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Light Curing (Underpolymerization (Inferior physical and mechanical…
Light Curing
Underpolymerization
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Loss of retention, breakage
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Light curing mechanism
- Photoinitator molecule absorbs a photon and is activated
- Change in molecular structure, forming radical
- Activated photoinitator starts polymerization reaction
- Stays active for a certain time and can integrate certain number of monomers into polymer network
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Deactivation mechanism
In theory reaction can go on forever, but terminations can stop the chain growth
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History of Light Curing
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LED
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Pros and cons
Advantages
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Frame can be easily cleaned, since no slots for ventilation are needed
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Consistent output, no with no bulbs to change
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Disadvantages
Due to their narrow emission spectrum, LEDs can only polymerise materials with an absorptoin maximum between 440 and 480 and CPQ as the photoinitiator
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Curing Time
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Maximum conversion rate: curing at lower intensities (<500mW/cm2) within extended polymerization intervals
Energy densities > 17 000mW/cm2, no further improvement of mechanical properties
Photoinitator
Visible light-- camphorquinone; co-initiator is a separate compound that does not absorb light but interacts with an activated photoinitiator to produce a reactive species, a tertiary amine
