Oral Health in Norway. The HUNT Study.

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
rate.
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