–49]. In addition, it was investigated through a questionnaire that assessed the volunteers' perception in terms of effectiveness, utility, and taste of the products examined.
The results reject the null hypothesis that there are no differences between the mouthwash test without alcohol and the control with alcohol, in favor of the traditional product with alcohol. The difference in efficacy, as assessed by the plaque index, is modest but statistically significant. There were no differences between the two groups in terms of compliance, taste perception, duration of taste, alteration in taste perception and convenience, while the volunteers considered the mouthwash with alcohol more effective in reducing plaque formation.