Curing Lights for Composite Resins

Now a days LED lights have become popular and cheap. They also do not need to have bulb replaced.
Light units have come a long way since the Nuva Light (Dentsply/Caulk) was introduced in the mid-1970s.It used ultra violet light to activate special kind of filling material, the standard now is visible light units that use a quartz-tungsten-halogen (QTH) bulb as their light source to produce a filtered blue light.

By following incremental placement of resin and proper maintenance of the curing units, these units perform well. New resin curing lights are being introduced now which utilize high intensity fast cure, low intensity slow cure and a combination of both.

Recent research indicates that there may be some advantages to curing composite resins by varying the intensity of the QTH light. Routinely the QTH light is turned on for 40-60 seconds for curing the resins and the light is turned off. This constant exposure to intense light source may cause the resin composite to polymerize too quickly. Stresses induced by rapid polymerization compromise the strength of the recently formed bond of the material to the tooth structure and lead to leakage.

By using a different light technique we may be able to reduce the amount of polymerization stress. There are two techniques, which use short duration, and low intensity light followed by a longer duration of high intensity

1. Stepped technique
2. Ramp mode
3. Pulse delay cure technique

Ramp mode:The ramp mode begins at reduced intensity before gradually moving to 100% intensity. This function is designed to reduce polymerization shrinkage.

Stepped technique: here, the low intensity exposure is immediately followed by the high intensity exposure. The first commercially available light unit this technique was Elipar Highlight (ESPE). It uses a 10-second exposure of light at 150 mW/cm Followed by 30-50 seconds at 700mW/ cm

Pulse delay technique incorporates a waiting period between exposures. The VIP light from BISCO used the pule delay cure technique, a very short (3 second) exposure at 200 mW/cm² is first used to harden the composite resin. After a waiting period of three minutes, a 30-second exposure at 600 mW/cm² is used. The waiting period allows stress relaxation and the restoration can be finished and polished at this time.

In both cases the low intensity light exposure theoretically allows the resin's newly induced stresses a chance to dissipate. These techniques are the subjects of research and it is wise to delay purchasing new units based on these technologies.

Curing

Traditional curing lights use 488 nm wavelength blue light, which is filtered and passed onto the composite resin to be cured. This generates a large amount of heat and a lot of energy is wasted. And its intensity is not strong enough. With Argon laser the wavelength is right for the curing of composite resin. Laser curing is deeper and faster because of its higher intensity. Studies have shown that laser curing of composite resin is more complete. This will lead to less post operative sensitivity and discomfort.

Accucure 3000 (Laser Med) utilises continuous energy output at 4 intensity levels of 320, 480, 640 and 730 mW/cm²

Plasma Arc System:

Newer resin composite formulations have an impressive hardness, better marginal adaptation and better control of internal stresses. When internal tension is reduced, the degree of shrinkage is less important. Some studies have shown that polymerization and shrinkage are not linked to the time of photo activation. Rapid polymerization, reducing the time of exposure to less than 5 seconds improves patient comfort and reduces the time needed to complete the procedure.

Apollo 95 E (DMD) is an example of plasma Arc lamp and it utilizes a maximum intensity output of 1930 mW/cm²

The lasers and plasma arc lights have been shown to produce highest heat increases on the surface (upto21 °C) and within the restoration upto 14 °C. Compared to these halogen lights produce most temperature increase within the pulp chamber ( increase of 2 °C)

Light Cure Units- What features to look for while buying

Light curing unit is an indispensible part of a dental clinic today. Below are some of the terms useful to understand choose right kind of light for your clinic.

Cordless: Light can be easily charged on its base and then can be moved easily for convinience or chair to chair in a operatory with many chairs.
Curing Light Foot Print Amount of space unit occupies when placed on your working space, smaller the better.

Intensity Curing light output range is measured in nanometers. Most composites utilize camphoroquinone(CQ) polymerizing initiators that are activated by light emitted in and around 468 nm. Other composites,including some flowable resins, require initiation in the 429 nm range.

Tip size Wand tip diameters should extend beyond the margins of the restoration. A larger restoration requires a wand tip that illuminates the entire surface of the composite simultaneously.A porcelain or direct veneer requires the largest wand tip, 12mm or wider.

Curing programs pulse, step, ramp

To understand exact differences between Plasma arc, LED and Halogen composite curing units ...CLICK HERE

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