published_or_final_version / Dentistry / Master / Master of Dental Surgery

Doctor of Philosophy / This thesis describes experiments which were carried out at the Institute of Dental Research in Sydney and within the Department of Prosthetic Dentistry at the United Dental Hospital of Sydney between February 1991 and May 1996. The study is concerned with finding practical means of treating chronic atrophic candidosis, also referred to as Candida-associated denture stomatitis and to this purpose two methods of denture disinfection are investigated, namely, sodium hypoclorite denture soak and microwave irradiation. Although the aetiology of denture stomatitis is generally considered to be multifactorial, there is sufficient evidence that Candida species and in particular C. albicans play an important role in the aetiology of the condition. In Chapter 1, therefore, the literature review, which provides relevant background information for the experiments to be described in later chapters, is primarily concerned with Candida species. The characteristics and distribution of Candida species are described and factors affecting the distribution of or Candida are discussed. The literature relating to the cause of chronic atrophic candidosis is vast and consequently a detailed description is given of Candida-associated denture stomatitis in the section concerned with oral diseases caused by Candida and their treatment. Each of the subsequent chapters, contains a brief literature review of material relevant to the subject of the particular chapter. Chapter 2 describes laboratory work to assess the effect of sodium hypochlorite on the adhesion of Candida species to oral surfaces and the ability of Candida to coaggregate with oral streptococci. The results showed that sodium hypochlorite decreased the ability of Candida species to adhere to both inert surfaces and BECs. However, coaggregation of Candida with streptococci was increased. Thus, hypochlorite if used as a denture soak may initially reduce the ability of Candida species to adhere to the denture surface and may therefore assist the treatment of denture stomatitis. The effects of hypochlorite on the characteristics of Candida species that are associated with tissue invasion are described in Chapter 3. The production of acid proteinase, the formation of germ tubes and presence of major cell wall proteins at 43 and 27 kDa are demonstrated. The ability of the whole cells of certain species of Candida to aggregate human platelets was assessed. The results showed that sodium hypochlorite did not affect proteinase production by Candida species but the rate of germ tube formation and the production of Candida cell wall proteins were increased. Hypochlorite did not affect the ability of certain Candida species to aggregate human platelets. Mechanisms to defend the host against candidal invasion are discussed and include platelet aggregation where aggregated platelets release antimicrobial factors that are active against Candida. Chapter 4 describes an in vitro study to test the effects of sodium hypochlorite and microwave irradiation on the survival of Candida species and oral streptococci on denture surfaces. The results showed that 0.02% sodium hypochlorite denture soak for 8 h will eliminate Candida species and reduce the growth of streptococci. However, microwaving of dentures at medium setting for 6 min will eliminate both Candida and streptococci. This information servers as baseline data for clinical assessments described in Chapters 7 and 8. Denture hygiene is an important factor in the prevention and treatment of Candida-associated denture stomatitis. Hence, a clinical study to assess the microbiology of denture plaque is described in Chapter 5. The results showed that denture plaque was composed mainly of Gram-positive streptococci with varying proportions of Gram-positive rods, Gram-negative cocci and rods and is similar to dental plaque. Candida was not always isolated and when detected constituted a very small proportion (< 1%) of the total aerobic bacterial count. The results of an investigation to test the effect of soft denture liners in lower dentures on the colonization of denture surfaces by Candida species and aerobic bacteria are given in Chapter 6. There was no significant difference in Candida /bacterial colonization of dentures with soft denture liners and those without liners. Chapter 7 describes a clinical study to test the efficiency of sodium hypochlorite (0.02%) over-night denture soak as an effective denture disinfecting agent. Treatment of dentures with hypochlorite over a trial period resulted in reductions of Candida and aerobic bacteria and although the reductions were not significant the effect over the trial period could be assessed. A significant finding was that for the palate, treatment with hypochlorite over the trial period prevented an increase in candidal load. Thus, sodium hypochlorite may function as an effective disinfecting agent when used as 0.02% denture soak for a prolonged period. A pilot study to assess the effectiveness of microwaving dentures for ten min (350 W, 240 MHz) as a potential method of denture disinfection is described in Chapter 8. For practical reasons the dentures were microwaved only once only and therefore the effect over a trial period could not be assessed. However, one treatment resulted in significant reductions in the levels of Candida and aerobic bacteria. These findings have indicated that future research should be carried out to test the effect of daily consecutive microwave treatments on candidal and bacterial growth. The general discussion in Chapter 9 summarizes the data presented in the previous chapters and from the findings conclusions are made concerning the prevention and treatment of Candida-associated denture stomatitis. The limitations of this thesis are recognized and some important aspects of the study are recommended for future research.

Doctor of Philosophy / This thesis describes experiments which were carried out at the Institute of Dental Research in Sydney and within the Department of Prosthetic Dentistry at the United Dental Hospital of Sydney between February 1991 and May 1996. The study is concerned with finding practical means of treating chronic atrophic candidosis, also referred to as Candida-associated denture stomatitis and to this purpose two methods of denture disinfection are investigated, namely, sodium hypoclorite denture soak and microwave irradiation. Although the aetiology of denture stomatitis is generally considered to be multifactorial, there is sufficient evidence that Candida species and in particular C. albicans play an important role in the aetiology of the condition. In Chapter 1, therefore, the literature review, which provides relevant background information for the experiments to be described in later chapters, is primarily concerned with Candida species. The characteristics and distribution of Candida species are described and factors affecting the distribution of or Candida are discussed. The literature relating to the cause of chronic atrophic candidosis is vast and consequently a detailed description is given of Candida-associated denture stomatitis in the section concerned with oral diseases caused by Candida and their treatment. Each of the subsequent chapters, contains a brief literature review of material relevant to the subject of the particular chapter. Chapter 2 describes laboratory work to assess the effect of sodium hypochlorite on the adhesion of Candida species to oral surfaces and the ability of Candida to coaggregate with oral streptococci. The results showed that sodium hypochlorite decreased the ability of Candida species to adhere to both inert surfaces and BECs. However, coaggregation of Candida with streptococci was increased. Thus, hypochlorite if used as a denture soak may initially reduce the ability of Candida species to adhere to the denture surface and may therefore assist the treatment of denture stomatitis. The effects of hypochlorite on the characteristics of Candida species that are associated with tissue invasion are described in Chapter 3. The production of acid proteinase, the formation of germ tubes and presence of major cell wall proteins at 43 and 27 kDa are demonstrated. The ability of the whole cells of certain species of Candida to aggregate human platelets was assessed. The results showed that sodium hypochlorite did not affect proteinase production by Candida species but the rate of germ tube formation and the production of Candida cell wall proteins were increased. Hypochlorite did not affect the ability of certain Candida species to aggregate human platelets. Mechanisms to defend the host against candidal invasion are discussed and include platelet aggregation where aggregated platelets release antimicrobial factors that are active against Candida. Chapter 4 describes an in vitro study to test the effects of sodium hypochlorite and microwave irradiation on the survival of Candida species and oral streptococci on denture surfaces. The results showed that 0.02% sodium hypochlorite denture soak for 8 h will eliminate Candida species and reduce the growth of streptococci. However, microwaving of dentures at medium setting for 6 min will eliminate both Candida and streptococci. This information servers as baseline data for clinical assessments described in Chapters 7 and 8. Denture hygiene is an important factor in the prevention and treatment of Candida-associated denture stomatitis. Hence, a clinical study to assess the microbiology of denture plaque is described in Chapter 5. The results showed that denture plaque was composed mainly of Gram-positive streptococci with varying proportions of Gram-positive rods, Gram-negative cocci and rods and is similar to dental plaque. Candida was not always isolated and when detected constituted a very small proportion (< 1%) of the total aerobic bacterial count. The results of an investigation to test the effect of soft denture liners in lower dentures on the colonization of denture surfaces by Candida species and aerobic bacteria are given in Chapter 6. There was no significant difference in Candida /bacterial colonization of dentures with soft denture liners and those without liners. Chapter 7 describes a clinical study to test the efficiency of sodium hypochlorite (0.02%) over-night denture soak as an effective denture disinfecting agent. Treatment of dentures with hypochlorite over a trial period resulted in reductions of Candida and aerobic bacteria and although the reductions were not significant the effect over the trial period could be assessed. A significant finding was that for the palate, treatment with hypochlorite over the trial period prevented an increase in candidal load. Thus, sodium hypochlorite may function as an effective disinfecting agent when used as 0.02% denture soak for a prolonged period. A pilot study to assess the effectiveness of microwaving dentures for ten min (350 W, 240 MHz) as a potential method of denture disinfection is described in Chapter 8. For practical reasons the dentures were microwaved only once only and therefore the effect over a trial period could not be assessed. However, one treatment resulted in significant reductions in the levels of Candida and aerobic bacteria. These findings have indicated that future research should be carried out to test the effect of daily consecutive microwave treatments on candidal and bacterial growth. The general discussion in Chapter 9 summarizes the data presented in the previous chapters and from the findings conclusions are made concerning the prevention and treatment of Candida-associated denture stomatitis. The limitations of this thesis are recognized and some important aspects of the study are recommended for future research.