Dental caries remains a common disease among school-aged
children and is thought to be increasing worldwide, especially
in developing countries. The Oral Health Country/Area Profile
Project reported that the Decayed, Missing and Filled Teeth
(DMFT) index, a standard indicator of oral health, increased
steadily from 1.15 in 2004 to 1.19 in 2011 in 12-year-old children
living in African countries . In contrast, a systematic
review of information published from 1967 to 1997 concluded
that the DMFT index among 11-13-year-old in Sub-Saharan
Africa had not increased significantly during this earlier time
period [2,3]. However, assessing long-term trends in the incidence
of dental caries is difficult due to the lack of nationwide
survey data in most African countries. Several studies have examined
oral health status among schoolchildren in Kenya, but
they have mainly been conducted in urban areas and cross sectional
in nature. Accordingly, neither the current oral health
status nor changes over time is adequately documented in rural
To create awareness regarding oral disease and promote
preventive behaviors in schoolchildren, a current perspective
on their oral health situation must first be obtained. This study
aimed to clarify the oral health situation among schoolchildren
in a rural Kenyan community. The second objective of
this study was to investigate the relationship between oral
symptoms and perceived general health. Previously, Meei-Shia et al.  reported that children with poor perceived general
health tended to report more dental symptoms than did children
with good perceived general health. Maintaining oral
health may therefore be an important factor in promoting
overall good health. However, to our knowledge, no study has
investigated the relationship between oral symptoms and general
health condition in rural Kenyan communities.
Materials and Methods
In 2006, the Nagasaki University Institute of Tropical Medicine
(NUITM) launched a Health and Demographic Surveillance
System (HDSS) devoted to collecting health-related data
in the Mbita District of Nyanza Province, about 300 km west of
Nairobi, Kenya . As of July 2011, this program had collected
data from 11,182 households and 55,929 inhabitants over an
area of 163.28 km2. The Mbita HDSS revealed that most people
earned their living through fishing on Lake Victoria; 89%
of households also used the lake for drinking water and only
1.9% of households had electric lighting . Importantly, no
dental facility existed in the Mbita District at the time of the
study; the nearest dental clinic was located in Homa Bay, approximately
50 km away.
This study was conducted in two primary schools (coded "U"
and "K") selected by the superintendent of educational affairs
of Mbita District. All participants were students aged 12 years
who attended one of these two primary schools. The schoolmasters
prepared lists of 12-year-old students, comprising 86
students from primary school U and 64 from primary school
K. After obtaining consent, oral examinations were conducted
and dental health surveys were administered to all eligible pupils
from 19 to 20 February 2011.
Two Kenyan dentists who were faculty members at the University
of Nairobi School of Dental Sciences (UNSDS) conducted
oral examinations. Dental caries was assessed and classified
according to the World Health Organization standard .
Gingivitis was evaluated around the anterior teeth according
to criteria used in oral examinations in Japanese schools.
If gingivitis was observed in only a few areas, gingivitis was
documented as requiring "observation only." If gingivitis was
observed in all areas around all anterior teeth, gingivitis was
documented as requiring "detailed professional examination
and treatment." The extent of dental plaque was evaluated on
the labial surfaces of anterior teeth and classified as covering
< 30% or =30%. To avoid inter-observer effects, oral examiners
were calibrated before beginning data collection.
Oral examinations were carried out in a classroom with
windows. The pupils' oral status was examined using a head
lamp to visualize the oral cavity and a disposable mirror and
dental probe to work within the mouth. When the dentists
conducting the examinations discovered a case that required
further dental treatment, the pupil was issued a referral letter
to the nearest dental clinic and/or a prescription for analgesic
medication, depending on the symptoms.
The original questionnaire was developed in English through
extensive consultation with staff members at NUITM and UNSDS.
The questionnaire was then modified with advice from
local community health workers (LCHWs) in the Mbita District.
LCHWs were hired to support the questionnaire portion
of the study and to conduct group oral-health education activities
after the oral examinations.
Perceived general and oral health conditions were
scored using a five-point scale as follows: excellent, very good,
good, fair, or poor. When analyzing the data, these items were
grouped into three categories: very good, good, and poor. Oral
health status was further assessed by questioning each student
about several specific symptoms.
Mean DMFT index values were compared between boys and
girls using Student's t-test. The chi-squared test was used to
determine the equality of proportions. All statistical tests were
conducted using IBM SPSS software (ver.20.0; IBM, Chicago,
Before the day of the study, we informed the study objectives
and procedures to all participants and their guardians by letter.
On the day of the study, the study objectives and procedures
were discussed again and written informed consent was obtained
from them. We did not conduct any invasive examination
procedures in this study. This study was approved by
the Kenyatta National Hospital Ethics & Research Committee
(P328/9/2010) on 8 December 2010.
Oral health status
DMFT index values were 0.26 and 0.23 among boys and girls,
respectively, and this difference was not statistically significant
(Table 1). Almost 90% of pupils had no dental caries. Furthermore,
filled or treated teeth (referred to as F-teeth) were not observed in any students (data not shown).
In contrast to the situation with dental caries, the prevalence
of gingivitis was significantly higher among boys than
among girls. More specifically, 12% of boys and 2% of girls
were judged as requiring "detailed examination."
Relationship between dental plaque and oral
Frequency of tooth brushing was significantly associated with
the extent of dental plaque on the labial surfaces of the anterior
teeth. The percentage of subjects with dental plaque covering
=30% of the labial surfaces of anterior teeth increased as the
frequency of tooth brushing decreased (Figure 1).
Dental plaque showed a direct, statistically significant
relationship with the prevalence of gingivitis, but not with
dental caries (Table 2).
Relationship between general health status and
oral health status
Self-reported acute and intelligible oral symptoms, such as
toothache, tooth fracture, and bad breath, were significantly
associated with general health status (Table 3). In contrast,
chronic and unintelligible oral symptoms, such as gum bleeding,
food impaction, bad dentition, and jaw joint noise, were
not associated with general health status. However, comprehensive
and subjective feelings regarding oral health status
were strongly associated with general health status.
Several published studies have examined dental caries among
schoolchildren and young adolescents in Kenya. Mean DMFT
index values among 13-15-year-old attending primary schools
in Nairobi ranged from 1.8  to 1.54 . Another study reported
that the mean DMFT index value among primary
schoolchildren (aged 12 years) in Nairobi was 0.76 . The
University of Nairobi Dental Hospital reported that the average
number of decayed teeth among patients was 3.7 . In
contrast, mean DMFT indexes in a rural Kenyan community
were reported to be 0.36 among children aged 12 years , 1.9
among children aged 12-18 years , and 1.9 among young
adults(18-24 years) . The overall mean DMFT index in the
present study (0.24) was much lower than these previously
reported values. This difference may be due to differences in
socioeconomic status and dietary habits.
The relationship between sugar consumption and caries
is not strong in Western countries , especially in the
modern age of widespread fluoride exposure . However, in
developing countries, dental caries tends to increase with sugar consumption, suggesting that sugar consumption remains an
important risk factor for the development of dental caries. Ismail
et al.  indicated that the consumption of desserts and
snacks with high sugar content might be increasing in urban
areas in some developing countries. Similarly, the difference in
high-sugar dessert and soda consumption may be increasing
between Kenyan cities and rural communities.
Approximately 12% of the young subjects in this study
reported eating sweets more than 4-5 days per week, whereas
only 1% reported drinking soda at a similar frequency. In addition,
most (92%) of the "sweets" consumed were raw sugarcane.
In contrast, Gathecha et al.  reported that 43% and
34% of subjects in an urban cohort consumed cake/biscuits
and soda, respectively, at a similarly high frequency; 34% and
10% of rural subjects in the same study reported consuming
cake/biscuits and soda. The children participating in the present
study may have had fewer opportunities to buy products
with high sugar content. This dietary habits, likely contributed
to the relatively low prevalence of dental caries.
Although the prevalence of dental caries was low
among children examined in this study, the frequent tooth
brushing was not so common. Overall, only 47% of schoolchildren
brushed their teeth once a day, compared to values
ranging from 77% to 97% in other studies [10,18-20]. This
relatively low rate of tooth brushing, which effectively removes
dental plaque, may explain our findings regarding dental
plaque and gingivitis. Only 4% of children examined in this
study lacked dental plaque on the labial surfaces of the anterior
teeth. We suspect that this value is low compared with previous
findings , although direct comparison is difficult due
to methodological differences in assessment. Nevertheless, we
found that the percentage of children in whom dental plaque
covered =30% of the labial surfaces of the anterior teeth decreased
significantly with increased tooth brushing frequency
(Figure 1). Likewise, our data showed that dental plaque coverage
had a significant relationship with the prevalence of gingivitis,
although not with dental caries. Although the subjects
in this study had poor oral health behavior and oral hygiene,
their relatively low sugar consumption may explain the absence
of an observed relationship with dental caries. Gibson et
al.  reported that a significant relationship between dental
caries and sugar consumption was present only among children
with poor tooth-brushing behavior. Thus, if the subjects
in this study experience a future dietary shift toward the inclusion
of more products with high sugar content, their generally
poor oral hygiene may leave them vulnerable to increased incidences
of gingivitis and dental caries.
The results of this study revealed that perceived general
health was closely associated with perceived oral health. This
result is supported by those of previous studies [4,22]. Acute
oral symptoms with pain were significantly associated with
perceived general health, but chronic oral health status was
not. For example, gum bleeding due to gingivitis was not related
to perceived general health, suggesting that participants
do not consider this chronic oral disease to constitute a health
These results, as well as our findings related to oral hygiene
habits, indicate an urgent need for increased oral health
education. Because oral hygiene habits, such as tooth brushing,
do not appear to be firmly established among children
in this community, oral health education programs delivered
through the school system may be useful. In addition to oral
hygiene, oral health education is required to teach children
about chronic dental conditions other than dental caries, particularly
gingivitis, and the consequences of this disease for
long-term oral health.
The overall mean DMFT index observed in the present study
(0.24) is markedly lower than those reported in other studies
conducted in Kenya. However, the percentage of children with
dental plaque on =30% of the labial surfaces of anterior teeth
increased with the decreasing frequency of tooth brushing.
The present findings indicate that although dental caries may
not be currently an issue in this population, oral health education
is urgently needed to promote dental hygiene, to combat
the current problems with dental plaque and gingivitis and to
protect these children against future dietary shifts that may
bring them into contact with high-sugar food and increased
risk of caries.
This study was sponsored by Nagasaki University, Nagasaki,
Japan. The authors appreciate the strong supports to this field
work by Nagasaki University Africa Station (Director: Prof.
Ichinose Y, Prof. Shimada M, Assist. Prof. Goto K) and NUITM
Kenya Station (Mr. Kazama H, Mr. Takato M, Mr. Diellah
P, Mr. Okumu S). The authors would like to thank all of the
children, school staff, and local authorities in Mbita District
for their cooperation in the study.
Competing interests statement
The authors declare that they have no competing financial interests.
HF wrote the proposal, participated in data collection, analyzed
the data, and drafted the paper. CN, EK, EG, and YH
approved the proposal and participated in data collection and
analysis. All authors read and approved the final manuscript.