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) ??

To solve bleaching Dilemma

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.

Operative Dentistry- Clinical

course- Text Book - Cairo

university.

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.

Now, what do you think ??

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

light cure (advanced)

Health & Medicine

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