Effect of angulation in different curing-light devices on color variation in composite resins

Effect of angulation in different curing-light devices on color variation in composite resins | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Effect of angulation in different curing-light devices on color variation in composite resins Mariana Menezes Vaz Fernandes, Ana Paula Menezes Vaz Queiroz Almeida, and 3 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-6475219/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Objective – The present study aimed to evaluate the influence of the tip angulation of two curing-light devices on the total color variation (ΔE) of conventional and flowable composite resins. Materials and Methods – A total of 120 disc-shaped specimens were prepared using three types of composite resins: Vittra APS®, Opallis Conventional®, and Opallis Flow®. The specimens were divided into 12 experimental groups, considering two tip angulations of the curing-light devices (0º and 45º) and two different devices: Valo Cordless® (third-generation LED with a broad spectral range) and Radii-cal® (second-generation LED with a narrow spectral range). The resins were photoactivated according to the manufacturers' instructions, and colorimetric analysis was performed using the CIELab* system at baseline and after 15 days, with a reflection spectrophotometer. Data were analyzed using Levene’s and Shapiro-Wilk tests, followed by three-way ANOVA and Tukey’s test, with a significance level of 5%. Results – Statistically significant differences were observed (p < 0.05): the Valo Cordless® resulted in lower color variation; the Opallis Flow® resin showed greater color stability; and increasing the tip angulation to 45º led to higher color variation in Vittra APS® and Opallis Conventional® resins when using the Radii-cal® unit. Conclusion – Both the type of composite resin and the curing-light devices, as well as its angulation, influence the color stability of restorations. Clinical Relevance – Clinically, these findings highlight the importance of proper light-curing technique and appropriate material selection to ensure the aesthetic quality and longevity of restorations. Polymerization. Dentistry. Color. Composite Resins Figures Figure 1 Figure 2 Figure 3 INTRODUCTION Composite resin is widely used as a direct restorative material in dentistry because of its ability to replicate the color and translucency of natural teeth. Its acceptance in the market is due to the combination of biological properties, such as biocompatibility and dental preservation, in addition to its mechanical characteristics, which include durability, low wear rate, and high strength [ 1 ]. In addition to these properties, composite resins have excellent esthetic properties that allow them to effectively reproduce the appearance of teeth. However, to ensure that these restorations maintain their properties over time, it is essential that the material undergoes proper photopolymerization. The composite resin consists of an organic matrix and an inorganic matrix covering the filler particles. In addition, it includes the silane bonding agent, which has the function of chemically bonding the filler particles to the matrix, as well as chemicals that facilitate or regulate the polymerization process[ 2,3]. Composite resins are classified as hybrids, microhybrids, microparticulates, and nanoparticulates, according to the properties of the filler particles in the inorganic matrix, especially in relation to their size [ 3 , 4 ]. Photopolymerization is the process by which composite resin becomes solid through exposure to light and depends on two fundamental elements: the wavelength of the light and the amount of energy applied [ 5 – 7 ]. The photoinitiator system of the composite resin can only capture light if it is emitted at a specific wavelength, which can activate the photoinitiators. Each photoinitiator reacts to specific wavelengths [ 5 – 7 ]. These elements are essential for the effective conversion of monomers into polymers, resulting in a solid polymeric structure [ 8 ]. With the advancement of curing-light devices, LEDs are now considered to be broad-spectrum light sources due to their ability to emit a wider range of wavelengths [ 9 , 10 ]. The efficacy of photopolymerization also depends on operational factors, such as the distance and angle of the curing-light tip in relation to the restoration surface, which impact the amount of light received by the composite resin and thus the polymerization process [ 6 ]. For example, increasing the inclination angle of the curing-light tip may reduce the amount of photons reaching the resin, resulting in shadowed areas at the ends of the restoration [ 11 , 12 ]. This can lead to inadequate polymerization and compromise the properties of the material [ 5 , 13 , 14 – 16 ] , in addition to causing the dissolution of the organic matrix, which can cause color changes and reduce the durability of the restoration [ 5 , 13 , 15 , 17 ]. Therefore, the appropriate delivery of light energy ensures effective polymerization [ 18 ]. The aim of this study was to evaluate the effect of the angulation of different curing light devices on the total color variation (ΔE) of composite resins. It was hypothesized that factors such as angulation, type of curing light, and resin material affect the photopolymerization process, thereby influencing the esthetic outcome of composite resin restorations. The present study tested the hypothesis that the Radii-cal® and Valo Cordless® curing light devices would exhibit similar performance. It also evaluated whether increasing the tip angulation of the curing-light units would lead to greater total color variation (ΔE) in composite resins. Additionally, the hypothesis that different resin materials would respond differently under the same conditions was assessed. MATERIALS AND METHODS a. Preparation of specimens One hundred and twenty specimens were prepared and divided into 12 experimental groups (n = 10) (Fig. 1 ). For this, Vittra APS® EA3,5 (FGM, Joinville-SC), Opallis Conventional® EA3 microhybrid (FGM, Joinville-SC) and an Opallis Flow® A3 microhybrid fluid resin (FGM, Joinville-SC) were used (Table 1 ). The mentioned resins were evaluated in association with two different angles (0º and 45º) of the tip of two high-power LED photocuring devices (Valo Cordless® 1000mW/cm², Ultradent, South Jordan, USA and Radii-cal® 1200mW/cm2, SDI, Victoria, Australia) (Table 2 ). Source: Authorship. Table 1 Materials used, with identification of their respective manufacturers, batches and basic chemical composition. Material (manufacturer); lot Basic Chemical Composition Composite resin (Vittra APS® EA3,5, FGM, Joinville - SC); Lot 010823. Active ingredients: monomeric mixture containing monomers such as UDMA (urethane dimethacrylate) and TEGDMA (triethylene glycol dimethacrylate), APS (Advanced Polymerization System) photoinitiator composition, co-initiators, stabilizer and silane. Inactive ingredients: zirconia, silica and pigment filler. Composite resin (Opallis Flow® A3, FGM, Joinville-SC); Lot 120924. Methacrylic monomers, camphorquinone, coinitiators, stabilizers, pigments and silanized inorganic charge composed of barium-aluminum borosilicate microparticles and silicon dioxide particles. Particles with an average size between 0.5 and 1.0 microns. Composite resin (Opallis Conventional® EA3, FGM, Joinville - SC); Lot 080124. Silannized radiopaque glass particles (70–80%), methacrylic monomers (15–25%), silicon dioxide (2–7%), photoinitiator composition (< 1%), stabilizers (< 1%) and pigments (< 1%). Particles with an average size of 0.5 microns. Source: Authorship. Table 2 Specifications of the curing light devices, with their respective wavelengths, light intensity used in the study. Curing light Specifications Valo Cordless® (Ultradent, South Jordan, USA) Serial Number: V41710 Wavelengths: 395 nm – 480 nm Broad spectrum Collimated beam Light intensity 1,000mW/cm² (standard mode) Lens diameter: 9.7mm Radii-cal® (SDI, Victoria, Australia). Serial number: 34655. Wavelengths: 440 nm – 480 nm Low spectral range Non-collimated beam Light Intensity: 1200mW/cm2 Lens Diameter: 7.2mm Source: Authorship. For the preparation of each specimen, the conventional resin and the selected fluid were inserted into a stainless steel matrix, with dimensions of 1.5 mm thick and 6 mm in diameter. A polyester matrix strip was positioned over the assembly, followed by the application of a 500 g weight for 30 seconds to promote better accommodation of the material (Fig. 2 ) – For the preparation of the fluid resin, the use of a weight was not required due to the material’s degree of fluidity, which allowed adequate flow of the material in the matrix. Subsequently, the surface was light-cured using LED light, following the manufacturer's instructions, 20 seconds for Vittra APS® EA3.5 and Opallis Conventional® EA3 and 40 seconds for Opallis Flow® A3 – the light intensity of the curing-light devices was checked using a radiometer (Radiometer®, 3H, USA) before preparing the specimens. The photoactivation followed the predetermined positioning of the light-emitting tip of the tested device (Valo Cordless® and Radii-cal®) in relation to the surface of the material of each group tested. The angulations of the curing lights devices tip were standardized by securing the device to a support set at a 45° angle (Fig. 3 ). Source: Authorship. Source: Authorship. Photocuring was performed following the predetermined positioning of the light-emitting tip of the tested devices (Valo Cordless® and Radii-cal®) relative to the material surface. For the control angulation, the curing light tip was positioned parallel to the specimen surface, i.e., at 0º of the matrix + resin + polyester strip set, in direct contact with the polyester strip. The protocols used in the present study are described below. Angulation: 0º ( Control) – The specimens were light-cured with the tip of the curing-light equipment positioned parallel to the material, i.e., at 0º of the matrix + resin + polyester strip assembly, in direct contact with the polyester strip. The Vittra APS® EA3,5 and Opallis Conventional® EA3 resin were light-cured for 20 seconds, and the Opallis Flow® A3 for 40 seconds, following the manufacturer's instructions. Angulation: 45º –A custom-made acrylic device was fabricated to ensure a consistent 45° angulation between the tip of the curing-light device and the resin placed within the matrix. The specimens were photoactivated with the tip of the curing-light device positioned at a 45° angle relative to the matrix–resin–polyester strip assembly. The Vittra APS® EA3.5 and Opallis Conventional® EA3 composites were light-cured for 20 seconds, while the Opallis Flow® A3 composite was cured for 40 seconds. Following specimen preparation, samples were stored in distilled water at 37°C for 24 hours in the absence of light exposure. After the storage period, the specimens were finished to standardize the surface smoothness and facilitate subsequent reading. For this purpose, the specimens were fixed with white wax on a glass plate and had the top surface polished in a metallographic polishing machine (Arotec S/A Indústria e Comércio, Cotia, SP, Brazil), with constant cooling, at a speed of 300 rpm, for 30 seconds, using water sandpaper, at 1,200 grit (JET401 Norton, Guarulhos, SP, Brazil). The samples were then immersed in distilled water and placed in an ultrasonic vat (PLANATAC model CBU-100/1L, Tatuapé, SP, Brazil) for 2 minutes, to remove any remaining residue. Finally, the samples were re-incubated (37oC) for 24 hours in relative humidity and then they were subjected to the first colorimetric reading analysis and then they were kept in an incubator and immersed in distilled water at 37oC for 15 days. After the 15-day storage period, specimens underwent a second colorimetric analysis to determine the total color variation (ΔE) b. Colorimetric evaluation with reflection spectrophotometer Color measurements of each specimen were performed using a reflection spectrophotometer (UV-2600; Shimadzu), operated with the UV Probe software (Shimadzu). Reflectance spectra were recorded within the visible light range (380–780 nm). To do this, the specimens were positioned individually in the equipment with the aid of a template, which allows their positioning to be reproduced by correlating the marking on the back of the specimen with the marking on the template. Then, the spectral curves recorded for each specimen were transported to the Color Analysis program, for color evaluation, following the parameters of the CIEL*a*b* (Commission Internationale de L'Eclairage) system, with standardization of the D65 illuminant. Color analysis was performed at two initial moments: (1) and (2) after 15 days, in order to verify the total color variation (ΔE) of each specimen. The parameters L* (luminosity), a* (green-red variation) and b* (blue-yellow variation) were collected separately and used to calculate the total color variation (∆E), for the reflection spectrophotometer and applying the formula: ∆E = √(L-L0) 2 + (a-a0) 2 + (b-b0) 2 . c. Statistical analysis The collected data were tabulated and evaluated for their homogeneity and normality, and the Levene and Shapiro-Wilk tests were applied, respectively, with a significance level of 0.05. Assuming the assumptions for the application of the parametric tests, the Analysis of Variance test was applied with 3 factors: 1. Material in 3 levels (Vittra®, Opallis Flow® and Opallis Conventional®), 2. Photopolymerizer in 2 levels (Radii-Cal® and Valo Cordless®) and 3. Activation angle in 2 levels (0° and 45°). Tukey's test was used as a post hoc test. RESULTS Table 3 presents the mean and standard deviation values of the total color variation (∆E) measured in each experimental group. Table 3 Mean values and standard deviations of total color variation (∆E) from colorimetric analysis using the Shimadzu Reflection Spectrophotometer for tested groups, considering different curing-light devices, resin compositions, and angulation variations Resin Radii-Cal® Valo Cordless® 0° 45° 0° 45° Vittra® 3.33 ± 1.63 Aa *6.59 ± 2.35 Ab 3.79 ± 1.84 Aa *3.24 ± 0.90 Aa Opallis Flow® 3.04 ± 2.31 Aa 4.34 ± 0.97 Ba 4.84 ± 2.64 Aa 4.05 ± 2.49 Aa Opallis Conventional® 3.66 ± 1.93 Aa 6.03 ± 1.33 ABb 3.85 ± 1.27 Aa 4.98 ± 2.13 Aa Legends: Different capital letters indicate difference between resins for the same curing-light device and angulation. Different lowercase letters indicate significant difference between the curing-light angle for the same resin and curing-light. *Indicates difference between curing-light devices for the same resin and activation angle. Source: Authorship. When the levels of the device factor were compared (Valo Cordless® vs. Radii-Cal®), statistically significant differences (p < 0.05) were observed between the mean values of total color change (ΔE) obtained by the two devices. The total color change (ΔE) value obtained with the Radii-Cal® curing-light unit at a 45° angle, using Vittra APS® resin, was statistically higher than that of the Valo Cordless® under the same condition, indicating a greater total color variation (ΔE). However, at a 0° angle, the devices behaved statistically similarly to each Other. In the comparison between the resins (Vittra APS® x Opallis Flow® x Opallis Conventional®), some statistically significant difference (p < 0.05) was observed between the mean values of total color variation (ΔE). With the Radii-Cal® device at a 45° angle, Vittra APS® was statistically different from Opallis Flow®, with Opallis Flow® showing a lower total color variation (ΔE). Finally, when the angulation levels (0° vs. 45°) were compared, some statistically significant differences (p < 0.05) were observed in the total color variation (ΔE) values. The total color variation (ΔE) values were higher at 45° with the Radii-Cal® device for the Vittra APS® and Opallis Conventional® resins, indicating that this angulation may increase the total color variation (ΔE). For the Opallis Flow® resin, however, no statistically significant difference was observed regarding angulation. When using the Valo Cordless® device, the change in angulation did not show any statistically significant difference. DISCUSSION The hypothesis tested in this study was partially accepted. In the comparison between the photocuring devices (Radii-cal® and Valo Cordless®) it was observed that the composite resins of regular consistency photoactivated by the Radii-cal® device showed greater total color variation (ΔE), when used with the 45º angle of the guide tip, compared to Valo Cordless®. A plausible explanation is that the Valo Cordless® device emits collimated light beam from its guiding tip. A collimated beam is directed, with light rays parallel to each other, propagating in the same direction, resulting in reduced light dispersion [ 19 , 20 ]. The parallelism of the light rays suggests a more focused direction of the light beam toward the composite resin, which enhances the efficiency of energy delivery, resulting in more effective polymerization and, consequently, improved properties of the resin material. André et al (2018), observed that, when compared to other light-curers, including Valo®, the light beam of Radii-cal® delivers a lower energy per area, resulting in a lower light penetration into the material. Unlike the Valo Cordless®, the Radii-Cal® device has an inhomogeneous light output across the tip, often concentrating a high irradiance peak in a small central area. As a result, it delivers high irradiance in the center of the small-diameter tip, while the peripheral regions of the tip exhibit significantly lower irradiance [ 22 ]. The amount of energy supplied to the composite by the tip of the curing-light has a great impact on the polymerization of the restorative material, being determined by multiplying the power intensity (1,200 mW/cm², typical value of modern curing-light machines) and the time of exposure to light (in seconds)[ 5 – 7 ] In the present study, light intensity does not appear to have been the decisive factor in the comparative performance between the devices. Although the Valo Cordless® was used with an intensity of 1,000 mW/cm², which is lower than that of the Radii-Cal® (1,200 mW/cm²), it still resulted in a lower total color variation (ΔE) for the tested resin. A plausible explanation is that, unlike second-generation curing-light devices like the Radii-Cal®, third-generation devices such as the Valo Cordless® emit light across both the blue and violet ranges, offering a broader spectrum. This broader range allows for the activation of all contemporary photoinitiators, in addition to camphorquinone [ 23 ]. The wavelength of the light emitted by the LED light, ranging from 400 to 500 nm, is directly related to the ability to sensitize photoinitiators, regardless of the amount of energy deposited on the restorative material [ 5 , 7 ]. Thus, the fact that the use of Valo Cordless® curing-light presented a lower total color variation (ΔE) for the composite resins of regular consistency tested, at an inclination of 45 degrees, can be attributed to its wider wave spectrum (395–480 nm), compared to the spectrum emitted by Radii-cal® (440–480 nm). This characteristic increases the ability to sensitize a wider variety of photoinitiators [ 7 , 9 ]. Curing-light resins contain photoinitiator systems that absorb light to generate excited states that initiate polymerization [ 12 ]. Therefore, the use of a light source with a visible spectrum compatible with the absorption characteristics of the photoinitiators is essential for absorption to occur and the polymerization reaction to be initiated [ 5 , 13 , 24 ]. According to the manufacturer, the Vittra APS® composite resin used in this study incorporates the APS (Advanced Polymerization System) photoinitiator system, which combines various photoinitiators, including a small amount of camphorquinone. The manufacturer states that the APS system has a light absorption spectrum for activation within the 400–500 nm range, although the specific presence or exact quantities of each photoinitiator have not been disclosed. According to the manufacturer of Opallis Flow®, it contains camphorquinone as a photoinitiator along with unspecified co-initiators. For the Opallis Conventional® resin, the manufacturer does not specify the photoinitiator used. However, the manufacturer recommends that photopolymerization be performed using a curing-light device with a wavelength in the range of 400–500 nm. When the exact composition of the resin material is not clearly defined, the use of a broad-spectrum light source, such as the Valo Cordless®, appears to be more effective, as observed in this study. This is evidenced by the fact that the Valo Cordless® resulted in a lower total color variation (ΔE) for the tested resin. It is important to emphasize that there are significant variations in the composition of the resins, which can lead to differences in the sensitivity of photoinitiators to certain wavelengths of light for their activation [ 7 ]. For example, alternative photoinitiators, such as Lucerin TPO and Ivocerin, are more reactive to shorter wavelengths, close to 410 nm, while camphorquinone has greater sensitivity to light with a wavelength of 468 nm [ 7 ]. The experimental hypothesis of the present study – that increasing the tip angulation of the curing-light devices would increase the total color variation (ΔE) of the composite resins – was partially accepted, since the 45º angle was able to increase the total color variation (ΔE) in the Vittra APS and Opallis Conventional® resins®, when only the Radii-cal® device was used. Regarding the 45° angle, an increase in the total color variation (ΔE) of the material was observed, which can be attributed to the increased angle of the device tip. This directs light to the resinous material, but also reduces radiation exposure. As the angulation increases, some of the light beams fail to reach the restoration, creating shaded areas in the peripheral regions and, thus, reducing the exposure of the material to radiant light [ 18 , 25 ]. Increasing the angle to 45° also increases the distance between the guide tip portion of the curing-light machine and the composite resin. The distance between the end point and the material was 8 mm during the experiment with Valo Cordless® and 9 mm with Radii-cal®. This difference of 1 mm between the devices is explained by the different shapes of the respective guide tips. This variation in distance may explain the decrease in the properties of the resin, as a greater distance between the light tip and the material results in less light reaching the resin, thereby reducing the energy delivered to the material and limiting the depth of polymerization [ 9 , 16 , 26 ]. The absence of a statistically significant difference in color variation (ΔE) between the angles of 0º and 45º with the Valo Cordless® curing-light device can be explained by its light-emitting technology. Valo Cordless® has a wider emission spectrum (395–480 nm) compared to Radii-cal® (440–480 nm), which allows for more efficient activation of various photoinitiators [ 7 , 9 ]. In addition, its collimated light beam, with parallel rays, results in less dispersion and greater light direction to the material, which ensures a more efficient delivery of energy to the resin [ 27 , 28 ], minimizing the impact of the change in angle. This justifies the stability of the polymerization results and color variation, even with the change in the tip angle. Catelan et al. (2015), highlighted that photopolymerization performed at a greater distance can impair the properties of the resin and compromise the durability of restorations. It should be noted that the minimum recommended distance between the tip of the curing-light device and the surface of the resin is 1 mm [ 29 ]. At a distance of 8 mm, the useful diameter of the light beam decreases, making it less effective at converting the monomers into polymers. This observation is corroborated by studies that indicate that deep restorations, such as class II restorations, may not be properly polymerized [ 30 ]. Svizero et al. (2012)[ 31 ], investigated the influence of curing tip distance (0, 5, 10 and 15 mm) and storage time on water diffusion and color stability of a composite. The results indicated that longer distances (10 and 15 mm) resulted in greater water sorption and color change, probably due to a less cross-linked polymeric structure, which facilitates water absorption and compromises the color stability of the material. Aguiar et al. (2005), found that when the photocuring tip is at a distance of 8 mm from the surface to be light cured, the base of the restoration is not adequately activated, resulting in inferior mechanical properties. Therefore, when there is greater tip angulation and/or greater distance, it is suggested that the polymerization time be prolonged [ 30 , 32 ]. However, more studies are needed to validate this recommendation. In addition, the impact of these different angles should be investigated considering other response variables, such as water sorption, solubility, and clinical longevity of restorations performed with composites. The experimental hypothesis of the present study, which suggested a different behavior between composite resins, was partially accepted. When comparing the different composite resins, the Opallis Flow® resin showed less total color variation (ΔE) in relation to the Vittra APS® resin when using a Radii-cal® device with a 45º angle. This was probably due to the differences in the composition of the resins and the difference in viscosity. The viscosity of a composite resin exerts a direct influence on the mobility of the free radicals generated during the activation of the photoinitiator, significantly impacting the polymerization process. In high-viscosity resins, such as Vittra APS, the movement of these radicals® within the organic matrix becomes more restricted, which can lead to a reduction in the polymerization rate and the degree of conversion of monomers into polymers [ 33 ]. Additionally, viscosity is closely related to the type and content of inorganic fillers in the resin. Materials with a higher content of filler particles tend to have higher viscosity, which can hinder the diffusion of free radicals, making the polymerization process less efficient [ 33 ]. During the propagation of light through the resinous material, light scattering occurs, a phenomenon that depends on the characteristics of the charging particles, the opacity of the resin, the presence and type of pigments, and even the thickness of the increment used [ 32 , 34 , 35 ]. Although Topcu et al. (2009), in their study indicate that the smaller size of the filler particles of the nanoparticulate composite resin results in less susceptibility to color variation, Poggio et al. (2016), reported that the increase in particle size leads to a smaller change in color [ 37 ]. Consistent with the findings of the present study, Poggio et al. [ 37 ] evaluated the color stability of various restorative materials after exposure to different solutions and found that the microparticulate composite, which contained larger filler particles, exhibited the lowest color variation compared to the other materials. The studies by Kao (1989) and Geha et al. (2021) show that the composition of the organic matrix of composite resins directly interferes with their behavior in the face of chemical and mechanical challenges. Kao [63] observed that resins with UDMA matrix were more susceptible to dissolution by food simulant liquids (FSL) than those with BisGMA matrix, demonstrating lower resistance. Geha et al.[ 39 ], in turn, found that the exposure of the resins to chemical agents such as citric and phosphoric acids, alcohol and distilled water resulted in different degrees of degradation, affecting the properties of the composite resin. These findings reinforce that the chemical composition of the organic matrix is an important factor for the resistance and color stability of composite resins under adverse conditions. The results of this study highlight the importance of considering both the choice of curing-light device and the application technique to minimize unwanted aesthetic changes, thereby enhancing the longevity and predictability of the procedures. CONCLUSION Based on the hypothesis that the variables of tip angulation, type of curing-light device, and type of resin-based material influence the photopolymerization process—and consequently, the aesthetic quality of composite resin restorations—this study demonstrated that these variables do, in fact, significantly impact the outcomes. It was observed that the Valo Cordless® device resulted in the lowest total color variation for the Vittra APS® composite resin when used at a 45° angle. Meanwhile, the Opallis Flow® resin showed better performance with the Radii-Cal® device, also at a 45° angle. Furthermore, it was found that increasing the angulation to 45° with the Radii-Cal® device significantly increased the total color variation in the Vittra APS® and Opallis Conventional® resins, confirming the hypothesis that the tip inclination can negatively affect the final aesthetic result. These findings reinforce the importance of selecting an appropriate curing-light device and paying close attention to tip angulation during the clinical procedure to ensure greater aesthetic predictability of the restorations. Declarations Conflicts of interest/Competing interests The authors have no conflicts of interest to declare that are relevant to the content of this article. Ethical Approval Not applicable. Funding This work was supported by a Ph.D. research scholarship granted by CAPES. Author Contribution M and P wrote the main manuscript text; A.P and R. prepared figures 1-3 and table 1-2; R prepared table 3; All authors reviewed the manuscript. Acknowledgements. 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Braz Dent J 27(1):83–89. https://doi.org/10.1590/0103-6440201600387 Aravamudhan K, Rakowski D, Fan PL (2006) Variation of depth of cure and intensity with distance using LED curing lights. Dent Mater 22(11):988 – 94. 10.1016/j.dental . 2005.11.031 Aguiar FHB, Lazzari CR, Lima DANL, Ambrosano GMVB, Lovadino JR (2005) Effect of light curing tip distance and resin shade on microhardness of a hybrid resin composite. Braz Oral Res 19(4):302–306. 10.1590/s1806-83242005000400012 Price RBT, Mcleod ME, Felix CM (2010) Quantifying light energy delivered to a class I restoration. J Can Dent Assoc 76(2):1–8 Davidovich L (2015) Os quanta de luz e a ótica quântica. Rev Bras Ensino Fís 37(4):4201–4205. 10.1590/S1806-11173732073 Bagnato VS (2001) Os fundamentos da luz laser. FnE 2(2):1–6 André CB, Nima G, Sebold M, Giannini M, Price R (2018) Stability of the Light Output, oral cavity tip accessibility in posterior region and emission spectrum of curing-light units. Oper Dent 43(4):398–407. 10.2341/17-033-L Soares CJ, Braga S, Price RB Relationship Between the Cost of 12 Curing-light Units and Their Radiant Power, Emission Spectrum, Radiant Exitance, and Beam Profile (2021). Oper Dent 1;46(3):283 – 92. 10.2341/19-274-L Rueggeberg FA, Giannini M, Arrais CAG, Price RBT (2017). Light curing in dentistry and clinical implications: a literature review. Braz Oral Res 31(61). doi: 10.1590/1807-3107BOR-2017.vol31.0061 Ccahuana-Vásquez RA, Torres CRG, Araújo MAM, Anido AA (2004) Influência do tipo de ponteira condutora de luz de aparelhos LED na microdureza das resinas compostas. Rev Odonto UNESP 33(2):69–63 Konerding KL, Heyder M, Kranz S, Guellmar A, Voelpel A, Watts DC et al (2016) Study of energy transfer by different light curing units into a class III restoration as a function of tilt angle and distance, using a MARC Patient Simulator (PS). Dent Mater 32(5):676–686. 10.1016/j.dental.2016.02.007 Corciolani G, Vichi A, Davidson CL, Ferrari M (2008) The influence of tip geometry and distance on curing-light efficacy. Oper Dent 33(3):325–331 Davidovich L (2015) Os quanta de luz e a ótica quântica. Rev Bras Ensino Fís 37(4):4201–4205. 10.1590/S1806-11173732073 Bagnato VS (2001) Os fundamentos da luz laser. FnE 2(2):1–6 Thomé T, Steagall W, Tachibana A, Braga SEM, Turbino ML (2007) Influence of the distance of the curing light source and composite shade on hardness of two composites. J Appl Oral Sci 15(6):486–491. 10.1590/S1678-77572007000600006 Price RB, Labrie D, Whalen JM, Felix CM (2011) Effect of distance on irradiance and beam homogeneity from 4 light-emitting diode curing units. J Can Dent Assoc 77:b9 Svizero NR, Alonso RCB, Wang L, Palma-Dibb RG, Atta MT, D’Alpino PHQ, N. R. et al (2012) Kinetic of water diffusion and color stability of a resin composite as a function of the curing tip distance. Mat Res 15(4):603–610. 10.1590/S1516-14392012005000070 Xu X, Sandras DA, Burgess JO (2006) Shear bond strength with increasing light-guide distance from dentin. J Esthet Restor Dent 18(1):19–27. 10.2310/6130.2006.00007 Pereira R, Carpio D, Carvalho O, Catarino S, Faria O, Souza J (2022) Relationship between the inorganic content and the polymerization of the organic matrix of resin composites for dentistry: a narrative review. RevSALUS 4(1). 10.51126/revsalus.v4i1.136 Schneider AC, Mendonça MJ, Rodrigues RB, Busato PMR, Camilotti V (2016) Influência de três modos de fotopolimerização sobre a microdureza de três resinas composta. Polímeros 26:37–46. doi.org/10.1590/0104-1428.1855 Tanthanuch S, Kukiattrakoon B (2019) The effect of curing time by conventional quartz tungsten halogens and new light-emitting diodes light curing units on degree of conversion and microhardness of a nanohybrid resin composite. J Conserv Dent 22(2):196–200. 10.4103/JCD.JCD_498_18 Topcu FT, Sahinkesen G, Yamanel K, Erdemir U, Oktay EA, Ersahan S (2009) Influence of different drinks on the colour stability of dental resin composites. Eur J Dent 3:50–56 Poggio C, Ceci M, Beltrami R, Mirando M, Wassim J, Marco C (2016) Color stability of esthetic restorative materials: a spectrophotometric analysis. Acta Biomater Odontol Scand 2(1):95–101. 10.1080/23337931.2016.1217416 Kao EC (1989) Influence of food-simulating solvents on resin composites and glass-ionomer restorative cement. Dent Mater 5(3):201–208. 10.1016/0109-5641(89)90014-6 Geha O, Inagaki LT, Favaro JC, González AHM, Guiraldo RD, Lopes MB, Berger SB (2021) Effect of chemical challenges on the properties of composite resins. Int J Dent 1:2021. 10.1155/2021/4895846 Additional Declarations No competing interests reported. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-6475219","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":451744521,"identity":"3270229c-58fb-4847-8cc3-5a3e127d51e7","order_by":0,"name":"Mariana Menezes Vaz Fernandes","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAABCUlEQVRIiWNgGAWjYJCCA3BWAhDzgxkFpGiRbAAxDEix0wBsAh4tuu1nHx74ucMu2uB4juGDh3ts7I3Pr0788MCAQZ5f7ABWLWZn0g0O9p5Jzt1w5o2xQcKzNGazG283SwAdZjhzdgJ2LQfSGA7wtjHnzpyRYyaRcOAwm9mNsxtAWhIMbuPQcv4Zw8G/bfUgLeY/gFp4jGec3fwDr5YbaQyHedsO5/ZL5JgxALVIGPD3bsNvy41nDIdl247n9vM8KwY6LM1A4gbvNosEAwncfjmfxvzxbVt1bht78saPPw7Y2PP3n91880eFjTy/NHYtSACmQALMkCCkHFkL/wFiVI+CUTAKRsEIAgCeiGa1GEo0MgAAAABJRU5ErkJggg==","orcid":"","institution":"Federal University of Bahia","correspondingAuthor":true,"prefix":"","firstName":"Mariana","middleName":"Menezes Vaz","lastName":"Fernandes","suffix":""},{"id":451744522,"identity":"0f914fcd-0460-4074-a1d9-f18a282711e3","order_by":1,"name":"Ana Paula Menezes Vaz Queiroz Almeida","email":"","orcid":"","institution":"Federal University of Bahia","correspondingAuthor":false,"prefix":"","firstName":"Ana","middleName":"Paula Menezes Vaz Queiroz","lastName":"Almeida","suffix":""},{"id":451744524,"identity":"f9e54b32-2d34-4b31-9819-47fc0bd1f01b","order_by":2,"name":"Rebeca Menezes Vaz Queiroz Fontes","email":"","orcid":"","institution":"Federal University of Bahia","correspondingAuthor":false,"prefix":"","firstName":"Rebeca","middleName":"Menezes Vaz Queiroz","lastName":"Fontes","suffix":""},{"id":451744529,"identity":"47f46858-7231-4943-ba6e-4bcd724384a8","order_by":3,"name":"Rafael Soares Gomes","email":"","orcid":"","institution":"UniFTC University Center","correspondingAuthor":false,"prefix":"","firstName":"Rafael","middleName":"Soares","lastName":"Gomes","suffix":""},{"id":451744530,"identity":"b8cee66a-13e3-43c2-8cc1-95106d405a01","order_by":4,"name":"Paula Mathias","email":"","orcid":"","institution":"Federal University of Bahia","correspondingAuthor":false,"prefix":"","firstName":"Paula","middleName":"","lastName":"Mathias","suffix":""}],"badges":[],"createdAt":"2025-04-18 02:08:06","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-6475219/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-6475219/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":82003881,"identity":"85950e93-467d-4655-aa1d-823c65536d36","added_by":"auto","created_at":"2025-05-05 20:46:01","extension":"jpeg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":103902,"visible":true,"origin":"","legend":"\u003cp\u003eDistribution of the experimental groups (n=10).\u003c/p\u003e","description":"","filename":"floatimage1.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-6475219/v1/2e2eac1e141a922d51f38810.jpeg"},{"id":82004228,"identity":"4d0a87aa-8907-4749-8ce9-917f17a2d526","added_by":"auto","created_at":"2025-05-05 20:54:01","extension":"jpeg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":65720,"visible":true,"origin":"","legend":"\u003cp\u003eIllustrative diagram of specimen preparation, including the matrix for composite resin insertion, the polyester strip placed over it, and the weight applied to remove excess restorative material.\u003c/p\u003e\n\u003cp\u003eSource: Authorship.\u003c/p\u003e","description":"","filename":"floatimage2.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-6475219/v1/702343d71c44dacbf094b796.jpeg"},{"id":82003327,"identity":"e9e68ba3-6d3f-4ac9-806b-c5ec475cba16","added_by":"auto","created_at":"2025-05-05 20:38:01","extension":"jpeg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":55199,"visible":true,"origin":"","legend":"\u003cp\u003eSchematic representation detailing the positioning protocol of the Valo Cordless® and Radii-cal® curing-light units. (A) Angular positioning of the curing tip at 45°, facilitated by a custom-made acrylic guide. (B) Device stabilization at the predetermined angle, followed by removal of the guide prior to photoactivation to eliminate potential interference with light transmission to the resin surface.\u003c/p\u003e\n\u003cp\u003eSource: Authorship.\u003c/p\u003e","description":"","filename":"floatimage3.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-6475219/v1/a770bb3de66bb25042e5196d.jpeg"},{"id":82992649,"identity":"6cb32cac-f2ff-459c-9624-894f3f396b9e","added_by":"auto","created_at":"2025-05-18 16:46:21","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":823468,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6475219/v1/f13bf667-dae1-4440-a84d-141bb0280137.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Effect of angulation in different curing-light devices on color variation in composite resins","fulltext":[{"header":"INTRODUCTION","content":"\u003cp\u003eComposite resin is widely used as a direct restorative material in dentistry because of its ability to replicate the color and translucency of natural teeth. Its acceptance in the market is due to the combination of biological properties, such as biocompatibility and dental preservation, in addition to its mechanical characteristics, which include durability, low wear rate, and high strength [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]. In addition to these properties, composite resins have excellent esthetic properties that allow them to effectively reproduce the appearance of teeth. However, to ensure that these restorations maintain their properties over time, it is essential that the material undergoes proper photopolymerization.\u003c/p\u003e \u003cp\u003eThe composite resin consists of an organic matrix and an inorganic matrix covering the filler particles. In addition, it includes the silane bonding agent, which has the function of chemically bonding the filler particles to the matrix, as well as chemicals that facilitate or regulate the polymerization process[ 2,3]. Composite resins are classified as hybrids, microhybrids, microparticulates, and nanoparticulates, according to the properties of the filler particles in the inorganic matrix, especially in relation to their size [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e, \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e].\u003c/p\u003e \u003cp\u003ePhotopolymerization is the process by which composite resin becomes solid through exposure to light and depends on two fundamental elements: the wavelength of the light and the amount of energy applied [\u003cspan additionalcitationids=\"CR6\" citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]. The photoinitiator system of the composite resin can only capture light if it is emitted at a specific wavelength, which can activate the photoinitiators. Each photoinitiator reacts to specific wavelengths [\u003cspan additionalcitationids=\"CR6\" citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]. These elements are essential for the effective conversion of monomers into polymers, resulting in a solid polymeric structure [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. With the advancement of curing-light devices, LEDs are now considered to be broad-spectrum light sources due to their ability to emit a wider range of wavelengths [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e, \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThe efficacy of photopolymerization also depends on operational factors, such as the distance and angle of the curing-light tip in relation to the restoration surface, which impact the amount of light received by the composite resin and thus the polymerization process [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]. For example, increasing the inclination angle of the curing-light tip may reduce the amount of photons reaching the resin, resulting in shadowed areas at the ends of the restoration [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e, \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e]. This can lead to inadequate polymerization and compromise the properties of the material [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e, \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e, \u003cspan additionalcitationids=\"CR15\" citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]\u003csup\u003e,\u003c/sup\u003e in addition to causing the dissolution of the organic matrix, which can cause color changes and reduce the durability of the restoration [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e, \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e, \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e, \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e]. Therefore, the appropriate delivery of light energy ensures effective polymerization [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThe aim of this study was to evaluate the effect of the angulation of different curing light devices on the total color variation (ΔE) of composite resins. It was hypothesized that factors such as angulation, type of curing light, and resin material affect the photopolymerization process, thereby influencing the esthetic outcome of composite resin restorations. The present study tested the hypothesis that the Radii-cal\u0026reg; and Valo Cordless\u0026reg; curing light devices would exhibit similar performance. It also evaluated whether increasing the tip angulation of the curing-light units would lead to greater total color variation (ΔE) in composite resins. Additionally, the hypothesis that different resin materials would respond differently under the same conditions was assessed.\u003c/p\u003e"},{"header":"MATERIALS AND METHODS","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003ea. Preparation of specimens\u003c/h2\u003e \u003cp\u003eOne hundred and twenty specimens were prepared and divided into 12 experimental groups (n\u0026thinsp;=\u0026thinsp;10) (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). For this, Vittra APS\u0026reg; EA3,5 (FGM, Joinville-SC), Opallis Conventional\u0026reg; EA3 microhybrid (FGM, Joinville-SC) and an Opallis Flow\u0026reg; A3 microhybrid fluid resin (FGM, Joinville-SC) were used (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). The mentioned resins were evaluated in association with two different angles (0\u0026ordm; and 45\u0026ordm;) of the tip of two high-power LED photocuring devices (Valo Cordless\u0026reg; 1000mW/cm\u0026sup2;, Ultradent, South Jordan, USA and Radii-cal\u0026reg; 1200mW/cm2, SDI, Victoria, Australia) (Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eSource: Authorship.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eMaterials used, with identification of their respective manufacturers, batches and basic chemical composition.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"2\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMaterial (manufacturer); lot\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eBasic Chemical Composition\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eComposite resin (Vittra APS\u0026reg; EA3,5, FGM, Joinville - SC); Lot 010823.\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eActive ingredients: monomeric mixture containing monomers such as UDMA (urethane dimethacrylate) and TEGDMA (triethylene glycol dimethacrylate), APS (Advanced Polymerization System) photoinitiator composition, co-initiators, stabilizer and silane.\u003c/p\u003e \u003cp\u003eInactive ingredients: zirconia, silica and pigment filler.\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eComposite resin (Opallis Flow\u0026reg; A3, FGM, Joinville-SC); Lot 120924.\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eMethacrylic monomers, camphorquinone, coinitiators, stabilizers, pigments and silanized inorganic charge composed of barium-aluminum borosilicate microparticles and silicon dioxide particles. Particles with an average size between 0.5 and 1.0 microns.\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eComposite resin (Opallis Conventional\u0026reg; EA3, FGM, Joinville - SC); Lot 080124.\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSilannized radiopaque glass particles (70\u0026ndash;80%), methacrylic monomers (15\u0026ndash;25%), silicon dioxide (2\u0026ndash;7%), photoinitiator composition (\u0026lt;\u0026thinsp;1%), stabilizers (\u0026lt;\u0026thinsp;1%) and pigments (\u0026lt;\u0026thinsp;1%). Particles with an average size of 0.5 microns.\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eSource: Authorship.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eSpecifications of the curing light devices, with their respective wavelengths, light intensity used in the study.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"2\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCuring light\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSpecifications\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eValo Cordless\u0026reg; (Ultradent, South Jordan, USA)\u003c/p\u003e \u003cp\u003eSerial Number: V41710\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eWavelengths: 395 nm \u0026ndash; 480 nm\u003c/p\u003e \u003cp\u003eBroad spectrum\u003c/p\u003e \u003cp\u003eCollimated beam\u003c/p\u003e \u003cp\u003eLight intensity 1,000mW/cm\u0026sup2;\u003c/p\u003e \u003cp\u003e(standard mode)\u003c/p\u003e \u003cp\u003eLens diameter: 9.7mm\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eRadii-cal\u0026reg; (SDI, Victoria, Australia). Serial number: 34655.\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eWavelengths: 440 nm \u0026ndash; 480 nm\u003c/p\u003e \u003cp\u003eLow spectral range\u003c/p\u003e \u003cp\u003eNon-collimated beam\u003c/p\u003e \u003cp\u003eLight Intensity: 1200mW/cm2\u003c/p\u003e \u003cp\u003eLens Diameter: 7.2mm\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eSource: Authorship.\u003c/p\u003e \u003cp\u003eFor the preparation of each specimen, the conventional resin and the selected fluid were inserted into a stainless steel matrix, with dimensions of 1.5 mm thick and 6 mm in diameter. A polyester matrix strip was positioned over the assembly, followed by the application of a 500 g weight for 30 seconds to promote better accommodation of the material (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e) \u0026ndash; For the preparation of the fluid resin, the use of a weight was not required due to the material\u0026rsquo;s degree of fluidity, which allowed adequate flow of the material in the matrix. Subsequently, the surface was light-cured using LED light, following the manufacturer's instructions, 20 seconds for Vittra APS\u0026reg; EA3.5 and Opallis Conventional\u0026reg; EA3 and 40 seconds for Opallis Flow\u0026reg; A3 \u0026ndash; the light intensity of the curing-light devices was checked using a radiometer (Radiometer\u0026reg;, 3H, USA) before preparing the specimens. The photoactivation followed the predetermined positioning of the light-emitting tip of the tested device (Valo Cordless\u0026reg; and Radii-cal\u0026reg;) in relation to the surface of the material of each group tested. The angulations of the curing lights devices tip were standardized by securing the device to a support set at a 45\u0026deg; angle (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eSource: Authorship.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eSource: Authorship.\u003c/p\u003e \u003cp\u003ePhotocuring was performed following the predetermined positioning of the light-emitting tip of the tested devices (Valo Cordless\u0026reg; and Radii-cal\u0026reg;) relative to the material surface. For the control angulation, the curing light tip was positioned parallel to the specimen surface, i.e., at 0\u0026ordm; of the matrix\u0026thinsp;+\u0026thinsp;resin\u0026thinsp;+\u0026thinsp;polyester strip set, in direct contact with the polyester strip.\u003c/p\u003e \u003cp\u003eThe protocols used in the present study are described below.\u003c/p\u003e \u003cp\u003e \u003cul\u003e \u003cli\u003e \u003cp\u003eAngulation: 0\u0026ordm; (\u003cem\u003eControl)\u003c/em\u003e \u0026ndash; The specimens were light-cured with the tip of the curing-light equipment positioned parallel to the material, i.e., at 0\u0026ordm; of the matrix\u0026thinsp;+\u0026thinsp;resin\u0026thinsp;+\u0026thinsp;polyester strip assembly, in direct contact with the polyester strip. The Vittra APS\u0026reg; EA3,5 and Opallis Conventional\u0026reg; EA3 resin were light-cured for 20 seconds, and the Opallis Flow\u0026reg; A3 for 40 seconds, following the manufacturer's instructions.\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003eAngulation: 45\u0026ordm; \u0026ndash;A custom-made acrylic device was fabricated to ensure a consistent 45\u0026deg; angulation between the tip of the curing-light device and the resin placed within the matrix. The specimens were photoactivated with the tip of the curing-light device positioned at a 45\u0026deg; angle relative to the matrix\u0026ndash;resin\u0026ndash;polyester strip assembly. The Vittra APS\u0026reg; EA3.5 and Opallis Conventional\u0026reg; EA3 composites were light-cured for 20 seconds, while the Opallis Flow\u0026reg; A3 composite was cured for 40 seconds.\u003c/p\u003e \u003c/li\u003e \u003c/ul\u003e \u003c/p\u003e \u003cp\u003eFollowing specimen preparation, samples were stored in distilled water at 37\u0026deg;C for 24 hours in the absence of light exposure.\u003c/p\u003e \u003cp\u003eAfter the storage period, the specimens were finished to standardize the surface smoothness and facilitate subsequent reading. For this purpose, the specimens were fixed with white wax on a glass plate and had the top surface polished in a metallographic polishing machine (Arotec S/A Ind\u0026uacute;stria e Com\u0026eacute;rcio, Cotia, SP, Brazil), with constant cooling, at a speed of 300 rpm, for 30 seconds, using water sandpaper, at 1,200 grit (JET401 Norton, Guarulhos, SP, Brazil). The samples were then immersed in distilled water and placed in an ultrasonic vat (PLANATAC model CBU-100/1L, Tatuap\u0026eacute;, SP, Brazil) for 2 minutes, to remove any remaining residue.\u003c/p\u003e \u003cp\u003eFinally, the samples were re-incubated (37oC) for 24 hours in relative humidity and then they were subjected to the first colorimetric reading analysis and then they were kept in an incubator and immersed in distilled water at 37oC for 15 days.\u003c/p\u003e \u003cp\u003eAfter the 15-day storage period, specimens underwent a second colorimetric analysis to determine the total color variation (ΔE)\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eb. Colorimetric evaluation with reflection spectrophotometer\u003c/h3\u003e\n\u003cp\u003eColor measurements of each specimen were performed using a reflection spectrophotometer (UV-2600; Shimadzu), operated with the UV Probe software (Shimadzu). Reflectance spectra were recorded within the visible light range (380\u0026ndash;780 nm). To do this, the specimens were positioned individually in the equipment with the aid of a template, which allows their positioning to be reproduced by correlating the marking on the back of the specimen with the marking on the template. Then, the spectral curves recorded for each specimen were transported to the Color Analysis program, for color evaluation, following the parameters of the CIEL*a*b* (Commission Internationale de L'Eclairage) system, with standardization of the D65 illuminant.\u003c/p\u003e \u003cp\u003eColor analysis was performed at two initial moments: (1) and (2) after 15 days, in order to verify the total color variation (ΔE) of each specimen. The parameters L* (luminosity), a* (green-red variation) and b* (blue-yellow variation) were collected separately and used to calculate the total color variation (∆E), for the reflection spectrophotometer and applying the formula: ∆E = \u0026radic;(L-L0) \u003csup\u003e2\u003c/sup\u003e + (a-a0)\u003csup\u003e2\u003c/sup\u003e + (b-b0) \u003csup\u003e2\u003c/sup\u003e.\u003c/p\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003ec. Statistical analysis\u003c/h2\u003e \u003cp\u003eThe collected data were tabulated and evaluated for their homogeneity and normality, and the Levene and Shapiro-Wilk tests were applied, respectively, with a significance level of 0.05. Assuming the assumptions for the application of the parametric tests, the Analysis of Variance test was applied with 3 factors: 1. Material in 3 levels (Vittra\u0026reg;, Opallis Flow\u0026reg; and Opallis Conventional\u0026reg;), 2. Photopolymerizer in 2 levels (Radii-Cal\u0026reg; and Valo Cordless\u0026reg;) and 3. Activation angle in 2 levels (0\u0026deg; and 45\u0026deg;). Tukey's test was used as a post hoc test.\u003c/p\u003e \u003c/div\u003e"},{"header":"RESULTS","content":"\u003cp\u003eTable\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e presents the mean and standard deviation values of the total color variation (∆E) measured in each experimental group.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab3\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eMean values and standard deviations of total color variation (∆E) from colorimetric analysis using the Shimadzu Reflection Spectrophotometer for tested groups, considering different curing-light devices, resin compositions, and angulation variations\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"5\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eResin\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"2\" nameend=\"c3\" namest=\"c2\"\u003e \u003cp\u003eRadii-Cal\u0026reg;\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"2\" nameend=\"c5\" namest=\"c4\"\u003e \u003cp\u003eValo Cordless\u0026reg;\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0\u0026deg;\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003e45\u0026deg;\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0\u0026deg;\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003e45\u0026deg;\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eVittra\u0026reg;\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e3.33\u0026thinsp;\u0026plusmn;\u0026thinsp;1.63 Aa\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e*6.59\u0026thinsp;\u0026plusmn;\u0026thinsp;2.35 Ab\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e3.79\u0026thinsp;\u0026plusmn;\u0026thinsp;1.84 Aa\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e*3.24\u0026thinsp;\u0026plusmn;\u0026thinsp;0.90 Aa\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eOpallis Flow\u0026reg;\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e3.04\u0026thinsp;\u0026plusmn;\u0026thinsp;2.31 Aa\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e4.34\u0026thinsp;\u0026plusmn;\u0026thinsp;0.97 Ba\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e4.84\u0026thinsp;\u0026plusmn;\u0026thinsp;2.64 Aa\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e4.05\u0026thinsp;\u0026plusmn;\u0026thinsp;2.49 Aa\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eOpallis Conventional\u0026reg;\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e3.66\u0026thinsp;\u0026plusmn;\u0026thinsp;1.93 Aa\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e6.03\u0026thinsp;\u0026plusmn;\u0026thinsp;1.33 ABb\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e3.85\u0026thinsp;\u0026plusmn;\u0026thinsp;1.27 Aa\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e4.98\u0026thinsp;\u0026plusmn;\u0026thinsp;2.13 Aa\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eLegends: Different capital letters indicate difference between resins for the same curing-light device and angulation. Different lowercase letters indicate significant difference between the curing-light angle for the same resin and curing-light. *Indicates difference between curing-light devices for the same resin and activation angle.\u003c/p\u003e \u003cp\u003eSource: Authorship.\u003c/p\u003e \u003cp\u003eWhen the levels of the device factor were compared (Valo Cordless\u0026reg; vs. Radii-Cal\u0026reg;), statistically significant differences (p\u0026thinsp;\u0026lt;\u0026thinsp;0.05) were observed between the mean values of total color change (ΔE) obtained by the two devices. The total color change (ΔE) value obtained with the Radii-Cal\u0026reg; curing-light unit at a 45\u0026deg; angle, using Vittra APS\u0026reg; resin, was statistically higher than that of the Valo Cordless\u0026reg; under the same condition, indicating a greater total color variation (ΔE). However, at a 0\u0026deg; angle, the devices behaved statistically similarly to each Other.\u003c/p\u003e \u003cp\u003eIn the comparison between the resins (Vittra APS\u0026reg; x Opallis Flow\u0026reg; x Opallis Conventional\u0026reg;), some statistically significant difference (p\u0026thinsp;\u0026lt;\u0026thinsp;0.05) was observed between the mean values of total color variation (ΔE). With the Radii-Cal\u0026reg; device at a 45\u0026deg; angle, Vittra APS\u0026reg; was statistically different from Opallis Flow\u0026reg;, with Opallis Flow\u0026reg; showing a lower total color variation (ΔE).\u003c/p\u003e \u003cp\u003eFinally, when the angulation levels (0\u0026deg; vs. 45\u0026deg;) were compared, some statistically significant differences (p\u0026thinsp;\u0026lt;\u0026thinsp;0.05) were observed in the total color variation (ΔE) values. The total color variation (ΔE) values were higher at 45\u0026deg; with the Radii-Cal\u0026reg; device for the Vittra APS\u0026reg; and Opallis Conventional\u0026reg; resins, indicating that this angulation may increase the total color variation (ΔE). For the Opallis Flow\u0026reg; resin, however, no statistically significant difference was observed regarding angulation. When using the Valo Cordless\u0026reg; device, the change in angulation did not show any statistically significant difference.\u003c/p\u003e"},{"header":"DISCUSSION","content":"\u003cp\u003eThe hypothesis tested in this study was partially accepted. In the comparison between the photocuring devices (Radii-cal\u0026reg; and Valo Cordless\u0026reg;) it was observed that the composite resins of regular consistency photoactivated by the Radii-cal\u0026reg; device showed greater total color variation (ΔE), when used with the 45\u0026ordm; angle of the guide tip, compared to Valo Cordless\u0026reg;.\u003c/p\u003e \u003cp\u003eA plausible explanation is that the Valo Cordless\u0026reg; device emits collimated light beam from its guiding tip. A collimated beam is directed, with light rays parallel to each other, propagating in the same direction, resulting in reduced light dispersion [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e, \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e]. The parallelism of the light rays suggests a more focused direction of the light beam toward the composite resin, which enhances the efficiency of energy delivery, resulting in more effective polymerization and, consequently, improved properties of the resin material. Andr\u0026eacute; et al (2018), observed that, when compared to other light-curers, including Valo\u0026reg;, the light beam of Radii-cal\u0026reg; delivers a lower energy per area, resulting in a lower light penetration into the material. Unlike the Valo Cordless\u0026reg;, the Radii-Cal\u0026reg; device has an inhomogeneous light output across the tip, often concentrating a high irradiance peak in a small central area. As a result, it delivers high irradiance in the center of the small-diameter tip, while the peripheral regions of the tip exhibit significantly lower irradiance [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThe amount of energy supplied to the composite by the tip of the curing-light has a great impact on the polymerization of the restorative material, being determined by multiplying the power intensity (1,200 mW/cm\u0026sup2;, typical value of modern curing-light machines) and the time of exposure to light (in seconds)[\u003cspan additionalcitationids=\"CR6\" citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e] In the present study, light intensity does not appear to have been the decisive factor in the comparative performance between the devices. Although the Valo Cordless\u0026reg; was used with an intensity of 1,000 mW/cm\u0026sup2;, which is lower than that of the Radii-Cal\u0026reg; (1,200 mW/cm\u0026sup2;), it still resulted in a lower total color variation (ΔE) for the tested resin. A plausible explanation is that, unlike second-generation curing-light devices like the Radii-Cal\u0026reg;, third-generation devices such as the Valo Cordless\u0026reg; emit light across both the blue and violet ranges, offering a broader spectrum. This broader range allows for the activation of all contemporary photoinitiators, in addition to camphorquinone [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThe wavelength of the light emitted by the LED light, ranging from 400 to 500 nm, is directly related to the ability to sensitize photoinitiators, regardless of the amount of energy deposited on the restorative material [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e, \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]. Thus, the fact that the use of Valo Cordless\u0026reg; curing-light presented a lower total color variation (ΔE) for the composite resins of regular consistency tested, at an inclination of 45 degrees, can be attributed to its wider wave spectrum (395\u0026ndash;480 nm), compared to the spectrum emitted by Radii-cal\u0026reg; (440\u0026ndash;480 nm). This characteristic increases the ability to sensitize a wider variety of photoinitiators [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e, \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]. Curing-light resins contain photoinitiator systems that absorb light to generate excited states that initiate polymerization [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e]. Therefore, the use of a light source with a visible spectrum compatible with the absorption characteristics of the photoinitiators is essential for absorption to occur and the polymerization reaction to be initiated [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e, \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e, \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eAccording to the manufacturer, the Vittra APS\u0026reg; composite resin used in this study incorporates the APS (Advanced Polymerization System) photoinitiator system, which combines various photoinitiators, including a small amount of camphorquinone. The manufacturer states that the APS system has a light absorption spectrum for activation within the 400\u0026ndash;500 nm range, although the specific presence or exact quantities of each photoinitiator have not been disclosed. According to the manufacturer of Opallis Flow\u0026reg;, it contains camphorquinone as a photoinitiator along with unspecified co-initiators. For the Opallis Conventional\u0026reg; resin, the manufacturer does not specify the photoinitiator used. However, the manufacturer recommends that photopolymerization be performed using a curing-light device with a wavelength in the range of 400\u0026ndash;500 nm. When the exact composition of the resin material is not clearly defined, the use of a broad-spectrum light source, such as the Valo Cordless\u0026reg;, appears to be more effective, as observed in this study. This is evidenced by the fact that the Valo Cordless\u0026reg; resulted in a lower total color variation (ΔE) for the tested resin.\u003c/p\u003e \u003cp\u003eIt is important to emphasize that there are significant variations in the composition of the resins, which can lead to differences in the sensitivity of photoinitiators to certain wavelengths of light for their activation [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]. For example, alternative photoinitiators, such as Lucerin TPO and Ivocerin, are more reactive to shorter wavelengths, close to 410 nm, while camphorquinone has greater sensitivity to light with a wavelength of 468 nm [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThe experimental hypothesis of the present study \u0026ndash; that increasing the tip angulation of the curing-light devices would increase the total color variation (ΔE) of the composite resins \u0026ndash; was partially accepted, since the 45\u0026ordm; angle was able to increase the total color variation (ΔE) in the Vittra APS and Opallis Conventional\u0026reg; resins\u0026reg;, when only the Radii-cal\u0026reg; device was used.\u003c/p\u003e \u003cp\u003eRegarding the 45\u0026deg; angle, an increase in the total color variation (ΔE) of the material was observed, which can be attributed to the increased angle of the device tip. This directs light to the resinous material, but also reduces radiation exposure. As the angulation increases, some of the light beams fail to reach the restoration, creating shaded areas in the peripheral regions and, thus, reducing the exposure of the material to radiant light [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e, \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e]. Increasing the angle to 45\u0026deg; also increases the distance between the guide tip portion of the curing-light machine and the composite resin. The distance between the end point and the material was 8 mm during the experiment with Valo Cordless\u0026reg; and 9 mm with Radii-cal\u0026reg;. This difference of 1 mm between the devices is explained by the different shapes of the respective guide tips. This variation in distance may explain the decrease in the properties of the resin, as a greater distance between the light tip and the material results in less light reaching the resin, thereby reducing the energy delivered to the material and limiting the depth of polymerization [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e, \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e, \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThe absence of a statistically significant difference in color variation (ΔE) between the angles of 0\u0026ordm; and 45\u0026ordm; with the Valo Cordless\u0026reg; curing-light device can be explained by its light-emitting technology. Valo Cordless\u0026reg; has a wider emission spectrum (395\u0026ndash;480 nm) compared to Radii-cal\u0026reg; (440\u0026ndash;480 nm), which allows for more efficient activation of various photoinitiators [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e, \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]. In addition, its collimated light beam, with parallel rays, results in less dispersion and greater light direction to the material, which ensures a more efficient delivery of energy to the resin [\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e, \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e], minimizing the impact of the change in angle. This justifies the stability of the polymerization results and color variation, even with the change in the tip angle.\u003c/p\u003e \u003cp\u003eCatelan et al. (2015), highlighted that photopolymerization performed at a greater distance can impair the properties of the resin and compromise the durability of restorations. It should be noted that the minimum recommended distance between the tip of the curing-light device and the surface of the resin is 1 mm [\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e]. At a distance of 8 mm, the useful diameter of the light beam decreases, making it less effective at converting the monomers into polymers. This observation is corroborated by studies that indicate that deep restorations, such as class II restorations, may not be properly polymerized [\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eSvizero et al. (2012)[\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e], investigated the influence of curing tip distance (0, 5, 10 and 15 mm) and storage time on water diffusion and color stability of a composite. The results indicated that longer distances (10 and 15 mm) resulted in greater water sorption and color change, probably due to a less cross-linked polymeric structure, which facilitates water absorption and compromises the color stability of the material. Aguiar et al. (2005), found that when the photocuring tip is at a distance of 8 mm from the surface to be light cured, the base of the restoration is not adequately activated, resulting in inferior mechanical properties. Therefore, when there is greater tip angulation and/or greater distance, it is suggested that the polymerization time be prolonged [\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e, \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e]. However, more studies are needed to validate this recommendation.\u003c/p\u003e \u003cp\u003eIn addition, the impact of these different angles should be investigated considering other response variables, such as water sorption, solubility, and clinical longevity of restorations performed with composites.\u003c/p\u003e \u003cp\u003eThe experimental hypothesis of the present study, which suggested a different behavior between composite resins, was partially accepted. When comparing the different composite resins, the Opallis Flow\u0026reg; resin showed less total color variation (ΔE) in relation to the Vittra APS\u0026reg; resin when using a Radii-cal\u0026reg; device with a 45\u0026ordm; angle. This was probably due to the differences in the composition of the resins and the difference in viscosity.\u003c/p\u003e \u003cp\u003eThe viscosity of a composite resin exerts a direct influence on the mobility of the free radicals generated during the activation of the photoinitiator, significantly impacting the polymerization process. In high-viscosity resins, such as Vittra APS, the movement of these radicals\u0026reg; within the organic matrix becomes more restricted, which can lead to a reduction in the polymerization rate and the degree of conversion of monomers into polymers [\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e]. Additionally, viscosity is closely related to the type and content of inorganic fillers in the resin. Materials with a higher content of filler particles tend to have higher viscosity, which can hinder the diffusion of free radicals, making the polymerization process less efficient [\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eDuring the propagation of light through the resinous material, light scattering occurs, a phenomenon that depends on the characteristics of the charging particles, the opacity of the resin, the presence and type of pigments, and even the thickness of the increment used [\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e, \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e, \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e]. Although Topcu et al. (2009), in their study indicate that the smaller size of the filler particles of the nanoparticulate composite resin results in less susceptibility to color variation, Poggio et al. (2016), reported that the increase in particle size leads to a smaller change in color [\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e]. Consistent with the findings of the present study, Poggio et al. [\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e] evaluated the color stability of various restorative materials after exposure to different solutions and found that the microparticulate composite, which contained larger filler particles, exhibited the lowest color variation compared to the other materials.\u003c/p\u003e \u003cp\u003eThe studies by Kao (1989) and Geha et al. (2021) show that the composition of the organic matrix of composite resins directly interferes with their behavior in the face of chemical and mechanical challenges. Kao [63] observed that resins with UDMA matrix were more susceptible to dissolution by food simulant liquids (FSL) than those with BisGMA matrix, demonstrating lower resistance. Geha et al.[\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e], in turn, found that the exposure of the resins to chemical agents such as citric and phosphoric acids, alcohol and distilled water resulted in different degrees of degradation, affecting the properties of the composite resin. These findings reinforce that the chemical composition of the organic matrix is an important factor for the resistance and color stability of composite resins under adverse conditions.\u003c/p\u003e \u003cp\u003eThe results of this study highlight the importance of considering both the choice of curing-light device and the application technique to minimize unwanted aesthetic changes, thereby enhancing the longevity and predictability of the procedures.\u003c/p\u003e"},{"header":"CONCLUSION","content":"\u003cp\u003eBased on the hypothesis that the variables of tip angulation, type of curing-light device, and type of resin-based material influence the photopolymerization process\u0026mdash;and consequently, the aesthetic quality of composite resin restorations\u0026mdash;this study demonstrated that these variables do, in fact, significantly impact the outcomes. It was observed that the Valo Cordless\u0026reg; device resulted in the lowest total color variation for the Vittra APS\u0026reg; composite resin when used at a 45\u0026deg; angle. Meanwhile, the Opallis Flow\u0026reg; resin showed better performance with the Radii-Cal\u0026reg; device, also at a 45\u0026deg; angle. Furthermore, it was found that increasing the angulation to 45\u0026deg; with the Radii-Cal\u0026reg; device significantly increased the total color variation in the Vittra APS\u0026reg; and Opallis Conventional\u0026reg; resins, confirming the hypothesis that the tip inclination can negatively affect the final aesthetic result. These findings reinforce the importance of selecting an appropriate curing-light device and paying close attention to tip angulation during the clinical procedure to ensure greater aesthetic predictability of the restorations.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e \u003ch2\u003eConflicts of interest/Competing interests\u003c/h2\u003e \u003cp\u003eThe authors have no conflicts of interest to declare that are relevant to the content of this article.\u003c/p\u003e \u003c/p\u003e \u003cp\u003e \u003cstrong\u003eEthical Approval\u003c/strong\u003e \u003cp\u003eNot applicable.\u003c/p\u003e \u003c/p\u003e\u003ch2\u003eFunding\u003c/h2\u003e \u003cp\u003eThis work was supported by a Ph.D. research scholarship granted by CAPES.\u003c/p\u003e\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eM and P wrote the main manuscript text; A.P and R. prepared figures 1-3 and table 1-2; R prepared table 3; All authors reviewed the manuscript.\u003c/p\u003e\u003ch2\u003eAcknowledgements.\u003c/h2\u003e \u003cp\u003eThe authors would like to thank CAPES for the financial support through the granting of the research scholarship.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eIlie N, Hickel R (2011) Resin composite restorative materials. 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Int J Dent 1:2021. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1155/2021/4895846\u003c/span\u003e\u003cspan address=\"10.1155/2021/4895846\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Polymerization. Dentistry. Color. Composite Resins","lastPublishedDoi":"10.21203/rs.3.rs-6475219/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-6475219/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003e\u003cstrong\u003eObjective\u003c/strong\u003e– The present study aimed to evaluate the influence of the tip angulation of two curing-light devices on the total color variation (ΔE) of conventional and flowable composite resins.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eMaterials and Methods\u003c/strong\u003e – A total of 120 disc-shaped specimens were prepared using three types of composite resins: Vittra APS®, Opallis Conventional®, and Opallis Flow®. The specimens were divided into 12 experimental groups, considering two tip angulations of the curing-light devices (0º and 45º) and two different devices: Valo Cordless® (third-generation LED with a broad spectral range) and Radii-cal® (second-generation LED with a narrow spectral range). The resins were photoactivated according to the manufacturers' instructions, and colorimetric analysis was performed using the CIELab* system at baseline and after 15 days, with a reflection spectrophotometer. Data were analyzed using Levene’s and Shapiro-Wilk tests, followed by three-way ANOVA and Tukey’s test, with a significance level of 5%.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eResults\u003c/strong\u003e – Statistically significant differences were observed (p \u0026lt; 0.05): the Valo Cordless® resulted in lower color variation; the Opallis Flow® resin showed greater color stability; and increasing the tip angulation to 45º led to higher color variation in Vittra APS® and Opallis Conventional® resins when using the Radii-cal® unit.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConclusion\u003c/strong\u003e – Both the type of composite resin and the curing-light devices, as well as its angulation, influence the color stability of restorations.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eClinical Relevance\u003c/strong\u003e – Clinically, these findings highlight the importance of proper light-curing technique and appropriate material selection to ensure the aesthetic quality and longevity of restorations.\u003c/p\u003e","manuscriptTitle":"Effect of angulation in different curing-light devices on color variation in composite resins","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-05-05 20:37:57","doi":"10.21203/rs.3.rs-6475219/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"4209a781-7f12-419e-bf17-965e9c9b2167","owner":[],"postedDate":"May 5th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2025-05-18T16:38:10+00:00","versionOfRecord":[],"versionCreatedAt":"2025-05-05 20:37:57","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-6475219","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-6475219","identity":"rs-6475219","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}