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Title: In vitro investigations into the antimicrobial and microecological effects of selected anti-plaque agents
Author: Mohamad, Mohamad
ISNI:       0000 0004 2703 7196
Awarding Body: University of Manchester
Current Institution: University of Manchester
Date of Award: 2011
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The prevalence of oral diseases such as dental caries and periodontitis and the universal need for effective control of oral health has stimulated a great deal of interest in oral hygienic formulations both scientifically and commercially driven. Such formulations are normally deployed as complex formulations commonly containing antimicrobial actives together with excipients, where both classes of ingredients may contribute to the bacteriological effect of the oral hygienic product. However, the mode of action and/or the bacteriological and microecological effects of exposure of microorganisms to oral hygiene products are poorly understood. In this context, this doctoral dissertation represents a series of investigations to contribute to knowledge in the area. The impact of selected oral antimicrobial actives (triclosan, sodium lauryl sulphate, stannous fluoride and zinc lactate) on a key aspect of bacterial cellular membrane function was investigated. This involved measuring major cellular respiratory pathways during exposure to the test agents using two types of tetrazolium dyes possessing different redox potentials as respiration pathway indicators. Spectrophotometric analyses indicated that sub-lethal levels of triclosan and sodium lauryl sulphate act as uncoupling agents, an observation not previously been reported. Sub-lethal concentrations of stannous fluoride and zinc lactate however, blocked cellular respiration with resulting shifts towards glycolytic/fermentative pathways. The contribution of a variety of test agents to the overall antimicrobial effect of a complex formulation (Listerine®) was investigated in order to understand the relative efficacy of the actives. This was achieved by testing the essential oils present in the formulation singly and in combination utilising in vitro models. The use of the hydroxyapatite disc model (HDM) to grow salivary microcosms to test the efficacy of the ingredients revealed hitherto unreported synergistic activity between the active ingredients thymol and menthol. Proprietary dentifrices (Colgate Total® and Crest ProHealth®) containing the antimicrobial agents triclosan or stannous fluoride/zinc lactate, respectively, were comparatively evaluated. This was performed by simultaneously establishing salivary microcosms in Sorbarod Biofilm Devices (SBDs). Following the establishment of dynamic steady-states, paired devices were dosed with each of the two proprietary dentifrices. Bacteriological data generated after multiple dosing indicated that both dentifrices were comparably effective in the reduction of all tested bacterial functional groups in the plaque models. However, data generated using HDM models indicated greater reductions in Gram-negative anaerobes after exposure to Colgate total®. The observations presented in this thesis may contribute to the development of oral formulations with optimised antimicrobial efficacies against adventitious pathogens present in the oral cavity and help in reducing the incidence of oral diseases and potentially related systemic interface.
Supervisor: Mcbain, Andrew ; Allison, David Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Oral antimicrobials ; Oral hygiene ; Dental plaque ; in vitro microcosms ; Biofilm models