The myosin light chains of platysma samples originating from 2 to 86 year old patients of the maxillo-facial surgery clinic were investigated. The platysma contained both fast and slow myosin. No change in the proportion of myosin type in relation to age was found. Female patients often displayed less fast myosin than male patients. Each time when the platysma muscle activity has been reduced a decrease in the amount of slow myosin light chains was observed. In the reported study, variations of the fast and slow myosin light chains resulted mainly from the platysma activity level, i.e. from the pathology requiring the surgery, rather than from the patients' age.

Bone sarcomatous cells derived from human malignant tumors were cultured. The mitotic index was recorded for 39 hr. When the cultured cells originated from patients with cancer disease before any chemotherapy, ultradian mitotic rhythms of a 6-9-hr period were detected, but in many cases only after a sensitive statistical analysis was performed. When the cultured cells originated from cancer patients undergoing chemotherapy, the mitotic index was decreased, and the amplitudes of the 6-9-hr component oscillations of the mitotic index were highly significantly increased. Damping and fading out of an ultradian mitotic rhythmicity was a bad prognostic portent in bone cancer. With reference to chemotherapy, the restored and amplified ultradian rhythmicity disclosed an appreciable antitumor effect and better survival prospects for the patient.

Masticatory muscles mediate the action of functional orthopedic appliances on mandible growth. When young rats were treated for four weeks with a postural hyperpropulsor of the mandible, an appliance designed to increase condylar cartilage growth rate, the proportion of fast non-fatigable fibres in the lateral pterygoid muscle increased significantly. Concomitantly, the amount of slow-myosin light chains increased in fibre extracts. This slow myosin originated from IIA fibres. By functional orthopedic treatment, the lateral pterygoid muscle was enriched in less fatigable fibres; the changes observed in the lateral pterygoid muscle were close to changes observed in other muscles after training.

The modus operandi and the time-dependent variations in the effects of the LSU-activator, an orthopedic appliance currently used in human orthodontic therapy, was experimentally analyzed in growing rats. This appliance causes a forward positioning of the lower jaw and a restriction of mandibular motility. After a 4-week treatment, the following changes were observed: (i) the growth rate of the condylar cartilage was accelerated, this growth-promoting effect being more pronounced when the LSU-activator was worn during the animal's rest span. (ii) the direction of condylar growth became more backward-oriented; no significant difference between day and night treatment, i.e. during the rest and activity spans could be detected; (iii) the supplementary lengthening of the mandible was greater in rats treated during rest than in rats treated during waking and (iv) the number of serial sarcomeres in the lateral pterygoid muscle was smaller. This growth retardation of the muscle was greater in rest-time than in waking-time treated individuals. The LSU-type activator's action implies a two-step effect: during the time of wearing the appliance, the more forward positioning of the mandible causes a reduced growth of the lateral pterygoid muscle; during the time the LSU-type activator is not worn, the mandible is functioning in a more forward position such a way that it stimulates the growth rate of the condylar cartilage and the subperiosteal ossification of the posterior border of the ramus. It is therefore essential, for a few hours every day, that the mandible be allowed to move freely from the appliance in a more forward position.

The growth rate of the cartilage of the mandibular condyle in the young rat exhibits: - a circadian cycle with a maximum of the 3H-thymidine labelled cells around 13(00) and a minimum around 01(00); with a maximum in the number of mitoses around 21(00) and a minimum around 09(00). - a circannual cycle with a maximum in May and a minimum between November and January, and with a difference in rhythms between May and November. The condylar cartilage growth in response to orthopaedical appliances of the mandible is modified and exhibits: - circadian variations. - circannual variations. The responsiveness of the condylar cartilage to orthopaedic appliances is greater when the condylar cartilage growth rate is higher.

Click to increase image sizeClick to decrease image sizeAbstracting keywords: Growth cyclesmandibular cartilagerat