Lecture 04 - Etiology of Periodontal Disease PDF

Microbiology of Periodontal Diseases DH 308 1 Virulence The presence of dental plaque is essential to the initiation and progression of gingivitis and periodontitis. Studies evaluating the relationship between oral hygiene and periodontal diseases have shown that...

Microbiology of Periodontal Diseases DH 308 1 Virulence The presence of dental plaque is essential to the initiation and progression of gingivitis and periodontitis. Studies evaluating the relationship between oral hygiene and periodontal diseases have shown that poor plaque control correlates to a greater prevalence and severity of periodontal diseases. 2 General Characteristics of Plaque Formation Dental plaque biofilms are defined as accumulations of microbes on the surface of the teeth or other solid oral structures, not easily removed by rinsing. Dental plaque biofilms are different than material alba, which are loosely adherent bacteria and tissue debris that can be easily removed by the mechanical action of a strong water spray. 3 General Characteristics of Plaque Formation (Cont.) Biofilm is a film of microorganisms bound in the sticky polysaccharide matrix they produce, the glycocalyx. Glycocalyx contains a network of channels and canals that allow for the exchange of nutrients among various microbes and for the removal of their waste products. The biofilm structure also provides protection for its microorganisms from invasion by intruders, including other bacteria, antimicrobial drugs, and antiseptic rinses. 4 Bacterial Characteristics Dental plaque biofilm consists mostly of bacteria. Biofilm is not a random accumulation of assorted types of bacteria but a specific and complex arrangement based on bacterial characteristics. 5 Bacterial Metabolism Bacteria need nutrients to grow, but their requirements and waste products vary. Gram-positive organisms, such as Streptococcus mutans, are fermentative or saccharolytic. These organisms obtain their energy by breaking down complex organic compounds, such as sugars, to smaller end products, such as lactic acid. 6 Oral Microbial Ecosystems The oral cavity is made up of several unique environments, or ecosystems, in which microorganisms thrive. The five major ecosystems are the: Tongue Buccal mucosa Saliva Supragingival tooth surfaces Subgingival tooth surfaces 7 Saliva Saliva represents an environment for microorganisms that is protective in nature. Saliva contains shed gingival tissue cells and plaque biofilm from other locations in the oral cavity on their way to being swallowed. Saliva is involved in the removal of biofilms from within the oral cavity because of fluid movement in the mouth. Antimicrobial proteins in saliva (Lysozyme) help regulate microbe attachment to oral cavity surfaces. 8 Tooth Surfaces  Small amounts of supragingival plaque biofilm are difficult to detect without placing a disclosing solution on the teeth or scraping the tooth surfaces with an instrument.  As plaque accumulation grows, it becomes visible as a white-yellow mass. 9 Pellicle Formation Step 1 of Biofilm Formation Proteins from the saliva salivary glycoproteins, attach to the tooth surface forming an amorphous and tenacious pellicle. Toothbrushing does not remove it; only polishing the teeth with an abrasive agent will remove the pellicle. Pellicle re-forms on the clean tooth surfaces within minutes. 10 Pellicle Formation (Cont.) Step 1 of Biofilm Formation (cont.) Influences the subsequent colonization of bacteria on the tooth surface. Certain proteins in saliva that form part of the pellicle can enhance the ability of specific microorganisms, such as the Actinomyces species, to bind to tooth surfaces. Not all of the bacteria available in saliva can attach to the pellicle binding sites for pellicle constituents. 11 Initial Bacterial Colonization of Pellicle Step 2 of Biofilm Formation Bacterial cells stick to the pellicle through specific receptor mechanisms. Oral bacteria vary in their ability to adhere to different surfaces. For example: Streptococcus mutans and S. sanguinis colonize in supragingival plaque. S. salivarius is present in high proportions on the tongue and in saliva. 12 Initial Bacterial Colonization of Pellicle (Cont.) Step 2 of Plaque Formation (cont.)  Initial plaque biofilm that forms on the pellicle Predominately gram- positive coccal facultative anaerobic bacteria, largely streptococci. *One day old plaque. Filament (F) 13 Initial Bacterial Colonization of Pellicle (Cont.) Step 2 of Plaque Formation (cont.)  The first organisms adhere and form a monolayer of cells, and, within a few hours, these organisms form small colonies.  These microcolonies of cocci form a series of columns that extend out from the pellicle. (F) Filaments, (C) Cocci 14 Growth and Maturation of Plaque Step 3 of Plaque Formation As plaque biofilm matures, it increases in mass and thickness. Maturation of plaque also requires that different types bacteria cells attach to each other. 15 Growth and Maturation of Plaque (Cont.) Step 3 of Plaque Formation (cont.) The material in the plaque among the bacteria is called the intermicrobial matrix. salivary material gingival exudate microbial substances polysaccharides. 16 Extracellular Polysaccharides Bacteria, such as Streptococcus mutans, S. sanguinis, S. mitis, and S. salivarius produce metabolic products from sucrose. energy source or as material to help retain the bacteria in the plaque. 17 Extracellular Polysaccharides (Cont.) A small amount of lipid and Lipopolysaccharide (LPS), endotoxin, from gram-negative cell walls is present in the biofilm. Inorganic components, primarily calcium and phosphate low in early plaque significantly increases as plaque is transformed into calculus. 18 Bacterial Coaggregation Bacterial coaggregation occurs when certain bacteria adhere to previously attached cells in plaque biofilm, forming complex aggregations. Filament-shaped bacteria become coated with cocci, presenting a “corn cob” appearance. 19 Bacterial Coaggregation (Cont.) “Corn Cob” formation is restricted to species with mutually attractive surface molecules that can bind to each other. The corn cob complex is made up of a central filament surrounded by cocci, usually a type of S. sanguinis. The filaments can be either gram-positive Actinomyces species and Corynebacterium matruchotii or gram-negative Fusobacterium nucleatum. 20 Bacterial Coaggregation (Cont.) Early colonizers streptococci or the Actinomyces species Late colonizers Fusobacteria species. 21 Bacterial Coaggregation (Cont.) In another type of bacterial aggregation, one organism acts as a bridge between two other bacteria that do not interact. For example, some strains of S. sanguinis aggregate with both Actinomyces naeslundii genospecies and Prevotella loescheii, which do not coaggregate with each other. These interactions may be an important mechanism for the attachment of new organisms and for the ability of organisms to resist the forces that would remove them. 22 Microbial Succession As the dental biofilm ages, its composition changes, which is referred to as microbial succession. Initial colonizers alter the environment at the tooth surface, enabling new and different bacterial species to inhabit the developing dental biofilm. After the first day of dental biofilm growth gram-positive streptococci decreases. Actinomyces and Veillonella strains become more prominent. 23 Microbial Succession (Cont.) During the next 3 weeks, cocci continue to decrease as a result of the increase in filamentous bacteria. These filamentous forms invade the dental biofilm and replace many of the streptococci in the deeper levels of the biofilm. 24 Microbial Succession (Cont.) As dental biofilm becomes thicker: It becomes more anaerobic. spirochetes and gram-negative rods. no additional bacterial species can join the dental biofilm. bacteria may continue to increase. maturation process supragingival dental biofilm has the potential to invade the subgingival space causing localized gingival disease. 25 Subgingival Dental Biofilm Formation The bacterial composition of subgingival dental biofilm is partly influenced by bacteria in the adjacent supragingival biofilm. more anaerobic more gram-negative more motile more asaccharolytic (using proteins rather than sugars for nutrients) than supragingival dental biofilm. 26 Subgingival Environment The maturation of supragingival dental biofilm is accompanied by inflammation in the gingiva. Formation of supragingival dental biofilm moves apically into the gingival crevice. Edema leads to gingival enlargement. Difficulty removing dental biofilm Facilitating dental biofilm accumulation and maturation 27 Subgingival Environment (Cont.) Gingival Crevicular Fluid (GCF) fluid that leaks into the gingival crevice Inflammation increases the GCF flow gingival bleeding nutrients for the bacteria in the biofilm. 28 Microbiologic Composition Subgingival and supragingival dental biofilm are different. Limited access to the oral cavity allows anaerobic bacteria to grow and restricts the addition of salivary bacteria. Subgingival area is not subject to the mechanical forces that dislodge bacteria from teeth. allows motile organisms that are completely unattached to the plaque matrix to proliferate and survive. REMEMBER THIS! 29 Tooth Surface The structure of the tooth-adjacent biofilm is similar to supragingival plaque. microbiota is dominated by gram-positive filamentous bacteria. Gram-positive and gram-negative cocci and rods are also present. In the apical portion fewer filamentous organisms are found gram-negative rods dominate the bacterial structure. REMEMBER THIS! 30 Tissue-Associated Subgingival Plaque Biofilm closest to the soft tissues of the pocket contain a large number of flagellated motile bacteria and spirochetes. loosely adherent to the surface. This loosely adherent mass is made up of late colonizing bacteria that activate the host response Breakdown of periodontal complex 31 Periodontal Microbiota Early theories concerning plaque suggested that the severity of inflammation was directly related to the quantity of plaque-biofilm in the mouth. These theories were based on the beliefs that biofilm was a homogeneous bacterial mass and that they all have equal potential to cause disease. Early theories centered on the nonspecific plaque hypothesis. 32 Periodontal Microbiota (Cont.) Improvements in microbial research led to the development of the specific plaque hypothesis. overgrowth of specific microbial species that are responsible for most cases of periodontitis. 33 Subgingival Health The gingival crevice harbors microorganisms in both healthy and diseased subgingival areas. In healthy subgingival areas, the gingival crevice harbors microorganisms found in the early stages of biofilm formation. gram-positive and facultative anaerobic species. Cocci 2/3 of the microorganisms. Gram-positive facultative anaerobic rods filamentous forms Actinomyces. 34 Gingivitis Gingival inflammation can be initiated by any number of bacterial species if they are present in high numbers as a result of poor oral hygiene. This type of gingival inflammation is in contrast to a specific infection, in which a limited number of bacteria are known to create progressive periodontitis lesions. 35 Periodontitis The continued presence and growth of pathogenic bacterial biofilm causes the inflammatory process to extend into the periodontal ligament, cementum, and alveolar bone loss of attachment 36 Periodontitis (Cont.) In the early stages bacterial components are similar to that of gingivitis. Becoming more complex as the biofilm matures. Chronic periodontitis higher proportions of anaerobes gram-negative spirochetes predominant organisms are gram-negative anaerobic rods 37 Periodontitis (Cont.) Porphyromonas gingivalis most important periodontal pathogen on the basis of its numeric presence and its possession of specific virulence factors LPS (endotoxins). 38 Periodontitis (Cont.) The RED COMPLEX bacteria Porphyromonas gingivalis Tannerella forsythia Treponema denticola. The orange complex bacteria are considered less virulent Prevotella intermedia Fusobacterium nucleatum Campylobacter species Eubacterium nodatum Peptostreptococcus micros And others. 39 Periodontitis (Cont.) The other complexes, referred to as yellow, green, and purple, are earlier colonizers reside deeper in the biofilm (closer to the tooth surface) less associated with clinical disease. 40 Socransky’s Postulates 41 Grade C: Rapid Rate Characterized by a rapid destruction of periodontal attachment over a short period. permanent incisors first molars Molar-Incisor Pattern Periodontitis (MIPP May affect healthy children / teenagers or young adults who exhibit relatively little dental plaque and gingival inflammation. 42 Grade C: Rapid Rate (Cont.) Genetically determined susceptibility. Defective polymorphonuclear neutrophils (PMNs) impaired ability to migrate to and phagocytose bacteria increasing the individual’s susceptibility to infection. 43 Grade C: Rapid Rate (Cont.) Gram-negative rods dominate including: Actinomyces naeslundii Fusobacterium nucleatum Campylobacter rectus In some populations, Aggregatibacter actinomycetemcomitans has been implicated as one of the major pathogens. 44 Necrotizing Ulcerative Gingivitis and Periodontitis Necrotizing ulcerative gingivitis (NUG) or necrotizing ulcerative periodontitis (NUP) is another form of aggressive periodontitis. Necrotic, ulcerative lesions of the interdental papillae, severe pain, rapid loss of supporting structures, and significant halitosis are clinical characteristics of NUG. NUG has a characteristic histopathologic profile. The outer surface bacteria of the supragingival biofilm are similar to the subgingival biofilm of periodontal lesions. 45 Necrotizing Ulcerative Gingivitis and Periodontitis (Cont.) A PMN-rich or a polymorphonuclear leukocyte (PML)–rich zone with a necrotic zone containing spirochetes and gram-negative rods characterizes NUG. The adjacent connective tissue is infiltrated with spirochetes. NUG is referred to as NUP when the infection invades the deeper tissues and bone loss occurs. 46 Necrotizing Ulcerative Gingivitis and Periodontitis (Cont.) NUG and NUP lesions have large numbers of spirochetes and Prevotella intermedia, with gram-negative rods accounting for more than 50% of the bacterial population. High levels of Fusobacterium and Selenomonad species have also been identified. 47 Virulence of Periodontal Pathogens The virulence or pathogenicity of a microorganism is its ability to cause disease. In general, virulence is related to three things: Proximity to the tissue Ability to evade host defenses Ability to destroy tissue 48 Proximity to the Tissue Proximity to the Tissue A microorganism must be in close proximity to the periodontal tissue, and it must be able to withstand the forces of saliva and GCF flow that are capable of washing it away. Colonization is mediated by cell surface characteristics. Fimbriae and extracellular polysaccharides, such as glucan Bacterial interactions are important for colonization and for the availability of nutrients. 49 Evasion of Host Defenses Ability to Evade Host Defenses Porphyromonas gingivalis, Tannerella forsythia, and Treponema denticola have enzymes (proteases) that degrade the host immune system proteins. Aggregatibacter actinomycetemcomitans produces a leukotoxin that kills or impairs PMNs. Porphyromonas gingivalis releases a factor that interferes with PMN (polymorphonuclear) movement to a site of infection. 50 Tissue Destruction Ability to Destroy Tissue inflammation produced by the human host cells. response to molecules released from bacteria, primarily the red and orange complexes of bacteria. some bacterial products directly injure the host cells and tissues. 51 Direct Effects Enzymes capable of damaging host tissues. Porphyromonas gingivalis produces collagenase, the enzyme that degrades collagen in the tissues. 52 Direct Effects (Cont.) Toxins LPS, a gram-negative bacterial cell wall component induces inflammatory reactions stimulates osteoclast-mediated bone resorption. Another type of bone-resorbing toxin is released from Aggregatibacter actinomycetemcomitans.. 53 Direct Effects (Cont.) Toxins (cont.) P. gingivalis, Prevotella intermedia, A. actinomycetem- comitans, and Capnocytophaga produce toxins that affect fibroblasts and, consequently, the synthesis and turnover of collagen. In addition, several pathogens release volatile sulfides inhibit both the synthesis of collagen and noncollagenous substances. 54 Indirect Effects Some microbial products have the potential to activate immune inflammatory reactions, which, in turn, cause tissue destruction. For example, LPS from P. gingivalis and other gram-negative organisms stimulate the release of prostaglandin E2, interleukin-1β, and C-reactive protein from macrophages and fibroblasts. These organisms have the potential to induce inflammation and bone resorption. 55 Inflammatory Response First line of defense is polymorphonuclear neutrophils (PMNs) Phagocytois occurs (eat and digest periodontal bacteria) Leaks enzymes (collagenase, beta-glucuronidase, alkaline phosphatase) Gingival Crevicular fluids contains high levels of these enzymes during periodontitis. Second line of defense is Macrophages. Remains in the inflamed connective tissue for months Pathways to secretion of prostaglandins and cytokines. 56 Bacterial Enzymes and Noxious Products Ammonia Hydrogen sulfide Butyric acid and propionic acid Proteases: Enzyme that can break down the periodontium protein structure elastin, and fibronectin. Collagenase: Enzyme that can break down the collagen fibers. Hyaluronidase: Enzyme that can break down hyaluronic acid. Increases tissue permeability. Elastases: Enzyme that affects the mucosa and blood vessels. Reduce tissue integrity. 57 Cytokines Soluble proteins produced by the stimulated immune cells such as neutrophils, macrophages and lymphocytes. Works as communication signals between cells Very complex with many other cell signaling proteins, such as Interleukins IL Tumor necrosis factors (TNF) Interferon (IFN) For periodontal pathogenesis: IL-1β and TNF-α are most studied Cytokines: lymphotoxin is found in large amounts in response to plaque bacteria antigens in 58 periodontal disease >> stimulates bone and Prostaglandins A group of lipid compounds derived from arachidonic acid (ARA) ARA (cell membrane Phospholipids) Cyclooxygenases (COX-1/Cox2) Prostagladin E2 (PGE2) Induction of Matrix Metalloproteinases (MMP) Osteoclastic bone resorption Major role in tissue damage in periodontitis 59 Matrix Metalloproteinases (MMPs) Proinflammatory mediator. Proteolytic enzymes that degrade collagen, gelatin and elastin Produced by neutrophils, macrophages, fibroblasts, epithelial cells, osteoblasts, and osteoclasts. Example: Gelatinases A = MMP-2 Collagenases1 = MMP-1 60