Curing Lights for Composite Resins
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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
- Stepped technique
- Pulse delay cure technique
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/cm2
Followed by 30-50 seconds at 700mW/ cm2.
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)
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