Abstract
Antibiotics and antiseptics are used as locally-delivered antimicrobial adjuncts in conjunction with scaling and root planing (SRP), mostly to treat non-responding and recurrent deep periodontal pockets. Adjunctive therapy is deemed necessary to support and optimise periodontal healing by eliminating or suppressing gram-negative bacteria associated with periodontal diseases. However, due to developing antibiotic resistance, alternative antimicrobials originating from plants have been considered. Bioactive substances from this source have potent antibacterial properties and wound healing potential. The research described in this thesis investigated the potential of manuka-derived products (manuka honey and manuka oil) as antimicrobials to be administered to periodontal pockets as an adjunct to SRP.
In vitro and in vivo investigations were performed to answer the research questions related to this topic. Antibacterial activities of manuka-derived products were assessed. Clinical and microbiological outcomes following SRP and application of manuka honey were measured. Toxicology profile of manuka oil was determined using cell culture methods. A delivery device for the administration of manuka oil to periodontal pockets was developed. This device was assessed for antibacterial activity and penetration into a single-species biofilm.
Manuka honey exhibited broad-spectrum antimicrobial activity against a variety of plaque-associated bacteria. The present in vitro investigation demonstrated that decreasing the concentration of honey not only reduced the antimicrobial activity but also promoted bacterial carbohydrate metabolism and consequent acid production by Streptocococcus mutans, further exacerbating demineralisation. Furthermore, manuka honey is slow-acting, thus limiting its efficacy in periodontal pockets due to significant dilution. The split-mouth clinical study of a three-month follow-up did not show additional improvement in clinical parameters when periodontal pockets were treated with manuka honey following SRP compared to SRP alone. In contrast, manuka oil showed encouraging potential as a therapeutic substance. When comparing the two manuka-derived products, manuka oil (effective concentration = 0.1% w/v) was more potent than manuka honey (effective concentrations ranged = 13-25% w/v).
Manuka oil also showed a relatively rapid bactericidal effect. The toxicology profile of manuka oil based on half maximal inhibitory concentrations (IC50) determined at 96 hours was four times higher than the effective antimicrobial concentration, whereas the IC50 of chlorhexidine was 100 times higher than its therapeutic concentration. This investigation suggests that apoptosis rather than necrosis may be the mechanism of cell death induced by manuka oil under cell culture conditions. The compositions of a delivery device demonstrated favourable rheological properties, that is, pseudoplastic or shear thinning behaviour and increased elasticity with increasing frequencies which may improve retention in periodontal pockets. The emulsion containing manuka oil under experimental conditions was more effective than chlorhexidine at reducing the proportions of bacteria in the biofilms, as indicated by the increased of red fluorescence (live/dead staining) viewed in the confocal scanning laser microscope images. In addition, the emulsion containing manuka oil was consistently active through the entire depth of the biofilm compared to chlorhexidine.
The major implication of this research project is to support the potential uses of bioactive substances derived from plants as antimicrobials in periodontal therapy. Manuka oil may be superior to manuka honey as an antimicrobial for intra-oral applications.