The purpose of this study is to evaluate the antiplaque effects of an alcohol-free essential-oil containing mouthrinse - Listerine Zero (LZ) and an alcohol-based essential oils (EO+) mouthwash compared to a positive control of 0.20% chlorhexidine (CHX) mouthwash, and a negative control of a placebo solution (saline), using an in vivo plaque regrowth model of 3 days.

Plaque is a biofilm of microorganisms responsible for the development of caries and periodontal disease. The daily removal of supragingival dental plaque represents a major factor in the prevention of caries, gingivitis and periodontitis. Plaque control is largely obtained by daily effective tooth brushing and inter-dental cleaning, but in some cases plaque removal can be improved by adding the use of a mouthwash.

An effective action of chemical formulation (especially antiseptics) to control plaque and gingivitis levels has been proved.

Most mouthwashes contain an alcohol (especially ethanol) in order to act as a carrier agent for active essential oils to penetrate the plaque, and to give the subject a "clean mouth sensation".

The alcohol content of mouthwashes, besides having antiseptic properties, serves the purpose of breaking down or dissolving active principles, in addition to that of preserving the formula components, although such content does not directly contribute to effective biofilm and gingivitis control.

However, there are some contraindications in the use of alcohol-based mouthwashes, like the use by infants, pregnant women, alcohol addicts and patients with mucosal injuries. There are also some undesirable effects, like burning or sore sensation, or a painful sensation for patients with existing soft tissue injuries, or a perception of dryness in the mouth.

In order to avoid the use of alcohol-based mouthwashes in particular conditions, scientific interest is becoming more widespread in introducing a mouthrinse with strong anti-plaque qualities and no alcoholic ingredients.

One of these product is the alcohol-free essential oil mouthwash Listerine Zero (LZ), that has little documentation with regard to its anti-plaque effects.

The aim of this study was to evaluate the antiplaque effects of an alcohol-free essential oil mouthwash (Listerine Zero, LZ) and a alcohol-based essential oil mouthwash (EO+), compared to a positive control of a 0.2% chlorhexidine mouthwash (CHX), and a negative control of a placebo solution (saline), using an in vivo plaque regrowth model of 3 days.

The study was designed as a double-masked, randomized, crossover clinical trial, involving 21 volunteers to compare four different mouthwashes, using a 3-day plaque regrowth model. After receiving thorough professional prophylaxis at baseline, over the next 3 days, each volunteer refrained from all oral hygiene measures and performed two daily rinses with 15 ml of the test mouthwashes. EO+ was compared to LZ. CHX rinse served as a positive control, and a placebo solution as a negative control. At the end of each experimental period, plaque index (PI) was assessed, and a panelists completed through a visual analogue scale (VAS) questionnaire evaluating the organoleptic properties of each product. Each subject underwent a 14-day washout period, and then there was another allocation.

Inclusion Criteria:

• dentition with ≥ 20 evaluable teeth (minimum of five teeth per quadrant)
• age between 20 and 50 years old

Exclusion Criteria:

• oral lesions
• severe periodontal problems (probing depth ≥5 mm or attachment loss >2 mm)
• removable prostheses or orthodontic bands/ or appliances
• Subjects allergic to several mouthrinse