The consumption of energy drinks has increased considerably, mainly amongst young people who are the main consumers of these products [6, 11, 13] Thus, original research is required to evaluate the erosive potential of energy drinks, since acids in food and beverage products are one of the main factors related to cervical dentine hypersensitivity .
The dentine specimens were sectioned tangentially at root dentine to expose the dentinal tubules in the same way when they occur in patients with dental root exposure .
After periodontal treatment, an irregular and amorphous layer is created on the root surface called the smear layer. The smear layer can obliterate the dentinal tubules and the dentine fluid movement will be blocked or reduced considerably. The dentine fluid movement is responsible for painful transmission after a stimulus in cervical dentine hypersensitivity . In the present study, smear layer was created by hand instrumentation with periodontal curettes prior to acid drinks exposure.
Eleven different energy drinks were assessed for their erosive potential in dentine and compared with the control group (distilled water). Two different application forms were used: topical and friction. Topical application was used to evaluate the effect of energy drinks on the dentin surface covered with smear layer. Friction application has evaluated the effect of brushing performed immediately after application of the different drinks on the dentinal tubules exposure [14, 17]. The dentine specimens were kept immersed in acidic beverages for 5 min, as it is the time necessary for saliva to neutralize and/or remove the acid of the tooth surfaces .
Despite the dentine surface showing higher dentinal tubule exposure in specimens immersed in energy drinks, significant statistical differences were only found for Flyinghorse™ and Bug™ energy drinks in comparison with the control group (topical application). In relation to friction application, statistically significant differences (P < 0.05) were observed comparing Burn™ , Flyinghorse™ , Gladiator™ and SportDrinks™ with the control group. According with our results, the null hypothesis tested was partially accepted.
Before immersing the specimens in the energy drinks, the pH were evaluated (Table 1). Although all the energy drinks evaluated have shown a pH below 5.5, which is considered critical for loss from enamel, mineral loss may begin even at higher pH . The lowest pH value was recorded for SportsDrinks™ , however, significant dentinal tubule exposure for this product was found only for the friction application.
The pH is an important factor that may influence dentine erosion. In addition, the pH is easily measured and frequently used to record the acidity of a product . However, pH values give only a measure of initial and dissociated hydrogen ion concentration, therefore, they do not indicate the presence of undissociated acid. Total titratable acidity is the more accurate measure of the total acid content of a drink .
There are other features that may influence dentine erosion, such as: buffering capacity of saliva, type of acid, including its chelating properties and sugar content [5, 17].
The comparison between application forms has shown higher dentinal tubule exposure for the friction application, although a statistically significant difference was found only for Army Power™ energy drink.
Previous studies have shown that a surface demineralized by acid is vulnerable to toothbrushing, favouring tooth structure removal and dentinal tubule exposure [6, 17, 20]. Although acid diet associated with or without toothbrushing is able to provoke dentinal tubules exposure, comparison among different acid beverages is not always significant. It may occur due to acid features of each beverage. The type of acid may also influence the erosion potential .
Citric acid is also called INS 330 acidulant. This acid is one of the most erosive acids due to its chelating capacity, which is responsible for calcium sequestration from saliva and teeth. Therefore, beverages with low pH and containing citric acid are considered to have the most erosive capacity .
The erosive potential showed for energy beverages may be related to presence of citric acid, since all energy drinks evaluated in the present study contain this acid.
In order to reduce the harmful effects on teeth, components have been added to or eliminated from some acid beverages . One of the approaches has been the supplementation with sodium citrate .
Studies were conducted to assess the benefits of the acid reduction provided by adding citrate [23, 24]. The results show benefits when citrate is used in low concentrations, increasing the pH in the oral cavity, and it can also increase salivary flow, leading to fast elimination of acid after acidogenic challenge .
However, sodium citrate has also chelating properties, which could favor the erosive effects. On the other hand, the chelating properties of citrate may be of little importance at the low pH levels of acidic beverages . Future studies should be developed considering the effects of citrate as modifying agents on erosive potential, since it seems to be poorly understood.
Non-reducing sugars of energy drinks may be another factor that explains the difference found for the erosive potential of the energy drinks. Cavalcanti et al.  assessed the erosive potential of 9 different energy drinks. Of the drinks analysed (Bad Boy Power Drink™ ; Red Bull™ ; Red Bull Sugar free™ ; Flying Horse™ ; Flying Horse light™ ; Burn™ ; Night Power™ ; Flash Power™ ; 220V Sports Drink™ ), Flying Horse™ showed the highest non-reducing sugar (sucrose – 54.3%) in comparison with the other energy drinks evaluated. This may explain the erosive potential presented by the Flying Horse™ in this study, which showed a significant exposure of dentinal tubules even when it was evaluated topically .
Few studies have evaluated the erosive potential and physical-chemical characteristics of energy drinks [11, 12], which complicates the comparison of the present study with previous research and also the explanation of the results obtained. Thus, it is important to evaluate the composition of these substances, since the consumption of energy drinks has been increasing over the years.
FlyingHorse™ and Bug™ energy were significantly different from the control group when applied topically, while Burn™ , FlyingHorse™ , Gladiator™ and SportsDrinks™ were significantly different from control when applied by friction (P < 0.05). Comparison between two application forms revealed greater exposure of dentinal tubules when ArmyPower™ was applied by friction. Thus, it is possible to observe from our results the influence of energy drinks as an etiological factor for cervical dentine hypersensitivity.