light curing units

1. Composite Light Curing Units
Dr. Jagadeesh. K
P.G 3rd
year

2. Contents
• Introduction
• Advantages
• Limitations
• Characteristics of light
• Photo polymerization
• Light curing unit

3. • Types
• New developments
• Exposure
• Inadequate polymerization
• Irradiance
• Total energy density
• Time required for adequate polymerization
• Soft start polymerization

4. • General considerations
• Maintenance
• Radiometer
– Hand held
– Built in
• Optical hazards
• Optical safety

5. INTRODUCTION
• Light activated resin system utilizes light energy to initiate
free radicals.
• Light cure composites were introduced to overcome the
limitations of self curing composites
– Less porosity and discoloration.
– Longer working time.
– Ease of manipulation.
– Increased hardness and wear resistance of superficial
layer.

6. • Available as single paste system in a light proof syringe.
• Consists of photosensitizer and an amine activator.
• Photosensitizer – Camphoroquinone (CQ)
absorbs blue light with wavelengths between 400-500 nm.
• Amine activator – dimethylaminoethyl methacrylate
(DMAEMA)

7. • Limitations:
– Limited curing depth so requires incremental building
up.
– Relatively poor accessibility in posterior &
interproximal areas.
– Variable exposure times due to shade differences.
– Sensitivity to room illumination.
– Requires more clinical time.
– Expensive due to cost of light curing unit.

8. Contact Pro2

9. Terms used to describe light sources for
polymerization of dental resins

11. Characteristics of Light
• Visible light
– 400-700 nm
• Most composites sensitive
– 400-520 nm (blue)
• Photo-initiator in resin
– absorbs photon energy
– combines with activator
• Amine (DMAEMA)
– creating free radicals
• initiates polymerization

13. Photo-polymerization
• Camphorquinone (CQ)
– most common
photo-absorbing material
– maximum sensitivity
• blue range
• 468 nm to 474nm

14. Other photoinitiators used
1-phenyl 1, 2-propanedione (PPD)
Bis acylphosphine oxide (BAPO)
Tri acyl phosphine

15. Light Curing Unit
• It is an instrument capable of generating and transmitting a
high intensity blue light with a wavelength oscillating
between 400-500 nm that is designed specifically to
polymerize visible light sensitive dental material.

16. UV light cure systems
• NUVA-fil introduced by L.D.CAULK CO in 1970 was the first
in Light Cure Composite resins
• UV light curing systems used Benzoin methyl ether as initiater
• UV radiation generated by a light source capable of emitting an
intense luminous radiation was used to polymerize the resins

17. • Wave length oscillating between 320 and 365nm
Disadvantages
• Limited depth of cure
• Harmful effects of UV radiation
• Opthalmological effects
• Carcinogenic
• Loss of intensity over time.

18. Types of Light Curing Units
• Four light curing
options
– Quartz tungsten
halogen
– plasma-arc
– laser
– LED

19. • In order of lowest to highest intensity
– LED lamps
– QTH lamps
– PAC lamps
– Argon laser lamps

20. Quartz-Tungsten-Halogen
• Most widely used dental curing light.
• Consists of a quartz bulb with a
tungsten filament in a halogen
environment.
• Electric current passes through an
extremely thin tungsten filament
which at about 3000o
C produces
Electro Magnetic radiation in the
form of visible light.

21. • Quartz
– encasing structure
– crystalline
– heat resistant
• Tungsten
– filament coil
– flow of electricity
• Halogen gas
– protects filament
• oxidation
– re-deposits tungsten
to filament

22. • Heat
• Cooling critical
– do not turn off fan
– bulb life dramatically decreases
• Power Density:
500-1500mW/cm2

23. • Filters
– band-pass
• restricts broader light
to narrow blue light
• 400-500 nm
• range of photo-initiators
– 99.5% of original radiant energy
filtered
• Decreased efficiency

24. • Advantages:
– Economical.
– Filters used to dissipate heat to the oral
structures & provide restriction of visible
light to narrower spectrum of initiators.
• Disadvantages:
– Diminished light intensity over a period
of time causes degradation of halogen
bulb & degradation of reflector.
– Shorter life about 100 hrs.
– High temperature production.
– Bond strength decreases with increase in
distance.

25. 460
camphorquinone
halogen
500420 nm
1
0.5
1
0.8
0.6
0.4
0.2
Emission
Absorptionunits
Spectral Emission / CQ Absorption

26. Plasma-Arc (PAC)
• Two tungsten electrodes
– small gap
• Pressurized chamber
– xenon gas
• High-voltage spark
– ionizes gas
• plasma
• High voltage is generated between two tungsten electrodes
creating a spark that ionizes Xenon creating a conductive
gas known as Plasma.

27. • High levels of IR and UV
– extensive filtering
• Blue light 400-500 nm.
• Heat generated.
• Has a highly filtered photosensor
which measures light coming from end
of curing tip based on which
microcomputer calculates the time
required for curing.

28. • Advantages:
– High irradiance up to 2400 mW/cm2
– claim 1-3 sec cure.
– Power density of 600-2050 mW/cm2
• Disadvantages:
– Expensive.
– High temperature development.
– Heavy so not portable.
– Requires an in built filter to produce
narrow continuous spectrum.

29. Argon Laser
• Laser photons travel in phase (coherent) & are collimated
such that they travel in same direction.
• High energy
– coherent, non-divergent
– non-continuous
• Highest intensity
• Emits single wavelength of 490nm.
• Very expensive

30. • Advantages:
– Produces narrow focused non divergent monochromatic
light of 490nm.
– Less power utilized.
– Thoroughness and depth of cure is greater.
– Laser curing bond strength did not decrease with
increasing distance.
• Disadvantages:
– Risk of other tissues being irradiated.
– Ophthalmic damage of operator and patient.
– Large in size and heavy.
– expensive

31. Light-Emitting Diodes (LED)
• Combination of two semiconductors - n
doped & p doped.
• n doped have excess of e-
& p doped
have holes.
• When both types are combined &
voltage is applied e-
& holes connect
resulting in emission of light of
characteristic wavelength.

32. • Initially used Silicon – Carbide electrode.
• Now Gallium – Nitride electrode.
• When LED of suitable band gap energy is used they produce
only the desired wavelength range.
• Narrow emission spectrum
– 400-490 nm
• peak at 470 nm
• near absorption max
of camphoroquinone
• efficient

33. • Advantages:
– Long service life of more than 10,000hrs.
– Low temperature development.
– No filter system.
– Low power consumption.
– Wavelength of 400-490nm.
• Disadvantages:
– Photoinitiator is only CQ.
– Requires longer exposure time to adequately polymerize
microfills & hybrid resin.

34. • First generation
– high cost
– low irradiance
• < 300 mW/cm2
• increase exposure time
Classification

35. • 2nd
generation (2002-2004)
• Using more powerful diodes than in first generation.
• Using LED chip design raising out put of LED to QTH
units.
• But it was expensive.
• High heat generation so manufacture incorporate external
fans for cooling or automatic unit shutoff to avoid over
heating.

36. • 3rd generation:
• In order to enable curing other restorative material not
only use (CQ) but use other intiators like (CQ+tertiary
amine), (1-phenyl propane), (trimethylbenzyl-diphenyl
phosphine enzyme), (Leucin TPO).
• These other initiators need near UV wavelength to activate
them.

37. Why do you think the manufactures go to
another photo initiators rather than (CQ) ??

38. • One of the main problem of
CQ initiator is there
yellow color rather than
their need to prolonged
light curing.
• Which give the RBC
undesirable yellow color
after polymerization
• So the manufactures turn
into another substitutes as
mentioned before

39. New Developments
• Narrow spectrum lights
– argon laser
– LED
• Other photoinitiators absorb at lower wavelengths
– Phenyl propanedione (PPD)
- Bis acylphossphine oxide(BAPO)
- Tri acyl phosphine
• Narrow spectrum lights may not polymerize materials containing
other initiators

40. 1
Spectral Emission / Absorption
1
460
halogen
LED
500420 nm
0.5
0.8
0.6
0.4
0.2
Emission
Absorptionunits
PPD
Phenyl propanedione
camphorquinone

41. Photo Initiators & Absorption Spectrum
Camphoroquinone
470 500400 430370
PPD
LED
Halogen
Argon Laser
Plasma Arc
Violet Blue Green
450
AADR Abstract 0042 Efficiency of Various Light Initiators after Curing with Different Light-curing Units
P. BURTSCHER, and V. RHEINBERGER, Ivoclar Vivadent, Schaan, Liechtenstein
J. Lindemuth 2003

42. From this graph we should see:
1- the peak of wave length of LED
units is perfectly matching the
wavelength needed to activate CQ
initiators.
2- the new initiators like Lucerin
TPO & PPD their peak near UV
wave length away from LED wave
length zone.
Poggio, C., Lombardini, M., Gaviati, S., & Chiesa, M. (2012).
Evaluation of Vickers hardness and depth of cure of six
composite resins photo-activated with different
polymerization modes. Journal of Conservative Dentistry :
JCD, 15(3), 237–41.

43. •As shown before 1st
and 2nd
generation of LED cannot activate
the new initiators of RBC.
•So the manufactures provide the their light cures with LED
chipsets that emit more than one wave length.(POLYWAVE
LED)
•It provide sufficient irradiance to cure any type of composite.

44. 1- has broader spectrum than QTH
2- easily handle with high power irradiance.(1000-3000
mW/cm2)
3- high battery capacity.
Advantages:

45. •Heat-sink features and automatic thermal cut out due to thermal
over heating.
•No stable irradiance or spectral stability so the new sensitive
initiators which are sensitive to spectrum of the wave length, are
not probably activated
Disadvantages:

46. Exposure
• Increased light exposure
– increased depth of cure
– increased conversion
• polymerization
– increased hardness
– up to threshold
• Decreased light exposure
– inadequate polymerization

47. Inadequate Polymerization
• Lack of retention
• Increased wear
• Color instability
• Microleakage
– post-op sensitivity
– secondary caries

48. Techniques of light curing
• Continuous curing techniques:
1) uniform continuous curing.
2) Step cure.
3) Ramp cure.
4) High-energy pulse cure.
• Discontinuous cure techniques:
1) pulse delay cure.

49. 1) Uniform continuous cure:
• Light of medium constant intensity.
• Applied to composite for period of time.
• The most familiar method that currently used.
• Carried out by QTH & LED curing units.

50. 2) Step Cure:
• Firstly used low energy and then stepped up to high energy
• The purpose for Step cure is decreasing the degree of
polymerization shrinkage and polymerization stresses by
allowing the composite to flow while it is in gel state.
• Step Cure cannot be carried out by plasma arc or laser.

51. 3) Ramp cure:
• The light is applied in low intensity and then
gradually increase over the time.
• It decrease initial stresses and polymerization
shrinkage.
• It cannot be carried out by plasma arc or Laser
curing unit.

52. 4) High energy pulse cure.
• High energy (1000-2800 mW/cm2
) which is three or six
times the normal power.
• It is used in bonding of ortho brackets or sealents.
• 8-10 sec.
• It carried out by argon laser, plasma arc, third generation
of LED.

54. 5) Pulse delay cure.
• Single pulse of light applied to restoration then followed by
pause then a second pulse with higher intensity and longer
duration.
• The first low intensity pulse slowing the rate of
polymerization, decreasing the rate of shrinkage and stresses
in the composite.
• While the second high intense pulse allow the composite to
reach the final state of polymerization.
• It carried out by QTH light cure.

57. Irradiance
• Power (mW) incident
upon an area (cm2
)
– surface area of the tip
of the light guide
• Large tips
– lower irradiance
• Small tips
– higher irradiance
Irradiance
mW
cm2
=Irradiance

58. • The use of a single “irradiance” value to describe the output
from a LCU should be interpreted with caution as it implies
that this single irradiance value describes the light that every
part of the RBC is receiving. This is not the case for dental
curing lights because they all deliver varying degrees of light
beam inhomogeneity
(Vandewalle et al. 2008; Price, Labrie, et al. 2010; Price,
Labrie, et al. 2011; Michaud et al. 2014; Price, Labrie, et al.
2014; de Magalhães Filho et al. 2015; Haenel et al. 2015;
Shortall et al. 2015).

59. • spectrometer-based systems that make many measurements
every second and have become the “gold standard” for
measuring the output from an LCU (Kirkpatrick 2005).
• Such systems are now readily available and can measure
radiant exposure (J/cm2
) over the entire output cycle of the
LCU as well recording radiant power (W), spectral radiant
power (W/nm), and radiant exitance (W/cm2
) at any given
moment.

60. Spectral Emission–Spectral Radiant
Power (W/nm)
• To be effective when photocuring an RBC, sufficient spectral
radiant power must fall within the spectral range required to
activate the photoinitiator(s) present in the resin (Nomoto 1997;
Price and Felix 2009; Leprince et al. 2013), but neither
thermopiles nor dental radiometers measure the spectral radiant
power.

62. Beam profile of the LCU

65. Type of Composite
• Microfills scatter light
• Darker shades impede energy transmission
• Glass fillers transmit light better
– hybrids > flowables

66. How long does it take to
adequately cure a composite?
• Depends on
– energy density
• irradiance of light x time
– distance from composite
– collimation of light
– wavelengths
• emitted
• absorbed
– composite type

67. So, how long should I cure the
composite?!
• Increase curing time
– lower irradiances
• LED
• Halogen
– microfill composites
– darker shades
– flowable composites
– greater distances
– poor collimation
• Decrease curing time
– higher irradiances
• Plasma arc
– hybrid composites
– lighter shades
– close distance
– good collimation
Refer to the manufacturer’s instructions for guidance

68. use high irradiance?
• Higher temperatures
• Accelerated polymerization shrinkage
– stress
• cracks, crazing

69. General Considerations
• A good rule of thumb is that the minimum power density
output should never drop below 300mW/cm2
• Shifting from a standard 11mm diameter tip to a small 3mm
diameter increases the light output eightfold.
• Ideally, the fiber optic tip should be adjacent to the surface
being cured but this will lead to tip contamination.

70. • Intensity of light is inversely proportional to the distance
from the fiber optic tip to the composite surface.
• Therefore, the tip should be within 2mm of composite to
be effective.
• Light transmitting wedges for interproximal curing & light
focusing tips for access into proximal boxes are available.
• Intensity of the tip output falls off from the centre to the
edges. So bulk curing of the composite produces bullet
shaped curing pattern.
• DC is related to intensity of light & duration of exposure.

71. • Most light curing techniques require minimum of 20 sec
for adequate curing.
• To guarantee adequate curing, it is a common practice to
postcure for 20-60 sec. postcuring improves the surface
properties slightly.
• More intense curing units have been developed to hasten
the curing cycles. E.g. PAC & laser units.
• Rapid polymerization may produce excessive
polymerization stresses & weaken the bonding system
layer against tooth structure.

72. Maintenance
• Periodic visual inspection of unit
– light guide
– filters
– bulb
• Check irradiance
– radiometer

73. Contamination of Light Tip
• Reduces passage of light
• Reflects light
– increases heat build-up
– shortens bulb life
• Remove debris
– polishing kit
– blade

74. Radiometer
• Consists of photosensitive diode
– specific for light
• Measures total light output at curing tip
– hand-held
– built-in
• Light-specific radiometers
– halogen
– LED

75. Optical Hazards
• Halogen laboratory study
– No thermal hazard
– Photochemical hazard
• Roll
– max 1 min/day reflected light
– 30 cm
• Satrom
– stare directly for > 2.4 minutes
– 25 cm distance

76. Optical Safety
• Do not look directly at light
• Protection recommended
– glasses
– shields
• May impair ability
to match tooth shades

77. PHOTOCURING TRAINING, EVALUATION, AND
PROCESS MANAGEMENT
The MARC Device and Training System
Four variables affect the extent to which a resin is polymerized
within the tooth:
operator technique,
type of curing light,
location of the restoration,
type of resin used.

78. • A recently introduced device, “MARC” (an acronym for
“managing accurate resin curing,” BlueLight Analytics Inc.,
Halifax, NS), takes these four variables into by measuring
both the irradiance and the energy received by simulated
preparations in a mannequin head.
• The MARC device combines precise, laboratory spectral
technology with clinically relevant measuring conditions
within prepared dentoform teeth in a mannequin head.

79. • Spectrum-corrected sensors inside the dentoform teeth are
attached to a laboratory-grade spectro radiometer embedded
within the manikin’s head to record the light received from
curing units.
• Output from the spectrometer is fed into a laptop computer,
where custom software provides real-time and accumulated
comparison data: spectral irradiance, total energy delivered over
a given exposure duration, and the estimated exposure duration
needed to deliver a specified energy dosage.

80. • In addition to providing real-time feedback to judge when
adequate photoenergy has been delivered, the MARC device
can also be used as a training aid for performing optimal
clinical photocuring. The effect of minor alterations in tip
distance and angle and movement during exposure is displayed
in real time, and the ultimate consequence in terms of altered
energy delivered is determined.
• The device can also be used to determine the ability of various
lamps to deliver adequate energy levels between different tooth
locations.

81. CONCLUSION
• The commonly used term of irradiance measured at the light
tip should no longer be used to describe the output of curing
lights as it implies that this is the irradiance the specimen is
receiving and takes no account of distance between the LCU
and the RBC or the effects of beam inhomogeneity.

82. • Ideally, both manufacturers and researchers should include
the following information about the LCU:
1. Radiant power output throughout the exposure cycle
and the spectral radiant power as a function of
wavelength
2. Analysis of the light beam profile and spectral emission
across the light beam
3. Measurement and reporting of the light the RBC specimen
received as well as the output measured at the light tip

83. References
• Phillips’ Science of Dental Materials – 12th
ed
• Craig’s Restorative Dental Materials – 13th
ed
• Light curing units: A Review of what we need to know
R.B. Price et al, Journal of Dental Research (2015)
• Advances in light-curing units: four generations of LED
lights and clinical implications for optimizing their use:
Part 2. From present to future, Adrian C C Shortall et al,
Dental Update · June 2012

84. • Text book of operative dentistry – vimal. k sikri 4th
ed