A zinc citrate coordination complex, [Zn(H2cit)(H2O)] n (1), was prepared from Zn(NO3)2 · 6H2O and citric acid at pH = 1.5–3.0 in aqueous solution. The complex was characterized by elemental analyses, IR spectroscopy and X-ray crystallography. The Zn(II) ion in complex 1 exists in an octahedral coordination environment. The citrate binds Zn(II) tridentately via its α-hydroxyl, α-carboxylate and one of the β-carboxylate groups. Complex 1 forms a chiral helical chain running along the α axis of the crystal via two bridged oxygens of the α-carboxylate group. The interconversions of different zinc citrate complexes in aqueous solution show their pH-dependent patterns.

The effect of 3 years’ continuous exposure to dentifrices containing different levels of sodium monofluorophosphate, with or without 0.5% zinc citrate, has been investigated on plaque growth inhibition. Additionally, changes in the plaque microflora during prolonged exposure to zinc have been monitored in children with high or low caries increments. Following long-term use the inhibitory effect of zinc citrate on plaque growth was fully maintained. There was no evidence that prolonged exposure to zinc caused shifts in the plaque population of Streptococcus mutans, Streptococcus sanguis, lactobacilli, or Actinomyces species. A positive association was observed between children with high caries increments and high numbers of S. mutans in plaque and saliva. Caries increments were also associated with total viable count per microgram plaque protein. A negative association was observed between combined caries increment and number of S. sanguis in plaque.

Zinc salts have previously been shown to possess antiplaque activity in solution but this activity has as yet not been reported for dentifrices. The purpose of the present investigation was to establish the effect of dentifrices containing zinc citrate (ZCT) on plaque growth and on the concentration of zinc in saliva and plaque. Plaque growth inhibition was studied over periods of time approximating to intervals for normal oral hygiene procedures. Zinc in saliva and plaque was measured by atomic absorption spectroscopy.

Elevated zinc levels in saliva were observed for 3–4 h after brushing with the zinc citrate dentifrice. Similarly, raised levels of zinc were encountered in plaque 1 h following contact with a slurry of a dentifrice containing ZCT. Increased concentrations of zinc were observed in plaque fluid and plaque residue.

The plaque growth data from 88 participants in 5 studies revealed that plaque regrowth over 16 h or 22 h was reduced by dentifrices containing 0.5% ZCT, compared to placebo dentifrices. Dentifrices which contained 0.5% ZCT or 0.4% stannous fluoride, had similar inhibitory effects on plaque.

Further analysis of the data showed that subjects with high rates of plaque growth benefited more from the zinc dentifrices than those with low rates of plaque growth. It is suggested that the effect on plaque was related to zinc concentration in the dentifrice rather than total dose applied, and that the main effect of zinc was to inhibit the extension of existing plaque.

Zinc is an essential trace element commonly found in red meat, poultry, and fish. It is necessary in small amounts for human health, growth, and sense of taste.

Zinc is found throughout the body. The body doesn’t store excess zinc, so it must be obtained from the diet. It’s needed for immune function, wound healing, blood clotting, thyroid function, and much more. It also plays a key role in maintaining vision and might have effects against viruses.

People commonly use zinc for zinc deficiency, diarrhea, and Wilson disease. Zinc is also used for acne, diabetes, anorexia, burns, and many other purposes. There is some scientific evidence to support its use for some of these conditions. But for most, there is no good scientific evidence to support its use. There is also no good evidence to support using zinc for COVID-19.


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General information

Zinc citrate is available as dihydrate and trihydrate and is produced by complete neutralisation of citric acid with a high purity zinc source, subsequent precipitation and dehydration.

Zinc citrate is mainly used in dental care products such as toothpastes, mouthwashes and chewing gums due to its antimicrobial and anti-inflammatory effects and its ability to reduce or inhibit the formation of dental plaque and tartar. In pharmaceuticals, zinc citrate fights common colds. Zinc is increasingly used in food supplements, functional foods and beverages.

As an organic mineral source it is preferred in many applications over inorganic sources because of its superior bioavailability, physiological compatibility and nearly neutral taste compared to other zinc salts.

Among the organic zinc salts zinc citrate has one of the highest zinc content (31%).

Zinc citrate is supplied as a white to almost white powder. It is practically odourless, slightly soluble in water, soluble in diluted acid and practically insoluble in ethanol (96%). Zinc citrate has an inverse solubility.

Metal Salt Solutions

Metal ions with an affinity for sulfur are efficient in capturing the sulfur-containing gases. Zinc is an ion with two positive charges (Zn++), which will bind to the twice-negatively loaded sulfur radicals and thus reduce the expression of VSCs. The same applies for other metal ions such as stannous, mercury, and copper. Clinically, the VSC inhibitory effect was copper chloride > stannous fluoride > zinc chloride (CuCl2 > SnF2 > ZnCl2). In vitro, the inhibitory effect was mercury chloride = copper chloride = cadmium chloride > zinc chloride > stannous fluoride > tin chloride > lead chloride (HgCl2 = CuCl2 = CdCl2 > ZnCl2 > SnF2 > SnCl2 > PbCl2).172

Compared with other metal ions, Zn++ is relatively nontoxic and noncumulative and gives no visible discoloration. Thus, Zn++ has been one of the most-studied ingredients for the control of oral malodor.161,172 Schmidt and Tarbet127 reported that a rinse containing zinc chloride was remarkably more effective than a saline rinse (or no treatment) in reducing the levels of both VSCs (±80% reduction) and organoleptic scores (±40% reduction) for 3 hours.

As mentioned, Halita, a rinse containing 0.05% chlorhexidine, 0.05% CPC, and 0.14% zinc lactate, has been even more efficient than a 0.2% chlorhexidine formulation in reducing VSC levels and organoleptic ratings.110,153 The special effect of Halita may result from the VSC conversion ability of Zn++, besides its antimicrobial action. The combination of Zn++ and chlorhexidine seems to act synergistically.171

Similar observations have been reported for a chlorhexidine-free mouthrinse. The addition of zinc ions to a basic formulation containing amino fluoride and stannous fluoride caused short- and long-term reduction of oral malodor indicators in volunteers with morning bad breath163,164 as well as in volunteers with obvious halitosis.22

In a study by Hoshi and van Steenberghe,52 a zinc citrate/triclosan toothpaste applied to the tongue dorsum appeared to control morning breath malodor for 4 hours. If the flavor oil was removed, however, the antimalodor efficacy of the active ingredients decreased. Another clinical study reported up to a 41% reduction in VSC levels after 7 days’ use of a dentifrice containing triclosan and a copolymer, but the benefit compared with a placebo was relatively small (17% reduction).90 Similar reductions were also found in two other more recent studies.53,89