Lect#22 .pptx

Lecture #22 The microbiology of Tooth decay Lecture Overview Here we will look at the role of microorganisms in dental diseases and the role that fermentation can play in dental caries. Lecture Objectives After todays lecture and reading appropriate portions of the text you should be able to: •...

Lecture #22 The microbiology of Tooth decay Lecture Overview Here we will look at the role of microorganisms in dental diseases and the role that fermentation can play in dental caries. Lecture Objectives After todays lecture and reading appropriate portions of the text you should be able to: • describe and define dental plaque formation • describe the diversity of species in dental plaque • describe the role of Streptococcus mutans in dental caries • describe gingivitis • describe the role of fluoridation in cavity prevention Microorganisms and Concepts Streptococcus mutans • dental plaque • calculus • biofilm • dental caries • dextran and lactic acid • fluoride http://www.youtube.com/watch?v=A8zl6MrAqr s The oral flora is one of the most ecologically diverse microbial populations known to man. -350 cultivable species (this many only be 50% of the flora) -saliva contains up to 100 million microbes per mL -large number of anaerobes -normally a balanced ecosystem- but can be disturbed by a variety of factors- some resident microbes can behave as opportunistic pathogens -Streptococci comprise a major part of the oral flora and play an important role in dental caries and oral infections Dental plaque formation -bacteria adhere to tooth surfaces -normally bacteria do not colonize clean enamel but interact with a layer of material on the tooth surface call the pellicle. -the pellicle is comprised of mucins, salivary glycoproteins, minerals and immuno-globins -the pellicle forms within seconds and reaches a maximum thickness in 90-120 minutes. -the pellicle is then colonized by pioneer bacteria Microcolonies of bacteria growing on a model tooth surface inserted in the mouth for 6 hr. This is a higher magnification. Note the diverse morphologies of microbes and the slime layer (arrow) holding the organisms together. -gradually microcolonies coalesce to produce a biofilm -dental plaque is a general terms for the complex microbial community found on the tooth surface, embedded in a matrix of polymers of bacterial and salivary origin. -co-aggregation between species can occur -an equilibrium exists between the forces of retention and removal Vegetable dye stains heavy plaque accumulations at the junction of tooth and gingiva. Time-course of plaque distribution. SEM of plaque with long filamentous bacteria and “corn cobs” that are mixed bacterial aggregates. What is calculus? -dental plaque can become calcified-saliva is saturated with calcium and phosphate ion which may be deposited within the plaque. -formation of an insoluble calcium phosphate crystal called calculus. -many anti-calculus toothpastes contain pyrophosphate compounds designed to adsorb excess calcium thus reducing intraplaque development. -calculus is porous thus allowing bacterial products to be absorbed -- calculus must therefore be removed from tooth surfaces to halt tissue damage and periodontal disease. Summary of events leading to: 1. periodontal disease. 2. dental caries and/or 2. 1. http://www.youtu be.com/watch?v= wUwzae1qIBQ&f eature=related 1. Periodontal damage caused by abrasions in the gingival membrane- resulting in inflammatory reaction. The damaged tissues are portals for bacterial infection. This is what happens if plaque is allowed to build up. The initial signs of gingivitis are swelling and redness. If the condition persists, a more serious disease called periodontitis results. Progression of the stages from a normal tooth (left) to calculus buildup and gingivitis (centre) and finally (right) late-stage periodontitis, with tissue destruction, deep pocket formation, loosening of teeth, and bone loss. 2. Tooth decay (dental caries). What is it? -Streptococcus mutans, a Gram+ coccus occurs in pairs and short chains. -adheres to tooth surfaces -important role in dental caries--> the acidic erosion of the protective enamel and deeper parts of the tooth. - results in a hole and nerves eventually exposed -three main factors (1) individual physiology (2) bacteria and (3) diet -diet rich in sugar promotes tooth decay. Why? http://www.youtube.com/watch?v=ft2SVyEs2SY&feature= related The enzyme glucosyltransferase (=dextransucrase) produced by oral bacteria (i.e. S. mutans) cause the assembly of glucose units from sucrose into glucans, and fructose is released. Sucrose, glucose and fructose are also anaerobically metabolized to produce lactate and other acids. Lactic acid is partially reponsible for enamal erosion and dental caries. Dextran of S. mutans cements bacteria to tooth enamel. Preventing tooth decay -minimize consumption of refined sugar (sucrose) -fluoridation (water or toothpaste) -clean teeth routinely The effect of fluoride on tooth decay. (a) normal tooth. (b) dental caries as a result of acid seeping between rods of enamel. (c) mineralization of fluoride between spaces of enamel rods preventing acid from seeping in. Sequencing ancient calcified dental plaque shows changes in oral microbiota with dietary shifts of the Neolithic and Industrial revolutions. Adler et al. Nature Genetics 45, 450–455 (2013) Impacts of evolutionary changes in human diet and culture on commensal microbiota remain almost unknown. Two of the greatest dietary shifts in human evolution involved the adoption of carbohydrate-rich Neolithic (farming) diets (beginning ~10,000 years before the present) and the more recent advent of industrially processed flour and sugar (in ~1850). -transition from hunter-gatherer to farming shifted the oral microbial community to a disease-associated configuration. The composition of oral microbiota remained unexpectedly constant between Neolithic and medieval times, after which (the now ubiquitous) cariogenic bacteria became dominant, apparently during the Industrial Revolution. Perhaps more notably, the decline in overall oral microbial diversity indicates that, over the past few hundred years, the human mouth has become a substantially less biodiverse ecosystem. Dominated by cariogenic bacteria such as S. mutans. Major changes in carbohydrate intake in human history seem to.have affected the ecosystem of the mouth, opening up pathological niches for periodontal disease in the early Neolithic period and caries in the recent past. “A genuine, affectionate smile is very important in our day to-day lives.” Dalai Lama