Composites - Understanding Light Curing of Restorative material

Despite routine presence of curing lights and ease for use, there are WHAT that must be followed for successful results?

techniques

Failure to follow these simple concepts can result in clinical failure of what?

uncured/fractured restorations, tooth sensitivity, low bond strength, microleakage, and recurrent decay

Success in Dentistry is the result of?

paying attention to details

All resin-based restorative materials belong to WHAT family?

methacrylate

These methacrylate-based monomers are linked to form polymers by a process called?

free radical addition polymerization

Though the polymerization process is generally the same, what is a difference?

how the free radicals are generated , the rate at which they generate and the number of free radicals produced

What is used in light-curable resins?

photo initator

Photo initiator

contains specific types of bonds that are only capable of absorbing EM radiation within certain wavelength ranges

When the photo initiator atom is stuck by a photon at the appropriate wavelength, an electron in the outermost orbit level does what?

absorbs the energy forming the free radical

What is most common photo initiator in dentistry?

camphor quinone (CQ)

Camphor quinone (CQ) is activated by what?

blue light in the 470 nm range

How many steps are there in free radical polymerization?

4 - activation, initiation, propagation, and termination

Activation (free radical polymerization)

external energy source (heat, uv light, visible blue light) is a catalyst for a free radical formation to seek another electron and form a covalent bond

Initiation (free radical polymerization)

activated free radical seeks out other carbon double bonds and forms new free radical agents

Propagation (free radical polymerization)

monomer molecules added to growing polymer chains

Termination (free radical polymerization)

chain length continues to grow, decreasing ability of chain to move as changes form to gel/solid until increase in length becomes impossible

Activation (photoinitiation)

process by which sufficient energy is provided to induce an initiator to generate free radicals and cause polymerization to begin

Activator (source of energy)

used to activate an initiator and produce free radicals (heat, chemical, visible light) supplies energy for photoinitiator in the presence of a photoinitiator such as CQ

Chemically active resin or cured composite

A resin-based system consisting of two pastes when blended release free radical that initiated polymerization. Self -cured

Degree of conversion

percentage of carbon-carbon double bonds (-C=C-) converted to single (C-C-) during curing to form a polymeric resin

Depth of cure

depth or thickness of a light-cured resin that can be converted from monomer to polymer when exposed to a light source

Dual-cure resin

composite that contains both a chemically activated and light activated components to initiate polymerization and overcome limits of either system

Gel point/gelation

point in the polymerization where sufficient cross linkage have formed producing a rigid, glossy state in which internal flow among developing polymer chains has stopped

- after the gel point, stress cannot be relieved but continues to increase

What are the different types of curing lights?

- plasma-arc lights argon -ion lasers

- quartz-tungsten -halogen (QTH)

- light-emitting diode (LED)

Plasma-arc lights argon -ion lasers

High power expensive, noisy, not portable exposure time 3-5 seconds

Quartz-tungsten -halogen (QTH)

uses a projector type bulb that requires a cooling fan, exposure time 30-60 seconds

Light-emitting diode (LED)

3rd generation, small portable battery operated

Original wavelength activation was between what?

440-500nm

Original wavelength activation was between 440-500nm was sufficient for most composite shade but had what?

a yellow tint

With the popularity of more esthetic lighter cosmetic shades, the yellow tint was not as esthetic so what was introduce to help neutralize the yellow tint?

co-initiator was

What is the co-initiator was added to the yellow tint in what range?

violet range 420nm

Multiple length LED with what?

3 blue chip and 1 violet led

What is the usual depth of cure

1.5-2mm

What is the depth of cure for bulk fil?

4-6mm

Distance to the target

closer the light is to the composite, the more depth of cure

Distance of what results in a 75% DECREASE in power?

8mm

The greater distance from the curing light tip to the target?

the weaker the amount of energy available for curing of composite

Infection control of materails

barriers should fit snuggly over entire unit

For infection control precautions, what should be avoided?

air vents (if present) should not be covered and the seam of the barrier should not be on the direct light source

Curing lights generate heat that can affect what?

the pulp

What can result in a 15% pulpal necrosis?

5.5 degree increase of intra-pulpal temperature

The increase in temperature is related to the amount of what?

energy delivered (irradiance and exposure time) and thermal properties (conductivity and diffusivity) of the tooth

It is suggested that curing lights that delivers an irradiance greater than WHAT used at most for 15 seconds per exposure?

1,200 mW/cm2

It is suggested that curing lights that delivers an irradiance greater than 1,200 mW/cm2 used at most for how long?

15 seconds per exposure

What can be created by the position of the curing light that causes incomplete curing to occur?

shadows

How do you prevent shadows?

by moving light around when curing

What is a way to reduce intra-pulpal temperature?

gentle stream of air

Soft tissue damage

light that generates significant heat

Erythema

redness of skin which can be caused by soft tissue damage

How can you prevent soft tissue damage?

moving the light around during curing

What does the operator and patient need to wear when using a curing light?

blue light blocking eye protection

What are the 2 major advantages of composite?

conservation and esthetics

What are the 2 major disadvantages of composite?

polymerization shrinkage and technique sensitive

What are the 2 major contridictions of composite?

isolation and operator skill

What are the 3 major components of the Composite?

1. resin matrix

2. coupling agents

3. inorganic fillers

What is the matrix that is mainly used?

BIS-GMA

The more inorganic filler will increase WHAT but reduce WHAT?

strength and polymerization shrinkage

Composite resin should contain at least what % of filler by weight?

75% filler

The smaller the particle size, the more what?

polishable and improved wear resistance

Small particle composite

.5-3 um

Micro filled composites

0.04 to .4 um

Hybrid composites

0.04 to 1 um

What is the classification of composites based on filler particle size, from biggest to smallest?

1. megafill

2. macrofill

3. midifill

4. minifill

5. microfill

6. nanofill

Megafill (filler particle size)

0.5 to 2 nm

Macrofill (filler particle size)

10 to 100 um

Midifill (filler particle size)

1 to 10 um

Minifill (filler particle size)

0.1 to 1um

Microfill (filler particle size)

0.01 to 0.1 um

Nanofill (filler particle size)

0.005 to 0.01 um

What filler particle size is known as the Hybrid?

midifill

Polymerization shrinkage

shrinkage that occurs when the composite resin is cured (polymerized)

More recent research indicates that the material does not shrink towards the light but rather?

shrinks away from the cavity walls going toward the center of the bulk of material

Curing in small increments does what?

decreases shrinkage

C-Factor

composite restoration describes the ratio of bonded surfaces to unbonded (free) surfaces in a cavity preparation

C-factor can cause a gap at the margins that allows for what?

microleakage of fluid and bacteria at the margin with possible tooth sensitivity and future staining at the margins and recurrent caries

Shrinking composite that is well bonded to buccal and lingual cavity walls can also do what?

put tension on the cusps of the tooth, pulling them slightly toward each other

When tension is put on the cusps of the tooth what does this cause?

discomfort when the patient bites down

The initial bond to what is the strongest?

enamel

When the composite shrinks near the cavosurface margins in enamel, occasionally what can happen?

some of the enamel rods pull away from the tooth

What is the result of some of the enamel rods being pulled away from the tooth?

microscopic cracking of the enamel

What does microscopic cracking of enamel look like?

white line around the margin

The effects of polymerization shrinkage can be minimize by placing the restoration how?

in small incremental layers - avoid joining opposing walls with one increment and curing each layer separately

Adhesive dentistry

simple relationship between bonds and stress

When is restorative technique deemed successful?

if the bonds can withstand the stress

Cracks from polymerization shrinkage results in poor technique in how long?

5 minutes after cure

Reducing stress can increase what?

bond strength

Increasing bond strength can maintain what?

the seal

Maintaining the seal can prevent what?

infection and fracture