The oral cavity is one of the most complex environments in the human body due to the continuous and simultaneously variation of homeostasis conditions. Over 700 diverse bacterial species have been identified as potential/usual colonizers of the many niches of the mouth, i.e., the surface of teeth and all the soft tissues of the oral mucosa such as the gingiva, the cheek, the tongue, the palate and the lips (1–3). The bacterial composition of the oral microbiota is responsive to different host intrinsic and host extrinsic factors. The host intrinsic factors are those factors not modulable by the host belonging to individually genetic factors (e.g., ethnicity, gender, host immune response, medical conditions, etc.), characteristics of the oral cavity such as the temperature, the saliva composition (pH, buffer capacity, hormones, and secreted substances) and characteristics of the attachment surfaces (e.g., roughness of tooth surface). The extrinsic factors come from the external environment, habits and lifestyle, are modulable or relatively modulable by the host and regard the hygiene, the diet, the use of drugs, smoking, medications, sex, access to dental care etc. (4–7). All these factors contribute together and along the host ageing to establish in the oral cavity the conditions suitable for the colonization and the growth of different pools of microorganisms. As a result of this complex interaction, the balance between beneficial and pathogen species is continuously altered, passing from a state of symbiosis and health to a dysbiotic state with the upcoming of oral pathologies such as caries, gingivitis and periodontitis (2,4).
Nevertheless, the new metagenomic approaches represented a vital advantage to unravel the correlations between different types of stimuli in the oral cavity and the enrichment of specific bacterial species, with particular interest for those species that increase their growth as cause/effect of oral diseases (3,8). Also, through sequencing methods, the relationship between beneficial and pathogenic species of the oral cavity has been extensively studied as well as the composition of the polymicrobial biofilm assemblies detected in the oral cavity on the tooth, on the gingiva or on the tongue surface, and in minor part, on other soft tissue (7). The biofilm structure constitutes a protect sub-environment in which various bacterial species interact to protect themselves from the possible surrounding perturbations and thus represents a survival strategy of cells, whose formation is often difficult to inhibit or to remove (9–11). In the oral cavity, the biofilm causes the onset of the most prevalent infectious diseases, such as the plaque and dental caries and inflammation phenomena regarding the gingiva, which cause gingivitis, periodontitis, etc. (7,12). The formation of oral biofilm is arranged on the following subsequent three stages of attachment, colonization and biofilm development (13). The involved species are identified as “early” and “late” colonizers. The early colonizers belong to the streptococci genera; among them, S. mutans is particularly enriched in supragingival plaque, in childhood caries and dentinal and root caries lesions. Indeed, thanks to its rapid metabolism and strong acid tolerance it is recognized as the most cariogenic bacteria of the oral cavity (6,12,13). The early colonizer species are involved in the first two stages of biofilm formation. Since their ability to bind salivary proteins, they adhere to nascent hard or soft tissues, colonize the oral niches and provide a substratum for subsequent colonizers (6,13,14). Between the first and late colonizers, the Gram-negative obligate anaerobe F. nucleatum is considered a key actor for the stage of maturation of the oral biofilm. Thanks to its coating adhesion molecules and polysaccharide receptors, it is able to co-aggregate and bind both with the streptococcal early colonizers and the late colonizers, mainly Gram-negative anaerobes belonging to the genera of Bacteroidetes and Spirochaetes (13–15). Apart from the bridge role in the bacterial network of biofilm assemblages, F. nucleatum plays an active role as a periodontal pathogen, as demonstrated by its enhanced prevalence within the deep periodontal pockets. Moreover, in these niches, F. nucleatum triggers the production of matrix metalloproteinases by the host contributing initially to the periodontal inflammation and the onset of irreversible periodontal diseases (15). This pathogen is also characterized by a significant haemolytic activity and the ability to produce hydrogen sulphide (H2S). In particular, the H2S, similarly to the methyl mercaptan (CH3SH) and the dimethyl sulphide (CH3SCH3)24, is one of the volatile sulphur compounds (VSCs) produced by periodontopathic anaerobic bacteria which cause the typical malodour of the halitosis (16–20). Consistently, the uncomfortable phenomenon of halitosis is often associated with the increase of VSCs producing species, in primis, F. nucleatum but also Porphyromonas gingivalis, Treponema denticola, Prevotella intermedia and Eubacterium (16,17,19,20). Actions aimed to reduce the presence of F. nucleatum in the oral cavity could represent an excellent double-sides strategy to reduce both the formation of the oral biofilm causative of plaque and other frequent oral diseases and the uneasiness associated with the halitosis. An even more efficient approach to massive prevent/reduce the development of oral pathologies could be represented by the simultaneous inhibition of S. mutans as the principal first colonizer of the oral biofilm. However, at the current point of knowledge, lifestyles modulation together with the use of innovative cosmetics or medicals are the only strategies to maintain or restore a balanced microbiome and the health of the oral cavity (2,4).
Indeed, mouthwashes and many dentistry products with antimicrobial compounds such as chlorhexidine, triclosan, cetylpyridinium chloride and chlorine dioxide are often used to treat the bad breath and to inhibit/disrupt the oral biofilm (17,18). However, the use of such products is always more often associated with the increase of the bacterial resistance as well as can cause the simultaneous killing of non-pathogenic commensal species with the consequent onset of undesirable dysbiosis states. The use of natural products is a more appreciated strategy to prevent and contrast the oral pathologies, even more if those substances impact more selectively on the pathogen species of the buccal microbiota. Moreover, the major acceptance of a “natural therapy” could modify the applicability of the therapy to a wider range of patients for ages and medical conditions, not only as curative but also as preventing therapy, both in paediatric and advanced ages. Products such as propolis, cranberry, tea, Galla chinensis, grapes, coffee, and cacao containing polyphenols have already demonstrated their activity against the oral biofilm, as well as hinokitiol, green tea powder, and eucalyptus extract made against the oral malodour (17,18).
Further, since it was found that oral disorders and pathologies are also associated with the oxidative stress that alters the microbial balancing, the activity of antioxidant substances against the oral bacteria has been studied as well. Well known non-enzymatic antioxidants are able to neutralize the Reactive Oxygen Species (ROS) causative of many oral pathologies. They are fat-soluble vitamins (vitamin A, vitamin E-tocopherol and b-carotene), water-soluble vitamins (vitamin C and vitamin B complex), trace elements (zinc, magnesium), and bioflavonoids (plant-derived) (21). The antioxidant compounds are generally assumed through a balanced diet with consumption of fruits and vegetables that contain considerable levels of those; interestingly, their presence is sensibly minor in individuals with oral diseases (4,21,22).
Regarding vitamin E, it is the major fat-soluble antioxidant in all cell membranes, exerts some anti-inflammatory properties and enhances the humoral immune response. Its positive effect on the oral health has been already documented with improvements of all periodontal parameters, principally the decreasing of plaque index and biofilm formation, of probing depth, clinical attachment level, and bleeding on probing (21–23).
Therefore, in this study, we in vitro tested the innovative product Vea® Oris against S. mutans and F. nucleatum, the two bacteria causatives of the most recurrent oral diseases. This product is composed of only two components, vitamin E as alpha-tocopherol and Caprylic/Capric Triglyceride obtained from coconut oil and glycerine. The effect of Vea® Oris at different concentrations was evaluated both on the growth and biofilm formation of S. mutans and F. nucleatum, and for F. nucleatum also on the production of the volatile compound H2S.