Ability of short exposures from laser and quad-wave curing lights to photo-cure bulk-fill resin-based composites

The power of light – From dental materials processing to diagnostics and therapeutics

“…Appropriate radiant exposure (the total energy delivered per unit area [J/cm 2 ] given by irradiance [W/ cm 2 ] × exposure time [s]) is required to adequately cure any photocurable polymer-based composite restoration. For these reasons, both the photoinitiator system [12][13][14][15][16][17][18][19][20][21][22][23][24][25] and the dental LCU [6,[26][27][28][29][30][31][32][33][34][35][36] have also been subject to much research and development, particularly with the introduction of new shorter wavelength, more efficient and faster reacting photoinitiators over the last two decades. The diversity in photoinitiator chemistry and light curing technologies has also led to guidelines for proper selection, maintenance and use of LCUs to be published [37][38][39][40].…”

“…Nevertheless, with lasers and laser modulation becoming more affordable, the most modern developments using diode lasers also exploit this trend and aim to further reduce curing time (1 s for 2.5 mm) through much higher power outputs (~1.4-2.0 W) and supposedly provide more consistent dispersion of energy and power at any distance (e.g. Monet, introduced in 2021) with the manufacturers claiming more reliable, more homogenous and complete cure through depth [29,30,34,45,95]. Indeed, these claims need to be confirmed and only likely to be valid under certain conditions due to limitations in materials chemistry and physics which suggest that the process of curing dental materials is a quantum process and strictly not dependent on the energy delivered to the surface [60,94].…”

“…Indeed, these claims need to be confirmed and only likely to be valid under certain conditions due to limitations in materials chemistry and physics which suggest that the process of curing dental materials is a quantum process and strictly not dependent on the energy delivered to the surface [60,94]. Despite this, modern lights that allegedly deliver high energy using high irradiances actually deliver less energy to materials in short 1-3 s exposures compared with 20 s exposures from LCUs delivering 1,000 mW/ cm 2 (a 20× increase in irradiance, that is 20,000 mW/cm 2 would be needed to even match the energy delivered of the latter for a 1 s cure) [34]. Nonetheless, Rocha et al [30] tested the depth of cure of several market leading conventional and bulk fill materials (A2 shade) using a laser diode and demonstrated a depth of cure of at least 1.5 mm in 1 s. This is likely due to optimised light-material interactions that improve light transmission and curing efficiency.…”

“…The sequential activation of different diode wavelength combinations throughout the irradiation cycle in 'full scan' mode allows the four different diodes to deliver a broad spectral output between 390 and 510 nm, supposedly allowing cure of all photocurable dental polymer-based materials, irrespective of photoinitiator chemistry with reportedly good conversion at depth while minimising heating effects [38]. Another recently marketed light is equipped with so called 'Quadwave' , technology, which uses four different wavelengths (UV -405 nm, blue -480 nm, red -640 nm and NIR -860 nm) to deliver a pink light that supposedly enhances curing performance (Figure 10B) [34,100]. The manufacturers claim that increased polymerisation is achieved by the NIR wavelengths, presumably through the increased heating as reported in a pulpal temperature rise in vitro study when low and high viscosity bulk fill composites were cured for 20 s compared with a laser diode and other contemporary LED LCUs used in standard modes of ≤10 s [101].…”

Effects of LED Lights on Bulk Fill Resin Polymerization

“…Changes are also frequently made in the light sources, such as LED (light-emitting diode) that have characteristics such as wavelength, polymerizing temperature, and power density, which allow more effective polymerization of the resins (Lempel et al, 2019;Maucoski et al, 2023). The LED sources may be divided into the single-peak blue LED emitting units, producing a very narrow band of wavelengths centralized between 450 and 470 nm; and the polywave (blue /violet) light-polymerization units.…”