Original study - ZZI 01/2009

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

5. if possible promote tissue regeneration in the sense of restitutio ad integrum.

 

Antimicrobial and anti-inflammatory characteristics are attributed to essential oils such as eucalyptus and tea tree oil [17]. These are employed frequently in traditional or complementary medicine, but are not accepted as a medication by the majority of clinicians with their roots in orthodox medicine. In contrast, the trust patients place in natural remedies is often re-markably striking. These oils are also experiencing a boom as cosmetics and can already be found, for instance, in oral rinses such as Listerine (www.listerine.com, McNEIL-PPC, USA) and toothpastes (Fig. 1). This induced us to conduct a pilot study of the antimicrobial effectiveness of a selection of essential oils against clinically relevant micro-organisms using scientifically accepted microbiological methods.

The aim is to develop potential new regimens for the treatment of peri-implant infections possibly based on essential oils.

 

Material and methods

The following essential oils, which are reputed in alternative medicine literature to have antimicrobial characteristics, were tested using in-vitro microbiological methods: eucalyptus oil, tea tree oil, thyme oil, lemon oil, lemongrass oil and clove bud oil. Only pure Australian oils obtained directly from Australian manufacturers were used, which were supplied without synthetic perfumes or solvents. Three oil mixtures and oral rinse formulations containing essential oils were also tested. These included our own oil combination, a mixture of several pure oils, which was designated KMPT Mix. KMPT Mix is a mixture of eucalyptus oil, tea tree oil, lemongrass oil, lemon oil, clove bud oil and thyme oil dissolved in 30 % ethanol. The other two mixtures were Liste-rine and Salviathymol (MADAUS GmbH, Cologne, Germany).

The controls employed in the study were standard water-soluble antiseptics such as ethanol (70 %), povidone iodine and chlorhexidine 0.1 %. The other lipophilic controls were olive oil and liquid paraffin, which were not expected to have any antimicrobial activity.

 

Bacterial and candida strains

The test substances were tested against strains of clinically relevant species (Staphylococcus aureus, Staphylococcus epidermidis, Streptococcus mutans, Streptococcus haemolyticus and Candida albicans) using the agar diffusion test. Clinical problem strains such as isolates of methicillin-resistant Staphylococcus aureus (MRSA) and Candida krusei were also tested. Each test was performed in duplicate.

Agar diffusion test

A colony of the micro-organisms to be tested was stirred into 10 ml physiological saline. 2 ml of the solution was added to nutrient agar (depending on the strain: Mueller-Hinton agar, Columbia agar with 5 % sheep blood, Sabouraud agar plus glucose), distributed uniformly and 1 ml of the solution was pipetted.

After drying the inoculated agar plates, test discs (Antimicrobial Susceptibility TEST DISCS from OXOID, diameter 6 mm) were placed in the centre of the plates using sterile forceps and 10 µl of the test oil was placed on them. The agar plates were then incubated for 18 hours at 37 °C. Streptococcal test strains underwent microaerophilic incubation.

Following this, the diameters of the growth-free inhibition zones that had occurred around the test discs if the test substance exhibited antimicrobial activity were measured. Inhibition zone diameters of 6 mm or less were classified as ineffective as this was the diameter of the test discs.

 

Analysis

The medians of the inhibition zone diameters were calculated for each essential oil and for the controls and were shown as column diagrams.

Results

All of the tested essential oils and oil mixtures showed good to moderate antibacterial and antimycotic effects against the tested strains. Inhibition zones of 6 mm to 49 mm were obtained.

Among the pure oils the greatest inhibition zones were obtained for lemongrass oil (up to 49 mm) and thyme oil (up to over 30 mm) with reference to all the tested strains. Of the oil mixtures, KMPT showed the greatest inhibition zones with reference to staphylococcal and candida strains. In the tests with streptococci, obvious inhibition zones for KMPT and Salviathymol were an expression of their good antimicrobial activity.

Even the tested resistant strains, such as MRSA and Candida krusei, reacted sensitively to the essential oils and oil mixtures, as confirmed by the obvious inhibition zones.

The olive oil and liquid paraffin controls had no antibacterial or antimycotic activity in any case, as the tested problem strains were able to grow uninhibited.

Inhibition zones up to 7 mm were obtained with 70 % ethanol in this experimental design. An inhibitory effect on bacterial and candida growth was confirmed for povidone iodine and chlorhexidine, which resulted in inhibition zones 10 mm to 25 mm in diameter generally.

The medians of the diameters of the inhibition zones are shown in figures 2a to 2c.

 

Discussion

The origins of the use of essential oils among Australian Aborigines probably go back centuries [10].

Since the start of the 20th century, essential oils have been used in Australia as antiseptics by immigrants and many of them are now commercially available [11]. In earlier studies, the antimicrobial effects of tea tree oil against pathogenic oral bacteria and oropharyngeal candidiasis were already described [8, 16], though it did not gain broad acceptance as an antiseptic in Europe or America.

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