Curing Lights in Dentistry – 2024 Complete Guide

Led curing light units

CURING LIGHTS IN DENTISTRY – THE COMPLETE REVIEW

In recent years, the two most popular types of dental curing lights use either quartz-tungsten-halogen (QTH) bulbs that deliver a broad spectrum of light between 400 nm and 500 nm, or light-emitting diodes (LED).

Quartz Tungsten Halogen VS LED Curing Lights

Many manufacturers ceased the production of QTH (Quartz Tungsten Halogen) curing lights a few years ago, primarily due to the superior efficiency of LED lights compared to QTH light sources. In QTH units, the bulb comprises a tungsten filament enclosed in a clear crystalline quartz casing filled with a halogen-based gas. The flow of electricity through the filament generates heat, causing tungsten atoms to vaporize from the wire surface.

This vaporization results in the release of significant amounts of electromagnetic energy, predominantly in the infrared spectral region, where the heat required for the curing process is generated. Consequently, these types of light units typically necessitate substantial cooling mechanisms to dissipate the generated heat, along with excess visible light that is not essential for the photocuring process.

LED Curing Lights: How do they work?

LED light-curing devices emit light in the blue segment of the visible spectrum, typically falling between 440 and 490 nm, and do not produce heat. These units can be powered by rechargeable batteries due to their low wattage requirements, and they operate more quietly than QTH units as they eliminate the need for a cooling fan. In their initial versions, LED units emitted light with lower intensity, but newer iterations incorporate multiple LEDs with varying wavelength ranges. This enhances the spectrum of emitted light and boosts overall intensity to effectively polymerize all dental materials activated by visible light.

Certain pencil-shaped curing light models utilized metal body casings, providing not only structural durability but also a substantial area for effective thermal dissipation.

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The Chemical Reaction Explained

Dental composite materials activated by visible light include an initiator, such as camphorquinone (CQ), which absorbs light at the specific wavelength of approximately 470 nm for CQ. When this initiator combines with an organic amine like dimethylaminoethyl methacrylate (DMAEMA), the ensuing reaction generates free radicals necessary for initiating polymerization.

The number of photons absorbed by the initiator, crucial for optimal polymerization, depends on the wavelength, intensity, and duration of light exposure. Importantly, variables such as the intensity of the light-curing unit, angle of illumination, tip diameter of the light source, distance from the light source, and exposure duration can significantly influence the formation of free radicals. Consequently, this system is highly sensitive to technique.

Furthermore, manufacturers of composite filling materials employ initiators different from CQ in visible light-activated substances. Since these initiators absorb light at wavelengths distinct from CQ, it is imperative that the light-curing unit emits light at the required wavelength for the specific initiator used.

Implications of LED Curing Lights Power

Modern light-curing units boast higher intensities, typically surpassing 1000 mW/cm2. This elevated intensity allows for either shorter curing durations for a specific depth or an increased depth of cure for a given curing period.
However, it’s essential to note that the use of these high-intensity lights may result in higher shrinkage stresses within the restoration.

It’s crucial to bear in mind that the type of light-curing unit and the chosen curing mode significantly influence polymerization kinetics, shrinkage, and associated stresses. These factors also impact microhardness, depth of cure, degree of conversion, color change, and microleakage in visible-light activated restorations.
Ensuring the safety of patients and clinic personnel when utilizing dental light-curing units is paramount, necessitating precautions such as protective eyewear and light shields.

Variations in the depth of light penetration, curing light intensity, tip diameter of the light source, and exposure time can lead to differences in polymerization.
Light-activated resin composites offer advantages such as ease of manipulation, control of polymerization, and the absence of the need for mixing. The absence of mixing in light-activated composites reduces the likelihood of incorporating air and forming voids in the mixture.

Understanding Power and Distance

The intensity of light at the surface plays a crucial role in achieving a thorough cure both at the surface and within the material. We strongly recommend keeping the tip of the light source within 1 mm of the surface for optimal exposure.

Most dental curing lights typically have a standard exposure time of 20 seconds, generally adequate to cure a light shade of resin to a depth of 2 or 2.5 mm, assuming the light guide is in immediate proximity to the restoration surface.

However, the tooth’s anatomy often prevents placing the light guide close to the restoration surface.
It’s important to note that the light beam is partially collimated and doesn’t spread sufficiently beyond the diameter of the tip at the emitting surface. Consequently, it becomes necessary to “step” the light across the surface of large restorations to ensure complete exposure across the entire surface.

Importance of the Power Supply (Batteries)

Recent advancements have significantly improved the electrical supply to dental LEDs.
Notably, the progress in lithium polymer battery technology has resulted in lighter and more durable power supplies. Additionally, the introduction of a dental light-curing unit completely devoid of batteries, operating through the charging and discharging of an “ultra-capacitor,” has substantially extended the lifespan of dental curing lights.

Curing Lights New Trends

The progression of LED technology led to the development of second and third-generation LED units. These newer devices exhibit significantly increased light output when compared to their predecessors. Consequently, the heat produced by the emitted light from these LED units is comparable to, or in some cases, even higher than the heat generated by QTH lights.

Furthermore, third-generation LED units incorporate blue and violet LED chips, allowing them to emit light with multiple wavelengths.

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