This document discusses light curing units used in dentistry to polymerize resin-based composites. It describes the advantages of light curing over self-curing composites. The key components of light curing units and different types are outlined, including quartz tungsten halogen, plasma arc, laser and LED lights. Factors that influence curing such as distance, exposure time, techniques and temperature rise are summarized. General considerations for use and maintenance of light curing units are also provided.

1. Light curing units

2. Contents
• Introduction
• Advantages
• Limitations
• Characteristics of light
• Photo polymerization
• Light curing unit
• Types of lCU
• Effect of light tip to resin
distance
• Exposure
• Techniques of light curing
• Time required for adequate
polymerization
• Effects of curing light on
the temperature rise of
the tissue
• General considerations
• Maintenance
• Radiometer
• Optical hazards
• Optical safety
• Conclusion
• References

3. 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.

4. • 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)

5. • 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

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

7. 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

9. Photo-initators
• Camphorquinone (CQ)
– Most common photo-absorbing material
– Maximum sensitivity
• Blue range
• 468 nm to 474nm

10. Camphorquinone
• One of the main problem of
CQ initiator is there is
bright canary yellow color
rather than their need to
prolonged light curing.
• Which give the RBC
undesirable yellow color
after polymerization

11. New Developments
• Phenyl propanedione (PPD) : A more broad-banded absorbing
photoinitiator, having absorption values more into the blue
spectral region
• Lucirin® TPO(2,4,6-Trimethylbenzoyldiphenylphosphine
oxide):TPO is currently combined with CQ (and other
photoinitiators) to provide enhanced resin curing, and decreased
restoration yellowing
• Ivocerin® (a dibenzoyl germanium derivative), has been
developed to provide an even broader spectrum of short wave
absorption
• Bis acylphossphine oxide(BAPO)
• Tri acyl phosphine
• Narrow spectrum lights may not polymerize materials containing
other initiators

12. 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.

13. 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
initiator
• UV radiation generated by a light source capable of emitting
an intense luminous radiation was used to polymerize the
resins

14. • 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.

15. Types of Light Curing Units
– Quartz Tungsten Halogen
– Plasma-arc
– Laser
– LED

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

17. 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 3000 C
produces Electro Magnetic
radiation in the form of visible
light.

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

19. • Heat is produced while filtering of radiant energy
• Cooling critical
– do not turn off fan
– bulb life dramatically decreases
• Power Density:
500-1500mW/cm2

20. • Filters
• Restricts broader light to
narrow blue light
• 400-500 nm range of photo-
initiators
• 99.5% of original radiant
energy filtered

21. • 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.

24. Plasma-Arc (PAC)
• These units utilize two
tungsten rods, held at a
specified distance, encased
in a high-pressure envelope
of xenon gas, having a
sapphire window through
which emitted radiation
escapes
• High voltage is generated
between two tungsten
electrodes creating a spark
that ionizes Xenon creating a
conductive gas known as
Plasma.

25. • 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.

26. • 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.

27. 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

28. • 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

29. Light-Emitting Diodes (LED)
• Combination of two semiconductors -
n doped & p doped.
• In a typical circuit, electrons are forced
to traverse from one side of a
semiconductor material (the “N”
material, having an excess of
electrons) to a substrate having an
electron deficiency (the “P” material).
• When electrons travel through this
potential energy “gap,“ they also emit
light, the specific wavelength of which
is determined by the composition of
each semiconductor substrate)

30. • 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

31. • 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.

32. Classification
• First generation
• high cost
• low irradiance
• < 300 mW/cm2
• increase exposure time
• Battery technology during this time was limited to
use of nickel cadmium NiCAD
• Suffered from memory effect-careful recharging
routines had to be followed

33. 2nd generation
• Use more powerful diodes than in first generation.
• Use 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
• Incorporation of the longer-lasting nickel metal
hydride (NiMH) units that had no ‘memory effect’.

34. 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
• Most contemporary curing lights now use lithium-
ion batteries. These stable, durable, long-usage
energy storage sources provide a reliable output
over extended clinical operation time

35. • 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.

36. Effect of light tip to resin distance
• Irradiance values stated by the manufacturers are
usually measured only at the light tip
• Lower irradiance may be reaching the surface of
the resin that is often at least 2 to 8 mm away from
the light tip
• Some curing lights deliver only 25% irradiance
measured at the tip at a distance of just 8 mm away
from the tip
• This may result in reduced bond strengths at this
critical part of the restoration

37. • Xu et al. When curing adhesives in deep proximal
boxes with a curing light of 600 mW/cm2, the
curing time should be increased to 40 to 60
seconds to ensure optimal polymerization.

38. Contact pro
• Has convex lens and
hyperbolic side profiles
• Displace the bulk of the
composite into thin
layers (.5mm-1mm)
against the walls and
margins of the proximal
box

40. • 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
•

41. • From this graph we should see:
• The peak of wave length of LED units is perfectly matching the wavelength
needed to activate CQ initiators.
• 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

42. Exposure
• Increased light exposure
–increased depth of cure
–increased conversion
• polymerization
–increased hardness
Exposure

43. • Decreased light exposure
• Inadequate polymerization
• Lack of retention
• Increased wear
• Color instability
• Microleakage
–Post-op sensitivity
–Secondary caries

44. 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.

45. 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.

46. 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.

47. 3) Ramp cure:
• The light is appliedin low intensity and then gradually
increase over the time.
• It decrease initial stresses and polymerization shrinkage.
• It cannotbe carriedout by plasmaarc or Laser curing unit.

48. 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.

50. • 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.
5) Pulse delay cure.

53. • Depends on
• Type of Composite
• Microfills scatter light
• Darker shades impede
energy transmission
• Glass fillers transmit
light better
– hybrids > flowables
How long does it take to adequately cure a
composite?

54. –Energy density
•irradiance of light x time
–distance from composite
–collimation of light
–wavelengths
•emitted
•absorbed

55. So, how long to 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

56. • Higher temperatures
• Accelerated polymerization shrinkage
– Stress, cracks, crazing
HIGH IRRADIANCE?

57. Effects of curing light on the temperature rise with
the pulp
• Curing light can lead temperature rise within
the pulp. Therefore, the curing light type, radiant
Exitance and radiant exposure values play an
important role in pulp temperature rise.

58. In this regard, curing lights emitting light with higher
radiant exitance for longer exposure periods
generate more heat than lights with lower radiant
exitance values LCUs with higher irradiance values
than 1,200 mW/cm2 may harm the pulp tissue

59. Clinicians should limit the exposure time to 20 s when
the irradiance from LED units ranges from 1,200 to
1,600 mW/cm2, while exposure period should not be
longer than 10 s when the LCU irradiance ranges from
2,000 to 3,000 mW/cm
Rueggeberg FA, Giannini M, Arrais CA, Price RB. Light
curing in dentistry and clinical implications: a literature
review. Brazilian oral research. 2017 Aug;31.

60. 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.

61. • 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.

62. • 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

63. • 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.

64. • 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.

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

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

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

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

69. 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.

70. • 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.

71. • Spectrum-corrected sensors inside the dento form
teeth are attached to a laboratory-grade spectro-
radiometer embedded within the manikin’s head to
record the light received from curing units.

72. • 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.

73. • 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.

74. • 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

75. • In order to avoid unwanted composite failure in
our day-to-day clinical practice the intensity of
the curing units but also other important factors
like battery, filters, cleanliness of tip should be
maintained for better patient care
CONCLUSION

76. 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 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

77. • 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
• Text book of operative dentistry – vimal. k sikri 4th ed
• Rueggeberg FA, Giannini M, Arrais CA, Price RB. Light curing in
dentistry and clinical implications: a literature review. Brazilian
oral research. 2017 Aug;31.
References

78. • The complete polymerization of the composite
may not be feasible in direct techniques.
• This can be accomplished in the laboratory by
polymerizing the composite under pressure,
vacuum, intense light, heat, inert gas or a
combination of these conditions

79. • An alternative photo activation system
• A higher intensity light source
• Developed -improve upon the curing properties of
composite
Laboratory photo-curing

80. • Originally- xenon lamps
Advantage
• strong and radiant light source
Disadvantage
• Its life is less

81. • An improved photo-curing unit equipped with metal
halide light source designed for use especially in
dental laboratory has been developed and marketed
as Hyper L II (Toho Dental Products, Japan)
• The unit consists of two metal halide lamps, a turn
table main switch and a sliding radiation timer. The
lamp consists of an arc tube and a reflector.

82. • The arc tube is approximately 5 mm in length, is
made of quartz glass, its discharge vessel
contains tungsten electrodes, and the tube is
filled with mercury and auxillary starting gas.
• Both near ultraviolet and visible radiations are
emitted from the light source

83. • Compared to the xenon counterparts
composites cured with metal halide lamps
show greater Knoop hardness number

84. • Laboratory light sources are used in closed photo-
curing systems, therefore harmful effects of UV
radiation exposure to the human body negligible
Advantage

85. Several commercial systems are available for fabrication of
composite inlays and onlays.
1. Concept
• Heat and pressure cured homogeneous reinforced
microfilled composite having 76% inorganic fillers
by weigh
• Generates 85% conversion rate
2. Art glass
• Micro hybrid polymer glass
• 75% conversion rate
3. Belle Glass HP
• microhybrid
• The conversion rate is 98.5%.

86. 4. Targis and Targis 99
This system is a microhybrid having 86% inorganic fillers by weight and has a
conversion rate of 90%
These systems are called polymer glasses, filled polymers or ceramic
optimized resins or ceromers