Light Cured Dental Composite Resins

Light Cured Dental Composite Resins

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“A particle-filed resin consisting of a single paste that becomes polymerized through the use of photosensitive initiator system (Camphoroquinone and an amine initiator) and light source activator (visible blue light).” is known as light-cure composite resin.

Classification of Light-cure Composite Restorative Materials:

Materials whose setting is affected by an application of energy from an external source such as blue light or heat.

These materials are subdivided as:

• Materials whose use requires the energy to be applied intraorally; this group consists of direct composite materials to be directly applied to teeth.
• Materials whose use requires the energy to be applied extra orally; this group consists of indirect composite materials for fabrication of inlays and onlays

Composition of Light-Cure Composite Restorative Materials: The light source activator is a tungsten halogen bulb of blue light with a wavelength between 400 to 500 nm.

These are single-paste systems containing:

• Photoinitiator: Camphoroquinone (0.25 wt%)
• Amine accelerator: dimethylamino ethyl methacrylate (DEAEMA) 0.15 wt %.

Light Activation of Direct Composites:

Initiation:

• Camphoroquinone/amine-photoinitiator/co-initiator system.
• Blue light (400-550 nm wavelength) activates camphor quinone and converts it to an excited state.
• The activated camphor quinone reacts with a co-initiator to form free radicals starting the polymerization process (activation and initiation stages).
• The free radical reacts with a monomer molecule and propagates the polymerization process (propagation).

Propagation and Chain Growth:

• Free radical joins with the monomer molecule and forms a covalent bond with it.
• This complex also releases a free radical which seeks another monomer molecule.
• This process continues till all C=C bonds are converted to C–C bonds.
• During polymerization the molecules group together to form a high molecular weight complex.
• This grouping of molecules results in less intermolecular distance which is seen clinically as volumetric shrinkage.

Properties of Light Activated Resin:

• It is a single-paste system.
• Mixing of pastes is not required in this system and results in less porosity.
• Light-activated resins are less sensitive to oxygen inhibition
• Since the resin does not cure till a light source is shown on it there is ample working time to manipulate the resin.
• The light-activated resin also allows incremental curing and results in a tightly compacted restoration.
• Polymerization is peripheral (towards the light source).

Extraoral Cure or Light Activated Indirect Composite Resins:

• Extraoral cure refers to light-activated composite resin restorations made in the laboratory and cured using a special curing unit.
• Extraoral heat or light results in a higher level of cure of the material since all portions of the restoration is cured in a uniform manner.
• It is used with the indirect technique, i.e. fabricated in the laboratory—inlays, crowns, and veneers.

Procedure or Light Activated Indirect Composite Resins:

• Chemical or light-cured composite is used to fill the cavity contours in the model.
• The model with the resin is transferred to an oven for light curing.
• The cured restoration is removed from the model and is finished and polished.
• The restoration is cemented with resin-based composite cement.

Advantages of Light Activated Resins:

• Mixing is not required therefore less porosity, less staining, and increased strength.
• An aliphatic amine can be used in the state of an aromatic amine as required for chemically cured resin, this enhances color stability.
• Control of working time.
• Insertion and contouring is possible before curing.
• Quick cure with no air bubbles.
• Reduction in laboratory procedures.
• Reduction in patient appointments.

Disadvantages of Light Activated Resins:

• Limited curing depth (maximum 2 mm thickness).
• Relatively poor accessibility in certain posterior and interproximal locations.
• Variable exposure time because of shade (hue, value, and chroma). Longer exposure time for darker shades.

Precautions or Light Activated Indirect Composite Resins:

• Resin paste should not be dispensed until it is to be used. Exposure to operatory lights for any appreciable time can initiate the polymerization of material.
• Exposure to sunlight should be avoided.
• Unused composite should never be returned to the syringe or kept for future use.
• Storage should be in a cool and dry environment to maintain the shelf-life of all composites.
• High-intensity light can cause retinal damage if one looks directly. Use protective eyeglasses.