ReviewA brief history of LED photopolymerization
Introduction
The introduction of resin-based dental materials near the middle of the last century was a revolution in restorative dentistry. Dental composites are esthetically pleasing since they possess a tooth-like appearance, are stable within the oral environment, are relatively easy to handle and set on command via self curing or light curing.
Today, almost all commercial dental composites utilize photopolymerization reactions initiated by blue visible light. Light curing units (LCUs) based on different physical principles, such as quartz-tungsten-halogen (QTH) bulbs, laser, plasma arc lights, and light emitting diodes (LEDs) are available. Nevertheless, LED LCUs are currently the standard devices in most modern dental practices.
In many cases, clinicians using LED LCUs on a daily basis are unaware of the physics and/or history of their development. This knowledge, however, is essential so that LED LCUs can be used to their full potential and are applied appropriately in any particular clinical situation.
In addition, there is currently no scientific review paper focusing on the LED photopolymerization of available dental materials. This review, therefore, addresses this need and is based mainly on peer-reviewed and frequently cited research articles in international journals available through the Web of Science. This current paper reviews the history of LED photopolymerization in the area of oral biomaterials/dental materials. Within this framework, the basic principles of LEDs, the history and evolution of commercial LED LCUs, the materials science of dental materials photopolymerized with LED LCUs, aspects of commercial LED LCUs as well as their clinical applications are discussed.
Section snippets
Basic physics and technology of LEDs
LEDs are a part of our daily lives. LED technology is applied in modern light sources for room lighting, car headlights and dashboards, traffic lights, state-of-the-art television flat screens or as LASER LEDs in CD or blue-ray DVD data/video storage equipment [1]. Compared to conventional light sources, LEDs are small and energy efficient. Hence, dental light curing units (LCUs) based on LEDs are relatively small and can be battery powered, using high performance nickel–metal hydride (NiMH) or
Materials science of dental materials photopolymerized with LED LCUs
There are several well-known examples in the history of science that show that change and new ideas are not always welcomed enthusiastically [20] and can be even opposed. This situation can be particularly the case if this change happens quickly and has the character of a paradigm shift. To some extent, this circumstance was also the case with the introduction of LED LCUs to photopolymerization of oral biomaterials. The authors recall submitting one of their first scientific papers reporting
Evolution of commercial LED LCUs
It was not until 2000 that the first commercial LED LCU became available: the LuxOMax LED LCU [46] was a large pen-like cordless battery-powered design using 7 discrete LEDs. The device had a tapered fused glass fiber light guide to concentrate the light output at the tip. The unit's irradiance measured 116 mW cm−2 [8]. The delay in bringing a commercial LED LCU into production was due to two main factors: the power output of the blue LEDs and their cost. The discrete blue LEDs used in these
Clinical aspects of LED LCUs
When commercial LED LCUs became available to dental practitioners after 2000, they slowly evolved and became serious contenders to challenge the dominance of QTH LCUs in clinical dentistry. It is natural for clinicians to want more powerful light-curing devices to reduce the time taken for a given procedure for patient comfort. LED LCUs can currently achieve irradiance values in excess of 3200 mW cm−2 [72]. This irradiance value in isolation is only an approximate guide of the clinical
Conclusions
The introduction of LED LCUs has revolutionized the photopolymerization of oral biomaterials. Until the introduction of LED LCUs, QTH lamp based LCUs were the standard curing devices in most dental practices. Due to the physical characteristics of the solid-state light emitting diodes, LED LCUs have almost entirely replaced QTH LCUs whose inherent problems include a decay of light output over time, blue light filter degradation, relatively limited time of life of the QTH source, high energy
Acknowledgement
We thank Dipl.-Phys. Matthias M.L. Arras, FSU Jena, for calculating the luminous intensity values of the LED and the QTH lamp.
References (88)
- et al.
Depth of cure and compressive strength of composites cured with blue light emitting diodes (LEDs)
Dental Materials
(2000) - et al.
The initiating radical yields and the efficiency of polymerization for various dental photoinitiators excited by different light curing units
Dental Materials
(2006) - et al.
Light emitting diode (LED) polymerisation of composites: flexural properties and polymerisation potential
Biomaterials
(2000) - et al.
Hardness evaluation of a dental composite polymerized with experimental LED-based devices
Dental Materials
(2001) - et al.
High power light emitting diode (LED) arrays versus halogen light polymerisation of oral biomaterials: Barcol hardness, compressive strength and radiometric properties
Biomaterials
(2002) - et al.
Pulp response to externally applied heat
Oral Surgery
(1965) - et al.
Polymerisation and light-induced heat of dental composites cured with LED and halogen technology
Biomaterials
(2003) - et al.
Photoinitiator dependent composite depth of cure and Knoop hardness with halogen and LED light curing units
Biomaterials
(2003) - et al.
Second generation LEDs for the polymerization of oral biomaterials
Dental Materials
(2004) - et al.
The influence of storage and indenter load on the Knoop hardness of dental composites polymerized with LED and halogen technologies
Dental Materials
(2004)