Inhibitory effect of essential oils against oral pathogens affecting titanium-based dental implants

Abstract

Periodontal diseases, that can lead to tooth damage, affect more than half of the adult population globally. Such diseases are mainly caused by bacterial infection that contaminates the surface of the teeth. Oral illnesses are introduced by bacterial contamination in oral cavities and these bacteria incendiary responses that will continue unless the source of contamination is eliminated through dental treatment. The development of dental caries involves Gram-positive bacteria producing acids as a byproduct of the metabolism of fermentable carbohydrates, such as Streptococcus mutans, Lactobacillus spp and Actinomyces. The food we eat can be infested with oral pathogens that can cause tooth damage and rehabilitation generally requires the insertion of implant material. Biomaterials utilised for implant manufacturing are not themselves antibacterial agents, thus their surfaces need to be coated with antimicrobial agents to prevent bacterial colonisation of the implant surface. Titanium and its alloys are the most frequently used dental implant materials to replace a missing tooth and have been used for a long time. The most preferred are pure titanium (cpTi) and Ti6Al4V, which give clinical success rates of up to 99% over a period of 10 years. Both these biometals are biocompatible and are capable of undergoing osseointegration. Titanium alloys are widely used in medical applications because they demonstrate excellent biocompatibility and good mechanical properties, such as less elastic modulus than stainless steel or CoCr alloys. However, although titanium alloys are good biomaterials, they can fail due to microbial colonization on the surface of the implant which causes infections and thus their surfaces must be modified to prevent implant infections. The current research focused on using natural products, particularly plantderived essential oils, to combat bacteria that colonise dental implants and later cause implant failure. The literature has revealed that natural products such as essential oils are promising antimicrobial agents. Rising knowledge about the emergence of antibiotic-resistant microorganisms has encouraged researchers to search for new antimicrobial agents that are more effective this background that the current study investigated the antibacterial activity of five commercially available plant-derived essential oils, namely Lavandula latifolia (lavender oil), Syzygium aromaticum (clove bud), Salvia officinalis (sage), Cinnamomum zeylanicum Blume (cinnamon) and Mentha piperita (peppermint). These essential oils were tested against three resistant pathogens, namely Staphylococcus aureus, Streptococcus mutans and Escherichia coli. The chemical components of the essential oils were analysed using gas chromatographymass spectrometry (GC-MS) and the main components of the essential oils were found to be terpenes and phenols. The antimicrobial activity of the essential oils was additionally investigated using agar diffusion bioassay from five essential oils. Of these, Cinnamomum zeylanicum Blume showed the highest antimicrobial activity against Escherichia coli and Staphylococcus aureus, whereas Salvia officinalis showed the highest antimicrobial activity against Streptococcus mutans. The minimum concentrations at which the essential oils inhibited bacterial growth were investigated using microdilution essay. Structural changes caused by the essential oils were evaluated using a scanning electron microscope and alterations such as damaged cell walls, holes in the bacterial cells, irregularity in size and some ruptured cells were observed. After scanning electron microscopy had been performed, Ti6Al4V (ELI) experimental dental implants (which are used to replace a missing tooth) were additively manufactured (3D printing) using EOS M280 direct metal laser sintering (DMLS) manufacturing technology. A subset of the laser powder bed fusion (LPBF) process was also employed. Next, the antimicrobial activity of the essential oils was investigated on the surface of the titanium implant materials. The essential oils were used to modify the surface of titanium implant materials to inhibit the growth of bacteria on their surfaces. The findings suggest that antimicrobial agents such as essential oils need to be considered as potential antimicrobials in the future because of their effective mechanism of action against bacterial cells. For instance, it was found that Cinnamomum zeylanicum Blume and Salvia officinalis essential oils penetrated the bacterial cell wall and gained entrance into the cell, thus causing disruption to the entire bacterial cell. Essential oils thus have the potential to be used as antimicrobial agents against Staphylococcus aureus, Streptococcus mutans and Escherichia coli. Scanning electron microscopy (SEM) results also showed radical structural alterations such as leakage of bacteria cell contents, cells becoming pleomorphic, irregularity in cell size and the rupturing of some cells when treated with Salvia officinalis and Cinnamomum zeylanicum Blume essential oils at their minimum inhibition concentrations. The bioassay results showed that Lavendula officianalis, Mentha piperita, Cinnamomum zeylanicum Blume and Salvia officinalis essential oils can act as effective antimicrobial agents against Staphylococcus aureus, Streptococcus mutans and Escherichia coli. It is noteworthy that Salvia officinalis and Cinnamomum zeylanicum Blume essential oils showed the most significant inhibitory effects on oral pathogens in the present work.