Download Level 4 Light cure devices Lec 2

Dental Curing Lights
Visible-Light Activation
• Photo-initiator reacts with amine co-activator
(electron donner- tertiary amine)
• Forms free radicals
• Initiates addition polymerization
Polymerization
IPT
• Initiation
– production of reactive free radicals
– chemical, light, heat
• Propagation
– monomer units
– polymer network
• Termination
Polymerization Shrinkage
• 1.5-7 % volume
• Open margins
–
–
–
–
Microleakage
Staining
Post-op sensitivity
Recurrent caries
Important terms about LCU
• Emission Spectrum (Wavelengths of Light) Colour
• Radiant power (mW)
•
Radiant exitance (mW/cm2)
• Misleading terms such as intensity, power density or
brightness
The eye is sensitive only to
the visible part of the
electromagnetic
spectrum
Emission Spectrum
(Wavelengths of Light)
I.
Camphorquinone (CQ) is the traditional initiator used in most RBCs
and it is mostly activated by blue light peaking at 468 nm wavelength
II. Trimethylbenzoyldiphenylphosphine oxide (Lucirin TPO, ranging from
375 to 410 nm)
III.1-phenyl-1,2-propanedione (PPD, maximum wavelength ≈ 410 nm)
Radiant exitance (mW/cm2)
➢Irradiance received at a surface (mW/cm2).
➢ It can only reflect an average value over the total
surface area
➢ It does not take into account any non-uniformity in
the light output across the tip of the LCU, or the
distance from the tip.
Photo-polymerization
• Many light curing
options
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–
–
Halogen
Plasma-arc
Laser
LED
Quartz-Tungsten-Halogen
• Most common dental curing light
• Quartz
– encasing structure
• Tungsten
– filament coil
Quartz-Tungsten-Halogen
• Halogen gas
– protects filament
• oxidation
Quartz-Tungsten-Halogen
• Filters
– band-pass
• restricts broader light
to narrow blue light
– 400-500 nm
– range of photo-initiators
Quartz-Tungsten-Halogen
• QTH bulb
– 30-50 hours useful life
– Not uniform out put
Plasma-Arc (PAC)
• Two tungsten electrodes
– small gap
• Pressurized chamber
– xenon gas
• High-voltage spark
– ionizes gas
• White light
Plasma-Arc (PAC)
• High levels of IR and UV
– extensive filtering
• down to 400-500 nm
Plasma-Arc (PAC)
• High irradiance
- > 2000 mW/cm2
- Claim 1-3 sec cure
• Expensive
- Bulbs >$600
- Heat generation
- Rapid polymerization
Argon Laser
• High energy
- Coherent, monochromatic
- Wave length 470 nm CQ max absorption
• Curing time 3-10 sec + DC
• Very expensive
• Warning signs required
Light-Emitting Diodes (LED)
• Semiconductors
– electrically-excited atoms
• Gallium-indium-nitride
• Narrow emission spectrum
– 430-490 nm
• peak at 470 nm
• near max absorption
of camphorquinone
• efficient
LED Curing Lights
• Long lasting light source
– minimal aging (Bulb life is 100
time more than QTH)
– minimal decrease in output
• Less lateral heat production
– minimal or no fan necessary
• No filters
• Typically cordless+ Work on battery
Duke Compendium 2001
LED Curing Lights
• First generation
– high cost
– Led cans
– low irradiance
• < 300 mW/cm2
• increase exposure time
60 sec needed for 2 mm composite
Leonard J Esthet Rest Dent 2002
LED Curing Lights
• Second generation
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–
–
–
–
Lower cost
Led chips ‘pads’
Large metal heat sinks
Internal cooling fans
higher irradiance
Price J Can Dent Assoc 2003
• 600-1000
• curing depth similar to halogen
But half of time needed
mW/cm2
Soh Oper Dent 2004
LED Curing Lights
• Third generation
- higher irradiance
• 1000-3000 mW/cm2
• Polywave spectrum which is suitable for
new photo initiators
PPD+TPO+MAPO+BAPO
• Familiar with all time\power profiles
• Ex :pulse delay
soft start
Ex:- Polywave
-Blue phase 20 I
Polymerization Modes
1. Uniform continuous cure:A light of constant intensity is applied to a composite for a
specific period of time.
2-Step cure:The composite is first cured at low energy, then stepped up to
high energy, each for a set duration.
“Soft-Start” Polymerization
• Stepped
– short, low initial burst
– full intensity
• Ramped
– gradual increase
from initial low level
• Pulsed delayed
– short, low level burst
– delay 3-5 min
– full intensity
Curing Modes
High Intensity
Pulsed
Standard Intensity
Ramped
Stepped
Pulse Delay
Time (seconds)
Yap PPAD 2004
Optical Safety
• Do not look directly at light
• Protection recommended
– glasses
– shields
• May impair ability
to match tooth shades
Maintenance
• Periodic visual inspection of unit
– light guide
– filters
– bulb
• Check irradiance
– radiometer
Strydom SADJ 2002
Contamination of Light Tip
• Reduces passage of light
• Reflects light
– increases heat build-up
– shortens bulb life
• Remove debris
– polishing kit
– blade
– replace light guide
Radiometer
• Consists of photosensitive diode
– specific for light
• Measures useful light output at curing tip
– hand-held
– built-in
• Light-specific radiometers
– QTH
– LED
Hand-held Radiometers
• Numerical
– analog
– digital
Built-in Radiometers
• Indicator lights
– range type
• Numerical
“Turbo” Light Guides
Factors that affect light curing of
composite
1.
2.
3.
4.
Exposure
Intensity
Temperature
Distance and angle between light
and resin
5. Angle and path of the light
6. Thickness of resin
7. Operatory lighting
8. Incandescent lighting
9. Fluorescent lighting
10. Improving working time
11. Air inhibition
12. Curing through tooth structure
13. Shade of resin
14. Type of filler
15. Amount of photoinitiator
16. Heat generated by light-curing
units
17. Room-light polymerization
Clinical recommendations when using
a curing light
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