The accumulation and maturation of oral biofilm in the gingival margin is widely recognised to be the primary aetiological factor in the development of chronic gingivitis. Based on this association, the current treatment of gingivitis is focused on biofilm disruption, which will normally include mechanical processes, both professionally and at home. However, for patients, it is not easy to achieve a proper level of plaque control. The efficient plaque control techniques are very time consuming and require a special motivation and skills for their optimum use. It was at this point where mouthwashes become important, due to the fact that they include diverse types of antimicrobial agents to complement the results of mechanical oral hygiene measures.

The essential oils have been presented as a realiable alternative to the "gold Standard" (Chlorhexidine). However, it use has been limited clinically due to their alcohol contain. Some years ago, a new alternative without alcohol has been launched to the market. This formulation has not been already deeply tested specific antiplaque studies in which the structure of the biofilm remained intact.

The aim of this study was to evaluate the in situ antiplaque effect of 2 antimicrobial agents (based on an essential oils formulation with and without alcohol) in the short term with a posterior analysis on "non-destructured" biofilm with Confocal Laser Scanning Microscope combined with fluorescence staining.

Inclusion Criteria:

• Systemically healthy adults.
• Minimum of 24 permanent teeth.
• No gingivitis (Community Periodontal Index score = 0).
• No periodontitis (Community Periodontal Index score = 0).
• Absence of untreated caries.

Exclusion Criteria:

• Smoker or former smoker.
• Presence of dental prostheses.
• Presence of orthodontic devices
• Antibiotic treatment or routine use of oral antiseptics in the previous 3 months.
• Presence of any systemic disease that could alter the production or composition of saliva.