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Uniformed Services University of the Health Sciences, Keesler Air Force Base, Biloxi, MSNow with Uniformed Services University of the Health Sciences, Offutt Air Force Base, Omaha, NE
It has been well-documented that highly acidic beverages containing sugar are capable of dental erosion. As dentin has a lower critical pH, it is more susceptible than enamel to erosion. This study aimed to examine the effect of sugar-free water beverages on the erosion of cervical dentin.
Methods
Eight beverages were selected, including a positive control and negative control. For each beverage, the pH (n = 5) and total acidity (n = 3) were determined with a digital pH meter. Freshly extracted human premolars were sectioned to create cervical dentin specimens (n = 48). Specimens were imaged using laser profilometry before and after the specimens were challenged with beverages for 24 hours. The 3-dimensional before and after scans were evaluated to determine the change in surface volume, erosion depth, and surface roughness. The data were analyzed with a Kruskal-Wallis with Dunn post hoc test (α = 0.05).
Results
The pH of all samples was less than 5.5, except for the negative control. Noncarbonated waters required significantly less base to neutralize the acid than carbonated beverages. A significant difference was realized through profilometry between the carbonated and noncarbonated beverages, with the former displaying increased volume loss, greater depth, and an amplified change in surface roughness.
Conclusion
Within the limitations of this study, carbonated beverages have greater potential to cause dentinal erosion. The low total acidity of the noncarbonated waters makes them more likely to be buffered in the oral environment than beverages with carbonation or higher total acidity.
Significant research has been devoted to understanding the capacity to erode tooth structure because of sugar-containing soft drinks. However, there are limited investigations into the potential for erosion on exposed root surfaces (cervical dentin) through sugar-free beverages. This study has revealed that carbonated beverages, especially those with additional flavoring agents, can erode the exposed tooth structure. Most commercially available waters have a pH acidic enough to allow for the demineralization of dentin. However, beverages without flavoring agents or carbonation can be easily buffered with naturally occurring saliva. It is recommended that everyone consume beverages that do not have added acidic ingredients.
Introduction
Erosion is a prevalent problem for human dentition with the increasingly acidic foods and beverages regularly consumed. The National Health and Nutrition Examination Survey (2003-2004) reported an estimated prevalence of 45.9% among children and 80% among adults.
dental erosion is described as the loss of dental hard tissue by a chemical process that does not involve bacteria; however, this terminology is inaccurate. The American Society for Testing and Materials Committee on Standards defines erosion as the progressive loss of material from a solid surface because of mechanical interaction between that surface and a fluid, a multicomponent fluid, impinging liquid, or solid particles.
As such, dental erosion would more properly be termed corrosion, but because of the overwhelming use of the term erosion in literature, this nomenclature will be maintained.
In 2007, other popular beverages like energy drinks were studied with similar effects owing to their total acid content and category of acid contained in the drink.
There has been a heightened awareness of making healthy choices since 2000. Many new products have come on the market to address these changing consumer demands.
These values are significant as they represent the pH at which saliva is no longer saturated with calcium and phosphate and the tooth substrate can be dissolved.
Another key issue with changing attitudes and behaviors toward beverages is that the frequency of exposure is critical. It is common for many people to operate under the assumption that the frequent sipping and recapping of an acidic beverage throughout the day is acceptable, but that is not true.
The salivary pH will drop for a certain period after consuming any acidic beverage, even if the beverage does not contain fermentable carbohydrates. If the acidic fluid continues to be consumed, the salivary pH does not return to its resting pH until the sipping is discontinued.
Keeping the oral cavity at an erosive pH (< the critical pH of 5.5) has been shown to cause enamel dissolution by losing hydroxyapatite from the enamel surface.
With much research being targeted toward the erosion of enamel, an equally important analysis is needed on the presence and level of erosion on the dentin substrate. Dentin is more prone to dissolution with its significantly higher critical pH and is exposed to worn dentition and gingival recession.
This is significant because one-half of the patients have an exposed dentinal substrate that is susceptible to erosion.
The purpose of this study was to determine if sugar-free beverages such as bottled water have the potential to cause dentinal erosion. The null hypothesis for this study is no differences between beverages when evaluating (1) pH, (2) total acidity, (3) erosion of dentin, and (4) change in dentin roughness.
Methods
Eight beverages were selected to be included in this study. All included drinks are commonly sold in the United States and do not contain sugar (except Coca-Cola [Coca-Cola Company] chosen as a corrosive beverage reference). These selections were made to serve as a broad sample of drinks available to the US consumer. The chosen beverages were Coca-Cola, Zevia Cherry Cola (Zevia), LaCroix Cran-Raspberry (National Beverage Corporation), Polar Seltzer Lemon (Polar Beverages), Perrier (Nestlé), Smartwater (Coca-Cola Company), Dasani (Coca-Cola Company), and Alkaline 88 (Alkaline Water Company). At least 3 separate containers were purchased for each beverage chosen to ensure all samples were not from the same container.
All selected beverages were randomly assigned an alternate name to ensure that the testing was blinded. pH measures the concentration of free hydrogen ions in a solution. It is calculated using a 0 through 14 logarithmic scale. Analysis was completed initially with a pH meter (FiveEasy, ± 0.01 pH; Mettler-Toledo). Before analyzing beverages, the pH meter was calibrated using 3 known solutions to enhance accuracy. After calibration, 50 mL of a freshly opened beverage was poured into a glass beaker, and an average of 5 pH readings were immediately recorded for each sample. Recalibration was completed after each beverage was tested. Three samples were analyzed for each beverage (n = 5).
Next, the total acidity was determined. This assessment was selected as it measures both the free and bound hydrogen ions within a solution instead of pH. Two solutions with a similar pH can have markedly different levels of total acidity based on the contained acid or acids; the higher the total acidity, the more buffering solution needed to neutralize the acid.
Each beverage (50 mL) beaker was placed on a magnetic stirrer plate (C-MAG HS 7; IKA). The pH of each beverage was constantly monitored as a solution of 0.1 M sodium hydroxide (NaOH) was slowly added with a motorized pipette (Pipet-aid; Drummond) until a pH of 8.20 was reached.
As the 0.1 M NaOH solution was added, the mixture was automatically stirred with cylindrical magnetic stirring bars (Radleys) at a speed of 4. This test was accomplished for each unique beverage (n = 3), and the arithmetic mean of the 3 readings was calculated.
Recently extracted human premolars were used to determine the erosive potential of these beverages on human dentin. An Exempt Research Determination offical review was completed by the Air Force Research Oversight and Compliance Division, and it was determined that the proposed research did not involve human participants and could proceed as designed. These specimens were stored in 0.1 M phosphate-buffered saline (PBS). As the teeth were deidentified tissue specimens, the fluoride intake of the owner was not known. Each tooth was sectioned into small squares of cervical dentin roughly 1.5 × 1.5 mm in dimension. The dentinal block was embedded into a cylinder of acrylic resin (Diamond D Self Cure Acrylic; Keystone Industries) with the superficial dentinal surface exposed. To standardize the variability of each mounted specimen, all were polished with a series of polishing plates in an automatic sample preparation system (Buehler Vanguard 2000; Buehler) to eliminate the superficial fluoride-rich layer and homogenize surface roughness and area. To remove the smear layer, the exposed dentinal surface was cleaned with 25% polyacrylic acid (Ketac Conditioner; 3M) with a microbrush for 10 seconds. Afterward, the specimens were rinsed for 30 seconds with deionized water. The samples were sonicated (Blazer Ultrasonic Cleaner; Blazer Products) for 180 seconds in 0.1M PBS and lightly air-dried for 10 seconds. The surface morphology was imaged with the laser microscope/profilometer (VK-X-1000 with 10× Nikon lens; Keyence).
After scanning, individual specimens were challenged with a freshly opened cold beverage (8 °C) by placing the sample in a container and gently pouring 40 mL of a beverage on the exposed dentinal surface. The samples were kept sealed for 24 hours. The tested specimens were then removed from the test solutions, sonicated in 0.1 M PBS for 180 seconds, lightly air-dried for 10 seconds, and after beverage laser imaging was conducted. Before and after beverage scans were aligned, and data were analyzed by a blinded examiner. Analysis was performed to determine the change in the surface volume, lesion depth, and surface roughness of a 1- × 1-mm area. The data did not meet the assumptions for parametric testing. Thus, the data were analyzed with a Kruskal-Wallis with Dunn post hoc testing (α = 0.05) using statistical software (SPSS; IBM).
Results
The pH of all beverages was less than 5.5, except for the negative control, Alkaline 88 (Table). The most acidic beverage was Coca-Cola (pH = 2.25), which was selected as the positive control. The other carbonated beverages (Zevia Cherry Cola [pH = 2.68], Polar Seltzer Lemon [pH = 3.71], LaCroix Cran-Raspberry [pH = 3.84], and Perrier [pH = 5.22]) all had pHs below the critical pH of enamel and dentin. The least acidic carbonated beverage, Perrier, was the only one that was unflavored. Zevia Cherry Cola was the most acidic drink and contained additional acids (tartaric acid, citric acid), unlike the other carbonated beverages. The noncarbonated beverages had pHs that were less acidic (Smartwater [pH = 5.19], Dasani [pH = 5.03]), although as acidic as Perrier but without carbonation. The noncarbonated beverages also had a pH beneath the critical pH of enamel and dentin. The negative control (Alkaline 88) had a pH much higher than all of the other tested drinks. The pH was assessed at 8.9, which approximated the advertised pH of 8.8, a value far above the critical pH of both enamel and dentin.
When NaOH was added to each beverage, there was a bimodal difference in their behavior. Alkaline 88 was not tested as its resting pH was above the titratable end point. Highest to lowest order with mL of NaOH added was Coca-Cola, Zevia Cherry Cola, LaCroix Cran-Raspberry, Polar Seltzer Lemon, Perrier, Smartwater, and Dasani. The carbonated beverages required a large volume of NaOH to reach the pH end point. This quantity amounted to 23.36 mL or 47% of the volume of the initial beverage. However, the noncarbonated waters (Dasani, Smartwater) required significantly less base to neutralize the acid than the carbonated beverages. Only 0.06 mL or 0.12% of the volume of the tested beverage was required to reach the titratable end point.
The bimodal distribution observed with base titration was again observed when analyzing the surface roughness from the acidic challenges. Change in surface roughness showed the 5 carbonated beverages were significantly higher than the noncarbonated waters and Alkaline 88 (Table). However, the Perrier samples presented a unique and statistically distinct third group separate from the highly acidic group (Coca-Cola, Zevia Cherry Cola, LaCroix Cran-Raspberry, Polar Seltzer Lemon) and the less acidic group (Dasani, Smartwater, Alkaline 88). This difference was statistically significant (P < .05).
All beverages were statistically different regarding their volume loss except for 2 paired groups that were not statistically similar. The first paired group with the greatest loss was Coca-Cola and Zevia Cherry Cola, and the second group with the next greatest loss was LaCroix Cran-Raspberry and Polar Seltzer Lemon (Figure 1). The order of volume loss was nearly identical to the rank order witnessed with the base titration. Smartwater had the lowest volume loss of the noncontrol beverages (Figure 2). The depths of the samples were also determined. Because the tested sections produced a uniform depth on a 1- × 1-mm section, the depths had an identical relationship to volume loss (Table).
Figure 1Profilometry scans for Zevia Cherry Cola (Zevia) sample.
This investigation exposed caries-free cervical dentin specimens to sugar-free acidic beverages for 24 hours. After the erosive challenge, 5 beverages produced significant erosion of cervical dentin. Previous studies used enamel specimens tested against significantly acidic beverages such as fruit juices and sodas. This study aimed to test waters and beverages considered healthier.
The pHs revealed that all of the tested beverages, except the negative control Alkaline 88, had a pH beneath the critical pH of dentin (5.5). To replicate an acidic challenge in the oral cavity, the dentin specimens were immersed in a selected beverage. Erosion can be a product of contact time between the acidic challenge and the dental substrate. In our study, no agitation of the beverages was performed, which would mimic the swishing that may occur in the oral cavity. The addition of agitation would likely further increase the erosion of the specimens.
Twenty-four hours of contact time between beverage and dentinal substrate was chosen for this study. This time interval corresponds to an actual year of beverage consumption. This calculation is based on an average beverage intake of 25 fl oz/d with a clearance time of 20 seconds.
This correlation parallels 1,500 minutes (25 hours) of beverage contact time. This exposure period led to a statistically significant amount of volume loss in all tooth samples of all beverages except the negative control, Alkaline 88. Similarly, a change in surface roughness in all but Alkaline 88, Smartwater, and Dasani. The greatest lesion depth was found with Zevia Cherry Cola at 37.56 μm. The smallest erosion depth occurred with Alkaline 88 with −0.38 μm, indicating that this beverage induced remineralization on the substrate. Among the noncontrol beverages, Polar Seltzer Lemon performed the worst (14.46 μm), and Smartwater performed the best (0.46 μm). Therefore, dentinal erosion is possible with sugar-free beverages in vitro.
Smartwater and Dasani, as representatives of noncarbonated, nonflavored bottled waters, produced the smallest changes on the dentinal substrates. This was primarily because of their lack of added acid. The beverages’ pH was acidic (5.03 for Dasani; 5.19 for Smartwater), but a small base was more than enough to titrate the acids past the neutral pH point. In healthy people, saliva serves this role and buffers the daily acidic challenges. Therefore, dentinal erosion from noncarbonated, nonflavored bottled waters is not likely to occur in people capable of producing natural amounts of saliva.
The flavored and carbonated beverages produced significantly more erosion on the dentin samples. The addition of carbonated water to these drinks greatly increased the amount of base added to reach a basic pH. Nearly 400 times the amount of 0.1 M NaOH was required to hit the titration end point compared with the noncarbonated waters. The carbonation enabled these beverages to generate significantly more volume loss and surface roughness than the noncarbonated waters.
Coca-Cola and Zevia Cherry Cola showed the greatest change in surface roughness, surface volume loss, and erosion depth. Both have a low pH because of their added acids (phosphoric acid for Coca-Cola; tartaric acid and citric acid for Zevia Cherry Cola) and the carbonated water they contain. However, the main difference between the 2 is the presence of sugar vs sugar substitutes (ie, Stevia). The presence of either does not seem to make a difference as both are the most likely to cause dentinal erosion in vivo.
Potential limitations of this investigation include beverage selection. The range of options chosen for our study could represent outliers or more or less acidic beverages than the average. In addition, the unknown origin or fluoride exposure of the teeth included could present a confounding variable. The specimens and their exposed dentinal surface were prepared and flattened in a standardized preparation system to account for this factor, but differences in specimens could persist. Results from this benchtop study may not extrapolate to an in vivo environment. Therefore, further testing is warranted to evaluate further the capacity of sugar-free waters to facilitate erosion of cervical dentin in the oral environment.
Conclusions
Within the limitations of this study, carbonated beverages have the potential to cause dentinal erosion. The low total acidity of the noncarbonated waters makes them more likely to be buffered in the oral environment than beverages with carbonation or higher total acidity. This research indicates that carbonated waters are not as benign as previously thought. The addition of acids and flavoring agents greatly affects their total acidity increasing their ability to cause dentinal erosion. From a public health standpoint, consuming beverages that do not have added acidic ingredients should be encouraged.
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