The Importance of Proper Curing Techniques

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The importance of proper curing of dental materials is undeniable. In early 2000, research from the University of Colorado identified photopolymerization as an essential part of practicing restorative dentistry. The authors suggested that dental professionals should develop an appreciation of the photopolymerization process and all the ups and downs that come with it to deliver esthetic and restorative care.¹

"These materials are all manufactured under certain specs that require us to deliver a certain amount of light energy for a certain amount of time to be able to guarantee that you're going to get a certain level of performance that's on the packaging and has been 510(k) cleared by the FDA," says Tim Bizga, DDS, FAGD, a general dentist practicing in Cleveland, Ohio.

Dr Bizga echoes a sentiment that is prevalent in restorative dentistry circles. Materials that are predictable and successful require a close look at the technique and the manufacturer's instructions. Many problems with insufficient curing lie with human error and not the materials themselves.

The research supports the critical nature of the clinician's curing technique. Photopolymerization occurs when dental professionals expose dental composite to intense blue light usually in the 400-500nm range, which creates physical changes to a deposited material, transforming it into a solid-state.² From there, composite resins cure in three phases, pre-gel, gel point, and post-gel. Each stage represents the transformation from semi-solid state to solid-state, which is achieved by cross-links in the polymer structure.

Research shows that problems with curing technique could influence the polymerization shrinkage of the composite during this photopolymerization process. Moreover, the incomplete curing of composite could reduce the mechanical properties and biocompatibility of the material, increase residual monomers and differing clinical performance esthetically, and increase the tendency of surface staining and the chances of marginal leaking. Throughout the dental literature, changes to curing techniques are the recommended way to overcome these problems.³

Jennifer Sanders, DMD, a general dentist in private practice in rural Frenchtown, Montana, says that stability is 1 of the most significant problems when dental restorative materials are not appropriately cured. Patients also complain more about sensitivity when there is a problem.

"Sometimes, we have a patient with sensitivity, and we don't know why," Dr Sanders says. "And under-curing is the mystery that's causing it."

"When we cut corners, we get into trouble," Dr Bizga adds. "When we under-cure it, nothing good happens."

There are many factors that contribute to human error with curing technique, and it is not always negligence, and even sometimes out of necessity, per Dr Bizga. Multiple priorities in the process—or the patient you happen to have in the chair—can contribute to improper curing, he says.

"Patient management is the biggest distraction," he says. "When our patients are not cooperative, it makes it difficult. You may not cure as long, and you are just trying to get through the procedure. It's not that you are trying to rush it; it's that you are working with somebody who is difficult."

For Dr Sanders, the problems with curing were a sum of little things. From having composite baked on the curing light to not positioning correctly during the cure or making too thick of a layer of material, it was no 1 large mistake that led to issues, but many small ones.

"I've made those mistakes before where I didn't know why the composite didn't bond or why we have sensitivity," Dr Sander says. "It was little things, all those little mistakes that we all make at some point in time."

Under-curing leads to underperformance of the materials, Dr Bizga explains. He uses the analogy of laying down a different type of composite—poured concrete. Concrete requires a specific amount of water, time, and conditions to set right. If you change any part of those specifics, there’ll be a loss of performance and the material may not perform as intended, he says. Something similar happens with dental composites.

"All these different composite materials, when they put the ingredients that make them light-dependent for setting if you don't meet the parameters required, it doesn't hit the performance. You're never getting what you think," Dr Bizga says. "It's the same thing if you didn't properly pour concrete for the foundation of your house. It makes your foundation weak and everything about that is bad."

"And here's the rub," he continues, "much like a home, you don't see the problems initially. You see them down the road. Not far down the road, but certainly not right away."

Tips for Improving Curing Technique

Both dentists have experience with curing composite and each offers advice for other clinicians that can help improve curing techniques.

Finding materials that work best with your workflow is the first step, Dr Bizga says. There are many choices of materials available, but if you find one you like working with, you can perfect your technique within that material's parameters, he says.

Knowing the curing light's timing and depth of cure is essential, says Dr Sander. She recommends focusing on the specifications of your curing light. She uses the Valo™ and the Valo Grand (Ultradent). She appreciates the Valo’s bigger lens and larger light surface, which offers space on positioning during the cure for her assistant. It also offers better ergonomics for her assistant and a 3-second cure.

"They say it will cure in 3 seconds to a couple of millimeters, the same as most lights will do in ten," Dr Sanders says. "But we still usually run it twice because you can't over-cure. But you can under cure."

Moreover, it is critical to ensure the curing light is properly maintained and in good working order. For example, Dr Sanders had curing problems and discovered it was because resin was on her light, preventing a proper cure.

"It can be something as simple as that," Dr Sanders says.

Testing the curing light is another essential part of keeping the light in good working order. Some more contemporary model lights come with a light irradiance tester attached, which will give a digital readout of the light’s output. Other manufacturers offer free light testing as well as recommendations, Dr Bizga explains.

"It is vital to know how much light energy you get every time you hit the power button,” he says.

Another helpful strategy is to invest time to train staff on proper curing techniques. Something as simple as a lunch-and-learn session with videos can help assistants brush-up on the basic, Dr Bizga says.

Things to Avoid When Curing

Light curing materials is a frequent, everyday experience for dental professionals, making it easy to slip into bad habits without even noticing.

Angulation is 1 such technique that slips over time, according to Dr Bizga. The curing light should be perpendicular to the restoration to get the best performance, he says.

"Don't assume that if the blue light touches the material that it has been cured. There is a difference between hardening and curing," Dr Bizga says.

Another common user error is when clinicians try to cure composite at a depth that the curing light is not suited for, Dr Sanders says.

"You should ensure you are using the depth of composite that the light is supposed to cure to," Sanders says. "If your light isn't strong enough to cure to 4 mm of bulk-fill composite, then don't try to do that."

It's also critical not to cure with a tip that has materials hardened on it. Dr Bizga recommends a regular part of the routine maintenance should be to ensure that the light has a clean surface.

"You can wrap it if you want. Some companies sell wraps and things you can put around it that will help," Dr Bizga says.

"Look at it and make sure it isn't gummed up and doesn't have anything on it," Dr Sanders says.

Dr Sanders also recommends taking some composite you don't use or is about to expire and put it into a straw and cure it with the light. Then, you can see—outside of placing a restoration in a patients' mouth—if the light is still curing the way you expect.

"Just don't waste your good composite on that," Dr Sanders says.

Dr Bizga recommends that of all the areas to save money in your practice, the curing light isn't one of them. It's a workhorse in most dental practices, so dental professionals should treat themselves to a quality light that performs well.

"You spend a lot of time with it," Dr Bizga says. "So, you might as well have something you love."

References

1. Stansbury J. Curing dental resins and composites by photopolymerization. researchgate.net. Published February 2000. Accessed February 26, 2021. https://www.researchgate.net/publication/8902124_Curing_Dental_Resins_and_Composites_by_Photopolymerization
2. What is photopolymerization in 3D printing? Monroe Engineering. Published August 6, 2020. Accessed February 26, 2021. https://monroeengineering.com/blog/what-is-photopolymerization-in-3d-printing/
3. de Camargo EJ, Moreschi E, Baseggio W, et al. Composite depth of cure using four polymerization techniques. J Appl Oral Sci. 2009; 17(5)446-450. Accessed February 26, 2021. doi: 10.1590/s1678-77572009000500018