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A report for the Rural Industries Research   and Development Corporation
by KA Hammer, L Dry, M Johnson, E Michalak, CF Carson, TV Riley

May 2003

RIRDC Publication No 03/019  RIRDC Project No UWA-55A

Executive Summary
The human mouth provides a habitat for a diverse range of bacteria, viruses, protozoa and fungi.  These micro-organisms colonise essentially every surface in the mouth, including the cheeks,  tongue, palate and teeth. Under certain circumstances, these organisms may cause diseases of the  oral cavity, although this usually only occurs when there is a break in, or loss of, maintenance of  oral hygiene. Loss of oral hygiene may lead relatively quickly to the development of oral diseases  or conditions such as gingivitis, halitosis (bad breath), dental plaque, dental calculus, dental caries  and periodontitis. More severe outcomes of poor oral hygiene include the loss of teeth and/or  bone.

These diseases are avoided in most individuals by the proper maintenance of oral hygiene. This is  usually achieved by the regular brushing of teeth, which may be combined with the use of  additional oral hygiene products such as mouthwashes. A recent trend has seen the inclusion of  antibacterial agents in many oral hygiene products such as toothpastes and mouthwashes, and there  may be a role for tea tree oil as one such agent.

The aim of this study was to determine the in vitro susceptibility of a range of oral bacteria to tea  tree oil and to use these data to assess the suitability of tea tree oil for use in the oral cavity.

A total of 162 bacterial isolates from the genera Actinomyces, Branhamella, Capnocytophaga,  Clostridium, Eikenella, Fusobacterium, Haemophilus, Lactobacillus, Neisseria,  Peptostreptococcus, Porphyromonas, Prevotella, Stomatococcus, Streptococcus and Veillonella  were tested for their susceptibility to tea tree oil. All isolates were inhibited and killed by  concentrations of tea tree oil ¡Ü 2%, and in fact most were inhibited and/or killed at concentrations  below this. Isolates with the lowest MICs and MBCs were from the genera Prevotella,  Porphyromonas and Veillonella and isolates with the highest MICs and MBCs were from the  genera Streptococcus, Fusobacterium and Lactobacillus. Streptococcus mutans has been strongly associated with the development of dental caries. As such,  it was of interest to investigate how quickly cells of S. mutans were killed when treated with tea  tree oil. Treatment with 4, 2, 1 and 0.5% tea tree oil resulted in a greater than 3 log decrease in  viable cells after only 30 seconds treatment. Also, after 5 and 10 minutes, viable cells could not be  recovered from these treatments. Less killing was evident when S. mutans cells were treated with

0.12 and 0.25% tea tree oil. Time kill studies conducted with an isolate of Lactobacillus  rhamnosus, a species also associated with dental caries, showed that L. rhamnosus was killed  rapidly at both 0.5 and 1% tea tree oil, but less rapidly at 0.25%. Studies with these two species  showed that tea tree oil exerts a relatively rapid killing effect. This in turn suggests that if tea tree  oil was used in a mouthwash formulation it may be effective in reducing the numbers of S. mutans,  L. rhamnosus or other bacteria within the mouth.

The data from this study suggest that tea tree oil may be of use in oral hygiene products. However,  the exact role for tea tree oil remains to be elucidated and clinical trials evaluating tea tree oil  formulations for a range of oral diseases or conditions are needed to establish this.

 

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Last updated: 19 May 2003
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