In 1832, the last words of the German genius, Johann Wolfgang von Goethe, were Mehr Licht (more light). This was either a plea for increased enlightenment or – more prosaically – “Do open the shutter of the bedroom so that more light may enter”!
Either way, the thought resonates with preoccupations in the Dental Materials community about achieving more consistent clinical success with resin-composites by efficient and effective photo-polymerization or light curing. Such has been the concern of Professor Richard Price that he has organized two seminal international conferences on this theme at Dalhousie University, Halifax, Nova Scotia. The first, held in October 2012, was supported by the Canadian government. The second in May 2014 was supported by dental industry and attended by scientists and other experts from Universities and industrial companies. Another is forthcoming in June 2015.
Also during 2014, the Nobel Prize in Physics was awarded jointly to Isamu Akasaki, Hiroshi Amano and Shuji Nakamura for their development in the early 1990s of efficient blue light-emitting diodes. Through the foresight and inventiveness of Jandt and Mills, these were then introduced quite rapidly into dentistry for LED light-curing units (LCUs) .
As we have noted previously , the energy-efficient but relatively narrow band width of LED light sources creates some problems for effective photo-initiation of cure through the challenge of matching output spectra of LCUs to some photo-initiator (PI) absorption spectra. Moreover, the shorter-wavelength violet light from polywave LCUs is somewhat less efficient at penetrating deeply into composite materials than blue wavelengths. Added to this, there is the complexity of uneven light-beam-profiles emerging from a number of LCU optic tips, particularly those mass-produced with poor design, safety features and quality control.
During the 2014 Dalhousie conference the goal was to achieve consensus on a number of issues. Firstly, it was helpful to adopt standard scientific nomenclature for physical quantities and units as expressed in Table 1 .
|Radiant exposure||Joule per square centimeter||J/cm 2|
|Radiant energy density||Joule per cubic centimeter||J/cm 3|
|Radiant flux or power||Watt||W or J/s|
|Radiant exitance/emittance||milliWatt per square centimeter||mW/cm 2|
|(Incident) irradiance||milliWatt per square centimeter||mW/cm 2|
|Spectral power||milliWatt per nanometer||mW/nm|
|Spectral irradiance||milliWatt per square centimeter per nanometer||mW/cm 2 /nm|