Dental caries is one of the most common oral diseases and continues to be a significant demand for restorative treatment throughout the world.[1] According to the World Health Organization (WHO), almost 3.7 billion people suffer from oral diseases worldwide, and untreated dental caries of permanent teeth is the most prevalent oral health problem.[2] In 2021, the estimated number of people with untreated caries in permanent teeth was 2.24 billion, which is about 27.5% of the population.[3] The composite materials that are resin based are therefore an important part of modern dentistry due to their favorable esthetic and adhesive properties, conservative preparation requirements, and their use in anterior and posterior composite restorations.[4]

Though resin composites offer these benefits, their physicochemical and surface properties affect the long term clinical performance.[5] Color stability and surface roughness are significant properties because loss of these may jeopardize the esthetic appearance and longevity of the restorations.[6] The color change could be due to intrinsic factors such as the composition of the resin matrix, polymerization characteristics, and the morphology of the fillers, and due to extrinsic factors such as dietary pigments.[7] Beverages such as coffee, tea, cola, fruit juices and red wine contain chromogenic and/or acidic components that can promote pigment adsorption, absorption, matrix degradation and discoloration.[8]

The surface characteristics are closely related to discoloration.[9] Increased surface roughness increases the surface area and irregularities for accumulation and retention of chromogenic substances, and can also promote biofilm adhesion.[10] Acidic drinks can also soften or destroy the resin matrix and change the filler-matrix interface, causing more irregularities on the surface.[11] Laboratory studies have shown that acidic drinks can affect both surface quality and colour stability of resin composites and thus, it is important to assess both properties simultaneously as opposed to discoloration only.[6, 12]

The staining potential of beverages is not uniform.[13] Previous research has shown significant differences with respect to the beverage and the restorative material.[14] In one comparative study, coffee, tea, cola and red wine caused increasing colour changes, whilst the other study showed that the type of resin composite and staining beverage were significant factors with regard to colour stability of the six contemporary resin composites studied.[15, 16] In addition, a 2023 scoping review revealed that there was significant variation in the color-stability response of resin-based composites when stained by beverages such as coffee, tea, cola and red wine, suggesting that the composition of composites can play a significant role in staining resistance.[17]

Bioactive resin composites are a significant progress in restorative material science. Conventional resin composites are made to restore the teeth in a mechanical and esthetic manner only, while bioactive resin composites are intended to be beneficial to both the mechanical and esthetic aspects of restoration as well as benefit the surrounding oral environment, with some bioactive resin composites capable of releasing or exchanging ions and facilitating mineral-related processes.[18] However, the incorporation of bioactive components and modifications of the resin matrix and filler system may influence water sorption, surface characteristics, staining susceptibility and color stability. However, bioactivity can also offer benefits to the biology, but does not necessarily translate to better esthetic durability than conventional composites. However, commercial resin composites can vary widely in roughness, water sorption, and color stability characteristics, as evidenced by contemporary studies, further emphasizing the need for material-specific evaluation.[19]

It is important to note that most research on beverage staining has focused on conventional, bulk-fill, nanohybrid, or microhybrid resin composites, and direct comparative studies of the effects of commonly consumed beverages on bioactive versus conventional resin composites remain relatively scarce. Additionally, the color change and surface roughening can be related; good initial color stability can be followed by surface degradation that increases sensitivity to subsequent stains. Recent experimental studies have shown that the esthetic response of restorative materials is related to the combination of beverage type, composite composition, and surface characteristics.[6, 20]

 In the above context, the present study was undertaken to compare two significant classes of restorative materials under controlled exposure to beverages in a clinically relevant fashion. The study aimed to evaluate the proposed bioactive advantage in combination with surface properties and color stability to ascertain if the proposed benefit is matched or enhanced esthetic and surface durability as compared to conventional resin composites. These findings could be used to specifically select materials for patients who are high consumers of staining or acidic beverages and could also be used to create restorative materials that are biologically active and yet are clinically durable. The aim of this study was to comparatively evaluate the color stability and surface properties of bioactive and conventional resin composites following exposure to commonly consumed beverages.

This in-vitro comparative experimental study was conducted in the Department of Dental Materials, Jinnah Medical and Dental College, Karachi, Pakistan. The study lasted for 6 months from 1st January 2026 to 30th June 2026. The sample size was calculated using OpenEpi version 3.01 based on the expected difference in color change between resin composite materials reported in a previous in-vitro study evaluating the effects of different beverages on the color stability and surface properties of composite materials. Özyurt and Kurt reported significant differences in color stability and surface roughness between direct and indirect composite materials after exposure to commonly consumed beverages.[21] In order to determine the minimum sample size, the effect size from the previous study, 80% power, and a 95% confidence level were considered. The minimum sample number was estimated considering the effect size from the previous study, the power of 80%, and the confidence level of 95%. A total of 64 composite specimens were added, with 32 specimens made from each material, to enable a balanced allocation and to offset any loss of specimens or reading error. They were then assigned to beverages according to an equal allocation procedure. A consecutive purposive sampling technique was used for selection of the commercially available resin composite materials and preparation of standardized specimens. Specimens were selected if they were prepared from only one selected bioactive resin composite or conventional resin composite, had uniform dimensions, were properly polymerized following the manufacturer's instructions, and the surface was smooth with no defects after finishing and polishing. Only baseline colour and baseline surface characteristics of acceptable quality were included in the final analysis. Those specimens that exhibited cracks, voids, fractures, incomplete polymerization, irregular dimensions, surface defects, or damage during preparation, polishing, or immersion were excluded. Specimens that were accidentally contaminated, lost during the experimental procedure, or produced readings that could not be reliably obtained from the measuring instruments were also excluded. Prefabricated molds with identical dimensions were used to produce standardized disc-shaped specimens from the bioactive and conventional resin composites. The composite materials were placed into the molds, and the surface was covered with a clear matrix strip for a standardized surface. Every specimen was light-cured for a period of time and at an intensity of light as recommended by the manufacturer. The finished and polished specimens after polymerization were obtained by using a standardized polishing procedure, which reduces operator variance. The specimens were then placed in distilled water at room temperature and left for 24 hours before baseline assessment. Color stability and surface roughness measurements were taken before beverage exposure. Color was measured with a calibrated digital spectrophotometer in the CIE L*a*b* system, and color difference (ΔE) was determined between baseline and post-exposure colors. The surface roughness was determined by a profilometer, and the arithmetic mean surface roughness (Ra, μm) was recorded. The samples were divided based on the type of material and beverage exposure. The control was distilled water, and the experimental staining/acidic agents were commonly consumed beverages such as tea, coffee, and cola. Each specimen was thoroughly dipped in its respective solution under standard conditions, and fresh liquids were prepared just before the exposure. The solutions used were changed at fixed time intervals to ensure the properties of the solutions remained the same. The specimens were exposed for the same duration to simulate multiple dietary beverage exposures, rinsed with distilled water, and then gently dried prior to measurements. Colour change and surface roughness were re-evaluated at the set point. Color change (ΔE) after beverage exposure was the primary outcome, and surface roughness (Ra) was the potential surface property outcome. Color alteration was also determined about surface roughness to see if any correlation could be drawn between the two. Analysis and data entry were done with SPSS Statistics, 26th edition of IBM. Shapiro–Wilk test was used to test continuous variables such as ΔE and surface roughness (Ra) for normality. Data that were normally distributed were represented as mean ± standard deviation, and those that were not normally distributed were represented as median (interquartile range). One-way analysis of variance (ANOVA) with a post hoc Tukey test was used to evaluate the differences among multiple beverage groups for normally distributed data. The paired t-test was used for paired comparisons between baseline and post-exposure measurements. The Pearson's correlation coefficient was used to assess the association between colour change and surface roughness depending on data distribution. A two-sided p-value <0.05 was considered statistically significant.

The study included 64 specimens, with 32 specimens prepared from each resin composite. Each material was equally distributed among distilled water, tea, coffee, and cola exposure groups, with eight specimens per beverage. Baseline color parameters and surface roughness were comparable between the two materials, with no statistically significant differences observed for L*, a*, b*, or baseline Ra values (Table 1 and Table 2).

Beverage exposure resulted in significantly greater color alteration in both materials. Coffee produced the greatest color change, followed by tea and cola, whereas distilled water produced minimal alteration. The conventional composite demonstrated significantly higher ΔE values than the bioactive composite after exposure to tea, coffee, and cola, while the difference after distilled-water exposure was not significant (Table 3 and Table 4).

Surface roughness also increased following exposure to the staining beverages. The greatest increase was observed after coffee exposure, followed by cola and tea. Compared with the conventional composite, the bioactive composite demonstrated significantly lower post-exposure surface roughness following tea, coffee, and cola exposure, whereas no significant difference was observed after distilled-water exposure (Table 6 and Table 7).

A significant positive correlation was identified between color change and surface roughness for both materials, indicating that specimens exhibiting greater increases in surface roughness also tended to demonstrate greater discoloration. The correlation was moderate for the bioactive composite and strong for the conventional composite (Table 8).

Table 1. Distribution of Resin Composite Specimens According to Material and Beverage Exposure (n=64)

Table 2. Baseline Color and Surface Roughness Characteristics of the Resin Composite Specimens

Table 3. Effect of Beverage Exposure on Color Change (ΔE) According to Resin Composite Type

Table 4. Comparison of Color Change (ΔE) Among Different Beverage Groups

Table 5. Within-Group Comparison of Color Parameters before and After Beverage Exposure

Table 6. Surface Roughness (Ra) Before and After Beverage Exposure

Table 7. Comparison of Post-Exposure Surface Roughness between Bioactive and Conventional Composites

Table 8. Correlation between Color Change and Surface Roughness

The present in vitro study showed that common drinks had a significant impact on the colour stability and surface properties of resin composites. The major finding was that the color change of the bioactive resin composite was significantly lower than that of the conventional resin composite for tea, coffee, and cola, whereas the surface roughness of the bioactive resin composite was significantly lower than that of the conventional resin composite. Coffee produced the greatest discoloration and increase in surface roughness in both materials, whereas distilled water produced minimal changes. In addition, there was a fairly strong correlation between color change and surface roughness, indicating that changes in surface roughness could be a factor in increased susceptibility to extrinsic staining. The results of the study indicated that the study hypothesis was accepted, as beverage exposure and material composition interact in determining the esthetic durability of resin composites. The higher discoloration seen with the conventional composite was similar to the results reported by Sajini et al. (2022), who performed a direct comparison between the bioactive material ACTIVA BioACTIVE and different restorative materials following immersion in coffee, black tea, cola, mixed berry juice, and saline. They showed that all materials, except for very small differences, had significant color changes, and of those, ACTIVA BioACTIVE or Filtek Z350XT showed comparatively good color stability, whereas the greatest color change occurred in the coffee.[22] In the present results, the same composite was found to be more resistant to beverage-induced discoloration than the conventional one, especially to coffee. This similarity is significant as it indicates that the positive color response seen with some bioactive formulations may be repeatable under various experimental conditions. The result of our study that the coffee caused the maximum color change was also similar to the result of the study carried out by Özyurt, Kurt (2021) after 64 direct and indirect dental composites were exposed to distilled water, tea, coffee and cola. They found that both the material and the beverage had significant effects on color stability, with coffee and tea giving significantly higher color changes than the control. They also discovered that the surface characteristics and color stability of the indirect material were superior to the direct composite.[21] The current study further confirmed these findings by showing that there is a similar material-dependent response between bioactive and conventional resin composites. Coffee has a special staining potential, which could be due to the chromogenic compounds and their ability to be penetrated and/or absorbed by the resin matrix. This high incidence of coffee-related stain in the present study was confirmed by Thakkar et al. (2024), who investigated nanohybrid, bulk-fill, and flowable composites for their staining with coffee, tea, red wine, and cola. Their study showed that the color of the composites changed for all beverages tested, with coffee and red wine causing the most discoloration. The longer the duration of immersion, the greater the colour change.[13] The high ΔE values obtained after exposure to coffee, however, as confirmed by the present study, reinforce the evidence that frequent exposure to strongly chromogenic beverages is an important challenge to the long-term esthetic stability of resin restorations, although the present study did not include red wine and multiple time points were not evaluated. The present findings also matched the results of the 2023 study by Rohym et al. that compared two single-shade resin composites after exposure to coffee and distilled water. Their study showed that the ΔE values after immersing them in coffee were significantly higher; the longer they were immersed, the higher the color change. Coffee immersion also resulted in a considerable increase in surface roughness, and a strong positive correlation was detected between the color change and the roughness.[23] Our study also revealed that coffee had the highestΔE and Ra values and showed that there was a significant positive correlation between discoloration and surface roughness. In our bioactive composite, the correlation was moderate (r=0.612), and in the conventional composite it was higher (r=0.704), but the direction of association was the same, which was in favor of the idea that a rougher surface would help to retain the pigment. The surface-roughness results were also similar to Kalita et al. (2023), who assessed surface roughness after three nanohybrid composites were exposed to chlorhexidine and coffee. The surface roughness and color change was significantly larger for the coffee solution when compared to the comparison solution, and the amount of change was different for the various composite materials.[24] The present study showed that after tea, coffee, and cola, the post-exposure roughness of the conventional composite specimens was significantly higher. This material-dependent response can be due to differences in resin chemistry, filler properties, filler-matrix bonds, and chemical degradation resistance of the polymer matrix. Likewise, Sahin and Ozyilkan (2026) recently showed that the surface characteristics such as surface roughness and color of resin-based composite materials were significantly influenced by the exposure to beverages. They compared Ormocer-based, nanohybrid, and microhybrid composites and evaluated them before and after thermocycling and beverage immersion. These recent findings, and the present findings, demonstrated that exposure to beverages did not only caused optical changes, but also physical changes in the surface properties of the tested restorative materials. The mutual agreement between studies gives added weight to the need for assessing color stability together with surface roughness when considering the durability of restorative composites.[20] The current observation that acidic beverages increased surface roughness was also supported by Büyükgöze-Dindar et al. (2025). They found considerable differences in the roughness of their direct and indirect resin-based restorative materials, depending on the material and the immersion solution, and they noted that the roughest surface degradation was caused by cola and red wine. The surface behaviour and colour stability of Cerasmart 270 and an indirect material were relatively good.[25] The present study findings also revealed increased roughness after cola exposure than after distilled water and indicated that the bioactive composite exhibited significantly lower roughness than the conventional composite. The results indicate that the resistance to acidic beverage exposure can be highly dependent on the chemical and physical properties of the material used to provide the restoration. A 2025 study, which tested resin based-composites against some of the most popular drinks among children, found a slightly different trend. That research evaluated the surface roughness, microhardness, and color stability following exposure to Coca-Cola, grape juice, chocolate milk, distilled water, and accelerated artificial aging. Exposure to beverages did not consistently result in significant changes in surface roughness, although changes in color and microhardness were observed.[26] This discrepancy with the present study results could be explained by the differences in the composition of composites, beverage composition, exposure protocol, measurement methods, and immersion time. However, both studies corroborated the overall finding that beverage exposure has a negative effect on the esthetic and physical properties of resin-based restorative materials. The results of the 2024 study by Siddiqui et al. on the effects of acidic drinks and surface properties of resin composites also lend support to the current results. Their investigation showed that acidic beverages may affect the surface characteristics and color stability, and that the effect of acidic beverages may vary depending on the differences in the formulations of the composite.[6] The findings of the current study also indicated that consumption of beverages correlated with the simultaneous changes in both color and surface roughness. The observations suggest that beverage-associated degradation can be viewed as a multi-factorial process, both with regard to the chemical properties of the beverage, and the intrinsic properties of the restorative material. Later, Kalawat et al. (2026) tested the ΔE and Ra of composite resin specimens after being immersed in artificial saliva, orange juice, tea, and Coca-Cola for 24 days. The highest surface roughness and colour variability was obtained for Coca-Cola and the lowest for the control, and increasing exposure time leads to more colour change and more roughening. Minimal changes were seen in the distilled water group, while there were significant changes after beverage exposure, similar to our findings.[27] The beverage with the highest effect i-e the present study coffee versus Coca-Cola in the 2026 study, could be due to differences in beverage acidity, chromogen concentration, exposure time, composite composition, and experimental temperature. This difference in itself illustrates why a single "most harmful" drink conclusion ought to be regarded within the context of the experimental protocol. In general, the results indicated that the composition of the material and the beverage exposure play significant roles in the esthetic durability of resin composites. The bioactive composite had more desirable staining, beverage, and surface-smoothing properties compared to the conventional composite. Coffee was the most difficult to discolor, whereas cola caused significant surface changes. The results were generally consistent with the current evidence from 2021-2026, but there were some differences in the size and rank of the effect of the beverages between different studies. This variation was probably due to different composite formulations, different sized fillers/loading, differing resin chemistry, polishing procedures, immersion time, temperature, and different color/roughness measurement methods. Hence, the present results suggest potential indications for the use of bioactive resin composites when esthetic stability is required for a long-term period and highlight the importance of beverage consumption as an environmental factor for restorative performance. There were some study limitations. The experimental setup did not fully mimic the complex oral environment essential for the experiment, such as the salivary flow rate, the diversity of food intake, chewing, temperature changes, behavioral development of biofilms, and the different beverage drinking habits. Only a limited number of subjects were evaluated, and only one bioactive and one conventional resin composite were used, so the results cannot be extrapolated to other commercially available materials. Only tea, coffee, cola, and distilled water were studied, but patients are drinking a much broader spectrum of drinks. In addition, the standardized immersion protocol might not fully reflect on intermittent clinical exposures. These results need to be confirmed in long-term clinical trials with various restorative materials and in various real dietary conditions.

The present study showed that the drinking liquids had a negative impact on the color stability and surface characteristics of resin composites. The most color change and surface roughness occurred with coffee, then tea and cola, with little change being seen in the distilled water. The bioactive resin composite showed significantly improved color stability and reduced surface roughness compared to the conventional composite following staining by beverages. There was also a significant positive correlation between color change and surface roughness that was significant. The findings indicated that bioactive resin composites have an acceptable esthetic performance in frequently stained or acid-consuming patients.

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