Oral Health in Norway.
The HUNT Study.
Prof. Dorthe Holst
Tannhelsetjenestens kompetansesenter Midt-Norge
Institutt for samfunnsmedisin
The oral health studies in Trøndelag
Oral health may obviously be associated with many other health factors. But data on
oral health was for the first time collected in a general health survey in Norway in the HUNT
Study 2006-08 ( HUNT3). Thus, this new joint initiative between the HUNT Research Centre,
Faculty of Medicine NTNU and the Odontological Faculty Oslo University, opens up new
opportunities. And due to that HUNT is population based and data is collected in 24
municipalities, oral health in the general population aged 20-100 years old may be mapped.
However, both questionnaire and clinical data have been collected in Norway earlier, as
part of the first WHO International Collaborative Study (WHO ICS-I) in 1973 (1). In 1983,
1994 and in 2006 oral health has been examined again in random samples of the same birthcohorts
that were selected in 1973 (11) (Figure 1). An analysis within 1983 showed that
social inequality in oral health was found in 13-14 year olds, and the inequality increased in
the older adult age-groups assessed cross-sectionally (2). Schuller (1999) analysed whether
the oral health improvement from 1983 to 1994 among 23-24 olds in Trøndelag was equally
distributed among high and low social status groups (2). Schuller found that improved oral
health was accompanied by more inequality among young adults. In the present study it has
been possible to follow samples of two birth-cohorts (1959-1960 and 1929-1938) and samples
of 35-44 year olds in time series for more than 30 years (Table 1).
Figure 1. The basic design of the Oral Health Trøndelag studies
Age 1973 1983 1994 2006 (HUNT3)
13-14 X X
23-24 X X
35-44 X X X X (+46,47)
45-54 X X
At the start of the 21 st century, all European countries are faced with substantial
inequalities in health and disease within their populations (3). Health and disease inequalities
are mainly caused by a higher exposure to material, psychosocial and behavioural risk factors
in lower socio-economic groups. A number of studies suggest that the relationship between
socio-economic status and disease forms of a social gradient from the top to the bottom of the
social hierarchy (4-6). According to the gradient theory inequality of health is not only
confined to the poorest members of society but runs right across the social spectrum (Marmot
5,6). The challenge in the gradient research is to provide further evidence of the obvious
interplay between psycho-social, material, cultural and behavioural explanations. In Norway
researchers and national health authorities have adopted the gradient explanation, and a
national strategy to reduce inequalities in disease and health outcomes has been launched (7-
The social distribution of oral health among adults in Norway has been studied
recently (3). The relationship between income quintiles and edentulousness and having a
functional dentition was analysed from 1975 to 2002 by four datasets from Statistics Norway.
The main finding was that in absolute terms oral health was more equally distributed in 2002
than in 1975, and the lowest income groups benefited the most. Among the elderly, however,
having a functional dentition was less equally distributed in 2002 than in 1985. The relative
differences increased for the oldest for each new birth cohort; thus the chances of being
edentulous was 7.5 times higher in the lowest income group versus the highest group in 2002,
whereas the chances were only 2 times higher in 1972.
Based on epidemiological clinical data on oral health of young and older adults gathered
by epidemiological field studies in 1973, 1983, 1994 and 2006, time series analyses of social
status and oral health have shown a socially unequal distribution of oral health most
pronounced during the period from 1973 to 1983. From 1983 to 2006 the inequalities in oral
health caused by social position did not seem to increase further (11). The direction of the
results seems to be dependent upon the choice of outcome measure. Ongoing research uses
outcome measures of both pathogenic and salutogenic nature as effect measures of social
inequality. It has been pointed out that social inequality research of oral health must make a
careful distinction between inequality of disease occurrence and inequality of treatment.
The purpose of this project is to map the distribution of oral health in the population, explore
the impact of health related behavior on oral health, to examine how self-perceived oral health
relate to clinical dimensions of oral health, and explore how periodontal status in 2006 will be
related to previous diabetic status.
Material and methods
The HUNT Study
The Nord-Trøndelag health study (HUNT) is one of the largest health studies ever performed.
It is a unique database of personal and family medical histories. So far three health surveys of
the general adult population in the Nord-Trøndelag County, Norway have been completed.
The HUNT1 cohort aged 20+ (established 1984-86)
In 1984-86 every citizen of Nord-Trøndelag County being 20 years or older (or turning 20
years during the year of survey) were invited. Totally 77 214 persons participated (89.3% of
those invited). Questionnaires and clinical measurements were applied. The design applied in
HUNT1 was largely repeted in HUNT2 and HUNT3.
The HUNT2 cohort aged 20 + (established 1995-97)
HUNT2 constituted both a new cross sectional survey and a follow-up of HUNT1. The
scientific programme was extended to include several large public health issues in accordance
with current national health priorities. These were cardiovascular diseases, diabetes,
obstructive lung disease, osteoporosis, headache, mental health, chronic musculoskeletal pain
and urinary incontinence. In addition to questionnaires, interviews and clinical examinations,
the participants contributed with blood samples for instant analysis and storage. A total of
65 237 participated in HUNT2 (69.5% of those invited).
The HUNT3 cohort aged 20+ (established 2006-08)
The scientific programme of HUNT3 included several main public health issues as in
HUNT2, but included also topics on oral health. In the HUNT3 survey participants were
asked about visiting a dentist last 12 mnds, how their dental health was perceived and the
impact of dental health on the general health. In addition, there was done a general dental
health examination on 600 participants in age-group
The oral health Trøndelag studies
The material comprised data from independently selected random samples of a population
living in four municipalities in the county of Nord-Trøndelag in 1973, 1983, 1994 and 2006.
The age-groups were selected according to the rules of cohort analysis in such a way that the
difference in years between the studies matches the age of the birth-cohort in the same year
(Figure 1). In addition, in each survey year samples of 35-44 year olds were draw. Table 1
shows that the 1959-1960 birth-cohort was 13-14 years old in 1973, 23-24 years old in 1983,
34-35 years old in 1994 and 46-47 in 2006 in 2006. The birth-cohort 1929-1938 was 35-44
years old in 1973, 45-54 years old in 1983, 46-54 in 1994 and 68-77 in 2006. Thus random
samples of two birth-cohorts were followed longitudinally. Thirty-five to forty-four year olds
were examined in 1973, 1983, 1994 and 2006, following a pattern of repeated cross-sectional
studies The age specific sample size for each of the participating counties were 500 in 1973
and in 1983 and was reduced to 350 in 1994 and 250 in 2006. The sample in the two-year
age-group 46-47 was 100 persons. Table 1 shows the size of the samples and the participation
The methods of data collection comprised standardized clinical measurements and selfadministered
questionnaires (10-11). In 1973, 1983, 1994, and in 2006 two, ten, eleven and
two calibrated dental teams, respectively, collected the data. Two senior researchers (DH and
AAS) followed and guided the procedures since 1973 in order to secure standardized
conditions and comparability among the surveys. Calibration exercises were conducted each
study year, and the results found satisfactory (15). The examinations took place at the public
dental clinics of the Nord-Trøndelag County. Permission was granted by public authorities
and by the participants’ informed consent. All necessary permissions were given through out
the study period and by the participants’ informed consent. In 2006 the study was approved
by the Regional ethical committee Middle of Norway and approved by the Norwegian
Council of Research.
The clinical variables were number of present teeth (PT), sound teeth and surfaces (ST,
SS) and functional teeth and surfaces (SFT, SFS) and DMFT and DMFS index. DMFT and
DMFS are the sums of DT/S, MT/S and FT/S, where DT/S is defined as the number of
teeth/surfaces with primary and secondary caries, including root and coronal caries. Only
caries with a distinguishable brake in the surface was recorded. Missing Teeth is the number
of missing teeth irrespective of cause. FT/S is the number of teeth/surfaces filled, both root
and coronal restorations, including all types of filling materials and crowns. The clinical
examination comprised recording of the condition of the visible part of the tooth.The analyses
were based on 28 teeth, because third molars were excluded for reasons of comparability
among the study years. DMFT was measured only at the tooth level in 1973. Unfortunately
the data files from 1973 were no longer available at the WHO Headquarters in Geneva.
Published results (10, 11) were used for descriptive statistics. In order to obtain an estimate of
DMF surfaces in 1973 the DMF parameters in 1973 was multiplied by the ratio between teeth
and surfaces for the parameters in 1983 in comparable age-groups.
1. Oral Health in a Norwegian County, The HUNT Study
In the first part of the planned study self-perceived oral health will be analyzed, and the
variation between age groups, gender, municipalities and socio-economic groups analyzed:
The epidemiology of oral health. Nord-Trøndelag has been considered a national average of
Norway with respect to many indicators of health and living conditions. Cause specific
mortality and trends in disability pension follows national trends closely. The data of selfperceived
oral health in Nord-Trøndelag will be related to a smaller national dataset (Holst
2008) that includes the same variable in order to rank self-perceived oral health in Nord-
Trøndelag compared to the national variation between counties. Cross tabulations and
regression based analyses will be utilized.
2. Self perceived oral health and health related behavior
In the second study we want to explore the impact of health related behavior, diet and BMI on
oral health. The ongoing marked changes in behavior, diet and BMI might have consequences
for oral health. Differences in oral health according to these factors might reveal unknown
important oral health promotion potentials. Data will also be used to analyze the role of health
related behavior regarding socioeconomic inequalities (Sabbah et al 2009). Data from
HUNT3 includes variables on diet components, physical exercise, smoking, alcohol
consumption and measurements of height and weight. Regression analyses will be utilized,
with control for confounding between relevant factors.
3. Health perception, an indicator of oral health or oral disease?
The third paper will examine at the validity of the general dental health perception question in
the HUNT Study, by comparing answers to the self-perceived oral health question with
dimensions of clinical registrations undertaken in the oral health subsample. Recent studies
indicate that the decayed missing and filled teeth (DMFT) index showed more variation than
the dental fluorosis according to the Thylystrup Fejerskov Index (TFI) in populations with
low level of disease and treatment experience. In populations with high levels of disease and
treatment experience, FST was more suitable to describe variation than DMFT. In their
analysis of the relationship between socio-economic status and oral status over time, socioeconomic
status was not clearly related to the oral status in young adults in 1994 when
expressed by the DMFT. Yet, socio-economic status was clearly related to oral status in the
same young adults when expressed by the FST. In older adults the conclusions were the other
way round. Holst and Schuller (1) concluded that the indices should not be used
interchangeable. They concluded that the choice of index must depend on whether a
salutogenic or a pathogenic index approch is relevant.
In then planned study the epidemiologically recorded data of oral health status comprise at
least five dimensions: 1) Sound conditions, good oral health, 2) untreated disease
unsatisfactory oral health, 3) past disease and treatment 4) total disease and treatment
experience and 5) lost oral health, no teeth left. It will be of great relevans to investiate how of
these dimensions are reflected in the self-perceived assessment of oral health. A better
understanding of these relationships may create a new platform for oral health promotion.
4. Inflammation and periodontal health
The association between diabetes/chronic inflammation and periodontal health is of interest.
A large part of the Norwegian adult population shows signs of past and present periodontal
disease in the gums. A lot of attention has been devoted to risk factors of development of
periodontal disease (11). Diabetes is one such often mentioned risk factor. The HUNT studies
offer a phenomenal opportunity to study the relationship between inflammation in the
periodontal tissues of the mouth and predisposing medical conditions. The Oral health
Trøndelag studies in 1994 and 2006 comprised an epidemiological assessment of the
periodontal status of the participants by clinical and x-ray examinations (Figure 1). By linking
anonymously the Oral Health Trøndelag data of periodontal status to previously registered
diabetic status in HUNT I and II the relationship can be longitudinal studied. The data are
ready for empirical analyses, but requires a careful linkage of files.
Organization and research community
The project is organized as a PhD project affiliated at the Dept. of Public Health and General
Practice at the Medical Faculty, NTNU. The student is affiliated at the HUNT Research
Centre. The major supervisor is Ass. prof. Steinar Krokstad at the HUNT Research Centre,
and the first co-supervisor is Prof. Dorthe Holst at the Odontological Faculty, University of
Oslo. A supervisor group is established in co-operation with Tannhelsetjenestens
kompetansesenter for Midt-Norge IKS. Krokstad and Holst developed a research co-operation
in 2004 during planning of HUNT3. Krokstad has as PI of HUNT3 thorough knowledge of
methods utilized in HUNT3, expertise in social epidemiology, and a wide research network
nationally and internationally. Holst has a long research career in oral epidemiology. Kari
Strand and the spesialists in Tannhelsetjenestens kompetansesenter for Midt-Norge IKS
ensure relevant clinical competence in the project.
Publication of results
The papers will be published in international referee based journals.
1. Holst D, Schuller AA, Dahl KE. Bedre tannhelse for alle? Tannhelseutvikling i den
voksne befolkning i Norge fra 1973 til 2006. Nor Tannlegeforen Tid 2007; 117: 804
2. Schuller AA. Better oral health, more equality? Empirical analysis among
young adults. Community Dental Health 1999.
3. Machenbach JP. Health inequalities: Europe in profile. Expert report commissioned
by, and published under the auspices of, the UK Presidency of the EU 2005.
4. Marmot M, Wilkinson RG. Social determinants of health. Oxford: Oxford
University Press; 1999.
5. Marmot M. Status Syndrome. London: Bloomsbury; 2005.
6. Krokstad S. Socioeconomic inequalities in health and disability. Social
epidemiology in the Nord-Trøndelag Health Study (HUNT), Norway. Verdal:
Norwegian University of Science and Technology, 2004. Thesis.
7. Næss Ø. Life course approaches to socio-economic inequalities in cause specific
mortality. A registry based epidemiological study of the population in Oslo. Oslo:
University of Oslo; 2005.
10. Holst D. Den orale helses sosiale determinanter. Er oral helse fortsatt skjevt fordelt?
In press. Temanummer i 4 nordiske tannlegetidsskrifter 2008: 118
11. Sabbah W, Tsakosa G, Sheihama A, Watta RG. The role of health-related behaviors
in the socioeconomic disparities in oral health. Soc Sci Med 2009;68:298-303.
12. Holst D. Social equality in oral health over 30 years in Norway. Community Dent
Oral Epidemiol 2008.