What are The Basics of Curing Light?

Only if understanding more reps about curing lights and how they work, can dentists service their patients better.

Curing light is used for the polymerization of light-cured resin-based materials. In the contemporary world of dentistry, curing lights have become an integral part of all specialties and dental practices. Today, almost all resin composites, dental adhesives and adhesive cements utilize light energy for complete polymerization, which further determines the long-term clinical success of a procedure. While much attention has been given to the details of diagnosis, preparation and the development of improved adhesives and resins, light curing is often taken for granted. It’s a well-accepted fact that inadequate polymerization of the materials can lead to clinical failures, such as sensitivity, marginal discoloration, fractured restorations and de-bonding issues, making it critical to select an ideal curing light.

As dental manufacturers continue to introduce a wider variety of curing lights, distributor sales reps need to ask several important questions:

  • How does one curing light differ from the next?
  • What factors determine the right curing light solution for each dental customer?
  • What light intensity is required to completely photo-polymerize the resin-based material?
  • How does the chemistry of the product, or the clinical application, affect the curing time of the restorations?

Understanding the technology

Curing lights provide light energy of an emission spectrum. Photo-initiators absorb this light energy and initiate chemical reactions to polymerize a composite material. This process is called photo-polymerization.

Both light intensity – or irradiance – and the dental application should factor into a dentist’s decision regarding his or her choice of curing light. For instance, irradiance is measured by calculating power output, or milliwatts (mW), of a curing light across the surface area of the curing light guide. A curing light must deliver a minimum irradiance of 400mW/cm2 for a time interval to adequately polymerize a 1.5-2mm thick resin composite.

Clinicians also should consider the clinical application at hand. It has been documented that irradiance of curing lights attenuate/decrease significantly when it passes through restorative materials, such as ceramic restorations or resin composites. The percentage of decrease in irradiance depends on filler type, filler loading, shades, refractive index, opacity, translucency and thickness of restorative materials. Curing lights with high irradiance compensate for the decrease in the loss of total energy and allow dentists to cure resin composites completely. In general, an irradiance of 1000mW/cm2 or higher is considered ideal to cure resin-based materials through indirect restorations.

Other factors that can affect the curing process include:

  • The diameter of the light guide/emission window. Sometimes a curing light tip with a wider diameter is required.
  • The design of the light probes. The design can optimize the use of curing lights in various situations. So, for instance, shorter light probes permits easier access to posterior teeth.

Advances in technology

There have been significant improvements in the curing light technology in recent years. Today, dental manufacturers can develops variety of curing lights, from plasma arc to argon laser curing lights. That said, two curing lights commonly used in the dental operatory are Quartz Tungsten Halogen (QTH) lights and Light-emitting diode (LED) lights.

Quartz Tungsten Halogen (QTH) lights. These lights have a quartz bulb with a tungsten filament that irradiate both UV and white light, which must be filtered to remove heat and all wavelengths except those in the violet-blue range. The lights have broad emission spectrum of approximately 390 nm to 500 nm, which is capable of curing all composites. However, the technology has its challenges, including:

  • The intensity of the bulb diminishes with use.
  • The filter can accumulate dust, crack or delaminate, which can alter the wavelengths and irradiance of light transmitted.

Light Emitting Diode (LED) curing lights. These curing lights use light-emitting diodes (LEDs) as a light source and do not require filters. The original LED lights had narrow emission spectrum and low power intensities, necessitating long curing times. This issue was overcome by 2nd generation curing lights with high power intensity. However, they maintained narrow emission spectrum, which restricted them to activate only camphorquinone, and thus could not fully polymerize some composite materials. Third generation curing lights feature broad emission spectrum (380nm to 515nm), along with high irradiance in the range of 1000mW/cm2 and higher, reportedly allowing these lights to light-cure all composites without restriction. Other advantages include:

  • A long lifespan without deterioration of power intensities.
  • Low wattage requirement.
  • Ability to be battery operated.
  • Reduced generation of heat.
  • Quiet to operate.

Advantages such as these have led to new-generation LED curing lights becoming a top choice among dentists.

The right solution for each customer

Curing lights vary according to their features; power intensities and energy delivered to the tooth; timing for use; availability of accessories; configuration of curing probes/tips available for a device; and price. The ideal light-curing unit features a broad-emission spectrum, sufficient light intensity, minimal drop off of energy with distance (collimated beam), a large emission window of light probe, ease of use and easy maintenance.

Sales reps can help guide their customers by discussing the advantages of contemporary curing lights and educating them on the difference a particular curing light solution can make for their dental practice.

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