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As the practice of dentistry evolved, new light curing units also emerged to keep pace with the new technologies. Innovation on light curing units are important technologies utilized for the polymerization of the various composite resins. Each of these technologies presents disadvantages and advanta...

As the practice of dentistry evolved, new light curing units also emerged to keep pace with the new technologies. Innovation on light curing units are important technologies utilized for the polymerization of the various composite resins. Each of these technologies presents disadvantages and advantages, that is important to remember and understand. The success of composite restorations are affected by polymerization processes, and one of these process is light curing of the restorative material. Types of Light Curing Units 1. Plasma Arc Curing Lamps (PAC) The PAC uses 2 tungsten electrodes which is surrounded by a gas (xenon). It uses a xenon gas that is ionized to produce a plasma. The white light that is of high intensity is filtered to remove heat and to allow blue light (about 400 to 500nm) to be emitted. The PAC also use specific light tips for particular situation requiring different emission spectra. 2. Laser (Argon Laser) The argon laser was considered to be a good choice for a high irradiance curing light unit because it could rapidly cure dental resins. Argon lasers have the highest intensity and emit a single wavelength (490nm), it also does not produce a broad spectrum light but many intense and well-defined emission peaks in the blue spectral region. 3. Quartz Tungsten Halogen Light Curing Unit (QHT) The QTH utilizes a bulb (quartz) with a tungsten filament. It irradiates both the UV and white light that is filtered to remove heat and all wavelength except the violet-blue range (about 400 to 500nm). Only 10% visible light is produced and.5% to 2% of the total energy input is emitted as useful blue light and 70% is converted into heat, making QTH curing light as inefficient. 4. Light Emitting Diode Curing Unit (LED) The LED emit radiation only in the blue part of the visible spectrum (440-480nm), because of this LED do not require filters. The LED is very efficient at converting electrical energy to electromagnetic radiation. 4.1 First Generation LED This type of curing unit was called “cool” lights, because it produced less heat, and less temperature rise in the pulp than the QTH light curing units. This low heat generation of this curing unit is due to their low radiant power output (470nm). This curing unit is incompatible with Lucirin and TPO. 4.2 Second Generation LED This curing unit use a new high output blue LED chips, which resulted to a reduced recommended exposure time than QTH. An internal cooling fan and a large metal sinks were added to this curing unit, because the increase radiant power output also increased heat output. This curing unit is incompatible with Lucirin and TPO. 4.3 Third Generation LED (Multiwave, Multipeak, Polywave) The light curing unit than can emit light of more than one wavelength range. This was achieved by incorporating different LED color chips, that can emit both lower wavelength of 390-430nm (violet light) and higher wavelength of 440-500nm. This curing unit can now activate all the photo initiators used for composite resins.