Lecture # 14-18 Microbiology of Dental Caries Flashcards
What are dental caries?
A disease of the mineralized tissues of the teeth (enamel, dentin, cementum). Caused by the action of microorganisms of the mineral portion of these tissues followed by disintegration of there organic matrix.
In the early stages, caries can be _____ and ________
- arrested
- remineralized
Worm theory ________
Pre-history - 18th century
Animalcule ___________
1680, A. van Leeuwenhoek
Acidogenic Theory_________
1897, Miller
- Plaque bacteria capable of fermenting dietary carbo substances to produce acid, causing plaque pH to fall below critical levels.
- Repeated exposure to acid= demineratlization initiating the carious process
Formation of carious lesions depend on what 4 factors?
1) Microbes (bacteria that can ferment sugars)
2) Metabolic substrates (Quantity and quality of dietary sugars)
3) Teeth of their environment (“Quality of the teeth, saliva, and immunity)
4) Time (The duration and frequency of sugar consumption)
What is the organic matrix made up of?
1) Protein( collagen, others), main component
2) Other organic (mucopolysaccharides, chondroitin sulfate, etc)
What is the Mineral made up of?
1) Hydroxyapatite- main component (calcium ions, phosphate ions, hydroxyl ions formed into hard crystal lattice)
Ca10 (Po4) 6 (OH)2
2) Other POSITIVE IONS: Lead, zinc, strontium, silver, nickel, iron, etc.
3) Other NEGATIVE IONS: Carbonate, fluoride, etc
4) Water
5) Cells (dentine)
What is the proportions: percent of weight for Organic Enamel and Dentine?
Enamel = 4
Dentine 20
What is the proportions: percent of weight for Mineral Enamel and Dentine?
Enamel = 95
Dentine =70
What is the proportions: percent of weight for Water Enamel and Dentine?
Enamel = 1
Dentine =10
What is hydroxyapatite ?
A structure held together by ionic bonds (positive and negative)
What are the F- Anti-caries mechanisms?
1) Systemic: DURING tooth development (per-eruption) 2) Topical: AFTER tooth eruption (MOST important) *During demineralization and mineralization
What are the major ways F- LOWERS carrier risk?
1) Most electronegative element. Holds hydroxyapatite structure more tightly together
- Therefore makes demineralization harder
- Remineralization easier
2) Lower CO2 content
(More ACID resistant)
3) Binds + posisons key metabolic enzymes in bacteria
(LOWERS acid production)
What is the basic level of of hydroxyapatite?
- It has a snowflake shape of calcium and phosphates ions surrounding a central hydroxyl ion core.
- Snowflakes align along an OH- core to form long straight structures.
- These long structures further align in parallel within a protein “form” to eventually make a “rod”-shaped structure. Enamel rods can extend from the D/E junction to the surface.
In the hydroxyapatite crystals lattice, other ions of appropriate size & charge, can substitute for the various inorganic ions.
Ca+?
Phosphate?
Hydroxyl?
Ca+ = lead, strontium, radium Phosphate = carbonate Hydroxyl= fluoride
The resistance of enamel to chemical attack depends on what?
1) The regularity w/ which the hydroxyapatite crystals line up.
- The more regular the alignment the more stable the physical structure
2) The presence of substitute ions that can either increase or decrease susceptibility to chemical attack, depending upon the particular substitution
With enamel maturation the regularity of hydroxyapatite crystals tends to increse spontaneously leading to what?
DECREASED caries susceptibility
Note: in mature enamel the crystals are very long and thin at times extending from the dentin/enamel interface to the enamel surface
What substances can be absorbed onto the hydroxyapatite surface?
Sodium-ion, magnesium-ion, calcium-phosphate, and calcium carbonate can be absorbed
Why is the mineral lattice porous?
So free ions can diffuse into it.
Note: composition of hydroxyapatite can very from one part of the tooth to another
Hydroxyapatite can be dissolved by _____________; this reaction is _________________
- Acid
- Reversible
Hydroxyapatite is essentially ____________ at neutral pH
-Insoluble
Calcium and phosphate ions are water soluble but at their normal concentration in body fluids they are near their ___________________
-solubility constant (saturated solution)
What is the critical pH in the mouth?
The pH below which dissolution predominates in the oral cavity is about 5.5
Ca10 (PO4)6 (OH)2 + 14 H+ 10Ca2+ + 6 (H2PO4-) + 2H2O
Which direction would if go if dissolution occur or re mineralization?
Right = dissolution Left = mineralization
What are the general characteristics of Caries-Susceptible Sites
1) Favorable for plaque retention (hard to “mow the lawn”)
2) Limited access for saliva
Susceptible sites?
1) Pits and fissures
- On occlusal surfaces of molars and premolars
- Buccal pits of molars and palatal pits of maxillary incisors
2) Approximal surfaces of adjacent teeth just cervical to the contact point
3) Cervical margin just coronal to the gingival margin
4) Exposed root surfaces, in patients with gingival recession
5) Margins of deficient restorations
6) Tooth surfaces adjacent to dentures and bridges
7) Braces..
The major caries susceptible sites have limited saliva access, which favors what?
- Plaque retention
- These sites allow the number of bacteria to become large & the plaque to become thick and less aerobic allowing cariogenic bacteria to accumulate and form sizable colonies
- Microaerophilic environment
Before _______ of age MOST Americans have had caries lesion ?
-18
Note: The most common debilitating childhood disease
What is the pH of gastric juices?
pH= 2.0
What is pH of persons teeth w/ bulemia ?
Highly acidic
-Erosion on lingual surface
What is the pH of saliva at rest vs while eating?
At rest= 6.6
Eating= 7.1
Optimally fluoridated tooth has a pH of what?
4.9
In lower critical pH?
More acid needed to demineralize tooth , more cariogenic bacteria spewing out more acid, and eat more sugar for bacteria to metabolize
Plaque development sequence?
Salivary proteins–> pelicle–> plaque biofilm–> Calculus
Pelicle (acquired pelicle)
Acellular, homogenous, organic film that forms on enamel and other hard surfaces by selective adsorption of salivary proteins and glycopreoteins
Characteristics of Pelicle?
1) Forms spontaneously on teeth
2) Bacteria not necessary for formation
3) Can be removed only by meticulous cleaning
4) if removed, forms again (minutes to hours)
5) Protective functions have been suggested but no proven
6) Forms suitable environment for bacterial pioneer species adherence & multiplication–> (plaque biofilm)
Plaque biofilm?
Soft, non-mineralized bacterial deposit that forms on teeth
Plaque biofilm composition?
1) Plaque-tooth interface (generally pelicle)
2) Microbial layers and colonies
3) Intercellular matrix (insoluble)
- Carbohydrates
- Protein
What are the carbohydrates in Plaque biofilm in the intercellualr matrix ?
Glucans (glucose polymer), fructans (fructose polymer), and other polysaccharides. Produced by plaque bacteria. Primary component of matrix
What is the role in caries in Plaque biofilm?
Suitable environment for acid-producing, bacterial metabolism, and diminishing the saliva protection mechanisms
Dietary carbohydrates, simple sugars are fermented by some plaque bacteria to produce what?
acid (H+) and extracellular polymers (glucans and fructans)
As plaque thickens what happens to the effects of saliva?
DECREASE, making the acid accumulation more pronounced.
If too much acid is produced and accumulates for extended periods _______________ is formed
A caries lesion
In bacterial metabolism, Appropriate bacteria must be present to produce caries. Do germ- free animals develop caries when fed a highly cariogenic diet?
No they do not
Through test on animals w/ known oral flora (= gnotobiotic animals) “germ-free” Which bacteria capable of causing caries identified as?
-Called ADD-BACK experiments: Step mutans (mostly), Lactobacillus spp, and Actinomyces spp.
What have the experiments conduced on germ-free animals (that have one or few known microbes added) shown?
1) That caries is an infectious disease
2) Both sugar and plaque bacteria (Mutans Strep. Strep, Lactobacillus, and Actinomyces are require to cause caries)
What are the characteristics that point to Step Mutans as the dominant cause of caries?
1) They have excellent sugar transport at low pH (most oral bacteria do not)
2) They are homolactic acid fermentors (produce only lactic acid as a by-product of sucrose fermentation)
3) They are aciduric- tolerating a highly acidic environment and acidophilic- actually preferring acidic environment
4) They utilize extra glucose to make insoluble glucans, which protects them from saliva, and increases the acid in the local environment
5) They utilize extra fructose to make EC levans, which they use as “snacks” between meals
Which acid is the worst for caries?
Lactate
Assachrolytic< EtOH< Acid, EtOH < Acid, Acid < Lactate, Acid< Lactate, Lactate
Most bacteria will use excess sugars to form what?
EC, non-branched, soluble, polysaccharide chains.
Strep mutans will use excess sugars to do what?
-What does this form?
- Can make branched, insoluble, extracellular, polysaccharide chains.
- This forms a protective “dome” over the S.mutan micro-colonies w/ the plaque biofilm, and localizes their acid production for longer periods of time on the tooth surface.
What does S. mutans use to form EC levans that it uses to snack on in between meals?
The excess fructose, which mostly comes from breaking the disaccharide sucrose.
S. mutans is also a homolactate fermentor which means what?
it produces 2 lactic acid molecules for every monosaccharide it ferments
How does S. mutans compete well in acidic environments (acidophilic)?
-By being relatively resistant to acid (= aciduric)
what does Xylitol and Fluoride do to S. mutans?
High concentration of fluoride and Xylitol are able to poison the Glycolytic Pathway and wound S. mutans
What does FT (Fructosyl Transferases) do? (Many bacteria)
- Breaks sucrose into 2
- Similar to GT, makes a chain of fructose molecules called LEVAN and sending GLUCOSE intracellular to generate the ATP.
- Polymers LEVAN & MUTAN are store “snacks” that can be degraded and used for energy when needed.
Ex: S. mutans, S. salivarius
What is GT? (Only Step. mutans group)
-Glucose Transferase is an Enzyme found in the outer membrane of S. Mutans. It breaks the covalent bond between glucose and fructose in a SUCROSE molecule.
-Sends Fructose into cell to go thru glycolysis and generate ATP.
-The remaining glucose molecules are covalently linked together forming an insoluble mutans polymer.
**Glucose form structural ECM: Glucan AKA Mutans
(insoluble in water/saliva)
Example: S. mutans
- No mutanase
- low (dexase)
Lactic acid is used up by what 2 bacteria and what do they metabolize it to?
1) Neisseria
2) Veillonella
- Metbolize to CO2 + Acetate “Food chain”
What are the ECM effects?
- barrier acid/buffer exchange
- Decrease pH–> dec neighbor ability –> increase mutans
- cell/cell adhesion
- plaque matrix
- decrease O2 influx
- increase CO2 load
What does invertase do?
breaks covalent bond
In the glycolytic pathway what does fluoride inhibit?
ENOLASE therefore decreases PEP
Most bacteria make ____________ non-branced_______
- Homopolymer
- dextran
Experiment feed strep mutans 2 sugars. Which one is more cariogenic?
1) Sucrose ** (MORE cariogenic)
2) HFCS (high fructose corn syrup)
Describe the effects of sucrose on strep mutans
-Needs invertase GT & FT
-Most of the glucose fructose will enter but not all
-Less lactic acid production
GF covalently bonded
Describe the effects of HFCS on strep mutans
-Does not use invertase FT or GT -Just use the glucose, fructose pumps -More lactic acid -GF not covalently bonded
what is an example of bacterial succession?
A diet high in sugar (cariogenic diet) can select for aciduric bacteria (able to tolerate high acid environment) including Step. Lacto., and Actino.
In healthy plaque S. mutans and Lactobacillus spp are found in ______
-Low numbers
GT gum drop dome only with what spp?
GT makes Mutan ECM
Note: has lower pH
- buffers against saliva so sucrose fed S. mutans will last longer
- produces lactic acid & mutan dome –> from excess sucrose only
After the feeding the plaque w/ sugar the aciduric bacteria such as S. mutans & L. casei will ?
-INCREASE
Note: this increase is most dramatic when buffers are excluded as would be the case in thick plaque or xerostmic patient
The pH of the environmental strongly affects metabolic production and results in bacterial succession because each bacterial species or strain has a limit to its what?
The ability to its grow at low pH, and has a limited acid-producing capacity at these lower pH conditions
Experiments have shown that plaque taken form active caries sites has a higher percentage of mutans strep, Actinomyces spp, lactobacillus leading to what?
Bacteria that succeed at more neutral pH to those that succeed at more acid pH ( cariogenic bacteria are acidophilic)
What is the progressive lesion and non-progressive for Strep. sanguis, Strep. mutans ?
Strep sanguis:
progressive lesion = 100 (6%)
and non-progressive- 87 (29)
S. Mutans:
progressive lesion = 100 (51%)
and non-progressive- 87 (13)
Bacteria can metabolize and produce acid at a ______ oH
-Neutral
mutans Strep species( S. mutans, S. sorbinus) are able to metabolize and produce _______ at a ______ pH
-acid
-at lower pH
= ACIDOPHILIC and compete best at these lower pH levels
Cariogenic mutans group can survive & still metabolize at ___________pH
acidic
Root surface caries is associates w/ both the _________ and ___________
- Mutans strep
- A. viscosus
What are some of the conceptual advances in the implications of mutans strep as probable prime cause of coronal caries in man
1) Endemic infection suggestion
2) Temporal correlation between colonization of tooth sites and white spot lesion development
3) Sucrose effect on level of colonization of tooth sites and of pooled plaque (and saliva)
4) Mother’s infection level is predictor of her child’s dat eof infection and caries experience, matrilineal transmission
5) Bacteriocin pattern identitiy of mother’s and child’s mutans streptococci
The tooth surface presents different ecological niches where caries can form and each site may promote what?
promote a different combination of acid-forming bacterial populations
What are the “Dentin lovers”
1) S. mutans
2) A. viscosus
3) A. ondontolyt
4) Lactobacilli sp
Pit and fissure caries lovers?
S. mutans
Smooth-surf caries lovers?
S. mutans
Pulp lovers?
6 m- rods anaerobic + facultative black-pigment forming bacteria
Root caries lovers?
1) S. mutans
2) A. viscosus
3) A. ondotolyt
4) Lactobacilli sp
In order for lactobacillus and atinomyces to work their magic and get thru enamel, which bacteria is needed to break through the enamel?
S. mutans
Dentin lovers?
S. mutans, but Actinomyces and Lactobacillus play increasing role as soon as the harder enamel is cracked open by the S. mutans
Endodonic infections?
Usually mixed infections of various gram-negative anaerobic bacteria
Gingivitis and periodontitis?
Caused primarily by gram (-) anerobic bacteria
In the future, which therapies will be used to prevent caries?
1) Caries vaccine
2) Replacement therapy (inoculation w/ genetically modified less pathogenic S. mutans)
3) Probiotic therapies ** (probably first to be used)
When did the explosion of coronal caries begin?
- Throughout most of history coronal (enamel) caries has been infrequent.
- It was only w/ the advent of farming and the production of inexpensive sugar that caused it
Why was the oral flora different in fossilized calculus teeth vs modern bacteria?
We added simple carbs to diet and selected for more cariogenic bacteria (S. mutans) w/ different genes. Better able to ferment and survive at low pH
Even though most bacteria in supragingival plaque utilize sugars as an energy source, what makes they different?
Various bacterial species produce an assortment of end-products from sugar breakdown, including many different acids.
Which acids are produced from bacterial metabolism (pyruvate) ?
1) Poionic acid
2) formic acid (3.7)
- In aqueous solution it dissociates into H2O
3) lactic acid ***MOST POWERFUL (3.8 pka)
4) succinic acid
5) acetic acid
What is the Stephan curve?
Use of micro electrons in plaque biofilm that measures the pH drop in plaque that accompanies a glucose rinse
Plaque associated w/ rampant caries start at a much ________ pH than does __________
*What does this allow ?
- Lower
- Healthy plaque on a caries free tooth
***This allows the pH to drop BELOW the CRITICAL pH for an extended period of time in plaque associated w/ rampant caries
Why does HFCS not as cariogenic as Sucrose?
Because it does not contain GT
The presence of _______________ is required to produce a pH at or below the critical value to metabolize sugars to acids?
Plaque
By simply brushing the tooth (mowing lawn) the amount of acid is ____________
Greatly reduced
What does the effectiveness of a given carbohydrate in promoting caries depend on?
1) Ability of cariogenic bacteria to metabolize the carbohydrate
2) The ability of the carbohydrate molecules to diffuse into plaque
What did the experiment to justify oral hygiene show?
- First you do a glucose rise and watch the pH fall below the critical pH.
- When you brush your teeth it doesn’t allow the pH to drop as much when you have “mowed the lawn”. Even if you do a 2nd glucose rinse the pH remains above the critical level.
Not all carbohydrates are _____________. Plaque bacteria have the ability to utilize simple sugars much more ___________ than more _____________________
- Created equal
- Effectively
- Complex carbohydrates
What makes different carbohydrates more or less complex for bacteria to utilize?
-The # of branches it has.
(When its raw or a complex sugar it is more difficult. Ex: Sorbitol, raw starch like a potato. Glucose, Sucrose “simple carbs” are much easier to break down )
The frequency of sugar consumption is much more important than the _________
amount
What did the experiment show for the 2 groups that ate the same amount of food in a day?
Group 1: Eat throughout the day (mini eating)
Group 2: eat 3 meals
-While grazing in an era of ubiquitous simple sugars is not.
Group 1: More time BELOW critical pH
Group 2: Less time BELOW critical pH
What is the definition of saliva?
Secretions of salivary glands and minor glands of the oral mucosa
What is the regulation of saliva?
1) Activated by autonomic reflexes
- Parasym= stim copious flow, watery
- Sym= Low flow, thick (mucoid)
What is saliva flow stimulated by?
1) sight, smell, etc of food
2) food in mouth
3) food in stomach
How can flow rate be affected with saliva?
1) Stimulated 1-2 ml/min
2) Between meals during the day: small
3) Sleep: very small
4) Many diseases and medical treatments can influence (usually lower) flow rate.
What are the major functions with saliva?
1) Aid in swallowing and digesting food
- Lubricates food to aid swallowing
- Dissolve food to enable stimulation of taste bud sensory endings
- Digest foods, carbohydrates (salivary amylase)
2) Protective
How does saliva provide the a protective barrier?
1) Mucoid coating on oral mucous membranes forms chemical barrier and thermal insulator
2) Reduces tendency to caries
- Flushes away carbohydrates
- Contains Ca++ and PO43- for tooth “remineralization”
- Acts as chemical buffer to maintian mouth pH near neutral (bicarb, buffer system)
- Source of recycled topical fluoride
What are the effects of lack of saliva (xerostomia “dry mouth”)
1) Tendency to oral ulceration
2) difficulty in swallowing dry foods
3) thermal and chemical sensitivity
4) altered taste
5) increased tendency to caries
Why is regular bedtime hygiene particularly important?
“Dry mouth” occurs in all people during sleep
What is Xerostomia caused by?
1) Disease
2) Drugs
3) Irradition (head/neck cancer)
4) Age
5) Sleep
What is the treatment for Xerostomia?
1) artificial saliva
2) increased oral hygiene
3) decreased sugars
4) fluoride therapy
Certain bacteria, Strep. mutans are able to ferment dietary sugars to ________
Lactic acid
If enough acid is produced the pH will fall below the critical pH and demineralization of the tooth hydroxyapatite structure will begin. What can help prevent this?
Saliva contains buffers that are able to somewhat mitigate this w/ Ca2+ and PO4- ions that can remineralize the tooth hydroxyapatite structure once the pH rises back above the critical pH
What is FRUCTANASE ( aka LEVANASE) ?
Is an enzyme that breaks down LEVAN ( beta 2,6 linkages) releasing individual fructose molecules to be taken INTRACELLULAR for ATP production when S. Mutans is in need
