According to the results of the present study, since there were differences between the color changes caused by IAMs, the null hypothesis was rejected.

Especially in anterior dental restorations, it is very substantial to know the color-resistant properties of DRMs by dental professionals in order to provide the patient with functional and esthetically long-lasting restorations. The color stability of resin-based DRMs could be affected by the type of material and light polymerization strategy [13]. The material is favored for dental restorations not only because of its mechanical properties but also because of its resistance to discoloration, particularly when used in aesthetically important areas. In the present study, restorative materials with variable proportions of filler and resin matrix were favored. To standardize the color of different DRMs, the A2 shade was used for all materials. Likewise, all samples were prepared with a standard mold in order to ensure equal and maximum polymerization in all parts of the materials. The oxygen inhibition layer is formed as a result of the contact of the surfaces of resin-based DRMs with air. This may affect the polymerization quality of the outer layer of resin-based DRMs [13, 14]. In the present study, mylar strips were placed on the lower and upper surfaces of the materials and polymerized in order to minimize the layer formed in resin-based DRMs as well as to obtain smooth and homogeneous surfaces. After the DRMs were polymerized, finishing and polishing procedures were applied to all samples.

Among the asthma medications available in various forms such as tablets, syrups and inhalers, IAMs are very important in the treatment of asthma. Because higher drug concentrations can be achieved locally in the respiratory tract with IAMs. At the same time, this route of administration has a low risk of systemic side effects. Therefore, IAMs can be administered several times a day using various forms of inhalers or nebulizers. However, the duration of use of the IAMs used in asthma treatment may differ. While short-term medication use is necessary for acute exacerbation, regular and long-term prescription of medications is required in children with chronic asthma due to the chronic nature of the disease. In the present study’s in vitro conditions, we evaluated 7-day medication administration to mimic acute exacerbations treatment and 21-day medication administration to simulate chronic treatment for childhood asthma.

Numerous aging/staining protocols have been used in the literature to evaluate the discoloration of DRMs. Miotti et al. [15] showed that the partial immersion method of DRMs in staining solutions results in lower color change values than the total immersion method. Theoretically, it has been reported that the clinical situation is better simulated when DRMs are immersed in staining solutions by partial immersion. However, the form (inhaler form/aerosol) of the medications used in the current study differs from studies in the literature that employ aging protocols involving medications/liquids (syrups, beverages). In the present study, inhaled medications were administered vertically, in in-vitro conditions, only perpendicular to the upper surfaces of the samples, as in clinical practice, since we think that DRM surfaces bonded to teeth will not interact directly with inhaler medications.

The preferable assessment methods in the studies should be identical to facilitate a clearer comparison between the results of the research and those of the literature. In light of this, color change evaluation (CIE LAB) formulations, which have been reported to be utilized more frequently in the literature [8], were utilized in the present study.

DRMs used in dentistry must be resistant to environments that cause color change. The factors affecting the color sensitivity of DRMs are water absorption / solubility properties, surface reactivity and polimerization reaction of the materials [16]. Color perception is a complex concept influenced by various factors such as transparency, opacity, type, and direction of light. Spectrophotometric color analysis is more accurate and repeatable compared to visual color evaluation [17]. In order to reduce subjective evaluation errors when determining the colors of the DRMs, a spectrophotometer, a dependable instrument for color analysis, was utilized in this study.

When the DRM thickness is on average 1–2 mm, the effect of the background used during color measurement on the color of the restoration is significant [18]. Consistent ΔEs can be compared if the color measurement is done on the same background each time. When the effect of the background / environment on the accuracy of visual color matching was investigated, it was found that the color match was best on black and white backgrounds [19]. In a previous study [20], color measurements were made on both black and white backgrounds, and it was reported that these two backgrounds could simulate two different clinical situations. They stated that the black background can mimic the situation where there is no dental structure behind the DRM, while the white background can mimic the situation that one of the dental walls is still present. However, it is still unclear which background is more suitable for dental color measurement [18]. In light of these considerations, the thicknesses of each of the DRMs in the present study were standardized as 2 mm, and color measurements were made on a standard background in the northward corner of the same room by the same person at the same time of the day.

Clinical manifestations of childhood asthma can range from mild to difficult to treat to severe. As a result, the medications used to treat asthma and the dosages required for treatment are highly variable [1]. It was evident in the present study that combined medication administration caused a higher color change in DRMs compared to other IAMs administrations. This is probably due to the fact that the MADD for combined medication therapy is higher than other IAMs. Moreover, different levels of ingredients such as citric and sulfuric acid in IAMs could affect the surface topography of DRMs [10]. The high ΔEs observed in the samples in the Ventoline and combined medication administered groups can be explained by the high MADD of these medications and the strong acidity of the sulfuric acid in the Ventoline nebul compared to the citric acid found in Budecort.

Rinsing the mouth after nebulization of some inhaled medications, particularly after the use of corticosteroids, reduces the risk of candidiasis and alleviates the unpleasant taste in the mouth [1]. To simulate the recommented mouth rinsing after nebulization, samples were rinsed under running distilled water in the present study. In contrast, the samples were not brushed because only the color change caused by IAMs was investigated.

The water sorption property of resin based composite restorative materials can promote hydrolysis of silane coupling agents and the loss of chemical bonds between inorganic fillers, promoting degradation of materials [21]. Water absorption/solubility could vary greatly depending on the formulation of the resin composite restorative materials. This situation is mainly due to the presence of more hydrophilic or hydrophobic monomers in the resin matrix component. Depending on the containing monomer type, there are differences in the water absorption of the polymers, and the hydrophilicity of the monomers is TEGDMA > Bis-GMA > UDMA > Bis-EMA, respectively [22, 23]. When the overall color change comparison of the DRMs in the present study was evaluated, it was seen that the three DRMs (Filtek Z550, Fusio Liquid Dentin and Dyract XP) with the lowest color change values contain UDMA monomer (Fig. 2). In spite of the fact that microhybrid composite and RMGIC contain UDMA, which is less hydrophilic than Bis-GMA and TEDGMA, a recent study [24] revealed that these materials exhibit significant discoloration. Thus, it is believed that monomers alone cannot determine the staining property of resin based DRMs.

Inorganic filler size might influence the optical characteristics of resin composites; in other words, it has been reported that materials with smaller filler sizes can maintain long-term optical stability [25]. In contrast, findings in another study revealed that composite resins with smaller filler sizes do not necessarily show low discoloration [26]. On the other hand, the sensitivity of the materials to coloration is not only affected by the inorganic filler size of the composite resins [27]. In our previous study [10], the effects of IAMs on the surface topography of restorative materials were investigated, and the surface roughness of Filtek Z550 and Filtek Ultimate was found to be similar. Therefore, in the present study, higher ΔEs of nanofilled composites compared to nanohybrid composites may show that the color change that occurs is not solely dependent on particle size or surface roughness. Bociong et al. [23] found that the water sorption of the Filtek Ultimate (nanofilled composite) is higher than that of the nanohybrid composites. Consequently, the fact that ΔEs of Filtek Ultimate are higher than ΔEs of Filtek Z550 after IAMs administration in the present study, may be due to the high amount of water sorption. The discoloration that occurs in DRM is multifactorial, and it is not possible to blame a single factor.

Similar to the results of the present study, in a previous study [28] evaluating the color changes of nanohybrid composite and RMGIC, the ΔEs of the materials were found to be nanohybrid composite < nanofilled composite < RMGIC, respectively. Abu-bakr et al. [16] showed that compomer and RMGICs are susceptible to discoloration as a result of exposure to various solutions for extended periods of time. Parallel to this study, while the hybrid composite showed the minimum detectable color change, ΔEs of RMGIC were found to be higher than the compomer. In a clinical study [29], the color match of the materials was determined to be 81.3% for Dyract and 28.6% for Fuji II LC. This situation supports the idea that higher ΔEs in Fuji II LC groups compared to Dyract groups may also occur clinically in this study conducted under in vitro conditions.

The idea that conventional GIC and RMGIC cements are not equally sensitive to surface discoloration due to their different material composition [5] is supported by the results of this study. In a previous study [30], conventional GICs exhibited lower water absorption values than RMGICs (excluding Equia Forte Fil). The hydrophilic nature of HEMA, which is in the composition of RMGICs and has water sorption property, may also cause this situation, as well as Bis-GMA, UDMA, etc. can also play a role. In addition, some of the RMGICs have also been reported to have a significant reduction in water absorption after a month of storage in water, due to the conversion of “loosely bound” water to “tightly bound” water in materials over time [31]. This may explain why the color change rate in Fuji II LC in this study was high in the first 7 days with medication administration, and the color change did not increase at the same rate during the following 14 days.

Futhermore, the high content of organic resin causes RMGICs to have a higher sensitivity to discoloration than conventional GICs, while the higher water content and less water absorption of conventional GICs make them less susceptible to discoloration [5]. These results support the findings that the color change in self cured-packable GIC in this study is less than the color change occurring in RMGIC.

In the in vitro conditions of the present research, the type of medications, the administration time-dosage, and the type of DRMs are important factors affecting the susceptibility to discoloration. However, the discoloration observed clinically in DRMs may be different. It should be kept in mind that the medications may dilute with saliva during the nebulization of inhaled medications in the oral environment, and the DRMs can be mechanically cleaned by chewing or brushing.

As it is not feasible to mimic the intraoral conditions in their entirety, this in vitro research into the effect of inhaled asthma medications on the color change of restorative materials has some limitations. A single color (A2) was selected for all DRMs in the present research, and capsulated forms have been preferred for the purpose of standardizing GICs. It was not feasible to replicate the clearance consequences of salivation or ingestion during the inhaler medication administration. Moreover, the artificial saliva utilized in the study lacks the proteins and enzymes found in natural saliva. The MADDs for children aged 6 years and older, as determined by the manufacturer’s insert of each IAM, were assessed in order to standardize the dosage of IAMs for the present study. Nevertheless, patients administer medications for varying durations and dosages in accordance with their age. Therefore, there may be different medication-dosage clinical scenarios in daily life for a asthmatic patient. In addition, translucency and whiteness parameters, which are other factors affecting the aesthetic clinical acceptance of the material, were not evaluated in this study.

Considering that DRMs are widely used in asthma patients, it is aesthetically important to evaluate the color changes of different DRMs caused by IAMs. Since the medications used in the treatment of chronic asthma are used for a long time, it will be beneficial for dental professionals to be careful in the selection of DRMs to reduce the esthetic concerns of the patients. Due to the administration of inhaler asthma medications, ΔEs increased for all DRMs. As a result, the exposure time of the DRMs to the medications increased, and higher ΔEs were detected. While the highest ΔEs were recorded in combined and Ventoline medication administered groups, the material with the highest ΔE was RMGIC.

The current in vitro study demonstrates that inhaled asthma medications can influence the color stability of dental restorative materials. When selecting DRMs for pediatric asthma patients, it is essential to consider the IAMs that these patients utilize. In the present in vitro study, it was found that combined IAM treatment caused more discoloration of DRMs than single IAM treatment options. The current research may reference future clinical research and contribute to the literature.