Author : Dr. Vipin Kumar (BDS, Post graduate student), Department of Periodontics, Saveetha dental college & hospitals, Chennai, India

ABSTRACT

Extracts of leaves from the tea plant Camellia sinensis contain polyphenolic components with activity against a wide spectrum of microbes. Studies conducted over the last 20 years have shown that the green tea polyphenolic catechins, in particular (−)-epigallocatechin gallate (EGCG) and (−) - epicatechin gallate (ECG), can inhibit the growth of a wide range of Gram-positive and Gram-negative bacterial species with moderate potency. Evidence is emerging that these molecules may be useful in the control of common oral infections, such as dental caries and periodontal disease. Sub-inhibitory concentrations of EGCG and ECG can suppress the expression of bacterial virulence factors and can reverse the resistance of the opportunistic pathogen Staphylococcus aureus to β-lactam antibiotics. The present review aims to highlight the potential role of green tea in periodontal health.

INTRODUCTION

Origin & Nature of tea

Tea originated in China, possibly as long ago as 2700 BC. Drinking water, boiled for reasons of hygiene, was made more palatable by the addition of leaves from the tea plant. In modern times, tea, in one form or another, is, with the exception of water, the world's most widely consumed beverage; more than two billion cups are drunk daily. For thousands of years, tea has anecdotally been considered to have health-giving properties; this has been amply confirmed in recent years by an accelerating research effort 1.

The word ‘tea’ has been used to describe the shrub Camellia sinensis; the fresh leaves of this shrub picked as ‘two and a bud’ for processing (also termed ‘flush’); the processed flush (macerated and heat-dried in the case of green tea); and the beverage made by infusing the processed leaves in boiling water 1.
Depending on the manufacturing process, teas are classified into 3 major types: 2 (Table 1)

1. Non- fermented Green tea ( produced by drying and steaming fresh leaves to inactivate polyphenol oxidase by non-oxidation)
2. Semi-fermented Oolong tea ( produced by partial fermentation of fresh leaves before drying)
3. Fermented Black and Red tea (Pu-Erh) produced by post harvest fermentation before drying and steaming.

Table 1: Classification of teas

	GREEN	BLACK	OOLONG
Manufacturing process	Leaves are steamed or pan fried; no fermentation occurs	Leaves are withered, rolled & crushed; fermentation of polyphenols occurs	Leaves are withered, rolled & fired before fermentation can occur
Major polyphenols	Epicatechin Epicatechin-3- gallate Epigallocatechin Epigallocatechin- 3- gallate	Theaflavin Thearubigin
Countries primarily consumed	China, Japan, India, North Africa, Middle East	Western countries, some Asian countries	South-eastern China,         Taiwan

COMPOSITION

Green tea chemical composition is complex: proteins (15–20% dry weight) whose enzymes constitute an important fraction; aminoacids (1–4% dry weight) such as teanine or 5-N-ethylglutamine, glutamic acid, trypto-phan, glycine, serine, aspartic acid, tyrosine, valine, leucine, threonine, arginine, lysine; carbohydrates (5–7% dry weight) such as cellulose, pectin‘s, glucose, fructose, sucrose; lipids as linoleic and linolenic acids; sterols as stigma sterol; vitamins (B, C, E); xanthic bases such as caffeine, theophylline, and pigments as chlorophyll and carotenoids; volatile compounds as aldehydes, alcohols, esters, lactones, hydrocarbons, etc.; minerals and trace elements (5% dry weight) such as Ca, Mg, Cr, Mn, Fe, Cu, Zn, Mo, Se, Na, P, Co, Sr, Ni, K, F and Al 3.

(Table 2)

Due to the great importance of the mineral presence in tea, the healthful properties of green tea are largely attributed to polyphenols, plant metabolites characterized by presence several phenol groups (i.e. aromatic rings with hydroxyls), which derive from L- phenylalanine4.

The most important green tea polyphenols (GTP‘s) are tannins and flavonoids. Flavonoids are phenol derivatives synthesized in substantial amounts (0.5-1.5%) and variety (more than 4000 identified), and widely distributed among plants. The United States Department of Agriculture (USDA) has recently published a Database for the Flavonoid content of Selected Foods 3.

The main flavonoids present in green tea include Catechins (flavan-3-ols). The 4 major catechins are Epigallocatechin-3-gallate (EGCG) that represent approximately 59%of total catechins; epigallocatechin (EGC) (19% approximately); epicatechin-3-gallate (ECG) (13.6% approximately) and epicatechin (EC) (6.4% approximately) 3. EGCG is the most studied polyphenol component in green tea and the most active. Green tea also contains gallic acid and other phenolic acids such as chlorogenic acid and caffeic acid, and flavonols such as kaempferol, myricetin and quercetin. Alkaloids including caffeine, bromine and theophylline are also present3.

(Table 3)

These alkaloids provide Green tea’s stimulant effects. The relative content of green tea Catechins depends on how the leaves are processed before drying 3. Other factors influencing catechin content are the geographical location and growing conditions (soil, climate, agricultural practises, fertilisers), the type of green tea (e.g., blended, decaffeinated, instant) and the preparation of infusion (e.g., amount of product used, brew time, temperature) 3. McKay and Blumberg reported that decaffeinating reduces slightly the tea catechin content, instant preparations and iced and ready-to-drink teas present less amount of catechins.2 Wu and Wei indicated that a cup of green tea (2.5gms of green tea leaves/200ml of water) may contain 90mg of EGCG which is mainly responsible for its anti-oxidant, anti-carcinogenic, anti-inflammatory and anti-microbial properties4.

Table 2: Mean Composition (%) of Green Tea. 5

Contents	% Dry weight
Proteins	15-20
Amino acids	1-4
Other Carbohydrates	7
Phenolic compounds	30
Minerals	5
Fibre	26
Pigments	2
Lipids	7

Table 3: Catechins 6

Catechins	%
Epigallocatechin-3-gallate (ECGC)	59
Epigallocatechin (EGC)	19
Epicatechin-3-gallate (ECG)	13.6
Epicatechin (EC)	6.4

BIOAVAILABILITY OF GREEN TEA CATECHINS

The potential health effects of catechins depend not only on the amount consumed but on their bioavailability which appears to be very variable. In order to know the catechin bioavailability and metabolism, it is necessary to evaluate their biological activity within target tissues7. Following oral administration of tea catechins to rats, the four principal catechins (EC, ECG, EGC, and EGCG) have been identified in the portal vein, indicating that tea catechins are absorbed intestinally [8]. In humans, EGCG may be less bioavailable than other green tea catechins. Catechin levels in human plasma reach their peak 2 to 4 h after ingestion 9.

A recent study in humans compared the pharmacokinetics of equimolar doses of pure EGC, ECG, and EGCG in 10 healthy volunteers; average peak plasma concentrations after a single dose of 1.5 mmol were 5.0µmol/L for EGC, 3.1µmol/L for ECG, and 1.3µmol/L for EGCG. After 24 h, plasma EGC and EGCG returned to baseline, but plasma ECG remained elevated10.

In humans, ECG has been found to be more highly methylated than EGC and EGCG, and EGCG has been found to be less conjugated than EGC and EC .Unfortunately, little published data are available on tissue distribution of catechins in humans after green tea consumption; however, there are some interesting data from studies with animals10.

Catechins are rapidly and extensively metabolized; studies in rats indicated that EGCG is mainly excreted through the bile, while EGC and EC are excreted through urine and bile11.

Lu et al observed that after oral administration of green tea to rats, about 14% of EGC, 31% of EC, and <1% of EGCG appeared in the blood; in mice, the bioavailability of EGCG was higher12. The effect of green tea drinking may also differ by genotype. To sum up, there appear to be species differences in the bioavailability of EGCG compared to other tea catechins. Further research results are largely consistent in demonstrating that the addition of milk to tea does not interfere with catechin absorption, but milk may affect the antioxidant potential of tea, depending upon milk fat content, milk volume added, and the method used to assess this parameter 13. Xu et al observed that the epimerisation reaction occurring in manufacturing canned and bottled tea drinks would not significantly affect antioxidant activity and bioavailability of total tea polyphenols14.

EFFECTS ON PERIODONTAL HEALTH

Periodontitis is a bacterially induced chronic inflammatory disease that destroys the connective and bone that support the teeth. The role of bacteria in the initiation of periodontitis is well documented and the end result viz., destruction of the alveolar bone and periodontal connective tissue is clearly observed. Bacteria induce tissue destruction directly by activating host defense cells, which in turn produce and release mediators that stimulate the effectors of connective tissue breakdown. A central feature of periodontitis is the remodelling of connective tissue that leads to a net loss of local soft tissues, bone and the periodontal attachment apparatus. Mediators including proteinases, cytokines and prostaglandins are produced as a part of the host response that contributes to tissue destruction 15. (fig.1)

Figure 1. Schematic model of pathogenesis of periodontal disease Periodontal pathogen Endotoxin, toxic cell membrane products Pro-inflammatory cascade Secretion of TNF-α, IL, proteinases Connective tissue destruction, bone resorption

Reactive versus proactive care

For over a century, dentistry has treated periodontal disease based on the medical model of disease therapy. That is, a reactive intervention to the active disease state rather than a proactive approach to dealing with the pre-disease state. Reactive care includes both surgical and nonsurgical therapies15. Both forms of care have engendered an increase in the use of systemic antibiotics and antimicrobial mouth rinses. While these are acceptable for limited cases and short spans of time, they can be misused, being applied as “shotgun therapy” to the majority of cases over excessive periods of time. It has been proven that this can cause the undesirable sequelae of allowing microbial strains to develop an increased resistance to other antibiotic therapies. This occurs because the longer a population of bacteria is subjected to an antibiotic, the more resistant the surviving bacteria become15.

In order to improve the success rate in periodontitis, a novel new treatment aimed at early intervention, the enhancement of host resistance and the inhibition of the biological and mechanical irritants involved in the onset of gingivitis and the progression to periodontal disease has been developed. This functional approach employs the use of biological plant extracts (e.g. green tea extract), selected co-enzymes and specific vitamins to strengthen and support the tissues of the oral cavity and the resistance of the host16.

Green tea extract has been used in the form of chewing gums, mouth rinses, gum paints and dentifrices as a part of preventive (proactive) periodontal maintenance regimen.

Green tea is a very popular beverage and in vitro studies have shown that green tea polyphenols inhibit the growth and cellular adherence of periodontal pathogens and their production of virulence factors. The epidemiological relationship between the intake of green tea and periodontal disease is a modest inverse association16.

Green tea catechins as anti-plaque agents

The formation of dental plaque, which plays an important role in the development of caries and periodontal disease in humans, could be initiated by several strains of oral Streptococci. The major aetiological players are thought to be the two α-haemolytic streptococci, Streptococcus mutans and S. sobrinus, potent cariogenic, although several other types of bacteria (notably lactobacilli and actinomyces) may also be involved. The carbohydrate substrates can become available either directly (sugar ingested in food or drink) or be derived from dietary starch by the action of bacterial or salivary amylases, or both. Mutans streptococci produce 3 types of glucosyltransferase (GTFB, GTFC, and GTFD), and synthesize an adherent and water-insoluble glucan from appropriate carbohydrate substrates, most favourably sucrose at low pH values, which causes the organisms to adhere firmly to the tooth surface. For many oral streptococci, glucans comprise an extracellular slime layer produced in the presence of sucrose that promotes adhesion and the formation of a dental plaque biofilm31.

Short –term studies in human volunteers have demonstrated an anti-plaque effect of tea extracts. You (1993)17 found that using a 0.2% green tea solution to rinse and brush the teeth reduced the plaque index significantly while similar findings were made both by Kaneko et al (1993)18 with a 0.25% catechin mouthwash and Liu and Chi (2000) using tablets consisting of tea polyphenols. Hara and Hattori (1992) obtained a US patent for the use of mixtures containing EGCG, ECG and other catechins as anti-plaque agents. A serious practical disadvantage of using catechins for this purpose is the unpleasant taste of such solutions, a factor that is likely to result in poor patient compliance 20.

Kaneko et al (1993)18 found that a four-week regimen of mouth washing with a dilute catechin solution reduced the mouth odour (halitosis) associated with periodontal disease; it was subsequently established that tea catechins deodorized methyl mercaptan, the main cause of halitosis (Yasuda and Arakawa 1995). These authors showed a clear correlation between efficacy and the antioxidative capacity of individual catechins, with EGCG being more effective than EGC and ECG. In addition, catechin gallates, especially EGCG (active at 250–500 μg/ml), inhibited growth and adherence to buccal epithelial cells of P. gingivalis (Sakanaka et al. 1996 19).

Yasuda et al (1996) evaluated the deodorizing reactions of EGCG, the main polyphenol in green tea, and to determine whether EGCG would chemically react with CH3SH to give new products. The non-volatile reaction products were purified and identified. They were found to be EGCG derivatives carrying methylthio and/or a methylsulphinyl groups on the B ring 35.

A crossover study of 15 male subjects investigated whether green tea powder reduces volatile sulphur compounds (VSCs) in mouth air, and compared its effectiveness with that of other foods which are claimed to control halitosis. The study concluded that green tea was very effective in reducing oral malodor temporarily because of its disinfectant and deodorant activities, whereas other foods were not effective 32.

Krahwinkel, Willershausen conducted a study for four weeks on 47 subjects to investigate how green tea catechins and polyphenols in the form of green tea dragées may influence the inflammatory behavior of the gingiva. While in the verum group a distinct improvement in both approximal plaque index and sulcus bleeding index values could be stated, slight worsening of the values were determined for the placebo group. Results indicate that the oral application of green tea catechins and polyphenols might have a positive influence on the inflammatory reaction of periodontal structures 34.

Hirasawa et al. (2002) 21 demonstrated bactericidal activity of green tea catechins at 1 mg/ ml against species of Prevotella and P. gingivalis, and found significant reduction in markers of gingivitis after the use of a slow-release buccal delivery system applied over a period of 8 weeks. More recent studies have shown that some virulence factors (toxic end metabolites, protein tyrosine phosphatase and gingipains) associated with these aetiological agents of periodontal disease are neutralized by EGCG (Okamoto et al. 2003, 2004; Sakanaka and Okada 2004) 22.

A study of 15 subjects was conducted to examine the inhibition of acid production from dental plaque and mutans streptococci by EGCG. The effect of EGCG solution on dental plaque pH was investigated. Subjects rinsed their mouths with 2 mg/ml EGCG solution and then, after 30-minute interval, rinsed their mouths with 10% sucrose. The pH values of plaque samples from 15 subjects were significantly higher after treatment with catechin than after treatment with water. Study results suggest that EGCG is effective in reducing acid production in dental plaque and mutans streptococci 33.

Several authors have reported that catechins are inhibitory for S. mutans and S. sobrinus, with MICs ranging between 50 and 1000 μg/ml, well within the concentrations found in brewed tea (Sakanaka et al. 1989; Kawamura and Takeo 1989; Rasheed and Haider 1998). A significant bactericidal effect was found after a brief exposure to 1 mg/ml of EGCg. Kubo et al. (1992) found that many of the ‘flavour compounds’ (e.g. nerolidol) found in green tea, although present in too low a concentration to have a direct antibacterial effect, might act synergistically with the abundant catechins 24.

Effects on bone and bone cells

Role of Oxidative Stress and Antioxidants in Periodontitis

Both osteoblastic and osteoclastic cells regulate bone metabolism, and both cell types are involved in the development of periodontitis. Osteoblasts are bone-forming cells located near the surface of the bone that produce cytokines. Cytokines, including macrophage-colony stimulating factor (M-CSF) and receptor activator of nuclear factor-κB (NF-κB) ligand (RANKL), are both essential for osteoclast differentiation, function, and survival 36.

Osteoclasts are bone-resorbing multinucleated cells that become tightly attached to mineralized bone surfaces through their integrins and form resorption lacuna by secreting protons, proteases, and superoxide through ruffled borders. Bone resorption by activated osteoclasts with subsequent deposition of a new matrix by osteoblasts causes the formation of bone structure and bone remodeling. Imbalance between bone formation and bone resorption is the key pathophysiological event in periodontitis in adult humans 36.

Oxidative stress is a pivotal pathogenic factor for periodontal bone loss in mice and rats leading to an increase in osteoblast and osteocyte apoptosis, among other changes, and a decrease in osteoblast numbers and the rate of bone formation via Wnt/β-catenin signalling. Recent studies showed that oxidative stress inhibited osteoblastic differentiation via extracellular signal-regulated kinases (ERK) and ERK-dependent nuclear factor-κB signaling pathways. Osteoblasts can produce antioxidants, such as glutathione peroxidase, to protect against ROS, as well as transforming growth factor-β (TGF-β), which is involved in a reduction of bone resorption. Reactive Oxygen Species (ROS) is a collective term which includes all oxygen derived free radicals, including those reactive intermediate oxygen species formed which are not true radicals but capable of radical formation in the intra- and extracellular environment (Chapple & Matthews 2007). ROS are also involved in bone resorption with a direct contribution of osteoclast-generated superoxide to bone degradation and oxidative stress increases differentiation and function of osteoclasts (fig 2).

It is only when ROS activity exceeds antioxidant defence capabilities or antioxidant defences are reduced that the balance shifts in favour of the ROS, resulting in oxidative stress and possible tissue damage (Chapple & Matthews 2007).

Several lines of evidence suggest a tight association between oxidative stress and the pathogenesis of periodontitis in humans. There is also a biochemical link between increased oxidative stress and reduced BMD in men and women 55 years and older. Dietary antioxidant intake has a beneficial effect on BMD. Since oxidative stress can contribute to bone loss, it is important to elucidate the role of antioxidants like green tea in mitigating bone loss during the development of periodontitis.

Figure 2. Role of host modulated inflammatory responses in destructive periodontal disease Genetic and environmental factors Interaction between periodontal pathogens & host modulatory responses Periodontal pathogens, Lipopolysachharides Toll-like receptor signalling PMN hyper-responsiveness: Reactive oxygen species (ROS), enzymes, cytokines  Lipid peroxidation and release of ROS, enzymes Effect on redox modulators Damage to periodontal tissues and bone loss

Possible mechanisms of green tea on periodontal osteo-protection
There are five main possible mechanisms through which green tea protects bone health: (1) by mitigating bone loss through anti-oxidative stress action, (2) by mitigating bone loss through anti-inflammatory action, (3) by enhancing osteoblastogenesis, (4) by suppressing
osteoclastogenesis, and (5) probably through osteoimmunological action.

1. Mitigating bone loss through anti-oxidative stress action

The most widely recognized properties of GTP are their anti-oxidative activities, owing to their ability to capture and detoxify ROS. Periodontal inflammation induces gingival oxidative stress by potentiating inflammatory responses. Imbalance between the levels of bacterial pathogens (e.g., lipopolysaccharide (LPS) and proteases) and the host immune response to infection contributes to the initiation or progression of periodontitis. In a periodontal lesion, polymorphonuclear leucocytes (PMNs) produce reactive oxygen species (ROS) as the initial host defence against bacterial pathogens. However, excessive production of ROS has a detrimental effect on the host defence system, and induces the oxidation of lipids and protein, contributing to tissue damage (oxidative stress). Investigations have demonstrated that oxidative stress plays a key role in the progression of periodontal inflammation. Therefore, antioxidant therapy targeting periodontal lesions may offer clinical benefits in the management of periodontal inflammation (fig.3).Maruyama et al in 2011 examined the effects of a dentifrice containing green tea catechins on gingival oxidative stress and periodontal inflammation using a rat model and concluded that adding green tea catechins to a dentifrice may contribute to prevention of periodontal inflammation by decreasing gingival oxidative stress and expression of pro-inflammatory cytokines.

2. Mitigating bone loss through anti-inflammatory action

Green tea catechins were reported to be effective in preventing periodontal and gingival inflammation. EGCG inhibit the m-RNA expression of COX- 2, MMP-1, IL-1, 6 and 8 by cultured cells. Effective concentration to achieve these effects was ≥ 1µg/ml. Catechins inhibit enzymatic activities of P.ginigivalis in a manner similar to that of chlorhexidine , doxycycline and non-antimicrobial chemically modified tetracycline derivatives. EGCG inhibit protein tyrosin phosphatase activity in P.intermedia..

3. Increasing osteoblast numbers, osteoblastogenesis, and bone formation

Green tea bioactive components may be beneficial to periodontal bone health by promoting an increase in osteoblast numbers and activity of osteoblasts. The evidence suggests that the components in green tea support osteoblastogenesis by increasing osteoblastic survival, proliferation, differentiation, and bone formation. Both TNF-α and IL-6 could modulate the life span of osteoblasts via apoptosis, thus regulating bone metabolism in chronic periodontitis.
EGCG may enhance the differentiation of osteoblasts to progress to the maturation level, thereby leading to increase the mineralization of bone matrix and bone formation .TGF-β is one of the most abundant cytokines in the bone matrix and plays a major role in the development and maintenance of the facial bones. PGD2 is also a potent regulator of osteoblastic functions. EGCG induced suppression of HSP (Heat Shock Protein) contributes to the modulation of osteoblastic cell function toward bone formation.

Figure 3.  Schematic diagram showing the role of ROS in generating chronic inflammation and tissue damage leading to periodontitis

(Chapple & Matthews 2007).

4. Suppressing osteoclastogenesis and osteoclastic activity

The effects of green tea include suppressing bone resorption, increasing apoptosis of osteoclasts, and inhibiting the formation of osteoclasts. EGCG’s the predominant component of green tea polyphenols inhibits both eukaryotic and prokaryotic cell derived collagenase activity. EGCG completely inhibits the growth of 3 strains of P.gingivalis at concentration of 250 or 500µg/ml and that of P.melaninogenicus at MIC (minimum inhibitory concentration) of 2000µg/ml. Inhibitory effect was pronounced with polyphenols (EGCG, ECG and EGC) having a galloyl moiety linked with an ester linkage with 3-OH of catechin structural molecules. The higher the concentration of EGCG and ECG more severe the inhibition.
GTP may induce osteoclasts’ apoptosis by involving a caspase dependent mechanism with downregulation of NF-κB .
Green tea bioactive components can suppress the formation of osteoclasts by inhibiting the release of matrix metalloproteinases (MMPs) by osteoblasts. EGCG prevents the increased MMP (Matrix Metallo Proteinase) expression from osteoblasts induced by P.gingivalis extracts. These findings suggested that EGCG may inhibit the alveolar bone resorption that occurs in periodontal diseases by inhibiting the expression of MMP’s in osteoblasts and the formation of osteoclasts.

5. Modulating osteoimmunological activity

The differentiation of the macrophage into osteoclasts is principally regulated by three cytokines: RANKL, macrophage-colony stimulating factor (M-CSF), and osteoprotegerin (OPG). EGCG has modulating effects on cytokine production by immune cells. An increased production of mononuclear cell immune cytokine products (such as IL-1, IL-6, IL-12, and TNF-1α) contributes to the enhancement of bone resorption. Green tea catechins inhibit nuclear translocation of NF- kappaβ activated by lipopolysacharide (LPS). Alveolar bone resorption and IL-1β expression induced by LPS were significantly reduced by oral administration or injection of green tea catechins.

FUTURE OF GREEN TEA IN PERIODONTAL HEALTH

Green tea catechins protective and therapeutic effects appear to have significant potential against periodontitis. Ingestion of green tea demonstrates a substantial antioxidant capacity for protecting cells from oxidative damage. Dietary supplementation of catechins enhances the host resistance and inhibits the oxidative stress by balancing the oxidant and antioxidant ratio of periodontal diseases. Application of catechins as local delivery systems like strips, chips and fibres for the treatment of periodontal diseases or in combination with regenerative procedures will make a mark in the near future.

CONCLUSION

The major bioactive components of green tea, the catechins, possess only moderate antibacterial activity, although these molecules may, in the foreseeable future, find utility in the treatment of topical and oral infections. Further, it is clear that they are able to aid dental wellbeing by, for example, exerting a positive influence on the composition of the periodontal flora. However, unless substantial chemical modifications to the catechin structure can be made that result in significant improvement in both antibacterial efficacy and stability in vivo, these molecules are unlikely to be useful as conventional anti-infective agents.
However, conflicting results between cohort studies conducted in different countries may also arise from confusion in the frequency and timing of intake, and the marked contrasts in the socioeconomic and lifestyle factors associated with tea drinkers. It is also important to consider the type of tea or its preparation (e.g., short time vs. long brewing time and hot tea vs. iced tea) due to the marked impact of these factors on polyphenol content and concentration. It is also important to draw attention on the need of further-in-depth studies on the nature and mechanisms of the active green tea compounds, on the bioavailability of the different Catechins in humans, and appropriate dose levels to act as functional food 3.

Since green tea beneficial oral health effects are being increasingly proved, it could be advisable to encourage the regular consumption of this widely available, tasty and inexpensive beverage as an interesting alternative to other drinks, which do not only show the beneficial effects, but are also more energetic, do contain caffeine (green tea contains less caffeine than black tea, coffee or cola soft-drinks), are rich in additives and/or CO2. While no single food item can be expected to provide a significant effect on periodontal health, it is important to note that a modest effect between a dietary component and a disease having a major impact on the most prevalent causes of morbidity and mortality, i.e., oral cancer should be given substantial attention. Taking all this into account, it would be advisable to consider the regular consumption of green tea in diet.

REFERENCES

1. Taylor PW, Hamilton-Miller JM, Stapleton PD. Antimicrobial properties of green tea catechins. Food Sci Technol Bull 2005; 2:71-81.
2. Diane L. McKay, Jeffrey B. Blumberg. The Role of Tea in Human Health: An Update. J Am Coll Nutr 2002; 21:1–13.
3. Carmen Cabrera, Reyes Artacho. Beneficial effects of green tea- A Review. J Am Coll Nutr 2006, 25: 79-99.
4. Wu CD, Wei GX. Tea as a functional food for oral health. Nutrition 2002; 18:443-44.
5. Vison J, Dabbagh Y, Serry M, Jang J: Plant flavonoids, especially tea flavonols, are powerful using an in vitro oxidation model for heart disease. J Agric Food Chem 43:2800–2802, 1995.
6. Stephano Petti, Crispian Scully. Polyphenols, oral health and disease: A review. Journal of Dentistry 2009, 37:413-23.
7. Manach C, Scalbert A, Morand C, Re´me´sy C, Jime´nez L: Polyphenols: food sources and bioavailability. Am J Clin Nutr 2004; 79: 727–747.
8. Okushio K, Matsumoto N, Kohri T, Suzuki M, Nanjo F, Hara Y: Absorption of tea catechins into rat portal vein. Biol Pharm Bull 1996; 19:326–329.
9. Shuman Ian E. The gentle art of periodontal maintenance: a protocol using essential oils. Dentistry today 2003; 22: 1-4.
10. Govindaraj J, Emmadi P, Puvanakrishnan R. Therapeutic effects of proanthocyanidins on the pathogenesis of periodontitis- An overview. Ind J Exp Biol 2011; 49:83-93.
11. Yasuda H and Arakawa T. Green Tea to Cure Bad Breath. The Role of Polyphenols Clarified. Polyphénols Actualités1996; 15: 4-7.
12. Lodhia P, Yaegaki K. Effect of Green Tea on Volatile Sulfur Compounds in Mouth Air.Journal of Nutritional Science and Vitaminology 2008; 54: 89-94.
13. Krahwinkel T, Willershausen B. The Effect of Sugar-Free Green Tea Chew Candies on the Degree of Inflammation of the Gingiva. European Journal of Medical Research 2000; 5: 463-467.
14. Hirasawa M, Takada K, Makimura M, Otake S. Improvement of periodontal status by green tea catechins using a local delivery system: a clinical pilot study. Journal of Periodontal Research 2002; 37:433– 438.
15. Mountford. The role of local and peripheral antioxidants in the pathogenesis of chronic periodontitis. Thesis University of Birmingham 2009; 1-168.