## 1 Introduction  
The oral cavity has been associated with several chronic diseases. There is emerging evidence that periodontitis is caused by oral pathogens, and it might be considered a risk factor for cardio-renal morbidity and the development of diabetes mellitus [1]. One of the most common diseases associated with significant economic impact is dental caries [2]. \(S\). _mutants_ is a Gram-positive, facultatively anaerobic bacterium, which is a very common cause of dental caries and other infections of organs such as the heart, skin, joints and central nervous system [2]. \(S\). _mutants_ is capable of synthesizing an extracellular polymer (designatedas glucan) from sucrose, thus forming biofilms and allowing colonization of teeth. It is a lactic acid bacterium producing organic acid from a wide range of carbohydrates [3].  
_C. albicans_ is a yeast-like fungus causing opportunistic infections of the oral cavity (candidiasis), and is one of the most common human fungal infections [4]. _C. albicans_ is able to metabolize glucose under both aerobic and anaerobic conditions, as well as to produce exopolysaccharides forming biofilms on dental surfaces [5; 6]. Both _C. albicans_ and _S. mutans_ are able to interact and form dental plaque biofilm associated with early childhood caries [6]. Therefore, both microorganisms should simultaneously be a target for antimicrobial agents.  
The growing bacterial resistance to antibiotics is a widespread problem nowadays [7], as well as the resistance of _Candida_ strains to the few available antifungal agents [8]. Furthermore, bacterial resistance to the oral antiseptic chlorhexidine has been significantly increased [9]. Essential oils (EOs), as well as hydrosols (HSs), of medicinal and aromatic plants have demonstrated high antibacterial and antifungal activity against multidrug resistance strains [10; 11; 12; 13]. These properties make EOs ideal candidates for replacing chemical antiseptics like chlorhexidine, which is commonly used in mouthwash and toothpaste against oral pathogens [9].  
EOs contain numerous terpenoid and aliphatic compounds. An essential oil usually contains two or three major compounds, ranging from 20% to 70%. Despite the fact that 20 to 60 different compounds can be detected in EOs [14], the most abundant compounds exert antimicrobial, anti-inflammatory and antioxidant activities [15; 16; 17].  
HSs are obtained during essential oil distillation from medicinal and aromatic plants. HSs consist of the condensing the water of the distillation process, and by water and non-water-soluble, polar and non-polar components. Less than 1 g/L of EOs constituent is dissolved in hydrosols during the distillation, thus contributing to their biological activity and organoleptic characteristics. HSs' chemical composition and active compounds might be divergent from the extracted essential oil [13]. HSs have demonstrated antimicrobial activity, depending on their composition. HSs are implemented in food industry, as well as cosmetics and perfume industries [18].  
Greek oregano (_O. vulgare_ spp. _hirtum_), European pennyroyal (_Menta pulgium_), and common sage (_S. officinalis_) are aromatic plants belonging to Lamiaceae, and they are cultivated and widely used worldwide, due to their pharmaceutical properties [19; 20; 21; 22]. Several studies reported the antimicrobial activity of their EOs [23; 24; 25; 26; 27; 28; 29], while the antimicrobial activity of their HSs has not been extensively studied [30]. The aim of this study was to investigate the chemical profile and the antimicrobial activity exerted by essential oils and their respective hydrosols of three important medicinal and aromatic plants grown in. Thessaly against oral pathogens for the first time, thus evaluating their potential use in oral hygiene products.