Light cure (advanced)

Dr. Yehia Hafez
Intern Resident In Operative department – Faculty of Oral and
Dental medicine – Cairo University.
Under supervison of :
Prof. Dr. Mai Yousry
Operative department – Faculty of Oral and Dental medicine
Cairo university.
Light cure

 The optical power out put of dental light cure with the extent
of spectral wave length determines its effectiveness.
 There are some definition we must know :-
 Power (Watt)
 Power intensity.
 Power density (irradiance) (mW/cm2).
Definitions :

From those def. what do you think the
most important one to measure the
efficiency of light cure ???

 Power Denisty (Irradiance) is most important one as it
measure the power per unit area .(mW/cm2)
 While power intensity has the variant of the distance from
the light source.

 Light composite began in 1970 using ultra violet light then
replaced by visible light.
 Photo initiator which was widely used is camphorquinone
which is sensitive to blue range 465 n.m.
Some important points :

 1) UV-curing:
 2) quartz- tungeston-halogen lights (QTH).
 3) Light emitted diodes (LED)
 a)1st generation
 b) 2nd generation
 c) 3rd generation
 4) plasma arc
 5) LASER
 6) Recent advances in light cuing polymerization.
History of light cure.

 Was introduced in dentistry 1970
 Used for benzoine ether type compound photo initiator which
was used in sealent at that time.
 Dis-advantage :
 Depth of cure is too short.
 Harmful effect on cornea due to short wave length energy.
1) U.V curing :
Pelissier, B. et al., 2011. Three generations of LED lights and clinical implications for
optimizing their use. 1: from past to present. Dental update, 38(10)

 Used in 1990
 Was first is very large equipement then manufactured in
smaller gun with flexible electric cord and glass bundle
cord.
 It emits wave length ranges from 400-500 mW/cm2 .
2) QTH
.

 Dis-advantage:
 Short curing depth.
 Gradual loss of high energy wave lengths in their light
output.
 Very high heat generation as most of it’s energy
dissepated in form of heat rather visible light.

 Was used in dentistry in middle of 1960s.
 It consists of 2 tungsten electrodes separated by small distance
in high pressure gas filled chamber.
 It’s out put may reach 2500 mW/cm2.
 it has broad band of wave lengths from 380-500 n.m. .
 The manufactures claim that it can cure the light cured
composite in 3-5 sec. .
3) Plasma arc.

Do you think the manufacture
allegation is true ??

authors Type of study Aim of the study conclusion
**(Hofmann et al.
2000)
Journal of clinical oral
investigation
In vitro study Tested for flexural strength,
modulus of elasticity &hardness
(Vickers, Knoop) 24 h after
curing.
after curing by plasma arc light
source & QTH curing units
plasma curing produced inferior
properties mechanical than
conventional curing
**(Sharkey et al. 2001)
Journal Quintessence
international
In vitro study 10 samples of composite were
cured using the appropriate
halogen lamp protocol, and 10
samples were cured using the
plasma lamp and the micro
hardeness was measured by
vicker
The plasma lamp yielded lower
hardness values for all surfaces
compared with the halogen source
And it also has high amount of
residual monomers

(Park, Krejci, and Lutz
2002)
Journal of operative
dentistry
In vitro study Study evaluated the
effectiveness of the plasma arc
curing (PAC) unit "Apollo 95E"
for composite curing. Vs.(QTH)
light curing units, the
microhardness of two
composites (Z100 and Tetric
Ceram)
Apollo 95E did not properly cure the
lower composite surface when the
layer thickness exceeded 2 mm. In
addition, three seconds of curing
time, which the manufacturer
recommended, was insufficient for
optimal curing of composites
(Knezević et al. 2002)
Journal of oral
rehabilitation
In-vitro study to measure the degree of
conversion and temperature
rise for three restorative
composite materials
uing conventional light cure,
soft start polymerization, strong
plasma light
The results revealed the degree of
conversion values in the case of
polymerization with plasma light to
be almost equal to those obtained
by curing with the halogen curing
unit, whereas the temperature rise
was almost negligible.

 1st generation :
 It has low power out put.
 Low irradiance level range from (100-280 mW/cm2) in
comparison to QTH (about 400mW/cm2).
 Cure 2m.m increment of composite in longer time than
QTH (60 Sec.).
Light emitted diode (LED) :

 But it was easy to handle with less heat generation without
using fans in comparison to QTH Light curing sytem.
 Has narrow spectral range suitable for Camphorquinone
(CQ) initiated composite resin.

 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.

 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.

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

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
http://www.scielo.cl/scielo.php?pid=S0719-01072013000300010&script=sci_arttext

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.

 As shown before 1st and 2nd generation of LED cannot activate
the new initiators of RBC.
 So the manfactures 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.
3rd generation of LED:

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

 Heat-sink features and automatic thermal cut out dueto
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.
Dis advantage:

 Elipar S10 (3M ESPE).
 Valo Ultra Dent.
Examples :

 Argon laser used in curing RBC and in office bleaching.
 It emit with specific bandwith :-
 514 nm ( not used in curing, used in hemostasis).
 458-468 nm
 476 nm (most suitable for activating CQ )
 Less infra-red radiation with less heat generation.
4) laser

 Highly coherent with small spot size, in case of large
restoration the clinician need multiple curing cycle.
 If we move away from the tooth or resotoration the spot
size will increase but with lower intensity and more curing
time.
 It is very expensive may reach 5000 $.
Dis-advantage :

 Continous curing techniques:
 1) uniform continuous curing.
 2) Step cure.
 3) Ramp cure.
 4) High-energy pulse cure.
 Discontinous cure techniques:
 1) pulse delay cure.
Techniques of light curing :

 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.
1) Uniform continuous cure:

 Firstly used low energy and then stepped up to gigh
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.
2) Step 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.
3) Ramp 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.
4) High energy pulse cure.

Operative Dentistry- Clinical
course- Text Book - Cairo
university.

 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.

Which of them Do you think the most
appropriate technique to use ??

 Process of light curing is variable process with different
factors affecting it.
 There is no single curing protocol that we can depend on
it completely in curing all types of composite.
To answer this question we need to know
some points :

 NO negative effects like marginal staining, restoration fractures.
 NO microleakage , debonding, recurrent caries or
postoperative pain.
 However, no clear correlation between contraction stress in
dental composites and the success of a composite restoration
was found clinically.
The ideal results from light curing RBC:

 cavity configuration (C-factor), the ratio bet. Bonded to un bonded
surface area of restoration and the method of cavity reconstruction.
 the introduction of stress absorbing intermediate layers or the
selection of the curing method.
Reduction of polymerization stress not
only by light curing technique, it also
depend on :

 Good contraction stress compensation is possible only for
restorations in which the material can flow during the pre-gel
state from the free surfaces to the bound surface.
 Class IV restorations are most favorable, since they offer
several free surfaces, whereas restorations of class I cavity
show the most unfavorable cavity configuration.
 but also, a slower polymerization rate is expected to increase
the ability of a material to flow, without damaging its internal
structure

Author & journal Type of study Aim of the study conclusion
(Ernst et al. 2003)
Journal of esthetic and
restorative dentistry.
In-vitro study evaluated the influence of a
soft-start light-curing exposure
and conventional light curing
method on polymerization
shrinkage stress and marginal
integrity of adhesive
restorations
* Soft-start polymerization may lead to a
significant reduction in marginal
microleakage of adhesive.
* The effect of soft-start curing mode
depends on the material itself.
(Hofmann et al. 2003)
American journal of
dentistry
In-vitro study To determine polymerization
shrinkage & heat generated by
light-cured resin-based
composites after high intensity
vs. soft-start irradiation
* Soft-start protocols produced less
contraction, and polymerization shrinkage.
* Less heat was generated by the soft-start
protocols
Some studies to evaluate different
techniques of light curing:

(Alomari and Mansour
2005)
dentistry
In-vitro study Evaluated cusp deflection
in upper premolar in MOD
cavities, using
Fast curing mode, pulse
curing mode, stepped
curing mode, visible light.
They found pulse curing & stepped
curing has the lowest cuspal deflection
then fast cure & visible light cure
respectively.
They found no significance difference
in micro hardeness at 2m.m depth of
cure.
(Soares, Liporoni, and
Martin 2007)
dentistry
In vitro study Evaluated the degree of
conversion (DC) of
composite at depth 2.5
m.m. cured by three
different light curing units
(LCUs) using soft-start and
normal protocols.
soft-start protocol did not produce
adequate DC at the depth of 2.5 mm.

***(Chan et al. 2008)
dentistry
Randomized
Control study
They used z100 composite in
class II and complex class I
to evaluate soft-start and
plasma arc light) improves
marginal seal & decrease
post-operative
hypersensitivity..
*They found concluded that restorations
placed with soft start technique did not
show significant changes in post-
operative sensitivity.
*It do not exhibit decreased signs of
marginal stress when compared to the
plasma arc curing technique.
(de Camargo et al. 2009)
Journal of applied oral
science : revista FOB
In-vitro Evaluated the effect of four
light-curing techniques on
depth of cure of a
composite resin by 4
techniques of curing
(stepped, ramped, pulse
delay and traditional).
* Traditional method of cure provided
higher microhardness values in all
composite depth.
* All light curing techniques will give
satisfactory results when the depth of
cure not exceed 2 m.m.

(Knezevic et al. 2010)
Journal of Quintessence
international
In vitro study Evaluated linear
polymerization shrinkage
for five composite materials
polymerized with curing
modes of two LED curing
units.
Soft start cure elongate pregel phase
of polymerization process and
decrease polymerization shrinkage
(Ilie, Jelen, and Hickel
2011)
Journal of clinical oral
investigation.
In vitro study They used soft-start
polymerization, Ramp cure,
pulse cure, fast cure.
To evaluate depth of cure
micro-hybrid composite at
2 m.m &6 m.m. depth
*They found that soft start can still use in
small cavities with small depth or with
small composite increment not exceed
2 m.m.
*But it give low mechanical prop. In 6
m.m. depth.

(Poggio et al. 2012)
Journal of conservative
dentistry
In vitro study Evaluated Vickers hardness
(VK) and depth of cure
(hardness ratio) of six resin
composites, polymerized with
(LED) curing unit by different
polymerization modes:
Standard 20 s, Standard 40 s,
Soft-start 40 s.
All the materials tested and with all the
polymerization modes, hardness ratio was
higher than the minimum value indicated
in literature in order to consider the
bottom surface as adequately cured
(0.80).
(Piccioni et al. 2014)
The journal of
contemporary dental
practice
In vitro study Investigated the effects of
different polymerization
protocols on the cuspal
movement in class II
composite restorations.
Standard protocol showed the highest
values of cuspal movement and was
statistically different from the pulse-delay
and soft-start curing modes.

 It is specialized light meter that quantifies blue light out put, to
measure the effectiveness of the curing unit.
 It may be built in or small handled device.
 It is advisable to test your light cure after 50 hr.s of work.
Dental radiometer and intensity
measurement:

 Organic light emitting diodes (OLEDs)
 It is flexible and extremely thin video display to be made but at
current technology there output level remain below LED chips
 It utilized in impression tray with walls and floor lined with these
emitting films which designed to evenly irradiate all surface of
photo curable impression material.
 used in vital bleaching and cementation of veneers
Future development in light curing system:
Rueggeberg, F. a. (2011). State-of-the-art: Dental photocuring - A review. Dental Materials, 27(1), 39–52

 quantum dots.
 These substances are semiconductors nano structure.
 Smaller crystals display a larger band gap. Thus, as the
difference in energy between the highest valence band
and lowest conducting band increases,
 more energy is needed to excite the dot, but also, more
energy is released when the crystal is back in its resting
state.

 Such technology allows fluorescence to occur at shorter
wavelengths than those of excitation.
 This condition would allow red light exposure to result in
emission of blue light, which might be used for
photoinitiation.

Quantum Dots with gradually stepping emission from violet to deep
red are being produced in a kg scale at PlasmaChem GmbH
http://www.plasmachem.com/shop/en/226-zncdses-
alloyed-quantum-dots

 such dots were incorporated into a photopolymerizable
resin composite, it might be possible to enable the entire
mass to release light within itself, resulting in a “curing from
within”.
 This aspect is a dream, but never realized for dental
applications.

 Alomari, Qasem D, and Yasar F Mansour. “Effect of LED Curing Modes on Cusp Deflection and Hardness of Composite Restorations.” Operative
Dentistry 30 (6): 684–89. http://www.ncbi.nlm.nih.gov/pubmed/16382590.
 Chan, Daniel C N, W D Browning, K B Frazier, and M G Brackett. 2008. “Clinical Evaluation of the Soft-Start (pulse-Delay) Polymerization Technique in
Class I and II Composite Restorations.” Operative Dentistry 33 (3): 265–71. doi:10.2341/07-120.
 De Camargo, Ericson Janolio, Eduardo Moreschi, Wagner Baseggio, Jaime Aparecido Cury, and Renata Corrêa Pascotto. 2009. “Composite Depth
of Cure Using Four Polymerization Techniques.” Journal of Applied Oral Science : Revista FOB 17 (5): 446–50. doi:10.1590/S1678-77572009000500018.
 Ernst, Claus-Peter, Nicole Brand, Ulrike Frommator, Gerd Rippin, and Brita Willershausen. 2003. “Reduction of Polymerization Shrinkage Stress and
Marginal Microleakage Using Soft-Start Polymerization.” Journal of Esthetic and Restorative Dentistry : Official Publication of the American Academy
of Esthetic Dentistry ... [et Al.] 15 (2): 93–103; discussion 104. http://www.ncbi.nlm.nih.gov/pubmed/12762473.
 Hofmann, Norbert, Tanja Markert, Burkard Hugo, and Bernd Klaiber. 2003. “Effect of High Intensity vs. Soft-Start Halogen Irradiation on Light-Cured
Resin-Based Composites. Part I. Temperature Rise and Polymerization Shrinkage.” American Journal of Dentistry 16 (6): 421–30.
http://www.ncbi.nlm.nih.gov/pubmed/15002959.
 Hofmann, N, B Hugo, K Schubert, and B Klaiber. 2000. “Comparison between a Plasma Arc Light Source and Conventional Halogen Curing Units
Regarding Flexural Strength, Modulus, and Hardness of Photoactivated Resin Composites.” Clinical oral investigations 4(3): 140–47.
http://www.ncbi.nlm.nih.gov/pubmed/11000318 (April 24, 2015).
Refrences:

 Ilie, Nicoleta, Esther Jelen, and Reinhard Hickel. 2011. “Is the Soft-Start Polymerisation Concept Still Relevant for Modern Curing Units?”
Clinical Oral Investigations 15 (1): 21–29. doi:10.1007/s00784-009-0354-5.
 Knezevic, Alena, Kristina Sariri, Ivica Sovic, Nazif Demoli, and Zrinka Tarle. 2010. “Shrinkage Evaluation of Composite Polymerized with LED
Units Using Laser Interferometry.” Quintessence International (Berlin, Germany : 1985) 41 (5): 417–25.
http://www.ncbi.nlm.nih.gov/pubmed/20376378.
 Knezević, A et al. 2002. “Photopolymerization of Composite Resins with Plasma Light.” Journal of oral rehabilitation 29(8): 782–86.
http://www.ncbi.nlm.nih.gov/pubmed/12220347 (April 25, 2015).
 Park, S Ho, I Krejci, and F Lutz. 2002. “Microhardness of Resin Composites Polymerized by Plasma Arc or Conventional Visible Light Curing.”
Operative dentistry 27(1): 30–37. http://www.ncbi.nlm.nih.gov/pubmed/11817467 (April 24, 2015).
 Piccioni, Máyra Andressa Rodrigues Valinhos, Flares Baratto-Filho, Milton Carlos Kuga, Eduardo Christiano Caregnatto de Morais, and
Edson Alves Campos. 2014. “Cuspal Movement Related to Different Polymerization Protocols.” The Journal of Contemporary Dental
Practice 15 (1): 26–28. http://www.ncbi.nlm.nih.gov/pubmed/24939260.
 Poggio, C, M Lombardini, S Gaviati, and M Chiesa. 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. doi:10.4103/0972-0707.97946
 Sharkey, S et al. 2001. “Surface Hardness of Light-Activated Resin Composites Cured by Two Different Visible-Light Sources: An in Vitro
Study.” Quintessence international (Berlin, Germany : 1985) 32(5): 401–5. http://www.ncbi.nlm.nih.gov/pubmed/11444075 (April 24, 2015).
 Soares, L E S, P C S Liporoni, and A A Martin. 2007. “The Effect of Soft-Start Polymerization by Second Generation LEDs on the Degree of
Conversion of Resin Composite.” Operative Dentistry 32 (2): 160–65. doi:10.2341/06-45

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