The effects of cola consumption on tooth discoloration among dentistry university students

Abstract

Background and aim

Carbonated drinks are popular beverages among the general population, including dental students. These drinks, such as Coca-Cola, contain high levels of sugar and acidic components, which can contribute to tooth discoloration. This cross-sectional in vivo study was designed to measure the impact of cola consumption on the colour change of the upper anterior six teeth in dentistry students. The objective was to assess colour changes exclusively. This study aimed to evaluate the discoloration on the anterior surface of anterior teeth of dentistry university students after one month of Cola consumption in different consumption groups.

Materials and methods

A cross-sectional study was conducted among first and second-year dental students (N:64). The upper six anterior teeth, including both canines, of each of the 64 students were measured by spectrophotometer, with three measurements taken to record L, a, b, C, H values per tooth region and the averages recorded. After one month of Coca-Cola consumption, the color measurements of these teeth were repeated.

Results

Cola consumption significantly impacted tooth discoloration among dentistry students. Anterior teeth in high-consumption groups showed greater color changes (p < 0.05) across L, a, H, Delta L (ΔL), Delta a (Δa), Delta H (ΔH), Delta E (ΔE) and Delta E₀₀ (ΔE₀₀) values, with marked differences between groups.

Conclusion

The findings suggest that Coca-Cola consumption is common among dental students and may be associated with tooth discoloration. This highlights the importance of oral health education and preventive measures among dental students to minimize the risk of tooth discoloration associated with carbonated drink consumption.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12903-025-06277-8.

Introduction

Carbonated beverages are the third most widely consumed non-alcoholic drinks worlwide. They typically contain sweeteners, carbon dioxide, high-fructose corn syrup, caffeine, phosphoric and citric acids, flavorings, and colorants. Due to their low pH and high sugar content, regular consumption has been linked to a range of adverse health outcomes, including obesity (due to reduced satiety from high-sugar drinks), diabetes (from increased sugar intake), tooth decay (from enamel demineralization), osteoporosis (from disrupting calcium-phosphorus balance), nutritional deficiencies, heart issues (from metabolic and hypertensive effects), and neurological disorders (from high caffeine content) [1].

Cola drinks, in particular, have experienced a marked increase in consumption among individuals within the age range of 18 to 35 years. Common motivations for cola intake among students include reducing fatigue, enhancing alertness during study or driving, alleviating hangover symptoms, and quenching thirst. The acidic environment created by phosphoric acid and citric acids (pH 2.5–3.5) increases enamel porosity, facilitating adsorption and absorption of synthetic colorants and thereby promoting extrinsic staining of natural teeth [2].

Despite awareness of the adverse health effects, carbonated beverages remain a frequently consumed beverage. Epidemiological evidence links regular intake to dental erosion, cavities bone fractures, obesity, non-alcoholic fatty liver disease, electrolyte disturbances (hypocalcemia, hypocalemia), chronic kidney disease, hypertension, hyperuricemia, gout, coronary heart disease, heatburn, and belching. Furthermore, elevated consumption may contribute to reduced bone mineral density [1].

Tooth structure is composed of tissues like enamel, dentin, and pulp. The light scattering and absorption properties of enamel and dentin significantly influence the actual color of teeth. Tooth discoloration has a multifactorial etiology, broadly clasified into internal or external causes. Internal discoloration may stem from conditions such as amelogenesis and dentinogenesis imperfecta, enamel hypoplasia, discoloration from tetracycline and fluorosis, root resorption, and the natural aging process. External discoloration, on the other hand, is frequently associated with poor oral hygiene, metal salts, smoking, and consumption of dietary beverages like tea, coffee, red wine, and cola [3].

Color is a complex phenomenon influenced by many factors, including the human eye, lighting conditions, light scatter, opacity and translucency. Therefore, in addition to visual methods, instrumental techniques are used to minimize these factors in the color selection of teeth and dental restorations. Visual color assessment is subjective, but instrumental techniques such as spectrophotometers, colorimeters and digital image analysis provide more objective results. Spectrophotometers, the most commonly used of these techniques, measure the amount of light energy reflected from an object in the visible spectrum. Spectrophotometers have a higher accuracy and provide a more objective comparison compared to traditional methods or evaluations performed by the human eye [3].

The CIELAB (Commission Internationale de l’Eclairage) color system is one of dentistry’s most widely used color measurement systems. The CIELAB system defines color by three coordinates: L*, a* and b*. The L* coordinate represents the lightness/darkness axis between white (+) and black (-). The a* coordinate represents the color axis between red (+) and green (-), while the b* coordinate represents the chroma axis between yellow (+) and blue (-). The CIEDE2000 color system, introduced as a better alternative to the CIELAB system, corrects inconsistencies and provides a better correlation between perceived and measured color change. It uses L for lightness, C for chroma (color intensity), and H for hue to more accurately reflect the perceptual and acceptance thresholds for color differences [3].

Despite extensive studies have evaluated the staining effects of various beverages on restorative and prosthetic materials, limited in vivo data exist on the short-term effects of cola consumption on natural anterior teeth, particularly under controlled dietary and oral hygiene conditions. Rather than aiming to establish a novel mechanism, this study was designed as a pilot investigation to assess whether measurable color changes could be observed within a short period of cola exposure among a homogenous population of dental students. By focusing on a real-world yet controlled setting, this study seeks to generate preliminary data that can inform the design of future longitudinal research with larger and more diverse populations [4, 5, 6, 7].

In this study, the color changes in the dental students’ six upper anterior teeth, including canines (FDI teeth; 11, 12, 13, 21, 22, 23), were measured before and after one month of cola consumption using a spectrophotometer. The L*, a*, b*, C*, and h* values were recorded and analyzed to determine the effects of cola on tooth color.

Material - Methods

Ethical approval

This study was approved by the Adıyaman University Non-Interventional Clinical Research Ethics Committee (Decision No: 2025/1–1, Date: 14/01/2025). Written informed consent was obtained from all participants before their participation in the study. Clinical trial number: Not applicable. All participants provided informed consent before participating in the study, and the research was conducted in accordance with the ethical guidelines outlined in the Declaration of Helsinki.

Study design and participants

The selection of participants for this study was made from a total of 300 dentistry students. The inclusion criteria required participants to be over 18 years old and to have all six upper anterior teeth (central, lateral, and canine; FDI teeth 11, 12, 13, 21, 22, 23) present. Given that a majority of students exhibited caries, restorations, or fillings in their posterior teeth, the study was standardized by selecting only the maxillary anterior teeth for evaluation. Participation in the study was entirely voluntary. Participants were divided into three groups based on weekly cola consumption: non‑drinkers (0 cans/week), low consumers (1–3 cans (330 ml)/week), and high consumers (≥ 10 cans (330 ml)/week).

Exclusion criteria included the presence of fixed orthodontic appliances, pregnancy, professional dental prophylaxis performed within the last six months, as well as restorations, endodontic treatment, or caries in the upper anterior teeth.

Participants were questioned about systemic medication use (e.g. iron supplements) and other conditions that may cause tooth staining. In addition, dietary control was ensured by instructing all participants to avoid tea, coffee, red wine and similar colouring foods/drinks during the study period.

The teeth of the 64 volunteers included in the study were screened. In this study, the measurement of shade values in the teeth of all participants was performed using a clinical spectrophotometer device (VITA EasyShade V, Vita Zahnfabrik, Germany). The device has a 1.5 × 2 inch touch screen and was calibrated before each measurement using an automatic calibration plate. The VITA EasyShade V is suitable for use in all lighting conditions and is not affected by halogen or ambient light. It measures color using both the CIELAB and CIEDE2000 color systems and has the ability to archive measurements.

The tooth color assessment was performed by a calibrated operator (H.Y.Y.K.). Measurements were taken between 10:00 a.m. and 2:00 p.m., the time of day when natural light is most consistent. Participants were instructed to keep their head still, lean on the headrest, and open their mouth slightly. To avoid tissue reflection in the incisal areas of the teeth, which could lead to erroneous measurements, the tongue was held in a resting position. The unit’s light was turned off during the measurements to eliminate any extraneous light interference.

Measurements began with the upper right anterior teeth, starting with tooth 11, followed by 12, 13, and continuing with 21, 22, and 23. The measuring tip of the spectrophotometer was positioned as perpendicular as possible to the buccal surface of the tooth. Color measurements were taken from three different areas of the buccal surface of each tooth, specifically the middle third, and the average of these three readings was recorded as the mean. The collected data were then transferred to a computer for analysis.

Spss statistics

The data of the study were analyzed using SPSS version 26 to assess color changes in the maxillary anterior six teeth of 64 dentistry students after one month of cola consumption. Normality of continuous data was assessed using the Kolmogorov–Smirnov and Shapiro–Wilk tests. Due to non-normal data distribution, non-parametric tests were employed (p < 0.05). The Mann-Whitney U and Kruskal-Wallis tests were conducted to assess differences between gender and consumption groups, respectively. Additionally, the Friedman test was used to evaluate color variation across the six anterior teeth, identifying any significant intra-individual differences. The study was conducted at a significance level of p < 0.05.

Results

Each of the 64 dentistry students who participated in the study had six maxillary anterior teeth examined. Three measurements were made for each tooth, for a total of 1152 (64 × 6 × 3) recorded measures.

ΔE₀₀ values across cola consumption groups, the findings from the Kolmogorov-Smirnov and Shapiro-Wilk tests indicate that the data do not follow a normal distribution, as shown in the Table 1.

Table 1.

Test of normality results of consumption groups for ΔE₀₀ values

	Consumption	Kolmogorov-Smirnova			Shapiro-Wilk
		Statistic	df	Sig.	Statistic	df	Sig.
Δ E00	none	,126	468	,000	,886	468	,000
	less consumption	,127	540	,000	,879	540	,000
	more consumption	,083	144	,016	,913	144	,000

Nonparametric tests were used since the data did not have a normal distribution. The ΔE₀₀ value, in particular, rises as cola consumption rises. Too much cola has been shown to affect the color of teeth.

The median ΔE₀₀ values in the high cola consumption group were significantly higher than in the no consumption and low consumption groups (p < 0.05). Table 2 indicates significant differences in L_Before, a_Before, H_Before, and ΔE₀₀ values among the cola consumption groups (Kruskal–Wallis test; p < 0.05). Median L_Before values were 80 (78–82), 79 (77–81), and 78 (76–80) for non‑drinkers, low consumers, and high consumers, respectively (p < 0.001). Median a_Before values were 0 (–1–1), 0 (–1–1), and 1 (0–1) (p < 0.001). Median H_Before differed across groups 90 (89–92), 90 (88–92), 90 (88–91); (p = 0.011). Median ΔE₀₀ values increased with consumption: 2.00 (1.3–3.0), 2.30 (1.4–3.2), and 2.70 (1.5–3.6) (p < 0.001).

Table 2.

Comparison of L_Before, a_Before, H_Before, and ∆E₀₀ values across consumption groups

Variable	None (Median, Q1-Q3)	Less Consumption (Median, Q1-Q3)	More Consumption (Median, Q1-Q3)	p
LBefore	80 (78–82)	79 (77–81)	78 (76–80)	0.000*
aBefore	0 (-1-1)	0 (-1-1)	1 (0–1)	0.000*
HBefore	90 (89–92)	90 (88–92)	90 (88–91)	0.011*
ΔE00	2 (1.3-3)	2.3 (1.4–3.2)	2.7 (1.5–3.6)	0.000*

As illustrated in Fig. 1, a comparison of ΔE₀₀ values among three different beverage consumption groups (none, low consumption, and high consumption) is presented. The Kruskal-Wallis test was conducted to evaluate differences in ∆E₀₀ values among the groups. The results show that the median ∆E₀₀ values for each group are as follows: 2.00 for none, 2.30 for less consumption and 2.70 for more consumption. This suggests that cola consumption may be associated with increased ∆E₀₀ values, indicating a potential impact on tooth color stability.

Fig. 1.

Comparison of ΔE₀₀ Values Among Three Different Beverage Consumption Groups

Higher cola consumption was associated with an increase in ΔE₀₀ values, suggesting a direct impact on color stability. These changes were perceptible but remained within the clinically acceptable threshold.

Among the consumption groups, the color changes were generally perceptible yet clinically acceptable. In the non-consumption group, the majority of ΔE₀₀ values indicated color changes that were perceptible to the human eye but remained within clinically tolerable limits. In the low consumption group, color changes were also perceptible but mostly within the clinically acceptable range. However, in some cases, values exceeded the acceptable threshold (4.8), suggesting that even low levels of cola consumption may increase color changes in certain instances. In the high consumption group, a similar pattern was observed; color changes were perceptible and primarily within clinically acceptable limits, yet several cases exceeded the threshold. These findings indicate that cola consumption levels may influence tooth color changes, though further research is necessary to confirm the long-term effects and underlying mechanisms.

Significant differences were observed between males and females in several dental color parameters before and after cola consumption (Table 3). At baseline, males and females showed significant differences in lightness (L_Before, U = 152,840, p = 0.020), red-green chromaticity (a_Before, U = 149,046.5, p = 0.002), yellow-blue chromaticity (b_Before, U = 136,485, p < 0.001), chroma (C_Before, U = 136,670.5, p < 0.001), and hue angle (H_Before, U = 151,152.5, p = 0.009). After one month of cola consumption, significant differences remained in lightness (L_After, U = 153,343.5, p = 0.025), yellow-blue chromaticity (b_After, U = 139,321, p < 0.001), and chroma (C_After, U = 139,118, p < 0.001), indicating that cola consumption affected these parameters differently between genders. Additionally, the overall color changes, as represented by ΔE₀₀ (U = 152,575.5, p = 0.018), were significantly different between males and females. These findings suggest that cola consumption leads to perceptible and statistically significant differences in dental color parameters between genders, both before and after consumption.

Table 3.

Comparison of color parameters (L, a, b, C, H) between genders

Color Parameters	Mann-Whitney U	Z-Score	P Value
LBefore	152,840	-2.324	0.020*
aBefore	149,046.5	-3.085	0.002*
bBefore	136,485	-5.221	0.000*
CBefore	136,670.5	-5.188	0.000*
HBefore	151,152.5	-2.630	0.009*
LAfter	153,343.5	-2.237	0.025*
bAfter	139,118	-4.754	0,000*
ΔE00	152,575.5	-2.359	0.018*

As indicated in the Table 4, significant differences were identified among teeth numbered 11, 12, 13, 21, 22, and 23 for each color parameter (L, a, b, c, h), with p-values less than 0.001.

Table 4.

Comparison of color parameters (L, a, b, C, H) across teeth numbers 11, 12, 13, 21, 22, and 23 using Kruskal-Wallis test

Color Parameters	Kruskal Wallis H	df	p
LBefore	174,117	5	< 0.001
aBefore	191,150	5	< 0.001
bBefore	217,404	5	< 0.001
CBefore	213,532	5	< 0.001
HBefore	178,034	5	< 0.001
LAfter	195,027	5	< 0.001
aAfter	214,695	5	< 0.001
bAfter	231,426	5	< 0.001
CAfter	229,048	5	< 0.001
HAfter	207,429	5	< 0.001

Post-hoc pairwise comparisons were performed to see which particular groups differed from one another. The p-values for each variable’s pairwise comparisons between tooth numbers 11 and 21, 12 and 22, and 13 and 23 are summarized in the Table 5 below:

Table 5.

Pairwise comparisons of tooth pairs with corresponding p-Values for each measurement

Measurement	Tooth pair	p
L	11–21	> 0.05
L	12–22	> 0.05
L	13–23	> 0.05
a	11–21	> 0.05
a	12–22	> 0.05
a	13–23	> 0.05
b	11–21	> 0.05
b	12–22	> 0.05
b	13–23	> 0.05
C	11–21	> 0.05
C	12–22	> 0.05
C	13–23	> 0.05
H	11–21	> 0.05
H	12–22	> 0.05
H	13–23	> 0.05

Discussion

Tooth darkening occurs due to the formation of chemically stable structures responsible for the progressive accumulation of stains. These stains are primarily composed of carbon-rich molecules. During the staining process, these molecules are broken down and converted into intermediate compounds with lighter colors. This chemical reaction alters the type, number, and relative positions of the atoms that make up these molecules [8]. The coloration effect of beverages is attributed to the presence of chromogenic polyphenols. These compounds bind to proteins as well as to the pellicle or bacteria on teeth. Once a protein or surface reaction site is saturated with the initial color from these polyphenols, it is no longer available for further coloration. Moreover, external factors such as brushing habits, salivary composition, and dietary intake may also influence the extent of staining, acting as modifying variables in the discoloration process. Exaggerated in vivo effect due to tooth brushing and tongue and cheek movements, which play an important role in cleaning tooth surfaces and are considered modifying factors, can also alter the coloration states [8].

It was previously demonstrated that cola-based soft drinks stain enamel, due to their lower pH, which increases enamel porosity and enhances the retention of coloring agents [9]. This acidic environment weakens the enamel structure, making it more susceptible to extrinsic staining over time. Consistent with Meenakshi and Sirisha’s [10] finding that Coca‑Cola produces the greatest degree of staining among acidic beverages while remaining within clinically acceptable ΔE thresholds for restorative composites, our results similarly demonstrate that habitual cola consumption yields perceptible yet clinically tolerable ΔE₀₀ shifts in natural enamel.

The ΔE values of the specimens were obtained in our investigation using the Vita Easyshade spectrophotometer, which is frequently used in dentistry research to determine CIELAB and CIEDE2000 coordinates. This instrument has been validated for its reliability in shade matching and color measurement, providing reproducible results. In one study proved that the Easyshade spectrophotometer is accurate. The VITA Easyshade V dental shade-matching device has an accuracy rate of 93.75%, offering accurate and exact measurements, according to the study’s evaluation of the device’s intradevice accuracy and repeatability in both in vitro and in vivo models [11]. In vivo measurements on natural enamel may be affected by factors like ambient lighting, tooth hydration, saliva, and operator variability. To minimize these, all measurements in our study were performed under standardized lighting, using a single calibrated device, by the same trained operator. Teeth were air-dried for 5 s before each measurement, and a custom-made jig ensured consistent angulation.

Recent studies support the feasibility of in vivo ΔE₀₀ measurements on natural teeth. Ntovas et al. [12] assessed color differences on maxillary central incisors using standardized digital imaging and CIEDE2000 calculations. Likewise, Tejada-Casado et al. [13] showed that perceptibility and acceptability thresholds vary with chroma and confirmed the applicability of CIEDE2000-based evaluations in clinical contexts. These findings reinforce the reliability of objective color assessment in natural dentition when proper protocols are followed.

Still, we recognize the inherent limitations of spectrophotometric measurements in vivo and recommend that future studies consider complementary techniques—such as cross-polarized photography or spectroradiometric validation—to further strengthen reliability.

Furthermore, although salivary factors were not directly assessed in the present study, it is important to recognize their potential impact on tooth discoloration outcomes. Salivary buffering capacity plays a crucial role in maintaining intraoral pH and modulating the effects of acidic and chromogenic beverages on enamel surfaces. Previous research demonstrated that both natural saliva stimulation and the composition of saliva could influence salivary pH recovery following acidic challenges, thereby potentially altering enamel susceptibility to extrinsic staining [14, 15]. Similarly, genetic predispositions affecting salivary flow rate and buffering capability may also contribute to interindividual variability in staining patterns, although these biological factors were beyond the scope of the present investigation [16]. Considering these findings, future studies should incorporate salivary parameters and genetic susceptibility assessments to provide a more comprehensive understanding of the multifactorial nature of tooth discoloration under dietary influences.

Values between 0.0 and 0.5, 0.5–1.0, 1.0–2.0, 2.0–3.5, 3.5–5.0, and ≥ 5.0 indicate an extremely slight color change, slight color change, noticeable color change, marked color change, extremely marked color change, and a shift to a distinctly different color, respectively, when measured using ΔE₀₀ values. These thresholds are tailored for ΔE₀₀ and may vary based on specific research or industry standards [17].

In our study, despite all students brushing their teeth under similar conditions, differences in staining were observed between the groups. This can be explained by the low pH of cola-based drinks, which increases enamel porosity and facilitates the retention of coloring agents. Additionally, the chromogenic polyphenols in these drinks can bind to proteins such as the pellicle or surface bacteria, contributing to extrinsic staining [9]. Although these large molecules cannot penetrate the enamel, which acts as a semipermeable membrane, they can adhere to the enamel surface, leading to external discoloration. These findings align with previous research indicating that acidic beverages not only erode enamel but also provide an environment conducive to the adsorption of staining compounds [18]. Consistent with Erdemir et al. [19], who reported that cola immersion produced perceptible but clinically acceptable color changes in natural tooth surfaces when measured by CIEDE2000, our findings likewise demonstrate that even high cola intake results in ΔE₀₀ values that, although exceeding commonly accepted thresholds such as 1.8, remain within the upper limit of acceptability reported for natural teeth in clinical settings. For instance, Tejada-Casado et al. [13] noted acceptability thresholds reaching up to ΔE₀₀ = 2.84 for low-chroma samples, and Ntovas et al. [12] found values as high as ΔE₀₀ = 4.5 when lightness differences were evaluated in maxillary central incisors by laypeople and dentists [13]. Therefore, the ΔE₀₀ value of 2.70, while perceptible, may still be interpreted as clinically tolerable in certain conditions involving natural enamel rather than restorative materials.

Therefore, despite similar brushing habits, variations in cola consumption likely led to the observed differences in staining between the groups.

Cola-based beverages, due to their acidic nature, have the potential to alter the ionic concentration of teeth, thereby affecting enamel surface properties. This change in ionic balance suggests an erosive potential that can impact tooth discoloration over time. Furthermore, the degree of cola consumption and the buffering capacity of an individual’s saliva may influence the extent of discoloration. Therefore, while cola drinks are widely consumed, their erosive properties, in combination with individual salivary factors, warrant further exploration in relation to tooth staining and enamel integrity [20]. The results of this pilot study suggest that short-term cola consumption may lead to perceptible but clinically acceptable color changes in natural anterior teeth, consistent with previous findings related to dietary staining. While the outcomes are not unexpected, the controlled conditions and homogenous population provide a focused assessment of cola’s early effects. These preliminary findings may inform future research efforts involving larger and more diverse populations over extended periods, allowing for a more comprehensive understanding of long-term exposure and its clinical relevance.

From an ethical standpoint, it is important to note that participants were not randomly assigned to cola consumption groups; instead, categorization was based on their pre-existing self-reported intake habits. Several students in the high-consumption group had already been consuming cola with every meal prior to participation, meaning that the study did not impose any new or increased exposure. The research protocol involved only non-invasive color measurements conducted using a spectrophotometer commonly utilized in dental research for objective shade analysis. All participants were informed about the potential for temporary extrinsic discoloration, and informed consent was obtained accordingly. Given that the participants were dental students, their prior knowledge of oral health and awareness of potential outcomes may have contributed to responsible participation. Overall, this study allowed for the structured observation of an already common behavior within a specific population, with the goal of generating preliminary insights to inform future public health efforts targeting dietary habits and esthetic dental outcomes in young adults.

64 participants were split into three groups for this study: no consumption, low consumption, and high consumption. This allowed researchers to evaluate the impact of cola intake on the color stability of dental students’ anterior teeth. Utilizing thresholds of 2.4 for perceptibility and 4.8 for clinical acceptability as specified by Abdalkadeer et al., ΔE₀₀ values were analyzed to ascertain the perceptibility and clinical acceptability of color changes brought on by cola exposure [21]. Although most discoloration remained within clinically acceptable limits, some individuals in the high-consumption group exhibited changes beyond the threshold, suggesting that prolonged cola consumption could have more pronounced effects. This study indicates that the amount of cola consumption has an effect on the color stability of the teeth of dentistry students. While the color changes in the none and low-consumption groups were perceptible, they were mostly within clinically acceptable limits. However, among high cola consumption groups, certain cases exhibited clinically unacceptable color changes. This highlights the potential role of acidic beverages in extrinsic staining, reinforcing the importance of preventive strategies such as limiting consumption and improving oral hygiene practices. Similarly, a study examining color changes in hybrid ceramics after exposure to different beverages found the highest color change in the tea group (ΔE = 8.06 ± 1.04) and coffee group (ΔE = 5.73 ± 0.99), both beyond clinical acceptability thresholds (ΔE > 3.3). In contrast, the cola group exhibited color changes within the clinically acceptable range (1 < ΔE < 3.3), supporting the finding that cola-induced discoloration may remain within acceptable limits under certain conditions [11].

The consumption of other carbonated and acidic beverages should be approached cautiously, as it was identified as a potential factor for discoloration in this study, even though only Coca-Cola was evaluated and the precise composition of commercial products may vary, making it difficult to generalize. Recognizing the limitations of our experimental design is also crucial. Three groups of participants—none, low consumption groups, and more consumption groups—were formed. While the other groups carried on with their usual drinking patterns, the non-drinkers received special instructions to abstain from cola during the study time [9]. Our findings, however, are more reliable than those from the laboratory. Nevertheless, self-reported consumption habits may introduce bias, and further controlled studies with objective intake measurements are recommended. Furthermore, only the nondrinkers were subjected to food restrictions. Another drawback is that the study population was primarily young adults without restorations and with high oral hygiene, thus these findings might not apply to older or less dentally healthy populations. The study population consisted of young adults with high oral hygiene and no dental restorations, which may limit the generalizability of the findings. This consideration may be particularly relevant for individuals encountered in clinical settings who present with broader age ranges, restorative histories, or systemic oral health conditions, and more diverse populations could be considered in future studies to reflect such variability.

A limitation of this study is that it only assessed the labial (front) surfaces of anterior teeth. However, in clinical scenarios, the palatal (back) surfaces of these teeth may be more exposed to acidic beverages such as cola, potentially leading to increased erosion and discolouration. Labial surfaces were chosen for standardization purposes, as they are more accessible for consistent spectrophotometric measurements and are the most visible areas in clinical aesthetic evaluations. Assessing the same surface across all participants also allowed for more uniform comparisons between groups. Nevertheless, as noted, palatal surfaces may have greater exposure to acidic beverages during consumption, and future studies should include these surfaces to gain a more comprehensive understanding of discoloration dynamics. This in vivo pattern parallels Maladkar et al.’s [22] observation that Coca‑Cola induced significantly greater enamel demineralization and surface degradation than other acidic beverages, reinforcing the link between extrinsic staining and early erosive changes on tooth surfaces. In addition, the study’s focus on 64 students may not be fully representative of the wider population, as individual variations in oral hygiene practices, dietary habits and genetic factors may influence susceptibility to tooth erosion and staining. Future research should incorporate larger sample sizes and consider long-term observational periods to better understand the cumulative effects of cola consumption on dental discoloration. Another limitation of this study is that participants were not matched based on their baseline L, a, and b values. Differences in initial tooth color among groups particularly in lightness (L) may have influenced the perceptibility or extent of discoloration, regardless of actual cola exposure. Future studies should consider baseline color adjustment or participant matching to better control for this potential source of confounding.

Although potential confounding factors were controlled in our study by excluding participants using discoloring medications and instructing all volunteers to avoid chromogenic foods and beverages, compliance was assessed solely by self‑report, which remains a limitation. Future studies may employ daily dietary records or biochemical verification methods (e.g., salivary biomarkers) to more accurately monitor adherence. While all participants were dental students who received standardized instructions on the modified Bass technique, their actual brushing behavior and compliance were not objectively monitored. Variations in brushing pressure, duration, and manual execution may have affected stain removal and thus remain a potential source of bias. Another limitation of this study is that participant adherence to dietary restrictions (e.g., avoidance of chromogenic foods and beverages) was monitored solely through self-reported compliance, which may be subject to bias. Although all participants were dental students with presumed high oral health awareness, objective verification methods such as dietary logs or biochemical markers were not employed.

Furthermore, individual physiological factors such as salivary flow rate, pH, and buffering capacity, which may influence both enamel erosion and extrinsic staining, were not assessed. Future studies may benefit from incorporating such parameters to better account for biological variability.

Conclusion

Regarding the limitations of the current study, cola consumption influenced the color stability observed in the students’ teeth. One month of cola consumption resulted in statistically significant color changes in the anterior teeth of students, with the degree of discoloration varying notably between the different consumption groups.

Electronic supplementary material

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Author contributions

HYYK: Contributed to the study’s conception and design, data collection, statistical analysis, interpretation of results, and was responsible for drafting and revising the manuscript.ZG: Involved in the design of the study, obtaining ethical approval.

Funding

The authors received no financial support for the research, authorship, and/or publication of this article.

Data availability

Availability of data and materials: The datasets generated and analyzed during the current study are not publicly available but are available from the corresponding author upon reasonable request.

Declarations

Ethics approval and consent to participate

This study was approved by the Adıyaman University Non-Interventional Clinical Research Ethics Committee (Decision No: 2025/1–1, Date: 14/01/2025). Written informed consent was obtained from all participants before their participation in the study. Clinical trial number: Not applicable. All participants provided informed consent before participating in the study, and the research was conducted in accordance with the ethical guidelines outlined in the Declaration of Helsinki.

Consent for publication

This study does not include any identifying images or personal details of participants that compromise anonymity; therefore, consent for publication is not applicable.

Competing interests

The authors declare no competing interests.