Introduction
Flurine is found in the environment as fluorides ,
mainly because it is the most electronegative and reactive of all chemical elements.
All natural waters have fluoride ranging from trace levels to several dozen mg/l.[1-2] Fluorine is an essential
micronutrient for human health, serving to strengthen the apatite matrix of
skeletal tissues and teeth. In regions where the fluoride (F−) concentration
of water is naturally low (<0.5 mg/l), some communities have chosen to add
thisconstituent to their drinking water to strengthen teeth and to minimize
cavities [ P.B. Maithani, R.
Gurjar, R. Banerjee, B.K. Balaji, S. Ramachandran and R. Singh, Anomalous[1].
On the other hand, high F− (>1.5 mg/l) results in dental
and skeletal fluorosis, renal and neuronal
disorders and myopathy [3].Endemic
fluorosis develops widely in many areas of
the world, such as China [4], India [5-7] and Mexico [8].
In Iran, the occurrence of high F− groundwater has been
reported in Dashtestan [9].
Exceptionally higher values were
also found such as flouride concentration in the water of some lakes in Kenya
where the content of fluoride
is over 2000 mg/l [2]. It is generally accepted that fluoride is an essential component
of all diets and that most of the body requirements are obtained from drinking
water. A small fraction of this fluoride
accumulates on the teeth and bones and most of it is eliminated in urine and
sweat. An excessive concentration of fluoride can cause fluorosis [3]. Water fluoridation
at the 1.0 mg/L level is supposed to be beneficial for caries prevention although
excessive ingestion of fluoride during maturation could cause dental fluorosis.
There is a big controversy on the usefulness of
fluoride in protecting tooth decay. In 1984 , world health organization
recommended keeping the concentration of fluoride in range of 0.5-1.5 mg/L in
order to prevent dental caries especially in children [13-14]. It is known that
relative effectiveness of systematic fluoridation has diminished over time
since the 1990s [10-15]. The aim of this study was to determine fluoride concentration in drinking water in
Shahroud city (northern Iran) and also to determine DMF index between school
age students in a duration of six years from 2004 to 2009.
Materials and methods
This cross sectional study was
carried out in Shahrood city in Northern part of Iran on drinking water as well
as measuring DMF among 7 year old school children (boys) from 2004 to 2009. A
sample size of students was estimated as 138 subjects based on: prevalence=20%, α=0.05
and precision (d=0.07). The subjects were selected randomly from the list of
all the 7 year old school children. A study questionnaire was completed. The
data analysis was performed in SPSS (version 11.5) using one way ANOVA test.
120 samples were taken from the
drinking water in Shahroud
city and the level of fluoride concentration was determined for each year. Fluoride concentration was
determined electrochemically, using approved USEPA ion-selective method (method 3402) [13] the
electrode used was a
fluoride/combination fluoride elector-orion 96-09 which was coupled to an Orion
420A electrometer (pH meter). Standards were prepared from a stock solution
(100mg/l) of sodium fluoride. This is applicable to the measurement of fluoride
in drinking water, surface water and saline waters in a range of concentration
from 0.1 up to 1000 mg/l.
Figure 1. Location of
Shahroud in Iran
Further, 138 students, aged 7 years old, were randomly
chosen and examined by a dentist in schools for determining the numbers of
decayed, missing and filled permanent teeth. Measuring both fluoride
concentrations and DMF index were repeated for six years as the sample of
students was followed up. In fact, the students were 8, 9, 10, 11 and 12 years
old in years: 2004, 2005, 2006, 2007, 2008 and 2009 respectively. Locations of
the samples where the water were taken during the study were not changed.
Samples were collected in clean fluoride free plastic bottles directly from 120
sites. Trace grade nitric acid was added to preserve the samples. The samples
were then stored at approximately 5 oc and the amount of fluoride
was determined in the laboratory of school of health.
Results
The mean
concentrations of fluoride in the water samples are shown in table 1. As it is
presented, the range of fluoride level during the six years of study was
between 0.45 and 0.75 mg/l. The lowest mean fluoride level was 0.45 mg/l for
2006 and the highest was 0.75 mg/l for 2009. The mean fluoride levels were
approximateiy the same for winter and summer in all of 120 locations that
samples were collected. A one way ANOVA was conducted to compare fluoride level
means in years :2004, 2005, 2006, 2007, 2008 and 2009. There was a significant
effect for time, Wilks’ Lambda=0.05, p<0.001. No fluoridation program has
been set for this city up to day. The numbers of decayed, missed and filled
tooth and mean values of DMF index and mean values of fluorid during the yesrs of study have been shown in table 1.
Discussion
Previous studies show that the DMF
prevalence among students of Baboul town was reported as 2.98 ±1.98 in the
12-year-olds [16]. The DMF value was higher in girls than in boys. In another
survey in Mashhad, the DMF was reported to be ,2.32 ± 2.34 in boys and 2.52 ±
2.12 in girls [10]. Majidi reported DMFT of 0.33 for boys 0.58 and for girls
0.087 [17]. The results of our study showed that as values of flouride
increase, DMF index increases too, but this association is not significant. In
places with low and optimal fluoride concentration in drinking water the
percentage of children with decayed teeth was different, but this difference was
not statistically significant. The percentage of affected deciduous teeth was
high in all places. In places with low fluoride concentration this percentage
was 4.2-12.7%, and in places with optimal concentration was reported to be
4-12%. The average value of DMF in all places is between 3.18-3.81. These
results show that the optimal fluoride concentration in drinking water
decreases the incidence of tooth decay, but this difference was not
significant. Our results showed that values of DMF index were higher than the national
average. DMF index for Iran on the basis of world health organization reports
is in range of 1.2 up to 2.4.
Studies
done in three communities of Iran showed that DMF index was 4.4, 6.0 and 5.0 in
students aged 9 years-old in Tehran(16), Semnan and Village of Dibaj, respectively [17]. These values are higher
than DMf index values for Shahroud city.
A study in England
[14] showed that DMF index was 2 in 2 –year-old children. Also, a study done in
Broken bow [15], showed that DMF index was 3.6. The mean
concentrations of fluoride in the water samples, during the six years of study
was between 0.45 and 0.75 mg/l which is placed in low to middle level and,
therefore flouride should be added to drinking water to increase fluoride
concentration to a minimum of 1 mg/L regarding the regional temperature
(approximately 25 oC). A study in Spain [11] showed that fluoride
concentration was between 0.001-1.9 mg/l in village of Almaluez. In another
study [19] fluoride concentration in tap water in chile [19] was
between 0.07-1.1 mg/L. Another study in Broken bow [9] showed that
fluoride level was low (<0.3 ppm). All the results of these studies show
that the natural amount of fluoride in drinking water are different all over
the world.
Conclusions
Fluoride continues to be the
cornerstone of dental caries prevention throughout the world, and there are a
variety of sources of fluoride that may contribute to the dietary intake of
fluoride. Eventhough Shahroud is considered as a non-endemic area for dental
fluorosis according to its low concentration of fluoride in drinking water, the
children in our study presented epidemiological indicators of overexposure to
fluoride. Epidemiological indexes showed simultaneously high prevalences of
caries. Because our knowledge is incomplete regarding the amount, duration, and
timing of fluoride ingestion which can result in dental fluorosis, further
research is clearly needed before definitive recommendations can be made
regarding the use of fluorides, including the recommended dietary intake of
fluoride. Further longitudinal studies are also needed to determine the safe
fluorine dose for Shahroud children, taking in account age, nutritional status,
altitude, geographical location and weather among other factors.
Acknowledgement
The authors
would like to acknowledge the research financial supports of Dean of Shahroud
University of Medical Sciences.
Conflict
of interest: Non
declared
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