While much attention has been paid to the diagnostic and tooth preparation phases of treatment as well as to the development of improved restorative materials, the final procedural step of dental curing light is sometimes taken for granted. This may partially explain why some reports indicate that the average lifespan of posterior resin-based composites is only about 6 years, and that secondary caries and fracture of the restoration are the two main reasons for replacement.
Light-cured adhesives and resin-based composites polymerize based on how much light energy they receive, not on the irradiance (ie, the brightness of the light) measured at the light tip. The energy is reported in Joules/cm2. This value is calculated by multiplying the irradiance (mW/cm2) by the light exposure time (seconds). Depending on the shade and brand of composite resin, the minimum energy requirements to photopolymerize resins range from 6 J/cm2 to 24 J/cm2 for a 2-mm increment of composite. Thus, if the irradiance output from the light is 1,000 mW/cm2 and the manufacturer’s instructions say to cure for 20 seconds, this means that, under ideal circumstances, 20 J/cm2 should be delivered and this should adequately cure the resin. However, less energy will be delivered if the light tip is damaged, contaminated with resin, or is some distance from the tooth.
Most dentists and dental assistants have never been trained in the art and science of light-curing. Many clinical technique articles typically only mention to “light-cure for xx seconds.” Using an innovative device, the MARC® Patient Simulator (Managing Accurate Resin Curing; BlueLight Analytics, http://www.curingresin.com), practitioners can now better understand how to optimally light-cure restorations.
MARC is a laboratory-grade light-curing energy measurement device with sensors that measure the irradiance and wavelength of light energy received by simulated restorations in a typodont head. The irradiance delivered to these simulated restorations is collected and displayed in real time by a chairside computer. Whether the dental equipment‘s users are dentists, dental hygienists, dental assistants, or dental students, MARC provides operators with immediate feedback on how to optimize their technique. MARC quickly shows users how even small changes in technique can have a significant impact on the ability to deliver sufficient light energy to a resin restoration. The obvious, but often overlooked, importance of safely watching what you are doing when light-curing can be easily demonstrated using MARC.
Providing adequate energy from the curing light is a key factor to the success of resin-based composite restorations. In many dental practices, the dental assistant has the primary responsibility to maintain the curing light and to cure the restorations placed by the dentist. Do not take light-curing for granted—pay attention to this vital step. Following the guidelines presented in this article will ensure safe and optimum photopolymerization of the restorations being placed in your practice. Also, by taking routine precautions such as the use of orange-colored eye protection and blue-light–blocking shields on the curing light tip, the chairside assistant and the clinician can protect their vision.