DPR’s guide to curing lights, material activation

3M scientist Joe Oxman recently was interviewed by DPR Editor in Chief Stan Goff and shared his vast knowledge on curing lights, dental materials and technology.

Here is the first part of his interview. Check back for Part 2 to come soon.  

Click here to view an infographic on curing lights.

DPR: Tell us a little about your background with 3M ESPE and in working with dental products?

Joe: I have a PhD in organic photochemistry from Northwestern University and have been with 3M for nearly 30 years. 3M has always had the reputation of being a leader in innovative solutions to customer based problems and very much a technology-savvy and technology-oriented company.

3M is also a significant technology developer and user of photo curing or photo polymerization technology. We are one of the largest in the world. Most people wouldn’t know that because many of the 3M products that utilize light curing technology are sold to the customer in final polymerized state as part of the manufacturing process. Obviously if we’re selling dental materials or products we provide the uncured material and the activator – the light is the source that induces the activation. So in that case we provide both.

Many products that 3M manufactures and sells – ranging from adhesive tapes to abrasives to optical films that are used in computer screens or in LCDs are manufactured by coating a light curable resin and using light to harden them into a very precise shape or configuration.

I’ve had one foot in the door of dental materials for the entire 30 years, but I’ve also been very active in the much broader photopolymerization technology platform within 3M. I’m also extremely involved in several academic collaborations as well.

DPR: How would you explain the science behind dental light curing technology?

Joe: Modern light curing or photo curing of dental materials has evolved significantly since it was first introduced in the late 1970’s using ultraviolet initiation and light sources . Today’s photocuring technology utilizes safer, lower energy visible blue light activation technology in combination with advanced LED light sources.

We combine reactive monomers, light sensitive initiators and an appropriate light source to activate, trigger or initiate a chemical reaction called  photopolymerization or photocuring. Some people believe that when you use a curing light that you are actually generating heat and that causes it to harden Others believe the light causes solvent evaporation. In reality, We’re actually using light to cause a reaction that’s induced by light not unlike photosynthesis. The light is actually the activator or trigger that is causing the reaction to take place.

DPR: How has this technology evolved over the years?

Joe: The light sources that we use today, utilize relatively low energy, blue light, that triggers a chemical reaction called polymerization that causes the crosslinking or hardening of dental resins. You are  essentially transforming small molecules into very large molecules that result in the formation of  hard, durable materials that are intended to replicate tooth structure.

There are numerous light curable products in dentistry including  dental adhesives composite filling materials, glass ionomers, dental sealants and orthodontic bracket adhesives. The common feature is the ability to apply a variety of dental materials with an infinite amount of working time. Upon a brief 5-10 second light exposure with the appropriate wavelengths of light, one can transform the material “on demand” to material with an entirely new set of properties.

Light curing of dental composite materials dates back approximately 35 years. Since then there’s been significant advancements on many different fronts. In the early days it was using exclusively high energy ultraviolet light.

Recognizing that there were some safety concerns and curing limitations using ultraviolet there was a movement toward using much safer, longer wavelength visible lights. That was a truly significant advance that took place about 30-35 years ago. Since then there have been numerous light curing advancements and enhancements.

Currently, we now use photocuring for a broad array of dental materials including adhesives, composites, cements, temporization materials to name a few. In addition, the lights have become significantly smaller as there has been a movement from ultraviolet to visible, and an evolution away from the halogen lights to light emitting diodes or LEDs.

LEDs provide the benefits of being energy efficient, long lived,  high output and portability since they can use a low energy source. There will be continued advancements in the lights, but it’s important to realize that the lights themselves don’t serve a useful purpose without the materials, and similarly the materials are not useful without the lights. It’s the combination or marriage of the material and the light that’s critical to the successful end result.

DPR: What trends have you noticed recently?

Joe: There are several interesting trends in the industry at present. We’re seeing growing  a desire for faster, more efficient processes. Clinicians are trying to reduce the number of procedural steps.  As a result there are an increasing number of products that are trying to address faster and/or easier clinical procedures.

Ultimately we try to develop products at 3M that provide not just innovative features, but also they have to provide clinically relevant benefits. A good example would be the recent introduction of bulk fill composite materials. We have introduced Filtek™ Bulk Fill Flowable Restorative that represents a great example of a material today that can be placed and light cured up to 4 mm in depth.

Traditionally there had been two limitations with bulk curable composite materials: No. 1 it has been challenging to achieve sufficient curing from top to bottom. Consequently,  it was difficult to adequately cure a 4mm restoration.

Perhaps the more significant issue was addressing the composite shrinkage stress that occurs when these materials are light cured. Too much shrinkage may lead to potential clinical issues such as white lines at the margins or microleakage, do to the material not anchoring well or adhering well to all the walls of the tooth structure.

3M has developed a new and novel material that be adequately cured 4 mm from top to bottom, has low shrinkage and shrinkage stress without compromising key mechanical properties and abrasion resistance.

This is a good example of how we try to combine materials along with light curing to provide a product that saves time without compromising a good clinical outcome.