Next to water, one of the top-ranked beverages was tea, which is consumed widely by eastern societies.¹⁵  However, within the western diet (particularly in the U.S.), tea is consumed less frequently than the popular soft drinks and coffee.  Brewed tea, unadulterated by additives such as sugar or preservatives, has been praised repeatedly in the literature for its systemic and dental health benefits.^15-19  These benefits have sparked a movement for increasing tea consumption among industrialized nations, particularly the U.S.  However, the erosive potential of tea on the human dentition has not been defined clearly.  It is essential to assess this potential before such a movement can be adopted.

Objectives

This study sought to identify the erosive effects of green and black tea on the human adult dentition and to monitor topographic and geometric profile changes that occurred among coronal segments that were exposed to these fluids for an extended duration.  For the relative comparison of tea solutions, a soda-type beverage and orange juice were used as examples of popular beverages, while vinegar and water acted as active and passive control fluids. 

Materials and methods

Under strictly controlled in vitro conditions, independent of the influence of the oral environmental factors, the tested fluids’ effects on the human dentition were monitored.  The methodology adopted in this study had been employed previously with proven efficacy.^20,21  Thirty-six sound human premolars, all extracted recently and stored in Cidex (Advanced Sterilization Products, Irvine, CA; 800.595.0200) for a week, were selected at random.  To ensure privacy, these teeth were neither identifiable nor traceable to the source.  The teeth were cleaned to remove hard and soft deposits and their surfaces were polished with slurry.  A No. 6 round dental bur was used to make a tunnel through the apical third of the root of each specimen in a mesiodistal direction.  The upper border of the tunnel was used as a stable stationary reference point for geometrical grade scale analysis of the digitized serial radiographs.  The apical two-thirds of the roots (including the bored tunnels) were coated with red nail varnish for protection from test fluids.  The cervical third of the roots and the entire coronal segments were left exposed. 

The initial baseline observation and subsequent follow-ups were documented by visual inspection, sequential photographs, and radio-graphs employing standardized techniques.  Changes in color, translucency, texture, and presence of enamel were assessed by visual evaluations and complemented by sequential photographs.  Radiographs of the specimens’ sagital (buccolingually) and coronal (mesiodistally) profiles were made with the paralleling technique, using a round position-indicating device (12 in. in diameter) and a GX-770 radiograph unit (Gendex Corporation, Lake Zurich, IL; 888.275.5286) at 70 kVp, 7 mA, and 10 impulses.  Radiographs were recorded using ANSI size 2 Kodak single film packets (Eastman Kodak Company, Rochester, NY; 800.933.8031).  After exposure, all radiographs were processed with the same automatic dental film processor (A/T 2000, Air Techniques, Hicksville, NY; 800.595.7871); these analog films were converted to digital images using a film scanner at 600 dpi (Epson Expression 1680, Epson America, Long Beach, CA; 800.463.7766). 

During the 20 weeks of testing, the crown and cervical root portions of the specimens were immersed in the corresponding static fluids (the four trial beverages and the two control fluids) at room temperature.  The four trial beverages were an orange juice and a cola type drink (Pepsi-Cola) and green and black tea.  The orange juice (pH = 2.8) contained organic acids:  citric acid (at a concentration of 0.64%), malic acid (concentration = 0.13%), succinic acids (concentration = 0.54%), and ascorbic acid.  The cola was an acidulated caramelized carbonated beverage (ACCB) with a pH of 2.7; it contained carbonated water, high fructose corn syrup and/or sugar, caramel color, caffeine, natural flavors, citric acid, and phosphoric acid. 

For the purpose of this study, a cup of green tea or black tea was prepared by infusing 2.5 g of tea leaves in 200 mL of boiling water for three minutes.¹⁸  Green and black teas contain similar amounts of proteins; amino acids; carbohydrates; lipids; minerals; pigments; caffeine; vitamins A, C, and E; and fibers.  The distinctive difference between the two teas is the percentage of phenolic compounds (flavonoids):  green tea contains approximately 30% non-oxidized phenolic compounds compared with black tea’s 5%.  Oxidized phenolic compounds constitute the remaining 25% of black tea’s flavonoid content.²²  The pH of black and green tea ranges from 4.9–6.5, depending on the method of preparation and the pH of the water used for infusion.²³  Vinegar (acetic acid 5.0%; pH = 2.4) was used as an active control, while tap water (pH 6.8) was used as a passive control.²⁴

At the baseline topographic observation, the crowns and exposed root trunks of all specimens displayed normal color, translucency, surface texture, consistency, and morphologic landmarks.  Initial radiographic profiles demonstrated intact delineation of specimen contours with sharply defined outlines.

Qualitative topographic observations

The specimens showed various changes.  The time and extent of these changes differed among the tested fluids.  These changes were manifested by alterations that included one or more of the following:  enamel translucency, color, texture, presence, and exposure of underlying dentin with subsequent color and texture changes.

Control fluids

The active control fluid specimens (acetic acid 5%) revealed loss of enamel translucency; at two weeks, their cervical root dentin appeared yellowish in color.  At three weeks, the increasing optical opacity of enamel was intensified further to an opaque white color with a recognizable loss of cervical enamel.  At four weeks, the topography of the enamel surface became rough and lacked morphological landmarks, while the yellowish discoloration of exposed root dentin turned darker, with colors ranging from yellow-brown to dark brown.  This dentin yielded under exploration and became leathery by 8–12 weeks.  At the end of eight weeks, the enamel caps had eroded completely in several acetic acid specimens, while the rest of the specimens demonstrated scattered remnants of enamel islands; considerable loss of height and radius of the enamel cap was noticeable.  These specimens lost their entire enamel cap between weeks 12 and 16, leaving a brown leathery underlying dentin that became darker thereafter.  The specimens incubated in water showed no change throughout the 20-week observation. 

Tea

Topographic observations of the specimens after one week of exposure to black tea revealed gradual changes in enamel and root trunk color.  This discolor-ation was superficial, initially yellowish but darkening over time and turning brown by the fourth week.  Green tea took longer to produce discoloration; when it did, the discoloration was less intense than that produced by the black tea.  None of the green or black tea specimens showed significant morphologic changes in coronal enamel or root dentin.  The surface consistencies of enamel and dentin maintained the normality of the pre-test levels for 12 weeks.  Slight changes in the surface textures of the black and green tea specimens began at the 16-week evaluation; by the 20-week evaluation, the surface roughness of the specimens had increased slightly.

Soda

By the second week, the soda samples displayed formation of scattered white spots on the enamel surface and turbidity of the exposed root dentin color; by the third week, the color of these specimens had changed to dark yellow.  At the four-week evaluation, the entire enamel surface of the soda specimens had lost its translucency and become opaque white in color.  The cervical enamel outline became progressively irregular, rough, and chalky white and was undermined by the seventh week, when it became brittle and crumbled easily to the touch.  By the eighth week, these specimens attained a surface texture that could be scored easily with an explorer tip.  A recognizable loss of enamel at the cemento-enamel junction (CEJ) was evident by 10–11 weeks.  This enamel’s disintegration further exposed the underlying coronal dentin, which soon changed to a brown color.  It was noted that the brown discoloration of the exposed coronal dentin was darker than that of the cervical root dentin.  By 12 weeks, soda specimens showed a distinct loss of coronal height due to erosion of the occlusal and cervical enamel.  These visual observations worsened during the remainder of the 20-week evaluation period, as more enamel thickness was lost and the intensity of dentin discoloration increased. 

Orange juice

Enamel topography of orange juice specimens changed at a slower rate and with less intensity than changes caused by acetic acid and soda.  These changes were demonstrated by a slight loss of enamel translucency at the four-week evaluation.  Subsequently, enamel color changed to an opaque white and continued this trend throughout the first eight weeks to become opaque yellowish in color.  At the 12-week assessment, both optical opacity and roughness of the enamel surface had increased and a yellow discoloration had appeared.  This discoloration continued to intensify and became brown by the end of the 20-week study.  Marked superficial losses of topographic and anatomic features of the orange juice specimens were evident, although none of the enamel caps were missing.

Quantitative radiographic findings

Control fluids

In general, acetic acid specimens displayed maximum enamel loss at the cusp tip height and cervical region, which resulted in a drastic reduction in enamel cap height compared to all other fluids tested.  At the fourth week, acetic acid specimens reported an average cusp tip height loss of 0.08 mm (0.6%) of crown height.  This amount rose suddenly to 2.0 mm (13.6%) by the eighth week and to 4.17 mm (28.33%) at 12 weeks.  By the 16-week assessment, the tissue lost from the cusp tips of these specimens amounted to 5.12 mm (40.22%) of crown height, with a weekly average of 0.32 mm.  The entire enamel thickness of the cusp was lost by the 16-week evaluation.  Continued incubation of the specimens in acetic acid solution increased the erosive action, which led to dissolution of the underlying dentin layers and an average loss of cusp tip height of 6.5 mm for all specimens at 20 weeks. 

At the four-week assessment, cervical enamel loss in an occlusal direction was more progressive than cervical enamel loss from the cusp tip (1.55 mm).  This loss amounted to 10.53% of the average pre-test height of the enamel cap and increased dramatically to 25.82% by the eighth week.  Enamel loss at the cervical region had reached 49.03% of the pre-test height of the enamel cap at 12 weeks and increased to 59.78% at 16 weeks.  The combined loss from the cusp tip height and cervical enamel led to a concomitant reduction of enamel cap height at the fourth week (3.19% of the pre-test height) and became increasingly evident by the eighth week (36.03%).  This reduction in enamel cap height nearly doubled by the 12-week evaluation (66.99%) (see Table 3 and Chart 3).  The enamel caps of the active control fluid specimens had disappeared completely by the 16-week evaluation.  The bucco-lingual and mesiodistal radii of the enamel caps of these specimens displayed proportionately simultaneous reductions.  Water specimens showed no changes for any of the evaluated parameters (see Table 4 and Chart 4).

Tea

Both black tea and green tea caused approximately 3.5% enamel loss from the cusp tip height; this loss was noted only at the 20-week assessment.  This percentage amounted to a 0.5 mm reduction of cusp tip height, with a weekly average of 0.03 mm.  The tea specimens displayed comparatively greater loss in the cervical enamel segment than in the cusp tip segment.  At the 12-week assessment, the black tea specimens averaged cervical enamel loss of 0.32 mm (2.18% of crown height), while the green tea average was 0.45 mm (3.16% of crown height).  Incubating the specimens in these fluids for 16 weeks increased the values for cervical enamel loss to an average of 0.82 mm (5.63%) for black tea and 0.95 mm (6.67%) for green tea.  At the end of 20 weeks, the total loss of enamel from the cervical segment was 1.65 mm (11.38%) for black tea and 1.45 mm (10.18%) for green tea, with a weekly average of approximately 0.08 mm.  A similar amount of tissue loss was reflected from the change in the enamel cap height.  For the black tea and green tea specimens, the average weekly loss of enamel from the crown radius in a buccolingual direction was approximately 0.04 mm, while the average weekly loss in the mesio-distal direction was not measurable for either tea.

Soda

By the end of the 20-week study, the soda specimens showed an average enamel loss that amounted to approximately half of the loss caused by acetic acid.  The decrease in cusp tip height due to soda exposure began at the fourth week (1.1%), progressed to 5.6% by the eighth week, became increasingly noticeable (10%) by the 12-week evaluation, and escalated to 16% by the 16-week assessment.  This pattern of enamel loss continued to progress in a linear fashion; by the end of the study, approximately 23% of the pre-test coronal height of the specimens was missing.  At that time, the average tissue lost from the cusp tip amounted to 3.4 mm, with a weekly average of 0.17 mm. 

Cervical enamel loss amounted to 1.6% of the crown height at the eight-week assessment.  This loss progressed in a linear fashion until the end of the study; at that point, the percentage loss of cervical enamel amounted to 18.3% of the coronal height (2.75 mm, with a weekly average of 0.14 mm).  The combined loss of tissue from cusp tip and cervical segments of the soda specimens led to a 28.3% loss of enamel cap height by the end of the study.  Simultaneously, the crown radii of these specimens lost 15% of the buccolingual and mesiodistal heights of contours. 

Orange juice

The average enamel loss caused by the specimens’ incubation in orange juice was similar to that of the specimens exposed to soda, with slight fluctuations in changes of the cusp tip height and cervical enamel loss.  Orange juice specimens showed slightly less enamel loss from the cusp tip than soda specimens, while the soda caused more cervical enamel loss than orange juice.  As a result, the combined average losses of the coronal height of orange juice and soda specimens were similar by the end of the study, with an enamel cap height loss of 28.3% (4.25 mm) for the soda specimens and 30.2% (4.5 mm) for the orange juice specimens.  The pattern of tissue loss associated with orange juice and soda also occurred at a similar rate.  It was noted that the amount of enamel lost from the height of the enamel cap was 1.5 times that recorded for the crown radius of both the soda and orange juice specimens, while the changes in the buccolingual and the mesiodistal radii were proportional.

Discussion

Both tooth enamel loss and dentin exposure resulting from the erosion process are caused by acid challenges from various sources.  These may be intrinsic (primarily the stomach fluid that may enter the oral cavity during regurgitation of purging) or extrinsic (such as acidic foods and beverages, while industrial acidic fumes produced by unregulated industries play a considerable role). 

A number of factors contribute to the degree and the rate of enamel loss:  the erosive agent (that is, the agent’s acid content, concentration, titerability, and pH and the presence of additives such as calcium), the state of the host individual’s systemic and orodental health (that is, if the patient has a condition that may induce a forceful purge of acidic stomach contents into the oral cavity, has pathologic conditions, or takes medications that alter the physiology of major salivary glands, salivary secretions, and saliva composition), the genetic make-up of the individual, the state of enamel and dentin formation and maturation, the fluoride content of enamel hydroxyapatite, the fluoride uptake from water fluoridation, topical fluoride applications, abrasiveness of materials used for oral hygiene, removal of bacterial plaque accumulation, the individual’s intake pattern of acidic beverages, and lifestyle (that is, the chronicity of intake, frequency of daily intake, the speed of fluid or food intake, the acidic fluid or food’s contact time with the dentition, if acidulated beverages and citrus fruit juices are used as a substitute for water or caloric intake, excessive daily consumption of citrus fruits and juices, illicit drug addiction, and chronic use of prescription medications). 

The incidence of dental erosion associated with the aforementioned factors has been cited in the literature and complemented by epidemiologic survey results and data generated from controlled laboratory tests.^1-10  Due to the irreversible nature of damage to hard dental tissues, clinical judgments based on case reports, rather than clinical trials, are necessary to identify the etiologic factors that cause dental erosion lesions.  Conducting clinical trials to investigate these etiologic factors would have neither therapeutic nor preventive values for participants and could damage their dental health irreversibly; as a result, these studies would not only be counterproductive but also could be considered by the review board to be an abuse of human subjects.  Furthermore, while testing individual ingredients of beverages in a laboratory study may provide much-needed information, these may not be directly applicable clinically. 

In view of these foreseeable consequences, an accelerated controlled laboratory test was conducted to evaluate the effects of representative beverages on freshly extracted human teeth, making it possible to establish and compare the erosive patterns of some beverages consumed daily by the public.  Clinical reports have noted drastic destruction after three years of frequent intake of large volumes of carbonated beverages.⁴  To achieve similar results, the concomitant erosive actions of the tested beverages were monitored by continually exposing specimens to acidic fluid challenges over a prolonged duration of 20 weeks.  The present study did not seek to duplicate the complex clinical situation but to provide an accurate comparison among the beverages tested with respect to their effect on human dentition. 

This study was conducted independent of oral environmental conditions.  Possible influencing factors (either environmental or physiologic) were rendered constant in this study to accurately detect the effect of each fluid tested and identify the differences among them.  The design of this investigative methodology was successfully employed in previous studies, the results of which provided the desired information.^20,21  Identical numbers of healthy disassociated human premolars were designated for each test and control fluid and each specimen was subjected to the erosive action of the corresponding fluid for the same period of time.  Topographic changes were observed on a weekly basis to detect subtle differences, while radiographic assessment of profile changes was carried out at four-week intervals, to measure the affected changes with a reasonable degree of discriminative accuracy.

Photographic and visual observation of the specimens’ topography revealed the degree of erosion from the active control fluid (vinegar) to be highest, while that from the passive control fluid (water) was the lowest.  Changes in color, texture, surface hardness, and anatomic landmarks of surface morphology that were caused by tested beverages compared with those caused by acetic acid demonstrated the two extremes of the erosive nature of the active and passive control fluids.  The data related to the soda and orange juice fell halfway within this scale; both fluids exerted significant erosion on the coronal segment of the human teeth.  This was demonstrated by the reduction of specimens’ cusp tip height, loss of cervical enamel, and consequent reduction of the vertical height of the enamel caps.  A similar and parallel pattern of change was noted with the reduction in the crown radius. 

During the course of the assessments, some fluctuations in the geometrical measurements of soda and orange juice specimens were observed.  Soda specimens demonstrated greater cusp tip height reduction than orange juice specimens, while orange juice had a higher value when cervical enamel loss was measured.  Within the scope of the 20-week test, both the soda and orange juice exhibited similar losses of enamel cap height.  The erosive effect of either fluid depends on the interplay of the aforementioned factors in the oral environment. 

By comparison, green and black tea produced almost similar results that varied slightly in terms of their timing.  Both groups displayed extrinsic enamel staining within one to two weeks and minor or no loss of enamel from the cusp tip height.  The average loss of cervical enamel recorded at the end of the study for tea was less than half of that demonstrated by the soda and orange juice specimens.  Cervical enamel for the green and black tea specimens was amplified by the percentage change, while the crown radii and enamel cap height of these specimens showed insignificant amounts of enamel loss. 

From the aforementioned data, the fluids tested in this study can be categorized in a descending order, according to the severity of their erosive capability.  The acetic acid had the highest erosive effect on human enamel, while orange juice and soda fell within the middle range.  The lowest degree of erosion occurred with black tea, green tea, and water.  The erosive nature of these two types of tea appeared to be so low that they closely resembled the tap water that was used for infusion; however, it was apparent that long-term exposure to tea induced low-grade damage, primarily to the cervical enamel.  This damage may be related to the tannic acid in tea that slightly decreases the pH at the tooth surfaces.²³

Among susceptible subjects, the cervical region is the location of clinically noticeable, commonly diagnosed erosion, abrasion, or combination lesions.  The authors have observed this phenomenon frequently among adult individuals of Asian heritage, whose essential beverage is tea.  These lesions are described as shallow, saucer-shaped, tooth-colored lesions that involve the coronal enamel and cervical root dentin, characteristics of dental erosion lesions in patients with a high level of oral hygiene care.

Among the four beverages tested, all specimens displayed slightly greater enamel loss from the cervical segment than from the cusp tip.  These findings concur with a 2001 study by Hammadeh and Rees, which concluded that there was little difference between cervical and cuspal enamel in terms of their susceptibility to erosion.²⁶  According to Maupome et al, the disparity in enamel loss between the cervical region and cusp tip height was due to structural differences in porosity and the development of the hydroxyapatite crystals rendering the cervical region more prone to erosion.²⁵  Based on the overall data of the present study, vinegar had the greatest erosive effect on the enamel and underlying dentin of human tooth crowns. 

The extent and the rate of damage caused by vinegar should raise questions about the validity of using vinegar in combination with baking soda for oral home care to combat dental plaque.  The use of accurate proportions of this acid-base mix may produce the desired result; however, in the authors’ experience, individuals practicing this method of oral home care tend to add excessive acetic acid to dilute the concoction and make it suitable for toothbrush application.  The free acid in the mix could harm the dentition.  Long-term repeated use of this homemade chemical recipe could actually destroy the teeth in the name of attempting to preserve the health of the peridontium—whose principle function is to support the dentition in the first place.  Losing the teeth to erosion would render the protected peridontium useless.

For those individuals whose chronic excessive consumption of soda or orange juice is an unwavering habit, serious irreversible damage to their dentition is inevitable.  The question that remains is not whether this irreversible damage to the dentition will happen but when it will happen and to what extent.  The results of the present study also demonstrate the relatively harmless effect of green and black teas.  Tea is a natural product that has provided health benefits and therapeutic remedy for thousands of years.  This beverage is produced by infusion of the leaves or the buds of a plant called Camellia sinensis.  This plant can be found in China, Japan, and some tropical countries.  The methods of processing the leaves or the buds of the tea plant determine the end product of tea varieties.  Apart from the white tea that was introduced to the market recently, there are three known major varieties of tea currently marketed worldwide:  green, oolong, and black. 

The green tea is a non-fermented variety that is produced from the fresh leaf buds that are harvested in the spring at the top of the plant.  These buds are dried and steamed to inactivate the polyphenol oxidase enzyme, thus preventing oxidation of the phenolic compound (flavonoids).  Accordingly, green tea is the highest quality tea, since it contains more non-oxidized flavonoids or catechins (30%) than either oolong or black tea.  Fresh drying of these tea buds allows for the retention of the distinguished green color of the tea leaves and the distinctive bitter taste that varies, depending on the soil and growing environment. 

Oolong tea (partially fermented) represents only 2.0% of the tea produced and consumed exclusively in China, Japan, and North Korea.²²  Oolong tea is produced by partially fermenting (oxidizing) the fresh tea leaves for a shorter period than black tea before drying.  Oolong tea falls between the green and black teas in terms of catechin concentrations and health benefits. 

The most popular variety is black tea, which accounts for approximately 76% of the total production of tea worldwide.  The processing of black tea involves fermenting the fresh tea leaves before drying and steaming.  Black tea is produced by rolling the leaves, thus allowing the oxidation process to take place and producing oxidized or fully fermented tea, although it contains a relatively low catechin concentration (5%).  The pH of black tea is approximately 6.3, although it can range from 4.0–6.5, depending on the dilution, the water used, and the temperature of the tea.²²

The beneficial qualities of tea are associated largely with the amount of phenolic compounds (flavonoids) that were not subjected to the oxidation process.  These unoxidized flavonoids, known as catechins, are strong antioxidant plant metabolites.^27,28  There are numerous systemic benefits associated with tea constituents:  the flavanoids can reduce blood pressure and cholesterol level while decreasing the risk of cardiovascular disease, while the saponin content of tea prevents fat from entering the bloodstream.^29-32  The tannin is considered responsible for the soothing effect on the stomach.  Epigallcatechinogallate is responsible for fighting the common cold and flu.  Caffeine and thiamine contents are stimulants, while vitamin C and minerals are resistance builders.²² 

Tea also is one of the few natural sources of fluoride that renders enamel resistant to acid; one cup of brewed tea contains 0.3–0.5 mg of fluoride.³³  It has been reported that tannins in tea inhibit salivary amylase that hydrolyzes starch and breaks down polysaccharides into monosaccharides in the oral cavity.  This byproduct is essential for the metabolism of cariogenic microbial organisms.³⁴  The literature has documented the inhibitory effect of tea polyphenols and tannin on the growth of cariogenic bacteria (Streptococcus salivarius and Streptococcus mutans) by preventing the adherence and growth of bacterial plaque on the tooth surface.^35-38  This dual action of brewed tea constituents contributes considerably to the prevention of caries while offering minimal erosive potential and substantial systemic health benefits, placing tea on the top of the preferred list of beverages for all ages, providing that the purity of this natural product is not adulterated by additives such as sweeteners, lemon, or milk.^21,39-41  Adding milk to hot tea decreases the benefits of the tea’s flavonoid contents, since the casein in milk combines with the flavonoids and renders their benefits obsolete.⁴¹  A 2002 study investigated the fluoride concentration and pH of iced tea products and concluded that most iced teas tested contained considerable concentrations of fluoride; excessive use in infants could put them at risk for an overdose.  Iced tea products were reported to be acidic enough (pH 2.63–4.04) to cause dental erosion if consumed excessively.⁴²

Conclusion

The results of this study clearly identified the differences in terms of the tested fluids’ erosive potential and offered conclusive evidence of brewed green and black tea’s minimal erosive action on the human dentition compared with soda and orange juice.  In view of the countless systemic and dental health benefits of brewed tea and its minimal potential for erosion of human enamel, this beverage should be encouraged as a substitute for acidic drinks.

Acknowledgements

The authors express their sincere appreciation to Theresa M. Thompson, RDH, and Professor Emeritus Robert L. Pollack for their assistance in the preparation of this article.

Author information

Dr. Bassiouny is a professor, Department of Restorative Dentistry, Temple University, School of Dentistry in Philadelphia, Pennsylvania, where Dr. Yang is an associate professor and director of Oral Radiology, Department of Oral Pathology, Medicine and Surgery.  Dr. Kuroda is in private practice in Tokyo, Japan.  At the time of this study, Dr. Kuroda was a visiting fellow, Department of Restorative Dentistry, Temple University School of Dentistry.

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