Evaluation of the roughness, color match, and color stability of two monochromatic composite resins: a randomized controlled laboratory study
Aesthetic and restorative dentistry aims to replace lost and/or compromised dental structures with restorative materials that have physical, biological and functional properties similar to those presented by natural teeth . Natural teeth are polychromatic structures composed of organic and inorganic structures that present distinct and complementary optical characteristics , making it difficult to choose the color of the restorative material. Many restorative techniques are performed in an attempt to copy all the properties inherent to natural teeth and allow for imperceptible restorations. The use of different colors and opacities of resins in the layering technique intends to camouflage the restorations . To facilitate and reduce the number of resin kits, it was created, in 2019, the monochromatic resins Omnichroma (Tokuyama Dental, Tokyo, Japan) and Vittra (APS Unique FGM, Joinville, SC, Brazil). These one-shade resins can copy the color of the dental substrate that will be restored, right after the material’s light-curing, so that they have high translucency and are known to produce a “chameleon effect” . The smart technology used can make the composite itself weakens or amplifies specific wavelengths of light to blend with adjacent tooth color . This material is considerably versatile, as it can be used in restorations in anterior and posterior teeth and can restore colors from A1 to D4 (Vita ® Classical scale), excluding the need for layering and color selection, allowing longer clinical work time under the light of the reflector . They also present a good response to polishing and reduction of the amount of resins arranged in the dental office, reducing the cost of materials . However, when there is no lingual or palatal wall at the time of the restorative procedure, these materials will transmit oral darkness . In this clinical situation, the monochromatic resin is indicated as the second layer, after the reconstruction of the lost wall by using opacifying or dentin resin . The evaluation of composite resins involves understanding the interplay between thermocycling, color stability, and surface roughness . Thermocycling is a method used to simulate the thermal stresses that materials undergo in the oral environment and the surface roughness is the value of the texture on the surface of a material . Both the spectrophotometers and the CIEDE2000 formula have been used to objectively measure color changes before and after thermocycling . Clinical and laboratorial studies have shown positive results for these newer composites when evaluating optical properties, encompassing translucency, opalescence, and their potential for color adjustment . The Omnichroma was the first genuinely developed one-shade composite resin . Since then, other one-shade composites have been developed with differences in chemical composition and pricing. Studies on these new composites are necessary to understand the behavior of the material and to evaluate the differences among the one-shade composites commercially available. No study was found in the literature that evaluated and compared the laboratory performance of two one-shade composite resins. Thus, the objective of the present study was to evaluate the efficacy of monochromatic resins in capturing the adjacent color in the different shades of the teeth in different types of cavities, before and after thermocycling. In addition, the surface roughness of the restorations was evaluated.   Sample This is a randomized controlled laboratory trial, approved by the Research Ethics Committee of the Federal University of the Vales do Jequitinhonha e Mucuri (UFVJM) (protocol number 5,960,089). All teeth were sterilized in an autoclave  for the protection of the researchers and kept in distilled water during the study. To determine the sample size, the calculation for proportion estimation adjusted for finite population was used. Calculations with a significance level of 5%, with a power of 80%, a color compatibility ratio of 84%  and a margin of error of 9% determined a minimum of 57 restorations per group. Mandibular central incisors and mandibular lateral incisors that belonged to the human teeth bank of the UFVJM School of Dentistry were included. Incisors with carious cavities, fractured teeth, restored teeth, or teeth with defective enamel were excluded. After the 40 teeth in the study were sterilized, Arabic numerals from 1 to 40 were inscribed on their roots and pigmented with blue nail polish (Fig. ). The study had two groups: Group 1 ( n = 20) - Omnichroma composite resin (Tokuyama Dental, Tokyo, Japan) and Group 2 ( n = 20) - Vittra APS Unique composite resin (FGM, Joinville, SC, Brazil). Randomization, allocation concealment, and masking procedures The resin to be applied to each tooth was randomized by an independent researcher (JCRG) through a simple draw, and the result was kept in an opaque envelope, which was revealed at the time of restoration. The operators (ICS, SSO) and evaluator (DWDO) were masked as to the resin used. The resins were dispensed into an opaque dappen dish and delivered to the operator at the time of resin insertion. The evaluator was unaware of which resin was applied to each tooth. Preparation of specimens Two researchers (ICS, SSO) performed the standardized classes III, IV and V cavity preparations (Fig. A) using a high-speed handpiece under refrigeration and with 1090 and 1017 diamond tip drills on all tooth. The drills were discarded and replaced after 5 cavities had been made. Class III – Using a 1017 diamond tip drill, the cavity was made from 3.0 mm from the incisomesial edge, shaped as a half cane, with 2.1 mm in height, 2.1 mm in axial depth and VL, maintaining the lingual wall. At every cavosurface angle a bevel was made with 0.1 mm at 45º with a flame-shaped diamond tip drill. Class IV – Prior to preparation, the crown/lingual surface was copied in condensation silicone, forming a mold for later reconstruction. Using a cylindrical round diamond tip drill (1090), the incisodistal angle was removed with the proportions of 0.8 mm MD and 0.4 mm incisocervical. At every cavosurface angle, the bevel was made with 1 mm at 45º with a flame-shaped diamond tip drill. Condensation silicone matrices were made prior to the preparation of the cavities in order to assist in the restoration of the lingual and incisal anatomy of Black’s class IV restorations. Class V – Using a 1017 diamond tip drill, the cavity was made at the root crown junction, in a spherical shape with 2.1 mm in height, 1.0 mm of depth of the axial wall that which should be parallel to the buccal surface (convex) and 2.1 mm of MD width. At every cavosurface angle in enamel, the bevel was made with 1.0 mm at 45º with a flame-shaped diamond tip drill. The three cavities of the same tooth received the same composite resin. Initially, the opperator performed selective conditioning with 35% phosphoric acid Potenza Attacco (PHS do Brasil, Joinville, Brazil) on enamel for 30 s (Fig. B). Then, the samples were washed thoroughly and dried with absorbent paper. Once this was done, the Ambar Universal adhesive system (FGM, Joinville, Brazil) was applied with a disposable brush and, after waiting 30 s for the solvent to evaporate, it was then polymerized for 20 s (Fig. C). The resins were inserted into each cavity in increments of 1.5 mm, connecting two opposite walls and immediate light polymerization for 40 s, operated in continuous mode (LED Photopolymerizer D, Gnatus, São Paulo, Brazil), in each increment. This procedure was repeated until the cavity was filled and the restoration was completed, reestablishing the anatomical contour of the cervical third of the buccal surface (Fig. F). For all class IV restorations, a previously prepared silicone matrix helped with the lingual and incisal anatomy (Fig. D). On the matrix in both groups, the Blocker Ominichroma resin (Tokuyama Dental, Tokyo, Japan) was applied with a thickness of 0.5 mm and taken to the cavity and, after accommodation, it was polymerized for 40 s (Fig. E). After 7 days, the restorations were polished (SEF) with Potenza Specchi diamond paste (PHS do Brasil, Joinville, Brazil) and polishing discs with decreasing grain sizes and a diamond master felt disc (FGM, Joinville, Brazil) (Fig. G). Table lists the materials used to create the restorations and their respective compositions. Thermocycling process The 40 restored teeth were kept in distilled water at 37 °C and replaced every day for 1 week. In them, 2000 thermal cycles (CT) were carried out in the thermocycling machine (Ética Equipamentos Cientifiques S/A, São Paulo, SP, Brazil) which consisted of water baths at two different temperatures (5 °C and 55 °C), for 30 s each and a transfer time of 5 s. After each cycle, the specimens were stored again in water at 37 °C . Visual color evaluation Restorations were evaluated using modified FDI and USPHS criteria , before and after aging, by a blinded researcher (DWDO). The USPHS (shape, margin and color) criteria were adopted as described : Alpha (A)- The restoration matches the color and translucency of the adjacent dental tissues; Bravo (B)- The restoration does not acceptably match the color and translucency of the adjacent dental tissues; Charlie (C)- The restoration does not match the color and translucency of the adjacent dental tissues to an unacceptable extent. The modified FDI criteria  were evaluated according to Table . For intra-examiner calibration, one examiner (DWDO) was trained to USPHS and FDI criteria using natural teeth extracted and restored with composite resin. The same restorations were evaluated by the same examiner at two different times, 14 days apart. Kappa agreement was K = 0.920 for USPHS and K = 0.899 for FDI. Surface roughness Class V restorations were submitted to three roughness readings, from which the mean roughness was measured. The instrument was calibrated with the standard specimen, with a roughness of 1.80 μm in Ra. Ra analysis means the calculation of the arithmetic mean between peaks and valleys of a given surface. The teeth were placed in a container filled with modeling clay for stabilization during the three roughness measurements. The measurements were obtained using a Digital Surface Roughness Tester - SRT-6210 (Merit-mi, Qingdao, China) with a cutoff of 0.25 mm before and after the aging process. The teeth were placed in a high-density EVA container and maintained in position using a tweezer for stabilization and standardization during the color measurements (Fig. ). Objective color evaluation Before and after aging, the teeth and restorations were evaluated using the SP62S spectrophotometer and the QA-Master I software (X-Rite Incorporated - Neu-Isenburg, Germany). In each restoration, three consecutive measurements were taken with the tip of the meter in the center of the restoration. The tooth color was read in the central region of the buccal surface, with three measurements being taken. The tooth color parameter and each restoration was determined by the arithmetic mean of the 3 measurements. Color measurements were taken using the CIE L* a* b* color system . The total difference between booth tooth and restoration color (ΔE*) was calculated by the following formula: ΔE* = [ΔL 2 + Δa 2 + Δb2 ] 1/2 . The following cut-off points were used for ΔE analysis: ΔE ≤ 1 – color difference that cannot be detected clinically; 1 < ΔE ≤ 3.7 – color difference clinically detectable by all observers and clinically acceptable; ΔE > 3.7 – clinically unacceptable color difference and poor adaptation . Statistical analysis Statistical analyses were performed using the SPSS ® for Windows ® (Statistical Package for the Social Sciences, IBM Corp., United States) statistical package in version 26. Exploratory analyses of the data provided frequencies, means, and standard deviations. The assessment of normality was verified by the Shapiro-Wilk test. Intragroup comparison of quantitative data was performed using the paired T-test, and intergroup analysis was performed using the independent T-test. Categorical variables were submitted to the Chi-Square test and Fischer’s exact test. The confidence interval used was 95%. The level of significance adopted was 5%. The magnitude of effect was analyzed for the difference of the ΔE between groups. It was used the Cohen’s d to calculate the size effect. The results were categorized as having a small (0.20 < d), medium (0.21 < d < 0.50), or large (d > 0.51) effect.   This is a randomized controlled laboratory trial, approved by the Research Ethics Committee of the Federal University of the Vales do Jequitinhonha e Mucuri (UFVJM) (protocol number 5,960,089). All teeth were sterilized in an autoclave  for the protection of the researchers and kept in distilled water during the study. To determine the sample size, the calculation for proportion estimation adjusted for finite population was used. Calculations with a significance level of 5%, with a power of 80%, a color compatibility ratio of 84%  and a margin of error of 9% determined a minimum of 57 restorations per group. Mandibular central incisors and mandibular lateral incisors that belonged to the human teeth bank of the UFVJM School of Dentistry were included. Incisors with carious cavities, fractured teeth, restored teeth, or teeth with defective enamel were excluded. After the 40 teeth in the study were sterilized, Arabic numerals from 1 to 40 were inscribed on their roots and pigmented with blue nail polish (Fig. ). The study had two groups: Group 1 ( n = 20) - Omnichroma composite resin (Tokuyama Dental, Tokyo, Japan) and Group 2 ( n = 20) - Vittra APS Unique composite resin (FGM, Joinville, SC, Brazil).   The resin to be applied to each tooth was randomized by an independent researcher (JCRG) through a simple draw, and the result was kept in an opaque envelope, which was revealed at the time of restoration. The operators (ICS, SSO) and evaluator (DWDO) were masked as to the resin used. The resins were dispensed into an opaque dappen dish and delivered to the operator at the time of resin insertion. The evaluator was unaware of which resin was applied to each tooth.   Two researchers (ICS, SSO) performed the standardized classes III, IV and V cavity preparations (Fig. A) using a high-speed handpiece under refrigeration and with 1090 and 1017 diamond tip drills on all tooth. The drills were discarded and replaced after 5 cavities had been made. Class III – Using a 1017 diamond tip drill, the cavity was made from 3.0 mm from the incisomesial edge, shaped as a half cane, with 2.1 mm in height, 2.1 mm in axial depth and VL, maintaining the lingual wall. At every cavosurface angle a bevel was made with 0.1 mm at 45º with a flame-shaped diamond tip drill. Class IV – Prior to preparation, the crown/lingual surface was copied in condensation silicone, forming a mold for later reconstruction. Using a cylindrical round diamond tip drill (1090), the incisodistal angle was removed with the proportions of 0.8 mm MD and 0.4 mm incisocervical. At every cavosurface angle, the bevel was made with 1 mm at 45º with a flame-shaped diamond tip drill. Condensation silicone matrices were made prior to the preparation of the cavities in order to assist in the restoration of the lingual and incisal anatomy of Black’s class IV restorations. Class V – Using a 1017 diamond tip drill, the cavity was made at the root crown junction, in a spherical shape with 2.1 mm in height, 1.0 mm of depth of the axial wall that which should be parallel to the buccal surface (convex) and 2.1 mm of MD width. At every cavosurface angle in enamel, the bevel was made with 1.0 mm at 45º with a flame-shaped diamond tip drill. The three cavities of the same tooth received the same composite resin. Initially, the opperator performed selective conditioning with 35% phosphoric acid Potenza Attacco (PHS do Brasil, Joinville, Brazil) on enamel for 30 s (Fig. B). Then, the samples were washed thoroughly and dried with absorbent paper. Once this was done, the Ambar Universal adhesive system (FGM, Joinville, Brazil) was applied with a disposable brush and, after waiting 30 s for the solvent to evaporate, it was then polymerized for 20 s (Fig. C). The resins were inserted into each cavity in increments of 1.5 mm, connecting two opposite walls and immediate light polymerization for 40 s, operated in continuous mode (LED Photopolymerizer D, Gnatus, São Paulo, Brazil), in each increment. This procedure was repeated until the cavity was filled and the restoration was completed, reestablishing the anatomical contour of the cervical third of the buccal surface (Fig. F). For all class IV restorations, a previously prepared silicone matrix helped with the lingual and incisal anatomy (Fig. D). On the matrix in both groups, the Blocker Ominichroma resin (Tokuyama Dental, Tokyo, Japan) was applied with a thickness of 0.5 mm and taken to the cavity and, after accommodation, it was polymerized for 40 s (Fig. E). After 7 days, the restorations were polished (SEF) with Potenza Specchi diamond paste (PHS do Brasil, Joinville, Brazil) and polishing discs with decreasing grain sizes and a diamond master felt disc (FGM, Joinville, Brazil) (Fig. G). Table lists the materials used to create the restorations and their respective compositions.   The 40 restored teeth were kept in distilled water at 37 °C and replaced every day for 1 week. In them, 2000 thermal cycles (CT) were carried out in the thermocycling machine (Ética Equipamentos Cientifiques S/A, São Paulo, SP, Brazil) which consisted of water baths at two different temperatures (5 °C and 55 °C), for 30 s each and a transfer time of 5 s. After each cycle, the specimens were stored again in water at 37 °C .   Restorations were evaluated using modified FDI and USPHS criteria , before and after aging, by a blinded researcher (DWDO). The USPHS (shape, margin and color) criteria were adopted as described : Alpha (A)- The restoration matches the color and translucency of the adjacent dental tissues; Bravo (B)- The restoration does not acceptably match the color and translucency of the adjacent dental tissues; Charlie (C)- The restoration does not match the color and translucency of the adjacent dental tissues to an unacceptable extent. The modified FDI criteria  were evaluated according to Table . For intra-examiner calibration, one examiner (DWDO) was trained to USPHS and FDI criteria using natural teeth extracted and restored with composite resin. The same restorations were evaluated by the same examiner at two different times, 14 days apart. Kappa agreement was K = 0.920 for USPHS and K = 0.899 for FDI.   Class V restorations were submitted to three roughness readings, from which the mean roughness was measured. The instrument was calibrated with the standard specimen, with a roughness of 1.80 μm in Ra. Ra analysis means the calculation of the arithmetic mean between peaks and valleys of a given surface. The teeth were placed in a container filled with modeling clay for stabilization during the three roughness measurements. The measurements were obtained using a Digital Surface Roughness Tester - SRT-6210 (Merit-mi, Qingdao, China) with a cutoff of 0.25 mm before and after the aging process. The teeth were placed in a high-density EVA container and maintained in position using a tweezer for stabilization and standardization during the color measurements (Fig. ).   Before and after aging, the teeth and restorations were evaluated using the SP62S spectrophotometer and the QA-Master I software (X-Rite Incorporated - Neu-Isenburg, Germany). In each restoration, three consecutive measurements were taken with the tip of the meter in the center of the restoration. The tooth color was read in the central region of the buccal surface, with three measurements being taken. The tooth color parameter and each restoration was determined by the arithmetic mean of the 3 measurements. Color measurements were taken using the CIE L* a* b* color system . The total difference between booth tooth and restoration color (ΔE*) was calculated by the following formula: ΔE* = [ΔL 2 + Δa 2 + Δb2 ] 1/2 . The following cut-off points were used for ΔE analysis: ΔE ≤ 1 – color difference that cannot be detected clinically; 1 < ΔE ≤ 3.7 – color difference clinically detectable by all observers and clinically acceptable; ΔE > 3.7 – clinically unacceptable color difference and poor adaptation .   Statistical analyses were performed using the SPSS ® for Windows ® (Statistical Package for the Social Sciences, IBM Corp., United States) statistical package in version 26. Exploratory analyses of the data provided frequencies, means, and standard deviations. The assessment of normality was verified by the Shapiro-Wilk test. Intragroup comparison of quantitative data was performed using the paired T-test, and intergroup analysis was performed using the independent T-test. Categorical variables were submitted to the Chi-Square test and Fischer’s exact test. The confidence interval used was 95%. The level of significance adopted was 5%. The magnitude of effect was analyzed for the difference of the ΔE between groups. It was used the Cohen’s d to calculate the size effect. The results were categorized as having a small (0.20 < d), medium (0.21 < d < 0.50), or large (d > 0.51) effect.   One sample of Omnichroma composite resin was lost (fractured) after thermocycling. At baseline, there was statistically significant difference between the class IV restoration of group 1 and the tooth when evaluating the parameters a* ( p = 0.004) and b* ( p = 0.002), as well as, between the class V and tooth for parameter b* ( p < 0.001) (Table ). After thermocycling, the ∆E varied from 3.53 (class III) to 3.80 (class V) (Table ). At baseline, there was no statistically significant difference between the class III restoration of group 2 and the tooth when evaluating the parameters L* ( p = 0.462), a* ( p = 0.252) and b* ( p = 0.335); however, there was statistically difference between tooth and the class IV for b* ( p < 0.001) (Table ). At baseline, the ∆E of group 2 varied from 4.35 (class III) to 5.52 (class V) (Table ). There was no significant difference between the ∆E of Omnichroma and Vittra resins ( p > 0.05) (Table ). The size effect ranged from 0.146 (small) to 0.343 (medium) (Table ). At baseline and after thermocycling, there was no significant difference ( p > 0.05) between the USPHS parameters between the Omnichroma and Vittra resins (Table ). At baseline, when analyzing color using the FDI criterion, statistical significance ( p < 0.001) was observed between Omnichroma and Vittra resins in class IV (Table ). When comparing the surface roughness of Omnichroma and Vittra resins, no statistically significant difference was identified between them either initially ( p = 0.564) or after thermocycling ( p = 0.690) (Table ).   Monochromatic composite resins eliminate the need for layering and allow the use of just one resin for the entire restoration , as their technology provides color and opacity adjustment equivalent to the dental substrate . The present study was necessary to evaluate the effectiveness of this innovative material. This study demonstrated that the Omnichroma and Vittra resins present similar performance and fulfill the purpose of adapting to any color of the remaining tooth. The CIEL*a*b* system is the most used in colorimetric evaluation in research that seeks to specify colors objectively . The present study showed that class V of Omnichroma resin was the one that differed most from the tooth both before and after aging. This difference is probably due to its location at the crown-root interface with possible color distortion at the time of reading. The composite resin Vittra APS Unique showed greater discrepancy in relation to the tooth in class IV at baseline and in class V after aging. This was probably due to the different reading locations, being in the center of the tooth and at the ends of the restorations, without considering the individual characteristics of each tooth, such as translucency, opacity, opalescence  in their different dental thirds, since natural teeth are polychromatic structures composed of organic and inorganic structures (enamel, dentin and pulp) that have distinct and complementary optical characteristics . Therefore, the better adaptability of both resins in Class III at baseline is justified, since it is closer to the spectrophotometric reading location in the middle third of the tooth. Also, it is expected that the color of resin composites changes after thermocycling, which significantly affects the surface texture . Hydrolytic degradation occurred after thermal cycling, and due to ruptures at the matrix-resin interface, fillers were exposed in some places and more pronounced scratches and grooves were formed . This fact may explain the discoloration that occurred with the monochromatic composites tested. When analyzing the ∆E, it was found that the Omnichroma resin was clinically unacceptable at baseline class V, which decreased after thermocycling, becoming clinically acceptable. Contrary to the present study, Martins (2022)  identified in his research that the Omnichroma resin presented higher ∆E values after 30 days, which occurred due to the immersion of the specimens in coffee, being considered clinically unacceptable at the end of the study. On the other hand, the composite resin Vittra APS Unique also showed low values of ∆E in the groups that were immersed in water  corroborating the findings of this study in which the ∆E, despite initially unacceptable in all classes, managed to adjust after thermocycling, becoming clinically acceptable, which suggests its improvement over time. Several factors justify the color variation between resins, such as differences in their chemical formulations . However, this study did not identify a statistically significant difference in the ∆E of the groups, which indicates that the resins have similar behavior in relation to clinical acceptability, as both present similar color in relation to the tooth. This statistical result was confirmed by the size effect analysis. The Cohen`s d identified a medium effect between the ∆E of the groups, it means that the difference in color compatibility between the two composite resins is not so pronounced as to consider one resin clinically more relevant than the other. The results suggest that, in both groups, the resins can capture the structural color of the surrounding tooth, controlled by the size of the filler particles . This study evaluated classes III, IV and V restorations using the criteria of the USPHS and modified FDI methods and, in both groups, the monochromatic resins were similar in terms of the parameters evaluated. Although subjective and imprecise, the USPHS clinical criteria for evaluating dental restorations, developed by Ryge in 1980 , is widely used in scientific circles to identify failed restorations that can be repaired or should be replaced . However, with the improvement in the quality of restorative materials, there was a need to adopt a more sensitive method, with greater discriminatory power, namely the FDI method, presented by Hickel et al. in 2007 , which has been gaining prominence in research. Although objective analysis by spectrophotometer provides precise and quantitative data on color , the visual evaluation offers a qualitative and practical perspective that can be crucial for clinical decision-making. Visual evaluation is an essential daily practice for the dentist in the selection and adjustment of dental restoration colors. The analysis conducted in this study reflects real-world clinical practice. Monochromatic resins may not be recommended for anterior restorations due to their high translucency value, capable of reflecting the background color of the oral cavity and leaving the restoration with a grayish appearance . However, the present study verified a good clinical behavior of class IV restorations, mainly in terms of brightness of the Omnichroma resin. This was possibly due to the use of the Blocker Ominichroma resin whose role is to provide high hue and chroma, reducing the brightness of the background color  in the creation of the missing lingual barrier. The roughness of composites plays an important role in plaque retention, abrasiveness, wear kinetics, tactile perception, coloration and the natural brightness of the restoration . Thus, the longevity of color in restorations in the oral cavity is influenced by the quality of the surface and is considered satisfactory when it resembles the natural aesthetics of tooth enamel and low levels of roughness . The surface smoothness of microhybrid resins is associated with larger particle sizes and non-standard shapes . In contrast, nanohybrid resins, in addition to having smaller particle sizes, also exhibit nanometric standardization in their shape. The results of the present study indicate that there was standardization in the finishing and polishing protocol of the restorations and, therefore, the surfaces of both resins reached the same degree of roughness, brightness, and surface wear. The roughness of the monochromatic resins evaluated in this study did not statistically change after thermocycling, a result that differs from the findings reported by Alex & Venkatesh (2024)  who reported a higher Ra value for the surface roughness of Omnichroma after simulating brushing. The use of this abrasive method  may explain the difference in roughness between the studies. Objective and subjective of color and surface roughness analyzes indicate that the two composite resins present similar result. This is probably due to the technology of both that captures the adjacent structural color through their nanometric spherical charges . The fillers are the exact size and shape needed to generate the red-yellow color as ambient light passes through the composite, without the need for added pigments or dyes. This color generated by the spherical fillings matches the color reflected from the surrounding tooth structure, creating the perfect match with the tooth color . Since Vittra and Omnichroma composites have similar roughness and color matching capabilities, the present results suggest that other factors such as cost, ease of application, durability, and clinical acceptance are also important in determining the choice of a single-shade resin composite. Furthermore, these resins eliminated the need for layering and prior color selection, reducing restoration time. The subjective outcomes (USPHS criteria) regarding optical behavior and marginal discoloration found in this study are consistent with the findings of Anwar et al. (2024)  who concluded that Omnichroma demonstrated excellent color matching and good color stability over 12 months. However, it is important to note that Anwar et al. (2024)  conducted a clinical study over one year, whereas the present study was a laboratory investigation. The similarity between the clinical results and those of this laboratory test suggests that the monochromatic resin is clinically acceptable. Randomization and masking are two strategies considered essential pillars of methodological rigor capable of minimizing research bias, preventing distortions in studies and ensuring more robust results . Once masked, the researchers in the current study ensured a more objective and unbiased assessment of the restorations, which increases the internal validity of the study. This study, although well conducted, has some limitations. The initial reading of tooth color was restricted to the middle third, not coinciding with the areas restored later in the extremities, and the non-use of chromatic substance during the aging process. Also, the scarcity of laboratory studies comparing two monochromatic resins prevented comparison to other results. It is suggested the development of studies in which the color reading occurs in the three thirds of the teeth in order to make the comparison between the resin and the tooth more reliable, as well as, evaluating the roughness surface by atomic force microscopy. In addition, studies are suggested to evaluate the behavior of monochromatic resins in posterior teeth and clinical trials evaluating the behavior of monochromatic resins in the long term.   It was concluded that the color match of the composite resins Omnichroma and Vittra APS Unique was found to be clinically satisfactory in visual analysis. In the spectrophotometer evaluation, these one-shade composite exhibited high ∆E values for baseline, and the ∆E was clinically acceptable after thermocycling. The monochromatic composite resins tested were similar to each other in terms of color match and color stability with the tooth structure, showing better adaptation after thermocycling. Both resins showed low surface roughness.   