An EnLIGHTening look at light sources in dentistry
This post was prepared in collaboration with BlueLight Analytics
On an experimental basis, we have asked a limited number of companies to provide us with practical “How To” answers to clinical questions. We were prompted to conduct this experiment when dental team members told us that they visit company websites and consult company representatives for practical clinical information. We look forward to receiving your feedback on this experiment.
On the surface, light curing appears to be very easy – literally! Point the curing light, turn it on and the surface hardens almost immediately. Unfortunately, surface hardness is not indicative of the depth of cure below this top layer. Depth of cure is affected by the several factors, some of which include: formulation of the selected resin composite, the output of the light used, and curing time.
BlueLight Analytics Inc. (Halifax, Nova Scotia) has compiled a database containing ~116 different brands of resin composite. The manufacturers’ “Directions for use” indicate that 3 – 48 Joules/cm2 of energy is required to optimally cure resin composite depending on the brand and shade selected by the dentist.
In the May 2012 Clinician’s Report, Dr. Gordon Christensen observed that dentists must often guess how long it takes to light cure. However, estimating cure time is less than ideal because only those resin composites that receive the manufacturer’s minimum required energy dose will deliver the intended properties and perform well in clinical situations.
To assist clinicians and manufacturers alike, BlueLight Analytics has developed a unique checkMARC® service that quickly and accurately measures the output of a curing light. The output is then compared to the manufacturer’s specification.
The checkMARC® service provides dentists with a user-friendly report that enables them, where required, to immediately adjust curing times based on scientifically accurate evidence of the performance of their curing light and on the manufacturer’s recommendations related to use of their selected resin composites (as well as the shade).
BlueLight CASE STUDY
Recently, BlueLight Analytics tested ~500 curing lights across Canada. Of these lights, it was identified that:
- 47% of light tips had adhered composite material (increased contamination risks and reduced output). See Practical How To: How do you clean your light curing unit?
- 26% of light tips were damaged
- 28% of curing lights performed as expected
- 200 curing lights delivered <80% of the manufacturer’s specified output (some as low as 4%)
Remarkably, when the light output was combined with the selected curing time of each individual dentist and then, compared to the energy requirements specified by the resin manufacturer, there was a 45-fold difference in the possible energy delivered to the selected resin composite, depending on the operatory and dental practice. In 39% of the cases, using one brand of resin composite, it was evident that dentists could not deliver the minimum energy dose required by the resin composite manufacturer because the combination of light output and curing times delivered an insufficient energy dose. Consequently, there is an increased risk that resin materials will under-perform in clinical situations.
CLINICAL IMPLICATIONS
When curing lights and protocols are compared between operatories within the same dental practice, there is often extensive variability. Even when the same curing times and brand of curing lights are used, dentists can unknowingly deliver a wide range of energy.
Table 1 illustrates a scenario in which a dentist uses a resin composite that requires 8 Joules/cm2 for lighter and more translucent shades and 16 Joules/cm2 for darker and more opaque shades. However, large variances often occur due to unobservable curing light degradation. In this case, the resin composites placed in Operatory #3 are under-cured and those in Operatory #2 are at increased risk of being under-cured. Under-cured resin composite materials have suboptimal material properties and are at increased risk of under-performing in clinical situations.
To deliver the same energy dose across all operatories, the curing time in Operatory #2 and #3 must be increased by 20 and 40 seconds, respectively, per increment. The increased cure time may potentially increase the scheduled time per restorative appointment resulting in decreased productivity overall; however, this could be offset by using a reputable light curing unit which is performing optimally.
Reference
- BlueLight Analytics Study: Essential Conditions for Clinical Success. Unpublished. Study presented during the 2014 Light Sources in Dentistry Global Conference (May 2014)
- Christensen, G. J. Critical Clinical Guidelines for New LED Curing Lights. Clinicians Report 2012, Vol 5 Iss. 5.