Only part of the story: The danger of soft drink beverages requires a closer look at the chemistry

ANNE NUGENT GUIGNON

The 18th century phrase, "A little knowledge is a dangerous thing," has withstood the test of time. Steadfast beliefs often shatter quickly when the scientific community brings forward new information. As responsible clinicians, we need to be open to what the research is telling us and figure out a way to translate the information into digestible sound bites that convey the most accurate information.

A perfect case in point is what researchers are now reporting about soft drinks and their impact on oral health. For years our focus has been on sugar-laden drinks. Until 10 years ago, sugar-free or diet beverages were considered an acceptable substitute, a belief quickly abandoned when scientists started considering pH levels.

In 2004, von Fraunhoffer published a landmark study that evaluated the erosive potential of 15 different drinks as compared to water. The study measured the overall weight loss of pieces of teeth exposed to commercial soft drinks over a period of two weeks, which clearly demonstrated that low pH beverages cause significant erosion issues.¹

There were several other key studies that involved drinks and teeth. Saliva was not a part of these study designs; therefore, there were no bacteria to increase the acid load and no saliva to neutralize the acid pH levels in the drinks. Of the 15 drinks studied by von Fraunhofer, the pH levels of the carbonated beverages and canned iced teas fell between pH 2.9 and 3.4. The only exception was root beer with a pH reading of 4.8.1

Study results reported a much higher erosive potential for citrus-based drinks and canned iced tea as compared to the brown, cola-based drinks. The erosive potential of both diet and regular Mountain Dew far surpassed all other products tested, while root beer had an erosive potential very close to water.¹ What was going on? Clearly, the dental community needed to rethink their recommendations.

In 2007, Owens and Kitchen looked at four popular beverages from a slightly different standpoint. Their study, also conducted over a 14-day period, used a standard microscope and scanning electron microscopy to determine the effects of Coke, Diet Coke, Gatorade, and Red Bull on enamel integrity. Third molars free of caries were used in the experiment. Half of the occlusal surface of each experimental tooth was coated with red nail polish to form a protective barrier from the drinks.²

Teeth exposed to the regular and diet cola beverages sustained substantial enamel erosion; however, the teeth subjected to Gatorade and Red Bull also developed erosive lesions that showed extensive damage to the enamel, exposing large areas of dentin.² Again, the study did not involve any bacteria, only teeth submersed in the test beverages over time.

Some basic chemistry

Before discussing the remaining results, let's review some basic concepts. For those of you who don't want to dust off your old chemistry books, here's a refresher on three critical principles. While the term pH gets tossed around a lot, remember pH measures the acid or alkaline level of a substance at a given point in time. The pH scale is logarithmic, so Coca Cola's pH of 2.49 is 10 times more acidic than Red Bull's pH at 3.41. If the pH value was the only information available, it would make sense to conclude that Red Bull might be the safer drink to consume. But this is where a little bit of information is dangerous.

Titratable acidity measures the total amount of acid, not the acid value at a point in time. The titratable acidity (TA) for Coke is 18.3, while the TA value for Red Bull is 51.9, a value nearly three times higher than that of Coke.² The Owens and Kitchen study demonstrates that a higher TA value is a critically important piece of information in understanding why energy drinks have such an impact on tooth structure.

A third basic chemistry concept impacts the findings from both of these studies. Citric acid is technically classified as a weak organic acid, but that can be misleading to those of us who are not chemists. In reality, citric acid is a strong chelator that tightly binds to calcium, thus increasing the erosive potential of citrus-based drinks over drinks that contain phosphoric acid, such as the brown drinks.³

Advising patients about beverages

Fast forward to the modern-day beverages such as energy and sports drinks, or even a legacy drink like Mountain Dew. Each of these is formulated with multiple organic acids, which results in a higher TA than colas that are formulated only with phosphoric and carbonic acid, the ingredient responsible for the fizz.

While there has been a dramatic downward shift in carbonated beverage consumption over the past 10 years, consider the explosion in the number of flavored waters, energy and sports drinks, and drops and powders designed to flavor water. Consumption of citrus and floral teas, beverages like kombucha, and drinks to support digestion are also on the rise.

Numerous studies over the last decade have found that the most erosive beverages are those with low pH that have a high titratable acidity.^4-10 A 2013 study evaluated the erosive potential of energy drinks as compared to sport drinks and found tooth erosion from energy drinks to be twice that of sports drinks.¹¹ A number of studies have concluded that the titratable acidity is a significant predictor for enamel dissolution. None of these studies included the role bacteria play in producing acids. The role of fermentable carbohydrates must also be considered as a contributor to the acid overload.

We need to start reading labels. Citric acid is not the only problem. Manufacturers use a wide variety of acids to improve the taste of foods and beverages. Acids are everywhere, and they each contribute to the specific flavor profile of beverages. The most widely used acids for flavoring are citric, malic, lactic, tartaric, and phosphoric. Each acid added to a food or beverage increases the TA.⁶

Research shows tap water, freshly brewed coffee and tea, plain carbonated water, black and green teas, root beer,1 and fruit smoothies that contain yogurt¹² all have a low erosive potential. Unlike other carbonated beverages, root beer contains only one acid, carbonic acid, and the proteins in yogurt bind the fruit acids in the smoothies.

Additional factors can further complicate the role of acids in the development of erosion and caries. When working with patients, remember to include factors such as dry mouth, eating frequency, unhealthy saliva, and ineffective biofilm disruption in the discussion. Understanding why beverages pose a significant chemical hazard to oral health will help us guide our patients to healthier selections. RDH

REFERENCES

1. Von Fraunhofer. Dissolution of enamel in soft drinks. agd.org/library/2004/aug/vonFraunhofer.pdf.
2. Owens BM, Kitchens M. The Erosive Potential of Soft Drinks on Enamel Surface Substrate: An In
3. Lussi A, Schlueter N, et al. Dental erosion--an overview with emphasis on chemical and histopathological aspects. Caries Res. 2011;45.
4. Hendricks JL, Marshall TA, et al. Erosive potentials of brewed teas. Am J Dent. 2013 Oct;26(5):278-82.
5. Singh S, Jindal R. Evaluating the buffering capacity of various soft drinks, fruit juices and tea. J Conserv Dent 2010;13:129-31
6. Beyer M, Reichert J, et al. Acids with an equivalent taste lead to different erosion of human dental enamel. Dent Mater. 2011 Oct;27(10):1017-23.
7. Ehlen LA1, Marshall TA, et al. Acidic beverages increase the risk of in vitro tooth erosion.Nutr Res. 2008 May;28(5):299-303.
8. Esquivel-Upshaw JF, Dieng FY, et al. Surface degradation of dental ceramics as a function of environmental pH.J Dent Res. 2013 May;92(5):467-71.
9. Lunkes, LB and Hashizume, LN. Evaluation of the pH and titratable acidity of teas commercially available in Brazilian market. Rev Gaúcha Odontol., Porto Alegre,. 2014; 62 (1):59-64.
10. Kukiattrakoon B1, Hengtrakool C, Kedjarune-Leggat U. Chemical durability and microhardness of dental ceramics immersed in acidic agents. Acta Odontol Scand. 2010 Jan;68(1):1-10.
11. Jain P, Hall-May E, Golabek K, Agustin MZ. A comparison of sports and energy drinks--Physiochemical properties and enamel dissolution. Gen Dent. 2012 May-Jun;60(3):190-7.
12. Blacker SM, Chadwick RG. An in vitro investigation of the erosive potential of smoothies. Br Dent J. 2013 Feb;214(4):E9.

ANNE NUGENT GUIGNON, RDH, MPH, CSP, provides popular programs, including topics on biofilms, power driven scaling, ergonomics, hypersensitivity, and remineralization. Recipient of the 2004 Mentor of the Year Award and the 2009 ADHA Irene Newman Award, Anne has practiced clinical dental hygiene in Houston since 1971, and can be contacted at [email protected].