MFD SSA Flashcards by Zaira Sattar

what is the stephan curve

• Plaque pH drops when challenged
- Food
• Oral pH drops with acidic food and drinks
• Measure at the point of dental plaque touches enamel
• Rise is much slower than drop
• Enamel dissolves more quickly below ‘critical pH’ (~5.5)

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what is Ksp

total no. Ions - allows understanding of the solubility of a salt; smaller the number the lower the solubility. Calcium hydroxyapaptite has a very low Ksp - very sparingly soluble.
If Ionic product < Ksp - dissolution

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Koch’s postulates: (modern day?)

Suspected pathogen must be present in all cases of the disease and absent from healthy animals

The suspected pathogen must be grown in pure culture

Cells from a pure culture of the suspected pathogen must cause disease in a healthy animal model

The suspected pathogen must be re isolated and shown to be the same as the original

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When Koch’s postulates cannot be applied precisely

f no infecting organism can be detected

If the bacteria cannot be grown in culture

If no suitable animal model is available

If more than one species of bacteria is involved

If it is the level rather than just the presence of the infecting bacterium that is important

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what is the difference between specificity and sensitivity

Specificity - how close it is to selecting/producing results for the attribute it is looking for; the quality or state of being specific or precise. True positives. True negatives/( true negatives+ False positives)x100

Sensitivity - reduced likelihood of false positives; all positive results are true positives. Detect low levels of particles. True positives/ (true positives+false negatives)x 100

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If 250 were in the test, the test predicted 14 would get periodontitis
In fact 10 got perio, 8 of those who were predicted. Fill in the table:

Disease ND

+test 8 . 6

test . 2 . 234

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Two molecular components that contribute to fighting off a fungal infection?

Azoles - block 14 alpha demethylase cytochrome p450 mediated step in the synthesis of ergosterol

Polyenes - binds to sterols in membranes forming an ion channel

Mitotic inhibitors - disrupt microtubules

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How can dental clinicians avoid the spread of antibiotic resistance?

Consider drainage for dental infections rather than the use of antibiotics

Discuss methods of controlling symptoms rather than prescribing antibiotics

Encourage and enforce patients to complete their antibiotic course and follow dose and duration guidelines

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Two advantages of amoxicillin over penicillin G

Looks for antigens, used to find group A streptococcus e.g. S. Pyogenes

Carbohydrate agar is non selective

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Why do people have different critical pH?

It is when the saliva and plaque fluid cease to be saturated with calcium and phosphate, thereby permitting the hydroxyapatite in dental enamel to dissolve

It is dependent upon calcium and phosphate concentrations and these are dependent upon salivary flow rate. Their concentrations will vary from person to person

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If HAP was left in water at pH 7.0 why would the temperature rise?

ond breaking, pH of the mouth is greater than 7, slightly alkaline so if hydroxyapatite is within a solution less than this then this encourages bond breaking (reaction to the right)

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Ecological plaque hypothesis

Dysbiosis in microbiota in the oral cavity leads to plaque and therefore caries

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Specific plaque hypothesis

One organism e.g. S.mutans leads to plaque and therefore caries

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Non-specific plaque hypothesis

Amount of plaque rather than what is present

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Function of peptidoglycan:

Forms a cell wall outside the membranes of bacteria consisting of NAG and NAM

Structural role in bacterial cell wall as well as resisting osmotic effects of cytoplasm

Binary fission during cell reproduction

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What is an opportunistic pathogen?

An organism which requires the host to have a pre existing defect in its immune defences in order for it to cause disease

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What is a pathogen?

An organism that can cause disease in an otherwise healthy individual

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What is a virulence factor?

Properties of a pathogen that contribute to virulence e.g. adhesins, toxins and tissue degrading enzymes

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What is virulence?

A measure of the capacity of an organism to cause disease. Used to measure lethal dose

What agents are not killed by sterilisation?

Prions

Why is saliva hypotonic?

To prevent loss of water from oral mucosa into oral cavity

The final product is hypotonic because duct cells are impermeable to water

Why do beta lactam antibiotics only work on growing bacteria?

Prevents the action of transpeptidase which forms the cross links in peptidoglycan.
Only growing cells are building new cell wall components

Why does the concentration of salivary sodium change when saliva stimulation is increased?

Sodium is removed from secretion in striated ducts by Na/H pumps. If flow rate is increased, less time for it diffuse across since it spends less time in the striated ducts and so overall output is higher in concentration of sodium than resting

3 factors which affect the Dawes model of clearance?

Flow rate of saliva
Volume of saliva held in the mouth
Sucrose concentration

Best sterilisation for hand pieces?

Best sterilisation for handpieces is autoclave, 134 C for 3 minutes or 121 C for 15 minutes. High pressure steam

What does Maconkey agar show?

Contains bile salts which inhibit G +ve growth; lactose in the agar medium differentiates bacteria that can ferment it (red indicator) It is selective and indicative - Enteric gram negative bacteria

Why does the number of CFU not equal the total number of bacteria?

Some bacteria form staphylococcal bunches/streptococci chains which is lots of bacteria, but only forms on CFU and therefore more bacteria than CFU. The viable count method does not directly count the number of bacteria in the sample. Only the microbes (‘units’) that give rise to a single colony are counted. Colony forming units are an estimate of the number of cells in a population It makes the assumption that all cells in the population will grow when cultured on agar or will give rise to distinct colonies that can then be counted

Saliva pH | Critical pH

Saliva pH - 7.1-7.5 | Critical pH - 5.5

Red group bacteria

annerella forysthia, Treponoma denticola, Porphorymonas gingivalis

Where are the subgingival environments in the mouth and why do obligate anaerobes live here?

Obligate anaerobes are killed by oxygen and so must live in low oxygen environments e.g. subgingivally

2 bacteria in mutans streptococci

Streptococci mutans and Streptococcus sanguinis

Alpha haemolysis Beta haemolysis - Gamma haemolysis

Alpha haemolysis - agar under the colony is dark and greenish - streptococci Beta haemolysis - sometimes called complete haemolysis, is a complete lysis of red cells in the media around and under the colonies: the area appears lightened (yellow) and transparent. Gamma haemolysis - a lack of haemolysis in the area around a bacterial colony - streptococcus mutans

curve of batch bacteria

1. lag phase- no increase in number of living bacterial cells 2. log phase- exponential increase in number of living cells of bacteria 3- stationary phase- plateay in number of living bacterial cells: rate of cell division and death roughly equal 4- death of decline phase: exponential decrease in number of living bacterial cells

what are 2 compounds that make halitosis

``` hydrogen sulphide and sulphur containing compounds; skatole cadaverine putrescine isovaleric acid ```

What is a plasmid

A genetic structure in a cell that can replicate independently of the chromosomes, typically a small circular DNA strand in the cytoplasm of a bacterium or protozoan.

What is an endotoxin

Part of the outer membrane of gram negative bacteria e.g. LPS or O-antigen or Lipid A

Neurotoxin produced by bacteria

botulinium

Frisee perio test

Healthy: 0.5 - 2 mm Diseased: >3 mm (periodontal pocket)

Autochtonous flora and | Allochthonous microbiota -

Autochtonous flora - Microorganisms characteristically found at a particular site Allochthonous microbiota - Microorganisms transiently present at a site

Facultative anaerobes

an organism that makes ATP by aerobic respiration if oxygen is present, but is capable of switching to fermentation or anaerobic respiration if oxygen is absent

Synder test

The Snyder Test is used to determine a person’s susceptibility to dental caries (cavities).The susceptibility is correlated with acid production that is assumed to result from fermentation by cariogenic Lactobacillus species on the teeth or in other areas of the mouth. lactobacillus It tests for aciduric and acidogenic bacteria - key virulence factors in order to cause caries (pH-5)

How does the polymer mutan help plaque:

70% of plaque extracellular polysacchardie Prevents acid leaching from the enamel surface -> cariogenesis Aids in adherence and aggregation; glucan binding proteins

Fluoride effect on critical ph and graph of ph after fizzy drink

Fluoride reduces the critical pH | Fizzy drink lowers the pH considerably (has a ph level of 1-3)

Non selective agar

Grow most bacterium; non selective or indicative

Main virulence factors of aggregatibacter actinomuycetemomitans?

``` Adhesins, bacteriocins, invasins Proteases Immunosuppression factors Surface antigens Heat shock proteins Antimicrobial resistance Localised aggressive PD ```