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Definition:

Cinnamon is a widely known culinary herb and traditionally used in medicine applications. The effect of cinnamon has been studied during pregnancy [16], for diabetes control [17], and gynecological problems [18]. Its anti-inflammatory, cardioprotective, antioxidative, and antimicrobial properties have also been researched [19]. Thus, cinnamon EO, cinnamon extracts, and pure compounds, due to their antibacterial, antifungal, and other properties, have potential uses in mouth rinses, toothpastes, or as a root canal irrigant, showing promise as an antimicrobial agent in dentistry.

1. Introduction

Dental medicine is one of the fields of medicine where the most common pathologies are of bacterial and fungal origins. Widely spread diseases like dental caries, periodontal disease, and endodontic lesions are caused by well-known bacterial and fungal pathogens: Streptococcus mutans, Streptococcus salivarius, Streptococcus sanguinis, Porfiromonas gingivalis, Prevotella intermedia, Actinobacilus actinomycetemcomitans, Enterococcus faecalis, Candida albicans, etc. [1]. Preventive medicine relies mostly upon reducing the bacterial biofilm via oral hygiene. The most often used active ingredients in mouth rinses and toothpastes are chlorhexidine, hyaluronic acid, and fluorides. Although effective, chemical products may have some clinical disadvantages: teeth discoloration, taste alterations, mouth dryness, supragingival calculus accumulation, and oral mucosal lesions [2–4].

The attention of many researchers has focused on the antimicrobial properties of traditional medical substances, like essential oils (EOs) [5–7]. EOs and extracts have demonstrated effective antibacterial and antifungal properties [8–11]. In the field of dental medicine, oral hygiene products based on herbal extracts are well-known [12–14]. One of the substances most used by dental professionals is eugenol, which is an active component in root canal sealers, cements, and others. One of the EOs subjected to investigation in dentistry is cinnamon (Cinnamomum spp., Lauraceae family) [15].

2. Antimicrobial Effect of Cinnamon EO and Cinnamon Extracts Against Oral Pathogens

2.1. Antimicrobial Effect Against Caries Pathogens

Methanolic extract from C. zeylanicum produced inhibition zone diameters of 14.00 mm against S. mutans and 16.67 mm against Lactobacillus acidophilus [64]. The mean MIC (mg/mL) values were 13.44 against S. mutans and 5.18 against L. acidophilus. The mean MBC were 23.6 and 16.4 mg/mL, respectively. A combination of cinnamon and clove methanolic extracts resulted in larger inhibition zones. Ethanolic extract of C. zeylanicum showed good antimicrobial activity against S. mutans ATCC-700610: MIC = 195 µg/mL and MBC = 390 µg/mL [65].

Cinnamon EO showed the highest antibacterial activity against S. mutans among eight other EOs tested, including lime, spearmint, wintergreen, peppermint, lemongrass, cedarwood, clove, and eucalyptus EOs [69]. In a vast study investigating the antimicrobial properties of 32 EOs against oral pathogens, S. mutans, Streptococcus sobrinus, and C. zeylanicum EOs proved to be the most effective based on the inhibition zone measurements [70]. The antimicrobial effects of cinnamon against S. mutans and Lactobacillus plantarum proved to be stronger in comparison to tea tree, manuka, arnica, eucalyptus, and grapefruit [71]. In another study, the cinnamon EO did not prove its antibacterial properties against S. mutans [72]. The composition of the EO used in this study was mainly cinnamyl-alcohol (88.45%), cinnamyl-acetate (6.13%), and p-Eugenol (2.98%) One of the main antibacterial chemical compounds, cinnamaldehyde, was only responsible for 0.39% of the composition.

Data based on the MIC and MBC of cinnamon essential oil against caries pathogens are summarized in Table 1.

Table 1. Minimal inhibitory concentration (MIC) and minimal bactericidal concentration (MBC) of cinnamon EO and cinnamon extracts against cariogenic bacteria.

2.2. Antifungal Activity of Cinnamon EO and Cinnamon Extracts

The combined effect of cinnamon, clove, and oregano obtained by hydrodistillation against several C. albicans strains, Candida tropicalis IP 2148.93, and Candida glabatra DSM 11226 was reported by Brochot A. et al. [24]. The MIC and the minimal fungicidal concentration (MFC) varied between 0.01% and 0.05% v/v.

The antifungal effects of the EO of C. zeylanicum leaves (eugenol content 68.96%) against several Candida spp., including reference strains and oral isolates of C. albicans, C. tropicalis, and C. krusei, showed a MIC from 62.5 to 1000 µg/mL and a MFC from 125 to 1000 µg/mL [76]. The MIC/MFC ratio was similar to that of nystatine. After exposure for 8 h, a significant reduction in the fungal growth was observed up to a concentration of 750 μg/mL. The suppression of biofilm formation at this concentration was also reported. Cinnamon EO was also able to reduce Candida spp. monospecies and multispecies in mature biofilm at 24 and 48 h. This concentration is safe to use, since no significant reduction in the viability of human peripheral blood mononuclear cells was observed with concentrations of up to 1000 μg/mL.

Another study [77] of the antifungal activity of C. zeylanicum leaf EO (eugenol content 82.30%) found that, at concentrations of 312.5 or 625.0 μg/mL, all 12 tested strains of C. albicans and C. tropicalis were inhibited. At the same concentrations, the authors observed a fungicidal effect of cinnamon EO against all 12 strains, except one (MFC was 312.5 or 625.0 μg/mL). The experimental mouth rinse, containing cinnamon EO at the MIC, used in this study did not significantly change the surface roughness or the Vickers microhardness of the heat-polymerized acrylic resin in contrast to the nystatine group. Even at low concentrations, C. zeylanicum EO has an inhibitory effect against C. albicans. The authors reported a MIC of 0.005% (0.05 µl/mL), an MFC of 0.01%, and a 90% reduction in bacterial biofilm at 0.039% [61]. A MIC <0.05 mg/mL for the methanolic extract of C. zeylanicum against C. albicans was reported in another study [78].

C. zeylanicum EO proved to be the most effective EO against 40 C. albicans isolates but to a lesser extent than the antifungal drugs and the mouthwashes [79]. A hydroalcoholic extract of C. zeylanicum was used to assess the antimycotic activity of cinnamon against fluconazole-resistant C. albicans. The MIC at a concentration of 15.62 μg/mL was reported [62]. The MIC and MFC at 65.5 μg/mL against C. albicans were reported by Cavalcanti et al. using C. cassia EO [80]. Khan et al. reported a MIC of 19.5 μg/mL and an MFC of 78 μg/mL against C. albicans ATCC-10231 [65].

2.3. Antimicrobial Effect Against Endopathogens

Some studies focused on the antibacterial and antifungal effects of cinnamon EO and extracts against certain endodontic pathogens. The main cause of endodontic infection is the presence of microorganisms isolated as planktonic cells or biofilms [82]. Enterococcus faecalis is the most prevalent bacterium found in unsuccessful root canal treatments; some studies focused on the root canal irrigant efficiency against C. albicans [83,84].

The antimicrobial effect of steam-distillated C. zeylanicum bark EO against E. faecalis ATCC 29212 was reported by Abbaszadegan et al. [85], with a MIC at 0.01 mg/mL and MBC at 0.1 mg/mL. Cinnamon EO and the triple antibiotic paste used in the study were able to eliminate planktonic E. faecalis after 4 and 24 h, while calcium hydroxide paste failed to do so. Cinnamon EO showed better biocompatibility with experimental fibroblast cells in comparison to the other two substances.

The MIC of C. zeylanicum exhibited against planktonic E. faecalis was 10%, with complete bacterial inhibition after 30 s [86]. In a biofilm susceptibility assay on a cellulose nitrate membrane, complete bacterial inhibition was achieved after 12 h, in contrast to the faster activity of 3% sodium hypochlorite (NaOCl) of 2 min. The effect of cinnamon EO as a root canal irrigant is weaker than 3% NaOCl but could lead to 80–85% intracanal bacterial reduction [87]. A 20% ethanolic extract of C. zeylanicum was found to be even more effective against E. faecalis ATCC 29212 compared to 3% NaOCl [88]. The significant antimicrobial effect of C. cassia EO was proved against C. albicans and E. faecalis (MIC was 0.56 mg/mL). A wider inhibition zone in comparison to chlorhexidine digluconate (0.12%) and 1% sodium hypochlorite solutions was also observed [89]. Khan et al. reported MIC and MBC against E. faecalis ATCC-29212 at 95.7 and 1560 μg /mL, respectively [65].

2.4. Other Studies Against Oral Pathogens

Cinnamon EO could be beneficial in halitosis treatment, since it reduced Solobacterium moorei biofilm formation, with MIC of 0.039% and MBC of 0.156% [93].

The antimicrobial effect of ethanolic extracts from C. zeylanicum and Salvadora persica against periodontal pathogens P. gingivalis, Tannerella forsythia, Treponema denticola, and A. actinomycetemcomitans was also studied. The results indicated the higher efficacy of cinnamon against all tested pathogens and the synergetic effect with antibiotics. The MIC ranged from 1.56 to 12.5 mg/mL and MBC from 6.25 to 75 mg/mL for different bacteria [94].

C. zeylanicum EO proved to be more effective in comparison to C. zeylanicum bark aqueous extract against Staphylococcus auricularis, Acinetobacter lwoffii, C. albicans, and Micrococcus species that were collected and isolated from volunteers’ oral cavities. C. zeylanicum EO was more effective than S. aromaticum EO, inhibiting the growth of all bacterial isolates [96]. This also indicates the activity of the experimental toothpaste used in the study containing: 35.00% calcium carbonate, 1.50% sodium lauryl sulfate, 30.00% glycerin, 1.00% sodium alginate, 00.12% sodium benzoate, 00.30% sodium saccharine, 2.50% plant extract, and purified water q.s.

Cinnamon EO could be useful in antibiotic treatments due to the possible synergetic effect. The combination of C. zeylanicum EO with amikacin showed a significant synergetic effect against Acinetobacter species with reduction of the MIC of amikacin [99]. The possible use of cinnamon bark EO as a modifying agent in the treatment of antibiotic-resistant bacteria was reported in combination with piperacillin [100].

This entry is adapted from the peer-reviewed paper 10.3390/molecules25184184