The green tea, originating from the Camellia sinensis plant, is one of the most popular drinks and has received special attention by presenting known effects on general health [1,2]. Among the components of this tea, Epigallocatechin-3-gallate (EGCG) is the substance found in greater amounts, constitutes about 59% of total substances and the most bioactive component [3].

In addition to these properties, can be highlight the antimicrobial action, several studies have reported the inhibitory effects of EGCG on both Gram-positive and Gram-negative bacteria, such as Enterococcus spp., Staphylococcus aureus, Streptococcus spp., Salmonella spp., and E. coli [1,2,4, 5, 6]. In Dentistry, this substance was proposed in toothpaste [7], because it presents a broad spectrum of action against Streptococcus mutans (S. mutans) and Streptococcus sobrinus (S. sobrinus). The action of catechin occurs preventing bacterial adhesion to the tooth surface by inhibiting glucosyltransferase enzyme and bacterial amylase [1,2,8].

The primary role of S. mutans in the pathogenesis of dental caries resides with it is ability to assemble an insoluble polymeric matrix [9]. This microorganism is considered the main and predominant etiologic agent of dental caries and contributes significantly to the virulence of the biofilm, especially in the presence of sucrose [10]. There are many studies regarding the use of EGCG in medicine, however few and recent studies have been conducted on the use of EGCG in Dentistry, since this substance is found in a very popular drink that contacts the oral mucosa, it may have antimicrobial efficacy and play an anticariogenic role. The research question behind this systematic review was: Does EGCG have antibacterial efficacy against S. mutans? The hypothesis of this study was: EGCG performs an antibacterial efficacy against the microorganisms S. mutans. This systematic review evaluated the antibacterial efficacy of the EGCG against S. mutans.

Originals in vitro studies that investigated the EGCG as an antibacterial agent were included, as well as those who evaluated the antibacterial activity of this substance against S. mutans, which have been published in the English language.

In vivo, ex vivo, in situ, animals, clinical studies, letters to the editor, case reports, case series, review and studies with explicit convenience sample (institutionalized/hospitalized individuals, vulnerable population, sample selection performed according to the researcher interest) were excluded, as well as patents, conferences, studies evaluating other extracts of green tea, other microorganisms and other studies that have been published in non-English language.

Electronic searches were conducted to identify the published literature in the Pubmed Medline (1966- Feb 2016), SciVerse Scopus (1960- Feb 2016), Web of Science (1900- Feb 2016) and Google Scholar databases. The Google Scholar was used as a program aimed at the international literature.

The search strategy was based on the following Medical Subject Heading terms (MeSH) and free terms: (“epigallocatechin-3-gallate” [MeSH] OR “EGCG” [MeSH] OR “Camellia sinensis” [MeSH] OR “green tea” [all]) AND (“Streptococcus mutans” [MeSH] OR “S. mutans” [all] OR “Mutans streptococci” [all]). Data was extracted and pooled in a table, to facilitate the visualization of information.

All papers were managed using the software EndNote X7 (Thomson Reuters, New York, NY, US). Duplicate papers were excluded. Titles and abstracts were screened independently by two reviewers based on the criteria mentioned above, (DCAF and SAFP). When there was some sort of disagreement, a third examiner was requested (ECK). After initial screening of titles and abstracts, full articles were evaluated by the same two reviewers. Structured data collection worksheets were employed for the assessment of each publication.

The Figure 1 presents a flow diagram, describing the process of selection of the studies about antimicrobial activity of EGCG against S. mutans. In Pubmed Medline database 40 studies were found, in Scopus database 48 studies were found, in Web of Science 109 studies were found, and finally 340 studies were found in the Google Scholar database.

Figure 1. Figure 1. Flow diagram showing the process of selection of the studies about antimicrobial efficacy of EGCG against S. mutans.

Studies were compared across all database and the studies in duplicate were excluded (91 studies). The remaining studies were analyzed and those, which did not meet the inclusion criteria, were excluded (434 studies). At the end, 12 studies were included in the full-text analysis and all were selected for inclusion in the systematic review. Table 1, 1a shows the characteristics of the selected studies. The results demonstrated that EGCG present a considerable efficacy against S. mutans, by using different methods to analyze the antibacterial activity against this microorganism. Of the 12 studies evaluated, 11 demonstrated that EGCG showed efficacy against the lineage of microorganisms in question. However, 2 of them presented low efficacy, verifying interference in the formation of the biofilm, without causing the total inhibition. Only 1 study showed that EGCG is not an effective agent against S. mutans.

Table 1. Table 1. Characteristics of the selected studies in regarding the method used for antimicrobial efficacy evaluation of EGCG on SM.

Note: Bold form indicates the EGCG superiority against the control. GIC means glass ionomer cement; SEM means scanning electron microscopy; CHX means chlorhexidine; SM means Streptococcus mutans.

Table 1 (Cont.) Table 1 (Cont.) Characteristics of the selected studies in regarding the method used for antimicrobial efficacy evaluation of EGCG on SM.

Note: Bold form indicates the EGCG superiority against the control. GIC means glass ionomer cement; SEM means scanning electron microscopy; CHX means chlorhexidine; SM means Streptococcus mutans.

Dental caries is the most common oral disease and is an irreversible infectious disease of multifactorial origin, which leads to the destruction of dental hard tissue [10]. The biofilm plays an important role in the cause of tooth decay, the cariogenic microorganisms such as Streptococcus mutans, Streptococcus sanguis, Streptococcus salivarius, Streptococcus mitis, Streptococcus oralis and Lactobacillus acidophilus play a vital role in the etiology of the dental caries [11]. Streptococcus mutans is the major causative agent of dental caries and plays an important role in cariogenic biofilm formation [12,13]. It has been demonstrated that S. mutans are the primary etiological agent of caries [12].

Medicinal plants have been used for therapeutic purposes for thousands of years and although their use has been popularly propagated between generations or described in pharmacopoeias, it has also aroused the interest of the current scientific community. Teas generally are rich in biologically active compounds such as flavonoids, catechins, polyphenols, alkaloids, vitamins and minerals that may contribute to the prevention and treatment of various diseases [14].

It is important to emphasize that this systematic review has shown that although the methods used in the included studies are different, the results clearly support the important role of EGCG as an antibacterial agent against S. mutans. The EGCG agent inhibits the formation of biofilm and prevents infections [15], it is effective in inhibiting the formation of fermentable carbohydrates involved in the caries formation, which explains it is antimicrobial role [16]. Per the findings of this review, 11 studies showed favorable results for EGCG as an effective antibacterial agent against S. mutans in in vitro studies, acting both inhibiting the growth of the microorganism, as in the biofilm formation and in decreased acids production. Only one study found a negative result regarding the use of EGCG in the decontamination of infected dentin. This lack of effectiveness was justified in the study by the authors for perhaps be some interaction between EGCG with specific sites in collagen molecular structure [17].

Several antimicrobial agents have been suggested, but the agent considered the gold standard is chlorhexidine gluconate (CHX). CHX widely used antimicrobial in Dentistry [18], due to it is strong antibacterial activity and ability to reduce the accumulation of oral biofilms [19]. Its efficacy can be attributed to bactericidal and substantivity effects [20], broad spectrum against microorganism, both aerobic and anaerobic, and selectively suppress the growth of caries-associated S. mutans [21]. CHX presents antimicrobial efficacy in vitro and in vivo (mouthwash) against salivary microbiota cariogenic and has a role in preventing the development of gingivitis [22]. Some studies compared EGCG with CHX [17, 23, 24, 25, 26]. The results of the comparison between CHX and EGCG showed that both substances were effective in inhibiting microbial the growth and biofilm formation. Other studies [26, 27, 28, 29, 30, 31] used as negative control the absence of EGCG and in these situations; it was observed that there was a marked growth of microorganisms compared to the experimental group. One study compared the antimicrobial activity of EGCG whit black, oolong and Pu-erh tea against growth of S. mutans [32] and another study had no control group [33].

Different methods have been used to evaluate the efficacy of EGCG against microorganisms, such as inhibition zone measurement, counting colonies forming units, counting of microorganisms and biofilm formation. In addition, different forms of manipulation of the EGCG, in some studies the solution was used [29, 30, 31], others incorporated into dental materials [24,27,28], and even as specific formula [26]. Despite all these variety in the method and material handling, the results suggested that it is a stable substance and with antimicrobial properties and able to inactivate the S. mutans, and thus inhibit the formation of biofilm. This systematic review demonstrates a clear efficacy of EGCG against S. mutans in in vitro studies. However, clinical studies are needed to determine this substance as a potential agent for the prevention of dental caries.