During the last decades, a new policy involving normalisation, integration, equality and deinstitutionalisation of mentally retarded (MR) individuals has been accepted in Sweden. Consequently, many institutions have been closed and an increased number of people with MR are now integrated into the Swedish community. The general aim of this thesis was to investigate if a greater degree of independence for MR adults influenced the prevalence of oral diseases. METHODS The caries incidence and prevalence, number of remaining teeth, incidence of tooth mortality and interproximal bone loss were investigated in a group of MR adults, aged 21-40 years, all with protracted, regular preventive dental care. The studied variables were related to living arrangements and degree of MR, and were followed during 8.5 years (Papers I, II and VI). Incidence and reasons for tooth mortality were studied during 10 years in institutionalised MR individuals (Paper III). In connection with the closing-down of an institution for MR adults, the changes of oral hygiene habits, sucrose intake and oral microbiological flora were studied in the new integrated living (Papers IV and V). RESULTS Less restrictive living arrangements and mild forms of MR were correlated to a high caries prevalence in persons with MR. After 8.5 years, the caries incidence had decreased in all subjects, but persons with mild MR and those who lived integrated still had a higher caries prevalence than other MR adults. With the exception of subjects with Down syndrome, the interproximal bone loss during 8.5 years was similar or lower compared to normal Swedish populations. Institutionalised MR subjects had lost an average of 3.72 teeth during 10 years. Periodontitis was the main reason for tooth mortality. Persons who cooperated well with dental treatment and those who used neuroleptics lost fewer teeth during the 10-year period compared to other MR individuals. The proportion of subjects with high levels of mutans streptococci and subjects who showed growth of P. intermedia/P. nigrescens decreased after deinstitutionalisation, and less subjects consumed sucrose frequently. The oral hygiene routines, and the levels of lactobacilli, P. gingivalis and A. actinomycetemcomitans were not influenced by the change in living arrangements. A simplified saliva sampling method, involving licking directly on the bacteria culture, was developed to count lactobacilli in saliva when delivering whole saliva was impossible. CONCLUSIONS Less restrictive living and a mild degree of MR were correlated to a high caries prevalence. Subjects with poor ability to cooperate with dental treatment and those with Down syndrome have an obvious risk of deteriorated oral health. However, compared to normal Swedish populations, the MR subjects studied in this thesis had, after several years of regular dental care, satisfactory oral health.