Knowing the mechanical and physical properties of different dental materials can contribute to increasing treatment alternatives [24]. Bioactive activity in dental materials is a new development that has emerged with advances in restorative dentistry technology. Bioactive materials exhibit superior properties such as ion release, stimulation of remineralization, and regulation of environmental pH [24, 25].

This study employed the thermal aging technique to compare the color stability of existing ion-releasing restorative materials with a commonly used nanohybrid composite resin. Valuable information was obtained regarding the effects of iron preparations on restorative materials. Color analysis across all groups revealed that the Equia Forte restorative material exhibited significantly greater color change than the other groups. Therefore, the hypothesis stating that “Iron preparations have no significant effect on the color stability of different restorative materials” was rejected.

Previous in vitro studies have mostly focused on the mechanical properties of materials [26, 27]. This study was strengthened by incorporating a thermal aging phase, simulating the oral thermal cycle, to better understand potential changes caused by clinical use. Based on the findings related to this technique, the other initial hypothesis, “Thermal aging has no significant effect on the color stability of different restorative materials,” was also rejected.

In the oral environment, restorative materials are frequently exposed to the acidic and staining properties of consumed foods and beverages. This exposure leads to a series of extrinsic and intrinsic changes in the materials, ultimately affecting their physical, mechanical, and esthetic properties [28]. The causes of external discoloration in children’s primary and permanent dentition are often attributed to inadequate oral hygiene, use of iron preparations, and chromogenic bacteria [29]. Supplementary foods prepared for children typically contain high sugar content and strong acidic properties. These features have raised concerns in various studies about whether such supplemental foods may increase the risk of tooth decay and erosion [30, 31]. Moreover, consuming these foods can cause discoloration of both teeth and restorations [32]. Based on these data, our study aimed to examine the staining effect of frequently used iron preparations on restorative materials.

Within the scope of our study, five different restorative materials with different mechanisms (hybrid glass ionomer, high-viscosity glass ionomer, alkasite, bioactive material, and resin composite) and two syrup-form iron preparations with different compositions (Ferrum and Microfer) were tested. The effects of these preparations on selected restorative materials were investigated in terms of color stability and lightness. These supplements, generally used for a short period, can significantly affect both the tooth surface and restorative material due to repeated use [33]. In our study, the preparations were immersed in different solutions for 72 h; however, some supplements may be used for shorter or longer durations [34]. In their study investigating the extrinsic tooth staining potential of high-dose and sustained-release iron syrups, color change was evaluated at 4, 8, 24, 48, and 72 h, and clinically significant staining (ΔE00 > 3) on teeth was observed in the 72-h waiting group [21]. For this reason, in this study, the samples were kept in the prepared solutions for 72 h.

Perceptible color changes in restorative materials are a criterion regarding the esthetics of restorations. While color changes negatively affect self-confidence and social adaptation in children and adolescents, they can also cause anxiety in parents [35]. The dentist may need to renew the discolored restorations in such clinical cases. The color stability of the restorative material is explained by the color change between two periods [36]. This value is determined from the ∆Eab and ∆E00 values calculated with the CIELab and CIEDE2000 formulas. Color coordinates can be calculated using the L* C* h* (lightness, hue, and chroma) parameters [19]. The CIEDE2000 formula is widely used in current studies on color change [19, 27, 37].

Therefore, the average CIEDE2000 values of the experimental groups were determined in this study to compare with related studies. In this system, the threshold value for perceiving color difference was determined to be ΔE00 = 0.8, and the clinically acceptable threshold value was determined to be ΔE00 = 3.1 [38]. Tuzuner et al. investigated the effects of different food supplements on the color change of polyacid-modified composite resin, composite resin, and conventional glass ionomer cement. Of the materials tested, the highest color change was recorded in composite resin; it was concluded that GICs showed acceptable color stability compared to composite or compomer materials [39]. In contrast, this study found that high-viscosity glass ionomer showed much more color change than an alkaloid, hybrid GIC, and composite resin. In another similar study on the subject, alkaloids and high-viscosity GICs were compared in terms of color change and it was reported that alkaloids were more prone to color change [1]. In a similar study, Çeliksöz et al. reported that the color stability of alkaloids should be improved [26]. We think that the results are different because the materials used in these studies have different properties, and pH is affected by their coloring properties.

In a study conducted in 2023 investigating the color stability of materials similar to this study, bioactive materials showed higher performance than hybrid GIS in terms of color change [40]. Among the materials tested in another study, hybrid GIC recorded significantly higher ΔE00 values compared to the other groups, indicating that it was more susceptible to color changes over time and after thermal aging. This is consistent with a previous study showing that GIC-based materials are more susceptible to color change than composite materials [41]. In another publication where the coloration potentials of resin-modified GIS and hybrid GIS were evaluated, and thermal cycling was used, hybrid GIS showed the highest color change [42]. This result is parallel to our study. This situation is thought to occur because of the high porosity of hybrid GIC materials and the ability of coloring agents to penetrate more into these pores.

In dentistry, the L* value in the CIE Lab* color system used in color measurement indicates the brightness or lightness of the color. In this system, the L* value varies between 0 and 100, with 0 representing perfect black and 100 representing perfect white. Therefore, an increase in the L* value causes the color to be perceived as lighter and brighter [43]. This relationship is important for accurate shade matching and esthetic restorations in dental practices.

In the study conducted by Pani et al. comparing the extrinsic tooth staining potential of high-dose and sustained-release iron syrups on primary teeth, the samples kept in the Ferric Oxide Polymaltose (FOP) Group did not create a statistically significant change in the L value compared to artificial saliva, whereas in this study when the material*solution interaction was examined, the samples in the Ferrum (FOP) group created a statistically significant difference [21].

In our study, when the initial and post-thermal cycling L1 and L2 values were examined, the EQ forte group was observed to be darker than the AB and SolareX groups. This result can be attributed to the internal porous structure of glass ionomer-based materials or potentially to bubble-filled mixing and application processes [44].

In addition, in a study examining the color differences of different composite materials, color measurements were made using CIE L* a* b* values, and the differences between these values were evaluated. Such studies are important for understanding the effect of the L* value on brightness and making the right color selection [45]. This information shows that increasing the L* value increases the brightness of the color, and this relationship is critical for esthetic applications in dentistry.

Since this study was conducted in vitro, it could not fully replicate the complex conditions of the oral environment. Additionally, aging was simulated solely by thermal cycling, without incorporating other mechanical or chemical challenges such as masticatory forces, pH fluctuations, or enzymatic activity. Therefore, the materials’ responses to mechanical loading, wear, and long-term intraoral conditions remain unassessed. Moreover, the simulation of iron preparation exposure may not fully mimic the complexity of their clinical application, including factors such as saliva flow, oral clearance, and individual patient usage patterns. Another limitation is the limited variety of restorative materials tested, which may restrict the generalizability of the results to other material types with different compositions and properties. Consequently, further well-designed clinical studies with a broader range of materials are necessary to validate and expand the applicability of the findings under real-life conditions.