In the natural world we are surrounded by photosynthesis, but probably seldom give this amazing phenomenon any extended thought. So also, dental clinicians and scientists have become so used to the process of photo-polymerization that it is taken for granted. Descriptions of complex restorative procedures can include the throw-away line: “…and then you light cure”.
The International Standards Committee TC106 has a remit of considering both Dental Materials and Devices . Certainly the critical and sometimes unique devices employed alongside dental materials include Light Curing Units (LCUs) or ‘Powered Polymerization Activators’, as ISO quaintly designates them. For many years I served on the ISO working group endeavoring to develop standards for LCUs. This was as much a political as a scientific and technological task, and the working group Convenor, Dr. P.L. Fan, had to be a diplomat as well as a scientist. In the event, the development of a standard for the classic QTH (quartz tungsten halogen) LCUs was somewhat overtaken by the arrival of dental LCUs based on LED technology and a second standard had to be written or adapted for these. I had the privilege of being shown the very first prototype LED unit for dental light curing. This was a small hand-torch sized unit developed by the innovation and initiative of two good friends: Dr. Robin Mills and Prof. Dr. Klaus Jandt, then working at the University of Bristol School of Dentistry in the UK. These authors provide a detailed history of the origins of LED units for dental photo-polymerization in the present issue . This contribution adds significantly to the knowledge of this area – a recent focus of this journal .
Jandt and Mills made a series of milestone academic contributions, backed up by Patents, to this subject of LED curing. These included not only the first published proposal for dental LED application, but also critically the first experimental demonstrations of the equivalence and then the eventual superiority of LED arrays to QTH sources. Of course, much depended on the development of LEDs for wider industrial applications; so someone else would eventually have made the connection with dentistry. But the historical fact remains that it was Jandt and Mills who made the definitive connection with their minds and experimental handiwork operating in tandem.
More recent developments in high power LEDs have raised a host of new issues, as discussed in several key symposia and publications. These include the non-uniform output of many light tips, where multiple LED chips are deployed in poly-wave LEDs, the advent of extreme high power LCUs and the quest for ultra-short irradiation times, together with the popularity of ‘bulk fill’ resin-composites and their need for enhanced depth-of-cure.
Along with the technical characteristics of LED LCUs and the further development of photoinitiators, there remains the critical role of the operator. Educational systems, notably the MARC™ system, developed by Richard Price and commercially available from BlueLight Analytics ( www.curingresin.com ), enable clinician light curing technique to be evaluated and improved, alongside detailed appraisal of their LCU equipment. All of this educational effort requires teamwork on the part of dental material scientists to raise awareness of the complexity, subtlety – and even the elegant beauty – of the photopolymerization process. As Michael Faraday said, with reference to his lectures on combustion to young audiences at the Royal Institution in London: “God give them brains to be surprised!” .