## 1 Introduction  
Many bacteria present in the mouth cannot be eliminated properly with daily brushing, and can be present in the preservation of healthy dental and periodontal tissues [1]. Gingivitis begins with plaque build-up, which will end in periodontitis [2]. In this context, much research has investigated the efficacy of several types of mouthwash, which are designed to improve plaque and gingivitis levels. V-Sol containing alcohol, as well as essential oils (E.O.), have been shown to offer beneficial effects on plaque and gingivitis index, where it seems to significantly improve oral health six months after use [3,4]. Different mouthwashes containing natural compounds (NCCM) versus E.O. mouthwash (Listerine(r)) demonstrated their effectiveness for plaque control [4,5]. Another study evaluated the effects of E.O. that reduces plaque and gingivitis compared to cetylpyridinium chloride (CPC) and a placebo. Essential oils showed a better effect than mechanical plaque control (MPC) and CPC, reducing plaque and gingival inflammation in patients who may suffer gingivitis. Therefore, mouthwashes containing E.O. should be the first option for mechanical plaque control [6, 7, 8]. The therapeutic application of natural compounds showed that these compounds have some efficacy in the fight against gingivitis and periodontitis [9, 10, 11, 12, 13]. However, evidence that the efficiency and effectiveness of NCCM, as routine methods that help mechanical oral hygiene practices for plaque control and gingivitis has remained low, and it seems that some NCCMs may offer various oral health benefits by reducing the plaque and gingivitis [14]. The main side effects of alcohol-containing mouthwashes (ACM) were oral pain, burning sensation, and taste disturbances [14, 15, 16, 17]. When the clinical efficacy of two 0.2% chlorhexidine mouthwash (CHX) formulations are compared, the alcohol-free chlorhexidine rinse demonstrated action levels similar to the use of frequently used alcohol-formed rinses [18]. Some of the most frequent side effects from the use of CHX are staining of the tongue and teeth, as well as taste alteration, as CHX is a rinse that is very effective in reducing plaque and gingivitis. Some authors describe moderate evidence when oxygenating agent (OA) and CHX work together to reduce teeth staining, without interfering with the inhibition of plaque growth [19,20]. Mouthwashes with seawater could offer a promising alternative for CHX to overcome its possible adverse effects. Balneotherapy with spa water or the Dead Sea water can be used to treat inflammatory skin diseases (psoriasis and atopic dermatitis). This effect of seawater has been attributed to the preservation of the skin barrier induced by NaCl and KCl [21]. Only one study has investigated the use of a mouthwash solution with sea salt in street children in Manila, demonstrating its effectiveness in reducing mild to severe forms of periodontal disease. The authors proposed sea salt mouthwash for its antimicrobial action, which is highly effective and well-tolerated by the user and could be implemented worldwide using low-cost resources [22]. This is considered to be the first pilot study t which compares the clinical efficacy of 0.2% chlorhexidine with a new mouthwash formulated with seawater (analyzed for the first time) and a saline solution, in reducing gingiva inflammation and plaque formation.