Guidelines for the selection, use, and maintenance of LED light-curing units - Part 1

Abstract

Light curing is a critical step in the restorative process when using light-activated resin-based composites, but it is frequently not given the attention it deserves. The selection of a reliable light curing unit (LCU) that meets the practitioner's needs is an important equipment purchase. Using an inappropriate LCU may seriously compromise the quality of care without the practitioner realising their mistake until years later. The importance of the subject is reflected by the rapidly increasing use of light-cured composites and the decline in the use of amalgam. Many changes have occurred in the equipment and materials available for making light-cured restorations in the last twenty years. This article is part of a two-part series that will describe those changes and recommend guidelines for the selection, use, and maintenance of light emitting diode light-curing units (LED LCUs). This paper (Part 1) discusses terminology, clinical studies, the development of LCUs in dentistry, the aims of light-curing, and the need to deliver an adequate amount of energy. The interaction between light source and material is briefly described to demonstrate the complex nature of the resin photopolymerisation process.

What's new for the clinician? Summaries of and excerpts from recently published papers

“…Many modern dental practices have introduced CAD/CAM technology into their rooms and these have been shown in a number of studies to significantly improve the accuracy of prosthetic frameworks compared to conventional cast frameworks. 1 In the conventional workflow, half of any misfit is introduced during the impression procedure and production of the stone cast, while the other half occurs while manufacturing the prosthesis. 1 Although CAD-CAM improved the accuracy of the latter, the initial step in the workflow, taking an impression and pouring the cast, remained the same.…”

“…Light curing is a critical step in the restorative process when using light-activated resin-based composites, but it is frequently not given the attention it deserves 1 . Often, imprecise terms such as high-power, high-intensity or high-irradiance are used to describe a curing light.…”

“…The radiant exposure is the radiant energy applied to a given surface area over time (irradiance × time = energy/area = J/cm 2 ). 1 Unlike lasers, different dental LED LCUs (Light emitting diode [LED] light curing units [LCUs])vary greatly in the extent to which they are collimated or can maintain irradiance with distance and irradiance figures described by manufacturers are often inaccurate because they are almost universally established at zero source distance 1 which is not clinically relevant. Irradiance is greatly affected by the tip diameter and light dispersion with distance from the light tip.…”

“…Irradiance may also vary greatly across different regions of the light guide exit window. 1 The power output (in watts) from the unit is a more useful measure of how powerful the LCU is because a high irradiance can still be achieved simply by using a small tip. Dentists should recognise that the manufacturer-stated LCU irradiance value is rarely achieved when the LCU is positioned at a clinically relevant distance of 4 mm or more away from the resin.…”

“…Thus, the material minimum energy requirement of the resin is often not achieved when LCU manufacturer directions for use are followed. 1 Photopolymerization dominates using blue light of a wavelength between 380 and 500 nm and with an irradiance of >450 mW/cm 2 . During the last 10 years, LCUs employing LED technology have largely taken over from the older quartz-tungsten-halogen (QTH) devices.…”