Al-Groosh, DHA; (2014) Opportunistic pathogens associated with orthodontic retainers. Doctoral thesis , UCL (University College London).

Abstract

Orthodontic retainers may be considered as removable implants and confer the same problems as other implants with regard to colonisation by microorganisms. Thus, biofilms forming on their surface may compromise the oral health of patients and jeopardise the efficiency of the therapy. The first part of the project involved a clinical study, a cross-sectional observational cohort, to assess the effect of orthodontic treatment on the oral microbiota and the carriage state of opportunistic pathogens during the course of treatment. High proportions of health-associated species were detected in the retainer group. However, Staphylococcus and Candida species were frequently (69% and 36% respectively) isolated from the retainers and the oral cavity of retainer wearers, where Staphylococcus spp. comprised up to 5% of the microbiota. The increase in Staphylococcus spp. including Methicillin Resistant Staphylococcus aureus (MRSA) on retainers was associated with an increase in numbers of these species on the oral mucosa of the cheek and tongue. Orthodontic retainers could, therefore, be a reservoir for pathogens and act as a source of cross-infection. A series of in vitro investigations were subsequently carried out to evaluate the effect of the surface characteristics of retainer materials, including surface roughness, hydrophobicity and surface free energy, which may affect colonisation by opportunistic pathogens. After polishing the surface of the acrylic substrata the results revealed that Atomic Force Microscope was the most appropriate device to measure the surface roughness of the acrylic and thermoplastic materials in a consistent manner. Additionally, the acid-base interactions, especially the electron donor interaction, influenced the bacterial attachment onto the thermoplastic samples. Finally, assessment of novel antimicrobial-containing acrylic resins was carried out. Firstly, incorporation of chlorhexidine showed a prolonged antimicrobial effect against MRSA but was detrimental to the mechanical properties. Thymol was successfully incorporated in heat cured acrylic materials. It reduced the surface free energy of the modified resin with no effect on the mechanical properties and was strongly antimicrobial against C. albicans. However, it showed a lesser antimicrobial effect against MRSA. This PhD has shown the potential of orthodontic retainers as reservoirs for opportunistic pathogens and that surface characteristics are significant in the retention and potential removal of these pathogens. The use of antimicrobial acrylic materials may be of potential therapeutic benefit following further development.

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