Light curing of restorative materials

Activation of free radicals that aggressively seeks another electron with which to form a covalent bond.

Activation

Activation requires an external energy source such as

-Heat

-An amine reducing agent

-Electromagnetic radiation light

-Visible blue light

-Microwave energy

• In dental resins, the activated free radical species seek out the electron-rich carbon double bond that is present in the methacrylate groups of a monomer molecule. The double bond gives up 1 electron to the newly initiated radical, and the other electron acts as the free radical agent. This process is called ?

Initiation

• As the initiated molecule approaches other methylmethacrylate molecules, the free electron interacts with the double bond of the methylmethacrylate molecule and a new, longer free radical is formed

Propagation

Occurs when:

• Molecular weight of the chain increases

• Resin changes from liquid to gel

• Inability of the growing polymer chains to readily find and join to additional unreacted methacrylate monomers

• And, when two free radicals interact and form a covalent bond.

Termination

Polymerization Strategies in Dentistry

1. Self curing direct restoration

2. Light-cured polymerization reaction

Self curing is also called as?

1. Cold cured

2. Autocured resins

initiator of free radicals

Benzoyl peroxide and aromatic amine

Self curing is available in 2 components package separately as

• Catalyst and Base

• The material can be used in bulk increments because free radicals are produced throughout the resin as the benzoyl peroxide and aromatic amine interact.

Sel-curing

Disadvantages of Self-curing

• Slow chemical reaction (delay polishing for 24 hours)

• Greater polymerization shrinkage

• Faster, less complicated method

• Uses light (electromagnetic energy) to generate free radicals

Light-cured polymerization reaction

Light cured polymerization Reaction contains components such as?

1. Photoinitiator (camphorquinone)

2. Amine activator DMAEMA (dimethylaminoethylmethacrylate)

3. Inhibitors

• After placing this _________ into a tooth, it is adjusted and contoured to achieve the correct shape, then exposed to light at specific wavelengths and for the specified time to activate the ________ and produce the necessary free radicals.

Light curable resin

Activates the photoinitiator

• Radiant exitance is effectively the same as the term ________ ________, measured in __________ per square centimeter (mW/cm²)

• Radiant exitance is effectively the same as the term incident irradiance, measured in milliWatts per square centimeter (mW/cm²)

This is commonly used to describe the output from a curing light

The radiant exitance (irradiance at 0 mm distance)

What is the unit of radiant exitance/irradiance?

milliWatts per square centimeter (mW/cm²).

What does “irradiance at 0 mm distance” refer to?

Radiant exitance—the irradiance measured directly at the curing-light tip.

What is radiant exitance commonly used to describe?

The output of a curing light.

Why does radiant exitance provide limited information?

Because it does not fully describe the curing light's performance.

What aspect of curing-light performance is NOT adequately shown by radiant exitance?

How powerful the curing light actually is.

How does tip-to-target distance affect curing?

Increasing the distance between the light tip and composite can reduce the irradiance received.

What information does radiant exitance provide limited information about?

How powerful the curing light is, tip-to-target distance effects, spectral radiant power, and beam uniformity.

Laws of Photochemistry

1. The Grotthuss-Draper law

2. The Stark-Einstein law

• states that light must first be absorbed by the chemical substance.

Grotthuss-Draper law

• states that, for each photon of light absorbed, only one molecule within the chemical system can be activated

Stark-Einstein law

Types of Photoinitiators used in Dentistry

Type I and Type II photoinitiators

Type I Photoinitiators

Type I photoinitiators

1. Phenyl propanedione

2. Lucirin TPO

3. Ivocerin

4. Bis acylphosphine oxide( BAPO)

5. Triacylphosphine

Type II Photoinitiator

1. Camphorquinone

2. Phenylpropanedione

• have a high quantum yield, meaning they require fewer photons to generate a free radicals

Type 1 photoinitiator

• Do not require additional co-initiators and break down directly into one or more free radicals when they absorb light at the correct wavelengths.

Type 1 photoinitiator

• Faster and more efficient

• Examples:

  • Lucirin, TPO, and derivatives of dibenzoyl germanium such as Ivocerin

Type 1 photoinitiator

A more broad-banded absorbing photoinitiator, having more absorption values more into the blue spectral region

Phenyl propanedione (PPD) 

• (2,4,6-Trimethylbenzoyldipheny|phosphine oxide) 

• Is currently combined with CQ (and other photoinitiators) to provide enhanced resin curing, and decreased restoration yellowing.

Lucirin TPO

What is Lucirin TPO combined with?

Camphorquinone and other photoinititators

Why is Lucirin TPO combined with (camphorquinone) CQ and other photoinitiators?

To provide enhanced resin curing and decreased restoration yellowing.

A dibenzoyl germanium derivative), has been developed to provide an even broader spectrum of short-wave absorption

Ivocerin

• Require more electrons to generate free radicals

Type ll photoinitiators

Aside from requiring more electrons to generate free radicals Type II photoinitiators also require an additional secondary electron transfer agent9 (this is typically an _____________) to generate a free radical

Aside from requiring more electrons to generate free radicals Type II photoinitiators also require an additional secondary electron transfer agent9 (this is typically an amine electron accepting agent) to generate a free radical

• Are slower and less efficient

Type ll photoinitiators

Examples of type 2 photoinitiators

Camphorquinone(CQ)

Phenylpropanedione(PPD)

The most common photo-absorbing material

Camphorquinone

What range of blue light does camphorquinone absorb?

• At 468- 474 nm

What color of light activates camphorquinone?

Blue light

What is the wavelength range of visible light?

400-700 m

What wavelength range are most composite resins sensitive to?

• 400-520 am (blue light)

What absorbs photon energy in composite resin?

Photoinitiators

What happens after photoinitiators absorb photon energy?

They combine/react with an activator.

What activator is creates free raqdicals ?

Amine (DMAEMA)

DMAEMA stands for?

Dimethylaminoethyl methacrylate

What do the free radicals initiate?

Polymerization

Light → Photoinitiator _____ photon → combines with _____→ Free radicals → _________

Light → Photoinitiator absorbs photon → combines with DMAEMA → Free radicals → Polymerization

What wavelength is ultraviolet light?

Less than 400 nm.

What is a disadvantage of ultraviolet light in resin curing?

It cannot penetrate deeply into the resin.

How thick is the resin increment recommended with ultraviolet light?

1mm thick

How does ultraviolet light affect chairside treatment time?

Increases chairside treatment time.

What are concerns associated with ultraviolet light?

Cataract formation and changes in oral bioflora.

What photoinitiator is very reactive to blue light?

Camphorquinone

What is the absorption peak of camphorquinone?

Near 470nm

What wavelength range does blue light deliver?

400-500nm

How deep can blue light penetrate into resin ?

Up to a 5 mm thick increment.

How does blue light affect chairside treatment time?

Reduces chairside treatment time.

Factors Affecting the Ability to Polymerize a Resin-based Composite

1. Depth of cure

2. Exposure time

What is the boundary between cured and uncured resin called?

Depth of cure

What is the depth of cure for conventional resin under optimum light-curing conditions?

1.5–2 mm deep.

What is the depth of cure for bulk-fill resin?

4–6 mm.

When is depth of cure reduced?

With poor access to the restoration or when using more opaque shades.

What is the relationship between degree of conversion and depth of cure?

Both are related to the radiant exposure received by the resin.

What factors mentioned affect the depth of cure?

Access to the restoration, opacity of the shade, and radiant exposure received by the resin.

How can exposure time be shortened?

1. Increasing the concentration of photoinitiator in the resin

2. Reducing the inhibitory concentration

3. Matching the refractive indices of the resin and filler

4. Increasing irradiance to a limited extent

What happens when the concentration of photoinitiator is increased?

Exposure time can be shortened.

What happens when the inhibitory concentration is reduced?

Exposure time can be shortened

How does matching the refractive indices of resin and filler affect exposure time?

It shortens exposure time.

Can increasing irradiance shorten exposure time?

Yes, but only to a limited extent.

the amount of light energy delivered to a surface per unit area.

Irradiance

What factors affect the number of photons reaching the depths of the resin?

1. Thickness of the resin increment

2. Wavelength of light delivered

3. Refractive indices of the resin and filler components

4. Filler content and size

5. Overall opacity of the material

What happens as the thickness of the resin increment increases?

Fewer photons reach the deeper parts of the resin.

What optical property of the resin and filler affects photon transmission?

Their refractive indices.

What filler characteristics affect the number of photons reaching the resin depth?

Filler content and size.

How does overall opacity affect photon penetration?

Greater opacity affects the number of photons reaching the deeper resin.

What does Rayleigh scattering cause?

Shorter wavelengths of energy are scattered much more than longer wavelengths.

When is light scattering greater?

When the filler particle size is equal to or smaller than the wavelength of light.

What does Beer-Lambert's law relate?

The attenuation of light to the properties of the material through which the light is travelling.

What influences the amount of light penetrating through the resin?

• Filler particles scattering the light

• Colorant absorbing the light

• Photoinitiator(s) using the light

• Differences between the refractive indices of the resin and fillers

What happens to shorter wavelengths according to Rayleigh scattering?

They are scattered more than longer wavelengths.

What happens when filler particle size is equal to or smaller than the wavelength of light?

Light scattering is greater.

What happens if the refractive indices of the resin and fillers match?

Light transmission through the resin is better and depth of cure is better

How does the refractive index of unpolymerized resin compare with the filler?

Unpolymerized resin has a lower refractive index than the filler.

What happens to most resins after light curing?

They become translucent.

Why should shade selection not be performed using uncured resin composite paste?

Because after light curing, most resins become translucent, so the appearance of the uncured paste may not represent the final cured shade.

The four types of Dental Curing Light

1.Quartz-Tungsten Halogen

2.Plasma-arc

3. Argon laser

4. Light Emitting diode

What is the order of curing lights from lowest to highest?

1. Argon Laser

2. Quartz-Tungsten Halogen (QTH)

3. Light-Emitting Diode (LED)

4. Plasma Arc

Which has the lowest irradiance?

Argon Laser

Which has the highest irradiance?

Plasma Arc

What was the first VLC used?

QTH low-voltage lights.

What type of bulbs do QTH lights use?

35–150-watt projector bulbs.

What does a QTH light consist of?

A quartz bulb with a tungsten filament in a halogen environment.

What does QTH stand for?

Quartz-Tungsten-Halogen.

• encasing structure, crystalline, heat resistant

Quartz

What is the function of quartz in QTH lights?

Encasing structure; crystalline and heat resistant.