Years ago, light polymerization wasn't much of a factor in restorations, because there wasn't a need for light activation. Today, there are many different adhesives and flowable composites that can be used as final restorations. Each of these components impacts how much polymerization is needed.
In the past, many dental school students were not given a great deal of instruction in light curing, but today, institutions are offering training and companies are making it possible to understand the performance of each light. When you put a light in place, the irradiance should not change over time. However, testing shows that often the light moves slightly — and this deviation away from the restoration can result in a lack of polymerization.
For proper curing to occur, adequate energy needs to get to the top and to the bottom of the specimen. The light needs to stay in place and staff needs to be trained appropriately in using lights. Yet the International Association of Dental Research found that 30% of lights on the market deliver only half the needed light.
Inadequate polymerization results in cracks and fractures, poor cross-linking between the adhesive and the resin and color shifts. It can also lead to secondary caries, poor bond strength and leaching into dentin/cytotoxicity.
Polymerization involves more than simply turning on a blue light. It's actually more complicated than that. However, if we have a solid understanding of the materials being used and the technology behind curing lights, this can make restorative dentistry quite predictable.
There are numerous factors that go into making a successful cure, including the characteristics of the restoration (such as the depth and proximity to the pulp), the type of restoration materials, the operator's technique, the curing light (including the light's battery health) and the energy delivered to the restoration. There needs to be enough energy to perform the task, without overheating the tooth. The longer the cure, the more heat is generated. Too much heat can negatively impact the pulp.
Light manufacturers identify the cure time for each light, based on factors such as enamel shade. Curing lights have hot spots, though, so they are not consistent. How the LEDs are set can drastically impact curing.
In his 2011 study, The Effect of Distance on Irradiance and Beam Homogeneity from 4 Light-emitting Diode Curing Units, Dr. Richard B. Price found that as you move the light away from the restoration, irradiance decreases. Without proper irradiance, polymerization may not occur at all.
Collimation — or having a consistent column of light — is also critical. When light is emitted, the diameter of the column of light should not change, because when the diameter increases, the intensity of the light decreases.
When choosing curing lights, look for one that delivers enough energy at the right heat component and has uniform distribution. Having a stable light output is important. Don't skimp on a curing light because it could cause restoration failures.
It's also instructive to test to see if the light is stable over its charge. An Operative Dentistry study conducted in 2017 found several curing lights had a dropoff in energy production when battery life got lower. The battery and light should be in sync. Otherwise, it may appear that polymerizing is occurring when it isn't.
Radiometers are a starting point for measuring irradiance at the surface. However, when you look at the irradiance, some manufacturers will shrink the diameter to increase the irradiance number — but this results in poor clinical outcomes.
To determine if you're delivering enough energy, there are testing mechanisms that pair a spectrometer with a smart device. You simply enter the restoration materials you're using, put the light in place and it displays if there is dropoff. This system also identifies if there is a heat issue, as well as the approximate curing times for each light. It's prudent to test lights on a daily or weekly basis to understand how each light is performing in each operatory. If you know the output of each light, you can determine with better accuracy how long curing will take with each light and material. This makes adhesive dentistry more predictable.
Restorative materials have been developed that allow efficiency and predictability when polymerized appropriately. Yet up to 50% of your revenue may be dependent on your curing light, so it's important to choose lights and test regularly. Creating a testing protocol for your practice can further increase the chance of success.
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