Key words:
Dental fluorosis - esthetics - Northeastern Nigeria - prevalence
INTRODUCTION
Adequate intake of fluoride plays an important role in the development of tooth enamel
and has so far been the most effective measure against dental caries, but is also
associated with the increasing prevalence of dental fluorosis (DF) as chronic excessive
consumption interferes with the matrix formation and calcification of tooth enamel.[1]
[2]
[3] The chronic toxic effect of excessive intake of fluoride has also been documented
to include skeletal fluorosis, neurological manifestations such as lowering of the
intelligence quotient (IQ), gastrointestinal tract (GIT) dyspeptic symptoms, and urinary
tract malfunctioning.[4]
[5]
[6] These symptoms, unlike DF, have been noted mostly at higher concentrations of fluoride
ranging from 2 mg/L for low IQ in children, 3.2 mg/L for GIT symptoms, 8 mg/L for
renal symptoms, and 10 mg/L for crippling skeletal fluorosis.[4]
[5]
[6] Among all these, DF is the most common unwanted effect of chronic exposure to fluoride,
and the importance of this condition is its role as the earliest indicator of excessive
fluoride exposure in a population.[7] Unlike the other chronic toxic effects, DF becomes evident in the population at
consumption concentrations above 1.5 mg/L. The therapeutic range of fluoride appears
to be narrow (1-1.2 mg/L), that is, between the concentration needed to protect against
dental caries and at the same time avoiding the occurrence of DF.[8] A balance therefore needs to be struck between the concentration necessary for caries
prevention which will result in objectionable DF.
Water remains the major source of fluoride intake, with lesser amounts consumed in
other sources such as fluoridated food supplements, toothpastes, and other dental
products.[9]
[10]
[11]
[12] Concentrations of fluoride in water sources for drinking of up to 1 mg/L for temperate
regions and 1.2 mg/L for the tropics have been recommended to provide a balance between
its anticaries effect and its potential to cause enamel defect.[8] Concentrations below 0.5 mg/L will not protect against dental caries, while DF may
be seen at a concentration of 1 mg/L, but can be acceptable since it is of low prevalence
and severity, as well as of little public concern in relation to the caries that would
have resulted with a lower fluoride concentration.[13]
[14] It is however agreed that concentrations above a threshold limit of 1.5 mg/L will
result in objectionable fluorosis.[15]
Severity of the resulting DF is determined by several factors including duration of
consumption, diet, duration of breastfeeding, use of fluoride supplements, age, weight,
nutritional status, and altitude.[16]
[17]
[18]
[19] Increased risk of DF has been noted with decreased duration of breastfeeding and
subsequent introduction of infant formulas;[12],[20] use of fluoridated toothpaste at an early age (<2 years of age);[20] younger aged children, as fluoride uptake by mineralized tissues decreases with
increasing age;[21] and the use of fluoride supplements.[22] Similar doses of fluoride may therefore produce different levels of severity of
DF depending on these factors. Studies have been carried out to explain the relationship
between these factors and the prevalence and severity of DF. The criticism of a majority
of them however has been the cross-sectional design nature of these studies, which
is not ideal for studying these factors.[19] Mild-to-moderate forms of DF present with fine opaque lines distributed to different
degrees over the enamel surface, while the severe forms become completely opaque and
porous acquiring stains, giving a brownish/black appearance. The appearance of this
discoloration as well as pitting of the enamel surface may become esthetically objectionable
enough to trigger social constraints for the sufferers.[23],[24] Furthermore, the resulting dentine exposure from enamel pitting has been documented
as an etiological factor for dentine hypersensitivity.[25]
Assessment of the prevalence and severity of DF has been carried out using several
diagnostic scoring indices. They include the Thylstrup-Fejerskov Index (TFI),[26] the Tooth Surface Index of Fluorosis,[27] the Fluorosis Risk Index,[28] and the Dean’s Fluorosis Index (DFI).[29] The two most commonly used are the TFI and the DFI. The DFI scores only the anterior
teeth unlike the TFI, which scores all fluorotic teeth and also reflects the histopathologic
features that correlate with the clinical features seen in these teeth.[26],[29] The DFI and its modifications however remain the gold standard index for DF and
has been in use the longest as well as the most widely used in epidemiological studies.[30]
Although it is a late measure of fluoride exposure in a population, DF remains the
most sensitive sign of prolonged high fluoride exposure.[31] This is exemplified by the prevalence rates and severity in populations that are
endemic for DF due to excessive amounts of fluoride in groundwater and surface water.
Prevalence rates of 11.3%–100% have been reported across populations, with the higher
rates and severity noted in endemic regions where the fluoride concentration far exceeds
the recommended guideline value.[32]
[33]
[34] High prevalence rates in places such as India, China, East African Rift valley region,
and Northern Nigeria have been linked to the high fluoride concentration in groundwater
sources of drinking water.[32],[33] In Nigeria, the occurrence of DF in schoolchildren and adults from four northeastern
areas of Adamawa, Yobe, Bauchi, and Bornu States had been reported by Wilson[35] as far back as 1954. More recent studies have provided prevalence rates ranging
from 11.3% in the southern part to 51% in the northern region.[34],[36]
[37] The higher rates in the northern part of the country have been related to the concentration
of fluoride in groundwater sources of drinking water, such as wells and boreholes.
High concentrations of fluoride in surface and groundwater in the north central and
northeastern regions have been noted by several researchers with values as high as
5.6 mg/ L in Maiduguri,[38]
[39]
[40] a region in which groundwater such as wells and boreholes remain the main source
of drinking water.[41]
Ascertaining the public health importance of DF with the intent of prevention and
treatment should include having definite prevalence figures, both for all levels of
fluorosis and for fluorosis of esthetic concern; concentration of fluoride in the
sources of drinking water; the perception of the effect of DF on those affected; and
the need for treatment as measured by the request for treatment by sufferers. Extensive
research has been carried out to assess the fluoride content of water in this region.
Although DF has been reported, there appears to be no documented prevalence or treatment
need in this region known to be endemic for the condition. The aim of this study was
therefore to assess the prevalence, severity of DF, and the request for treatment
as a measure of the burden of the condition among adult patients seen at a tertiary
health facility in Maiduguri, Borno State.
MATERIALS AND METHODS
Study design and participants
This was a cross-sectional descriptive study involving all adult patients who presented
at the oral diagnosis clinic of the University of Maiduguri Teaching Hospital, Maiduguri,
over a period of 12 months. Ethical approval for the study was granted by the Research
and Ethics Committee of the hospital. Informed consent was sought and obtained from
each patient and participation was voluntary. Data were collected by means of a predesigned
questionnaire, which collected demographic information as well as patient’s primary
reason for attendance, previous treatment for DF, place of residence during the first
8 years of life, and sources of drinking water during that period. Dental examinations
for presence and assessment of severity of DF were conducted by two trained and calibrated
examiners using the DFI. Precalibration of the two examiners was carried out prior
to the study during a pretest where the examiners conducted duplicate examinations
on patients with DF using the DFI. A strong measure of agreement (Cohen’s Kappa) was
observed between the two examiners (κ = 0.92).
For assessment of DF, the teeth were dried with gauze and then the facial/buccal surface
of all the upper permanent teeth was evaluated by visual inspection in natural light,
using a dental mirror and explorer. The registry of DF was based on the two most affected
teeth using the DFI to classify the severity for each patient as “normal,” “questionable,”
“very mild,” “mild,” “moderate” or “severe,” coded as 0, 1, 2, 3, 4, and 5, respectively.
Data analysis
Data analysis was done with Statistical Package for Social Sciences (SPSS) for Windows
(version 20, SPSS Inc., Chicago, IL, USA). The prevalence of DF was determined by
the following formula:
Where P = Prevalence
To determine the Community Fluorosis Index (CFI) as proposed by Dean and Elvove,[42] each grade/classification of DFI severity was given a statistical weight, p, with
values 0, 0.5, 1, 2, 3, and 4 for “normal,” “questionable,” “very mild,” “mild,” “moderate,”
or “severe,” respectively. The CFI was then estimated as follows:
Dean and Evolve[42] stated that a CFI that is above 0.6 indicates that the condition is a public health
problem and it justifies an increased attention to the population. Chi-square test
was used to determine the association between sociodemographic distribution (age and
gender) and prevalence of DF at 95% confidence interval. Where necessary, the level
of statistical significance was set at P < 0.05.
RESULTS
A total of 1032 adult patients with a mean age of 31.8 ± 10.4 years were seen during
the study period. Three hundred and twelve of these patients were diagnosed with DF.
This gave an overall hospital prevalence rate of 30.2%. Prevalence was highest among
the 16-25 years’ age group and decreased with increasing age among the patients (P = 0.000). Prevalence was also higher among the female patients examined [Table 1].
And the scores are as interpreted below:
|
CFI value range
|
Public health significance
|
|
CFI: Community fluorosis index
|
|
0.0-0.4
|
Negative
|
|
0.4-0.6
|
Borderline
|
|
0.6-1.0
|
Slight
|
|
1.0-2.0
|
Medium
|
|
2.0-3.0
|
Marked
|
|
3.0-4.0
|
Very marked
|
Table 1:
Prevalence of dental fluorosis by age group and gender
|
DF
|
|
Present, n (%)
|
Absent, n (%)
|
Total, n (%)
|
|
Likelihood ratio (age: χ;2=123.140, df=5, P=0.000), Pearson’s Chi-square test (gender: χ
2=10.037, df=1, P=0.002). DF: Dental fluorosis
|
|
Age group (years)
|
|
|
|
|
16-25
|
148 (14.3)
|
164 (15.9)
|
312 (30.2)
|
|
26-35
|
126 (12.2)
|
251 (24.3)
|
377 (36.5)
|
|
36-45
|
25 (2.4)
|
193 (18.7)
|
218 (21.1)
|
|
46-55
|
13 (1.3)
|
77 (7.5)
|
90 (8.7)
|
|
56-65
|
0
|
29 (2.8)
|
29 (2.8)
|
|
66-75
|
0
|
6 (0.6)
|
6 (0.6)
|
|
Gender
|
|
|
|
|
Male
|
123 (11.9)
|
361 (35.0)
|
484 (46.9)
|
|
Female
|
189 (18.3)
|
359 (34.8)
|
548 (53.1)
|
|
Total
|
312 (30.2)
|
720 (69.8)
|
1032 (100.0)
|
Seven hundred and forty-eight (72.5%) patients had resided in the northeastern states
during early childhood. None of the patients who resided outside the region was diagnosed
with DF, thus the actual prevalence, that is, the prevalence of DF among patients
who resided in the region was 41.7% [Table 2].
Table 2:
Prevalence of dental fluorosis by place of residence among northeastern patients
|
Residence
|
DF
|
|
Pearson’s Chi-square tests (residence: χ
2=117.031, df=5, P=0.000). DF: Dental fluorosis
|
|
Present, n (%)
|
Absent, n (%)
|
Total, n (%)
|
|
Borno
|
236 (31.6)
|
168 (22.5)
|
404 (54.0)
|
|
Yobe
|
46 (6.1)
|
85 (11.4)
|
131 (17.5)
|
|
Adamawa
|
15 (2.0)
|
80 (10.7)
|
95 (12.7)
|
|
Gombe
|
10 (1.3)
|
50 (6.7)
|
60 (8.0)
|
|
Bauchi
|
5 (0.7)
|
41 (5.5)
|
46 (6.1)
|
|
Taraba
|
0 (0)
|
12 (1.6)
|
12 (1.6)
|
|
Total
|
312 (41.7)
|
436 (58.3)
|
748 (100.0)
|
The ages of the patients diagnosed with DF ranged from 20 to 53 years with a mean
age of 33.8 ± 9.2 years. The majority of the patients were in the 16-25 (47.4%) years’
age group, while the gender distribution showed a preponderance among females (P = 0.003) [Table 3]. Prevalence of DF was affected by the source of drinking water among the patients
from the northeastern region [Table 4]. A higher proportion of those who sourced water from wells were diagnosed with DF
than those who used other sources.
Table 3:
Gender distribution of patients with DF by age groups
|
Age group (years)
|
Male, n (%)
|
Female, n (%)
|
Total, n (%)
|
|
Fisher’s Chi-square test (χ2=13.681, df=3, P=0.00). DF: Dental fluorosis
|
|
16-25
|
46 (14.7)
|
102 (32.7)
|
148 (47.4)
|
|
26-35
|
55 (17.6)
|
71 (22.8)
|
126 (40.4)
|
|
36-45
|
12 (3.8)
|
13 (4.2)
|
25 (8.0)
|
|
46-55
|
10 (3.2)
|
3 (1.0)
|
13 (4.2)
|
|
Total
|
123 (39.3)
|
189 (60.7)
|
312 (100)
|
Table 4:
Prevalence of dental fluorosis by source of drinking water
|
Source of water
|
DF
|
|
Present, n (%)
|
Absent, n (%)
|
Total, n (%)
|
|
Likelihood ratio (χ
2=13.855, df=6, P=0.031). DF: Dental fluorosis
|
|
Wells
|
33 (4.4)
|
26 (3.5)
|
59 (7.9)
|
|
Boreholes
|
97 (13.0)
|
123 (16.4)
|
220 (29.4)
|
|
Public water supply
|
69 (9.2)
|
98 (13.1)
|
167 (22.3)
|
|
Rivers
|
0 (0.0)
|
3 (0.4)
|
3 (0.4)
|
|
Wells + boreholes
|
16 (2.1)
|
29 (3.9)
|
45 (6.0)
|
|
Wells + public water
|
15 (2.0)
|
39 (5.2)
|
54 (7.2)
|
|
Boreholes + public water supply
|
82 (11.0)
|
118 (15.8)
|
200 (26.7)
|
|
Total
|
312 (41.7)
|
436 (58.3)
|
748 (100.0)
|
Among the 312 patients diagnosed with DF, 201 (64.3%) had fluorosis of esthetic concern
(mild, moderate, or severe) [Figure 1], but only 9.3% attended clinic primarily to seek treatment for the condition. Statistics
showed this to be statistically significant only for the degree of severity among
the patients. The majority of the patients with DF seeking treatment had the severe
form of enamel defect [Table 5]. The CFI for the patients was calculated to be 0.62 [Table 6] which is in the “slight” category of public health importance.
Table 5:
Distribution of the reason for clinic attendance by age group, gender, and severity
of fluorosis
|
DF, n (%)
|
Others, n (%)
|
Total, n (%)
|
|
Pearson’s Chi-square test (gender: χ2=3.128, P=0.077), Likelihood ratio (age group: χ2=3.966, df=3, P=0.265), Severity of fluorosis (χ2=53.514, df=4, P=0.000). DF: Dental fluorosis
|
|
Age group (years)
|
|
|
|
|
16-25
|
16 (5.1)
|
132 (42.3)
|
148 (47.4)
|
|
26-35
|
12 (3.8)
|
114 (36.5)
|
126 (40.4)
|
|
36-45
|
1 (0.3)
|
24 (7.7)
|
25 (8.0)
|
|
46-55
|
0 (0.0)
|
13 (4.2)
|
13 (4.2)
|
|
Gender
|
|
|
|
|
Male
|
7 (2.2)
|
116 (37.2)
|
123 (39.4)
|
|
Female
|
22 (7.1)
|
167 (53.5)
|
189 (60.6)
|
|
Severity
|
|
|
|
|
Questionable
|
0 (0.0)
|
24 (7.7)
|
24 (7.7)
|
|
Very mild
|
0 (0.0)
|
87 (27.9)
|
87 (27.9)
|
|
Mild
|
4 (1.3)
|
96 (30.8)
|
100 (32.0)
|
|
Moderate
|
11 (3.5)
|
56 (17.9)
|
67 (21.5)
|
|
Severe
|
14 (4.5)
|
20 (6.4)
|
34 (10.9)
|
|
Total
|
29 (9.3)
|
283 (90.7)
|
312 (100.0)
|
Table 6:
Community Fluorosis Index
|
Dean’s severity levels of DF
|
Dean’s statistical weight for DF (a)
|
Frequency of patients per severity level (b)
|
Product (a.b)
|
CFI index (a.b/c)
|
|
severity
|
statistical
|
of patients
|
(ab)
|
(a.b/c)
|
|
CFI: Community Fluorosis Index, DF: Dental fluorosis
|
|
Normal
|
0
|
720
|
0
|
|
|
Questionable
|
0.5
|
24
|
12
|
|
|
Very mild
|
1
|
87
|
87
|
0.62
|
|
Mild
|
2
|
100
|
200
|
|
|
Moderate
|
3
|
67
|
201
|
|
|
Severe
|
4
|
34
|
136
|
|
|
Total
|
|
C=1032
|
|
|
Figure 1: Distribution of severity of dental fluorosis among the affected patients
DISCUSSION
DF can serve as an indicator of excessive fluoride exposure in a population. In a
review of oral health in Nigeria, DF was identified as one of the oral health concerns
that is endemic in the northern part of the country.[43] The prevalence of the condition in any population is one way of determining its
public health significance. This study presents two prevalence figures: one (30.2%)
among the total number of patients seen in an outpatient dental clinic of a teaching
hospital and second (41.7%) among a subgroup of the patients who resided in the region
in their early years and were exposed to water sources containing excessive amounts
of fluoride in an area endemic for DF. Both of these figures are in the higher range
of prevalence figures reported in Nigeria (11.3%-51%) and closer to that reported
in other endemic areas of Northern Nigeria.[34],[36],[37] Okoye[34] reported 11.3% in the southeast, 11.4% by Ajayi et al.[44] in the southwest, while Akosu et al.,[17] Wongdem et al.,[37] and El-Nadeef and Honkala[36] reported prevalences of 22.2%, 26.1% and 51% in the northcentral region. The higher
values reported in the northcentral region in Plateau State have been related to the
high levels of fluoride concentration found in the sources of drinking water in the
region.[37] Likewise, recent studies in the northeastern region have reported fluoride concentrations
that ranged from 0.02 to 5.0 mg/L, with several samples above 1.5 mg/L spanning across
five of the six northeastern states.[40],[45],[46] Although the prevalence values from this study may be compared to that from other
endemic regions of the globe, occurrence of DF can vary widely among different locations
having almost the same fluoride concentrations in the drinking water. This is so as
exposure to other sources of fluoride intake, as well as other factors that determine
the occurrence and severity of DF, differs among populations.
The other way of determining the public health importance of DF is by calculating
the CFI for the population. The CFI in this study is a little over 0.6, indicating
a fluorosis level that is of public health concern. The CFI can be considered to be
a better measure of public health significance compared to prevalence alone as it
measures both prevalence and severity in the study population. Due to the higher statistical
weights assigned to the higher levels of severity of DF, the CFI values would be higher
in populations with more individuals in the higher levels of DF severity. Although
a high prevalence of 41.7% was observed in this population, the CFI was just slightly
above borderline since the majority of those affected had very mild or mild forms
of DF. Prevalences have been found to vary between the genders, while some other studies
have found no association of DF to gender.[33],[47]
[48]
[49] With the higher female clinic attendance in this study, it is not surprising to
find a higher prevalence of DF among females. This may also be explained by the closer
attention that females tend to pay to their health and appearance, as shown by a higher
proportion of the females attending clinic primarily for treatment of DF. In like
manner, the findings of this study wherein the prevalence of DF was observed to decrease
with increasing age may be a fall out of the desire for improved esthetics among the
younger age group.
It is established that DF results from prolonged exposure to excessive fluoride during
tooth mineralization. Therefore, if there is no exposure to excess fluoride during
childhood, it is unlikely for DF to occur. The findings of this study tend to support
this assertion as none of the patients who resided outside the region was diagnosed
of DF. This however does not explain the reason for the absence of DF among the other
patients who resided in the region. A higher proportion of those who had water from
the same type of water sources were not diagnosed with DF in this study. This can
be explained by the difference in concentration of fluoride in water sources at specific
locations as well as other factors that are considered to be essential in the pathogenesis
of DF.[16],[18]
Patients who used wells as their sole source of drinking water had the highest proportion
of DF, while those who consumed water from rivers had the least. This is similar to
observations from a similar study by Sudhir et al.[47] The result from the present study should however be interpreted with caution since
only three patients used rivers as their source of drinking water. Fluoride is present
in both surface waters (rivers, springs) and groundwater (wells, boreholes). The concentration
could however be higher in groundwater than in surface water due to physical, geological,
and chemical contents of the aquifer, the temperature, the action of other chemical
elements, and the depth of wells or boreholes.[50]
There is controversy in the literature about the level at which DF becomes esthetically
objectionable. In this study, DF of esthetic concern was recorded as Dean’s fluorosis
severity levels of “mild” and above and accounted for the majority (64.3%) of those
affected. The request for treatment among the affected patients was however low. The
reason for this is unknown, but may be due to social norms and beliefs in the region
that could have an impact on the perception of esthetics. On the other hand, other
researchers have stated that severity levels of “mild” and below may not be associated
with esthetic concerns. This may be the reason why the moderate and severe forms accounted
for majority of the few patients who attended the dental clinic primarily to seek
treatment for the condition. Hence, though the proportion of the sufferers seeking
treatment in the present study is quite low, there seems to be more esthetic concern
with increasing degree of severity of the DF which is similar to reports of other
studies.[51],[52] Like the prevalence values in this study, the distribution of severity levels may
be compared to other studies,[48],[53] but its significance may be limited if fluoride mapping of sources of drinking water
and other sources of fluoride is not compared at the same time among these populations.
CONCLUSIONS
This study shows that DF has a high prevalence among dental patients from the northeastern
region and should be seen as a condition of public health significance. The prevalence
of esthetically objectionable fluorosis is also high among these patients as is shown
by their request for treatment. It would therefore be of public health benefit to
conduct a community-based prevalence study as well as fluoride mapping of the northeastern
region. It is important as well to determine other factors, including other sources
of fluoride intake that may contribute to its occurrence in this population.
Financial support and sponsorship
Nil.
