Lecture 14-18 Caries part 1 Flashcards
Define dental caries
A disease of the mineralized tissues of teeth (enamel, dentin, and cementum) caused by the action of microorganisms on fermentable carbohydrates. It is characterized by demineralization of the mineral portion of these tissues, followed by disintegration of their organic matrix.
T or F, In its early stages, caries can be arrested and remineralization can occur
True
What is the acidogenic theory and when did was it proposed?
1897 - WD Miller
- Some plaque bacteria are capable of fermenting suitable dietary carbohydrate substrates to produce acid, causing plaque pH to fall below critical levels. Repeated exposure to acid pH in time may result in demineralization at susceptible sites on the tooth surface, thus initiating the carious process.
The formation of carious lesions depends on a combination of four factors:
- Microorganisms (Quality and number of bugs)
- Metabolic Substances (Quant. & Qual. of sugars)
- Teeth and their environment (Quality of teeth, saliva)
- Time (Duration and Frequency)
What is the Flouride anti caries mechanism? (2) How long is it good for?
- Systemic
- During tooth development - Topical (much more important because it lasts lifetime of tooth)
- After tooth eruption
- This is only good until tooth eruption
What makes up the organic matrix of tooth hard tissue:
- Protein (collagen, others) –> main component
- Other organic (mucopolysaccharides, chondroitin sulfate)
What makes up the mineral portion of tooth hard tissue:
- Hydroxyapatite –> main component
- (calcium, phosphate, hydroxyl formed into hard crystal lattice)
- Other positive ions: Lead, zinc, strontium, silver, nickel, iron
- Other negative ions: Carbonate, Fluoride
Fluoride brings down the critical pH of hydroxyapatite to what?
pH 5.5 to a pH 4.9
Cells in percent by weight within the composition of tooth hard tissue
Enamel:
- Organic (4%)
- Mineral (95%)
- Water (1%)
Dentin:
- Organic (20%)
- Mineral (70%)
- Water (10%)
3 major ways that fluoride lowers caries risk
- Most electronegative element
- Holds hydroxyapatite structure more tightly together
- Makes demineralization harder
- Remineralization easier - Lower CO3(2-) content
- More acid resistant
- Lowers pH threshold of hydroxyapatite - Binds & Poisons key metabolic enzymes in bacteria
- Lowers acid production
Co3(2-) is what percentage the most common substitution
3% most common substition
Hydroxyapatite is a structure held together by what bonds?
Ionic bonds (positive & negative charges)
In hydroxyapatite crystal lattice, other ions of appropriate size and charge, can substitute for the various inorganic ions
- For Calcium
- For phosphate
- For hydroxyl
Calcium: Lead, Strontium, Radium, etc.
Phosphate: Carbonate, etc
Hydroxyl: Fluoride, etc
The resistance of enamel to chemical attack depends (in part) on: (2)
- The regularity with which the hydroxyapatite crystals line up. The more regular the alignment, the more stable the physical structure.
- The presence of substitute ions that can either increase or decrease susceptibility to chemical attack, depending upon the particular substitution.
T or F, The mineral lattice is completely non-porous so that free ions cannot diffuse into it.
False, It is porous so free ions can diffuse into it. Thus the composition of hydroxyapatite can vary from one part of a tooth to another
T or F, Hydroxyapatite can be dissolved by acid; the reaction is irreversible
False, the reaction is reversible (pH dependent)
2 general characteristics of caries-susceptible sites
- Favorable for plaque retention (hard to mow lawn)
2. Limited access for saliva
6 susceptible sites of caries
- Pits and fissures
- Approximal surfaces of adjacent teeth just cervical to the contact point
- Cervical margin just coronal to the gingival margin
- Exposed root surfaces
- Margins of deficient restorations
- Tooth surfaces adjacent to dentures and bridges
What percent risk is there for white caries lesions under braces
80%
T or F, The major caries-susceptible sites have limited saliva access, which favors plaque retention.
True
Pits and fissures that are considered susceptible sites to caries can be found where?
- Pits and fissures on occlusal surfaces of molars and premolars
- Buccal pits of molars and palatal pits of maxillary incisors
What is the sequence to plaque development:
Salivary proteins –> Pellicle –> Plaque biofilm –> (Calculus)
Pellicle defintion:
Acellular, homogeneous, organic film that forms on enamel and other hard surfaces by selective adsorption of salivary proteins and glycoproteins.
6 characteristics of Pellicle
- Forms spontaneously on teeth
- Bacteria not necessary for formation
- Can be removed only by meticulous cleaning
- If removed, rapidly forms again (minutes to a few hours)
- Protective functions have been suggested but not proven
- Forms suitable environment for bacterial pioneer species adherence and multiplication –> Plaque biofilm
Plaque biofilm definition:
soft, non-mineralized bacterial deposit that forms on teeth
Composition of plaque biofilm
- Plaque-tooth interface (generally pellicle)
- Microbial layers and colonies
- Intercellular matrix (insoluble)
- Carbs (primary component of matrix)
- Protein
T or F, As the plaque thickens, the effects of saliva decrease, making the acid accumulation more pronounced
True
Definition of Calculus:
Plaque biofilm in which inorganic deposits have caused mineralization. Greatly increases risk for developing periodontitis
What is a gnotobiotic offspring
Animals used in experiments with known oral flora
What is an add-back experiment
In the experiment talked about in class, bacteria capable of causing caries was identified and added after oral flora in experimental animals was known
What were the 3 scenarios described in the add back experiment with gnotobiotic mice
- Non infected animals were added to the same cage as infected animals = Both became carious
- Non infected animals were inoculated with S. mutans = became carious
- Non infected animals were given a smear with plaque or feces containing cariogenic bacteria from the infected animals = Became carious
What was the main information identified in the add back experiment
- That caries is an infectious disease
- Both sugar and plaque bacteria - most specifically s. mutans, Lactobacillus, and Actinomyces are required to cause caries.
Name 6 properties to Mutans Streptococci
- Sugar transport good at low pH
- Acid production = Homolactic fermenter (only Lactic acid)
- Aciduricity = Ability to live in acid in decreased pH
- Acidophilic = Grows well at low pH - Produces insoluble Glucan (Mutan) to protect from saliva
- Utilize extra fructose to make extracellular levans, which they use as snacks between meals.
- Bacteriocins
What is the most virulent factor for S. mutans
The polysaccharide chain or the branched mutan that is made by Glucosyl-transferase to protect the bacteria from saliva and other antibiotic substances.
What enzyme in S. mutans has the highest affinity for Sucrose?
Invertase. If there is a large concentration of sucrose, it will also be delivered to Fructosyl transferase and Glucosyl transferase
T or F, The branched mutan chain that is made by S. mutans to protect it from saliva is insolubale
True
T or F, Fluoride inhibits PEP which decreases the amount of lactic acid produced, why?
True, this occurs by decreasing enolase activitity. The glycolytic pathway is “poisoned” and thus wounds S. mutans
What enzyme is used to break down Levan for S. mutans to be able to use it as snack food
Levanase
Lactic acid is used by what bacteria?
it is a fuel source for secondary feeders such as Neisseria and Veillonella
T or F, Most bacteria will use excess sugars to form extracellular, non-branched, soluble, polysaccharide chains including S. mutans
False, not S. mutans. S. mutans is different and makes branched, insoluble, extracellular, polysaccharide chains that forms a protective dome over the S. mutan micro-colonies within plaque biofilm and also localizes their acid production for longer periods of time on the tooth surface
T or F, S. mutans is a homolactate fermentor - it produces 3 lactic acid molecules for every monsaccharide it ferments
False, 2 lactic acid molecule for every monosaccharide it ferments
Acidophillic definition:
Competes well in acidic environments
Aciduric definition:
relatively resistant to acid
What molecule does a similar thing to fluoride by “poisoning” the glycolytic pathway and decreasing the amount of lactic acid produced by S. mutans
Xylitol
