Light Curing of Restorative Materials (Chapter 6)

What happens if resin is not cured all the way?

- Fracture

- Increased wear

- Low bond strength

- Increased micro leakage

Resin based restorative materials belong to the --- family

methacrylate

Methacrylate monomers form polymers via ---

free radical polymerization

What are the steps in free radical polymerization?

Activation

Initiation

Propogation

Termination

How is methacrylate based free radical polymerization activated/initiated.

External energy source = UV light or chemical reaction

Propagation of methacrylate based free radical polymerization

Free radical formed reacts with monomers = forms covalent bond

polymer chain grease longer

What happens as methacrylate based resin chain grows?

Polymer gets stiffer / becomes a solid

How does methacrylate based free radical polymerization terminate?

the 2 free radical chains formed meet and form a covalent bond

What adds strength to free radical polymerization?

Cross linking between chains

Polymers that have little to no cross linking tend to be --- and ---

weak and flexible

What modifies cross linking?

the type of light curing

Benzoyl peroxide

chemical curing agent

True / False: Commonly used terms to describe the output from a curing light such as intensity, power density, or energy density are not SI terms, they are confusing as to what they mean, and ideally they should not be used.

true

The longer the wavelength the --- the frequency

smaller

The shorter the wavelength the --- the frequency

higher

What light is used for light curing today?

Camphorquinone (CQ) = a type of blue light

Factors that affect the ability to polymerize a methacrylate resin based composite

1. depth of cure

2. exposure time

3. thickness of material

4. interaction between light and particles

Degree of conversion

Extent to which resin has been polymerized

depth of cure

Boundary between cured and uncured resin

True / False: As the resin composite thickness increases, exponentially fewer and fewer photons reach to the bottom, thus potentially reducing the degree of conversion of the resin at the bottom

True

The closer the --- of the resin and the filler are matched, the better will be the light transmission through the resin composite and the better the depth of cure

refractive index

Resins become more translucent before or after light curing?

After

If they resin and filler are perfectly matched, the filler particles will optically disappear, but the increased translucency will mean that the resin composite will appear --- In the mouth.

gray

In an un-polymerized state does resin have a higher or lower refractive index compared to the filler particles?

lower

After polymerization does resin have a higher or lower refractive index compared to the filler particles?

higher

True / False: the light source inside the unit can degrade over time and decrease the light output

true

True / False: it is important to use a dental radiometer to routinely measure the output from the curing light.

True

True / False: the light tip can have a significant impact on how much light is delivered to the restoration

true

True / False: the output from curing lights should be tested on the radiometer with the barrier over the light tip

true - barrier reduces light intensity and must be taken into consideration for infection control

True / False: Where the pulp is at greater risk, such as in deep cavities with little overlying dentin, consideration should be given to the choice of LCU and light exposure program. It has been recommended that the tooth should be air-cooled during light exposure from the opposite side.

TRue

Pulpal temperature starts to -- after light exposure

rise

--- tissue damage can be caused by excessive heat from light curing or excessive amounts of light energy delivered to the oral tissues

soft tissue damage

What protects the eyes from blue light?

Orange shields

To maximize the radiant exposure delivered, the light tip should be held both close to and --- to the surface of the restoration

perpendicular