Is light polymerization a necessary evil or just a short intermediate step?

The Canadian dental clinician and researcher Richard Price at Dalhousie University in Halifax has spent the better part of the past few decades studying curing light technology. In an interview with Dental Tribune he shared his advice on how to light cure properly and explained why polymerization lights are so important for the success of your dental office.


Dr. Price, you have been instrumental in researching curing light technologies. Would you mind sharing your thoughts about compromised polymerization and its potential effects on clinical success?

Thank you for this opportunity to discuss the undercuring of dental resins. The problem as I see it is that most dentists have never been taught about the importance of proper light curing or what to look for in a good curing light. Even the cheapest light and the sloppiest technique will produce a resin restoration that is hard to touch. The problem is that the dentist cannot determine whether the bottom or the inside of the restoration has been adequately cured. An under-cured restoration is weaker and more prone to fracture, the bond strength to the tooth is reduced or even non-existent, post-operative sensitivity occurs, the color stability of the resin is compromised, and more chemicals are released into the body from the partially cured resin. These are all very undesirable outcomes of inadequate light curing, and none of them need to occur.

What should dental professionals consider key attributes of curing lights?

Curing lights are defined as medical devices, and only approved medical devices should be used on patients. If we look at Ivoclar Vivadent’s curing lights, they are not only approved medical devices, but they are also functional, ergonomic, reliable and thoroughly tested according to international standards. Furthermore, the broad emission spectrum of Bluephase lights means that they will cure all known dental resins and bonding systems.

Which key attributes of the Bluephase PowerCure will clinicians find helpful?

In addition to the new Polyvision technology, the light's high power and irradiance can cure both direct and indirect resin restorations. Depending on the thickness of the indirect restoration, the light can photocure the resin cement used to bond most indirect restorations to the tooth. I like to use the high output settings to photopolymerize the resin under my indirect restorations and the regular output settings for my direct resin restorations.

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The patented Polyvision technology has been described as an inbuilt personal polymerization assistant. How does it work?

The Polyvision feature should assist clinicians in achieving reliable curing results by automatically detecting unwanted movement of the light tip away from the tooth. When it detects movement, it alerts the operator using vibration or an acoustic signal and automatically increases or interrupts the curing exposure cycle.

Your research shows the importance of uniform beam profile and irradiance. Why is this an important factor to consider?

Ivoclar Vivadent recognizes that the success of its resin-based products depends on adequate light curing. Consequently, it makes excellent curing lights.

Should dentists regularly measure the light output from their curing lights, and is a built-in radiometer helpful?

Manufacturers often state that their light has a high irradiance. This may be true, but the power output may be rather low. How can this be? I think that the way the international standards are written is the cause of a significant problem when describing lights. These standards require the manufacturer to measure the total power from the light and then divide this power by the area of the light tip. This means that to deliver the same irradiance, a light with a 7 mm diameter light tip need only produce half the power of a light with a 10 mm diameter light tip (area of a 7 mm diameter tip is half that of a 10 mm tip). In addition, this method provides a single irradiance value that is an averaged value across the tip; however, there are often hot spots of high irradiance and areas where the irradiance is rather low across the light tip. I see this all the time in budget lights.

In contrast, the current range of Bluephase lights delivers an exceptionally uniform light output. Certain models of Bluephase lights also include a radiometer in the charging base, and an integrated tester makes it easy to test the light every day. I know that may seem unnecessary to some, but if you only test your light once a week or once a month, what will you do when the light fails the test, because it will fail at some point? Are you going to recall and redo all of the restorations you placed since the last successful test?

Can you please advise on the correct polymerization technique for dental professionals?

When light curing, I recommend the following steps:

Step 1

Read the instructions for use for the curing light and the resin you are using. For example, the 3s exposure time on the Bluephase PowerCure should only be used with Ivoclar Vivadent’s Tetric PowerFill and Tetric PowerFlow resins. The 3s exposure mode does not apply to all resins.

Step 2

Identify what you want to be cured. I know this sounds obvious, but I have often seen the assistant hold the curing light over the wrong tooth, at least for some of the exposure time.

Step 3

Position the light tip perpendicular to and directly over the restoration, not at an angle. Light travels in a straight line; it does not magically compensate for any light tip misangulation.

Step 4

For a direct restoration, start to light-cure a few millimeters away from the surface because you do not want to flatten your beautiful anatomy. Then, because the surface will be hard after just 1 second, bring the light tip as close as you can to the restoration and hold it there over the restoration. Use two hands if needed to keep the light tip over the restoration.

Step 5

Watch what you are doing through orange protective glasses or a shield and keep the light tip over the restoration.

Step 6

Follow the resin manufacturer’s instructions and light-cure for the recommended exposure time.

Do you have any other tips to consider during polymerization that will help clinicians in their light curing?

For Class II situations, I also cure from the buccal and lingual aspects after the matrix band is removed. 

I use the same technique for indirect restorations, but I usually use a tacking tip first, clean up the excess cement and then light-cure with the tip in contact with the indirect restoration.

Disinfect the light using the manufacturer’s recommended disinfectant. Some disinfectants can damage the light.

Check that the end of the curing light tip is clean and has no chips, cracks or cured resin on it. Using a barrier over the light helps with infection control and prevents resins from bonding to the light. However, extra care needs to be taken for optimized functioning of Polyvision Technology when there is an infection control barrier over the light tip of the Bluephase PowerCure, and G4 light. In these cases, the best option is to use two hands and hold the light tip over the restoration and watch what you are doing with that light tip.

Editorial note:

Dr. Price is a prosthodontist and the director of digital dentistry at Dalhousie University in Halifax in Canada. He received his BDS from the University of London in England in 1979 and his DDS from Dalhousie’s Faculty of Dentistry in 1988. He completed his specialty training at the University of Michigan in 1984 and his Doctorate in Oral Technology and Dental Materials at the University of Malmö in Sweden in 2001. He is actively involved in teaching light curing and researching dental resins and has authored more than 190 peer-reviewed articles, and co-authored the chapter on light curing in the 7th edition of Sturdevant’s textbook, Art and Science of Operative Dentistry.

Dr. Price organizes symposia on light curing in dentistry. Consensus statements based on these symposia help dentists to deliver the best dental restorations for their patients and have been published in English, French, German, Spanish and Portuguese.