The aim of this work was to examine the degree and direction of asymmetry in the condyle path, and its associations with facial and dental midline asymmetry in patients with treated and untreated unilateral cross-bite. The subjects were 22 patients, 16 female and 6 male, aged from 9 to 50 years. Nine patients had a history of treated unilateral cross-bite, the mean age of this group being 11.1 years. The children had been treated with removable or fixed expansion appliances at an age of 5-8 years. Thirteen patients had untreated unilateral cross-bite, their mean age being 23.4 years. The clinical examinations were performed by two orthodontists and standard PA roentgenograms were taken in a cephalostat. The condyle path was recorded from the inversion of a face bow fixed rigidly on the anterior mandibular teeth, the positions of the bow being first recorded with the teeth in maximal intercuspation and then in protrusion with the midline unchanged. The condyle path was found to be asymmetric in both the treated and untreated lateral cross-bite groups and to be steeper on the side of the diagnosed or treated cross-bite. The degree of asymmetry was found to be twice as great in the untreated as in the treated group. The facial asymmetry parameters describing the position of the mandible showed the strongest correlation with condyle path asymmetry. The results stress the importance of early treatment of lateral cross-bites.
The aim of this study was to measure the effect of decreased temporomandibular loading on the proliferative activity and the level of matrix production of the condylar cartilage. The effect of reduced joint loading on the activity of stromelysin-1 (MMP-3), which has been associated with conditions of articular cartilage matrix breakdown, was also examined. Eighty 14-day-old female rats were assigned to two groups. Following weaning at 20 days, the experimental group was fed a soft diet and the incisors were shortened regularly to keep them out of occlusion. The controls were fed a hard diet. The activity of tritiated thymidine incorporation and the incorporation of radiolabelled sulphur were measured 2, 6, 12, 24 and 48 hours after initiation of the experiment. The radiolabelled sulphur intake was significantly lower in the condylar cartilage of the experimental group 6-24 hours after initiation of the experiment, and tritiated thymidine activity was lower after 12-24 hours, indicating lower proliferation and matrix production. The cartilage in the experimental group showed marked immunostaining against MMP-3 in all cartilage layers 9 days after initiation of the experiment. In the control group, the staining was clearly seen only in the superficial fibrous layer and in the erosion front. A marked reduction in proliferative activity and proteoglycan synthesis in mandibular condylar cartilage was found after a continuous soft diet and suppressed incisal mastication in the rat. The results show that sufficient loading is important for condylar cartilage growth, to maintain both ideal proliferation and matrix chondrocyte production.
The effects of mechanical factors on the growth of the mandibular condyle were studied by monitoring the maturation of the mesenchymal cells in 55 rats. Thirty-five animals were fed normal pellet food, and 20 were fed a soft diet and their incisors were cut regularly. 3H-thymidine was injected intraperitoneally three days before death at 18, 23, or 33 days. Histologic sections showed the most advanced 3H-thymidine-labeled cells to occur deep in the cartilage, in the lower hypertrophic cell layer in anterior and posterior regions of the condyle, and in the upper hypertrophic cell layer in the superior region at the age of 18 days. A distinct difference in the maturation state of the labeled cells could also be observed between these regions. In animals fed a soft diet, maturation was slower in the superior region of the condyle and faster in the posterior region than in the normal rats. The rate at which cells stepped out of the proliferating cell pool was measured by use of monoclonal antibodies against proliferating cell nuclear antigen. The ratio between labeled cells in the proliferating cell layer and the number of labeled cells beneath it was greater in control animals than in the soft-diet animals. The rate of differentiation and maturation of mesenchymal cells into chondrocytes seems to be controlled by mechanical factors.
The aim of this study was to determine the long-term effects of early headgear (HG) treatment on craniofacial structures. The total study group comprised 68 children (40 males and 28 females) aged 7.6 years (standard deviation 0.3 years). The children, who had a Class II tendency in occlusion and moderate crowding, were randomly divided into two groups of equal size. In the first group, HG treatment was initiated immediately. In the second group, which served as a control group, only minor interceptive procedures were performed during the first follow-up period of 2 years. During the 8 year follow-up, orthodontic therapy, including fixed appliances and possible extractions, was carried out when necessary. The results showed that the most evident difference between the groups was the wider and longer dental arches in the HG group, which could only partly be explained by the higher rate of extractions in the control group. For the cephalometric measurements, the most significant difference was in the maxillary plane orientation. The peer assessment rating (PAR) score, showing the general outcome of treatment, was at the same level in both groups at follow-up. The deficit of the early HG treatment was the longer mean total treatment time, resulting from the two-phase treatment.
Mandibular asymmetry in the frontal plane is a common finding, the left side of the mandible being more often the longer one, and a progressive trend for a more post-normal occlusion on the right side as compared to the left has been reported recently. The aim of the present work was to measure bicondylar asymmetry using computed tomography (CT) and to determine whether this is correlated with certain occlusal characteristics in young adults with no gross malformations. The subjects were 49 adults aged from 15 to 33 years, mean 24.2 years (SD 3.79 years). All of them had a complete or nearly complete dentition. The left condyle was found to be more anteriorly located on average and to be positioned closer to the skull base midline than the right condyle. The joint space between the condyle and the posterior wall of the glenoid fossa was larger on the left side. The asymmetry in bicondylar position correlated with the occlusal asymmetry. Subjects with lateral malocclusions showed a more asymmetric position of the condyles with respect to the posterior wall of the glenoid fossa. This may be of clinical importance and stresses the necessity for early correction of such malocclusions, as complete adaptation does not seem to occur in these cases.
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