Abstract
A cross-sectional study of the prevalence of masticatory muscle disorders and temporomandibular joint disorders was carried out on 672 individuals (304 males and 368 females, age range 20-92 years) who were selected randomly in Okayama City, Japan. Many subjects who lacked supernormal temporomandibular functions as well as temporomandibular disorders, being assumed in adaptive state, were observed. The aim was to investigate signs, prevalences and risk factors of the adaptive population.
In the population the incidence of slight TMJ noise was the highest (83%) and most of the noises seemed likely to be the previous stages of disk displacement or degenerative joint disease. The frequency of the adaptive population was 24% in all subjects and no significant sex and age differences were found for the distribution of clinically relevant findings. The adaptive population was found to relate risk factors-life stresses, trauma, health condition, behavior and occlusion. Concerning occlusal factors, subjects who had abnormal static occlusal findings were found significantly more frequently in the adaptive population than in the asymptomatic population.
Moreover, subjects who had abnormal relationships between the upper and lower arches and who had balancing side and/or protrusive interferences were found significantly more frequently in the dysfunctional population than in the adaptive population. Histories of temporomandibular disorders (pain, noise and trismus) were found more frequently in the dysfunctional population than in the other populations, and histories of TMJ sounds were found more frequently in the adaptive population than in the asymptomatic population. These data suggest that there exist many subjects in an adaptive state of temporomandibular disorders in the Japanese adult population.
