Dental Caries Flashcards
Apatite
Naturally occurring isomorphous mineral group that has repeats of Ca5(PO4)3X
5 of Ca (2+)= +10
3 of PO4 (3-) = -9
So… X must have a net charge.
X can be….
- Hydroxyl (OH)– hydroxyapatite
- Fluoride (F)– fluorapatite
- Chloride (Cl)– chlorapatite
Hydroxyapatite
Ca10(PO4)6(OH)2
Atomic arrangement of hexagonal cells. Can be found as a white powder in its pure form, which is biocompatible for bone implants.
Low bioresorption rate and does not imitate the inorganic portion of our bones and teeth
Carbonate-Substituted Hydroxyapatite (CHA)
Form of naturally occurring hydroxyapatite substituted with carbonate groups (CO3) and is the main component of enamel and dentin
Carbonate substitution increases the solubility of hydroxyapatite and makes it more susceptible to decay
Tooth composition is ___% hydroxyapatite by volume, or ___% by weight
85% hydroxyapatite by volume
95% hydroxyapatite by weight
Enamel Rods
Made by ameloblasts stacking HA units on top of each other to form crystallites
Enamel rods have a keyhole pattern with a head and a tail
The tail has a higher organic composition with less mineral content– tail is MORE SUSCEPTIBLE TO DECAY
Enamel Composition variability based on site
Superficial enamel– more fluoride substitution due to contact with fluoridated water and products
At DEJ– more carbonate substitution
- so, the deeper a cavity penetrates, the more soluble enamel is because there is higher carbonate substitution
Lactic Acid effect on phosphate ions
H+ ions from lactic acid complex with the (PO4)3- ions to form phosphoric acid (H3PO4). This drives equilibrium towards the dissolution of hydroxyapatite due to Le Chatlier’s
Critical pH
pH at which dissolution of tooth begins via demineralization
Carbonate-substituted hydroxyapatite (CHA) has a critical pH of 5.5
Fluoroapatite has a critical pH of 4.5
Dentin and cementum have critical pH of 6.2-6.7
Salivary Buffering
Saliva contains weak base called bicarbonate (HCO3-) which complexes with H+ to form carbonic acid (H2CO3)
This prevents formation of phosphoric acid, which allows the oral pH to neutralize 30 minutes after exposure to acids or sugars
Remineralization
Saliva contains Ca2+ ions– drives the equilibrium towards hydroxyapatite formation
Ca2+ and (PO4)3- are reincorporated into tooth structure
Products like MI paste contain buffers that increase the concentration of free minerals in saliva to shift towards reminaralization
Fluoroapatite
Ca5(PO4)3F
More stable apatite crystal, stronger bond to calcium ion
Increases tooth hardness and resistance to acid damage
Critical pH is 4.5
Shifts equilibrium towards incorporation of Ca2+ and (PO4)3-. Decreasing enamel solubility (lower critical pH)
Enamel Surface Caries Zone
When intact, lesion can be remineralized and is classified as a reversible white spot lesion
White spot lesions may become caveated after 1-2 years, and would be irreversible, requiring restoration.
Infected Dentin Caries Zone
bacteria loaded, superficial, mushy, soft, wet, necrotic
Infected dentin must be completely removed
Affected Dentin Caries Zone
deeper dry, demineralized, leathery
affected by bacterial toxins/acids, but not invaded by bacteria
Affected dentin does NOT have to be removed during restoration because it does not contain any bacteria
Incipient Caries
Reversible
On a smooth surface it will appear white and opaque when air dried
Cannot be detected when wet
Occurs during enamel demineralization and some dentin demineralization stages
Cavitated Caries
Irreversible
Enamel surface no intact and the lesion can progress to dentin
Occurs during enamel cavitation to dentin cavitation stage
Simple Caries
one surface of a tooth (occlusal most common)
Compound Caries
2 surfaces of a tooth (ex. DO)
Complex Caries
3 or more surfaces of a tooth (ex. MOL)
Acute/Rampant Caries
immediately damages tooth structure
light-colored, very infectious, soft
Chronic/Slow Caries
demineralized tooth structure that has nearly remineralized, discolored, and is hard
Arrested Caries
brown/black
Becomes caries resistant when exposed to fluoride
Arrested caries often accompanied by sclerotic dentin that prevents bacterial ingress
Streptococcus Mutans
Gram Positive Cocci
Acidogenic (makes lactic acid from sucrose by fermentation)
Aciduric (can handle acidic environments without being harmed)
produces glucosyltransferase (GTF) which converts sucrose to extracellular polysaccharides (gluons and fructans) that aid in adherence
produces bacteriocins– kill of competing microbes
Bacteria responsible for caries lesions in different locations (Specific Plaque Hypothesis)
Streptococcus Mutans– enamel caries
Lactobacillus– dentinal caries
Actinomyces– root caries
Saliva Components
Urea and other buffers
Glycoproteins– string bacteria together to aid in elimination during swallowing
Lactoferrin– binds and sequesters irons that bacterial enzymes need
Lysozyme– breakdown bacterial cell walls
Lactoperoxidase– inactivates certain bacterial enzymes
sIgA– salivary antibodies that bind bacteria
Ca2+/PO4 3-/F ions– remineralization
Statherin, cystatin, histamine, proline rich proteins– proteins used for remineralization
