The wide use of the different shades of adhesive composite as esthetic restoration in anterior and posterior teeth paid attention to its multiple steps and the time consumption that produced challenges for dentists.16 Recently, many manufacturers introduced a new single-shade resin composite as it has the advantage of reducing chair time and reducing the time of shade selection. 16 Moreover, it was reported that any discoloration in the resin composite will affect the aesthetic 17, 18 so, the current study presented the problems of color stability of resin composite after exposure to commonly consumed drinks of different storage periods. The null hypothesis in this study was totally rejected due to statistically significant differences in color and surface roughness values of both resin composite materials before and after immersion at evaluation with the Vita easy shade, profilometer, and AFM.
The color stability and surface characteristics of the two single-shade resin composites used depends on the different compositions; fillers, particle size, and distributed resin matrix. A commercially available supra-nanofiller resin composite (omnichroma) was compared against a nanohybrid resin composite (Venus pearl). Nanotechnology applications introduced in the fillers size range within 0.1- 100nm to improve properties 19. Studies that evaluated the stability of single structured resin composite are severely lacking the limit proper assert its chemical performance. It was stated that details of the fabrication conditions for the organic filler distributed inside the Omnichroma resin are not clear. 20
The esthetic and mechanical properties of resin composite are influenced not only by their chemical composition but also by the environment to which they are exposed such as chemical agents found in saliva, foods, and beverages either intermittently or continuously. Coffee is a strong stain popular 4,21 and favorable drink used daily by most of the population. So, it was chosen as one of the experimental immersing solutions. While distilled water was used as a control to investigate the behavior of the resin composite itself. 14 It is worth mentioning that artificial saliva and distilled water have the same effect on resin composite. 22
In this study each step was made to standardize the methodology; the specimens’ thickness of 2mm for the light cure unit and the curing time was adjusted to 40sec with 20sec exposure time for the top and 20sec for the bottom respectively 23, miller strip and the standardized finishing and polishing procedures. Specimens were immersed in distilled water for 24 hours before immersion in the tested solutions to complete polymerization. 17
In the current in-vitro study, a static immersion was done for all specimens for one day and 14 days which was equivalent to one month and 14 months of consumption, respectively. 17 The increase in temperature will accelerate color change in the restoration 24, specimens were incubated in to adjust the temperature at 37⸰c all the storage time to simulate the oral environment. Coffee was replaced with a new proportion every 24 hours to minimize bacterial growth.
Visual perception of color is a psychological point-view and unfortunately depends on the observer’s skill. 14 In order to overcome the problem of visual assessment of the color, many color-evaluating devices have been used as Colorimeters and Spectrophotometers that are more precise than the naked eye. 14 Color assessments in our study were done using a digital spectrometer device Vita Easy shade V. This device is considered a reliable tool to measure the color change not only in clinical applications but also for research purposes in evaluating color interactions of human teeth and dental materials. 25
Color measurement is usually done by using the CIELAB color system. 14 CIEL*a*b system is very popular and it provides a standardized technique with useful analysis of ΔE* values accurately. This system can define small color changes accurately and have many advantages including, objectivity, repeatability, and sensitivity. 14
Surface roughness refers to the finer irregularities of the surface texture that refers to the action of the production process or the material’s features.8 Currently several available methods are present to measure the surface texture of any material including contact stylus tracing, scanning electron microscopy, laser reflectivity, non-contact laser metrology, and atomic force microscopy. Contact stylus tracing was used in the current study because it was fast, simple, and reliable for the comparative assessment of surface roughness properties of both tested single-shade composite resins. 26Atomic force microscopy (AFM) is a technique for analyzing the topography of the surface. It is an effective technique for characterizing nanoparticles and nanomaterials because it offers qualitative and quantitative information on several physical properties such as size, shape, surface texture, and roughness with a demonstrating image for any surface type, including polymers, ceramics, composites, glass, and biological materials.27
A strong and positive correlation between color stability and surface roughness results in our study was explained by the structure and chemical composition of both resin composite materials used. Based on the fact that composite resins with smaller filler size exhibit smoother surface property 28 and less color change 4, both resin composite materials exhibited statistically significant difference behavior regarding surface roughness at baseline. The O groups showed superior surface smoothness than the V groups which could be related to the lower filler size 4 and higher filler loading 29as mentioned in table (1). The specimens immersed in the coffee solution reported greater color change and surface roughness when compared to the specimens immersed in distilled water. This could be due to both adsorption and absorption of the yellow stains which have low polarity. This low polarity of yellow stain has the ability to penetrate into deeper layers of resin composite 14, in agreement with many studies. (4, 17) On the opposite side, a study found an acceptable color change after immersion in coffee for 48 hours E < 3.3, this may be due to difference in immersion solution preparation methods and concentration. 30
Group O2 and V2 demonstrated unacceptable color change (˃3.3) after 14 days of immersion in distilled water which was in consistent with a study that had an unacceptable color change of resin composite after immersion in distilled water for 5 days. 14 Moreover, it has been reported that the water absorption of composite resins reaches its highest level in 7–60 days. 17 In contrast to Farah and Elwi who found that immersion in distilled water for 7 days resulted in imperceptible color changes (ΔE ≤ 1). 31
It was stated that, when inorganic fillers de-bond from the resin matrix this may lead to leaving voids, resulting in an increase in the surface roughness forming a surface susceptible to external stains. 8, 32Additionally, the resin matrix plays an important role in staining susceptibility. 14,33,34 Many studies stated that the ability of resin composite to discolor depends on the hydrophilicity of the resin matrix and the ability of a material to absorb water. 32, 35Both materials have matrix composition based on triethylene glycol dimethacrylate (TEGDMA) and urethane dimethacrylate (UDMA). It was reported that TEGDMA monomer is responsible for color change due to high water absorption and an increase in coloration. 4,17 In agreement with a study where the most color change was related to the nanofilled single shade resin composite (Omnichroma) after immersion in coffee for 1 day in comparison to multi-shade resin composite that could be due to TEGDMA in its composition. 4 Different opposite study in findings, they stated that no correlation between color and roughness. 36
Nanohybrid (Venus Pearl) composite was more color unstable than nano-filled composite (Omnichroma). According to the data provided by the manufacturer (Kulzer GmbH) who claimed that, Venus Pearl with novel low shrinkage composition of tricyclodecane (TCD)-urethane monomer which is characterized by big molecular size that demonstrate good chemical stability. 3 Although nanohybrid (Venus Pearl) contains tricyclodecane TCD urethane-based monomer, which in turn gives high resistance to discoloration 3, its lower filler content and presence of agglomerated particles (nanoclusters) could be the reason for the less color resistant in comparison to the nanofilled resin composite (Omnichroma). This agreed with another study which concluded that nanohybrid resin composite has inferior color stability and surface roughness compared to nanofill type.8, 9 This explains that the staining process of dental composite is a multifactorial issue. It depends not only on the type of resin matrix but also on filler size, degree of polymerization, water sorption, degree of smoothness, type, and exposure time to staining solution. Moreover, environmental factors such as pH and temperature play roles in the staining process. 17
The mean color values and surface roughness after 14 days period was the highest for both Groups O1 and V1. This could be due to increase the interaction between the resin and the chemicals. More penetration of water inside resin with staining substances of the coffee solution occurred. These conclusions agree with many previous studies. 4, 9, 14, 17
Although the present study confirmed the detrimental effects of tested solutions on single-shade resin composite material, there are several limitations in our study. Similarly, to other in vitro studies, there are factors affecting the restorations in the oral cavity: microbiota, saliva circulation, temperature, and pH changes. Therefore, the oral cavity could not be imitated exactly. 17