Original study - ZZI 01/2009

Essential oils: antimicrobial effects and potential treatment options in dental implantology

To investigate antimicrobial effectiveness with microbiological tests, the antimicrobial activity of different essential oils on several pathogenic micro-organisms was tested in this study. As a guide, strains of Staphylococcus aureus, Staphylococcus epidermidis, Streptococcus mutans, Streptococcus haemolyticus and Candida albicans were tested first. All of these strains are clinically relevant in oral and maxillofacial surgery and are often a cause of oral, odontogenic and cutaneous infections. Special attention was paid to the problem pathogens MRSA and Candida krusei, which were also tested. Because the common antibiotics of first choice are no longer effective against MRSA and last-resort reserve antibiotics often have to be used, this strain is becoming an increasing problem especially in intensive care patients and acute hospitals. Candida krusei is often resistant clinically to common antimycotic agents and is a problem particularly in immunosuppressed patients and transplant recipients [16, 20]. Since the common treatment regimens are increasingly exhausted, the effective essential oils might be a therapeutic option for local use. Some of the tested oils showed marked inhibition zones of up to 49 mm, e. g. in the case of lemongrass oil against Candida krusei. Lemongrass oil achieved an inhibition zone of over 30 mm against MRSA also. The controls such as chlorhexi-dine and povidone iodine achieved inhibition zone diameters of 10 mm to 25 mm. Direct comparison of the inhibition zone diameters of different substances is not entirely admissible in the agar diffusion test. However, the marked inhibition zone diameters with the essential oils are impressive evidence of their antimicrobial effectiveness.

For peri-implant infections, anaerobes (e. g. Porphyro-monas gingivalis) certainly play a weightier role than the cocci tested here. However, the methods for testing essential oils in an anaerobic milieu (highly negative redox potential) have not yet been standardized and validated. Thus, this study has a more orienting character. However, the effectiveness against staphylococci and streptococci is clear evidence of an antibacterial action. Activity against the leading strains that cause peri-implantitis would therefore be likely. Essential oils might thus be a potential option for the treatment of peri-implant infections. The literature also provides further evidence of the antimicrobial effectiveness of essential oils which would be relevant for implantology [2].

Terpenen-4-ol, linalool and alpha-terpineol have been described as active components, e. g. of tea tree oil [4, 5, 15, 18]. It has been shown that these substances, especially terpinen-4-ol, can destroy the bacterial cell wall and cause changes in the potassium concentration gradient [6]. Moreover, inhibition of glucose-dependent cell respiration has been demonstrated [6, 9]. This suggests that effectiveness against anaerobes of relevance in peri-implantitis might be achieved. Consequently, use of these oils in the local treatment of peri-implant infections might be considered in order to circumvent the problems of local antibiotic use with regard to the development of resistance.

Clinical and immunological studies also provide evidence that the essential oils have anti-inflammatory characteristics [17], which may be due in part to inhibition of production of inflammatory mediators by the monocytes [13, 24]. Anti-inflammatory effects would be of considerable benefit in the treatment of peri-implantitis since inhibition of inflammatory mediator secretion would also help to limit bone atrophy due to inflammation. Promotion of wound healing by essential oils has been described and might assist the ideal goal of restitutio ad integrum [24, 26]. This would give them a clear and clinically relevant advantage compared to classic antiseptics such as povidone iodine and chlorhexidine.

The pure oils were tested in undiluted or undissolved form. In pure form, essential oils can have an intense intrinsic odor and would be too viscous for use in a spray bottle. They are therefore frequently dissolved in alcohol in order to improve their characteristics, especially for use in aromatherapy. In general, citric oils such as lemongrass oil or lemon oil are highly acceptable to patients. Melaleuca-like oils such as tea tree oil or eucalyptus oil sometimes encounter rejection, as we discovered in odor tests with patients and nursing staff. The combination of several oils can have synergistic effects and can improve the overall odor considerably (results of these studies not shown).

The essential oils on sale in Germany often have ethanol or synthetic perfume added to increase evaporation and make them suitable for aromatherapy requirements. The three oil mixtures tested here were also dissolved in alcohol (max. 30 %). With our own KMPT mixture, the readier evaporation induced by the alcohol should promote the pleasant intrinsic odor of the oils, allowing them to be used as an antiseptic spray in wound treatment. This has been confirmed in clinical use [24].

A frequent criticism is that the added ethanol alone is the cause of the antimicrobial characteristics. That is why ethanol in the high concentration of 70 % was tested as a control, achieving inhibition zones of up to 7 mm. Since the pure oils without added alcohol and the oil mixtures containing much less added alcohol produced marked inhibition zones, the antimicrobial pharmacological effects can essentially be attributed to the substances in the oils themselves.

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