In all, 125 individuals, 13-23 years old, with intact dentitions and 163 individuals, 13-20 years old, with dental fillings were included in a series of studies. The results of the studies suggest that subjects with intact dentitions have a lower prevalence and degree of signs and symptoms of mandibular dysfunction than subjects with restorations in the teeth. However, most signs and symptoms in both groups were mild and infrequent. The most common symptoms in both groups were TMJ-sounds, tiredness during chewing, and headache, and the most common clinical signs were TMJ-sounds and muscles tender to palpation. Fossa bottom facets were more common in restored dentitions and they often involved fillings. In restored dentitions, dentin facets were more common, the worn area was on average larger and the distal marginal crest of the second lower molars were more often worn indicating a difference in functional activity between the groups, with more parafunctional activity in restored dentitions. According to the Karolinska Scales of Personality (KSP), the subjects with restored dentitions had higher values on the "muscular tension" and "somatic anxiety" scales, i.e. dental restorations were more common in subjects with autonomic and motor disturbances related to anxiety-proneness. The subjects with restored dentitions had lower bite force values during "gentle biting" in the frontal region. The occlusal perception increased from the more posterior test position to the anterior one in both groups. The best tactile sensibility was found in the incisor region, where the subjects with restored dentitions tended to have better values. The higher prevalence and degree of clinically recorded dysfunction in subjects with restored dentitions was confirmed in the follow-up study. The findings of this investigation indicate a possible etiological significance of dental filling therapy in mandibular dysfunction. For the moment, however, we do not know if, how and to what extent occlusal factors, psychological differences between the subjects, or combinations of these or other factors are responsible for the development of signs and symptoms in the masticatory system. Nevertheless, the findings indicate that the factor "dental filling therapy" merits more consideration and more extensive research and should be included in epidemiological studies in the future. There is no indication in the results that toxic effects of the fillings could have influenced the results but further studies might be desirable, especially longitudinal comparisons between subjects with intact and restored dentitions.