LO 8

Question 1

Describe normal oral microbiota

Answer 1

1. First exposure to oral microorganisms is at birth through the birth canal
2. Short-lived (transient), and do not establish themselves
3. To establish themselves, they must “attach” to surfaces and be allowed to multiply
4. 42 known genera of bacteria exist orally!
5. Different sites in the mouth (tongue, buccal epithelium, supragingival tooth surfaces, subgingival tooth surfaces, and crevicular epithelial surfaces) support different combinations of microorganisms.
6. As one grows older, more and more microorganisms colonize.

Question 2

Describe dental plaque

Answer 2

1. Dental plaque can be defined as the soft deposits that form the biofilm adhering to the tooth surface or other hard surfaces in the oral cavity, including removable and fixed restorations.
2. Plaque is a biofilm composed of bacterial cells embedded in an intercellular matrix
3. As the plaque accumulates in the absence of oral hygiene, potentially harmful products from the multiplying bacteria accumulate and may cause damage to the teeth (caries) or to the nearby periodontal tissues (gingivitis or periodontitis). In some persons, plaque can mineralize (accumulate calcium) forming a hardened material referred to as calculus or tartar.

Question 3

Dental caries, gingival and periodontal infections are all caused by microorganisms in ___________

Answer 3

Dental biofilm

Question 4

What are the mechanisms of attachment for microorganisms in the oral cavity?

Answer 4

1. Adherence - active attachment of a bacterium to a host surface - S. sanguis attaches to hard surfaces; S. salivarius attaches to epithelial surfaces, usually via fuzzy coat
2. Aggregation - active attachment of one bacterium to another of the same or different kind - Dextran facilitates this for S. mutans

Question 5

What is a corncob?

Answer 5

A unique type of aggregation wherein cocci are arranged around a central rod or filiment

Question 6

What are the stages of biofilm formation?

Answer 6

1. Pellicle formation
2. Colonization
3. Bacterial growth and maturation
4. Dispersion

Question 7

Describe pellicle formation

Answer 7

1. Deposition of salivary components (acquired pellicle)
2. Protective function (barrier to acids); also serves as initial site of attachment for planktonic bacteria beginning first stage of biofilm development
3. A tenacious, insoluble, acellular protein film composed of glycoproteins found within saliva on oral surfaces

Question 8

Salivary proteins and peptides promote __________

Answer 8

bacterial adhesion to oral surfaces

Question 9

After cleansing of tooth surfaces, pellicle begins to reform on exposed surfaces; within _________, planktonic microorganisms attach to acquired pellicle and begin sessile colonies

Answer 9

1 hour

Question 10

Dental caries is an _________ and is caused by a demineralization of tooth structure by acids produced during __________ of dietary sugars by bacteria associated with the tooth surface.

Answer 10

1. Infectious disease
2. Metabolism

Question 11

What are the 4 factors necessary for caries to occur?

Answer 11

1. Susceptible host (person must be susceptible to disease)
2. Microorganisms (bacteria capable of causing caries must be present in mouth)
3. Substrate (primarily sucrose)
4. Time

Question 12

Define a susceptible host

Answer 12

1. Not all individuals are susceptible to all infectious diseases. Some people are resistant to caries and are caries-free.
2. Resistance comes from many factors:
   May involve characteristics of saliva, anatomic differences in teeth, nature of oral microbiota

Question 13

What are 2 important things to remember regarding bacteria and dental caries?

Answer 13

1. Not all bacteria in the mouth cause caries.
2. Bacteria that do cause caries need to be closely associated with the teeth, in the form of dental plaque.

Question 14

In which areas can plaque gather?

Answer 14

1. The margin between the tooth and the gum
2. The fissures in the occlusal surfaces of molars
3. The approximal areas

Question 15

What is the most caries-conducive bacteria in the mouth?

Answer 15

Mutans streptococci

Question 16

Why is mutans streptococci so closely associated with dental carries?

Answer 16

1. They have all three pathogenic properties important for caries formation - Production of acids from carbohydrates (being acidogenic); Survival at low pH (being aciduric); Accumulation on teeth
2. After the bacteria mutans streptococci have initiated the tooth destruction, then Lactobacillus species are thought to be more important in the progression of a carious lesion.
3. mutans streptococci have special enzymes (glucosiltransferases) that split sucrose, linking together the glucose units of the sucrose molecules to form polysaccharides called glucans . The remaining fructose part of sucrose is taken into the cell and processed through catabolic fermentation reactions to produce energy with mainly lactic acid as a waste product .
4. The glucans bind to the cells and act as bridges that bind to other cells. This binding permits new daughter cells to attach to the cell mass and accumulate in the developing dental plaque

Question 17

Describe the Lactobacillus species (L. Casei, L. Acidophilus)

Answer 17

1. Important in progression of carious lesion after other bacteria initiate tooth destruction
2. Less important in the “initial” attack on the tooth
3. Lack attachment mechanisms

Question 18

Describe Actinomyces naeslundii

Answer 18

1. Good plaque former and can accumulate into high numbers
2. Slightly acidogenic, NOT aciduric
3. Important in root caries formation

Question 19

Describe substrates

Answer 19

1. A dietary substrate that oral bacteria metabolize through is also needed for caries development.
2. Sucrose is the most caries-conducive component of our diet.
3. Oral bacteria can also metabolism fructose, glucose, lactose and starch to contribute to progression of disease

Question 20

Describe the importance of time in caries formation

Answer 20

1. Time to form carious lesions can be called “incubation time”
2. Time is also needed to recognize an infection disease (incubation time).
3. Dental checkups are scheduled at 6-month intervals because this is the usual incubation time for clinically detectable caries.

Question 21

Describe the specific plaque hypothesis

Answer 21

1. Out of the diverse collection of bacteria in plaque, only a very limited number of species are involved in disease.
2. These species can be regarded as specific pathogens that can be targeted with specific anti-caries therapies

Question 22

Describe the non-specific plaque hypothesis

Answer 22

1. Plaque is a microbial community; disease results from the outcome of the interactions among all of the component species
2. Prevention would be by plaque control

Question 23

Describe the ecological plaque hypothesis

Answer 23

1. Disease results from shifts in the balance of the resident plaque microflora
2. Potentially cariogenic bacteria can be present in health, but at levels that are not clinically relevant
3. Disease could be controlled not only by targeting putative pathogens but also by interfering with the factors responsible for driving the deleterious shifts in the microflora.

Question 24

Describe the acidogenic theory of caries formation

Answer 24

1. This is the most popular theory today
2. The cariogenic bacteria can cause the plaque pH to drop below pH 5.5, which is the critical pH for dissolution of enamel (apatite)

Question 25

What are the risk factors for caries?

Answer 25

1. Amount of plaque 2. Type of bacteria 3. Type of diet 4. Frequency of carbohydrates 5. Saliva secretion 6. Saliva buffer capacity 7. Fluourides

Question 26

What is dental calculus?

Answer 26

1. Tartar 2. Mineralized oral biofilm (by calcium and phosphate in saliva) 3. Not the causative factor in caries or periodontal disease, but facilitates attachment/retention of oral biofilm

Question 27

Describe supragingival calculus

Answer 27

1. Above free gingival margin 2. Chalky white colour 3. Most commonly located to sublingual and parotid salivary gland ducts

Question 28

Describe Subgingival Calculus

Answer 28

1. Found below the free gingival margin 2. Dark green/brown/black colour 3. Most frequently found in interproximal spaces 4. Takes on several forms from veneers/thin layers, spurs, rings

Question 29

Describe calculus formation

Answer 29

1. Formation follows stages of biofilm formation 2. Forms and grows by apposition of new layers of biofilm 3. Mineral source is saliva, gingival crevicular fluid and inflammatory exudate

Question 30

Tartar fighting toothpastes contain __________ designed to ___________ thus reducing intra-plaque mineral deposition.

Answer 30

1. pyrophosphate compounds 2. absorb excess calcium