Quantitative testing of dental composite curing lights improves fracture resistance
An Incomplete Cure
Light activated resin-based composite fillings have become the standard of care for dental restorations, yet they typically last only six years. Their susceptibility to bulk failure and chipping or marginal fractures is complicated by the variability of the light curing process conducted in the dental chair. Manufacturers recommend minimum exposure intensities and times for their composites to ensure sufficient polymerization, yet these values are often obtained under ideal curing conditions in a laboratory environment.
More Variation than Consistency
In reality, there are many clinical variables that affect curing including light source design and performance, distance between the light tip and the composite, access to the area, and operator technique and curing time. Researchers in the dental school at the University of Birmingham, UK, decided to look at differences in the fracture resistance of 10 commercially available composites, contrasting those cured optimally in laboratory conditions to those cured using a clinically relevant energy dosage (quantified in J/cm2). To conduct this research they used two purpose-built instruments called the MARC® patient simulator (MARC® PS) and the MARC® resin calibrator (MARC® RC) from BlueLight Analytics. The MARC® PS was used to determine a clinically relevant energy dosage and the MARC® RC was used to enable specific energy dosages to be delivered to the composite specimens prior to fracture resistance testing.
What the researchers found was that the fracture resistance of notched composite samples representing posterior teeth increased with radiant exposure time; more dramatically for some formulations than others. They also found that the exposure time required to achieve the same strength varied considerably between composites, depending on their filler content.
Straight from the Mannequin’s Mouth
To assess the role of operator dependence, a group of 10 untrained students and experienced staff irradiated a tooth in a MARC®-PS simulation system from BlueLight Analytics. This dental mannequin head is fitted with two CC-3 cosine correctors that simulate dental restorations (cavities) connected to a bifurcated fiber optic cable that routes light to an Ocean Optics USB-series spectrometer calibrated for absolute irradiance spectral measurements. The high variability in the energy delivered to the simulated restoration demonstrated the importance of proper training to maximize fracture resistance. Even for the trained staff group, delivered energy varied by up to 15%.
From Measurement to Mastery
With so many variables affecting the fracture resistance of composite fillings in a clinical setting, it is clear that dental curing involves much more than a quick “point and click.” Proper operator training, accurate measurement of lamp output, and an understanding of the optimal radiant exposure for the specific composite will help improve the lifetime of our dental restorations, greatly aided by simulation and measurement systems like the MARC®. To learn more about the MARC® systems, visit www.curingresin.com.
Read more about the American Dental Association’s recommendations to improve curing light effectiveness, featuring the MARC® Patient Simulator system, in the ADA Professional Product Review, Volume 9, Issue 4, page 26.
Optical System – Irradiance
- USB4000 spectrometer (300–950 nm)
- Custom 400 μm bifurcated optical fiber
- CC-3-UV-T cosine correctors with PTFE diffuser (2)
- HL-2000-CAL radiometrically calibrated tungsten halogen light source
Initial fracture resistance and curing temperature rise of ten contemporary resin-based composites with increasing radiant exposure. Shortall, A.; El-Mahy, W.; Stewardson, D.; Addison, O.; Palin, W. Journal of Dentistry, 2013, 41, pp 455–463.