Evaluation of a Novel "Quad" Wavelength Light Curing Unit

Thermography and conversion of fast-cure composite photocured with quad-wave and laser curing lights compared to a conventional curing light

OBJECTIVES

This study investigated effects of the different emittance-mode protocols from three light curing units (LCUs): (i) a Laser (Monet); (ii) a quad-wave (PinkWave); (iii) a conventional LED (Elipar S10) on the temperature rise (ΔT) and degree of conversion (DC) when photo-curing fast or conventional bulk-fill resin-based composites (RBC). The aim was to correlate ΔT and DC, and the radiant exposure delivered to RBC specimens.

METHODS

A 3D-printed resin mold of 4 mm depth was filled with two bulk-fill RBCs: Tetric PowerFill® (fast photo-polymerised composite) (TPF) or Tetric EvoCeram® Bulk-Fill (EVO). Three LCUs were used: (i) Monet laser for 1 s and 3 s (MONET-1 s, MONET-3 s); (ii) PinkWave quad-wave used for 3 s in Boost mode (PW-3 s) and for 20 s in standard mode (PW-20 s); (iii) Elipar S10 for 5 s (S10-5 s) and for 20 s in standard mode (S10-20 s). 2-dimensional temperature maps were obtained before, during and for 60 s after the LCU had turned off using a thermal imaging camera. Thermal changes were analysed at five depths: (0, 1, 2, 3, and 4 mm from the top surface of the RBC). The maximum temperature rise (Tmax) and the mean temperature rise (ΔT) were determined. Cylindrical-shaped specimens were prepared from each material using a stainless-steel split mold (4 × 4 mm) and light-cured with the same protocols. The DC was measured for 120 s and at 1 h after LCU had turned off using Fourier Transform Infrared Spectroscopy (FTIR). Data were analysed using Three-way ANOVA, One-way ANOVA, independent t-tests, and Tukey post-hoc tests (p < 0.05).

RESULTS

Radiant exposures delivered by the various irradiation protocols were between 4.5-30.3 J/cm2. Short exposure times from MONET-1 s and PW-3 s delivered the lowest radiant exposures (4.5 and 5.2 J/cm2, respectively) and produced the lowest ΔT and DC. The longer exposure times in the standard modes of PW-20 s, S10-20 s, and MONET-3 s produced the highest Tmax, ΔT, and DC for both composites. The ΔT range among composites at different depths varied significantly (31.7-49.9 °C). DC of TPF ranged between 30-65% and in EVO between 15.3-56%. TPF had higher Tmax, ΔT for all depths and DC compared to EVO, across the LCU protocols (p < 0.05), except for PW-20 s and MONET-3 s. The coronal part of the restorations (1-2 mm) had the highest ΔT. There was a positive correlation between ΔT and DC at 4-mm depth after 120 s SIGNIFICANCE: Longer, or standard, exposure times of the LCUs delivered greater radiant exposures and had higher DC and ΔT compared to shorter or high-irradiance protocols. The fast photo-polymerised RBC had comparatively superior thermal and conversion outcomes when it received a high irradiance for a short time (1-5 s) compared to the conventional Bulk-Fill RBC.

Real-time multispectral transmission of hard tooth tissues and dental composites with their heating

The objective of the study was to investigate the real-time transmission of Violet, Blue, Red and Near Infra-Red (NIR) irradiation through 2 or 4 mm thick dental composites and tooth tissue samples at varying positions of Light Curing Unit (LCU) with polymerization temperature monitoring.

METHODS

The composites tested were: Filtek Universal Restorative (FUR), Filtek One Bulk Fill (FBF), Tetric EvoCeram (TEC), Tetric Bulk Fill (TBF) and Tetric PowerFill (TPF). The new LCU Pinkwave (a four-wavelength source manufactured by Vista Apex, USA) was placed either centrally or eccentrically for 3 mm above the sample. A Fiber spectrometer detected irradiation and Infrared Thermal camera polymerization temperatures.

RESULTS

All eccentric LCU positions significantly weaken transmitted spectra for all composites in both thickness, jeopardizing Blue light. The LCU position did not affect transmitted irradiation for tooth tissues. The reduction in wavelength intensity when penetrating through thicker compared to thinner composite samples was 62%, 50% and 31% for Blue, NIR and Red, respectively, and 90%, 50% and 35% for tooth tissue samples, respectively. The temperature of bulk fill composites with additional photoinitiators rises faster. Eccentric LCU positions cause a significant decrease in both speed and the maximal value of temperature rise. Red and NIR irradiations contribute to the polymerization temperature.

SIGNIFICANCE

Tested LCU source cause considerable inhomogeneity in the emitted and transmitted spectra. Tooth tissues homogenize irradiation, but drastically attenuates it. Red light has better potential than Blue light concerning penetration and could be further investigated as the wavelength for activation of an adjusted photoinitiator.