Erosive Potential of Industrialized Teas : An in vitro study

Objective: To evaluate the erosive potential of manufactured teas according to pH, titratable acidity and buffering capacity. Material and Methods: Eight types of manufactured teas of different brands and flavors acquired in supermarkets of João Pessoa, Brazil, were investigated. Indaiá® mineral water and Coca-Cola® were controls. The pH measurement and titratable acidity for pH 5.5 and 7.0 were performed in triplicate in 50 ml of each beverage. The buffering capacity was calculated based on pH and titratable acidity for pH 7.0. ANOVA, Tukey, and Pearson correlation, with p <0.05, were used for data analysis. Results: Data showed normal distribution by Kolmogorov-Smirnov test for all variables. There was a statistically significant relationship between groups analyzed in all variables (ANOVA, p <0.001). The pH of teas ranged from 2.70 (Black Tea with lemon-Leão Fuze®) to 4.03 (Natural Mate Tea Matte Leão®). The following significant correlations (p <0.01) were observed: pH and titratable acidity; buffering capacity and pH; buffering capacity and titratable acidity. Conclusion: All teas analyzed were potentially erosive; however, Black Tea with lemon (Leão Fuze®) had the lowest pH, the highest titratable acidity and buffering capacity, demonstrating that the saliva will have greater difficulty in buffering this tea in the oral environment.


Introduction
Dental erosion is the physical result of pathological, chronic, localized and painless loss of mineralized dental tissue chemically submitted to acid attack without bacterial involvement [1].This type of loss of dental tissue can be caused by extrinsic and intrinsic factors.Intrinsic causes have been linked to anorexia nervosa and bulimia as well as to any persistent gastroesophageal disorder that puts the gastric acid in direct contact with the hard dental tissues, resulting in the loss of minerals.Extrinsic causes involve acidic drugs such as vitamin C, in addition to the consumption of acidic foods and beverages [2].Dental erosion is a multifactorial condition 2 whose chemical, biological and behavioral interactions help explain why some individuals have more manifestations of this pathology than others [3].However, the most relevant acids that can cause dental erosion are from the diet [4] and from the stomach [5].
Currently, the population has consumed a large number of beverages and processed foods, due to their easy access, low cost and convenience [6].In addition, the constant care of the body and the physical beauty has led to a constant search for practical and healthy drinks and foods, which includes industrialized teas as an alternative to coffee [7].Tea is prepared by the infusion of plant leaves, flowers or roots, usually with hot water, varying the taste depending on the processing adopted, which can be with or without fermentation, toasted or not, add of aroma or spices [8].
Many people believe that because it is tea, the frequent use of this beverage would be beneficial.In the past, teas were considered therapeutic beverages, mainly due to their high amount of flavonoids [8].However, INMETRO [8] questions the real benefits of this component in the composition of the teas.
Dental erosion has become a frequent pathology among many populations [9], with estimated prevalence of 30.4% among children and adolescents aged 9-19 years, according to a systematic review [7].In addition, during the last decade, a significant increase in the severity of dental erosion lesions has been observed, particularly in children and adolescents [7,[9][10][11].In Brazil, prevalence of up to 34.1% has been observed in adolescents aged 13-14 years [12].Currently, increasing data on the prevalence of dental erosion have attracted the attention of the dental community for the development of many studies [13].
However, it is noteworthy that erosion differs from dental caries, as the latter occurs in areas covered by biofilms, while erosion occurs in biofilm-free areas on all exposed surfaces [1].Initially, the most common feature of erosion is loss of enamel glaze, leaving the surface polished.The lesion is generally broad and shallow, frequently U-shaped with no evident angles.When it invades the dentin, it causes sensitivity to cold, heat, and osmotic pressure, and restorations may become more prominent and projected off the surface [14].Therefore, late diagnosis or inadequate preventive intervention may lead to advanced tissue loss, compromising vitality, functionality or tooth aesthetics [15].The aim of this study was to analyze the erosive potential of industrialized teas of different brands and flavors through pH, titratable acidity and buffering capacity.

Selection of Beverages
Eight types of industrialized teas of different brands and flavors were acquired in the supermarket chains of the city of João Pessoa, Brazil, as described in Chart 1. Beverages were stored according to the manufacturer's instructions.For the negative control, mineral water was used and for positive control, a cola-based soft drink was used.

Data Collection
Immediately after opening, the pH of the selected beverages was measured using an electrode coupled to a pH meter (Orion, model 420A-Thermo Fischer Science Inc., Waltham, MA).
Titratable acidity was performed with the addition of 1M NaOH to 50ml of each beverage in 0.2ml increments until reaching pH 5.5 (critical) and pH 7.0 (neutral).Measurements were performed with constant stirring in triplicate to obtain an average value to be used.The buffering capacity (β) was calculated through Eq. ( 1), according to Lussi et al. [1]: Results were evaluated through descriptive and inferential analyses.After analyzing data normality, the parametric ANOVA test, followed by the Tukey test, was used to compare pH, titratable acidity and buffering capacity variables.Correlations between variables were made with the Pearson correlation test.The significance level adopted was 95% (p <0.05).

Results
Data presented normal distribution by the Kolmogorov-Smirnov test for all variables (pH, titratable acidity and buffering capacity), allowing the use of parametric tests (Table 1).A statistically significant relationship was observed between groups analyzed in all variables (ANOVA, p <0.001).The pH of beverages ranged from 2.70 (Black Tea with Lemon -Leão Fuze ® ) to 4.33 (Indaiá ® Mineral Water).Black Tea with lemon (Leão Fuze ® ) obtained pH lower than the positive control (Coca-Cola ® ).Among teas, it was observed that the highest pH was 4.03 for Natural Mate Tea (Matte Leão ® ).The highest titratable acidity for pH 5.5 was found for Black Tea with Lemon (Leão Fuze®) and the lowest for Mineral Water (Indaiá ® ).However, among teas, Natural Mate Tea (Matte Leão ® ) obtained the lowest titratable acidity value.In titration for pH 7.0, the lowest value was found for Indaiá ® mineral water and the highest value for Coca-cola ® .Among teas, Natural Mate Tea (Matte Leão ® ) obtained the lowest value while the highest was found for Black Tea with lemon (Leão Fuze ® ). the buffering capacity, the highest value (11.41) was found for the positive control group (Coca-Cola ® ) and the lowest (0.194) for the negative control (Indaiá ® mineral water), as expected.For the group of teas, Black Tea with Lemon (Leão Fuze ® ) obtained the highest value (8.30), while the lowest (3.78) was found for Natural Mate Tea (Matte Leão ® ), following the pattern presented by initial pH and titratable acidity.

Discussion
The present study observed that all beverages analyzed had pH value lower than the critical value for enamel and dentin.In addition, Black Tea with lemon (Leão Fuze ® ) had pH value lower than that of Coca-Cola ® .Mineral water (Indaiá ® ) also had pH lower than value considered critical for dental tissues; however, its high buffering capacity facilitates its neutralization by the saliva, when present in the oral environment, thus being considered the beverage with less erosive potential.Due to these characteristics, mineral water (Indaiá ® ) was used as a negative control in this research, since it does not present any erosive substance in its composition [3].
Black tea with lemon (Leão Fuze ® ) and Green tea with cranberry (Feel Good ® ) analyzed in this study presented the highest buffering capacity values, being only lower than positive control.It was observed that Coca-Cola ® , used as positive control, had high buffering capacity value, showing to be a beverage difficult to be buffered by saliva, and therefore very harmful to dental tissues, demonstrating a faster reactive potential on hydroxyapatite than the other beverages analyzed, corroborating previous study [16], who reported the same for Pepsi ® .Coca-Cola ® and Pepsi ® contain phosphoric acid in their compositions, which has been shown to be highly erosive compared to other organic acids such as citric, malic and lactic acids [17].
The buffering capacity depends on the total amount of the conjugable acid and available base and indicates the amount of acid or base that may be added before the buffer loses its ability to resist pH change [18].In the oral environment, saliva has buffering action, with remineralizing effects, neutralizing the acids present in beverages.The pH of the mouth is around 6.8, and when we drink some acidic beverage, the pH decreases dramatically, taking about 25 minutes for the saliva to take action in the environment and perform its function [4].
It was observed that Black Tea with lemon (Leão Fuze ® ) presented the lowest pH value and the highest titratable acidity values for pH 5.5 and 7.0 and buffering capacity, showing high erosive potential.This can be explained by its composition [19], since this tea has citric and phosphoric acids in its composition [3], and also due to the addition of concentrated lemon juice, fruit with high citric acid content [19].Acid is added to accentuate the taste of lemon, but has high capacity for chelating minerals and is responsible for tooth erosion [20].
This finding is consistent with some authors [3], who performed an erosive challenge using Black Tea (Leão ® ) and observed a significant change in the surface hardness of the dental enamel exposed to this tea, before and after the erosive test, despite presenting fluoride in its composition.It was observed that the amount of fluoride present was unable to promote enamel protection when there is a previous erosive challenge with HCl or in the presence of acids from carbonated beverages [3].
Natural Mate Tea (Matte Leão ® ) presented the highest pH value and the lowest titratable acidity values and buffering capacity, demonstrating that saliva will not find it difficult to buffer this beverage.These findings indicate its low erosive potential, which is in agreement with previous report [11].However, the multifactorial character of dental erosion should also be considered [21].
In the present study, it was found that, in general, fruity teas had higher erosive potential than natural ones, which is in agreement with the literature [22].In a systematic review that included a number of epidemiological, cutoff, laboratory, and case-control studies published between 2000 and 2012 with human and animal specimens, it was found that fruity green and black teas, with added herbs and sugar, had high erosive potential [23], corroborating the results of this study.
Therefore, the erosive potential should not be attributed solely to pH, but also the differences among the components of each type of tea, since, in their composition, fruity teas present fruit juices that generally have high citric acid content [24].In addition, the present study observed significant correlation between pH, titratable acidity and buffering capacity; therefore, these chemical characteristics are important to explain the erosive potential of beverages.
Within the limitations of the present study, the composition of teas and / or their flavor may have influenced the results obtained, demonstrating the importance of these characteristics to evaluate their erosive potential.These findings are relevant as they alert the population about the dangers of these beverages to dental erosion, since they are generally considered healthy and frequently consumed.

Conclusion
All teas analyzed are potentially erosive, since they present initial pH lower than value considered critical for enamel (5.5) and dentine (6.5).Black Tea with lemon (Leão Fuze ® ) had the lowest pH and the highest titratable acidity values and higher buffering capacity, demonstrating that saliva will have greater difficulty in buffering this product in the oral environment.