Colour Flashcards
what is the mechanism of whitening?
not fully understood, but though to involve oxidizing reagent that decomposes into free rads (e.g. hydrogen peroxide)
-free rads break down bonds of large pigmented molecules on the enamel surface; into smaller less pig molecules –> easily move out of the tooth now; but an intrinsic stain (e.g. tetracycline) is harder to remove
mode of action II: bleach passes into tooth through enamel and dentin and into pulp within 5-15 min; in the pulp it’s degraded to water, oxygen, and oxygen free rads; the most active rads are OH (95% activity)-, OOH-, and O-
the oxygen ‘cules then bind to C=C bonds in stain ‘cules, breaking them down into single bonds–> disrupts internal colours; these single bonds relfect light –> teeth appear whiter
what are the main whitening agents?
- carbamide peroxide –> weaker agent, more stable; turns into urea, H2o2, h2o, and OFRs in the presence of saliva
- hydrogen peroxide –> decomposes into h2o and oxygen free rads
- superoxol and sodium perborate
what are the major ingredients for carbamide peroxide?
- h2o2
- stabilizer for h2o2: urea, sodium stannate
- thickening agent–carbopol; carbopol can also help prevent breakdown of whitening agents by by enzymes in the mouth; also extends active-oxygen-releasing up to 4 times
- viscosity agent: glycerin or propylene glycol
- surfactant
- preservatives: phos. acid, citric acid (whitening agents are more stable at a lower pH, but is neutralized in saliva)
- flavouring: methanol
- some have fluoride
what are the major indications for whitening tx?
- esthetic shade change
- preop lighting
what are the major contraindication for whitening tx?
- unrestored carious teeth
- defective resto
- exposed dentin
- pre-existing sensitivty
- TMJ pain
- exposed root surfaces
- pregnancy, lactation/nursing
- patients with high unrealistic expectations
- existing crownes/large restos
- if pts can not afford to change existing restos post-bleaching
- elderly pt with recession and yellow roots (don’t bleach as readily)
what are the disadv of whitening?
- dossp;ution of HA enhance discolouration
- decrease hardness, increase wear
- increase roughness, plaque retention
- remineralization?
- may weaken of enamel
- decreases fracture toughness
- can decrease bond strength
- if teeth have been whitened, comp restos shoukd be delayed as o2 bubbles diffuse from the teeth and can interfere with polymerization of comp (air/oxygen-inhib layer)
- sensitivity – usually caused by an IMPROPERLY FORMED TRAY, as well as strong h2o2;
what are some vehicles used to deliver the whitening agents to teeth?
- toothpastes, gels, chewing gums, floss, strips, and paint on wands
what is internal bleaching?
- -“walking bleach”
- bleach tooth from the inside, during root canals; usually has to be done a few times before the shade is reached
- can unfortunately lead to root resorption and loss of tooth
- can use sodium perborate and hydrogenperoxide placed in the pulp chamber
what are used in place of h2o2 if they are sensitive to it?
NaF and KNO4
whitening agents can cause cements to dissolve, amalgam to corrode, tarnish, increase roughness, and may release mercury; leads to oxygen inhib layer from bubbles–incomplete pol of restos
- heat from the acceleration of bleaching materials can cause transient sensitivity
ye
teeth whitening agents can kill cariogenic bacteria; but can be cytotoxic to endothelial cells
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dentist dispensed whitners are the only products to earn the ADA’s seal of acceptance; now OTC products recieved it; carbamide is in most approved products, whereas h2o2 is in OTC
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