dental plaque.pptx

DENTAL PLAQUE

PRESENTED BY;DR. POOJA BHASALE

INTRODUCTION Dental caries and periodontal diseases are the two most common diseases of the oral cavity. Their prevalence is recorded along with history of man after his appearance on earth. Experimental and epidemiologic studies have demonstrated that these diseases are dependant on the microorganisms present in plaque. It is the build up of plaque that serves as an irritant to the gingiva.

• Dental plaque is defined clinically as ‘a structured resilient, yellow-grayish substance that

adheres tenaciously to the intra oral hard surfaces, including removable and fixed

restorations.’ – Bowen WH 1976

• Dental plaque- ‘highly complex structural entity which comprises of large species of

microorganisms embedded in a mucinous matrix’-American Academy of Periodontology

1986

COMPOSITION OF DENTAL PLAQUE• Composed of bacteria in a matrix of salivary glycoproteins and extra cellular

polysaccharides

• One gram of plaque - 1011 bacteria.(Schroeder etal 1970)

• Number of bacteria in supragingival plaque on a single tooth surface - > 109

• In a periodontal pocket - 103 to 108

• A single individual may harbor 150 or more different species.

• More than 500 distinct microbial species are found in dental plaque.(Moore etal 1994).

• Nonbacterial microorganisms found in plaque include Mycoplasm species yeasts protozoa viruses

Carranza’s Clinical Periodontology 10th edition

TEETH AS PORT OF ENTRY OF PERIOPATHOGENS

The unusual anatomic feature, that a mineralized structure, the tooth, passes through the integument, so that part of it is exposed to the external environment while part is within the connective tissues.

The tooth provides a surface for the colonization of a diverse array of bacterial species.

In contrast to the outer surfaces of most parts of the body,the outer layers of the tooth do not shed, and thus microbial colonization is facilitated.

In addition the tooth provides sanctuaries in which organisms can hide,persist at low levels during treatment and the re-emerge to cause futher problems.

• Clinical Periodontology & Implant Dentistry 5th edition • Jan Lindhe

CLASSIFICATION Dental plaque is classified as SUPRAGINGIVAL or SUBGINGIVAL

SUPRAGINGIVAL- found at or above the gingival margin, when in direct contact with the gingival margin it is referred as marginal plaque

SUBINGIVAL- below the gingival margin, between the tooth and the gingival pocket epithelium.

STRUCTURE OF SUPRAGINGIVAL PLAQUE

•Stratified organization of a multilayered accumulation of bacterial morphocytes

•Gram positive cocci and short rods predominate at the tooth surface, where as gram negative rods and filaments as well as spirochetes predominate in the outer surface of the mature plaque mass

•1st bacteria to colonize are streptococci species and Actinomyces. Veillonella is also an early colonizer

•Plaque grows by cell division of adherent bacteria

•‘Corncob’ structures (Listgarten et al. 1973)

•Feature of older plaque is the presence of dead, lysed cells. Provide nutrients to the still viable bacteria in the neighbourhood. (Theilade and Theilade 1970)

Clinical photo of 10 day old supragingival plaque. The first symptoms of gingival inflammation (arrows) are becoming visible.

STRUCTURE OF SUPRAGINGIVAL PLAQUE

•The material present between the bacterial cells- Intermicrobial matrix

•3 sources contribute to it- the plaque microorganisms, the saliva, gingival exudate

•Intermicrobial matrix varies in regions - fibrillar component between gram +ve cocci - granular or homogenous in other regions - in the presence of gram –ve organisms, vesicles seen. These vesicles contain endotoxins and proteolytic enzymes and are involved in adherence of bacteria (Hofstad et al. 1972, Grenier & Mayrand 1987)

Long standing supragingival plaque near the gingival margin demonstrates ‘corncob’ arrangement

STRUCTURE OF SUBGINGIVAL PLAQUE Subgingival microbiata differs in compostion

from the supragingival plaque primarily because:

a) Local availability of blood products.

b) Low oxidation-reduction (redox) potential which characterizes the anaerobic environment.

c) Gingival crevice or pocket is bathed by the flow of crevicular fluid.


SUBGINGIVAL PLAQE

STRUCTURE OF SUBGINGIVAL PLAQUE• A relatively thin layer of adherent bacteria covers the tooth surface.• Rods and filaments tend to be arranged in a palisading pattern, with the long

axis of the cells perpendicular to the tooth surface.• Unique bacterial aggregates, resembling test-tube brushes, can be found

attached to the adhering plaque and extending into the space between the bacterial layer and the adjacent soft tissue wall.

• The “bristles” of these test-tube brush formations are gram-negative filamentous bacteria, some of which may be flagellated.

• The axial portion of the test-tube brush consists of a single or several long filaments held together by an amorphous extracellular matrix.

• The bulk of the subgingival microbiota consists of a complex mixture of predominantly anaerobic bacteria that surround and cover the test- tube brush formations.

• The structure of Dental plaque- Max. Listgarten, Periodontology 2000, Vol 5. 1994

STRUCTURE OF SUBGINGIVAL PLAQUEThe subgingival plaque has two regions- 1). Tooth associated region of subgingival plaque and 2). Tissue associated region of subgingval plaqueBoth morphologic and microbiologic studies reveal distinction between the tooth associated and tissue associated regions of subgingival plaque.(Listgarten etal 1970)

TOOTH ASSOCIATED PLAQUE Filamentous microorganisms dominate Increased number of gram positive rods and cocci are

seen. In the deeper parts - filamentous organisms are fewer

and in the apical region - absent.

The apical border of the plaque mass is separated from the junctional epithelium by a layer of host leukocytes, and the bacteria of this apical tooth associated region show an increased number of gram-negative rods.

Tooth associated plaque- S.mitis, S.sanguis, A.viscosus, A.naeslundii, Eubacterium species seen predominatly


TISSUE ASSOCIATED PLAQUE• Primarily contain gram-negative rods and cocci, large numbers of filaments, flagellated

rods, and spirochetes.

• The multitude of spirochetes and flagellated organisms are motile bacteria and there is no intermicrobial matrix between them. This outer part of the microbial accumulation in the periodontal pocket adheres loosely to the soft-tissue pocket wall. (Listgarten1976).

• Host tissue cells e.g. white blood cells and epithelial cells are also found.

• Soft tissue plaque- S.oralis, S.intermedius, P.gingivalis, P.intermedia, T.forsythia and Fusobacterium Nucleatum. (Dzink etal 1989)

• Subgingivally located bacteria appear to have the capacity to invade dentinal tubules, the openings of which have become exposed as a consequence of inflammatory driven resorptions of the cementum (Adriaens et al. 1988). Such a habitat might serve as the source for bacterial recolonization of the subgingival space following treatment of periodontal disease.


PERIIMPLANT PLAQUE

•Plaque forms on oral implants as well

•Similarities between peri-implant and subgingival microbial deposits have been demonstrated in cross sectional studies (Mombelli et al. 1987,1995) and longitudinal studies (Mombelli et al. 1988; Pontoriero et al. 1994)


SITE SPECIFICITY OF PLAQUE• Marginal plaque Gingivitis

• Supragingival plaque and tooth associated subgingival plaque Calculus and root caries

• Tissue associated sub gingival plaque tissue destruction Periodontitis

FORMATION OF DENTAL PLAQUEPLAQUE FORMATION

AT ULTRASTRUCTURAL

LEVEL

1.Formation of the pellicle on

the tooth surface

2.Initial colonization by bacteria

3.Secondary colonization and plaque maturation

FORMATION OF PELLICLE•All surfaces of the oral cavity, hard and soft get coated with a pellicle

•Within nanoseconds after prophylaxis, saliva derived ‘acquired pellicle’ formed

•Composition- Glycoproteins, proline-rich proteins, phosphoproteins, histidine-rich proteins, enzymes

•Studies indicate that bacteria can be part of the early deposit (Ronstrom A, Edwardsson S, Atistrom R, 1977)

•Composition of pellicle differs from saliva indicating it forms by selective adsorption of environmental macromolecules

•Forces involved are- Van der Waals, electrostatic and hydrophobic forces

•Functions as a protective barrier and also provides a substrate to which bacteria in the environment attach

INITIAL COLONIZATION OF TOOTH SURFACE

The dental pellicle that is formed, alters the charge and free energy of the surface which in turn increase the efficiency of bacterial adhesion.

Within few hrs. bacteria are found on the dental surface. In fact with in 5min. 106 bacteria colonize per cm2 the tooth surface.

Initial bacteria that colonize the tooth surface are predominantly gram +ve facultative micro organisms such as A. viscosus and S. sangius.

Adhesion of bacteria is determined by the enviroment and the physio-chemical surface properties of the bacterium and the substratum.

MECHANISM OF ADHESIONElectrostatic forces

Hydrophobic forces

Short range forces(<1nm from the surface)

SECONDARY COLONIZATION AND PLAQUE MATURATIONThese include micro organisms that do not initially

colonize tooth surface and includes P.intermedia, P.loesheii, Capnocytophaga, F. nucleatum and P. gingivalis .

The micro organism may interact with pellicle, bacterial polysaccharide or there may be direct interaction between bacterial cell surfaces.

This last bacterial cell to cell interaction is termed as co-aggregation and was first described by Gibbons and Nygaard in 1970.

Mc Intire, et al in 1978 described co-aggregation between A. naeslundii and S. oralis. This interaction was between proteinaceous molecule which acted as a lectin on A. naeslundii and a carbohydrate receptor on S. oralis.

Direct cell to cell interaction were also noticed in early electron microscopic studies of dental plaque. Clearly observed in these studies were morphologic forms arising from the direct association of different cell types.

The interaction of filamentous cells with coccal cells were particularly noticeable and these co-aggregated cells were labeled “corncobs”or “test tube brushes” or bristle brush due to their appearance.

“corncobs” The name corncobs was

coined by Jones in 1971.It was first described by

Vincentini in 1897 and thought that the structures were composed of a single microbial species and named them Letotrix racemosa.

It is now known that corncob unit consists of a central filamentous bacterium covered by coccal cells.

Electron micrographs of cross section of corncobs indicated that that attachment of cocci to the filament occurred via hair like appendages that are commonly found on some species of oral streptococci.(co-aggregation)

These fimbrae were found to be located on one pole rather than uniformly distributed over the cell surface as found in other oral streptococci.

Another feature of corncobs was the firmness of attachment between component micro organism.

Attempt to separate component micro organism by sonification failed.

In 1997 Mouton, et al used a combination of

micromanipulation and culture to isolate both filamentous organism and the attached streptococci.

Lancy, et al 1980 developed a quantitative assay for corncob formation.

Using this assay and electron microscope it was subsequently found that F. nucleatum also formed corncobs with S.cristae. This was a very important finding since F. nucleatum is a major inhabitant of sub gingival plaque

Thus formation of Fusobacterial corncobs could provided a connective link between supra and sub gingival plaque

Multi generic co-aggregationAnother important feature during secondary colonization

and plaque maturation includes the concept of multi generic co-aggregation.

Kolenbrander and Andersen 1986 showed that multi generic aggregates are a composite of independent inter generic co-aggregates.

Bridging is also the property of co aggregating cells and have important ecological implication. Bridging refers to observation that two non-aggregating strains may participate together in a multi generic if they recognize a common partner by distinct mechanism.

E.g :- A. israelii does not co-aggregate with S. oralis. However P. loescheii co-aggregates with both strain by means of different adhesins. When the three were mixed, all three cell types were found in aggregated form. Kolenbrander 1985 .

Another concept put forward by Kolenbrander, et al in1990 that play a role in plaque formation is the possibility that intra generic co-aggregation between different streptococci.

Of all the bacteria that participated in intra generic co-aggregation only Fusobacteria and streptococci were capable of intra generic co-aggregation.

. F. nucleatum acts as a bridge between early and late colonizers, which may partially explain why fusobacteria are so numerous in samples from both healthy and diseased sites

• In addition to interactions with oral bacteria and host cells, F. nucleatum interacts with and binds host-derived molecules, such as plasminogen.

• F. nucleatum is generally nonproteolytic, but organisms that coexist with it, such as P.gingivalis, are highly proteolytic and can activate fusobacterium- bound plasminogen to form fusobacterium-bound plasmin,a plasma serine

• protease .

• Acquisition of proteolytic ability on its cell surface confers on the fusobacteria a new

• metabolic property, the ability to process potential peptide signals in the community.

• These peptides may be used as nutrients by fusobacteria or by other biofilm residents. coaggregates with all the late colonizers.

• Coaggregation bridges are mechanisms of cooperation because they bring together two species that are not coaggregation partners.

MICROBIAL COMPLEXES• The association of bacteria within mixed biofilms is not

random, rather there are specific associations among bacterial species

• Socransky et al.(1998) examined over 13,000 subgingival plaque samples from 185 adult subjects and used cluster analysis and community ordination techniques to demonstrate the presence of specific microbial groups within dental plaque

• Six closely associated groups of bacterial species were recognized


• These included the Actinomyces,

• A yellow complex consisting of members of genus Streptococcus

• A green complex consisting of Capnocytophaga species, A.actinomycetemcomitans serotype a, E. corrodens and Campylobacter concisus

• A purple complex consisting of V.parvula and Actinomyces odontolyticus

• These groups of species are early colonizers of the tooth surface whose growth usually precedes the multiplication of the predominantly Gram-negative orange and red complex

• The orange complex consists of Campylobacter gracilis, C. rectus, C. showae, E. nodatum, F. nucleatum subspecies, F. periodonticum, P. micros, P. intermedia, P. nigrescens and S. constellatus


• The red complex consists of B.forsythus, P. gingivalis and T.denticola (and sometimes Eubacterium nodatum)

• The "red complex" was associated more commonly with clinical indicators of periodontal diseases

• Red complex species increased strikingly in prevalence and numbers with increasing pocket depth.

• The species of the red complex are also elevated at sites exhibiting gingival inflammation, as

measured by gingival redness, bleeding on probing and suppuration.

• Thus red complex species are not only related to periodontal disease status in a subject, but to

disease status at the periodontal site.

• Other species did not show this relationship•

• Clinical Periodontology & Implant Dentistry 5th edition Jan Lindhe

DENTAL PLAQUE AS BIOFILM

The term biofilm describes the relatively undefinable microbial community associated with tooth surface or any other hard, non-shedding material (Wilderer and Charaklis 1989).

A biofilm is a well organized community of bacteria that adheres to surfaces and is embedded in an extracellular slime layer(Jill S.Nield-Gehrig).

BIOFILM: ANALOGY TO A CITY

NATURE OF BIOFILM• Preferred method of growth for microorganisms● Provides advantages for colonizing species• Protection from• Competing microorganisms• Environmental factors, host defense• Toxic substances, such as lethal chemicals, antibiotics• Facilitate processing and uptake of nutrients, cross-

feeding,removal of harmful metabolic products• Development of an appropriate physico-chemical environment.


COMPOSITION OF BIOFILM• Composed of micro colonies (15-20% by volume) distributed in a shaped matrix or

glycocalyx (75-80% volume)

• Presence of voids or water channelso Permit the passage of nutrients and other agents, acting as ‘circulatory’• system

• Organic constituents include:o Polysaccharideso Proteins o Glycoproteins o Lipid materialo Albumin

• Inorganic components are mainly calcium and phosphorus with trace amounts of other minerals including sodium, potassium and fluoride.


Exopolysaccharides-backbone of the biofilm

• DRY material-exopolysaccharides,proteins,salts,cell material

• Exopolysaccharides-major component(50-95%)

• Plays major role in maintaining the integrity of biofilm

• Several different polysaccharides

• Some are neutral(mutans),some highly charged polyanionic

• Protects microbial cells from dessication & attack by harmful agents

• Creates a local nutritionally rich enviorment by binding to essential nutrients

• Acts as a buffer

• Maintain biofilm structure-formation of networked cross linked linear macromolecules

• Type and not the quantity of exopolysaccharide has an effect on biofilm.

DEVELOPMENT OF DENTAL PLAQUE BIOFILM

Stages of biofilm maturation

•Begins with pellicle formation

•Pellicle- thin coating of salivary proteins

•Acts as a double-sided adhesive tape

•Adhering to tooth surface on one side and providing a sticky surface for bacterial attachment on the other side

• Bacteria connect to each other and pellicle by fimbrae, fibrils

Attachment

•Once they stick,bacteria produce substances that stimulate other free flowing bacteria to get attached

•2 days of no tooth cleaning tooth surface colonized by gram +ve cocci(streptococci species)

•Attachment to a solid surface stimulates bacteria to secrete extracellular slime layer that helps in anchoring and protection for attached bacteria.

I-physical properties• Increased surface roughness>increased surface

area>increase colonisation

II-chemical properties• Chemical composition of surface;eg-brass,polyvinyl

chloride• Cohesiveness of conditioning film(Bos R 1999)• Surronding saliva and its flow rate

FACTORS AFFECTING ATTACHMENT OF BIOFILMS

Formation of microcolonies•Begins after tooth surface is covered with attached bacteria

•Biofilm grows primarily through cell division of adherent bacteria

•Bacteria begin to grow away from the tooth

•Plaque grows quickly in early development and slower in more mature biofilms

•Bacterial blooms- specific species grow at rapid accelerated rates

Secondary colonization and biofilm maturation

•Prevotella intermedia, Prevotella loescheii, Capnocytophaga, Fusobacterium nucleatum ,Porphyromonas gingivalis – Secondary colonizers

•Adhere to cells of bacteria already attached

•Adhere to one another by coaggregation

•Bacteria cluster together to form sessile,mushroom-shaped micro colonies that are attached to tooth surface at a narrow base

•Results in formation of a complex array of different bacteria linked to another

Detachment •Essential to allow colonization of new habitats

•Cells detach in different fashions--Erosion-detachment of single cells in a continuous fashion-Sloughing-sporadic detachment of large group of cells-intermediate process where large pieces of biofilm are shed

•Rate of detachment not clear (Watnick P, Kolter R, 2000)

• Rate of growth in many biofilms is slow and detachment is an uncommon event

•Cells in such biofilms are metabolically active and capable of growth once released from the biofilm

•Detachment is active ongoing process

Factors affecting biofilm development and behaviour

•Shear stress--high shear-thinner and denser biofilms,colonies are elongated and capable of rapid oscillation-low shear-roughly circular cluster of cells separated by voids,colonies are tower/mushroom shaped

•Hydrodynamics--Biofilms under laminar flow(low shear) and turbulent flow(high shear) are different

•Changes in nutrient concentration-addition of nutrients to a biofilm increased both mass and structure Stoodley et al 1999

Bacterial behavior within the biofilm•Bacteria growing in microbial communities do not behave the same as those growing in a planktonic state

•E.g. the resistance of bacteria to antibiotics is increased in the biofilm about 1000-1500 times compared to those in their planktonic state (Costerton JW 1999)

•Mechanism of increased resistance in biofilms differs from species to species, antibiotic to antibiotic and biofilms growing in different habitats

•Resistance of bacteria to antibiotics is affected by their nutritional status, growth rate, temperature, pH and previous exposure to sub effective concentrations of antimicrobials (Brown MRW, Collier PJ, Gilbert P,1990)

•Slower rate of growth of bacteria within the biofilm also makes them less susceptible to some antibiotics (Brooun A, Liu S, Lewis K, 2000)

•Matrix performs a ‘homeostatic function’

-cells deep in the film and that at the periphery experience different growing conditions or cells growing planktonically

-growth rates of the cells also differ

-slow growing cells(deeper cells)express non-specific defense mechanisms i.e shock proteins and multi drug efflux mechanisms and so increased exopolymer synthesis

-this exopolymer has certain properties that retards diffusionClinical Periodontology & Implant Dentistry 5th edition

Jan Lindhe

• Eg-strongly charged or chemically highly reactive agents fail to reach the deeper zones of biofilm as the biofilm acts as an ion exchange resin removing such molecules from solution

• Extracellular enzymes get trapped and concentrated in the extracellular matrix ,thus inactivating positively charged hydrophilic antibiotics

• Hydrophobic antibiotics like macrolides though positively charged are unaffected

• ability of extracellular matrix to act as a barrier depends on the type of antibiotic,its binding to the matrix,levels of antibiotic

• As reaction between agent and matrix will reduce the level of agent,a biofilm of greater bulk will deplete the agent more

• Alteration in genotype and phenotype of bacteria is also important


• Recently a subpopulation of cells within a biofilm that are ‘super-resistent’ was proposed

• Such cells explained the elevated levels of resistance to ceratin antibiotic

• Brooun et al 2000 examined multi drug resistant pumps to antibiotic resistance of organisms grown in biofilms

• These pumps extruded the chemically antimicrobial agents from the cell

• Extrusion placed the antibiotics outside the cell membrane,hence offering protection to the biofilm from the antibiotics targeting the cell wall synthesis


Quorum sensing

•Comes from the same term used in a committee when enough members are present to legally take some action

•It was first observed in the marine bacterium Vibrio fischeri, which can produce light after a sufficient population of this bacterium has developed

•Is the ability of the bacteria and microcolonies to communicate with each other in the biofilm

• Involves the regulation of expression of specific genes through the accumulation of signaling compounds that mediate inter cellular communication(Prosser 1999)

• depends on cell density

• At threshold level, (quorum cell density) gene expression is activated

• Cell signaling appears to be mediated by an N-acyl homoserine lactone encoded by a lux1 gene

Though planktonic cells secrete chemical signals (HSLs, for homoserine lactones), the low concentration of signal molecules does not change genetic expression. Biofilm cells are held together in dense populations, so the secreted HSLs attain higher concentrations. HSL molecules then re-cross the cell membranes and trigger changes in genetic activity

•Autoinducer-2 a universal signal molecule is recently discovered in mixed species communities(Kolenbrander et al 2006)

•Physiological properties of bacteria in a community may be altered(Cooper et al 1995)

•Plays a role in- antibiotic resistance at high cell densities-encourages growth of beneficial species-discourages growth of competitors

QUORUM SENSING• Quorum sensing systems bacteria have been generally

divided into at least three classes:• (1) LuxI/LuxR–type quorum sensing in Gram-negative

bacteria, which use acyl-homoserine lactones (AHL) as signal molecules. ( Lux- bacterial luciferase gene).

• (2) Oligopeptide-two-component-type quorum sensing in Gram-positive bacteria, which use small peptides as signal molecules.

• (3) luxS-encoded autoinducer 2 (AI-2) quorum sensing in both Gram-negative and Gram-positive bacteria.

• Autoinducer-2 a universal signal molecule is recently discovered in mixed species communities(Kolenbrander et al 2006)

• AI-2 allows for inter-species communication, so it is called a “universal language”used for cross-species communication.

• AI-2 is produced from S-adenosylmethionine through several steps, including the required enzymatic conversion of the intermediate S-ribosylhomocysteine by LuxS to 4,5-dihydroxy-2,3-pentanedione, which is unstable and is predicted to cyclize spontaneously (133, 134) into a variety of molecules called pro-AI-2 before forming a mature AI-2–LuxP complex.

• The luxS gene, encoding S-adenosylhomocysteinase (LuxS) is present in the genome sequencesof many oral bacteria.

• The discovery of AI-2 that is produced and detected by a large number of diverse bacteria implies that bacteria have a means to assess the cell density of other species in a microbial community, facilitating interspecies communication and social interactions among species in the community.

• Communication among Oral Bacteria (Paul E. Kolenbrander,* Roxanna N. Andersen, David S. Blehert, Paul G. Egland, Jamie S. Foster, and Robert J. Palmer Jr)MICROBIOLOGY AND MOLECULAR BIOLOGY REVIEWS, Sept. 2002

DE NOVO SUPRAGINGIVAL PLAQUE FORMATION: CLINICAL ASPECTS• Plaque formation follows an exponential growth curve (Quirynen et al 1989) • Negligible in the 1st 24 hours . Increases rapidly in the next 3 days and then

slows down• There is a shift toward anaerobic and gram-negative flora• Follows a typical topographic pattern. Initial growth along the gingival

margin and interdental space (areas protected by shear stress)• Can also start from grooves, cracks, perikymata or pits• Rough intra oral surfaces accumulate and retain more plaque (Quirynen and

Bollen)• Plaque formation occurs much faster in the lower jaw, molar areas and buccal

tooth surfaces and interdental regions. (Lindhe etal 1992)• More rapid on teeth with inflamed gingival margins (Sorensen etal 1986)• No difference in de novo plaque formation with age (Fransson etal 1995,

Holm-Pedersen etal 1975, Winkel etal 1987)

DE NOVO SUBGINGIVAL PLAQUE FORMATION

• Technically impossible to record the dynamics of subgingival plaque formation

• Studies show that tooth surfaces harbor plaque and calculus after scaling. These remain the primary source for subgingival recolonization

• Leknes et al in 1994 did a study on beagle dogs. Studied the extent of colonization in 6mm pockets. Observed that smooth surfaces harbored significantly less plaque

PHYSIOLOGIC PROPERTIES OF DENTAL PLAQUE

• Transition from gram positive to gram negative is accompanied by physiologic transition in the developing plaque

• Early colonizers lower the redox potential of the environment and favour the growth of anaerobic species

• Lactate and formate, by products of metabolism of streptococci and actinomycetes maybe used in the metabolism of other plaque microorganisms

• Host is also an important source of nutrients

• Physiologic interactions occur between different microorganisms in plaque and between the host and plaque microorganisms

• Nutritional interdependencies are critical for growth and survival of the microorganism in dental plaque and partly explains the highly specific structural interactions among bacteria in plaque

• Some researchers say the pathologic flora is due to ‘ecological plaque hypothesis’

NONSPECIFIC PLAQUE HYPOTHESIS(Theilade 1986)

Mid 1900’s- periodontal disease was thought to be due to:• - accumulation of plaque over time• - decreased host response• - increased host susceptibility

• This hypothesis maintains that periodontal disease results from the “elaboration of noxious products by the entire plaque flora”.

• The theory maintains that control of periodontal disease depends on control of

the amount of plaque accumulation.

• Although discarded in favor of the Specific plaque hypothesis, clinical treatment is still based on this theory.

• Carranza’s Clinical Periodontology 10th edition

NONSPECIFIC PLAQUE HYPOTHESIS• Contradictions of theory:

• Individuals with considerable amounts of plaque, calculus and gingivitis did not develop destructive periodontitis.

• Individuals with periodontitis demonstrated site-specificity in the disease pattern.

• Some sites were unaffected whereas adjacent sites were affected by the disease.

• In the presence of uniform host response,these findings were inconsistent with the concept that all plaque was equally pathogenic

• Led to a renewed search for specific pathogens in periodontal disease.


SPECIFIC PLAQUE HYPOTHESISSir Walter Loesche 1979

•States that only certain plaque is pathogenic

•Pathogenecity depends on presence or increase in specific microorganisms

•Plaque which has specific bacterial pathogens results in periodontal disease- these organisms destroy host tissues

•Association of specific bacterial species with disease originated in 1960

•Acceptance of specific plaque hypothesis came about by the recognition of A. actinomycetemcomitans as a pathogen in localized aggressive periodontitis.


ECOLOGICAL PLAQUE HYPOTHESIS• Proposed by PD Marsh in 1991• Says that a change in a key environmental factor will trigger a

shift in the balance of the resident plaque microflora which might predispose a site to disease

• In health, these organisms are only weakly competitive and not significant clinically. Microbial specificity in disease is because only certain species are competitive under the new environmental conditions

• It is a basic tenet of microbial ecology that a major change to an ecosystem produces a corresponding disturbance to the stability of the resident microbial community (Brock 1966; Alexander 1971; Fletcher et al. 1987)

ECOLOGICAL PLAQUE HYPOTHESIS

CRITERIA FOR IDENTIFICATION OF PERIODONTAL PATHOGENS

• In the 1870’s Robert Koch developed classic criteria by which a microorganism can be judged to be a causative agent in human infections

• These criteria, known as KOCH”S POSTULATES, stipulate the following for the causative agents:

• Must be routinely isolated from diseased individuals

• Must be grown in pure culture in the laboratory

• Must produce a similar disease when inoculated into susceptible laboratory animals

• Must be recovered from lesions in a diseased laboratory animal


• Difficulties exist in the application of these criteria in the case of periodontitis as:

1. The inability to culture all the microorganisms that have been associated with the disease.(spirochetes).

2. Difficulties inherent in defining and culturing sites of active disease

3. Lack of good animal model system for study of periodontitis.


In 1992, Sigmund Socransky , a researcher at Forsyth Dental Institute at Boston proposed criteria by which periodontal microorganisms maybe judged to be potential pathogens

These criteria are:

•Must be increase in the number of organisms at diseased sites

•Must be decreased at sites that show improvement with treatment

•Must demonstrate a host response

•Capable of causing disease in experimental animals

•Must demonstrate virulence factors responsible for enabling the microorganism to cause destruction of the periodontal tissues


Association of plaque microorganisms with Periodontal disease

• 3 factors determine occurrence of active periodontitis:

• Susceptible host

• Presence of pathogenic species

• Absence or a small proportion of ‘beneficial bacteria’

• The clinical manifestations of periodontitis are due to an interplay between specific pathogens in plaque and host tissues


SUSCEPTIBILITY OF HOST• Partially hereditary. Maybe influenced by smoking, diabetes

stress

• Genetic mutations have been identified that alter host response to bacteria and are associated with periodontal disease

• Grossi et al. 1998 found a direct relation between periodontitis and the level of smoking

• Diabetics are at higher risk for periodontal destruction

• Severe stress conditions also aggravate periodontal destructionCarranza’s Clinical Periodontology 10th edition

Marsh PD, Devine DA. How is the development of dental biofilms influenced by the host? JClin Periodontol 2011;

PRESENCE OF PATHOGENS• Presence of pathogens in sufficient numbers is essential

• Key pathogens- Aggregetibacter actinomycetemcomitans, Tannerella Forsythia and Porphyromonas gingivalis

• Moderate evidence for etiology- Prevotella intermedia, Prevotella nigrescens, Campylobacter rectus, Peptostreptococcus micros, Fusobacterium nucleatum, Eubacterium nodatum (past a certain threshold level)

• Evidence based on epidemiologic data and results of animal innoculation

• Mere presence of pathogens is not enough. An elevation to a critical level is required

• Periopathogens may be present in the gingival crevice, although in lower numbers,as members of the normal resident flora.(Tanner etal 1991)


ROLE OF BENEFICIAL SPECIES• Affect disease progression in the following ways: - occupying a niche that might otherwise have pathogens - limiting pathogens ability to adhere to appropriate tissue surfaces - affecting the growth of the pathogen - affecting the ability to produce virulence factors - degrading virulence factors produced by the pathogen

• e.g. S. Sanguis produces hydrogen peroxide that kills A. actinomycetemcomitans. (Hillman etal 1985)


MICROBIAL SHIFT DURING DISEASE• Gram positive to gram negative

• From cocci to rods (later to spirochetes)

• Non motile to motile organisms

• Facultative to obligate anaerobes

• Fermenting to proteolytic speciesCarranza’s Clinical Periodontology 10th edition

Microbial shifts during dental biofilm re-development in the absence of oral hygiene in periodontal health and diseaseNaciye G. Uzel1,†, Flavia R. Teles1,2, Ricardo P. Teles1,2, Xiaoging Q. Song1, Gay Torresyap1,‡, Sigmund S. Socransky1, Anne D. Haffajee1

Journal of Clinical PeriodontologyVolume 38, Issue 7, pages 612–620, July 2011

• Abstract• Aim: To monitor microbial shifts during dental biofilm re-development.• Materials and methods: Supra- and subgingival plaque samples were taken separately from 28 teeth in 38

healthy and 17 periodontitis subjects at baseline and immediately after tooth cleaning. Samples were taken again from seven teeth in randomly selected quadrants during 1, 2, 4 and 7 days of no oral hygiene. Samples were analysed using checkerboard DNA–DNA hybridization. Species counts were averaged within subjects at each time point. Significant differences in the counts between healthy and periodontitis subjects were determined using the Mann–Whitney test.

• Results: The total supra- and subgingival counts were significantly higher in periodontitis on entry and reached or exceeded the baseline values after day 2. Supragingival counts of Veillonella parvula, Fusobacterium nucleatum ss vincentii and Neisseria mucosa increased from 2 to 7 days. Subgingival counts were greater for Actinomyces, green and orange complex species. Significant differences between groups in supragingival counts occurred for 17 of 41 species at entry, 0 at day 7; for subgingival plaque, these values were 39/41 taxa at entry, 17/41 at day 7.

• Conclusions: Supragingival plaque re-development was similar in periodontitis and health, but subgingival species recolonization was more marked in periodontitis.

http://onlinelibrary.wiley.com/doi/10.1111/jcpe.2011.38.issue-7/issuetoc




STRATEGIES TO PREVENT PERIODONTAL DISEASES

• Conventional methods involve mechanical removal of subgingival plaque along with antimicrobial therapy

• Ecologic approach- alter the environment of the pocket to prevent growth of pathogens

• Can be done by:• - Antimicrobial and anti-inflammatory agents• - Oxygenating and redox agents

• Novel drugs that specifically target quorum sensing systems are capable of attenuating bacterial infections in a manner that is less likely to result in the development of resistant mutants.(eg Furanones)

1) Quorum Sensing and Bacterial Social Interactions in Biofilms(Yung-Hua Li 1,2,* and And Xiaolin Tian ) Sensors 2012,12

OMNIGENE• These are DNA probe systems for a number of

known periodontopathogen subgingival bacteria.

• A paper point sample of sub-gingival plaque is placed in the container provided and mailed off to the company for assay.

• Probes are available for the detection of A. actinomycetemcomitans, P. gingivalis, P. intermedia, F. nucleatum, C. rectus, T. denticola and E. corrodens.

• Reports are provided within very short time periods (few hours to few days).

EVALUSITEEvalusite is a kit that employs a novel membrane-based enzyme immunoassay for the detection of three putative periodontopathogens: Aa, Pg and Pi.

A sub-gingival sample is collected using paper points and added to a sample tube. The eluent is then added to the kit, which employs a sandwich-type ELISA (enzyme-linked immunosorbent assay); a pink spot is displayed if the test organism is present.

The main weaknesses of this test kit reside in 1) the assumption that the three detected organisms are causing

disease;2) (2) it is a multistage test; 3) (3) it has a subjective calorimetric end point and 4) (4) there is no permanent record of the results [11].

PERIOSCAN• Perioscan is a diagnostic test kit that utilizes the BANA (N-benzoyl-DL-arginine-2-

naphthylamide)-hydrolysis reaction, developed to detect bacterial trypsin-like proteases in the dental plaque .

• A trypsin-like activity has been identified in strains of P. gingivalis, T. denticola, T. forsythia and some Capnocytophagia strains. BANA is an example of a substrate-conjugated beta-nepthylamine (p-NA), which is hydrolyzed by this trypsin-like enzyme to release free p-NA. The latter is a chromophore and reacts with a variety of dyes (e.g. Fast-Garnet GBC) to produce colored products.

Subgingival plaque is collected and placed on a BANA-containing strip, which is then folded to contact a second strip containing the “Fast-Black” dye reagent.

• The folded card is placed inside an oven for 15 min at 55°C and any blue-black color that appears is scored positive for the above species.

•

One of the potential difficulties of this test is that it may be positive at clinically healthy sites and might remain so after treatment.

CONCLUSION• Dental plaque biofilm cannot be eliminated. However, the

pathogenic nature of the dental plaque biofilm can be reduced by reducing the bioburden (total microbial load and different pathogenic isolates within that dental plaque biofilm) and maintaining a normal flora with appropriate oral hygiene methods that include daily brushing, flossing and rinsing with antimicrobial mouthrinses. This can result in the prevention or management of the associated sequelae, including the development of periodontal diseases and possibly the impact of periodontal diseases on specific systemic disorder

REFERENCESCarranza’s Clinical Periodontology- 9th , 10th Edition

Clinical Periodontology and Implant Dentistry- Lindhe, 4th,5th Edition

The structure of Dental plaque- Max. Listgarten, Periodontology 2000, Vol 5. 1994

Microbial ecology of dental plaque and its significance in health and disease- P.D. Marsh

Dental biofilms:difficult therapeutic targets- Sigmund Socransky and Anne D Haffajee, Periodontology 2000, Vol 28. 2002

Dental plaque biofilms: communities, conflict and control.P. D. Marsh Periodontology 2000 vol 55 2011

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