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A randomly selected sample of 1992 adults (995 men and 997 women) representing four equally sized age groups of 25-, 35-, 50-, and 65-years-old inhabitants of West Bothnia were studied for prevalence of symptoms and clinical signs of mandibular dysfunction. Of the sample 79% completed a questionnaire and a clinical examination. The chewing inability increased with age. Recurrent headaches (once a week or more often) were reported to occur in 11% to 15% of the four age groups, and the duration of headaches was generally more than 2 years. Tooth-clenching, which was the most frequent oral parafunction, was reported significantly more often in women, whereas attrition was more severe in men. The commonest clinical finding was temporomandibular joint clicking, which varied between 13% and 35% in the different age groups. Crepitation was observed more often in women and increased with age. The jaw muscles were more frequently tender to palpation in women and the elderly. The mean maximal mouth opening capacity varied between 55 mm and 44 mm, decreasing with age, and was for the whole sample significantly higher among men. Since signs and symptoms of craniomandibular disorders were common findings in all age groups, routine dental examination should always include functional evaluation of the stomatognathic system.

– Electromyographic (EMG) activity of the superficial masseter and the anterior temporal muscles versus the bite force was studied in 10 young women. They were fully dentate and had no dysfunction of the stomatognathic system. The descending part of the trapezius muscle was also chosen for EMG registration. The average bite force between the first molars was 396 N (Newton). Steeper slopes for the EMG versus force regression curve at high contraction levels than at low contraction levels for the superficial masseter muscle may indicate that this muscle has a recruitment pattern that differs from that of the anterior temporal muscle. In the case of the anterior temporal muscle there was no difference between the slopes for the EMG‐force regression at low and high contraction levels. There was significantly increased activity in the descending part of the trapezius muscle mainly during high bite force levels in half the subjects.

With the aid of questionnaires symptoms of mandibular dysfunction and some general and oral conditions were studied in a group of previous patients and in a randomly selected population sample. From the two materials answers were obtained from 82 persons (81%) and 1.106 (91%) respectively. The results confirmed that women are heavily overrepresented in patient materials. This differs from the fairly equal sex distribution found in population studies of mandibular dysfunction. The most frequent symptoms of mandibular dysfunction were TMJ-sounds which appeared in 39 and 79% and pain on opening the mouth which appeared in 12 and 42% of the population and patient samples respectively. All symptoms of mandibular dysfunction, headache, clenching of the teeth and unilateral chewing appeared significantly more often in the previous patients, but the number of natural teeth did not differ in the two samples. The general state of health was poorer and general joint -- muscle symptoms were more common in the previous patients as well as in those of the population sample with symptoms of mandibular dysfunction. This finding suggests that functional disturbances of the masticatory system often may be related to impaired general health.

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