Introduction

Nowadays aesthetic appearance of dental restorations is the biggest expectation of both pediatric and adult patients. For this reason, color stability is of great importance during the selection of the restorative material to be used. In order to meet this expectation, the most frequently used restorative materials in pediatric dentistry include composite, compomer and glass ionomer materials [1].

Although conventional glass ionomer cements are often preferred in pediatric dentistry due to their advantages such as chemical adhesion to dental tissues, fluoride release and recharge ability and anticariogenic properties, they also have disadvantages such as limited fracture/abrasion resistance, poor esthetic properties and moisture sensitivity. In order to avoid these disadvantages, high-viscosity bulk-fill glass ionomer materials with a more viscous structure, increased powder/liquid ratio, and modified particle size and distribution have been developed [1, 2]. However, the materials should not only meet the aesthetic expectations, but also have features such as clinical longevity and high fracture/abrasion resistance. For this reason, new materials continue to be produced and existing materials continue to be developed day by day. Recently, the newer alkaline composite resin with various glass fillers and calcium releasing properties was introduced [3, 4]. This material is a bioactive, tooth colored restorative material with high strength and excellent esthetics [5, 6]. Cention N (IvoclarVivadent, Liechtenstein) is classified as an “alkasite,” which has been defined as a subgroup of composite materials. It also has the advantage of being cost-effective and simple to use, as it does not require any particular equipment or abilities [7].

The fact that aesthetic appearance is often associated with social acceptance and professional success dental restorations are not just important for the treatment of caries, but also for the psychological and physiological development of individuals [8]. For this reason, it is desired that restorative materials can maintain their long-term color stability. According to the literature, various extrinsic and intrinsic factors cause the discoloration of restorations after a long period. Intrinsic factors have been shown as insufficient polymerization, filler dimension and content. Moreover, extrinsic factors include exposure to various foods and beverages, drug formulations containing coloring compounds and oral hygiene [2, 8]. Analgesics, antibiotics, antihistamines, antiepileptics, multivitamins, and antitussives are among the most commonly prescribed drugs for children [8]. Drug formulations in the form of syrups or suspensions are typically supplied to young children suffering from acute and/or chronic disorders. These liquid formulations' constituents include sugars, acids, buffering agents, and coloring compounds that are both oil- and water-soluble. Low endogenous pH and viscosity of these drugs may pose undesirable consequences like erosion and intrinsic/extrinsic discoloration of teeth and dental restorations [1, 9]. Color measuring in dentistry can be assessed with the help of a color scale or with digital measuring devices. While numerous factors, including the physician's experience and the light source can influence the color choice by visual assessment, measurements made with digital measurement devices, such as the spectrophotometer, produce repeatable and more accurate data. The Commission Internationale de l'Eclairage (CIE) Color System is often used to evaluate the color change in dental materials. The CIELab color system has three coordinates, L*, a*, and b*. L* refers to the lightness of the color, while a* and b* denote the hue of the color. The total color stability of a material can be evaluated by calculating the total change in color ΔE when all three values are taken into account [10].

Previous studies in the literature have mostly focused on comparing the physical properties of Cention N with other dental materials like composite and glass ionomer cements [11,12,13]. In addition, there are only few studies conducted on the staining effect of beverages on alkasite material [3, 14]. To the best of our knowledge, no study has compared the staining ability of Cention N after immersion in drugs. Thus, the present study aimed to compare the staining susceptibility of three restorative materials, including Cention N, after immersion in different pediatric drugs for 1 week. The purpose of this study was to increase awareness regarding the usage of drugs that cause discolouration on restorations. First null hypothesis was that the alkasite restorative material show better color stability than the other materials. Second hypothesis was that exposure to different pediatric drugs will not cause the discoloration of dental materials.

Materials and Methods

Preparation of specimens

A glass ionomer cement, a composite and an alkasite restorative material in A2 shade were used to evaluate the color changes in this study (Table 1). 32 disk‑shaped specimens (5 mm in diameter × 2 mm thickness) were obtained from each of material by using a teflon mold. In order to obtain a smooth surface, a celluloid tape was placed over the mold, and it was held between two glass slides, to eliminate air voids. The manufacturer’s instructions were followed in preparing a total of 96 samples of restorative materials. Equia Forte Coat (GC Corporation, Tokyo, Japan) was applied in glass ionomer group according to the recommendation of manufacturer. Light-polymerized materials polymerized for 20 s using a light device (Valo Grand, Ultradent, USA). After polymerization, the surfaces of the samples were polished using polishing discs (Sof-lex, 3 M Espe, St.paul, Minn, USA). The discs were applied dry at 12,000 rpm for 60 s, respectively, according to their thickness, using a clinical contra-angle handpiece and a micromotor. All specimens were kept in distilled water at 37 °C for 24 h to complete the polymerization process.

Table 1 Composition of the restorative materials used in the study
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Staining procedure

Prepared specimens were kept in distilled water for 24 h. The specimens were then cleaned and dried using filter paper, and baseline color values were recorded using a clinical spectrophotometer (VITA Easyshade V, Vita Zahnfabrik, Bad Säckingen, Germany). The specimens prepared in each material (n = 32) were then separated into four subgroups (n = 8) based on the pediatric drugs formulations to be examined. Table 2 presents the characteristics of the pediatric drugs used in this study.

Table 2 Characteristics of pediatric drugs used in this study
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During a 7-day test period, each subgroup was immersed for 2 min in a different 10 ml undiluted pediatric drugs solution three times a day at 8-h intervals. After each immersion period, the specimens were rinsed and stored in distilled water until the next immersion period. All the solutions were refreshed on a daily basis. After 1 week of immersion periods, second measurements for each materials were performed using the same method described for the baseline measurements and recorded as 7-days values. According to these measurements (ΔE*) of each groups was calculated.

Color change measurement

Color values for each sample were recorded using a clinical spectrophotometer (VITA Easyshade V, Vita Zahnfabrik, Bad Säckingen, Germany) and the Commission internationale de l'éclairage (CIE) L*a*b* system. All measurements was performed at the center of each specimen, against the white reference background tile relative to the standard illuminant D65 [15, 16]. Prior to taking the measurements, the device was calibrated for white balance using the manufacturer's instructions and the accompanying calibration block. Three measurements were taken for each specimen and the average of these measurements was recorded. By using the L*, a* and b* numerical values, the color change (ΔE*) values were calculated with the following formula:

$$\mathrm{\Delta E}= [(\mathrm{\Delta L})2+(\mathrm{\Delta a})2+(\mathrm{\Delta b})2] 1/2$$
$$(\mathrm{\Delta L}=\mathrm{ L}2*-{\text{L}}1*,\mathrm{ \Delta a}={\text{a}}2*-\mathrm{ a}1*\mathrm{ and\;\Delta b}={\text{b}}2*-{\text{b}}1*)$$

The L2, a2, and b2 values are the CIE L* a* b* values measured at day 7, whereas the L1, a1, and b1 values are the baseline CIE L* a* b* values. Depending on the literature, values with ΔEab* value greater than 3.3 were considered clinically unacceptable color change [17].

Statistical analysis

All statistical analyses were performed using a standard statistical software package (SPSS 20.0, Chicago, Illinois). The means and SD values of L*, a*, b* were statistically analyzed using a two-way analysis of variance. Two-way ANOVA was employed to assess the type of material and effect of the staining agent on color change. p < 0.05 was considered statistically significant.

Results

The mean color changes (ΔE) for all drugs/restorative materials ranged from 1.81 to 8.08. The mean color differences (ΔE) and the standard deviations of all groups are presented in Table 3. The most prominent alteration was found in Grintus-Cention N (8.08 ± 2.62) and the least one was found in Grintus-Equia (1.81 ± 0.74) pairwise. Two-way ANOVA results demonstrated that ΔE ∗ values were only significantly influenced by restorative material factor (p < 0.001) whereas no effects were found for pediatric drug (p = 0.71) and interactions (pediatric drug x restorative material) (p = 0.122).

Table 3 The mean and standard deviations of ΔE values
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When the effects of different drugs within the same material were evaluated, no significant difference was observed in any group. When the differences between materials were compared, it was found that only in the cough syrup (Grintus) group, the color change observed in Cention N was statistically significantly higher than in Equia (p < 0.05) (Table 3).

When ΔL, Δa and Δb values are evaluated separately; a statistically significant difference was found in ΔL, Δa and Δb values. It was observed that the ΔL value of Equia was positive and lower than composite and Cention N, while it was determined the Δa value was higher. When the color change of the same material in different drugs was evaluated, no significant difference was observed in terms of ΔL and Δa values (Figs. 1 and 2).

Fig. 1
figure 1

The mean and standard deviations of ΔL values

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Fig. 2
figure 2

The mean and standard deviations of Δa values

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When the Δb values of the materials were examined, the lowest Δb value was observed in the Cention N in the antibiotic and analgesic groups, and this difference was statistically significant. In the cough syrup group, the highest Δb value was determined in Cention N. When the effects of the drugs on the materials were evaluated, it was observed that the composites kept in antibiotics and analgesics had a higher Δb value than the cough syrup group. In the Cention N group, the most color change was observed in the cough syrup group, and in the Equia group, the Δb values of the samples kept in antibiotics were found to be statistically significantly higher than the cough syrup (Fig. 3).

Fig. 3
figure 3

The mean and standard deviations of Δb values

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When the ΔE values of the materials were examined, it was observed that only Equia remained below the acceptable threshold of 3.3, while visible color changes were observed in each group in other materials (Composite and Cention N).

Discussion

This study indicated that the ΔE value of the Cention N group kept in cough syrup was significantly higher. It was observed that keeping the same material group in different drug groups did not cause a significant color change between the samples. Therefore, the hypotheses of the research were rejected.

The perceptibility or acceptability threshold for color changes in restorative materials varied across the investigation, ranging from 1 to 5.5 [18, 19]. The threshold value of 3.3 published by Douglas et al. [17] was used in this in vitro study as the acceptability threshold.

In previous studies, the first, seventh, and 28th days following immersion in beverages were used to examine color changes in restorative materials [20, 21]. According to studies, the first week is when colors change the most [22, 23]. In this study, just like in earlier studies, pharmacological stimulation of material samples was done for a week to simulate drug usage on a daily basis [22, 23].

There are limited studies on the effect of drugs used in children on dental restorative materials. An extensive literature search shows that there are no studies of the color stability of Cention N, which is in the group of alkacid restorative materials, with pediatric drugs. In color studies with Cention N, the effects of beverages such as cola, ice tea, green tea, coffee and herbal tea were evaluated [3, 14, 24]. Therefore, this study is the first to evaluate the color change of Cention N alkacid material with pediatric drugs.

In the study of Chakravarthy et al., Cention N kept in herbal tea showed more color change than the composite [3]. In the study of Majeti et al., color changes in coffee, green tea and cola were also evaluated, and it was reported that Cention N showed more color changes in all beverages, similar to the results of Chakravarthy et al. [3, 24]. In the study of Karakaş and Kuden, in the evaluation of the effect of daily consumed beverages on color change, Cention N showed the most color change in all beverages, and more color change was observed in alkacid and composite than glass ionomer [14]. In our study, the most color change was observed in the Cention N group, which was kept in cough syrup. These findings are similar to previous study findings [3, 14, 24]. The final matrix of Cention N contains 12–40% leachable monomers, and the higher color changes are considered to be the result of fluoride release from the material [24].

The material's hydrophilic resin matrix and sensitivity to water absorption raise the potential of discoloration [14]. Excessive water absorption results in the resin matrix expanding and plasticizing, and the material develops microcracks. These microcracks also cause color penetration and discoloration [25]. In contrast to glass fillers, the resin matrix has a higher water absorption capacity [26]. Glass fillers only show water absorption on the surface of the material. This situation can explain the less color changes of glass-filled Equia Forte compared to alkacid and composite. Previous studies have shown that composite materials are more sensitive to color changes [25, 27].

In our study, the alkacid restorative material was known as the composite subclass-exhibited more color changes when kept in Argivit and Grintus syrup than the composite. The type and particle size of the filler particles can affect the color change of resin-based composite materials [3, 28]. According to the literature, composite resins with small filler particles have less tendency to discolor [29]. The fact that the resin matrix type of the alkacid is different from the composite and the filler particle size is larger suggests that it shows more color change than the composite.

In studies with pediatric syrups, drug brands such as augmentin, macrol, calpol, dolven, ibufen, sudafed, prospan, ventolin were used as drug groups [1, 2, 8, 9, 30]. This study attempted to evaluate the effect of pediatric drug types from 4 different brands (Amoklavin, Iburamin, Argivit, Grintus) not used in other studies on color stability of tooth-colored restorative materials. In the study conducted by Yılmaz et al., the effect of drugs on the color change on primary teeth was evaluated and the highest color change was found in the pseudoephedrine drug group with the highest acidity [30]. In this study, a statistically significant difference was found among the materials in terms of color change in Grintus cough syrup, which has the lowest pH value. The most color change was observed in Cention N material kept in Grintus cough syrup. The drugs with the lowest pH cause roughness by causing erosion on the tooth surface, and depending on this roughness, the color pigments in the drug can stick to the tooth surface more [31,32,33,34]. The low pH value in Grintuss cough syrup may have caused roughness on the surface of Cention N material and increased color change.

Glass ionomer-based restorative materials displayed superior color stability than resin-based restorative materials in studies assessing the effect of pediatric drugs on color stability [2, 8, 9, 30]. In our study, the material group that showed the most color stability was Equai Forte. This suggests that the Equia Coat applied to the material surface may be related to the elimination of the erosive effect of pediatric syrups. In our study, unlike other pediatric drug studies, the changes in L, a and b values were evaluated as well as the ΔE value. While the L values of the composite and alkacid groups decreased after being kept in the drugs, an increase was observed in the L value of the glass ionomer-based Equia Forte material. Changes in L values were found to be significantly less in all drugs in the Equia group than in the other two restorative material groups. When the changes in a value were examined, Equia forte showed a significantly greater decrease in the group kept in amoclavine compared to cention. On the other hand, in the Grintus group, the Equia forte material showed a greater change in terms of the change in 'a' value compared to both the composite and alkacid groups. These increases and decreases in L and a values are similar to the studies of Vecek et al. [35]. In their study, while the L value increased in equia forte, it decreased in cention restorative material, and the changes in Δa value were positive in cention and negative in Equia forte [35]. In addition, as in the study of Vecek et al. [35], the Δb value in the Equia was found to be negative in our study. The fact that the effect of pediatric syrups was not the same among materials in terms of changes in L, a and b values suggests that it is due to material degradation, which affects color changes differently along the L*, a* and b* axes for each material.

However, the high color changes of the resin-containing materials were associated with the chemical changes in the initiator system, the activator and the water absorption properties of the composite monomers [2]. In addition, the type/size of the resin/filler particle and the adsorption and absorption properties of colorants are considered as factors that negatively affect color stability [36].

This research is significant since it investigates the discolouration of pediatric drugs on dental restorative materials. The current study assessed various drug categories and current brands that are commonly prescribed in children. Simultaneously, the impact of surface coating application on color change was examined. The study's limitations include its inability to fully mimic in vivo conditions, which excludes the effects of saliva.

Pediatric drugs did not caused significant discolorations for all tested materials. In comparison to other materials, alkasite had larger color alterations with all medications, while HVGIC displayed improved color stability with all drug formulations. In terms of color stabilization, alkasite should be less preferred clinically.