FLUORIDE
Fluoride ions promote the formation of fluorapatite in enamel in the presence of calcium and phosphate ions produced during enamel demineralization by plaque bacterial organic acids.
Fluoride ions can also drive the remineralization of previouslydemineralized enamel if enough salivary or plaque calcium and phosphate ions are available.
availability of calcium and phosphate ions can be the limiting factor for net enamel remineralization to occur
this is highly exacerbated under xerostomic condition.
FLUORAPATITE
when the fluoride is applied, for every two fluoride ions, 10 calcium ions and six phosphate ions are required toform one unit cell of fluorapatite (Ca10(PO4)6F2)..
Fluoride mechanisms
1) Free fluoride ion combines with H+ to produce hydrogen fluoride, which migrates throughout acidified plaque.
This ionized form is lipophilic and can readily penetrate bacterial membranes.
Bacterial cytoplasm is relatively alkaline, which forces the dissociation of H+ and F-.
Fluoride ion inhibits various cellular enzymes (enolase, proton extruding ATPase)key to sugar metabolism.
Hydrogen ions simultaneously acidify the cytoplasm, thus slowing cellular activities and inhibiting bacterial function
2) Fluoride integrated in the enamel surface (as fluorapatite, FAP) makes enamel more resistant to demineralization than HAP during acid challenge.
FLUORAPATITE formed is less soluble,this is due to incorporation of fluoride and carbonate is washed out (Tencate).
3) Fluoridated saliva not only decreases critical pH, but also further inhibits demineralization of the deposited CaF2 at the tooth surface.
DCNA,1999
Australian Dental Journal,2008
Wednesday, February 04, 2009
Tuesday, February 03, 2009
MECHANISM OF CALCIUM HYDROIDE IN ROOT CANAL
CALCIUM HYDROXIDE
Since its introduction in 1920 (Hermann 1920), calcium hydroxide has been widely used in
endodontics.
It is a strong alkaline substance, which has a pH of approximately 12.5. In an aqueous
solution, calcium hydroxide dissociates into calcium and hydroxyl ions.
Antimicrobial activity of calcium hydroxide is related to the release of hydroxyl ions in an aqueous environment.
Hydroxyl ions are highly oxidant free radicals that show extreme reactivity.
Damage to the bacterial cytoplasmic membrane
Hydroxyl ions induce lipid peroxidation, resulting in the destruction of phospholipids, structural components of the cellular membrane.
Hydroxyl ions remove hydrogen atoms from unsaturated fatty acids, generating a free lipidic radical.
This free lipidic radical reacts with oxygen, resulting in the formation of a lipidic peroxide radical, which removes another hydrogen atom from a second fatty acid, generating another lipidic peroxide.
peroxides themselves act as free radicals, initiating an autocatalytic chain reaction, and resulting in further loss of unsaturated fatty acids and extensive membrane damage.
(Halliwell 1987, Cotran et al. 1999).
Protein denaturation
The alkalinization provided by calcium hydroxide induces the breakdown of ionic bonds that maintain the tertiary structure of proteins.
These changes frequently result in the loss of biological activity of the enzyme and disruption of the cellular metabolism.
(Voet & Voet 1995).
Damage to the DNA
Hydroxyl ions react with the bacterial DNA and induce the splitting of the strands.
Genes are then lost , Consequently, DNA replication is inhibited and the cellular activity is disarranged.
Free radicals may also induce lethal mutations.
(Imlay & Linn 1988).
...
It has been suggested that the ability of calcium hydroxide to absorb carbon dioxide may contribute to
its antibacterial activity (Kontakiotis et al. 1995).
Since its introduction in 1920 (Hermann 1920), calcium hydroxide has been widely used in
endodontics.
It is a strong alkaline substance, which has a pH of approximately 12.5. In an aqueous
solution, calcium hydroxide dissociates into calcium and hydroxyl ions.
Antimicrobial activity of calcium hydroxide is related to the release of hydroxyl ions in an aqueous environment.
Hydroxyl ions are highly oxidant free radicals that show extreme reactivity.
Damage to the bacterial cytoplasmic membrane
Hydroxyl ions induce lipid peroxidation, resulting in the destruction of phospholipids, structural components of the cellular membrane.
Hydroxyl ions remove hydrogen atoms from unsaturated fatty acids, generating a free lipidic radical.
This free lipidic radical reacts with oxygen, resulting in the formation of a lipidic peroxide radical, which removes another hydrogen atom from a second fatty acid, generating another lipidic peroxide.
peroxides themselves act as free radicals, initiating an autocatalytic chain reaction, and resulting in further loss of unsaturated fatty acids and extensive membrane damage.
(Halliwell 1987, Cotran et al. 1999).
Protein denaturation
The alkalinization provided by calcium hydroxide induces the breakdown of ionic bonds that maintain the tertiary structure of proteins.
These changes frequently result in the loss of biological activity of the enzyme and disruption of the cellular metabolism.
(Voet & Voet 1995).
Damage to the DNA
Hydroxyl ions react with the bacterial DNA and induce the splitting of the strands.
Genes are then lost , Consequently, DNA replication is inhibited and the cellular activity is disarranged.
Free radicals may also induce lethal mutations.
(Imlay & Linn 1988).
...
It has been suggested that the ability of calcium hydroxide to absorb carbon dioxide may contribute to
its antibacterial activity (Kontakiotis et al. 1995).
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