composites - the art of light curing

1. Composite curing devices

2. Polymerization of Composite Resins
According to polymerization method, the
composite
resins can be divided into two main categories:
1. Self curing composites
2. Light-activated composites.

3. Self Curing Composite Resin
The earliest self curing composite resins were
mixed as a powder and liquid. Soon after, the
composite resins were made available in
paste/paste mixed system in form of a
catalyst and a base material

4. One part of this consists of non organic tertiary
amine accelerator and the other part consists of
benzoyl peroxide initiator. Catalyst and base
materials are mixed in a ratio of about 1:1. On
mixing, their polymerization process is
chemically activated.
These chemicals showed poor color stability.

5. • Mixing time 20 – 30 sec.
• The spatula should be plastic not metal to
avoid filling discoloration.
• Working time 1 – 1.5 min.
• Setting time 4 – 5 min.

6. light-activated Composite Resins
in the late 1960s and early 1970s, ultraviolet
(UV) light cured composite resins were
introduced.
These composite resins tried to overcome some
of the problems of self cured composites but the
problem with UV light polymerization was the
limited depth of cure.

7. In late 1970s, visible light curing of composites
replaced the UV light curing.
Light activation in visible light curing ranges
between 460–470 nm wavelength.
On activation, photoinitiator(camphoroquinone)
combines with amine accelerator and releases
free radicles which start the polymerization.

8. visible light cured composite resins showed
improvement in the color stability of
composite resins.

9. Several techniques have been used for curing of
light cure composite resins:
1.Tungsten-Quartz halogen curing unit (TQH)
2.Plasma Arc Curing unit (PAC)
3.Light emitting diode unit (LED)
4.Argon laser curing unit.

10. 1: Tungsten-quartz Halogen Curing
Unit (QHL)
Tungsten-quartz halogen curing unit is conventional and
most commonly used curing light for composite resins.
It is incandescent lamp which uses visible light in the
wavelength in the range of 410-500 nm. Halogen bulbs
have limited effective lifetime of around 100 hours. At
the start of curing cycle, this light emits a low power
density (400-900 mW/cm2). It mean there is a lesser
polymerization at the start of cycle and maximum
polymerization at the end of cycle.

12. Disadvantages of this technique are:
1. Limited bulb life, i.e. 100 hours.
2. Intensity of bulb decreases with time.
3. Time consuming.

13. Light Emitting Diode Unit (LED)
Light emitting diode unit usually have long life and
emits powerful blue light. This light falls in narrow
wavelength range of 400-500 nm which is in the
range of camphoroquinone photoinitiator found
in most of composite resins.

15. Advantages
1. Low power consumption.
2. Can be used with batteries also.
3. Does not require filter.
4. Long life, i.e. 10,000 hours (approximately).
5. Minimal changes in light output over time.

16. Disadvantage
Only suitable for camphoroquinone based
composites
(because it has limited wavelength spectrum).

17. Argon Laser Curing Unit
Nowadays, composite resins are being cured
with argon laser. Argon laser light has a
wavelength of 470nm which is monochromatic
in nature. It produces intensity of 200–300 mW.

19. Advantages Argon Laser Curing Unit
1. Polymerization is uniform, not affected by
distance.
2. Greater depth of curing achieved with this
light.
3. Degree of polymerization is higher with dark
shades as compared to conventional halogen
lights.

20. Disadvantages Argon Laser Curing Unit
1. May affect adjacent restorations.
2. Chances of damage to pulp can occur due to
rise in temperature.

21. The End