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The Oral Cavity From a Microbe's Perspective The mouth is warm and moist, and is able to support the growth of a wide range of microorganisms, including viruses, mycoplasma, bacteria, Archaea, fungi, and protozoa  Colonization of the oral cavity also starts close to the time of birth steri...

The Oral Cavity From a Microbe's Perspective The mouth is warm and moist, and is able to support the growth of a wide range of microorganisms, including viruses, mycoplasma, bacteria, Archaea, fungi, and protozoa  Colonization of the oral cavity also starts close to the time of birth sterile oral cavity is colonized by low numbers of mainly facultative and aerobic bacteria. second day - anaerobic bacteria can be detected in the infant’s edentulous mouth Gradually change in microflora - as a result of exposure to external environment 700 commonly occurring species, approximately half of which can be present at any time in any individual. Streptococcus salivarius Streptococcus sanguinis and Streptococcus mitis Lactobacillus spp. Fusobacterium spp. and Streptococcus oralis. and Prevotella spp. sugar-based  PROOF Aggressive periodontitis - loss of colonization of S. sanguini commensal microbiota is required for Porphyromonas gingivalis–induced bone loss Increased mass and /or pathogenicity Suppression of commensal or beneficial bacteria Reduced host response Microbiota lives in harmony with its host (commensal or beneficial bacteria ) ( HEALTH ) (Disease)  Different complexes or microbes are Why? found in different parts of the oral cavity ( niche)  Major ecosystems (also called niches) The intraoral and supragingival hard surfaces (teeth, implants, restorations, and prostheses) Subgingival regions adjacent to a hard surface, including the periodontal/peri-implant pocket (characterized by the presence of crevicular fluid, the root cementum or implant surface, and the pocket epithelium) The buccal palatal epithelium and the epithelium of the floor of the mouth The dorsum of the tongue The tonsils The saliva  Core microbiome Rothia spp., and Actinomyces spp.), Proteobacteria (Neisseria spp., Members of the phyla Firmicutes Bacteroidetes (Prevotella spp., Campylobacter spp., and (Streptococcus spp., Veillonella Capnocytophaga spp., and Haemophilus spp.), Actinobacteria spp., and Granulicatella spp.), Porphyromonas spp.), and (Corynebacterium spp) Fusobacteria (Fusobacterium spp.) What are various factors helps in attachment and survival of this bacteria Nutrients Host defenses Microbial interaction Genetics  What are Temperature various The mouth is maintained at a temperature of factors helps around 35–37°C in attachment Temperature - increase at subgingival sites and survival during inflammation, and this can alter bacterial gene expression - growth and of this protease activity of some putative periodontal bacteria pathogens  Redox potential What are various factors helps (Eh), the in attachment and survival of measure of the this bacteria degree of NUG - suspect the patient have HIV oxidation– reduction at a Hydrogen peroxide - removes necrotizing membranes (bacteriocidal) site. Bacterial metabolism in mature oral biofilms results in sharp gradients of oxygen and Eh,  pH is a major determinant of bacterial distribution and metabolism. After sugar consumption, the pH in plaque can fall rapidly to below 5.0 by the What are production of acidic fermentation products various factors Depending on the frequency of sugar helps in intake, the bacteria in plaque will be attachment and exposed to varying challenges of low pH survival of this The pH of the healthy gingival crevice is bacteria approximately 6.9, but this rises to between pH 7.2 and 7.4 during inflammation, with a few patients having pockets with a mean pH of around 7.8.  Adhesion of bacteria – to colonize the area and What are invade the tissue- first step is to adhere various factors helps There are many factors which in prevents colonization attachment Flow of saliva and GCF and survival of this Shedding of the epithelial cells bacteria Neutrophils and other host factors Do epithelial cells plays a role in adhesion ? Periodontal Infections - resistant vs susceptible to gingivitis - difference in adherence rate of P. gingivalis and P. intermedia strains to gingival epithelial cells An in vitro study of cultured human pocket epithelial cells showed a similar tendency when patients who were resistant to periodontitis were compared with patients with severe periodontal breakdown. What happens in pocket epithelium during continuous inflammation Areas of gingival inflammation are characterized by an increased number of adhering bacteria. -Adhering bacteria can also infiltrate the pocket wall in relatively large numbers and reach the underlying stroma Positive correlation exists between the adhesion rate of pathogenic bacteria to different epithelia and the susceptibility of the affected patient to certain infections  Hard tissue – tooth – adhesion Teeth were considered as a “porte d'entrée” for periodontopathogens. Teeth are the primary habitat for periodontopathogens – HOW DO WE KNOW THIS ? Soon after a full-mouth tooth extraction in patients with severe periodontitis, key pathogens such as A. actinomycetemcomitans and P. gingivalis disappeared from the oral cavity, as determined by bacterial culturing techniques. P. intermedia and other black-pigmented Prevotella spp. remained, but at lower detection frequencies and numbers. Once established, the microbial composition of the biofilm at a site remains stable over time, unless a major perturbation occurs in a key environmental determinant, such as a major change in diet or an alteration to the immune status of the host DENTAL PLAQUE Dental plaque Dental plaque is defined clinically as a structured, resilient, yellow-grayish substance that adheres tenaciously to intraoral hard surfaces, including removable and fixed restorations.  Materia alba refers to soft accumulations of bacteria, food matter, and tissue cells that lack the organized structure of dental plaque and that are easily displaced Other type of with a water spray deposits on the tooth surface Calculus is a hard deposit that forms via the mineralization of dental plaque and that is generally covered by a layer of unmineralized plaque dead microorganisms  it is possible to remove plaque by rinsing or with the use of sprays – give reason for your answer Materia alba - that is easily say true or false displaced with a water spray- give reason for your answer Calculus is a hard deposit that can be removed with the toothbrush- give reason for your answer  Supragingival plaque - found at or above the gingival margin; when in direct contact with the Dental plaque- gingival margin- marginal plaque. classification Subgingival plaque is found below the gingival margin, between the tooth and the gingival pocket epithelium. Sub gingival plaque – classification  Marginal plaque - prime importance during the initiation and development of gingivitis. Role of different type Supragingival plaque and tooth- associated subgingival plaque are of plaque in critical in calculus formation and root caries. periodontal disease Tissue-associated subgingival plaque is important in the tissue destruction that characterizes different forms of periodontitis.  The tooth-associated cervical plaque that adheres to the root cementum does not markedly differ from that observed in gingivitis. causes dental caries, root caries, At this location, filamentous microorganisms and early stages periodontitis dominate, but cocci and rods also occur. removed by brushing and mechanical debridement This plaque is dominated by gram positive rods and cocci, including S. mitis, S. sanguinis, Actinomyces oris, Actinomyces naeslundii, and Eubacterium spp..  Tissue associated plaque. give AB because mechanical alone is not enough The layers of microorganisms that face the soft tissue lack a definite inter-microbial matrix and contain primarily gram-negative rods and cocci, as well as large numbers of filaments, flagellated rods, and spirochetes. in pocket - in crevicular epithelial cells – there is predominance of species such as S. oralis, S. intermedius, Parvimonas micra (formerly Micromonas micra and Peptostreptococcus micros), P. gingivalis, P. intermedia, Tannerella forsythia and F. nucleatum. Host-tissue cells (e.g.,white blood cells, epithelial cells) may also be found in this region Bacteria are also found within the host tissues, such as in the soft tissues and within epithelial cells as well as in the dentinal tubules Dental plaque – composition- Microorganisms One gram of plaque (wet The number of bacteria in Dental plaque is weight) contains supragingival plaque on a composed primarily of approximately 10 single tooth surface can microorganisms. 11bacteria. exceed 109 cells. 130-180 In a periodontal pocket, Nonbacterial organisms 750 distinct microbial counts can range from 10 can also be found in the phylotypes can be present 3 bacteria in a healthy dental plaque biofilm, as natural inhabitants of crevice to more than 108 including archaea, yeasts, dental plaque bacteria in a deep pocket. protozoa, and viruses Supragingival plaque typically demonstrates the stratified organization of a multilayered accumulation of bacterial morphotypes Gram-positive cocci and short rods predominate at the tooth surface, whereas gram-negative rods, filaments, and spirochetes predominate in the outer surface of the mature plaque mass.  AA is found in shallow pockets spirochete are motile (they move in the tissue and can go deep) In subgingival plaque - strict anaerobes are found in the deeper pockets and in shallow subgingival pocket – mix of both aerobic and anaerobic organisms are found The apical part is more dominated by spirochetes, cocci, and rods, whereas in the coronal part more filaments are observed.  organic inorganic The intercellular source for supra gingival - from Saliva, matrix source of subgingival from - Gingival crevicular fluid, bacterial and host by products. Organic constituents Polysaccharides, Proteins, Glycoproteins, Lipid material endotoxins, caused by gram negative bacteria DNA Details of few organic constituents Albumin - originates from crevicular fluid, The lipid material consists of debris from the membranes of disrupted bacterial and host cells, bacterial vesicles, and possibly food debris. Glycoproteins from the saliva are important components of the pellicle that initially coats a clean tooth surface, but they also become incorporated into the developing plaque biofilm. Polysaccharides produced by bacteria also contribute to the organic portion of the matrix. - major role in maintaining the integrity of the biofilm. CHX can prevent adhesion of aquired pellicle (or delayed) The inorganic components calcium phosphorus, trace amounts of other minerals such as sodium, potassium, and fluoride. The source of inorganic constituents of supragingival plaque primarily saliva. As the mineral content increases, the plaque mass becomes calcified to form calculus  Factors affecting the Dental plaque dysbiosis Formation of dental plaque Microbial complex Stages/steps in the plaque formation The formation of the Acquired pellicle on the tooth surface. The initial adhesion/attachment of bacteria – devided in to 3 steps Transport to the surface, Reversible adhesion Permanent attachment secondary colonization/plaque maturation. - divided in to 2 steps Co- adhesion/coaggregation Plaque maturation Detachment Formation of acquired pellicle Acquired pellicle. Coating of a tooth with layer of organic material. What is the composition of acquired pellicle ? More than 180 peptides, proteins, and glycoproteins, including keratins, mucins, proline-rich proteins, phosphoproteins (e.g., statherin), histidine rich proteins, and other molecules What is the function of these constituetns ? – act as adhesion sites (receptors) for bacteria  It forms within a minute after brushing or polishing how quick or the tooth surface how fast acquired pellicle forms on the tooth surface It becomes stable within 2 hours – it will get matured till several hours later. Transmission electron microscopy –( TEM) observation of the pellicle Pellicle to be composed of two layers: Thin basal layer that is very difficult to remove, even with harsh chemical and mechanical treatments -permanently covered with pellicle from the moment that teeth erupt ( dental cuticle) A thicker globular layer, up to 1 μm or more, that is easier to detach.- This is acquired. what is the role of acquired pellicle on the formation of dental plaque Act as adhesion sites (receptors) for bacteria. But pellicle is not a Passive adhesion matrix.- just simply do not allow any bacteria to come and attach There are proteins with enzymatic activity – like peroxidases, lysozyme, and α-amylase - may affect the physiology and metabolism of adhering bacterial cells close  what is the composition of Answer the acquired pellicle questions. why pellicle is NOT considered as passive adhesion matrix What is the clinical importance of understanding the formation of pellicle  Ecologic relationship Dental plaque samples produced in between the vitro biofilms only if the surface on pellicle and its which they were grown contained a salivary pellicle belonging to the associated patient who donated the plaque microbiology sample. No biofilm could be grown on a pellicle that came from a different subject. Initial Adhesion/Attachment of Bacteria Colonizing bacteria can be detected within 3 minutes The initial steps in colonization of teeth by bacteria- three phases. Phase 1 is transport to the surface. Phase 2 is initial reversible adhesion. Phase 3 is strong attachment. Phase 1: Transport to the Surface Random contacts bacteria to the toothsurface Brownian motion (average displacement, 40 μm/hour), through sedimentation of microorganisms, through liquid flow (several orders of magnitude faster than diffusion), or through active bacterial movement (chemotactic activity). what prevents its attachment saliva flow mechanical contact between oral soft tissues and teeth. Phase 2: Initial Adhesion Initial reversible adhesion of the bacterium. Long- and short-range forces, including van der Waals attractive forces and electrostatic repulsive forces, operate at this distance (separation distance, ≈50 nm). At the physiologic ionic strength of saliva, the van der Waals forces result in a net attraction of bacterial cells at distances of tens of nanometers from the surface- Electrostatic repulsion prevents bacterial cells from being even closer to the surface.  Stronger binding between bacteria and acquired pellicle Bacterial adhesins and receptors in the salivary pellicle Microbial cell surfaces are not uniformly coated with a negative charge. Some regions of the cell surface may be positively charged, and, for these areas, electrostatic interactions with a negatively charged surface will tend to be attractive Many cells possess structures, such as fimbriae, that protrude from the cell surface – these act beyond the charged surface and attach bacteria to the tooth surface Bacteria associated with shed epithelial cells- These host cells acts as transporters bring bacteria close to the tooth surface. Phase 3: Strong Attachment The binding between the bacteria and the pellicle is mediated by specific adhesins on the bacterial cell surface (usually proteins) and complementary receptors (proteins, glycoproteins, or polysaccharides) in the acquired pellicle. Antigen I/II family adhesins are 160- to 180-kDa proteins expressed on the surfaces of many oral streptococci, Gp340 is present in fluid-phase saliva, and it is a component of the salivary pellicle. In the fluid phase, interactions between antigen I/II proteins and gp340 result in the aggregation of bacteria  “primary The primary colonizer provide new binding sites for adhesion by other oral colonizers” of bacteria. tooth Streptococcus tends to dominate, usually accounting for >20% of bacteria surfaces. obligate aerobes - such as Haemophilus spp. and Neisseria spp., facultative anaerobes, including Actinomyces spp. and Veillonella spp Colonization and Plaque Maturation Co-adhesion - The primary colonizing bacteria (Table 8.3) adhered to the tooth surface provide new receptors for attachment by other bacteria Strong cell–cell binding - determined by the presence of adhesin proteins or carbohydrates on one partner and complementary receptor proteins or carbohydrates on the other. adhesin–receptor interactions are mediated by the fundamental physicochemical forces (i.e.hydrophobic, electrostatic, and van der Waals), but they are highly specific. Well-characterized interactions of secondary colonizers with early colonizers include the coaggregation of F. nucleatu with S. sanguinis, Prevotella loescheii with A. oris, and Capnocytophaga ochracea with A. oris  Special examples of coaggregations the corn cob formation, in which streptococci adhere to filaments of Corynebacterium matruchotii or Actinomyces spp. the test-tube brush formation, composed of filamentous bacteria to which gram-negative rods adhere  Secondary colonizers P. intermedia, P. loescheii, Capnocytophaga spp., F. nucleatum, and P. gingivalis do not initially colonize clean tooth surfaces but rather adhere to bacteria that are already in the plaque mass The transition from early supragingival dental plaque to mature plaque growing below the gingival margin involves a shift in the microbial population from primarily gram-positive organisms to high numbers of gram-negative bacteria. During the later stages of plaque formation, coaggregation among different gram-negative species is likely to predominate. F. nucleatum with P. gingivalis or Treponema denticola Microbial 13,000 plaque samples that looked for 40 subgingival complexes microorganisms using a DNA- hybridization methodology defined color-coded “complexes” of periodontal microorganisms that tend to be found together in health or disease  DENTAL BIOFILM CHARACTERISTICS  Biofilm – way back Around 50 years later that sessile microbial populations were The importance of surfaces for considered to be sufficiently microbial growth was recognized different from free living as early as the 1920s microorganisms ( planktonic) - the term biofilms was coined Difference between Planktonic and biofilm. PLANKTONIC BIOFILM The bacteria exist and proliferate free floating; within the intercellular matrix through which the channels run. in solutions such as saliva or crevicular fluid Substances produced by bacteria within the biofilm are retained and concentrated, which metabolic interactions among the different bacteria  Biofilm bacteria are often up to 1000 times more resistant to antimicrobial agents than their planktonic counterparts Bacteria that grow in multispecies biofilms interact closely with neighboring cells. Sometimes these interactions are mutually beneficial - one organism removes another's waste products and uses them as Biofilm an energy source. characteristics Bacteria compete with their neighbors by secreting antibacterial molecules such as inhibitory peptides (bacteriocins) or hydrogen peroxide (H2O2) Biofilm mode of growth facilitates cell–cell signaling and deoxyribonucleic acid (DNA) exchange between bacteria  Biofilms are heterogeneous: Biofilm variations in biofilm structure exist within individual biofilms, characteristics between different types of biofilms, and between individuals  Contain microcolonies of bacterial cells Water channels are commonly found in biofilms, and these can form a primitive Structural circulatory system that removes waste features of products and brings fresh nutrients to the deeper layers of the film. biofilms Steep chemical gradients exist, such as those of oxygen or pH, and these produce distinct microenvironments within the biofilm.  Communication Between Biofilm Bacteria Bacteria have the capacity to communicate with each other - Quorum sensing What is quorum sensing ? Bacterial cells communicate with each other by releasing, sensing and responding to small diffusible signal molecules autoinducers. This process of intercellular communication, called quorum sensing Many bacteria are known to regulate their cooperative activities and physiological processes through this quorum sensing (QS).  Two types of signaling molecules have been detected from dental plaque bacteria: Specific CTP Quorum Peptides released by gram-positive organisms. - The streptococcal peptides are sensing – known as competence-stimulating peptides signalling molecules “Universal” signal molecule called autoinducer 2 (AI-2). - AI-2 produces wide- ranging changes in gene expression, in some cases affecting up to one-third of the entire genome  This molecule has been demonstrated to play a role in mutualistic interactions between S. oralis and A. oris Quorum sensing – signalling molecules In vitro model system, neither S. oralis nor A. oris formed biofilms in Example for - Role of monoculture. AI- 2 When cultured together, these organisms grew abundantly on surfaces to form thick, confluent biofilms. Quorum sensing – signalling Modulating the expression of genes for antibiotic resistance molecules- Encouraging the growth of beneficial species Function of in the biofilm AI- 2 Discouraging the growth of competitors. e.g. Tetracycline is not used anymore due to gene expression (bacteriocidal)  Many evidences are existing to show that there is interaction among the plaque bacteria Evidence 1 - Studies have shown that, there is increase in Interactions S. mutans after periodontal therapy Among Evidence 2 - Nonpathogenic organisms in subgingival Dental dental plaque can modify the behavior of periodontal pathogens. Plaque For example, long and short fimbriae of P. gingivalis are required for adhesion and biofilm formation. The Bacteria expression of long fimbriae is down-regulated in the presence of Streptococcus cristatus, and short fimbriae are downregulated by S. gordonii, S. mitis, or S. sanguinis  Many evidences are existing to show that there is interaction among the plaque bacteria Evidence 3 -proteomics approach to probe the P. Interactions gingivalis, it has been shown that the expression of almost 500 P. gingivalis proteins is changed in model Among oral microbial communities that contain S. gordonii and F. nucleatum Dental Plaque Evidence 4 - competitive interactions between different bacteria exist. For example, S. mutans Bacteria produces antimicrobial peptides that have broad activity against bacteria in vitro. Other oral streptococci compete with S. mutans by excreting the strongly oxidizing molecule H2O2  Many evidences are existing to show that there is interaction among the plaque bacteria Interactions Among Evidence 5 : Oral streptococci have been shown to modulate bacteria–host interactions Dental Plaque that involve both F. nucleatum and A. actinomycetemcomitans. Thus, S. cristatus and Bacteria other oral streptococci attenuate the ability of F. nucleatum to stimulate interleukin-8 production by host oral epithelial cells.  Organisms in a biofilm are 1000 to 1500 times more resistant as compared with antibiotics in their planktonic state. WHY ? Resistance of bacteria to antibiotics - reasons Biofilms and Nutritional status, Antimicrobial Growth rate, Temperature, Resistance pH, prior exposure to sub-effective concentration of antimicrobial agents. slower rate of growth of bacterial species in a biofilm, which makes them less susceptible to many but not all antibiotics Other properties of biofilm - can retard antibiotic penetration Physical barrier to the diffusion ( lesser extent ) Strongly charged or chemically highly reactive agents can fail to reach the deeper zones of the biofilm- because the biofilm acts as an ion-exchange resin that removes such molecules from solution. penecillin Extracellular enzymes such as β-lactamases, formaldehyde lyase, and formaldehyde dehydrogenase may become trapped and concentrated in the extracellular matrix, and as such inactivate some antibiotics (especially positively charged hydrophilic antibiotics) Super resistant” bacteria were identified within a biofilm. These cells have multidrug resistance pumps that can extrude antimicrobial agents from the cell Antibiotic resistance may be spread through a biofilm via the intercellular exchange of DNA. - Conjugation (i.e., the exchange of genes through a direct interbacteria connection formed by a sex pilus), transformation (i.e., the movement of small pieces of DNA from the environment into the bacterial chromosome), plasmid transfer, and transposort transfer have all been shown to occur in biofilms Bacterial One locus to another Transmission One person to another and This can occur through Translocation - intraoral transmission - vertical transmission - horizontal transmission Bacterial “Are oral bacteria transmissible between humans?” Transmission and YES , Molecular fingerprinting Translocation techniques have clearly illustrated that periodontal pathogens are transmissible within members of a family  Genetic fingerprinting method called arbitrarily primed-polymerase chain reaction to genotype A. actinomycetemcomitans isolates from family members. Bacterial Transmission In 11 of 12 families, these investigators found and identical A. actinomycetemcomitans genotypes among family members. ( horizontal Translocation transmission or may be combination horizontal and vertical transmission) – proof especially molar-incisors periodontitis This finding suggests the transmission of this microorganism among family members Bacterial Transmission and That children carried a genotype Translocation- identical to one of their parents than that spouses carried an vertical identical genotype.- vertical transmission transmission  The existence of an “intraoral” translocation of bacteria Bacterial Transmission Loesche and coworkers showed that streptomycin- resistant strains of S. mutans grown on a dental and inlay were spontaneously transmitted to the Translocation- neighboring teeth (probably via saliva) and could even reach the contralateral quadrant after probing and transmission with a dental explorer Christersson and coworkers demonstrated a exploring the translocation of A. a via periodontal probes in caries site. localized juvenile periodontitis patients. These investigators were able successfully to colonize previously non-infected pockets with A a. Bacterial Transmission and Translocation- pocket and implants. The existence of an “intraoral” translocation of bacteria A large series of articles compared the microbiota in pockets around teeth with that found in peri-implant pockets in partially edentulous patients and reported a striking similarity. Several studies have investigated the subgingival colonization of such “sterile” peri-implant pockets in partially edentulous patients. Periodontopathogens could already be detected in this niche 30 minutes after abutment placement Teeth may act as a reservoir for the (re)colonization of the subgingival area around implant Bacterial Transmission and Translocation – Clinical significance The existence of an “intraoral” translocation of bacteria Guided tissue regeneration and membrane contamination after the treatment of mandibular bony defects Jn a group of patients with a healthy periodontium in the remaining dentition or a group of patients with multiple deep pockets and numerous pathogens. The healthy group showed significantly less membrane contamination both immediately after insertion and at their removal after 6 weeks. The healthy group also showed significantly more clinical gain in attachment (3.4 mm versus 1.4 mm).  Bacterial Transmission and Translocation – Clinical significance Mombelli and coworkers - compared clinical and microbial changes when tetracycline fibers (local applications of antibiotics)were applied only to the two deepest pockets in the mouth (without further treatment to the remaining pockets) with the changes obtained when all teeth were cleaned and every pocket with a depth of more than 3 mm was treated. After 6 months, significant “additional” improvements (clinical as well as microbiologic) were recorded in the group of patients with the more global approach. Their pockets showed a probing depth reduction (1.7 mm) and attachment gain (0.7 mm) that was significantly higher than that found in the pockets of patients with some remaining pockets (0.9 and 0.3 mm, respectively). The investigators concluded that, most likely, pathogens were transferred via saliva from infected untreated periodontal lesions or other niches to the treated sites  Bacterial Transmission and Translocation – Clinical significance Quirynen and coworkers - “one stage, full-mouth disinfection” This strategy attempted to suppress the translocation of periodontopathogens from all of their intraoral habitats (i.e., mucous membranes, tongue, and saliva) to root-planed periodontal pockets. Several comparative studies between the one-stage, full mouth approach and the standard therapy from the Leuven group (i.e., root planing per quadrant with 2-week intervals that allow for translocation) the impact of bacterial translocation in relation to the obtained gain in attachment, pocket depth reduction, and changes in the microbiota Changing concepts in the etiology of periodontal disease  Please pick the right statement which complies with the concept of Non-specific plaque hypothesis a. A. a is responsible for an aggressive form of periodontitis b. Quantity rather than quality of plaque is responsible for periodontal disease c. The treatment of scaling and root planing is based upon this concept d. Some sites have more destruction and other sites have less destruction in the presence of the same amount of plaque. Nonspecific plaque hypothesis “Elaboration of noxious products by the entire plaque flora.” Quantity rather quality. Small amounts of plaque are present, the noxious products are neutralized by the host. Large amounts of plaque would cause a higher production of noxious products, which would essentially overwhelm the host’s defenses.  What is the concept of key stone pathogen and which specific microorganism has been related with this concept Contradiction to this theory Some individuals with considerable amounts of plaque and calculus, as well as gingivitis, never developed destructive periodontitis. Individuals who did present with periodontitis demonstrated considerable site specificity with regard to the pattern of disease. Some sites were unaffected, whereas advanced disease was found in adjacent sites In the presence of a uniform host response, these findings were inconsistent with the concept that all plaque was equally pathogenic Treatment according to this hypothesis Control of periodontal disease depends on the reduction of the total amount of plaque - Scaling and root planing, use of antibiotics The nonspecific plaque hypothesis has been discarded in favor of other etiologic hypotheses- Most of the therapeutic interventions are still based on the basic principles of the nonspecific plaque hypothesis Specific Plaque Hypothesis The pathogenicity of dental plaque depends on the presence of or an increase in specific microorganisms Plaque that harbors specific bacterial pathogens may provoke periodontal disease because key organisms produce substances that mediate the destruction of host tissues A. actinomycetemcomitans as a pathogen in localized aggressive periodontitis P. intermedia in pregnancy gingivitis Newer bacteria - Synergistetes- clear association with periodontal disease. The association of Socranksy's “red complex” bacteria (P. gingivalis, T. forsythia, and T. denticola) with periodontal disease Possible treatment tried ( hypothetical ) is replacement therapy, where specific antagonistic microorganism can be used as the treatment to eliminate pathogen. For A.a associated sites. Strptococcus can be introduced which will halt the progression of A.a associated sites.  Contradiction to this theory Disease association studies do not reveal whether the presence of specific bacteria causes or correlates with the presence of disease Periodontal disease can occur even in the absence of defined “pathogens,” such as red complex bacteria. “Pathogens” may be present in the absence of disease. Ecologic Plaque Hypothesis Proposed by Marsh and coworkers in 1990 changes in the environment made by the bacterial composition responsible for the periodontal disease Both the total amount of dental plaque and the specific microbial composition of plaque may contribute to the transition from health to disease ( combination of specific and nonspecific ) The health associated dental plaque microbiota is considered to be relatively stable over time and in a state of dynamic equilibrium or “microbial homeostasis.” - Perturbations to the host response may be brought about by an excessive accumulation of nonspecific dental plaque, by plaque- independent host factors (e.g., the onset of an immune disorder, changes in hormonal balance [e.g., during pregnancy]), or by environmental factors (e.g., smoking, diet). Ecological hypothesis  Disease-associated organisms are minor components of the oral microbiota in health; these organisms are kept in check by interspecies competition during microbial homeostasis Disease is associated with the overgrowth of specific members of the dental plaque biofilm when the local microenvironment changes, but it is not necessarily the same species in each case Clinical importance - Eliminating the etiologic stimulus whether it is microbial, host, or environmental—will help to restore microbial homeostasis Treatment based on this concept is possible – ozone therapy and hyperbaric oxygen therapy. Keystone Pathogen Hypothesis and Polymicrobial Synergy and Dysbiosis Model Certain low abundance microbial pathogens can orchestrate inflammatory disease by remodeling a normally benign microbiota into a dysbiotic one. Certain pathogens may trigger the disruption of microbial homeostasis, thereby leading to the development of periodontal disease, even when they are present only in low numbers. Specific pathogen-free mice exposed to P. gingivalis developed periodontal bone loss even when the pathogen was present in less than 0.1% of the total microbiota Keystone Pathogen Hypothesis and Polymicrobial Synergy and Dysbiosis Model P. gingivalis subverts the host immune system and changes the microbial composition of dental plaque, ultimately leading to periodontal bone loss On this basis, P. gingivalis was labeled a “keystone” pathogen; this means that it is an organism that is central to the disease process, even when it is at a relatively low abundance. “keystone pathogen” mechanisms proposed for P. gingivalis P. gingivalis can manipulate the Toll-like receptor 4 (TLR4) response It acts as an agonist of TLR4, activating the immune system, or as an antagonist of TLR4, dampening the immune response This is dependent on the concentration of iron. In the mouth, the most important source of iron is hemin from the gingival crevicular fluid. So during inflammation, gingival crevicular fluid increases, and P. gingivalis acts as antagonist of TLR4, thus inhibiting the immune response P. gingivalis can inhibit the synthesis of interleukin-8 (also in response to other bacteria).This phenomenon is called “local chemokine paralysis” and leads to delayed polymorphonuclear leukocytes transmigration, impairing the host to confront the microbial challenge keystone pathogen” mechanisms proposed for P. gingivalis P. gingivalis is able to interfere with the complement system, a component of the innate immune system. On one side, it suppresses its activation by degradation of C3 and capturing of C4b-binding protein. On the other side, by paradoxically using the proinflammatory C5a through a crosstalk mechanism between its receptor and TLR2. Polymicrobial synergy and dysbiosis model ( PDS) Interspecies communication between keystone pathogens and other members of the community (known as accessory pathogens) is considered one important factor that leads to overgrowth of the more pathogenic microbiota and to a dysbiotic microbial community Functioning link between oral streptococci and more pathogenic organisms including P. gingivalis and A. actinomycetemcomitans