Spectrophotometric Analysis of Fluoride Concentration in Dentifrices for Children in India

Abstract

Background:

There is a need to monitor the fluoride content of dentifrices used for children in a country like India, where there is prevalence of endemic fluorosis.

Aim:

To evaluate the fluoride content of dentifrices for children available in India.

Settings and Design:

In vitro study in a laboratory setting.

Methods:

About 27 major supermarkets/departmental stores in Chennai city were approached by the investigator. All dentifrices indicated for children, available in these stores were included in the present study. A total of four different dentifrice brands were procured from these outlets. For each brand of dentifrice, three samples were randomly chosen and used for fluoride analysis. The fluoride content was assessed in triplet by using spectrophotometric analysis, by a single blinded examiner. The test sample was compared to a standard solution, in a calibration curve to determine the fluoride concentration.

Results:

The mean fluoride content of dentifrices, indicated for children was 449.5 ± 26.1 ppm.

Conclusions:

All brands of commercially available dentifrices indicated for children had optimum amount of fluoride.

Fluoride concentration in commercial dentifrices indicated for children in India, using spectrophotometry.

INTRODUCTION

Maintenance of oral health relies on effective oral hygiene practices. Cleaning the teeth using toothbrush and dentifrice is the most common and widely used oral hygiene practice.[1] Fluoride, in dentifrice, is indispensable in dental caries prevention. Globally, the major source of daily exposure to fluoride is contributed by fluoridated dentifrices. Regular use of fluoridated dentifrice resulted in global decline in dental caries during 1980s.[2] Earlier systematic reviews concluded that dentifrices containing 500 ppm fluoride effectively prevents dental caries in children, which is additionally supported by the current international standard level.[3] Neverthless, regular exposure to fluoride has its own share of disadvantages.

Inadvertent swallowing of injudicious amount of fluoridated dentifrice while tooth brushing may lead to chronic fluoride toxicity in the form of dental fluorosis. Cochrane review reports that usage of fluoridated dentifrice before 12 months of age is associated with an increased risk of developing dental fluorosis.[4] Dentifrice alone accounts for 81.5% of fluoride intake on daily basis among 1–3 year old children.[5] In order to reduce the risk of dental fluorosis, fluoride concentration of 400–500 ppm is recommended for dentifrices manufactured for children.[6]

Some commercial dentifrices contain the recommended amount of fluoride, many show deficit in fluoride content.[7,[8,9] Hence, it is necessary to monitor the fluoride level in dentifrices indicated for children. According to Bureau of Indian Standards, the fluoride ion concentration in ppm along with other details such as net mass, month, and year of manufacture and the expiry date has to be mentioned in the label of dentifrice packing.[10] In spite of such specifications, the exact fluoride level in dentifrices is not reported by the manufacturers, as it is bound to fluctuate.

Till date, no study has reported the fluoride concentration of dentifrices indicated for children in India. Since dentifrices indicated for children are available as Over the Counter (OTC) products in India, this information will aid the policy-makers, professionals and the public to make informed decision. Hence, the current study aims to assess the fluoride concentration in dentifrices indicated for children in the Indian market.

METHODS

Since the list of all commercially available dentifrices in the Indian market, was not readily available, the principal investigator personally approached 27 major supermarkets/departmental stores in Chennai city which supply to a wide population base. All commercial dentifrices indicated for children, was included in the study for fluoride analysis. Totally, four different brands of dentifrices indicated for children, was procured in this manner. All samples were procured from supermarkets, where the dentifrices were stored in the proper conditions. Samples of all included dentifrices were such that it was manufactured within 2 months of procurement date and hence was due for expiry after more than 20 months.

Based on the information available on its label, the dentifrices were categorized as fluoridated dentifrices indicated for children. Three samples from each brand were randomly selected and included in the fluoride analysis. The first five centimeters of the squeezed dentifrice were discarded and the remaining amount in each sample was emptied into sterile containers. The containers were alphabetically coded from A, B, C and D to facilitate blinded analysis of fluoride content. The containers were transported to the laboratory, at room temperature. After the fluoride analysis was done, the containers were decoded to know the respective brands. The fluoride content in the dentifrices was analyzed by Spectrophotometric method.

Procedure for spectrophotometric analysis of fluoride content in dentifrices

The fluoride stock solution was prepared by dissolving 221 mg of anhydrous sodium fluoride (NaF) in distilled water and made up to 1000 ml in a volumetric flask. Then, the standard fluoride solution was prepared by diluting 100 ml of stock fluoride solution in distilled water and made up to 1000 ml.

The spectrophotometric analysis of the fluoride content in dentifrices was carried out as described by Rice WE et al.[11] In brief, 500 ml each of 0.191% SPADNS (Sodium 2-(Parasulfophenylazo)-1, 8 dihydroxy-3,6-napthalene disulphonate) reagent and 0.0266% of Zirconyl acid reagent were prepared. The reference solution was prepared by mixing ten ml of SPANDS solution in distilled water and made up to 100 ml, after adding 7 ml of concentrated HCl. The resultant solution was used to set the spectrophotometer (Cary 60 UV-VIS spectrophotometer, Agilent technologies, U. S. A) to read zero absorbance every time.

Preparation of calibration curve

Fluoride standards in the range of 0.1–1.40 mgF/L (0.2, 0.4, 0.6, 0.8, 1.0, 1.2 and 1.4 mg/l) were prepared by adding appropriate quantities of distilled water to set 50 ml of standard fluoride solution. Ten ml of SPANDS-Zirconyl acid reagent mixture was added to each standard and mixed well. The ultraviolet–visible spectrophotometer was set at zero absorbance with reference solution and the readings of the standard solution were obtained at 570 nm wavelength of visible light. A calibration curve of microgram fluoride versus absorbance relationship was then plotted [Graph 1].

Graph 1.

Calibration curve of the microgram fluoride versus absorbance relationship

Depending on the colour, 0.5–1.5 g of dried dentifrice sample was kept in a Teflon crucible and digested with 5 ml of concentrated HCl at moderated temperature on a hot plate in a fume cupboard. After heating for 3–4 h, 5 ml of HCl was added again and heated till fuming seized. The Teflon crucible was then cooled and rinsed. Distilled water was mixed to the existing dentifrice mixture and was made up to 100 ml. Sample readings were recorded at 570 nm. The test samples were matched with the calibration curve and their fluoride concentration was determined. From the calibration curve, the concentration of Fluoride present in each sample was obtained in μg which converted into ppm using the formula, μg F/sample weight in ml.

RESULTS

The mean concentration of four dentifrices indicated for children was 449.5 ± 26.1 ppm as shown in Table 1. NaF and sodium monofluorophosphate were the most common fluoride compounds present in these dentifrices. Silica based abrasives were found in majority of the dentifrices.

Table 1.

Fluoride content in the dentifrices indicated for children

Category of dentifrice	Product blinding code	Abrasives	Fluoride compound	Total fluoride concentration (ppm)
Fluoridated dentifrices indicated for children	A	Silica	NaF	486
	B	Not mentioned	Sodium monofluorophosphate	424
	C	Water hydrated silica	NaF	445
	D	Not mentioned	Sodium monofluorophosphate	443

NaF: Sodium fluoride

DISCUSSION

The current study was conducted to assess the fluoride concentration of the commercially available dentifrices in Indian market. This study is of importance, as literature on fluoride content of dentifrices sold as OTC products in India is not available. Further, it can be considered that the brands of dentifrices included in this study are most commonly used by the public because all brands available in major supermarkets/departmental stores were included. Also, this study included most of the commercially available OTC brands when compared to the previous studies. The methodology adopted for analyzing the concentration of fluoride concentration in this study is more accurate and less time consuming than other methods like ion selective electrophoresis.[11]

The fluoride content of the dentifrices indicated for children were found to be very close to the optimum level of 500 ppm. This finding was similar to the study conducted by Borremans et al.[12] which reported fluoride concentration of 500 ppm in dentifrices indicated for children. Dentifrices sold in Tanzanian market have <400 ppm.[13] Thus, there is widespread disparity in the fluoride ion concentration in the dentifrices available in different part of the world.

Although the Bureau of Indian Standards demands the manufacturers of dentifrices to clearly specify the concentration of fluoride in ppm, it was not reported in any of the brands. In most of the labels, the manufacturers merely mention that the fluoride concentration in the dentifrice does not exceed 500 ppm. It is well known that the fluoride concentration in dentifrices decreases over time due to interaction between the abrasives and the fluoride compound. This might the reason for the manufactures not mentioning the exact concentration of fluoride in their product labels.

Fluoride in dentifrices can be present as ionic or nonionic forms. The protective effect of fluoride in dentifrices, against dental caries largely depends on its bioavailability of ionic fluoride. It is reported that the concentration of freely soluble ionic form decreases on storage, due to interaction with other ingredients in the dentifrice.[7] This study assessed only the total fluoride concentration and not specifically the ionic fluoride content in the dentifrices. Thus, it can be presumed that the availability of biologically essential ionic fluoride from dentifrices sold in Indian market might actually be even lesser. Hence, future studies are strongly recommended to assess the ionic and nonionic fluoride concentration in dentifrices available in Indian market. The present study determines the different concentration of fluoride available as OTC products in Indian market.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.