Effectiveness of photopolymerization in composite resins using a novel 445-nm diode laser in comparison to LED and halogen bulb technology

Evaluation of tooth color change after a bleaching process with different lasers

The aim of this in vitro study was to evaluate the efficiency of diode laser-activated bleaching systems for color change of teeth. 75 extracted teeth were studied in five different bleaching protocols. Group 1: diode laser 445 nm, 320 µm fiber, 0.5W, continuous wave mode, dose 53 J/cm2. Group 2: diode laser 970 nm, 320 µm fiber, 1W, continuous wave mode, dose 106.10 J/cm2. Group 3: diode laser 940 nm, bleaching handpiece, 7W, continuous wave mode, dose 105 J/cm2. Group 4: diode laser 940 nm, 300 µm fiber, 2W, continuous wave mode, dose 47.16 J/cm2. Group 5: bleaching process without laser activation. In groups 1, 2 and 5, teeth were bleached with Perfect Bleach Office + and in groups 3 and 4, LaserWhite20 bleaching gel was used. Tooth color was determined immediately after the bleaching process using a spectrophotometer. Color change data on the CIE L * a * b* system was analyzed statistically by the one-way ANOVA and Tukey's HSD test. All bleaching procedures resulted in a change of color. All laser groups (∆E * ab > 3) have statistically larger ∆E * ab values than the control group (∆E * ab = 0.73) (p < 0.05). The diode laser 445 nm has the largest ∆E * ab value (∆E * ab = 4.65) and results in a significantly higher color difference than all other groups. In terms of color score difference in VITA Shades, all laser-activated groups lead to a lightening effect while the control group leads to only a slight lightening effect. The diode laser 445 nm produced the greatest color difference. Laser-activated bleaching is more effective than conventional bleaching without light activation. The diode laser 445 nm performs best in this in vitro study.

Blue Laser for Polymerization of Bulk Fill Composites: Influence on dentin bond strength and temperature rise during curing and co-curing method

Blue diode lasers are alternative curing devices for dental composites. The aim of this study was to investigate the influence of blue diode laser polymerization on shear bond strength of bulk fill composites to human dentin and temperature rise during two types of polymerization. Composite cylinders of SDR Plus(SDR) and Ever X Flow(EX) were bonded to dentin slabs using Adhese Universal and curing devices blue diode laser (449 nm, 1.6 W) and Power Cure LED. For each material and curing device there were two polymerization approaches: 1)conventional: separate curing of adhesive; 2)co-curing: simultaneous adhesive and composite curing. Polymerization modes for each material in conventional and co-curing(c) approach were: blue laser 2000 mW/cm2 for 5 s (L5 and L5c); blue laser 1000 mW/cm2 for 10 s (L10 and L10c); Power Cure 2000 mW/cm2 for 5 s (LED5 and LED5c); Power Cure 1000 mW/cm2 for 10 s (LED10 and LED10c). Temeperature was measured using thermal vision camera. For SDR, the highest bond strength was 24.3 MPa in L10c, and the lowest 9.2 MPa in LED5c. EX exhibited the highest bond strength(21.3 MPa) in LED5, and the lowest in L5(7.7 MPa). The highest temperature rise for SDR was in L10 and L5 (7.3 and 7.2 °C), and the lowest in LED5(0.8 °C). For EX, the highest temperature rise was in L5 (13.0 °C), and the lowest in LED5 (0.7 °C). Temperature rise was higher during blue laser polymerization, especially at high intensity and with conventional curing. Preferable blue laser curing mode is co-curing at 1000mW/cm2 for 10 s.

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.

A timeline of surgical lighting - Is automated lighting the future?

High quality surgical lighting is central to successful performance in the operating room and therefore to both patient care and treatment. This article discusses the origins of surgical lighting from the 1800s to today, with a focus on the four main forms. Their uses, advantages, and disadvantages are evaluated in an effort to identify the improvements required to improve today's current state of surgical lighting. Whilst these four mainstream types have served well for the past thirty years, the literature exposes opportunities for improvement and can be used to guide the pathway to transition from manual conventional methods to a more automated lighting (AL) approach. The concept of AL has been proposed using established and known technical approaches such as artificial intelligence (AI), 3D sensor tracking algorithms and thermal imaging. Whilst AL seems incredibly promising, further focused research must be undertaken to maximise its' effectiveness and allow for successful integration of this new technology into operating rooms today.

Effect of a Diode Laser (445 nm) on Polymerization Efficiency of a Preheated Resin Composite Used for Luting of Indirect Composite Restorations

PURPOSE

The aim of this study was to evaluate the polymerization efficiency of a preheated resin composite used as a luting agent for indirect restorations light-cured by a blue diode laser (445 nm).

METHODS

Bronze molds were used to prepare cylindrical specimens of a laboratory composite (Ceramage) with dimensions 2, 3, and 4 mm in height and 8 mm in diameter. The molds had additional height of 120 μm for the placement of the preheated resin composite. A nanohybrid resin composite (Enamel Plus HRi) was preheated at 55°C to use as a luting agent. Photopolymerization was followed for 20 seconds using three light sources: a diode laser emitting at 445 nm (SiroLaser Blue) and two light-emitting diode (LED) units (Bluephase Style and Valo). Degree of conversion (DC) of the preheated resin composite was evaluated using Fourier transform infrared spectroscopy.

RESULTS

The results indicated that the main effects of the analysis were significant for both material thickness (p<0.001) and polymerization method (p<0.001). The preheated resin composite was not polymerized under 4-mm-thick specimens, independent of the light-curing unit. For 2-mm material thickness, there was no difference among the three light-curing units (p=0.383), while 3-mm Bluephase Style presented very low DC.

CONCLUSIONS

Diode laser (445 nm) achieved better polymerization efficiency at the same fluence compared to the LED unit at 3-mm depth, implying a better mechanical behavior and potential improved adhesion of the luting material to dentin.

Temperature changes and hardness of resin-based composites light-cured with laser diode or light-emitting diode curing lights

The temperature and Vickers Hardness (VH) at the top and bottom surfaces of three resin-based composites (RBCs) were measured when light-cured using five light-curing units (LCUs). The spectrum, power, and energy delivered to the top of the RBCs and transmitted through the RBCs were measured. Starting at 32℃, the temperature rise produced by the Monet Laser (ML-1 s and 3 s), Valo Grand (VG-3 s and 10 s), DeepCure (DC-10 s), PowerCure, (PC-3 s and 10 s) and PinkWave (PW-10 s) were measured at the bottom of specimens 2 mm deep × 6 mm wide made of Filtek Universal A2, Tetric Evoceram A2 and an experimental RBC codenamed Transcend UB. The VH values measured at the top and bottom of these RBCs were analyzed using ANOVA and Scheffe's post hoc test (p < 0.05) to determine the effects of the LCUs on the RBCs. The transmitted power from the ML was reduced by 77.4% through 2 mm of Filtek Universal, whereas light from PW decreased by only 36.8% through Transcend. The highest temperature increases from the LCU combined with the exothermic reaction occurred for Transcend, and overall, no significant differences were detected between Filtek Universal and Tetric Evoceram (p = 0.9756). Transcend achieved the highest VH values at the top and bottom surfaces. The PinkWave used for 10 s produced the largest temperature increase (20.2℃) in Transcend. The Monet used for 1 s produced the smallest increase (7.8℃) and the lowest bottom:top VH ratios.

In-vitro pulpal temperature increases when photo-curing bulk-fill resin-based composites using laser or light-emitting diode light curing units

OBJECTIVE

To evaluate the in vitro pulpal temperature rise (ΔT) within the pulp chamber when low- and high-viscosity bulk-fill resin composites are photo-cured using laser or contemporary light curing units (LCUs).

MATERIALS AND METHODS

The light output from five LCUs was measured. Non-retentive Class I and V cavities were prepared in one upper molar. Two T-type thermocouples were inserted into the pulp chamber. After the PT values reached 32°C under simulated pulp flow (0.026 mL/min), both cavities were restored with: Filtek One Bulk Fill (3 M), Filtek Bulk Fill Flow (3 M), Tetric PowerFill (Ivoclar Vivadent), or Tetric PowerFlow (Ivoclar Vivadent). The tooth was exposed as follows: Monet Laser (1 and 3 s), PowerCure (3 and 20 s), PinkWave (3 and 20 s), Valo X (5 and 20 s) and SmartLite Pro (20 s). The ΔT data were subjected to one-way ANOVA followed by Scheffe's post hoc test.

RESULTS

Monet 1 s (1.9 J) and PinkWave 20 s (30.1 J) delivered the least and the highest amount of energy, respectively. Valo X and PinkWave used for 20 s produced the highest ΔT values (3.4-4.1°C). Monet 1 s, PinkWave 3 s, PowerCure 3 s (except FB-Flow) and Monet 3 s for FB-One and TP-Fill produced the lowest ΔT values (0.9-1.7°C). No significant differences were found among composites.

CONCLUSIONS

Short 1- to 3-s exposures produced acceptable temperature rises, regardless of the composite.

CLINICAL SIGNIFICANCE

The energy delivered to the tooth by the LCUs affects the temperature rise inside the pulp. The short 1-3 s exposure times used in this study delivered the least amount of energy and produced a lower temperature rise. However, the RBC may not have received sufficient energy to be adequately photo-cured.

The Effect of Femtosecond Laser Irradiation and Plasmon Field on the Degree of Conversion of a UDMA-TEGDMA Copolymer Nanocomposite Doped with Gold Nanorods

In this work, the effects of femtosecond laser irradiation and doping with plasmonic gold nanorods on the degree of conversion (DC) of a urethane dimethacrylate (UDMA)–triethylene glycol dimethacrylate (TEGDMA) nanocomposite were investigated. The UDMA-TEGDMA photopolymer was prepared in a 3:1 weight ratio and doped with dodecanethiol- (DDT) capped gold nanorods of 25 × 75 or 25 × 85 nm nominal diameter and length. It was found that the presence of the gold nanorods alone (without direct plasmonic excitation) can increase the DC of the photopolymer by 6–15%. This increase was found to be similar to what could be achieved with a control heat treatment of 30 min at 180 °C. It was also shown that femtosecond laser impulses (795 nm, 5 mJ pulse energy, 50 fs pulse length, 2.83 Jcm⁻² fluence), applied after the photopolymerization under a standard dental curing lamp, can cause a 2–7% increase in the DC of undoped samples, even after thermal pre-treatment. The best DC values (12–15% increase) were obtained with combined nanorod doping and subsequent laser irradiation close to the plasmon resonance peak of the nanorods (760–800 nm), which proves that the excited plasmon field can directly facilitate double bond breakage (without thermoplasmonic effects due to the short pulse length) and increase the crosslink density independently from the initial photopolymerization process.

Contributions of photochemistry to bio-based antibacterial polymer materials

Surgical site infections constitute a major health concern that may be addressed by conferring antibacterial properties to surgical tools and medical devices via functional coatings. Bio-sourced polymers are particularly well-suited to prepare such coatings as they are usually safe and can exhibit intrinsic antibacterial properties or serve as hosts for bactericidal agents. The goal of this Review is to highlight the unique contribution of photochemistry as a green and mild methodology for the development of such bio-based antibacterial materials. Photo-generation and photo-activation of bactericidal materials are illustrated. Recent efforts and current challenges to optimize the sustainability of the process, improve the safety of the materials and extend these strategies to 3D biomaterials are also emphasized.

Use of Blue and Blue-Violet Lasers in Dentistry: A Narrative Review

Introduction: Blue and blue-violet diode lasers (450 and 405 nm) seem to represent an interesting approach for several clinical treatments today. The aim of this narrative review is to describe and comment on the literature regarding the utilization of blue and blue-violet lasers in dentistry. Methods: A search for "blue laser AND dentistry" was conducted using the PubMed database, and all the papers referring to this topic, ranging from 1990 to April 2020, were analyzed in the review. All the original in vivo and in vitro studies using 450 nm or 405 nm lasers were included in this study. All the articles on the LED light, laser wavelengths other than 405 and 450 nm and using lasers in specialties other than dentistry, as well as case reports, guideline papers and reviews were excluded. Results: From a total of 519 results, 47 articles met the inclusion criteria and were divided into 8 groups based on their fields of application: disinfection (10), photobiomodulation (PBM) (4), bleaching (1), resin curing (20), surgery (7), periodontics (1), endodontics (1) and orthodontics (3). Conclusion: Blue and blue-violet diode lasers may represent new and effective devices to be used in a large number of applications in dentistry, even if further studies will be necessary to fully clarify the potentialities of these laser wavelengths.

The effect of halogen bulb and light-emitting diode light curing units on temperature increase and fibroblast viability

Background: This study aimed to compare the temperature increase produced by halogen bulb (HAL) and light-emitting diode (LED) light curing units (LCUs) by irradiating dentin discs (0.5 mm and 1 mm thickness), and to evaluate their cytotoxic effects on fibroblast culture in the presence of dentin discs due to the increasing demand on resin composite restorations and teeth bleaching for esthetic purposes. Methods: A total of 20 bovine incisors were used to obtain dentin discs and divided into four experimental groups (n=10): HAL0.5: irradiation with halogen-tungsten bulb Curing Light XL 3000 at an intensity of 470 mW/cm2 over a dentin disc of 0.5 mm; LED0.5: irradiation with LED Optilight Max (GNATUS- Ribeirão Preto, SP, Brazil) at an intensity of 1200 mW/cm2 over a dentin disc of 0.5 mm; HAL1: irradiation as in HAL0.5 but over a dentin disc of 1 mm; LED1: irradiation as in LED0.5 but over a dentin disc of 1 mm. The temperature increase was measured using a digital thermometer and the cytotoxicity was evaluated using an MTT assay with a mouse fibroblast cell line (L929). Parametric Data were analyzed by ANOVA and Tukey and non-parametric data were analyzed by Kruskal Wallis with Conover-Iman for non-parametric data (all with α=0.05). Results: A significant statistical difference was found between the groups HAL0.5 and HAL1 and both were different of LED0.5 and LED1 which presented higher temperature. All the experimental groups were different of the control group (without irradiation), and promoted reduction of cellular viability. Conclusions: HAL LCU promoted a lower temperature change in the dentin compared to LED, regardless of the dentin thickness (0.5-1 mm). Both HAL and LED LCUs decreased fibroblast viability; however, LED promoted more significant cytotoxic effects.

Evaluation of photopolymerization efficacy and temperature rise of a composite resin using a blue diode laser (445 nm)

The purpose of this study was to evaluate the photopolymerization efficacy of a diode laser (445 nm) for use with a composite containing camphorquinone and to estimate the safety of the method related to the temperature rise. Five cylindrical composite specimens were prepared for each thickness: 1, 2, and 3 mm. Three light-curing modes were investigated: a light emitting diode (LED) unit and a diode laser (445 nm) with output powers at 0.7 W or 3 W. Evaluation of the polymerization efficacy was based on Vickers hardness measurements, and the highest temperatures at the bottom of the specimens were recorded using a K-type thermocouple. The highest microhardness was observed after the diode laser curing operating at 3 W. A comparison of the microhardness of the 0.7 W laser cured specimens with the LED cured specimens showed a statistically significant difference in favor of the laser curing. Laser curing operating at 3 W resulted in extremely high temperatures. Laser curing at 0.7 W resulted in statistically significantly higher maximum temperatures than did LED curing for both 1 mm thick (52.9°C against 45.4°C) and 3 mm thick (43.6°C against 40.9°C) specimens. Diode laser (445 nm) may be an alternative for photopolymerization of composite materials and may result in a higher degree of conversion and depth of cure of composites than what has been seen with LED curing units when they emit at the same energy density.

The effect of laser-activated bleaching with 445 nm and 915 nm diode lasers on enamel micro-hardness; an in vitro study

BACKGROUND

The appearance of the teeth is of great importance to patients, particularly tooth color. In recent years, tooth whitening has been one of the most popular ways to restore tooth color. Bleaching gels can be affected by heat, light or laser, which can improve its effects. This study intends to examine the effects of two different wavelengths of diode laser (445 & 915 nm) after the bleaching process, on the enamel micro-hardness.

METHODS

A total of 65 caries-free humans third molars were randomly divided into five groups (N = 13): first group: bleaching gel activated with 915 nm diode laser (1.5 W), second: bleaching gel activated with 915-nm (2.5 W), third: bleaching gel activated with 445-nm (1 W), fourth: bleaching gel activated with 445-nm (1.5 W), fifth (control group): bleaching gel without laser activation. Micro-hardness test (Vickers test) was performed before and after the treatment. The data were submitted to repeated measurement ANOVA and Tukey's HSD post hoc test (α = 0.05).

RESULTS

Enamel micro-hardness did not change significantly in groups 3 and 4 but decreased in groups 1 and 2. Group 2 showed the most reduction in micro-hardness. There were no significant changes in the control group.

CONCLUSION

According to the results of this study, 445 nm Diode laser did not reduce enamel micro-hardness, making it suitable for bleaching treatments. However, more studies are required to consider other factors, such as color changes and pulp temperature.