Color stability is an important requirement affecting the choice of restorative materials. At present, esthetic appearance is desired by both children and parents. To meet this increased esthetic demand, various compositions of restorative materials have been developed for clinical use. The most common tooth-colored restorative materials used in pediatric dentistry include composite resins, glass ionomer cements (GIC), and compomers. ¹

Several advantages, including physicochemical adhesion to tooth tissues, fluoride release, anticaries properties on restoration edges, thermal expansion coefficient similar to that of the natural tooth tissue, and elevated remineralization in adjacent proximal caries, are reported for GIC. ² , ³ Nevertheless, conventional types of GIC suffer from drawbacks including limited fracture/abrasion resistance, poor esthetic features, and moisture sensitivity, weakening the physical properties of a material. ⁴ As a result, a novel restorative material has been recently developed (Equia, GC, Tokyo, Japan).

Equia contains an extremely viscous type of GIC (EQUIA Fil, previously known as Fuji IX GP Extra) covered with a newly developed nanofilled coating material (Equia Coat, formerly known as G-Coat Plus). The developed material was fortified through alternating the powder/liquid ratio, particle size, and distribution. Equia was developed for application in permanent restoration belonging to Class I, II, and V cavities. ⁵ In general, various extrinsic and intrinsic elements cause the discoloration of restorations after a long period. ⁶ Factors affecting the discoloration of materials include insufficient polymerization, filler dimension and content, exposure to various foods and beverages, and oral hygiene. ⁷ , ⁸ , ⁹ , ¹⁰

Liquid oral medicines are usually recommended to treat chronic diseases for prolonged periods. ¹¹ The ingredients used in these liquid formulations include sugars, acids, buffering agents, permitted coloring agents in the form of oil, and/or water-soluble agents. ¹² , ¹³ Low endogenous pH and high titrable acidity of these medicines may pose unfavorable effects such as surface degradation of restorations. ¹⁴ With this background in mind, the current study aimed to compare the staining potential of pediatric drugs using an in vitro staining model.

Specimen preparation

The present in vitro study was approved by the Research Ethics Committee of Ardabil University of Medical Sciences, Ardabil, Iran (with the ethics code of IR.ARUMS.REC.1396.246). Four groups of drugs commonly consumed by children were tested in the present study Table 1. A2 color shades of four restorative materials were selected in this study Table 2.{Table 1}{Table 2}

A total of 160 samples with disc shapes were fabricated using each material (with a diameter of 5 mm and thickness of 2 mm) according to the manufacturer's instructions using plastic molds. A light cure was applied on the top and bottom surfaces of each specimen for 20 s using a light-emitting diode light-curing unit. All the discs with voids or irregularities in shape or surface were excluded from the study. The specimens were randomly classified into four groups (n = 40; from each material). After the removal of the specimens from the molds and provision of smooth surfaces using Mylar strips, the samples were maintained in distilled water at 37°C for 24 h for rehydration and completion of their polymerization.

Staining process

The samples (n = 5) were randomly selected from each material and immersed in each of the eight drug liquids three times/day for 2 min at 37°C within a test period of 7 days. All the solutions were renewed on a daily basis. The specimens were kept in artificial saliva (Glandosan ^®, Helvepharm AG, Frauenfeld, Switzerland) between the immersion periods.

Color change measurement

The restorative materials' baseline color was measured using a digital spectrophotometer (Vita Easyshade, Vita Zahnfabrik, Bad Säckingen, Germany). Before the measurement of the specimens' color, the device was calibrated with the use of its calibration block based on the manufacturer's instructions. Following the completion of the immersion time, the specimens' color was calculated using the spectrophotometer as previously described. Changes in each specimen's color were investigated according to color specifications with the use of the CIE L*a*b* color space system.

A three-dimensional color space containing lightness (L), red-green (a), and yellow-blue (b) components are represented by the CIE L*a*b* system. The color variation (ΔE) was measured 1 week after storage and at baseline as two color positions with the use of the following formula:

ΔE (L*a*b*) = ([ΔL*]2+ [Δa*]2+ [Δb*]2]1/2.

Where ΔL* is the difference between the L* values; Δa* is the difference between the a* values; and Δb* is the difference between the b* values.

Statistical analysis

The Kolmogorov–Smirnov test was utilized to assess the normal distribution of the collected data. Two-way analysis of variance (ANOVA) was employed to assess the type of material and effect of the staining agent on color change. The SPSS software (version 23; SPSS, Chicago, Ill., USA) was used for data analysis.

Table 3tabulates the mean and standard deviation of ΔE for each material. The mean color changes (ΔE) varied within the range of averaged 3–9.7 for the entire drugs and restorative materials. The most and the least prominent alterations were detected in Vitane-resin modified GIC and Vitane-Filtek Z250 XT, respectively.{Table 3}

The maximum and minimum ΔE* values were observed for sodium valproate and cephalexin in EQUIA Fil conventional reinforced GIC, respectively. Significantly higher and lower ΔE* values were reported for vitane and ibuprofen in resin-reinforced GIC, respectively. Cephalexin and vitane induced the maximum and minimum ΔE* values in Filtek Z250 XT, respectively. In Filtek Z350 XT, the maximum and minimum ΔE* values were observed for cephalexin and acetaminophen, respectively Table 3.

As the results of two-way ANOVA demonstrated, the interactions between all the materials and staining drugs were significant (P < 0.001). The Games-Howell posthoc test was utilized to analyze restorative materials and drugs used in the present study. Subgroup analysis also confirmed significant differences between ΔE and different restorative materials as well as ΔE and drug types (P < 0.001). However, no significant difference was detected between the color change values of various drugs in the materials Table 4and Table 5.{Table 4}{Table 5}

Since oral restorations are persistently exposed to staining foods and beverages, the color durability of tooth-colored dental materials is a crucial element. The replacement of the discolored restoration, especially in pediatric patients, is associated with increased costs and time of parents as well as behavior management problems in children. ¹⁴ For the purpose of submitting the entire materials to the same staining protocol without any probable bias, the present in vitro study was conducted under standardized staining conditions. This process enabled full control of all the variables. In addition, it does not expose children to superfluous drug prescriptions.

To the best of our knowledge, there have only been a limited number of studies on the effect of drugs on dental materials in children. Therefore, the present study attempted to assess the impact of four pediatric medication types on color stability in various tooth-colored restorative materials. For the prevention of bias resulting from polishing and simulating the most extreme but clinically related situation, the surface did not undergo polishing, and surface smoothness was provided by Mylar strips.

In the present study, the color measurement was calculated with CIE Lab because it is a repeatable method and sensitive for small color changes similar to the method used in the abovementioned studies. ¹⁵ Based on the human eye's capability in differentiating color, variations in color values were distinguished using three different intervals, including ΔE <1 undetectable with the human eye, 1.0< ΔE <3.3 distinguishable by a skilled individual, and ΔE >3.3 easily observable with naked eyes. The ΔE value of 3.3 or below is clinically regarded as acceptable in dentistry. ¹⁶ According to the results of the current study, the ΔE in all groups was higher than 3.3.

The color stability of esthetic restorative material is relevant to resin matrix hydrophilicity, filler particle dimensions, polymerization depth, and surface properties. ¹⁷ , ¹⁸ , ¹⁹ Materials with less filler and rough surface are more prone to discoloration. ²⁰ An increase in particle size causes increased water absorption through polymer chains. ¹⁸

In the present study, GIC showed a greater color change, compared to composite resin in all the immersion drugs. The relative susceptibility of GIC for staining could be attributed to the porosity of the glass particles, dehydration after setting and drying, and microcracks allowing staining and discoloration of the restoration. In addition, the glass filler particles can absorb water onto the surface rather into the bulk of the material; ²¹ however, based on the literature, hydrophobic substances, such as resin composites, are claimed to have higher color stability and stain resistance, compared to hydrophilic substances, such as GICs and compomers. ²² The results of the current study also supported the aforementioned conclusion.

Resin-modified glass ionomer (RMGI) showed a greater color change in comparison to other restorative materials in all the immersion drugs. The RMGI and conventional GIC both have a similar ion-releasing glass; nevertheless, smaller filler particles were utilized in RMGI. The light triggers the primary setting reaction subsequently undergoing an acid-base reaction after water absorption. ²³ According to the evidence, during the polymerization of RMGI, the color of glass change and water absorption affected by resin content and HEMA copolymers in this material can cause water absorption up to about 80% of weight. ²⁰ , ²⁴

Equia Forte Fil is offered in the form of encapsulation, simplifying material transportation to the cavity without the need for manual mixing. In this study, Equia Forte Fil demonstrated lower discoloration in comparison to RMGI. The reason might be the nanofilled coating of resin, enabling an enhanced initial filling material stabilization in the curing stage as well as elevated infiltration and closure in GIC superficial defects.

Tüzüner et al. studied the effects of pediatric drugs on color stability in different restorative materials among children. They reported significant discoloration values in composites in comparison to those of GIC and compomers. The results of the aforementioned study showed no interaction between restorative materials and drugs which is contrary to the findings of the current study. ²⁵ This can be due to the ingredients of the materials and surface texture differences. In another study, Afzali assessed the effect of ingested liquids on the color change of composite resin; unlike the present investigation, they concluded that the discoloration values did not depend on the type of staining solution. ²⁶

Nanohybrid composite resins are potential alternatives to conventional composite due to better strength, gloss, and lower shrinkage. ²⁷ Filtek Z350XT Flowable composite resin containing nanofillers showed higher discoloration in comparison to Filtek Z250 XT composite resin. The color change of composite resins depends on their surface topography, size, and amount of filler particles, water sorption, and hydrophilic nature of their resin matrix. ²⁸ The higher stainability of Z350XT can be due to its high monomer content, lower filler, and orientation of filler particles.

The results of a study carried out by Khatri and Nandlal revealed that an examined conventional composite resin had higher susceptibility to color change within various media over an extended period in comparison to nanocomposites. ¹⁰ Elwardani et al. reported that Filtek Z250 and Filtek Supreme showed no significant difference in surface roughness and color change at all measurement times. Immersion solution had a significant effect on surface roughness and color change. ²⁹

In another study, Yazici et al. indicated that nanocomposites (Filtek Supreme) have greater color changes than microhybrid composites (Clearfil AP-X) 30 days after dipping in tea. ³⁰ Adusumilli et al. evaluated the color stability of conventional GIC and giomer when immersed in various consumable drinks and foods at different immersion periods and observed conventional GIC demonstrating greater ΔE values, compared to giomer. ³¹

The present in vitro study did not mimic the real oral environmental conditions and multiple factors affecting discoloration which is considered a limitation. However, it is recommended to perform further studies for the evaluation of surface irregularities, degree of polymerization, and water sorption, finishing, and polishing of these restorative materials. Furthermore, a study should be carried out on the role of different staining properties of examined pediatric drugs in stabilizing the color of restorative dental materials, probably in terms of sugar contents and pH levels.

Despite the limitations of the current study, color changes were observed in all restorative materials after immersion in drugs. In addition, GIC had a greater color change in comparison to nanohybrid composite resins.

Financial support and sponsorship

Nil.

Conflicts of interest

The authors of this manuscript declare that they have no conflicts of interest, real or perceived, financial or nonfinancial in this article.