DHYG 263 - Oral Biofilm and Periodontal Infection

Changing Evidence for the Role of Bacteria in Periodontitis

Over the years, three main hypothesis have been proposed to explain the etiology of periodontal disease 1) Nonspecific plaque hypothesis 2) Specific plaque hypothesis 3) Host response hypothesis

Gram Staining

Purple → Gram positive (a single thick cell membrane) Pink → Gram negative (double cell membrane)

Structure of Plaque Biofilm - Fluid Channel

Fluid channel directs fluid in and out of the biofilm bringing the nutrients and oxygen to the bacteria

Host Response Hypothesis - Current Perspective

"Plaque biofilm is necessary but not sufficient for periodontal destruction (microbial homeostasis - host response hypothesis). It is the host response, not the type of bacteria, which determines whether periodontal destruction develops. At that point, inflammation drives the changes in the microbial environment, not vise versa." - Biofilm microbe population associated with periodontal health appears to remain stable. - Decades of research have failed to identify specific bacterial pathogens that cause tissue destruction. Evidence has shown that the immune response is the cause for tissue destruction.

Nonspecific Plaque Hypothesis

"Proposed accumulation of plaque biofilm adjacent to gingival margin led to inflammation and then periodontal destruction" BUT.. - Fails to explain why most cases of gingivitis do NOT progress into periodontitis - Some patients with light biofilm progress to periodontitis, while others with heavy accumulation of biofilm fail to develop periodontitis - Does not explain why some sites in a patient's periodontium have much periodontal destruction, while other sites are unaffected

Specific Plaque Hypothesis

"Proposed specific pathogenic bacteria present in subgingival biofilms with their toxic products result in periodontal tissue destruction. Shift occurs with bacteria in biofilm to be predominantly gram-negative aerobes, from being gram-positive." - As a result of this hypothesis, research efforts focused on identifying specific microorganisms that associated with periodontal disease and conditions

Free Floating Bacteria

*AKA Planktonic Bacteria - Until recently, most research done on bacteria was conducted on free-floating bacteria

Tissue Associated Plaque Biofilms

*Bacteria adhere to the epithelium - Bacteria adhere loosely to epithelium of pocket wall - They are distinctly different microorganisms from tooth-associated biofilms - Bacteria can invade gingival connective tissues, periodontal connective tissues, and surface alveolar bone

Attached Bacteria

- Bacteria can attach to surfaces and to one another - Communities of bacteria that attach to each other and to a surface are described as living in a BIOFILM - Once a bacterium attaches to a surface, it activates a whole different set of genes that give the bacterium a different characteristic from those it had as a free-floating organism

Phase 4 of Dental Plaque Formation: Continued Growth

*Extracellular slime layer and microcolony formation - The act of attaching to the tooth surface stimulates the bacteria to excrete a slimy, glue-like substance called the extracellular slime layer. This layer provides protection for the attached bacteria. - Once the tooth surface is covered with attached bacteria, the biofilm grows through cell division rather than through attachment of new bacteria

Phase 2 of Dental Plaque Formation: Attachment of Early Colonizers

*Within a few hours after pellicle formation - Bacteria accumulate on pellicle to form dental plaque - During this initial stage, Gram positive bacteria are predominantly found on the dental pellicle

Phase 1 of Dental Plaque Formation: Formation of Pellicle

*Within minutes after cleaning the tooth surface - A film forms over the tooth surface. This film, the ACQUIRED PELLICLE, is composed of a variety of salivary glycoproteins (mucins) and antibodies

Bacterial Colonization of the Tooth Surface

- A mature biofilm does NOT consist of only one species of bacteria - The biofilm develops by stacking on bacterial species on top of another bacterial species

Structure of Bacteria

- A protective later encloses nearly all bacteria called the CELL MEMBRANE - Through Gram staining in the laboratory, based on the permeability of the bacterial cell membranes, the cell membrane can appear either purple or red in color under a light microscope. This method is used to identify and classify bacteria into one of two groups: GRAM POSITIVE OR GRAM NEGATIVE

Characteristics of Bacteria

- Bacteria are the simplest organisms that can only be seen through a microscope - Bacteria can replicate quickly. This ability to divide quickly enables it to adapt rapidly to changes in the environment

Tooth Associated Plaque Biofilms

- Bacteria attach to the tooth surface extending from the gingival margin to the junctional epithelium at the base of the pocket - Subgingival bacteria have the ability to invade the dentinal tubules of the cementum - COCCI and RODS are the microorganisms that dominate tooth-associated biofilms

Mechanisms of Bacterial Survival

- Biofilm bacteria are extremely resistant to antibiotics, antimicrobial agents, and the body's immune system - The extracellular slime layer may prevent the drug from penetrating fully into the depth of biofilm - Some bacteria produce enzymes that degrades antibiotics - Some bacteria may become dominant during the antibiotic course of treatment and reactive after the treatment is finished - Antimicrobial agents work best when used in conjunction with mechanical cleaning that disrupts the plaque biofilm *arrestin?

Structure of Plaque Biofilm - Communication

- Cell-to-Cell communication system - Bacterial signaling

Socransky Microbial Complexes

- Grouped microorganisms into complexes and assigned each complex a color - Colors are assigned based on association with health and disease - YELLOW and GREEN complexes are EARLY COLONIZERS that are believed to be compatible with gingival health - ORANGE and RED complexes are thought to be MAJOR ETIOLOGIC AGENTS OF PERIODONTAL DISEASE

Biofilm

- If the biofilm is adequately disrupted by daily self-care, the biofilm will always be reforming and the entire process of bacterial succession starts over beginning with early colonizers

Bacteria lives EVERYWHERE

- It is ALWAYS present on the skin and in the digestive tract and respiratory systems of humans - Based on their lifestyle, bacteria are classified into: *Free-floating bacteria; "planktonic bacteria" *Attached bacteria; "living in a biofilm" **More than 99% of all bacteria on earth live as attached bacteria

Phase 5 of Dental Plaque Formation: Mature Biofilm

- Maturation of plaque mass takes place by the growth of bacterial species attached to it. As well as by the colonization and growth of new species of bacteria. - During this phase, bacteria change from aerobic environment "gram-positive bacteria" to a highly anaerobic environment "gram-negative bacteria"

Intermediate and Late Colonizers

- Most join the biofilm in the proper sequence Tooth surface → Pellicle → Early Colonizer → Intermediate/Late Colonizer - Intermediate species includes Fusobacterium nucleatum

Phases of Plaque Biofilm Formation

- Plaque formation begins immediately after a tooth surface is cleaned. It takes 4-9 days for plaque to become fully mature. - Dental plaque formation is divided into phases: 1) Formation of Pellicle 2) Attachment of Early Colonizers 3) Colonization of Additional Bacterial Species 4) Continued Growth 5) Mature Biofilm

Control of Plaque Biofilm

- The cleaner the tooth surface, the less complex the bacterial formation - Toothbrush and floss cannot reach the subgingival plaque biofilm located within pockets *Must be removed professionally (by hygienist)

Sequence of Colonization: Early Colonizers

- The first bacteria to colonize the tooth surface - Nonpathogenic - Includes may Streptococcus species, such as Streptococcus mitis and Streptococcus oralis. Another early colonizer is Acitomyces viscosus. - Release chemical signals that indicates the next group of bacteria that conditions are favorable for them to join the biofilm - The early streptococcal colonizers are able to coaggregate with many of the other early colonizers and intermediate species.

Phase 3 of Dental Plaque Formation: Colonization of Additional Bacterial Species

- These bacteria do not adhere to the tooth surface, they adhere to the other bacteria ("early colonizers"). This process of micro-organisms attaching to one another is called COAGGREGATION.

Transmission of Periodontal Bacteria

- Transmission is the transfer of bacteria from the oral cavity of one person to another - Transmission is NOT contagion - There is little evidence that periodontal infections are communicable - Studies indicate kissing is the primary means by which saliva and its bacterial content is transmitted

Three Major Stages in Biofilm Life Cycle

1) Attachment 2) Growth 3) Detachment

Structure of Plaque Biofilm - Fluid Forces from the Saliva

Fluid forces from the saliva influence the shape of biofilm and result in exchange of genetic information among bacteria

What is biofilm?

A biofilm is a living film - containing a well-organized community of microorganisms that grows on a surface. Usually biofilms consist of many species of bacteria. *Biofilms thrive wherever there is water

Sequence of Bacterial Attachment

Acquired pellicle formation → Bacterial adhesion → Supragingival calculus (6 hours) & Plaque maturation (Day 7) → Well-differentiated subgingival biofilm (12 weeks)

Structure of Plaque Biofilm - Extracellular Slime Layer

Acts like a shield that protects microcolony from antibiotics and body immune system

Coaggregation of Bacteria

Coaggreation: the cell-to-cell adherence of one oral bacterium to another - Coaggregation is NOT random; each bacterial strain only has a limited set of bacteria to which they are able to adhere - The ability to adhere and coaggregate is important in the development of the bacterial biofilm

What is the process in which micro-organisms attach to one another?

Coaggregation

Structure of Plaque Biofilm - Bacteria Microcolonies

Each microcolony has different environmental conditions within a biofilm. This means that the bacterial population is very diverse. Which increases the plaque biofilm survivability.

Unattached Bacteria

The periodontal pocket may also have free-floating, unattached bacteria that is not part of the biofilm

Problem with Specific Plaque Hypotheses...

The species that were thought to have caused periondontal diseases were found on healthy people with no periodontal disease