Composites-The art of light curing and their devices

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: Self curing composites 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 C uring 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.

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

12. 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.

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

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

15. 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 .

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

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

18. The End