PHOTOPOLYMERIZED COMPOSITIONS AND LIGHT SOURCES FOR DENTAL PRACTICE (REVIEW)

The review presents an analysis of articles published for the period 2005-2021. in top-rated publications devoted to the research results in the field of creating light-curing (photopolymerizable) compositions for use in dental practice. The information concerning the main ingredients of the compositions: di (meth) acrylate monomers, fillers, pigments, and photoinitiators is summarized. A comparative assessment of light sources, which determine the curing efficiency of materials of such a functional purpose, is presented. The results of a patent search, in the PatentScope database, are presented. For the period 2000-2021. have been identified 692 patents, which are related to the creation of dental photopolymer composites.

INVESTIGATION OF LIGHT INTENSITY OF LIGHT CURING UNITS AFTER DIFFERENT PERIODS OF USE

Quartz-tungsten halogen light curing units (LCUs) have been the main source of light for the polymerization of resin based composites (RBCs) for several decades. Since the beginning of the 20th century, however, their use has been reduced due to the invention and improvement of LED LCUs. Various factors can cause a decrease in the light intensity of LED LCUs, one of which is diode aging. The aim of the present paper is to study the change in light intensity of LCUs after different periods of intensive use. For this purpose, the light intensity of 94 regularly used LED LCUs aged between 1 and 10 years was measured with a digital radiometer. The devices were used in conventional mode with maximum light intensity. It was found that regardless of the type and model of LCU, there is a direct relationship between the time of use and light intensity - the longer the operation period of a device is and the more used it is, the lower its intensity is. The decrease in light intensity as devices age is different for different models, as well as for different devices of the same model. In the studied LCUs with a 10-year period of use, 77.5% have light intensity lower than the required minimum of 400 mW/cm2, which makes them unusable. It can be concluded that dentists should regularly monitor and measure the light intensity of their LCUs, especially as they age, to ensure the longevity of their restorative procedures.

Influence of Tip Diameter and Light Spectrum of Curing Units on the Properties of Bulk-Fill Resin Composites

Objective The aim of this study was to evaluate the influence of different light-curing units (LCUs) with distinct tip diameters and light spectra for activating bulk-fill resins. Materials and Methods The specimens (n = 10) were made from a conventional composite (Amaris, VOCO) and bulk-fill resins (Aura Bulk Fill, SDI; Filtek One, 3M ESPE; Tetric Bulk Fill, Ivoclar Vivadent) with two diameters, 7 or 10 mm, × 2 mm thickness. Following 24 hours of specimen preparation, the degree of conversion (DC) was evaluated using the Fourier-transform infrared unit. Knoop hardness (KHN) readings were performed on the center and periphery of the specimens. Data were assessed for homoscedasticity and submitted to one-way and three-way analysis of variance followed by the Tukey's and Dunnett's tests, depending on the analysis performed (α = 0.05). Results LCUs and specimen diameter significantly affected the DC. The Tetric Bulk Fill provided increased DC results when light-cured with Valo (54.8 and 53.5%, for 7 and 10 mm, respectively) compared with Radii Xpert (52.1 and 52.9%, for 7 and 10 mm, respectively). No significant differences in KHN results were noted for the conventional resin composite (Amaris) compared with LCUs (p = 0.213) or disc diameters (p = 0.587), but the center of the specimen exhibited superior KHN (p ≤ 0.001) than the periphery. Conclusion The light spectrum of the multipeak LCU (Valo) significantly increased the DC and KHN of the bulk-fill resin composite with additional initiator to camphorquinone (Tetric Bulk Fill) compared with the monowave LCU (Radii Xpert). The tip size of the LCUs influenced the performance of some of the resin composites tested.

Development of a New Formulation Based on In Situ Photopolymerized Polymer for the Treatment of Spinal Cord Injury

Spinal Cord Injury (SCI) promotes a cascade of inflammatory events that are responsible for neuronal death and glial scar formation at the site of the injury, hindering tissue neuroregeneration. Among the main approaches for the treatment of SCI, the use of biomaterials, especially gelatin methacryloyl (GelMA), has been proposed because it is biocompatible, has excellent mechanical properties, favoring cell adhesion and proliferation. In addition, it can act as a carrier of anti-inflammatory drugs, preventing the formation of glial scars. The present work presents the development and in situ application of a light-curing formulation based on GelMA containing a natural extract rich in anti-inflammatory, antioxidant and neuroprotective substances (hydroalcoholic extract of red propolis—HERP) in an experimental model of SCI in rats. The formulations were prepared and characterized by time of UV exposition, FTIR, swelling and degradation. The hydrogels containing 1 mg/mL of HERP were obtained by the exposure to UV radiation of 2 μL of the formulation for 60 s. The locomotor evaluation of the animals was performed by the scale (BBB) and demonstrated that after 3 and 7 days of the injury, the GelMA-HERP group (BBB = 5 and 7) presented greater recovery compared to the GelMA group (BBB = 4 and 5). Regarding the inflammatory process, using histomorphological techniques, there was an inflammation reduction in the groups treated with GelMA and GelMA-HERP, with decreases of cavitation in the injury site. Therefore, it is possible to conclude that the use of GelMA and GelMA-HERP hydrogel formulations is a promising strategy for the treatment of SCI when applied in situ, as soon as possible after the injury, improving the clinical and inflammatory conditions of the treated animals.

Additive Manufacturing of a Special-Shaped Energetic Grain and Its Performance

In order to solve the problems of the complicated forming process, poor adaptability, low safety, and high cost of special-shaped energetic grains, light-curing 3D printing technology was applied to the forming field of energetic grains, and the feasibility of 3D printing (additive manufacturing) complex special-shaped energetic grains was explored. A photocurable resin was developed. A demonstration formula of a 3D printing energetic slurry composed of 41 wt% ultra-fine ammonium perchlorate (AP), 11 wt% modified aluminum (Al), and 48 wt% photocurable resin was fabricated. The special-shaped energetic grains were successfully 3D printed based on light-curing 3D printing technology. The optimal printing parameters were obtained. The microstructure, density, thermal decomposition, combustion performance, and mechanical properties of the printed grain were characterized. The microstructure of the grain shows that the surface of the grain is smooth, the internal structure is dense, and there are no defects. The average density is 1.606 g·cm−3, and the grain has good uniformity and stability. The thermal decomposition of the grain shows that it can be divided into three stages: endothermic, exothermic, and secondary exothermic, and the Al of the grain has a significant catalytic effect on the thermal decomposition of AP. The combustion performance of the grain shows that a uniform flame with a one-way jet is produced, and the average burning rate is 5.11 mm·s−1. The peak pressure of the sample is 45.917 KPa, and the pressurization rate is 94.874 KPa·s−1. The analysis of the mechanical properties shows that the compressive strength is 9.83 MPa and the tensile strength is 8.78 MPa.

Hardness investigation of conventional, bulk fill and flowable dental composites

Purpose: of the present paper is to investigate the micro-hardness of three types of resin-based composites – conventional, bulk fill and flowable. Design/methodology/approach: Cylindrical specimens with a diameter of 5 mm and thicknesses of 2, 3 and 4 mm were made from each composite. They were light cured for 20, 40 and 60 s with light intensity of 600, 1000 or 1500 mW/cm2. The Vickers micro-hardness was measured on the top and bottom surface of the specimens. Findings: The highest micro-hardness was measured in bulk fill composite, followed by conventional and the lowest was measured in the flowable one. Increasing the light intensity leads to increase of the micro-hardness on both surfaces of the three composites. The increase of the irradiation time results in increase of the micro-hardness mainly on the bottom surface of the composites. The change of the layer thickness influences the conventional and the flowable composites and almost does not affect the hardness of the bulk fill composite. Research limitations/implications: The limitations of this study concerns to the values of the light intensity, which are defined by the light curing unit (LCU) used. There are many LCUs on the market; consequently, constant investigations of dental composites micro-hardness are needed. Practical implications: The investigation of the micro-hardness of the three types of composites in different modes would be very helpful for clinicians to obtain successful polymerization of composite restorations in their everyday practice. Originality/value: The micro-hardness of three types resin-based dental composites – conventional, bulk fill and flowable is investigated and compared in varying of three mode parameters – light intensity, curing time and layer thickness.

Effect of Light-Sources and Thicknesses of Composite Onlays on Micro-Hardness of Luting Composites

The aim of this study was to compare three different light-curing-units (LCUs) and determine their effectiveness in the adhesive cementation of indirect composite restorations when a light-curing resin cement is used. Two resin composites were selected: Enamel Plus HRI (Micerium) and AURA (SDI). Three thicknesses (3 mm, 4 mm and 5 mm) were produced and applied as overlays and underlays for each resin composite. A standardized composite layer was placed between underlay and overlay surfaces. Light curing of the resin-based luting composites was attained through the overlay filters using LCUs for different exposure times. All specimens were allocated to experimental groups according to the overlay thickness, curing unit and curing time. Vickers Hardness (VH) notches were carried out on each specimen. Data were statistically evaluated. The curing unit, curing time and overlay thickness were significant factors capable of influencing VH values. The results showed significantly decreased VH values with increasing specimen thickness (p < 0.05). Significant differences in VH values were found amongst the LCUs for the various exposure times (p < 0.05). According to the results, a time of cure shorter than 80 s (with a conventional quartz–tungsten–halogen LCU) or shorter than 40 s (with a high-power light-emitting diode (LED) LCU) is not recommended. The only subgroup achieving clinically acceptable VH values after a short 20 s curing time included the 3 mm-thick overlays made out of the AURA composite, when the high-power LED LCU unit was used (VH 51.0). Composite thickness has an intense effect on polymerization. In clinical practice, light-cured resin cements may result in insufficient polymerization for high thickness and inadequate times. High-intensity curing lights can attain the sufficient polymerization of resin cements through overlays in a significantly shorter time than conventional halogen light.