
In modern society, the consumption of healthy functional foods is increasing to address nutritional imbalances caused by irregular eating habits and increased junk food1). According to the Ministry of Food and Drug Safety, vitamins, and mineral products will rank fourth in sales within the health functional food sector as of 20222). Vitamin C, known for its antioxidant properties, is an essential nutrient for maintaining health, including fatigue recovery and immune function enhancement. However, because the human body lacks gulonolactone oxidase, an enzyme required for vitamin C synthesis, it cannot endogenously produce vitamin C, classifying it as an essential nutrient3).
The oral cavity is the first part of the body to come into contact with food and is influenced in various ways depending on the type of food consumed4). Once the dental hard tissue is damaged, it does not regenerate naturally, accumulating damage with age5). Dental erosion results in the loss of hard dental tissue and is categorized into intrinsic and extrinsic factors. Intrinsic factors include dental erosion caused by stomach acid entering the oral cavity due to reflux or vomiting, whereas extrinsic factors include exposure to acidic substances in the workplace or consumption of acidic foods and medications6). Among the extrinsic factors, consuming acidic foods is the primary cause of dental erosion. When teeth are exposed to acidic solutions with a pH below 5.5 for a certain period, biochemical demineralization occurs, and solutions with a pH below 4.5 chemically erode the teeth7). Numerous studies have examined the effects of carbonated drinks8), hangover beverages9), and pediatric syrup medications10), which are potential causes of dental erosion.
In a study by Heo et al.1), all children’s vitamin nutritional supplements were found to have a pH lower than the critical threshold of 5.5 for enamel demineralization, indicating that frequent consumption may lead to dental erosion owing to their low pH levels. Kang et al.11) measured the pH of five commercially available vitamin drinks and found that all were below 3.0, highlighting their potential for enamel erosion. Giunta12) reported a case of dental erosion in a patient who regularly consumed chewable vitamin C tablets. Vitamin C is available in various forms, including gummies, liquids, and tablets. While numerous studies have examined the effects of these products on dental health, research on the impact of powdered vitamin C on tooth surfaces remains limited.
In this study, based on previous research indicating that vitamin C has a low pH, we aimed to evaluate the effects of powdered vitamin C on the enamel surface of bovine teeth to assess its potential to induce erosion. Additionally, we aimed to provide basic data on oral health by proposing oral care methods to monitor the consumption of powdered vitamin C.
This article does not require IRB screening because human origin is not used.
Three commercially available products with high online sales in Korea, Lemona (Kyungnam Pharmaceutical Co., Asan, Korea), Vitagran (SD foods Co., Bucheon, Korea), and Korea Eundan (Korea Eundan Healthcare Co., Ansan, Korea) were selected for the experiment. Coca-Cola (Coca-Cola Beverage Co., Yangsan, Korea) was chosen as the positive control and artificial saliva was designated as the negative control. The experimental and control groups were divided into five groups, and their characteristics are summarized in Table 1.
Characteristics of the Experimental Materials Used in This Study
Group | Brand name | Ingredient | Manufacture | |
---|---|---|---|---|
Control groups | Artificial saliva | Kolmar | Calcium chloride hydrate, carboxymethylcellulose sodium, dibasic potassium phosphate, D-sorbitol, sodium chloride, magnesium chloride, potassium chloride | Kolmar Korea Co., Sejong, Korea |
Coca Cola | Coca Cola | Purified water, high fructose corn syrup, white sugar, carbon dioxide, caramel coloring, phosphoric acid, natural processing agent, natural caffeine (flavor enhancer) | Coca-Cola Beverage Co., Yangsan, Korea | |
Experimental groups | Lemona | Kyungnam Pharmaceutical | Ascorbic acid coated, riboflavin, pyridoxine hydrochloride, other additives: lactose hydrate (animal derived ingredient, cow’s milk), sugar, flavor, hydroxypropyl cellulose, D-mannitol | Kyungnam Pharmaceutical Co., Asan, Korea |
Vitagran | Dong-A Pharmaceutical | Vitamin C, hydroxypropyl methylcellulose, microcrystalline, sucrose esters of fatty acids | SD foods Co., Bucheon, Korea | |
Korea Eundan | Korea Eundan | Vitamin C, vitamin D3 mixture, zinc oxide, isomalt, xylitol, magnesium stearate, lemon flavor mixture, enzyme-treated stevia, sucralose (sweetener) | Korea Eundan Healthcare Co., Ansan, Korea |
A powdered vitamin C solution was prepared by dissolving 10 g of powdered vitamin C in 10 ml of distilled water. This process was repeated multiple times, and the resulting solutions were combined to obtain a final volume of 20 ml. The solution was then distributed into identical containers for the experimental and control groups. The experiment was conducted under the same conditions, with the mixture left at room temperature for 6 hours. The pH was measured using a pH meter (S20K pH meter; Mettler-Toledo, Greifensee, Switzerland) after calibration with buffer solutions of pH 4.0 and 7.0. The average pH was calculated based on three measurements.
The titratable acidity (TA) was determined by measuring the volume of 0.1 M NaOH required to reach pH 5.5 and 7.0. All measurements were performed three times under the same conditions, and the average values were calculated.
(1) Preparation of bovine teeth specimen
Bovine teeth with sound, caries-free surfaces were selected. Residual soft tissues and calculi were removed, and the teeth were cleaned with pumice. The tooth was sectioned into pieces measuring 5 mm in width and height using a cutting disc. A plastic mold was created using a 3D printer, and the tooth sample was placed in the mold and embedded in resin. To prepare a specimen surface appropriate for the surface microhardness measurement, it was polished sequentially using silicon carbide abrasive paper of grit sizes #220, #600, #1,000, #1,200, #2,000, and #4,000.
(2) Surface microhardness measurement
To determine the surface microhardness of the polished specimens prior to immersion in the experimental solution, a load of 200 g was applied to four areas of each specimen (top, bottom, left, and right) using a Vickers hardness tester (MMT-X7B; Matsuzawa, Akita, Japan). After applying a vertical load for 10 seconds, the Vickers hardness number (VHN) was measured at 400× magnification, and the average value was calculated. Fifty-five specimens with surface microhardness values between 280 and 310 VHN were selected, and 11 specimens were randomly assigned to each group.
After dispensing 20 ml each in the same container into the experimental and control groups, 11 specimens per group were immersed in each container. The immersion time was 15 minutes for 7 days. Additionally, after 1, 3, 5, and 7 days of immersion in the powdered vitamin C solution, the specimens were rinsed with distilled water for 30 seconds. Surface microhardness was measured in an area adjacent to the pre-immersion measurement point using the same method.
To observe the morphological changes on the bovine tooth surface, one specimen from each group was selected after 7 days of immersion. Each specimen was dehydrated in order of increasing alcohol concentration, followed by drying with a critical point dryer (HCP-2; Hitachi, Tokyo, Japan). The dried specimen was mounted on an aluminum stub and coated with gold-palladium to a thickness of 200 nm using an ion sputter (E-1030; Hitachi). Finally, the specimens were observed using a scanning electron microscope (SEM) (S-4700; Hitachi) at an accelerating voltage of 10 kV and 1,000× magnification.
A paired t-test was used to compare the surface microhardness of the specimens before and 7 days after immersion in the powdered vitamin C solution for each group. One-way analysis of variance (ANOVA) was used to compare the surface microhardness between groups. Repeated-measures ANOVA was used to compare the surface microhardness according to the immersion period for each group. Tukey’s honestly significant difference was applied for all post hoc tests, and statistical analysis was performed using IBM SPSS ver. 21.0 (IBM Corp., Armonk, NY, USA).
The pH of the test groups used in this experiment was as follows: Lemona (2.04±0.04), which was the lowest, followed by Vitagran (2.56±0.01), the positive control group Coca-Cola (2.60±0.03), Korea Eundan (3.14±0.02), and the negative control group artificial saliva (7.06±0.05), in that order. The TA of the test groups was highest at pH 5.5 in the following order: Lemona (17.50±0.03), Vitagran (8.05±0.00), Korea Eundan (7.10±0.00), Coca-Cola (0.10±0.01). At pH 7.0, the TA was higher in the following order: Lemona (18.53±0.00), Vitagran (9.53±0.02), Korea Eundan (8.24±0.00), Coca-Cola (0.43±0.01) (p<0.05, Table 2).
pH and Titratable Acidity of Test Groups
Group | pH | Titratable acidity (ml) | |
---|---|---|---|
pH 5.5 | pH 7.0 | ||
Artificial saliva | 7.06±0.05 | - | - |
Coca-Cola | 2.60±0.03 | 0.10±0.01 | 0.43±0.01 |
Lemona | 2.04±0.04 | 17.50±0.03 | 18.53±0.00 |
Vitagran | 2.56±0.01 | 8.05±0.00 | 9.53±0.02 |
Korea Eundan | 3.14±0.02 | 7.10±0.00 | 8.24±0.00 |
Values are presented as mean±standard deviation.
The surface microhardness significantly decreased with the immersion period (p<0.001, Fig. 1), and a significant difference was observed when measuring the surface microhardness of the specimens before and after 7 days of immersion (p<0.001). The difference in surface microhardness (∆VHN) before and after 7 days of immersion was greatest in the experimental group, Lemona (–201.22±20.60), followed by Vitagran (–190.02±14.73), Korea Eundan (–189.27±27.14), and the positive control group Coca-Cola (–99.28±17.21). The negative control group, artificial saliva (–10.99±9.94), showed the smallest change. Moreover, the surface microhardness differed significantly between the groups according to the immersion period (p<0.001, Table 3).
Microhardness Changes of Bovine Teeth by Immersion Time (unit: VHN, n=11)
Group | Immersion (d) | Difference | ||||
---|---|---|---|---|---|---|
Before | 1 |
3 |
5 |
7 |
||
Artificial saliva | 297.56±6.92 | 295.06±14.53a | 291.88±7.94a | 291.62±12.67a | 286.57±10.07a | –10.99±9.94 |
Coca-Cola |
295.97±5.41 | 278.64±7.77ab | 251.07±17.25b | 231.82±17.24b | 196.68±15.87b | –99.28±17.21 |
Lemona |
301.99±4.50 | 232.31±19.53d | 148.35±23.66d | 107.73±16.95d | 100.78±19.45c | –201.22±20.60 |
Vitagran |
299.18±4.82 | 266.88±13.91bc | 170.05±16.02cd | 113.69±39.67d | 109.16±14.96c | –190.02±14.73 |
Korea Eundan |
298.67±5.61 | 261.80±10.57c | 192.84±36.14c | 150.36±19.47c | 109.39±24.72c | –189.27±27.14 |
Values are presented as mean±standard deviation.
VHN: Vickers hardness number.
*By paired t-test.
**By one-way ANOVA.
***By repeated measures ANOVA.
a,b,c,dThe same letter indicates no significant difference by Tukey’s test at α=0.05.
Using a SEM to observe the enamel surface of the bovine tooth, surface changes were observed in all groups after 7 days of immersion in the powdered vitamin C solution, except for the artificial saliva group (Fig. 1C∼1F). The negative control (artificial saliva) showed a soft and smooth surface similar to that of the specimen before immersion (Fig. 1B). In contrast, the Coca-Cola positive control group showed significant enamel loss, resulting in a rough surface with visible micropores in some areas (Fig. 1C). Among the experimental groups, Lemona showed notable enamel loss, characterized by an overall very rough surface, with some cracks and micropores (Fig. 1D). Vitagreen had a generally flat enamel surface, although a pitted pattern was evident in certain areas owing to the merging of multiple micropores (Fig. 1E). Korea Eundan showed a partially flat surface, but its overall appearance was somewhat rough, with numerous small micropores (Fig. 1F).
As powdered vitamin C has a pH below 5.5, which is the critical point for enamel demineralization, changes in oral pH when consuming these products can be a risk factor for dental health. In this study, the degree of erosion was evaluated by measuring the surface microhardness of the enamel of bovine teeth. In the study by Kim et al.13), there was a significant difference in the change in surface microhardness after 15 minutes of immersion in both the red vinegar drink and the red vinegar drink groups diluted with bottled water, and milk. Therefore, the immersion time was 15 minutes. Additionally, considering that one packet of powdered vitamin C served in 2 g and the amount of saliva secreted during stimulation is 1.5 to 2.0 ml per minutes14), the powdered vitamin C and distilled water were mixed at a ratio of 1:1 to prepare the experimental solution.
Several studies have reported that pH affects dental erosion. Reddy et al.15) stated that if the pH of a drink is less than 3.0, the risk of tooth erosion is very high; if the pH is less than 4.0, there is a risk of tooth erosion; and if the pH is more than 4.0, the possibility of tooth erosion is minimal. Moreover, Gregory-Head and Curtis16) reported that the solubility of enamel increases by 7 to 8 times each time the oral pH decreases by 1, from 6.5. The average pH of the three powdered vitamin C solutions used in this study was less than 3.0, confirming the high risk of tooth erosion.
TA is also an important factor in evaluating the erosion ability of enamel and is said to exhibit the characteristics of acidic beverages that neutralize acid and resist pH changes17). Furthermore, it refers to the time taken for oral pH to return to neutral after consuming acidic foods18). In this study, a decrease in the surface microhardness was confirmed in the three experimental groups with high TA. Additionally, the SEM results revealed some loss of enamel. These findings correspond to those of Larsen and Nyvad19), who reported that higher TA leads to greater dental erosion; Min18), who observed mineral loss from mouthwashes with high TA; and Li et al.20) who found that vitamin C has both low pH and high TA. Moreover, according to Kim et al.21), as the TA of acidic beverages increases, the depth of enamel erosional lesions also increases, with a reported correlation of 88%. Furthermore, the specimen immersed in the beverage with the highest TA content exhibited the greatest decrease in the surface microhardness21). This was consistent with the finding that Lemona, which had the highest TA among the experimental groups in this study, showed the greatest decrease in surface microhardness, indicating that TA is highly correlated with dental erosion. The TA of Lemona was higher than that of the other two powdered vitamin C products. According to Walstra et al.22), pH and TA do not have a direct relationship; however, the pH generally decreases as TA increases. This explains why Lemona has a high TA at low pH. The differences in TA among the experimental groups suggest variations in the type or number of acidic components present. Al Fata et al.23) reported that vitamin C exists in two biologically active forms: L-ascorbic acid and L-dehydroascorbic acid. L-ascorbic acid is highly sensitive to technological processing methods, temperature, and the presence of oxygen, which leads to its decomposition. Therefore, it is believed that variations in the form of vitamin C used or the degree of degradation during the different manufacturing processes resulted in the observed differences in TA.
The difference in surface microhardness before and after 7 days of immersion was small when immersed in artificial saliva, the negative control group. In contrast, the three types of powdered vitamin C and Coca-Cola, the positive control group, showed large differences in surface microhardness. Moss24) confirmed that ascorbic acid (vitamin C) added to various drinks and candies can cause extrinsic dental erosion Al-Dlaigan et al.25) reported a significant correlation between the prevalence of dental erosion and the intake of vitamin C tablets and foods. Furthermore, vitamin C intake increased the risk of dental erosion by approximately 1.16 times20). The results of this study confirmed that the surface microhardness significantly decreased depending on the immersion period. This finding aligns with the study by Valera et al.26), which showed that the surface microhardness decreased over time when dental restorative materials were immersed in multivitamins. Additionally, Sozen Yanik et al.27) reported that the VHN of effervescent vitamin-treated human enamel decreased significantly from 24 hours to 30 days. A decrease in the surface microhardness was also observed when immersed in artificial saliva, similar to the study by Kim et al.28), which showed a decrease in the surface microhardness of specimens immersed in bottled water.
In this study, the surface of bovine enamel was observed using a SEM. The specimens before immersion and those immersed in artificial saliva as a negative control showed a similarly smooth surface. Specimens immersed in Lemona, Vitagran, Korea Eundan, and the positive control, Coca-Cola, had a rough appearance. This result is similar to that of a study by Jeong et al.29), who confirmed enamel cracking and demineralization when bovine teeth specimens were immersed in effervescent vitamins for 10 minutes. This confirms the effect of powdered vitamin C on the enamel surface.
Based on the results of this study, it is believed that it is important for oral health professionals and consumers to be aware of the possibility of dental erosion due to the intake of powdered vitamin C. Owing to the nature of healthy functional foods, it is necessary to educate people on how to minimize tooth erosion and remineralize the enamel rather than restricting intake. Hemingway et al.30) reported that tooth wear increased when the teeth were brushed immediately after ingestion. Lee et al.31) recommended rinsing teeth with water immediately after consuming acidic foods and brushing teeth after a certain period to allow remineralization through saliva. In addition, Attin et al.32) reported that it is necessary to leave at least 60 minutes between brushing teeth and consuming acidic food. Therefore, after consuming powdered vitamin C, it is necessary to rinse the mouth with water to reduce the acid residue and then brush the teeth after approximately an hour.
This study is an in vitro experiment using bovine enamel, so the limitation is that the buffering effect caused by saliva was not reproduced. Future research to reproduce the oral environment needs to be conducted.
This research was supported by 2024 Eulji University Innovation Support Project grant funded.
Conflict of interest
No potential conflict of interest relevant to this article was reported.
Ethical approval
This article does not require for IRB screening because human origin is not used.
Author contributions
Conceptualization: Na-Ra Min, Ye-Jin Seo, Su-Min Han, and Do-Seon Lim. Data acquisition: Ha-Rin Kim, Na-Ra Min, Ye-Jin Seo, Yeo-Jin Lee, Eun-Bi Lee, and Su-Min Han. Formal analysis: Ye-Jin Kim, Su-Min Han, Im-Hee Jung, Hee-Jung Lim, and Do-Seon Lim. Supervision: Ye-Jin Kim, Im-Hee Jung, Hee-Jung Lim, and Do-Seon Lim. Writing-original draft: Ha-Rin Kim, Ye-Jin Kim, and Su-Min Han. Writing-review & editing: Ye-Jin Kim, Im-Hee Jung, Hee-Jung Lim, and Do-Seon Lim.
Funding
None.
Data availability
The supporting data of this study are available from the corresponding author upon reasonable request.
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