| Class II division 1 malocclusion is common in clinic. It has great unfavorable effects on the oralfacial morphology and function. Early treatment with functional appliance can stimulate dental, occlusal, skeletal and facial development. The material consisted of 27 Class n. division 1 malocclusion cases, of which 17 were treated with the domestic Herbst appliance and the other 10 cases served as control. To evaluate the clinical effects of early treatment, the cephalometric roentenograms, TMJ lateral tomograms, EMG, Helkimo index and MKG were used. The mechanism of Herbst appliance treatment was invstigated through the study on the adaptive modification of hard and soft tissues, TMJ and masticatory muscles. Results:1. After 6-8 months (average 7 months) of Herbst appliance therapy, Class n malocclusal relationships were corrected to Class I occlusal relationships. Class II molar correction averaged 6.9mm,of which 46.38% was due to skeletal and 53.62% due to dental changes;.33.33% was due to maxillary and 66.67% due to mandibular effects overall. Overjet correction averaged 7.2mm,of which 44.44% was due to skeletal and 55.56% due to dental changes; 34.72% was due to maxillary and 65.28% due to mandibular effects.2.Mandible changed significently. SNB degree, mandibular ramas height (Co-Go), mandibular length (Co-Pg), mandibular body length (Go-Pg) and thedistance from Pg to Olp plane increased. The increase was beyond the growth changes in nature and was significant in clinic. It also inhibited maxillary growth, which resulted in reduction of SNA degree and the distance from A to Olp plane. Sagital changes appeared with the decrease of ANB by 3.31?and that of Wits value by 1.6mm. Vertical changes came with the increase of anterior facial height (N-Me), lower anterior facial height (ANS-Me), posterior facial height (S-Go), lower posterior facial height (Ar-Go). It showed that Herbst appliance therapy stimulated the growth of lower facial hard tissue and corrected discrepancy between sagital and vertical skeletal relationship.3.Herbst appliance therapy brought about a reduction of the facial soft tissue profile convexity. Upper lip base angular (S-N'-Sn), upper lip angular (LsSn-SN) remained unchanged before and after treatment. Lower lip base angular (S-N'-Si), lower lip angular (LiSi-SN), soft tissure mental angular (S-N'-Pg') increased and H angular, upperlower lip base angular (Sn-N'-Si) and mentalabial sulcus depth decreased. It showed that Herbst appliance treatment stimulated growth of lower facial soft tissue and was beneficial to reduce facial convexity. However, decrease of mentalabial sulcus thickness suggested the modification of soft tissue fell behind skeletal growth.4. At the beginning of Herbst appliance therapy, temporary mild TMD symptom appeared in 4 patients (17 in all) and Helkimo index increased. After therapy, TMD symtom was relieved. Initial study revealed that Herbst appliance therapy seem not to worsen TMD.5.Before therapy, the condyle was nearly in the middle of glenoid fossa, but slightly forward. After patients worn Herbst appliance for a week, condyle moved forward and downward .The distance of upper and posterior glenoid space increased, and that of anterior glenoid fossa space decreased. So the ratio of anterior and posterior space area reduced. After 7 months' active treatment, condyle returned to its former position.6.After therapy, masticatory muscles activities changed greatly. At rest position DA activity dropped from a high level to almost the normal. MM, TA activity reduced during forward and backward movements. With maximal clenching and chewing gum movement, MM activity increased, but still lower than normal, and DA activity declined to almost normal. Contusions:The telescoping system of Herbst appliance was used to correct Class II malocclusion .It keeps mandible in constant forward position 24 hours a day, which stimulated condyle growth and induced adaptive changes of neruomuscle and skeleton. It led to the increase of mandibular leng...
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