The light-curing unit: An essential piece of dental equipment

Abstract

Introduction: This article describes the features that should be considered when describing, purchasing and using a lightcuring unit (LCU). Methods: The International System of Units (S.I.) terms of radiant power or radiant flux (mW), spectral radiant power (mW/nm), radiant exitance or tip irradiance (mW/cm 2), and the irradiance received at the surface (also in mW/cm 2) are used to describe the output from LCU. The concept of using an irradiance beam profile to map the radiant exposure (J/cm 2) from the LCU is introduced. Results: Even small changes in the active tip diameter of the LCU will have a large effect on the radiant exitance. The emission spectra and the effects of distance on the irradiance delivered are not the same from all LCUs. The beam profile images show that using a single averaged irradiance value to describe the LCU can be very misleading. Some LCUs have 'hot spots' of high radiant exitance that far exceed the current ISO 10650 standard. Such inhomogeneity may cure the resin unevenly and may also be dangerous to soft tissues. Recommendations are made that will help the dentist when purchasing and then safely using the LCU. Conclusions: Dental manufacturers should report the radiant power from their LCU, the spectral radiant power, information about the compatibility of the emission spectrum from the LCU with the photoinitiators used, the active optical tip diameter, the radiant exitance, the effect of distance from the tip on the irradiance delivered, and the irradiance beam profile from the LCU.

Utilizing Light Cure Units: A Concise Narrative Review

“…LED LCUs also have a higher luminous efficacy in comparison to QTH [ 40 ], having light and solid-state emitters. LEDs are currently the most popular type of LCU [ 40 , 41 , 42 ].…”

“…Terms such as “power density”, “energy density” and “intensity” are often confusing to researchers and clinicians alike, because their definitions vary from paper to paper [ 37 ]. The radiant exposure, LCU output, and wavelength in nm received by the dental resin composite have frequently not been reported [ 45 ], which puts the validity of the clinical results from these studies under question [ 42 ]. This, in turn, has led to inadvertent spread of incorrect information about LCUs or dental polymer systems which are light-cured [ 46 ].…”

“…To standardize the description of light from the LCU, it is recommended that the International System of Units (S.I.) be used by manufacturing companies, researchers, and clinicians [ 42 ]. Table 1 displays the terms suggested for use by clinicians.…”

“…For RCs to cure adequately, the photo-initiators must be exposed to the correct wavelength of light. QTH LCUs emit a broad spectrum of both blue and violet light and are capable of activating all photo-initiators used in contemporary dental composites [ 42 ]. On the other hand, as mentioned previously, LEDs deliver a narrow range of wavelengths, with many of them not emitting light below 420 nm [ 44 ].…”

“…When using a single-peak LED, any initiators which need wavelengths below 420 nm are not activated. Multi-peak LEDs do deliver light below 420 nm, which should effectively activate all other commonly used photo-initiators [ 42 ].…”